Molybdenum and Tungsten Alkylidene Complexes for cis- and trans-selective RingOpening Metathesis Polymerization
by
MASSACHETS ILNSTITUTE
OF TECHNOLOGY
Hyangsoo Jeong
NOV 0 9 2015
B.S. in Chemistry (2010)
Korea Advanced Institute of Science and Technology
LIBRARIES
Submitted to the Department of Chemistry
in Partial Fulfillment of the Requirements for the Degree of
Doctor of Philosophy
at the
Massachusetts Institute of Technology
September 2015
C 2015 Massachusetts Institute of Technology. All rights reserved
Signature of Author
Certified by
___nature
rE
d acted
Departme it of Chemistry
July 9, 2015
Signature r
Adacted
Richard R. Schrock
Frederick G. Keyes Professor of Chemistry
Thesis Supervisor
Accepted by
Signature redacted
Robert W. Field
Haslam and Dewey Professor of Chemistry
Chairman, Departmental Committee on Graduate Students
2
This doctoral thesis has been examined by a Committee of the Department of Chemistry as
follows:
Signature redacted
Professor Christopher C. Cummins
Chairman
Signature redacted
Professor Richarid R. Schrock
Thesis Supervisor
Signature redacted
Professor Yogesh Surendranath
3
4
Molybdenum and Tungsten Alkylidene Complexes for cis- and trans-selective RingOpening Metathesis Polymerization
by
Hyangsoo Jeong
Submitted to the Department of Chemistry on July 09, 2015
in Partial Fulfillment of the Requirements for the
Degree of Doctor of Philosophy in Chemistry
ABSTRACT
Chapter 1 describes the synthesis of tert-butylimido alkylidene complexes for molybdenum
and tungsten. A dimer species [W(N-t-Bu)2C1(p-Cl)(t-BuNH2)]2 served as a bisimido precursor.
After alkylation with Grignard reagent, alkylidene formation is accomplished using pyridinium
chloride. W(N-t-Bu)(CHCMe3)C2(py)2 crystallizes as a dimer [(W(N-t-Bu)(CHCMe3)Cl(pICl)(py)]2 with a loss of pyridine for each W center. For the case of molybdenum, addition of
pentafluorophenol to the diimido dialkyl precursor affords Mo(N-t-Bu)(CHCMe3)(OC6 F5 )2(NH2t-Bu). Dipyrrolide complexes for both Mo and W are synthesized and isolated as a 2,2'-bipyridine
adduct. Addition of a sterically encumbered terphenol along with ZnCl2(dioxane) affords
monoalkoxide pyrrolide (MAP) complexes M(N-t-Bu)(CHCMe3)(pyr)(OHMT) (pyr = pyrrolide;
HMT = 2,6-(2,4,6-Me3)C6H3; M = Mo, W).
Chapter 2 investigates Z-selective ring-opening metathesis polymerization (ROMP) of 3Mo
and
W
MAP
catalysts.
substituted
cyclooctenes
(3-RCOEs)
by
and W(N-tMo(NAd)(CHCMe2Ph)(pyr)(OHMT),
Mo(N-t-Bu)(CHCMe3)(pyr)(OHMT),
Bu)(CHCMe3)(pyr)(OHMT) all produced >98% cis,HT-poly(3-RCOE) (HT = head to tail; R =
Me, n-Hex, Ph). The key in forming high molecular weight polymer instead of cyclic oligomer
species was to run the reaction neat. Surprisingly, the fastest initiator was W(N-tBu)(CHCMe3)(pyr)(OHMT) among all three MAP species. Polymerization proceeds via a
propagating species in which the R group is of C2 position of the propagating chain, giving HT
polymers with high regioselectivity.
Chapter 3 describes the synthesis and reactivity of compounds containing a tert-butylimido
ligand. Chelating alkylidenes can be synthesized either by alkylidene exchange or by traditional
routes in forming alkylidene complexes from diimido dialkyl species. A W MAP complex
containing a chelating alkylidene can be synthesized and its reactivity is comparable to that of
neopentylidene analogue in 1-octene homocoupling. Complexes with a chelating diolate ligand
W(N-t-Bu)(CHCMe3)(BiphenCF3)(py)
and
W(N-t-Bu)(CHCMe3)(BiphenMe)(py)
were
synthesized. However, attempts to remove the pyridine ligand induced C-H activation of one tertbutyl group on Biphen ligand to form alkyl complexes.
Chapter 4 presents the synthesis of high sequence-regular alternating trans-AB copolymers
by ROMP initiated by Mo(NAr')(CHCMe2Ph)(OCMe(CF 3)2 )2 (NAr'= 2,6-dimethylphenylimido).
5
Monomers employed were 2,3-dicarbomethoxy-7-isopropylidenenorbomadiene (B), dimethyl
spiro[bicyclo[2.2.1]hepta-2,5-diene-2,3-dicarboxylate-7,1'-cyclopropane] (B'), cyclooctene (A),
and cycloheptene (A'). All four combinations afford structures containing a high degree of
monomer alternation. Evidence suggests a catalytic cycle proceeding through a syn alkylidene
arising from insertion of B (syn-MB) reacting with A to form an anti alkylidene (anti-MA) and a
trans-AB linkage. A MAP complex Mo(NAr)(CHCMe2Ph)(Me 2 Pyr)(OCMe(CF 3)2) (NAr = 2,6diisopropylphenylimido; Me2Pyr = 2,5-Me 2NC4H 2) was also found to form trans-poly[A-alt-B']
with >90% alternating dyad sequences. Variations on imido and alkoxide ligands were surveyed
as well as both A and B type monomers.
Thesis Supervisor: Richard R. Schrock
Title: Frederick G. Keyes Professor of Chemistry
6
Table of Contents
Title Page
1
Signature Page
3
Abstract
5
Table of Contents
7
List of Figures
10
List of Schemes
16
List of Tables
19
List of Abbreviations
21
General Introduction
25
Chapter 1: Synthesis of Molybdenum and Tungsten Alkylidene Complexes Containing a
37
tert-butylimido Ligand
Introduction
38
Results and Discussion
40
I. Routes for the Synthesis of tert-butylimido Alkylidene Complexes
40
A. Synthesis of [W(N-t-Bu)2CI(p-Cl)(t-BuNH2)]2
40
B. Synthesis of W(N-t-Bu)2(CH2CMe3)2
43
C. Synthesis of W(N-t-Bu)(CHCMe3)C2(py)2
44
D. Synthesis of Molybdenum Alkylidene Complexes
46
E. Tungsten Alkylidene Formation Using Milder Acids
47
II. Synthesis of MonoAlkoxide Pyrrolide (MAP) Complexes of Mo and W tert-butylimido
48
Species
A. Synthesis of Bispyrrolide Complexes
48
B. Synthesis of Mo and W tert-butylimido MAP Complexes
50
Conclusions
54
Experimental
55
References
74
7
Chapter 2: Z-selective
Ring-Opening Metathesis
Polymerization
of 3-Substituted
Cyclooctenes
77
Introduction
78
Results and Discussion
80
I. Polymerization of 3-RCOEs by Various MAP Catalysts
80
A. Formation of Z-selective Poly(3-RCOEs)
80
B. Molecular Weight Determination of Poly(3-RCOEs)
86
C. Catalyst Screenings in ROMP of 3-RCOEs
89
D. Expansion of Monomer Scope in ROMP of Substituted Cyclooctenes
90
II. Determination of the Origin of Selectivity
93
A. Nature of Propagating Species
93
B. Determination of kp/ki
99
Conclusions
100
Experimental
101
References
111
Chapter 3: Synthesis and Reactivity Studies of Tungsten Alkylidene Complexes Containing
113
a tert-butylimido Ligand
Introduction
114
Results and Discussion
115
I. Synthesis and Reactivity Studies of Mo and W tert-butylimido Species Containing
115
Chelating Alkylidenes
A. Synthesis of Chelating Alkylidene Complexes
115
B. Studies of Chelating Alkylidene Complexes for W tert-butylimido MAP Species
119
II. Synthesis of Tungsten tert-butylimido Bisaryloxide Species
120
A. Synthesis of Bisterphenoxide Complexes
120
B. Synthesis of Chelating Diolate Complexes
123
III. Synthesis of Tungsten tert-butylimido Metallacyclobutane Species
128
Conclusions
129
Experimental
130
References
152
8
Chapter 4: Synthesis and Mechanistic Studies of Alternating trans-AB Alternating
155
Copolymers by Molybdenum Alkylidenes
Introduction
156
Results and Discussion
158
158
I. Formation of trans-AB Alternating Copolymers
A. Stereoselective ROMP of Four AB Alternating Copolymers with a Molybdenum
Catalyst
158
B. Determination of Rate Constants for trans-poly[A-alt-B] in Various Solvents
163
C. Kinetic Studies of Alkylidene Rotation for Mo(NAr')(CHCMe2Ph)(OCMe(CF3)2)2
164
D. Stoichiometric Reactions of B with Mo(NAr')(CHCMe 2 Ph)(OCMe(CF3)2)2
166
E. Reaction of B with in situ Generated Cyclooctene Linkages
170
F.
Proposed
Mechanism
for
the
Formation
of
trans-poly[A-alt-B]
by
171
Mo(NAr')(CHCMe 2 Ph)(OCMe(CF3)2)2
II. Variation of Catalysts and Monomers in Alternating Copolymerization
174
A. Catalyst Variation for Alternating Copolymerization
174
A-1. Screening of Bisalkoxide Catalysts
174
A-2. Screening of MAP and Biphen Catalysts
176
B. Expansion of Monomer Scope in Alternating Copolymerization
179
B-1. Monomer Scope in B Type
179
B-2. Monomer Scope in A Type
181
Conclusions
183
Experimental
184
References
227
Curriculum Vitae
229
Acknowledgements
231
9
List of Figures
GENERAL INTRODUCTION
Figure 1. Two types of metal-carbon double bonds: Fischer carbene and Schrock carbene.
27
Figure 2. Several types of olefin metathesis reactions.
27
Figure 3. Three generations of Ru-based catalysts.
28
Figure 4. Examples of Mo and W based metathesis catalysts (M = Mo, W; R = Me or Ph).
28
Figure 5. The structure of [Ta(CHCMe3)(Cl)3(PMe3)]2
33
CHAPTER 1
Figure 1.1. Representative Z-selective Mo and W olefin metathesis catalysts bearing bulky
aryloxide and pyrrolide ligands (1,2) and an asymmetric Mo catalyst bearing an adamantylimido
38
ligand (3).
Figure 1.2. X-ray crystal structure of 1w.
42
Figure 1.3. X-ray crysal structure of 3w'.
45
Figure 1.4. X-ray crystal structure of 16w.
52
Figure 1.5. Thermal ellipsoid drawing of Mo(N-t-Bu)(CHCMe3)(pyr)(OHMT) (6 mo).
54
Figure 1.6. 'H NMR spectrum of W(N-t-Bu)(CHCMe 3)(pyr)(OHIPT) (in C6 D 6 , 500 MHz).
61
Figure 1.7. 'H NMR spectrum of W(N-t-Bu)(CHCMe3)(pyr)(OHMT) (in CD6 , 500 MHz).
62
Figure 1.8. 'H NMR spectrum of W(N-t-Bu)(CHCMe3)(pyr)(ODFT)(py) (in C 6 D6 , 400 MHz).63
Figure 1.9. 'H NMR spectrum of Mo(N-t-Bu)(CHCMe3)[OCH(CF3)2]2(NH2-t-Bu) (in C 6D6, 500
64
MHz).
Figure 1.10. ' H NMR spectrum of Mo(N-t-Bu)(CHCMe3)(OC 6F)2(NH2-t-Bu) (in C 6D 6 , 500
MHz).
66
Figure 1.11. 'H NMR spectrum of Mo(N-t-Bu)(CHCMe3)(pyr)2(bipy) (in CD2 Cl2, 500 MHz). 65
Figure 1.12. 'H NMR spectrum of Mo(N-t-Bu)(CH-t-Bu)(pyr)(OHMT) (in C 6D 6 , 500 MHz). 67
CHAPTER 2
Figure 2.1. Mo(NAd)(CHCMe 2Ph)(pyr)(OHIPT) (1).
79
Figure 2.2. Generation of cis,syndiotacticpolymers from various monomers using catalyst 1. 79
10
Figure 2.3. The three catalysts for ROMP of 3-RCOEs.
80
Figure 2.4. Olefinic region of the 'H NMR spectrum of W(N-t-Bu)(CHCMe3)(pyr)(OHMT) with
81
5 equivalents of 3-HexCOE (C 6D 6 , 500 MHz).
Figure 2.5. (a) Reaction of 3-HexCOE with Ic formed uninitiated catalyst along with cyclic
oligomers. (b) Observed cyclic dimer species with GC/MS.
81
Figure 2.6. Olefinic (1H) and olefinic and aryl (13C) regions of the 'H (top) (500 MHz in CDCl3)
and 13C (bottom) (125 MHz in CDCl 3) NMR spectra of isolated >98% cis,HT-poly(3-RCOE) (R
83
= Ph (a,d), Hex (b,e), Me (c,f)) prepared using la.
Figure 2.7. Proton NMR spectra of the olefinic region of cis,HT poly(3-MeCOE) prepared from
84
lc after (a) 1 h and (b) 42 h (C6D6, 500 MHz).
Figure 2.8. The 1H-1H COSY spectrum of the olefinic region of cis,HT-poly(3-MeCOE)
prepared from 1c after 42 h.
85
Figure 2.9. 'H NMR spectrum of a mixture of cis,HT-poly(3-HexCOE) prepared using la and
trans,HT-poly(3-HexCOE) prepared using Grubbs' 2 "d generation catalyst (CDCl3, 500 MHz).86
Figure 2.10. Concentration detection of five different concentrations of poly(3-MeCOE) using
88
dRI detector (CHCl 3 , 40 'C).
Figure 2.11. Differential refractive index versus concentration for poly(3-MeCOE).
88
Figure 2.12. Proton NMR spectra of the alkylidene region of poly(3-RCOE) in CDCl 3 prepared
through polymerization of bulk 3-RCOE treated with 1c (500MHz) : (a) R = Hex, 100 quiv; (b)
R = Ph, 100 equiv; (c) R = Me, 200 equiv. A peak at 8.16 ppm indicates the remaining initiator
96
alkylidene proton.
Figure 2.13. (a) Proton NMR spectrum of the alkylidene region of W(N-tBu)(CHCHMeEt)(pyr)(OHMT) prepared as follows: 3 equivalents of 3-methyl-i -pentene was
treated with lc followed by removal of volatiles in vacuo (CDCl 3 , 500 MHz). (b) Proton NMR
spectrum of the alkylidene region of W(N-t-Bu)(CHCHMeEt)(pyr)(OHMT) after
97
homodecoupling at 3.74ppm (CDCl 3 , 500 MHz).
Figure 2.14. 'H-1H COSY spectrum of W(N-t-Bu)(CHCHMeEt)(pyr)(OHMT) (CDCl 3, 500
MHz).
97
Figure 2.15. Proton NMR spectrum (-20 'C) in the tungstacyclobutane region after addition of 399
methyl-1-pentene to Ie (CDCl3, 500 MHz).
Figure 2.16. TBP metallacyclobutane intermediate of both P1 and P2 approach with 3-MeCOE
99
monomer and 1c. The pyrrolide ligand was omitted for clarity.
Figure 2.17. 'H NMR spectrum of cis,HT-poly(3-MeCOE) (CDCl 3, 500 MHz).
103
Figure 2.18. 13C NMR spectrum of cis,HT-poly(3-MeCOE) (in CDCl3, 125 MHz).
104
Figure 2.19 'H-1H COSY spectrum of cis,HT-poly(3-MeCOE) (in CDCl 3 , 500 MHz).
104
11
Figure 2.20. 'H NMR spectrum of cis,HT-poly(3-HexCOE) (in CDC1 3, 500 MHz).
105
NMR spectrum of cis,HT-poly(3-HexCOE) (in CDC1 3 , 125 MHz).
106
Figure 2.21.
13C
Figure 2.22. 'H-1H COSY spectrum of cis,HT-poly(3-HexCOE) (in CDCl 3 , 500 MHz).
106
Figure 2.23. 'H NMR spectrum of cis,HT-poly(3-PhCOE) (in CDCl 3 , 500 MHz).
107
Figure 2.24. 13C NMR spectrum of cis,HT-poly(3-PhCOE) (in CDC1 3, 125 MHz).
108
Figure 2.25. 'H-1H COSY spectrum of cis,HT-poly(3-PhCOE) (in CDCl3, 500 MHz).
108
CHAPTER 3
Figure 3.1. Thermal ellipsoid plots shown at 50% probability level of 3 mo.
118
Figure 3.2. [Biphenme]H2 and [BiphenCF3]H2 ligands.
124
.
Figure 3.3. 'H NMR spectra of W(N-t-Bu)(CHCMe3)(BiphenCF3)(py) and W(N-tBu)(CH2CMe3)(BiphenCF3). Top: 'H NMR spectra of W(N-t-Bu)(CHCMe3)(BiphenCF3)(py) in
C 6D 6 .Bottom: 'H NMR spectrum of W(N-t-Bu)(CH2CMe3)(BiphenCF3) obtained in situ in C 6D6
125
Figure 3.4. Thermal ellipsoid (50 %) drawing of W(N-t-Bu)(CH2CMe3)(BiphenCF3) (10W).
126
Figure 3.5. 'H NMR spectrum of W(N-t-Bu)(CH-o-MeOC 6H4)(Cl)2(py) (in C 6D6, 500 MHz) .132
Figure 3.6. 'H NMR spectrum of Mo(N-t-Bu)(CH-o-MeOC6H4)(OC6F5)2(t-BuNH2)
500 MHz).
(in C 6D 6,
133
Figure 3.7. 'H NMR spectrum of W(N-t-Bu)2(CH2-o-MeOC6H4)2 (in C 6D 6 , 500 MHz).
134
Figure 3.8. 'H NMR spectrum of Mo(N-t-Bu) 2(CH 2-o-MeOC 6H4)2 (in C 6D 6, 500 MHz).
135
Figure 3.9. 'H NMR spectrum of Mo(NAr)2(CH 2-o-MeOC6H4) 2 (in C 6D 6, 500 MHz).
136
Figure 3.10. 'H NMR spectrum of W(N-t-Bu)(CH-o-MeOC6H4)(pyr)(OHMT) (in C 6D 6, 500
138
MHz).
Figure 3.11. ' H NMR spectrum of W(N-t-Bu)(CHCMe3)(OHMT)(Cl)(py) (in C 6D 6, 500 MH z).
139
Figure 3.12. 'H NMR spectrum of W(N-t-Bu)(CHCMe 3)(OHMT)2 (in C 6D6, 500 MHz).
41
Figure 3.13. 'H NMR spectrum of W(N-t-Bu)(CHCMe 3)(ODFT)2 (in C 6D 6 , 400 MHz).
[42
Figure 3.14. 'H NMR spectrum of W(N-t-Bu)(CHCMe3)(BiphenCF3)(py) (in C6D6, 500 MHz).
143
Figure 3.15. 1H NMR spectrum of W(N-t-Bu)(CH2CMe3)(BiphenCF3) (in C 6D 6 , 400 MHz).
144
Figure 3.16. 'H NMR spectrum of W(N-t-Bu)(CHCMe3)(Biphenme)(py) (in C 6D6 , 400 MHz).145
12
Figure 3.17. 'H NMR spectrum of W(N-t-Bu)(C3H 6 )(pyr)(ODFT) (in C 6D 6 , 500 MHz).
146
Figure 3.18. 'H NMR spectrum of W(N-t-Bu)(C 3H 6)(ODFT)2 (in C 6D 6 , 500 MHz).
147
CHAPTER 4
Figure 4.1. The two catalysts for ROMP of alternating copolymerizations.
158
Figure 4.2. 'H NMR spectrum of isolated >90% trans-poly[A-alt-B] using 1 (500 MHz, CDCl3).
159
Figure 4.3. Olefinic regions of the 'H NMR spectra of poly[A-alt-B] using various conditions
prepared from 1: (a) B:A = 1:2, r.t. (50:100 equivalents to 1; 500 MHz in CDCl 3 ) (b) B:A = 2:1,
r.t. (100:50 equivalents to 1; 400 MHz in CDCl3) (c) B:A = 1:1, 65 'C (50:50 equivalents to 1;
500 MHz in CDCl3) (d) B:A = 1:1, r.t. (50:50 equivalents to 1; 400 MHz in CDCl3).
161
Figure 4.4. Measurement of ka/s at various temperatures.
165
Figure 4.5. Construction of the Eyring Plot for 1.
166
Figure 4.6. 'H NMR spectrum (left, alkylidene region; right, olefinic region) of the first insertion
168
product of 1 with B (500 MHz, toluene-d).
Figure 4.7. Proton NMR spectrum of a mixture of syn-MBei, and syn-MBtrans at -10 'C
(500MHz, toluene-d8) (* is the residual B).
169
Figure 4.8. (a) In situ formation of MA upon reaction of A (15 equiv) with 1 (THF-d8 , 500 MHz)
171
(b) Addition of B (0.5 equiv) to (a) (THF-d8, 500 MHz).
Figure 4.9. Alkylidene regions of the 'H NMR spectra (500 MHz) of polymerization of AB by 1
(A:B:1 = 50:50:1) in Toluene-d8 at three different conversions : (a) 48% conversion; (b) 75%
conversion; (c) 94% conversion. Assignment of syn-MB and anti-MB was based on 'JHH
173
coupling constants.
Figure 4.10. Alkylidene regions (* = syn-1) of the 'H NMR spectra (500 MHz) of polymerization
of AB by 1 (A:B:1 = 50:50:1) in THF-d8 at three different conversions : (a) 9% conversion; (b)
174
15% conversion; (c) 72% conversion.
Figure 4.11. Variation of imido and alkoxide ligands in bisalkoxide framework.
174
Figure 4.12. Olefinic regions of 'H NMR spectra (CDCl 3 , 500 MHz) of polyAB (various
initiators and monomers as indicated). Note that 'H NMR spectra are from reaction aliquots ((a)
176
,
and (b)) or isolated polymers (c).
Figure 4.13. Olefinic regions of 'H NMR spectra (CDCl 3 , 500 MHz) of polyAB (various
initiators and monomers as indicated). Note that 'H NMR spectra are from reaction aliquots (a)
178
or isolated polymers ((b) and (c)).
Figure 4.14. Olefinic regions of 'H NMR spectra (CDC1 3, 400 MHz) of polyAB (various B
monomers as indicated). Note that all 'H NMR spectra are from isolated polymers.
13
181
Figure 4.15. Olefinic regions of 'H NMR spectra ((a) CDC3, 500 MHz; (b), (c) CDCl 3, 400
MHz) of polyAB (various A monomers as indicated). Note that all 'H NMR spectra are from
isolated polymers.
183
Figure 4.16. 'H NMR spectrum of W(NAr')(CHCMe2Ph)(OCMe(CF 3 )2)2 (in C 6D6 , 500 MHz).
186
Figure 4.17. 'H NMR spectrum of Mo(NAr')(CHCMe2Ph)(OCMe(C 6F 5)2)2 (in C 6D 6, 500 MHz).
187
Figure 4.18. 'H NMR spectrum of trans-poly[A-alt-B] (in CDCl 3 , 500 MHz).
Figure 4.19.
13 C
NMR spectrum of trans-poly[A-alt-B] (in CDCl 3, 125 MHz).
189
189
Figure 4.20. 1H-1H gCOSY spectrum of trans-poly[A-alt-B] (in CDC1 3 , 500 MHz).
190
Figure 4.21. IR spectrum of trans-poly[A-alt-B] (neat).
190
Figure 4.22. 'H NMR spectrum of trans-poly[A-alt-B'] (in CDCl 3, 500 MHz).
192
Figure 4.23.
13 C
NMR spectrum of trans-poly[A-alt-B'] (in CDCl 3 , 125 MHz).
192
Figure 4.24. 'H-'H gCOSY spectrum of trans-poly[A-alt-B'] (in CDC1 3 , 500 MHz).
193
Figure 4.25. IR spectrum of trans-poly[A-alt-B'] (neat).
193
Figure 4.26. 'H NMR spectrum of trans-poly[A'-alt-B'](in CDC1 3, 500 MHz).
195
Figure 4.27.
13 C
NMR spectrum of trans-poly[A'-alt-B'] (in CDCL 3 , 125 MHz).
195
Figure 4.28. 'H-1H gCOSY spectrum of trans-poly[A'-alt-B'] (in CDCL 3, 500 MHz).
196
Figure 4.29. IR spectrum of trans-poly[A'-alt-B'] (neat).
196
Figure 4.30. 'H NMR spectrum of trans-poly[A'-alt-B] (in CDCl 3 , 500 MHz).
198
Figure 4.31.
13 C
NMR spectrum of trans-poly[A'-alt-B] (in CDCl 3, 500 MHz).
198
199
Figure 4.33. IR spectrum of trans-poly[A'-alt-B] (neat).
199
Figure 4.34. Comparison of the olefinic region 'H NMR spectrum of trans-poly(A-alt-B')
formed from 1 (left) and 2 (right) in CDCl 3
201
Figure 4.35. Comparison of the olefinic region 'H NMR spectrum of trans-poly(A'-aIt-B')
formed from 1 (left) and 2 (right) in CDCl 3
201
.
.
Figure 4.32. 'H-'H gCOSY spectrum of trans-poly[A'-alt-B] (in CDC1 3 , 500 MHz).
Figure 4.36. Comparison of the olefinic region 'H NMR spectrum of trans-poly(A'-aIt-B)
formed from 1 (left) and 2 (right) in CDC1 3
.
202
.
Figure 4.37. Comparison of the olefinic region 'H NMR spectrum of trans-poly(A-alt-B) formed
from 1 (left) and 2 (right) in CDC1 3
202
14
Figure 4.38. 'H NMR spectrum of polyB formed from 1 (in CDC1 3 , 500 MHz).
207
Figure 4.39. 1 H NMR spectrum of trans-poly[A-alt-B3] (in CDC 3 , 400 MHz).
214
Figure 4.40.
13C
NMR spectrum of trans-poly[A-alt-B3] (in CDC 3 , 100.61 MHz).
Figure 4.41. 'H NMR spectrum of trans-poly[A'-alt-B3] (in CDC 3 , 400 MHz).
Figure 4.42.
13C
NMR spectrum of trans-poly[A'-alt-B3] (in CDC1 3, 100.61 MHz).
Figure 4.43. 'H NMR spectrum of trans-poly[A-alt-B4] (in CDC 3 , 400 MHz).
Figure 4.44.
13C
NMR spectrum of trans-poly[A-alt-B4] (in CDC1 3 , 100.61 MHz).
Figure 4.45. 'H NMR spectrum of trans-poly[A-alt-B6] (in CDC 3 , 400 MHz).
Figure 4.46.
13C
NMR spectrum of trans-poly[A-alt-B6] (in CDC 3, 100.61 MHz).
Figure 4.47. 'H NMR spectrum of trans-poly[Ai-alt-B] (in CDC 3 , 500 MHz).
Figure 4.48.
13 C
NMR spectrum of trans-poly[Ai-alt-B] (in CDC1 3, 125 MHz).
Figure 4.49. 'H NMR spectrum of trans-poly[A3-alt-B] (in CDC1 3 , 400 MHz).
Figure 4.50.
13C
NMR spectrum of trans-poly[A3-alt-B] (in CDC1 3, 125 MHz).
15
214
216
216
218
218
220
220
222
222
224
224
List of Schemes
GENERAL INTRODUCTION
Scheme 1. The olefin metathesis reactions.
26
Scheme 2. The accepted mechanism of olefin metathesis proposed by Chauvin.
26
Scheme 3. General synthetic procedures for Mo and W olefin metathesis catalysts.
29
Scheme 4. The proposed mechanism of Z selectivity of MAP species bearing a bulky
terphenoxide ligand.
30
Scheme 5. Z-selective homocoupling olefin metathesis reactions of terminal olefin and 1,3dienes.
31
Scheme 6. Z- and enantioselective ring-opening cross metathesis by Mo MAP complex.
32
Scheme 7. Generation of high cis,syndiotacticpolymers of 2,3-dicarbomethoxynorbornadiene
with MAP catalyst.
32
Scheme 8. The two isomers of high-oxidation-state Mo and W alkylidene complexes.
33
CHAPTER 1
Scheme 1.1. Generation of alkylidene complexes employing pentafluorophenol or pyridinium
chloride as acid sources.
39
Scheme 1.2. Synthesis of [W(N-t-Bu)2(p-Cl)Cl(NH2-t-Bu)]2 (1w).
41
Scheme 1.3. Synthesis of W(N-t-Bu)2(CH2CMe3)2 (2w).
43
Scheme 1.4. Synthesis of W(N-t-Bu)(CHCMe3)C 2(py) 2 (3w).
44
Scheme 1.5. Synthesis of Mo(N-t-Bu)(CHCMe 3)(OR)2(NH 2CMe 3) (R = CH(CF 3)2 , 3 mo; R
=C 6 F5 , 4 mo).
46
Scheme 1.6. Synthesis of several W(NAr)(CHCMe 2Ph)C 2(bipy) species (Ar = 2,6-Me2C6H3,
2,6-i-Pr2C6H3, 2,6-Cl 2 C6H 3 , 2-i-PrC6H4; bipy = 2,2'-bipyridine). Only trans isomer was drawn.48
Scheme 1.7. Synthesis of W tert-butylimido bispyrrolide complexes, 1 2 w and 13w.
49
Scheme 1.8. Synthesis of Mo(N-t-Bu)(CHCMe3)(pyr)2(bipy) (5 mo).
50
Scheme 1.9. Synthesis of W(N-t-Bu)(CHCMe3)(2,5-Me 2pyr)(OHMT) (14w).
50
Scheme 1.10. Synthesis of W(N-t-Bu)(CHCMe3)(pyr)(OHIPT) (15w) and W(N-tBu)(CHCMe3)(pyr)(OHMT) (1 6 w).
51
Scheme 1.11. Synthesis of W(N-t-Bu)(CHCMe3)(pyr)(ODFT)(py) (1 7 w).
53
16
CHAPTER 2
Scheme 2.1. Synthesis of trans,HT-selective 3-substituted cyclooctenes by a Ru catalyst.
78
Scheme 2.2. Polymerization of 3-substituted cyclooctenes where R substituents are methyl, n82
hexyl, and phenyl groups.
Scheme 2.3. Synthesis of 3,4- and 5,6-substituted cyclooctene monomers.
91
Scheme 2.4. Polymerization of oxygen-containing cyclooctene monomers.
92
Scheme 2.5. Two possible 3-RCOE monomer approach to MAP catalyst (P = polymer chain). 93
Scheme 2.6. Four possible propagating alkylidenes for a given configuration at the metal center.
93
CHAPTER 3
Scheme 3.1. Previously reported synthesis of Mo and W chelating alkylidene complexes.
115
Scheme 3.2. Synthesis of Mo(N-t-Bu)(CH-o-MeOC 6H4)(OC6F5)2(t-BuNH2) (1mo) and W(N-t116
Bu)(CH-o-MeOC6H4)(Cl)2(py) (iw).
Scheme 3.3. Synthesis of Mo(N-t-Bu)2(CH2-o-MeOC6H4)2 (2 mo) and W(N-t-Bu)2(CH2-0MeOC6H4)2 (2w).
117
Scheme 3.4. Synthesis of Mo(N-t-Bu)(CH-o-MeOC6H4)(OR)2(t-BuNH2) (R = C6 Fs, C(CF3)3).
117
Scheme 3.5. Synthesis of W(N-t-Bu)(CH-o-MeOC6H4)(C)2(py) (1w).
119
Scheme 3.6. Synthesis of W(N-t-Bu)(CH-o-MeOC6H4)(pyr)(OHMT) (5w).
120
Scheme 3.7. Synthesis of W(N-t-Bu)(CHCMe3)(Cl)(OHMT)(py) (6w).
121
Scheme 3.8. Synthetic route to form W(N-t-Bu)(CHCMe3)(OHMT)2 (7w).
122
Scheme 3.9. Synthesis of W(N-t-Bu)(CHCMe3)(ODFT)2 (8w).
123
Scheme 3.10. Synthesis of W(N-t-Bu)(CHCMe3)(BiphenCF3)(py) (9w) and its alkylidene C-H
125
activation.
126
Scheme 3.11. Regeneration of 9w from 10w.
Scheme 3.12. ROMP of DCPD with catalyst 9w and 9w in the presence of B(C 6F5 )3 or B(C 6H5 )3.
127
Scheme 3.13. Synthesis of W(N-t-Bu)(CHCMe3)(BiphenMe)(py) (11w).
128
Scheme 3.14. Synthesis of W(N-t-Bu)(C3H6)(pyr)(ODFT) (1 2 w) and W(N-t-Bu)(C 3H 6)(ODFT)2
129
(13w).
17
CHAPTER 4
Scheme 4.1. Alternating copolymerization of 1 -subsitutted cyclobutene and cyclohexene.
156
Scheme 4.2. Synthesis of cis,syndio,alternatingpolymers employed by
Mo(NAd)(CHCMe2Ph)(pyr)(OHMT).
157
Scheme 4.3. Polymerization of 2,3-dicarbomethoxy-7-isopropylidenenorbomadiene (B) with
W(O)(CHCMe3)(Me2pyr)(PMe2Ph)(OHMT).
157
Scheme 4.4. Formation of a first insertion product of B with Mo(NAr)(CHCMe 3)(O-t-Bu) 2. 158
Scheme 4.5. Formation of trans-poly[A-alt-B] by 1.
159
Scheme 4.6. Synthesis of four >90% trans-poly[A-alt-B] using 1.
162
Scheme 4.7. Kinetic studies of reactions between MB with A and MA with B in a pseudo-firstorder regime.
163
Scheme 4.8. Anti and syn alkylidene isomers of 1.
164
Scheme 4.9. Four possible geometries from the first insertion product.
167
Scheme 4.10. Two isomers of the first insertion product.
168
Scheme 4.11. Four possible isomers of B insertion to 1.
170
Scheme 4.12. Proposed mechanism of forming trans-poly[A-alt-B] by 1 (P = polymer).
172
Scheme 4.13. Several MAP catalysts and a biphen catalyst used in this study.
177
Scheme 4.14. B-type monomers for alternating ROMP.
179
Scheme 4.15. A-type monomers for alternating ROMP.
181
18
List of Tables
CHAPTER 1
Table 1.1. Comparison of hydrogen bonding distances.
43
Table 1.2. Comparison of 1-octene homocoupling of 15w with W(3,5Me2C 6H3N)(C3H6)(pyr)(OHIPT).
52
Table 1.3. Crystal data and structure refinement for [W(N-t-Bu) 2Cl(p-Cl)(t-BuNH2)]2 (1w).
70
Table 1.4. Crystal data and structure refinement for [W(N-t-Bu)(CHCMe3)C2(py)]2 (3w).
71
Table 1.5. Crystal data and structure refinement for W(N-t-Bu)(CHCMe3)(pyr)(OHMT)(16w).72
Table 1.6. Crystal data and structure refinement for Mo(N-t-Bu)(CHCMe3)(pyr)(OHMT) (6 mo).
73
CHAPTER 2
Table 2.1. Summary of ROMP reactions in bulk 3-RCOE to give >98% cis,HT polymer.
82
Table 2.2. Characterization Data for cis,HT-poly(3-RCOE) Prepared using 0.02 mol% initiator
88
lc at 22 C.
Table 2.3. Variation of B(C6 F 5)3 equivalents for ROMP of 3-HexCOE (5000 equiv, neat, 22 'C)
90
using W(O)(CHCMe3)(Me2Pyr)(OHMT)(PMe2Ph) catalyst.
CHAPTER 3
Table 3.1 .Reactivity tests of W(N-t-Bu)(CHCMe3)(pyr)(OHMT) and 5w in 1 -octene
homocoupling.
120
Table 3.2. Reactivity tests of W(N-t-Bu)(CHCMe3)(pyr)(OHMT) and 6w' in ROMP of
DCMNBD.
123
Table 3.3. Polymerization of DCPD by W(N-t-Bu)(CHCMe3)(BiphenCF3)(py) (9w) in the
presence of Lewis acid.
127
Table 3.4. Crystal data and structure refinement for 3 mo.
150
Table 3.5. Crystal data and structure refinement for 10w.
151
CHAPTER 4
Table 4.1. List of kobs values of monomer A/B or A'/B' using catalyst 1.
164
Table 4.2. Determined rate constants for 1 at various temperatures.
166
19
Table 4.3. Summary of alternating copolymerization reactions with various bisalkoxide catalysts.
175
Table 4.4. Summary of alternating copolymerization reactions with various MAP and biphen
catalysts.
178
Table 4.5. Summary of alternating copolymerization reactions with various B monomers with A.
179
Table 4.6. Summary of alternating copolymerization reactions with various A monomers with B.
182
20
List of Abbreviations
0C
degrees Celsius
Ad
1 -adamantyl
Anal. Caled
analysis calculated
anti
isomer in which alkylidene substituent points away from the imido ligand
Ar
2,6-diisopropylphenyl
Ar'
2,6-dimethylphenyl
Ar*
2,6-(2,4,6-trimethylphenyl)C6H3
bipy
2,2'-bipyridine
COSY
Correlation Spectroscopy
d
doublet
DCMNBD
2,3-dicarbomethoxynorbomadiene
DCPD
endo-dicyclopentadiene
DFT
2,6-(C 6F5 ) 2C 6H 3
DME
1,2-dimethoxyethane
Et20
diethylether
eq (equiv)
equivalent
GC-MS
gas chromatography - mass spectrometry
h
hours
HIPT
2,6-(2,4,6-triisopropylphenyl)C6H3
HMT
2,6-(2,4,6-trimethylphenyl)C6H3
HSQC
Heteronuclear single quantum coherence
Hz
hertz
i-Pr
isopropyl
k
rate constant
K
Kelvin
kcal
kilocalories
ka/s
rate constant for alkylidene rotation from anti to syn
ks/a
rate constant for alkylidene rotation from syn to anti
Keq
equilibrium constant
21
m
multiplet
M
molar
MAP
monoalkoxide pyrrolide
Me
methyl
mol
mole
Me2pyr
2,5-dimethylpyrrolide
Mes
mesityl, 2,4,6-trimethylphenyl
mL
milliliter
mmol
millimoles
MPCP
3-methyl-3-phenylcyclopropene
"JAB
the coupling constant between atoms A and B through n bonds
OTf
OSO 2 CF 3
Ph
phenyl
ppm
parts per million
py
pyridine
pyr
pyrrolide
q
quartet
rac
racemic
ROMP
ring-opening metathesis polymerization
r.t.
room temperature
s
seconds or singlet
syn
isomer in which alkylidene substituent points toward the imido ligand
t
triplet
T
temperature
t-Bu
tert-butyl
THF
tetrahydrofuran
TMS
trimethylsilyl
tol
toluene
6
chemical shift
AST
entropy of activation
AHt
enthalpy of activation
22
AG+298
Gibbs free energy of activation at 298K
pL
microliter
pmol
micromolar
23
24
General Introduction
25
Formation of carbon-carbon double bonds has emerged as one of the most powerful tools
in chemistry. Specifically, olefin metathesis reactions involving exchange of substituents on
olefins between two different molecules using transition metal-based catalysts have been applied
to various fields of chemistry and materials science (Scheme 1).
2
R'
R
R'
2R
7-
+
/=_1
-1.
/-S
R'
R
R
Scheme 1. The olefin metathesis reactions.
The initial discovery of this reaction goes back as early as the 1950s, when Eleuterio
observed the genseration of 2-butene and ethylene from propylene using heterogeneous
olefin
molybdenum on aluminum catalysts.' Independently, several researchers observed similar
in
disproportionation results, including Peters and Evering in 19602 as well as Banks and Bailey
1964.3 The accepted mechanism, in which olefin metathesis is initiated by a metal carbene (M=C)
forms a
species, was proposed by Chauvin in 1971.4 The metal carbene reacts with an olefin and
metallacyclobutane intermediate. Subsequently, the metallacyclobutane breaks apart to form a new
olefin and a new metal carbene species. This new metal carbene species combines with another
olefin to continue the catalytic cycle (Scheme 2).
R,
R2\
M
, R2
R1R
.VM-/ R2
M""
-/ R1,
R2
cycloreversion
cycloaddition
Scheme 2. The accepted mechanism of olefin metathesis proposed by Chauvin.
The existence of metal-carbon double bonds was discovered by Fischer in 1964, and this
5
are
helped Chauvin to develop the olefin metathesis mechanism. Fischer carbenes
characteristically polarized such that the metal center is nucleophilic and the a-carbon is
electrophilic. In addition, Fischer carbenes tend to occur in low-oxidation-state late transition
metals, and are classified as singlet carbenes. Another type of metal carbene was discovered by
6
Schrock in 1974, firstly in the form of [(t-BuCH 2)3Ta=CHCMe3] species. The Schrock carbenes
are distinct from Fischer carbenes in that they are derived from triplet carbenes, the metal center
is highly electron-deficient, and the M=C bond is polarized such that the metal center is relatively
positive and the a-carbon is a nucleophilic center (Figure 1).
26
6- OMe
(OC) 5W=K6+
Ph
6+
CMe 3
(t-BuCH 2) 3Ta&(H
Fischer Carbene
Schrock Carbene
Figure 1. Two types of metal-carbon double bonds: Fischer carbene and Schrock carbene.
Olefin metathesis has progressed into a versatile catalytic transformation ever since.
Common types of olefm metathesis can be divided based on the substrates and products involved.
Terminal olefin cross metathesis is characterized by the exchange of substituents of two olefins to
form a new olefin and ethylene. Formation of ethylene is a driving force to this reaction. The
reverse reaction is ethenolysis which breaks up an internal double bond to form two terminal
olefins. Ring-closing metathesis involves the formation of cyclic olefins from acyclic olefins while
generating ethylene as a byproduct. The driving force for ring-opening cross metathesis and ringopening metathesis polymerization (ROMP) is the release of ring strain of the cyclic olefin
reactants. Polymers can also be formed using acyclic diene metathesis polymerization. Generic
examples of the aforementioned reactions are shown in Figure 2.
Cross metathesis
+
R1
_R2
I
R,
R2
+
=
Ethynolysis
Ring-Closing metathesis
+
+_
n
R1
Ring-Opening cross metathesis
_____________S,_R,
Ring-Opening metathesis polymerization
n
Acyclic diene metathesis polymerization
n
+ n
n
Figure 2. Several types of olefin metathesis reactions.
27
=
Many olefin metathesis catalysts have been developed, and the most successful catalysts
are based on Mo, W, and Ru. A class of Ru phosphine dichloride catalysts was introduced by
Grubbs in 1992,7 and several generations of Grubbs catalysts have been reported (Figure 3).8,9
PCy 3
Cl
I
N/N
Ph
N
ROPh
Ph
CI |
PCy 3
"N
X
PCy 3
X
Grubbs III
Grubbs 11
Grubbs I
Figure 3. Three generations of Ru-based catalysts.
The ruthenium catalysts in Figure 3 are 16e complexes and require dissociation of a
phosphine ligand in order to react with olefin species.1 0 Ru catalysts tend to be stable in the
presence of water and acidic functionalities, which makes them widely used among synthetic
chemists. Another major class of olefin metathesis catalysts is based on high-oxidation-state Mo
and W; three generations of such catalysts developed by Schrock are shown in Figure 4.11 Although
Mo and W catalysts are generally not stable in the presence of water, they are more stable to basic
functionalities such as phosphines or amines. In addition, they are generally more reactive than
Ru-based catalysts.
R"
R"I
I F3 C,,
N|
R
O
R"
R'
F3C
0
0
1
R'NM
R
OR'
CF3
CF 3
Bisalkoxide
Monoalkoxide Pyrrolide (MAP)
Chiral diolate
Figure 4. Examples of Mo and W based metathesis catalysts (M
=
Mo, W; R = Me or Ph).
The most common types of Mo and W catalysts have four-coordinate ligand environments
(including an imido ligand, an alkylidene ligand, and two other X-type ligands) and are 14e
systems. The imido ligand is either a substituted phenylimido with varying steric and electronic
effects12,1 3 or a tertiary alkylimido (tert-butyl or adamantylimido). 4"
The alkylidene ligand is
typically either a neopentylidene or neophylidene. Three generations of catalysts have been
28
identified based on their differing sets of X-type anionic ligands. Bisalkoxide catalysts contain two
identical tert-butoxide-based ligands; fluorinated tert-butoxide species tend to provide higher
reactivity due to enhanced electrophilicity at the metal.1 6 A second generation of catalyst contains
a enantiomerically pure chiral diolate ligand (biphenolate, binaphtholate); this class of catalyst has
shown excellent performance in asymmetric ring-closing metathesis reactions." In addition, this
geometry forces substituted norbornadiene monomers to approach one unique face of the catalyst
8
in each ROMP step, so that the isolated polymers contain high levels of cis, isotactic linkages.'
After the first discovery of the synthesis of MAP (MonoAlkoxide Pyrrolide) complexes in 2007,19
catalysts bearing both pyrrolide and alkoxide ligands were extensively studied. This third
generation of olefin metathesis catalysts are typically synthesized from bispyrrolide complexes,
9
and have shown superior reactivity compared to bispyrrolide complexes.'
The most commonly
used synthetic routes to the three generations of Mo and W catalysts are shown in Scheme 3.
W0 2C 2(DME)
or
2ArNH 2
4 NEt 3 , 8 TMSCI
_
_
Ar
N
Cl,, 1-,N'
---
_
ROH
R
-
N
Li
N
OTfR
/0
"Universal precursor"
- 2 LiOTf
Oj"".R
RO"
OR'
Bisalkoxide
"Universal precursor"
MAP
Ar
Ar
N
2 LiOR
OTf
OR'
R
R
Ar
2N
- 2 LiOTf
pyrrole
N OTf,
ArNH30Tf
R =Ph, Me
Ar
N
R
R
2
M =Mo, W
Ar
Ar
3TfOH
DME
_ _M
- 2 MgC
0
DME
Na2 MoO 4
2 RMe 2CCH 2MgCI
C
'
Ar
Ar
N
K-N
Ar
R
O
*
Chiral diolate
Scheme 3. General synthetic procedures for Mo and W olefin metathesis catalysts.
The synthesis of Mo and W olefin metathesis catalysts starts from metal oxo salts:
W02C12(DME) or Na2MoO4. Na2MoO4 is commercially available, but W02C12(DME) is typically
20
synthesized from WCl6 with treatment of TMS 20 in the presence of DME. Each metal salts is
treated with 2 equivalents of ArNH2, 4 equivalents of NEt3, and 8 equivalents of TMSC to form
M(NAr) 2 Cl2(DME).
Treatment
with
equivalents
two
of
Grignard
reagent
yields
M(NAr)2(CH2CMe2R)2 (R = Me or Ph) complexes. Addition of three equivalents of triflic acid to
M(NAr)2(CH2CMe2R)2 gives the 18e bistriflate complex M(NAr)(CHCMe2R)(OTf)2(DME) along
21 22
with the formation of anilinium salt and alkane from a-hydrogen abstraction. , This bistriflate
serves as a "universal precursor" and subsequent addition of alkoxide salts leads to formation of
bisalkoxide or chiral diolate species. In these complexes, DME does not remain bound to the metal
29
due to the crowded steric environment. To move forward in the synthesis of MAP complexes,
bistriflate complex is treated with lithium pyrrolide to form bispyrrolide complexes. MAP
complexes can be synthesized by protonating off one pyrrolide ligand via the addition of one
equivalent of alcohol.
One interesting characteristic of MAP complexes is that their reactivity toward olefins is
often superior to that of bispyrrolide or bisalkoxide complexes. According to a theoretical study
for M(NR)(CHCH3)(X)(Y) (M = Mo, W; R = Me or Ph) by Eisenstein, complexes with two
different X and Y ligands show enhanced reactivity as compared to complexes with identical X
and Y ligands. 2 3 Based on this result, MAPs, which have one good c-donor ligand (pyrrolide) and
a poor donor ligand (alkoxide), could produce enhanced reactivity over bisalkoxide catalysts with
two poor i-donor ligands. The lowest energy pathway for olefin coordination to the metal involves
olefin approach trans to a good donor ligand (pyrrolide). In addition, a new olefin product leaves
metallacyclobutane intermediate trans to the pyrrolide while interconverting the configuration at
the metal center. This prediction was corroborated experimentally by using PMe3 as a model for
ethylene. It was shown that PMe3 preferentially coordinates trans to the pyrrolide ligand to form
16e Mo MAP species. 24 In addition, interconversion of stereochemistry at the chiral metal center
is observed through a five-coordinate species containing a PMe3 adduct. A more recent paper by
Eisenstein posits that the combination of alkoxide and pyrrolide ligands not only improves the
efficiency of the catalytic cycle, but hinders decomposition of metallacyclobutane via P-H transfer,
which is a major deactivation pathway for catalysts of this type.25
The development of MAP complexes allows for various new types of reactivity, especially
Z-selective formation of small molecule product or polymers. Z selectivity can be achieved by
catalysts bearing a relatively small imido group and a bulky terphenoxide ligand. The proposed
mechanism dictates that when an olefin approaches an alkylidene trans to pyrrolide and forms a
metallacyclobutane intermediate, all substituents on the metallacyclobutane point up towards the
imido group and away from the terphenoxide due to steric reasons. When the metallacyclobutane
breaks up, Z olefin is formed and the stereochemistry at the metal center is inverted (Scheme 4).14
R
R (small)
N
(S)
1
Myr
pyr"' k
OR'
R2
R
R1
pR
pyr
2
OR' (large)
_
(R)
R'OM
V"
pyr
+
R1
R2
Scheme 4. The proposed mechanism of Z selectivity of MAP species bearing a bulky terphenoxide ligand.
30
Examples of Z-selective metathesis in homocoupling of terminal olefins and 1,3-dienes
have been reported. 2 6 ,27 Using W(NAr)(C3H6)(pyr)(OHIPT) (NAr = N-2,6-i-Pr2C6H3, OHIPT =
O-2,6-(2',4',6'-i-Pr3C 6H2)2C6H3), >90% Z-selective internal olefin products can be formed from
terminal olefin substrates with various substituents. In addition, >90% E,ZE-triene species can be
formed from 1,3-diene substrates, which proves the excellent chemo- and regioselectivity of this
catalyst (Scheme 5). Z-selective reactions are synthetically useful because mixtures of E and Z
products are typically difficult to separate.
2
>90% Z
R = n-butyl, n-hexyl, CH 2 Ph, CH 2 SiMe 3 , (CH 2 )ACO2Me,
(CH 2 )7CO 2Me, CH 2 Bpin, CH 2OBn, CH 2 NHTos, CH 2NHPh
N
0
R
2
R_\__ R
R
_
R
/
R
R
R'
R'
R'
>90% Z
R
=
Me, Ph, n-hexyl, R' = Me or H
Scheme 5. Z-selective homocoupling olefin metathesis reactions of terminal olefin and 1,3-dienes.
Z-selective metathesis can also be applied to a variety of cross metathesis reactions with
high enantioselectivity. A ring-opening cross metathesis reaction from the Hoveyda group between
a
strained
alkene
(oxabicycle)
and
a
(NAd
Mo(NAd)(CHCMe2Ph)(Me2pyr)((R)-OBr2Bitet)
Me 2C4H2N,
(R)-OBr2Bitet
where
terminal
=
alkene
(styrene)
adamantylimido,
(R)-Br2BitetOH
=
employing
Me2pyr
=
2,5-
(R)-3,3'-Dibromo-2'-(tert-
butyldimethylsilyloxy)-5,5',6,6',7,7',8,8'-octahydro-1,1'-binaphthyl-2-ol) is one example (Scheme
6).28 Careful selection of a strained cyclic alkene and a terminal olefin that are not easily
homocoupled was key to the initial success of these reactions, and various other cross partners,
including enol ethers or substituted aryl olefins, were reported.29
31
Ph
N
0
Br
Br
Br
TBSO
OTBS
R
QBSRR
0
R = 0-n-Bu, Ph
>98% Z, 98:2 er
Scheme 6. Z- and enantioselective ring-opening cross metathesis by Mo MAP complex.
Another application of Z-selective metathesis is in ROMP of norbomene and substituted
norbornadienes. Since the chirality at the metal center inverts at each productive metathesis step
and monomer approaches transto pyrrolide ligand every insertion, the resultant polymer contained
a highly cis,syndiotacticmicrostructure.1 4 The proposed mechanism for cis,syndiotacticROMP of
2,3-dicarbomethoxynorbomadiene is shown in Scheme 7.
R'E
r-
ROR-
/
1
R"
RO' M
MOZZzy
pyr
-
E
R
<E
E/
E
p-
y-M
OR
(R)
E
>
yI-M
Mo
/'
R
E'
EN
E
R
EI
R)
(S)
R"
M
pyr
RO (S)
(R)
E
E
E COOMe
cissyndiotactic
R= 2,6-mesityI 2CH3
Scheme 7. Generation of high
catalyst.
E
py'~N
cis,syndiotactic polymers of 2,3-dicarbomethoxynorbornadiene with MAP
An important feature of four-coordinate Mo and W alkylidene complexes is the existence
of syn and anti alkylidene rotational isomers. When the alkylidene substituent points toward the
imido ligand, it is deemed the syn isomer, whereas the anti isomer is formed when the substituent
points away from the imido ligand (Scheme 8). The imido ligand forms two n-bonds with d orbitals
from the metal (dxz and dyz if M=N is the z axis) so that the n-bond component of the M=C bond
has to be perpendicular to the metal-imido plane in order to maximize overlap with dxy orbital of
the metal. 30 In sum, the N=M=C-R moiety must be coplanar, so two possible isomers exist.
32
N
N
F3C
O
CF3
||
M
0
''CF
F3C
R
F3'C
'H
O"M
R
CF 3 0
F3C'CF 3
3
F3C
anti
syn
Scheme 8. The two isomers of high-oxidation-state Mo and W alkylidene complexes.
Typically, the syn isomer is thermodynamically more stable than the anti isomer due to the
existence of an a-agostic interaction between the C-H bond of the alkylidene and the metal. Syn
and anti isomers can be distinguished by NMR spectroscopy from the IJCH coupling constant of
the alkylidene C-H bond. IJCH of a syn alkylidene typically is -110-120 Hz, which is smaller than
that of a typical sp 2 -hybridized C-H bond (150 Hz), while an anti alkylidene shows a 'JCH of -140150 Hz.3 1 As a clear example of the agnostic interaction, the Ta=C-C angle from a neutron
diffraction study of [Ta(CHCMe3)(Cl)3(PMe3)]2 is 161 , and the angle for Ta=C-H is 850; the latter
2
is significantly different from the ideal angle for an sp -hybridized carbon (Figure 5). The
alkylidene ligand is distorted due to the aforementioned a-agostic interaction, and the C-H bond
32
has high p character, which explains its low IJCH value (90 Hz).
H
CI PMe 3
-Ta
---
C i'-*
C
C,
T6 j~
Me 3 PC1
161
0
H 85 0
Figure 5. The structure of [Ta(CHCMe3)(Cl)3(PMe3)2
Extensive studies on rotational isomers in the first generation of the Schrock catalyst
Mo(NAr)(CHR')(OR")2 (vide supra) were carried out. Rate constants for each isomer
3
interconversion and activation parameters were determined. 1 The barriers to rotation (AG
29 8)
of
30
the alkylidene ligand in four-coordinate systems are in the range of -15-18 kcal/mol. Electron-
withdrawing functionalities on the alkoxide ligands effect significant changes in the rate constants
for each interconversion. Mo(NAr)(CHR')(OR")
2
complexes favor the syn isomer over the anti by
a factor of 102-103 in non-coordinating solvents at room temperature. A more recent study on Mo
and W species bearing the sterically encumbering imido (2,6-dimesitylphenylimido) ligand show
33
that this ligand forces more anti formation, and the ratio of syn and anti isomer is approximately
1:1.1333 Studies on rate constants for isomer interconversion are important because the relative
timescale of interconversion versus reaction affects the microstructure of the product polymers. 31
Impressive advances in Z-selective reactions using the MAP framework inspired us to
explore the synthesis and reactivity of new types of catalysts. Chapter 1 of this dissertation will
focus on the synthesis of new tungsten tert-butylimido MAP complexes. Using these catalysts,
successful cis- and head-to-tail-selective polymerization of 3-substituted cyclooctenes were
performed and will be described in Chapter 2. The origin of the high selectivity is explored by the
observation of propagating species during the reaction. Chapter 3 delves into more understanding
of tungsten tert-butylimido complexes through ligand modifications. Finally, Chapter 4 describes
the first successful alternating copolymer formation using molybdenum catalysts from substituted
norbornadiene and cyclooctene monomers. The proposed mechanism for the high trans-selective
alternating copolymerization is thought to rely on interplay between syn and anti isomers. A series
of monomers and catalysts are tested for alternating ROMP and some general trends will be
discussed.
34
REFERENCES
(1)
Eleuterio, H. S. J. Mol. Catal. 1991, 65, 55-61.
(2)
Evering, B. L.; Peters, E. F. Catalysts and their preparation, 1960.
(3)
Banks, R. L.; Bailey, G. C. I&EC Prod. Res. Dev. 1964, 3, 170-173.
(4)
Jean-Louis Herisson, P.; Chauvin, Y. Die Makromol. Chemie 1971, 141, 161-176.
(5)
Fischer, E. 0.; Maasb6l, A. Angew. Chem. Int. Ed. Engl. 1964, 3, 580-58 1.
(6)
Schrock, R. R. J Am. Chem. Soc. 1974, 96, 6796-6797.
(7)
Nguyen, S. T.; Johnson, L. K.; Grubbs, R. H.; Ziller, J. W. J. Am. Chem. Soc. 1992, 114,
3974-3975.
(8)
Scholl, M.; Ding, S.; Lee, C. W.; Grubbs, R. H. Org. Lett. 1999, 1, 953-956.
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Love, J. A.; Morgan, J. P.; Trnka, T. M.; Grubbs, R. H. Angew. Chem. Int. Ed. 2002, 41,
4035-4037.
(10)
Sanford, M. S.; Love, J. A.; Grubbs, R. H. J Am. Chem. Soc. 2001, 123, 6543-6554.
(11)
Schrock, R. R. Chem. Rev. 2009, 109, 3211-3226.
(12)
Oskam, J. H.; Fox, H. H.; Yap, K. B.; McConville, D. H.; O'Dell, R.; Lichtenstein, B. J.;
Schrock, R. R. J Organomet. Chem. 1993, 459, 185-198.
(13)
Gerber, L. C. H.; Schrock, R. R.; Mnller, P.; Takase, M. K. J Am. Chem. Soc. 2011, 133,
18142-18144.
(14)
Flook, M. M.; Jiang, A. J.; Schrock, R. R.; MUller, P.; Hoveyda, A. H. J Am. Chem. Soc.
2009, 131, 7962-7963.
(15)
Jeong, H.; Axtell, J. C.; Tr6k, B.; Schrock, R. R.; MUller, P. Organometallics2012, 31,
6522-6525.
(16)
Schrock, R. R.; DePue, R. T.; Feldman, J.; Schaverien, C. J.; Dewan, J. C.; Liu, A. H. J
Am. Chem. Soc. 1988, 110, 1423-1435.
(17)
Alexander, J. B.; La, D. S.; Cefalo, D. R.; Hoveyda, A. H.; Schrock, R. R. J. Am. Chem.
Soc. 1998, 120, 4041-4042.
(18)
Totland, K. M.; Boyd, T. J.; Lavoie, G. G.; Davis, W. M.; Schrock, R. R. Macromolecules
1996, 29, 6114-6125.
35
(19)
Singh, R.; Schrock, R. R.; MUller, P.; Hoveyda, A. H. J. Am. Chem. Soc. 2007, 129,
12654-12655.
(20)
Dreisch, K.; Andersson, C.; Stailhandske, C. Polyhedron 1991, 10, 2417-2421.
(21)
Schrock, R. R.; Murdzek, J. S.; Bazan, G. C.; Robbins, J.; DiMare, M.; O'Regan, M. J
Am. Chem. Soc. 1990, 112, 3875-3886.
(22)
Schrock, R. R.; DePue, R. T.; Feldman, J.; Yap, K. B.; Yang, D. C.; Davis, W. M.; Park,
L.; DiMare, M.; Schofield, M. Organometallics1990, 9, 2262-2275.
(23)
Poater, A.; Solans-Monfort, X.; Clot, E.; Copdret, C.; Eisenstein, 0. J. Am. Chem. Soc.
2007, 129, 8207-8216.
(24)
Marinescu, S. C.; Schrock, R. R.; Li, B.; Hoveyda, A. H. J Am. Chem. Soc. 2009, 131,
58-59.
(25) Solans-Monfort, X.; Coperet, C.; Eisenstein, 0. J Am. Chem. Soc. 2010, 132, 7750-7757.
(26)
Jiang, A. J.; Zhao, Y.; Schrock, R. R.; Hoveyda, A. H. J. Am. Chem. Soc. 2009, 131,
16630-16631.
(27)
Townsend, E. M.; Schrock, R. R.; Hoveyda, A. H. J. Am. Chem. Soc. 2012, 134, 1133411337.
(28)
Ibrahem, I.; Yu, M.; Schrock, R. R.; Hoveyda, A. H. J Am. Chem. Soc. 2009, 131, 38443845.
(29)
Yu, M.; Ibrahem, I.; Hasegawa, M.; Schrock, R. R.; Hoveyda, A. H. J Am. Chem. Soc.
2012, 134, 2788-2799.
(30)
Schrock, R. R.; Crowe, W. E.; Bazan, G. C.; DiMare, M.; O'Regan, M. B.; Schofield, M.
H. Organometallics1991, 10, 1832-1843.
(31)
Oskam, J. H.; Schrock, R. R. J Am. Chem. Soc. 1993, 115, 11831-11845.
(32)
Wood, C. D.; McLain, S. J.; Schrock, R. R. J Am. Chem. Soc. 1979, 101, 3210-3222.
(33)
Gerber, L. C. H.; Schrock, R. R.; MUller, P. Organometallics2013, 32, 2373-2378.
36
Chapter 1
Synthesis of Molybdenum and Tungsten Alkylidene Complexes
Containing a tert-butylimido Ligand
Portions of this chapter have appeared in print:
Jeong, H.; Axtell, J. C.; T6r6k, B.; Schrock, R. R.; Mtiller, P. Syntheses of Tungsten tertbutylimido and Adamantylimido Alkylidene Complexes Employing Pyridinium Chloride As the
Acid. Organometallics, 2012, 31, 6522 - 6525.
Jeong, H.; Kozera, D. J.; Schrock, R. R.; Smith, S. J.; Zhang, J.; Ren, N.; Hillmyer, M. A. ZSelective
Ring-Opening
Metathesis
Polymerization
of 3-Substituted
Cyclooctenes
by
Monoaryloxide Pyrrolide Imido Alkylidene (MAP) Catalysts by Molybdenum and Tungsten.
Organometallics,2013, 32, 4843 - 4850.
37
0
INTRODUCTION
Over the past three decades, high-oxidation-state Mo and W imido alkylidene complexes
have progressed into highly active and tunable catalysts for olefin metathesis. Enantiomerically
pure chiral metathesis catalysts were developed that contain chiral diolate ligands and these
catalysts have been shown to form cis,isotactic polymers"2 as well as enantioenriched ringclosing metathesis products. 3 Recently, much effort has focused on the development of olefin
metathesis catalyst with monoalkoxide pyrrolide (MAP) ligands (Figure 1.1). Complexes bearing
sterically demanding aryloxide ligands have been shown to be highly Z-selective in
homocoupling of terminal olefins, 4 homocoupling of 1,3-dienes, 5 ring-opening metathesis
polymerization, 6 and ring-opening cross-metathesis. 7
Ph
oPh
N"/N
R
R
0
N
R
R
0
tBu
R
R
H
R = Me or i-Pr
1
2
3
Figure 1.1. Representative Z-selective Mo and W olefin metathesis catalysts bearing bulky aryloxide and
pyrrolide ligands (1,2) and an asymmetric Mo catalyst bearing an adamantylimido ligand (3).
Several molybdenum adamantylimido complexes have shown superior reactivity
compared
to
arylimido
complexes
in
some
metathesis
reactions.
For
example,
Mo(NAd)(CHCMe2Ph)(pyr)(OR) (1, NAd = adamantylimido, OR = 2,6-dimesitylphenoxide or
O-2,6-(2',4',6'-i-Pr3C 6H2) 2C 6H 3) catalysts are highly effective in generating cis,syndiotactic
polymers of 2,3-dicarbomethoxynorbomadiene. 6 Mo(NAd)(CHCMe2Ph)((S)-OBiphenme) (3, (S)OBiphenMe = 3,3'-di-tert-butyl-5,5',6,6'-tetramethyl-1,1'-biphenyl-2,2'-diolate) has proven to be
an efficient catalyst in asymmetric ring-opening/cross-metathesis
reactions.8
These Mo
alkylimido compounds are known to be distinct from phenylimido complexes in terms of
electronic and steric properties. 9 Since no W alkylimido alkylidene complexes have previously
been synthesized, W catalysts bearing an adamantylimido or any alkylimido group are of great
interest. In addition, since the catalyst W(NAr)(C3H 6 )(pyr)(OHIPT) (2, NAr = N-2,6-i-Pr2C6H3,
38
= O-2,6-(2',4',6'-i-Pr 3C6H2)2C6H3)
OHIPT
and Z-selectivity for
shows higher chemo-
homocoupling of terminal olefins and 1,3-dienes than its Mo analogue, synthesis of W
alkylimido species would allow direct comparison of the catalytic properties with Mo alkylimido
species.
Generation of the alkylidene functionality is the key step in the synthesis of Mo and W
imido alkylidene complexes. Typically, this can be achieved by using 3 equivalents of triflic acid
to protonate and remove one imido group from a Mo or W dialkyl diimido species. Subsequent
a-hydrogen abstraction and loss of an alkyl group result in formation of an alkylidene species
(See General Introduction). Currently, complexes of the type M(NR)(CHR')(OTf)2(DME) (M =
Mo or W, R' = CMe3 or CMe2Ph, DME = 1,2-dimethoxyethane, OTf
=
OS02CF 3 )
serve as
universal precursors to olefin metathesis catalysts.'"' The triflate ligands are easily displaced
with alkoxides or pyrrolides in the next step of the synthesis. However, in certain cases, triflic
acid does not successfully induce the formation of alkylidene complexes and other acids must be
used (Scheme 1.1).
F
F
2 HOC6 F 5
N
F
F
- Me 3 CPh
O N
N
F
0Mo
F
F
PPh
F
F
Ph
NH2
F
HCI
Mes
Mes
3
-- N
_N
- t-BuNH 3CI
-
Ph
Ph
Mes
Mes
C1, NN
II Ni
CI MO,
Me 3CPh
Ph
Mes = mesityl
Scheme 1.1. Generation of alkylidene complexes employing pentafluorophenol or pyridinium chloride as acid
sources.
As shown in Scheme 1.1, Gibson et al. previously reported the synthesis of the alkylidene
complex Mo(NAr)(CHCMe2Ph)(OC6F5)2(NH2-t-Bu)
from Mo(NAr)(N-t-Bu)(CH2CMe2Ph)2 by
treatment with 2 equivalents of pentafluorophenol.1 2 Pentafluorophenol selectively protonates the
39
more basic tert-butylimido rather than 2,6-diisopropylphenylimido ligand. Another example
employing other acid sources instead of triflic acid in generating alkylidene species is the
synthesis of Mo(NAr*)(CHCMe2Ph)C2(L) (NAr* = 2,6-dimesitylphenylimido; L = pyridine or
3,5-lutidine) from the mixed imido species Mo(NAr*)(N-t-Bu)(CH 2 CMe 2 Ph) 2 and pyridinium
chloride or 3,5-lutidinium chloride.' 3 This was the first example of the formation of an imido
alkylidene complex using HCl derivatives, and the coordination of pyridine ligands is thought to
play a significant role. Another interesting aspect in these examples is that although the
aforementioned two examples contain mixed-imido species, similar acid sources could be
employed on bis(tert-butylimido) complexes to generate tert-butylimido alkylidene complexes.
Catalysts bearing the MAP framework are particularly desirable because their reactivity
toward olefins is sometimes much greater than that of bisalkoxide or bispyrrolide complexes.14
Therefore, research has focused on synthesizing MAP complexes of Mo and W tert-butylimido
species. Part I of this chapter details the routes for the synthesis of Mo and W tert-butylimido
alkylidene complexes and Part II will discuss the synthetic routes towards MAP complexes.
RESULTS AND DISCUSSION
I. Routes for the Synthesis of tert-butylimido Alkylidene Complexes
A. Synthesis of [W(N-t-Bu)2Cl(p-Cl)(t-BuNH2)2
A logical
starting material for tungsten tert-butylimido
complexes is W(N-t-
Bu)2C12 (DME) because W(NAr)2C1 2(DME) is the first step for arylimido complexes. 10 However,
attempts to prepare W(N-t-Bu)C1 2(DME) from W0 2C1 2(DME), tert-butylamine, NEt 3 , and
TMSC under analogous conditions employed for arylimido species did not yield W(N-tBu)2C12(DME). W(NC 6Fs)C1 2 (DME) can be synthesized by treatment of W0 2C 2 (DME) with 2
equivalents of C 6F 5NSO under a flow of argon in refluxing DME and toluene with the extrusion
of SO 2 .15 However, it was reported that synthesis of W(NAd)C1 2 (DME) was not successful upon
treatment of W0 2 C12 (DME) with Ad-N=S=0 (Ad = I-adamantyl).
There was no literature
17
report of W(N-t-Bu)Cl2(DME). However, W(N-t-Bu)2C1 2(py) 2 had been reported previously. "18
16
Another diimido compound, W(N-t-Bu)2C12(NH 2-t-Bu), was prepared previously by
Nielson et al. through addition of 4 equivalents of t-BuNH(TMS) to WCl 6 .1 9 This compound also
40
can be synthesized by adding 7 equivalents of tert-butylamine to WCl 6 in benzene or in a
reaction between WO2Cl 2(DME) and t-BuNH(TMS). 2 0 Nielson concluded that W(N-tBu)2C12(NH2-t-Bu) is a dimer in which the tert-butylimido ligands bridge between the tungsten
metal center and the two chloride ligands are trans to each other to alleviate steric congestion.
This conclusion was based on IR spectroscopy and by analogy with [{WCl2(u-NPh)(N-tBu)(NH2-t-Bu)}2] and [{WCl2 (p-NC 6H4Me-p)(N-t-Bu)(NH2-t-Bu)}2] .21 Both of these mixedimido compounds have been analyzed by X-ray crystallography; the arylimido groups are ptbridging
and
the tert-butylimido
groups
are
terminal.
As reported,
[W(N-t-Bu)2(U-
CL)Cl(NH2CMe 3)]2 (1w) can be synthesized by treatment of WCl1 with 4.5 equivalents of N-tbutyltrimethylsilylamine in toluene for 24 h at room temperature in 63% yield (Scheme 1.2).
Compound 1w can be prepared on a 15g scale. However, the X-ray crystal structure of 1w that
we obtained showed that two chloride ligands are bridging between the two W centers (Figure
1.2). Each tungsten atom bears two imido groups (N(2), N(3) for W(I) and N(5), N(6) for W(2))
and one amine group. The tungsten-amine distances are -2.2 A and the tungsten-imido distances
are -1.7 A, which match well with previous examples. 22 It is interesting to note that the two
independent imido groups have quite different C-N-W bond angles: 159.360 for C(5)-N(2)-W(1)
and 177.24* for C(9)-N(3)-W(1).
4.5 (t-Bu)NHTMS
N
WC16
NH2
Cl
CIN
W
VV
Toluene
24 h, r.t.
N
I CII
CI
H 2N
1w (67%)
Scheme 1.2. Synthesis of [W(N-t-Bu)2(p-C1)C(NH2-t-Bu)2 (1w).
41
N
C2)
C(1
N(1)h
C(17)
NM
N&5
CM4)
NO3
C(
5)
C(21)
C)
N(2)
N(4
Figure 1.2. X-ray crystal structure of 1w. Thermal ellipsoid plots shown at 50% probability level; Hydrogen
atoms are omitted for clarity. Selected bond distances (A) and angles(*): W(1)-Cl(1) = 2.3942(6), W(1)-CI(3)
= 2.6104(6), W(1)-CI(4) = 2.8063(6), W(1)-N(1) = 2.210(2), W(1)-N(2) = 1.754(2), W(1)-N(3) = 1.743(2), W(2)Cl(2) = 2.4034(6), W(2)-Cl(3) = 2.7825(6), W(2)-CI(4) = 2.6065(6), W(2)-N(4) = 2.208(2), W(2)-N(5) = 1.758(2),
W(2)-N(6) = 1.744(2), W(1)-N(1)-C(1) = 126.63(15), W(1)-N(2)-C(5) = 159.36(18), W(1)-N(3)-C(9) =
177.24(19), W(2)-N(4)-C(13) = 127.09(15), W(2)-N(5)-C(17) = 153.56(18), W(2)-N(6)-C(21) = 175.18(18).
In this structure, the W(1)-Cl(3) distance (2.6104(6)
A)
trans to the linear imido group is
shorter than the W(1)-Cl(4) distance (2.8063(6) A) trans to the bent imido group. This seems
counter to the general principle that linear imido groups exert a stronger trans influence than do
bent imido groups. However, it was postulated that the dimer structure was held together not by
bridging chloride ligands, but by hydrogen bonding between a hydrogen of the t-butylamine
ligand and a terminal chloride on the neighboring tungsten center. The H4A .Cl(1) distance is
2.448 A and the N4-.Cl(1) distance is 3.340 A. Similar examples in which t-butylamine ligands
are involved in intramolecular N-H.Cl interactions within the dimeric unit can be found in the
phenylimido and p-tolylimido bridging dimeric structures of [{WCl2(U-NPh)(N-t-Bu)(NH2-tBu)}2] and [{WCl 2(U-NC 6H4Me-p)(N-t-Bu)(NH2-t-Bu)}2], respectively (Table 1.1). However,
the hydrogen bonding distances in compound 1w are slightly longer than those in the two
examples and those in a database study. 23 It was reported that a monomeric derivative of 1w can
18
be formed through addition of pyridine or phosphine ligand. However, in the case of
[W(NAd) 2(U-Cl)Cl(NH2Ad)]2, which is the 1-adamantylimido analogue of 1w, heating in DME
at 120 *C for 24 h did not lead to a monomeric DME adduct.16
42
Table 1.1. Comparison of hydrogen bonding distances.
Compound
H .Cl (A)
N Cl (A)
[W(N-t-Bu)2(u-Cl)Cl(NH 2-t-Bu)] 2 (1w)
2.448
3.340
[{WCl2(u-NPh)(N-t-Bu)(NH 2-t-Bu)}2]
2.173
3.241
[{WCl 2(u-NC 6H 4Me-p)(N-t-Bu)(NH 2-t-Bu)}2]
2.179
3.245
B. Synthesis of W(N-t-Bu)2(CH2CMe3)2
Preparation of W(N-t-Bu) 2(CH2CMe 3)2( 2 w) was accomplished in 87% yield by treating
1w with 2 equivalents of neopentylmagnesium chloride. Despite of presence of the NH2-t-Bu
ligand in 1w, formation of monomeric 2 w proceeded smoothly in diethyl ether (Scheme 1.3). The
synthesis of M(NAr*)(N-t-Bu)(CH2CMe2Ph)2 (M
=
Mo, W; NAr* = 2,6-dimesitylphenylimido)
has also been reported from the reaction of M(NAr*)(N-t-Bu)Cl2(NH2CMe3) with Grignard
reagent.' 3 Through bypassing W0 2 C12 (DME), the synthesis of di(alkylimido) dineopentyl
complexes can be achieved in one less step compared to the synthesis of analogous arylimido
complexes. Complex 2 w is obtained as a brown oil, which solidifies only at -20 'C. Sublimation
(60 mtorr, 50 "C) has been attempted in order to see whether pure solid product can be obtainable.
However, 2w was not obtained as a solid, and minor decomposition was observed via 'H NMR
spectroscopy after the sample was heated up to 100 'C. Analogous alkylimido compound
W(NAd) 2 (CH 2CMe 3)2 and W(NAd)(CH2CMe2Ph)2 have been isolated as solids.'
N
NH2
N
Cj"
CI
CI
CI
H 2N
N
2 Me 3 CCH 2MgCI
N
N
Diethyl ether
N
6
-30 'C to r.t.
4 h
2w (87% per W)
1w
Scheme 1.3. Synthesis of W(N-t-Bu)2(CH2CMe3) 2 (2 w).
43
C. Synthesis of W(N-t-Bu)(CHCMe3)C2(py)2
With complex 2w in hand, alkylidene synthesis was attempted using a variety of acids.
Previously, alkylidene compounds have been synthesized from bisarylimido species upon
treatment of triflic acid.'
0
Reaction of 2w with three equivalents of triflic acid yielded a product
that showed four alkylidene peaks in the 'H NMR spectra, along with W-CH2 resonances and
multiple tert-butyl peaks. Clean isolation of the desired compound was not successful. Other acid
reagents were tested with
2
w: 3 equivalents of HCl in diethyl ether/DME, 2 equivalents of
pentafluorophenol, and 2 equivalents of perfluoro-tert-butanol. Alkylidene peaks were observed
by 'H NMR spectroscopy in some cases, but isolation of the desired product was not successful.
W(N-t-Bu)(CHCMe3)Cl2(py)
2
(3w) can be synthesized by treating
2w
with 3 equivalents of
pyridinium chloride in diethyl ether (Scheme 1.4). A similar reaction with 2 equivalents of
pyridinium chloride has also been attempted with the goal of generating compound
3w
and t-
butylamine (bp = 46 C), which can be separated by filtration or removed in vacuo. However, 2
equivalents of acid cannot fully convert the starting material into product, and the corresponding
workup does not allow for clean isolation of the desired product.
N
3 pyHCI
N
C
Diethyl ether
-30 IC to r.t.
C
19 h
3
2w
Scheme 1.4. Synthesis of W(N-t-Bu)(CHCMe3)C1
2 (py)2
w (73%)
(3 w).
An X-ray diffraction study of 3w was conducted on crystals obtained through
recrystallization of 3 w from a mixture of methylene chloride and pentane. The structure was
determined to be a dimer, [(W(N-t-Bu)(CHCMe 3 )Cl(p-Cl)(py)] 2 (3w'), with two bridging
chloride ligands (Figure 1.3). The neopentylidene ligand is found to be in the syn orientation and
is highly disordered. One pyridine ligand is bound to each tungsten center. It is postulated that
the more electron-donating t-butylimido group (compared to arylimido groups) renders the
second pyridine ligand labile and dimer formation upon recrystallization. Compound 3w'
crystallized in the monoclinic space group P2 1/c with half a molecule 3w' in the asymmetric unit.
The second half is generated by the crystallographic inversion center. The W(1)-N(1) bond
44
length is 1.687(6), which is the shortest W = N bond known amongst analogous adamantylimido
(W=NAd bond length is ~1.71 A) and other arylimido alkylidene complexes. Only one
compound with a shorter W=N-t-Bu distance than 3w was found from the Cambridge Structural
Database: W'v(N-t-Bu)(silox) 2 (silox = t-Bu3SiO) where the W=N distance is 1.658 A. Other
bond length and angles are normal, as expected for W imido alkylidene species; values are given
in Figure 1.3. W(l)-Cl(l) bond length is shorter compared to W(l)-Cl(2) and W-Cl(2A) because
it is terminal whereas the other two are bridging between two tungsten centers.
CI1A)
C01)
NO2
N 2 A)
CA
NMN
C(.2) CM
10
CI1)
Figure 1.3. X-ray crysal structure of 3w'. Thermal ellipsoid plots shown at 50% probability level; Hydrogen
atoms are omitted for clarity. Selected bond distances (A) and angles(*): W(1)-Cl(1) = 2.4055(13), W(1)-Cl(2)
= 2.6085(13), W(1)-Cl(2A) = 2.6781(13), W(1)-N(1) = 1.687(6), W(1)-N(2) = 2.207(5), W(1)-C(1) = 1.923(9),
W(1)-Cl(2)-W(1A) = 105.28(4), W(1)-N(1)-C(11) = 169.8(5), W(1)-C(1)-C(2) = 147.0(12).
Generation of alkylidenes using pyridinium chloride has several advantages over using
triflic acid. Pyridinium chloride is cheap, non-volatile, and handling it inside of the glove box is
much easier compared to triflic acid. In addition, substitution of a single chloride ligand from
dichloride alkylidene complexes has shown to be easier than substitution of a single triflate
ligand in bistriflate alkylidene complexes: M(NAr*)(CHCMe2Ph)C2(py) (M
=
Mo, W)
compound was synthesized employing pyridinium chloride; and various monoalkoxide
monochloride compounds can be synthesized by substitution reaction of one chloride ligand with
lithium alkoxide.13 ' 24 W(O)(CHCMe 3)Cl(OHIPT)(PMe2Ph) is another example, which was
25
synthesized from the reaction of W(O)(CHCMe 3)C2(PMe2Ph)2 with LiOHIPT. Although there
45
_____/ _______I
is one report of a monotriflate complex, Mo(NAd)(CHCMe 2Ph)(OTf)(OHIPT), which was
synthesized by the reaction between Mo(NAd)(CHCMe 2Ph)(OTf) 2 (DME) and LiOHIPT, this
synthetic route could not be applied to other imido complexes. Attempts to synthesize a
monotriflate complex with LiOHMT (HMT = 2,6-(2,4,6-Me 3C6H 2)2C 6H 3) were not successful
for other Mo(NAr) species (Ar = N-2,6-i-Pr2C6H3, N-2,6-Me2C 6H 3, N-2-i-PrC 6H4).2 6
D. Synthesis of Molybdenum Alkylidene Complexes
Previously reported molybdenum tert-butylimido complexes Mo(N-t-Bu)2Cl2(DME) 27
(Imo) and Mo(N-t-Bu)2(CH2CMe3)2 2 8 (2 mo) were synthesized in high yield. As previously
reported,
2 mo
2 mo
was obtained as an oil as was 2 w. Attempts to precipitate
in MeCN were not
successful, so it was carried to the next step as an oil. Osborn et al. reported the synthesis of an
molybdenum tert-butylimido alkylidene species by treating 2 mo with hexafluoro-2-propanol (pKa
=
9.3)29
to generate Mo(N-t-Bu)(CHCMe 3)(OCH(CF 3)2)2(NH2-t-Bu) (3mo). 2 8 Compound
3 mo
was
reported as an oil, and the reported yield was 80%. However, in our hands, it was obtained as an
off-white solid in 26% yield; the low yield was probably due to its high solubility even in
pentane. When two equivalents of pentafluorophenol (pKa = 5.5)30 were used instead, Mo(N-tBu)(CHCMe3)(OC6F5 )2(NH2-t-Bu) (4 mo) could be obtained with superior yield (84%) (Scheme
1.5).
Na2 MoO4
DME
18 h, 70 0 C
-
2 t-BuNH 2
8 TMSCI
4 Et 3N
N
2 Me 3CCH 2 MgCI
C
11N
/
o
ION
"*CI
Mo,
N
Diethyl ether
-30 C to r.t.
C
2 h
Diethyl ether
-30 *C to r.t.
4h
2
IMo (92%)
N
2.2 ROH
0
H2N
0'
3
Mo (92%)
4
Scheme 1.5. Synthesis of Mo(N-t-Bu)(CHCMe3)(OR)2(NH2CMe3)
(R = CH(CF3)2,
3
Mo
/e \
OR
M0 R = CH(CF 3) 2 (26%)
Mo R = C6 F 5 (84%)
mo; R =C6FS,
4
mo).
Several other acid sources were explored to generate alkylidene species: perfluoro-tertbutanol, 2-trifluoromethyl-2-propanol, phenol, pyridinium chloride, HCl solution in diethyl
ether/DME, and triflic acid. No fluorinated alcohols having t-butanol frameworks were
successful in generating alkylidene species; presumably steric effects might hinder the formation
of 5-coordinate species as in compound
3 mo
or 4 mo. Attempts using phenol (pKa = 9.97)31, and
HCl-drived acids were also unsuccessful. When triflic acid (pKa
46
=
-15) was used to generate
alkylidene species from
2 mo,
the product could not be isolated as a DME or THF adduct,
although it could be isolated as a solid that contains two pyridine ligands.
E. Tungsten Alkylidene Formation Using Milder Acids
As HCl-based acid sources proved to be highly effective in generating tert-butylimido
alkylidenes, the use of other acids instead of triflic acid in generating W arylimido alkylidene
complexes was explored. W(NAr')2(CH2CMe2Ph)2 (4w, NAr'= N-2,6-Me2C6H3) was synthesized
according to the literature report10 and treated with 3 equivalents of HCl solution in Et 2 O/DME.
However, no identifiable alkylidene peak was observed by 'H NMR spectroscopy. It was found
that the addition of 1 equivalent of 2,2'-bipyridine to 4w followed by addition of two equivalents
of HCl in Et2 O or pyridinium chloride gives W(NAr')(CHCMe2Ph)C2(bipy) (5w, bipy = 2,2'bipyridine) which was isolated in 90% yield. 5w was insoluble in Et 2 0 and could be isolated
cleanly from soluble byproducts, 2,6-dimethylaniline and t-butyl benzene. No other byproducts
were observed by 'H NMR spectroscopy. The alkylidene 'H NMR peaks 5w at 11.29 ppm and
10.48 ppm in CD 2 Cl2 are ascribed to cis and trans isomers, respectively. The trans isomer shows
two peaks in the alkyl region, one for the equivalent methyl groups on the imido ligand and one
for the neophylidene ligand. However, the cis isomer shows 4 peaks in the alkyl region, one for
each of four inequivalent methyl groups. The ratio of cis and trans isomers varies with the
concentration of the sample, according to 'H NMR spectroscopy.
'JCH
values for each isomer of
5w were found to be 124 Hz (cis isomer, 11.29 ppm) and 115 Hz (trans isomer, 10.48 ppm), so
both isomers contain a syn alkylidene under these conditions. 32 Three other analogs that contain
different imido groups (2,6-diisopropylphenyl imido (7w), 2,6-dichlorophenyl imido (9w), orthoisopropylphenyl imido (11w)) were synthesized via this route. The best results were obtained
with HCl as the acid source instead of pyridinium chloride (Scheme 1.6). It should be noted that
previous attempts to synthesize a 2,6-dichlorophenylimido neophylidene complex using triflic
acid have failed; only neopentylidene species have been reported for this imido complex. 33
47
Ar
1NAr
Ph
1. 2,2'-bipyridine
2. 2 HCI in Et 2O
Ph
Diethyl ether
-30 C to r.t.
Ar
I
CIN
, Ph
N
N
15 h
Ar
=
2,6-Me 2C6 H 3 (4 w)
2,6-i-Pr2 C 6 H 3 (6 w)
2,6-C 2 C6 H 3 ( 8 w)
2-i-PrC6 H4 (0Ow)
2,6-Me 2C 6 H 3 ( 5 w), 90%
2,6-i-Pr2 C 6 H 3 ( 7 w), 60%
2,6-C 2 C6 H 3 (9 w), 54%
2-i-PrC 6 H4 (I1w), 57%
,
Scheme 1.6. Synthesis of several W(NAr)(CHCMe2Ph)C2(bipy) species (Ar = 2,6-Me2C6H3, 2,6-i-Pr2C6H 3
2,6-Cl2C6H3, 2-i-PrC6H4; bipy = 2,2'-bipyridine). Only trans isomer was drawn.
With these promising results, attempts to make alkylidene complexes using other
coordinating ligands have been pursued. However, HCl in Et 20 in the presence of one equivalent
of TMEDA, PMePh 2, or Cy 2PCH2 CH 2PCy 2 were not successful in making alkylidene complexes
in these systems. When 2 or 3 equivalents of pyridinium chloride were added to 4 w, formation of
W(NAr')(CHCMe 2Ph)Cl2(py) 2 was observed by 'H NMR spectroscopy, but the isolated yield
was low (8.4%); This contrasts with 3w, which can be synthesized upon treatment of 2 w with 3
equivalents of pyridinium chloride. Based on the results discussed above, it is likely that
coordination of 2,2'-bipy increases the steric congestion around the tungsten center which
induces a-H abstraction with elimination of t-butylbenzene to afford a stable neophylidene
complex. Although it is not exactly clear when 2,2'-bipy binds during this reaction, coordination
of 2,2'-bipy to
4w
before addition of acid was excluded because there was no sign of adduct
formation based on 'H NMR spectroscopy when 1 equivalent of 2,2'-bipy was added to 4 w at
room temperature.
II. Synthesis of MonoAlkoxide Pyrrolide (MAP) Complexes of Mo and W tert-butylimido
Species
A. Synthesis of Bispyrrolide Complexes
Bispyrrolide complexes are useful precursors for synthesizing MAP complexes.' 4 Upon
addition of one equivalent alcohol, MAP compounds can be synthesized and isolated easily by
removing the pyrrole in vacuo. Synthesis of bispyrrolide complexes bearing either 2,5-
48
dimethylpyrrolide ligands or pyrrolide ligands were attempted with Mo and W tert-butylimido
alkylidene complexes.
Li
2 Lipyr
Toluene
N'
-30
C to r.t.
8h
1 2 w (58%)
Toluene
Toluene
W0
CN
0.95 (2,2'-bipy)
|-30
Cl
"C to r.t.
3 h
r.t., 12
NWr>
I
N
h
N
13W (83%)
3w
Scheme 1.7. Synthesis of W tert-butylimido bispyrrolide complexes, 1 2 w and
13 w.
Treatment of 3w with 2 equivalents of lithium 2,5-dimethylpyrrolide in toluene generated
W(N-t-Bu)(CHCMe3)(2,5-Me2pyr)2 (1 2 w) in 58% yield. The 'H NMR spectrum of 12w showed
that pyridine is labile so typically less than 1 equivalent of pyridine is observed. Upon
recrystallization of the crude product pyridine-free 1 2 w can be isolated. However, attempted
synthesis of W(N-t-Bu)(CHCMe3)(pyr)2 in the same manner as 1 2 w was not successful.
Therefore, synthesis of a 2,2'-bipyridine adduct of the bispyrrolide species was attempted in
order to isolate the desired compound cleanly. This method was adapted from a recent report, 34
in
which
various
dipyrrolide
species
could
be
prepared
in
situ
from
Mo(NR)(CHCMe2Ph)(OTf)2(dme) complexes and subsequently treated with 0.8-0.9 equivalents
of 2,2'-bipyridine to produce the insoluble bipyridine adduct of the dipyrrolide complex.
Compound 3w was treated with 2 equivalents of Lipyr at -30 'C. The mixture was allowed to
warm to room temperature over 3 hours in toluene, at which time complete consumption of
starting material was observed by 'H NMR spectroscopy. The mixture was filtered through a pad
of Celite to remove salts. Subsequently, 0.95 equivalents of 2,2'-bipyridine were added to the
reaction mixture and the mixture was stirred overnight. W(N-t-Bu)(CHCMe3)(pyr)2(bipy) (13w)
was isolated by filtration in 83% yield. The 'H NMR spectrum of 13w obtained in CD 2Cl 2
showed three alkylidene resonances at room temperature. However, after the sample was heated
up to 100 'C overnight, the 'H NMR spectrum showed just one major alkylidene signal. In
addition, there was a coupling between the tungsten and the alkylidene proton ( 2 JWH -5 Hz).
'JCH
values for each isomer of 13w were found to be 118 Hz (11.09 ppm), 110 Hz (10.86 ppm), and
118 Hz (10.46 ppm), so all isomers contain a syn alkylidene under these conditions.
49
Attempts to form Mo(N-t-Bu)(CHCMe3)(pyr) 2 from 4 mo with 2 equivalents of lithium
pyrrolide were not successful, so the 2,2'-bipyridine adduct Mo(N-t-Bu)(CHCMe3)(pyr)2(bipy)
( 5 mo) was synthesized using the same method for 1 3 w.
-
To u n
0.95 (2,2'-bipy)
Tol uen
2 Lipyr
5H0
2 ,N
C6 F0,11:-
N
H-2N
OC6F5
4
Toluene
-30 C to r.t.
3h
I NN
Toluene
r.t., 12 h
5
Mo
Mo ( 6 1 %)
Scheme 1.8. Synthesis of Mo(N-t-Bu)(CHCMe3)(pyr)2(bipy) (5mo).
B. Synthesis of Mo and W tert-butylimido MAP Complexes
Several Mo and W tert-butylimido bispyrrolide complexes were treated with 1 equivalent
of alcohol in order to prepare MAP complexes. Compound 1 2 w was treated with 1 equivalent of
HMTOH in benzene at 60 'C for 3 hours, and W(N-t-Bu)(CHCMe3)(2,5-Me 2pyr)(OHMT) (1 4 w)
was formed in 67% yield (Scheme 1.9). In order to synthesize a more sterically encumbered
MAP species, 1 equivalent of HIPTOH was added to 1 2 w. However, there was no conversion to
MAP
species
upon
heating
to
80
'C
overnight.
Considering
that
W(3,5-
Me2C6H3N)(CHCMe2Ph)(2,5-Me2pyr)(OHIPT) is synthesized from the bispyrrolide precursor in
benzene at 80 'C overnight, the tert-butylimido group seems to be more sterically demanding
than the 3,5-dimethylphenylimido group. Therefore, 1 equivalent of HIPTOLi was added to 3 w
in C6 D 6 in an attempt to synthesize W(N-t-Bu)(CHCMe 3)Cl(OHIPT). However, in addition to a
new alkylidene peak, free HIPTOH was also observed by 'H NMR spectroscopy at room
temperature, and the desired product could not be isolated cleanly.
N
N
HMTOH
C6D6
N'
0
60 C, 3 h
12w
14w (67%)
Scheme 1.9. Synthesis of W(N-t-Bu)(CHCMe3)(2,5-Me2pyr)(OHMT)
50
(1 4 w).
The same procedure was employed to synthesize Mo(NR)(CHCMe2Ph)(pyr)(OHMT)
from Mo(NR)(CHCMe2Ph)(pyr)2(bipy); 13w was treated with 1 equivalent of ZnCl2(dioxane) (in
order to remove 2,2'-bipyridine) and 0.84 equivalent of HIPTOH in toluene in a Schlenk flask.
The flask was then placed in an ultrasonic sonicator for 16 h. The mixture changed from a red
suspension to a yellow/brown solution. Filtration of the crude reaction mixture through a pad of
Celite removed insoluble materials. The filtrate was dried in vacuo, extracted with a minimum
amount of pentane, and filtered through a pad of Celite again. This filtrate was dried in vacuo to
obtain pure W(N-t-Bu)(CHCMe3)(pyr)(OHIPT)
(15w). Only one alkylidene resonance is
observed in the 'H NMR spectrum, suggesting that there is no exchange of the pyrrolide ligand
with chloride ions. The HMTO MAP complex W(N-t-Bu)(CHCMe 3)(pyr)(OHMT) (1 6 w) can
also be synthesized using this route (Scheme 1.10).
0.84 ROH
N
_____I_
S-pyrrole
N
13
N
ZnC 2(dioxane)
N
<X
N
R
R
RR
ZnCI 2(bipy)
-dioxane
-
RR
15W R = HIPT (67 %)
16w R = HMT (99 %)
w
Scheme 1.10. Synthesis of W(N-I-Bu)(CHCMe3)(pyr)(OHIPT) (15w) and W(N-t-Bu)(CHCMe3)(pyr)(OHMT)
(16w).
Several W MAP complexes bearing an OHIPT ligand have shown to be excellent Zselective catalysts in homocoupling of 1-octene to form (Z)-tetradec-7-ene. 21,31,
36
Therefore, Z-
selectivity of 15w was examined in homocoupling experiment. The reaction was performed in
neat substrate (6.4 M) with 2 mol% catalyst at room temperature. The reaction conditions were
adapted
from
the
previously
reported
1 -octene
homocoupling
with
W(3,5-
Me 2C 6H 3N)(C 3H6)(pyr)(OHlPT) (Table 1.2). 15w was highly Z-selective, but the reaction was
much slower than that of 3,5-dimethylphenylimido catalyst.
51
Table 1.2. Comparison of 1-octene homocoupling of 1 5 w with W(3,5-Me2C6H3N)(C3H6)(pyr)(OHIPT).
2 mol % cat
neat
22 0C, 6.4 M
Catalyst
Time
Conv (%)
Z (%)
W(3,5-Me2C6H3N)(C 3 H6)(pyr)(OHIPT)
1 h
4h
33h
1 h
4h
24h
37
54
75
9
30
81
>99
>99
>99
>99
>99
>99
W(N-t-Bu)(CHCMe3)(pyr)(OHIPT) (15w)
The structure of 16w was obtained through an X-ray study (Figure 1.4). It is interesting to
note that the distance between tungsten and the imido nitrogen is quite short, compared to that
seen in MAP complexes of arylimido tungsten species. Compound 16w has W=N distance 1.670
A, whereas several 2,6-diisopropylimido and 3,5-dimethylphenylimido MAP compounds have
W=N distances of ~1.75-1.77
A.36 37 The
short W=N distance is presumably due to the greater
electron donating ability of tert-butylimido ligand compared to that of arylimido ligands.
N(22
C(41)
CO)
Figure 1.4. X-ray crystal structure of 1 6w. Thermal ellipsoid plots shown at 50% probability level; Hydrogen
atoms and disorder are omitted for clarity. Selected bond distances (A) and angles(*): W(1)-N(1) = 2.021,
W(1)-N(2) = 1.670, W(1)-C(41)= 1.916, W(1)-O(1) = 1.870, W(1)-N(2)-C(31) = 170.5, W(1)-C(41)-C(42) =
141.8, W(1)-O(1)-C(1) = 173.8, N(2)-W(1)-C(41) = 105.9, O(1)-W(1)-C(41) = 108.0, N(2)-W(1)-N(1) = 105.4,
O(1)-W(1)-N(1) = 109.3, C(41)-W(1)-N(1) = 100.6, N(2)-W(1)-O(1) = 125.0.
Another interesting aryloxide ligand is 2,6-bispentafluorophenylphenoxide
Several Mo(NAr)(CHCMe 2Ph)(ODFT)2 (Ar
=
(ODFT).
2,6-Me2C6H3, 2,6-i-Pr2C6H3, C6F5 ) complexes
52
have shown to form cis, isotactic poly(2,3-dicarbomethoxynorbornadiene).38 Initially, W(N-tBu)(CHCMe3)(pyr)(ODFT) was targeted. When the same synthetic procedure for 15w or 16w
was employed using DFTOH, the desired product was not formed cleanly. Instead, three
alkylidene peaks were observed by 'H NMR spectroscopy. The three peaks were assigned to be
the desired MAP complex, a bisODFT complex, and a complex in which a pyrrolide had
exchanged with chloride. The ODFT ligand is smaller compared to OHMT or OHIPT ligand, so
that the formation of bisODFT complex is a major byproduct in this reaction. Formation of
bisODFT species was confirmed by a separate synthesis of W(N-t-Bu)(CHCMe3)(ODFT)2
complex (see Chapter 3). Isolation of W(N-t-Bu)(CHCMe3)(pyr)(ODFT) from the reaction
mixture was not successful. It was proposed that the electron-withdrawing ODFT ligand might
encourage adduct formation, so DFTOH was added to W(N-t-Bu)(CHCMe3)(pyr)2(py) generated
in situ. Indeed, W(N-t-Bu)(CHCMe3)(pyr)(ODFT)(py) formed readily and could be isolated in a
73% yield (Scheme 1.11).
w
N
2 Lipyr
0.85 DFTOH
Toluene
-30 C to r.t.
Toluene
r.t., 12 h
F
QFN/
F
F
3w
0
F
F
17W (73 %)
Scheme 1.11. Synthesis of W(N-t-Bu)(CHCMe3)(pyr)(ODFT)(py)
Mo(N-t-Bu)(CHCMe3)(pyr)(OHMT)
(1 7 w).
(6 mo) was synthesized through the reaction of
Mo(N-t-Bu)(CHCMe3)(pyr)2(bipy) (5mo) with 1 equivalent of ZnCl2(dioxane) in the presence of
0.84 equivalent of HMTOH. An X-ray study of
6 mo
(Figure 1.5), which crystallized in the
monoclinic space group P21/n with one molecule in the asymmetric unit, showed that the two
tert-butyl ligands were disordered over multiple positions. Bond angles and lengths are within
the typical Group 6 MAP complexes. The neopentylidene ligand is in a syn orientation, as in 16w,
and the Mo=N distance is short (1.659
A).
53
C(2)
C06)
N(1)
N
C1
N(2)
Mo~l)
0(1)
1)
6
Figure 1.5. Thermal ellipsoid drawing of Mo(N-t-Bu)(CHCMe3)(pyr)(OHMT) ( mo). Disorders were omitted
for clarity. Selected distances (A) and angles (0) : Mo(1)-N(1) = 1.6590(18), Mo(1)-C(1)= 1.904(2), Mo(1)-O(1)
= 1.8833(9), Mo(1)-N(2) = 2.0342(12), N(1)-Mo(1)-O(1) = 126.52(8), N(1)-Mo(1)-C(1) = 104.91(10), N(1)Mo(1)-N(2) = 104.53(7), Mo(1)-O(1)-C(21) = 174.14(10), Mo(1)-C(1)-C(2) = 140.9(3), Mo(1)-N(1)-C(6)=
168.7(3).
CONCLUSIONS
Synthetic routes to previously inaccessible Mo and W alkylidene MAP complexes have
been developed. Precursors for molybdenum tert-butylimido complexes have been reported
previously. For tungsten species, tert-butylimido complexes were formed through reaction of
tungsten hexachloride with N-t-butyltrimethylsilylamine. Both Mo and W tert-butylimido
alkylidene complexes have been synthesized using milder acids than triflic acid, which is
typically used for arylimido complexes. Tungsten tert-butylimido complexes can be synthesized
readily employing pyridinium chloride, whereas pentafluorophenol is optimal for Mo tertbutylimido complexes. Both chloride and pentafluorophenoxide ligands are easily displaced by
pyrrolide ligands, and both Mo and W dipyrrolide complexes have been synthesized as the 2,2'bipyridine adducts. Several MAP complexes have been synthesized upon addition of a
substituted 2,6-terphenol along with ZnCl2(dioxane) to remove 2,2'-bipyridine. This synthetic
route is applicable for preparing OHMT or OHIPT complexes, but not ODFT complexes. Instead,
a ODFT MAP complex is synthesized as a pyridine adduct. X-ray diffraction studies revealed
54
that Mo and W tert-butylimido OHMT MAP complexes have the shortest M=N (M = Mo, W)
distance among MAP complexes.
EXPERIMENTAL
General Considerations
All air and moisture sensitive materials were manipulated under a nitrogen atmosphere in a
Vacuum Atmospheres glovebox or on a dual-manifold Schlenk line. All glassware, including
NMR tubes, was dried in an oven prior to use. Diethyl ether, pentane, toluene, dichloromethane,
1,2-dimethoxyethane, and benzene were degassed, passed through activated alumina columns,
and stored over 4 A Linde-type molecular sieves prior to use. Deuterated solvents were dried
over 4 A Linde-type molecular sieves prior to use. 'H, 19 F, and
13 C
NMR spectra were acquired
at room temperature using Varian 300 MHz, Bruker 400 MHz, or Varian 500 MHz
spectrometers. Chemical shifts for 'H and 13C spectra are reported as parts per million relative to
tetramethylsilane and referenced to the residual 'H or
13 C
resonances of the deuterated solvent
('H (6) : benzene 7.16, chloroform 7.26, methylene chloride 5.32;
13 C
(6) : benzene 128.06,
chloroform 77.16, methylene chloride 53.84). Sonications were performed on a Bransonic
Ultrasonic Cleaner
151OR-MT purchased from Branson Ultrasonics Corporation.
N-t-
butyltrimethylsilylamine was either prepared from TMSC1 and t-BuNHLi in ether or purchased
from Sigma-Aldrich. Pyridinium chloride was purchased from Sigma-Aldrich or Alfa Aesar and
sublimed before use. Ethereal solutions of HCl were prepared by bubbling HCl gas into diethyl
ether and were titrated before use. Mo(N-t-Bu)2Cl2(dme), 27 Mo(N-t-Bu)2(CH2CMe3)2, Mo(N-tBu)(CHCMe 3)(OCH(CF3)2)2(NH2-t-Bu), 2 8 4w, 6w,
HIPTOH, 4 ' DFTOH,
5
8 w,
neopentyl Grignard,3 9 HMTOH,40
and ZnCl2(dioxane) 42 were prepared according to literature procedures.
All other reagents were used as received. Midwest Microlabs, Inc., and the CENTC Elemental
Analysis Facility at the University of Rochester provided the elemental analysis results.
[W(N-t-Bu)2Cl(U-Cl)(t-BuNH2)]2 (1w).
The following procedure was adapted from a recent
publication. 17,18 A solution of N-t-butyltrimethylsilylamine (25 g, 172 mmol) in 30 mL toluene
was added slowly over a period of 50 min to WC1 6 (15.2 g, 38.33 mmol) in 150 mL of toluene.
The reaction mixture was stirred for 24 h at room temperature.
55
The dark green mixture was
filtered through a pad of Celite, and the solvent was removed from the filtrate in vacuo. Pentane
was added and the yellow suspension was cooled to -30 'C and filtered to yield 12.03 g of the
yellow product (67%). X-ray quality crystals were grown from a mixture of methylene chloride
and pentane at -30 'C.
W(N-t-Bu)2(CH2-t-Bu)2 (2 w). An ether solution of Me3CCH2MgCl (2.83 M, 14.2 mL, 40.16
mmol) was added to a -30 'C solution of [W(N-t-Bu)2Cl2(H2N-t-Bu)]
2
(9.44 g, 20.08 mmol) in
60 mL of diethyl ether. The reaction mixture was stirred for 6 h at room temperature. A white
precipitate formed and the yellow solution turned to an ivory color. The mixture was filtered
through a pad of Celite and the solvent was removed from the filtrate in vacuo to yield a brown
oil. Pentane was added to the oil and the mixture was cooled to -30 'C. A light yellow powder
was filtered off and a brown oil (8.20 g, 87%) was obtained: 'H NMR (500 MHz, C 6D 6) 6 1.55
(s, 4H, CH2, 2 JWH = 10 Hz), 1.44 (s, 18H, Me), 1.18 (s, 18H, Me);
84.59, 66.36, 34.62, 34.37, 33.50.
13 C
NMR (125 MHz, C 6D 6) 6
Anal. Calcd for C1 8 H4oN 2W: C, 46.16; H, 8.61; N, 5.98.
Found C, 45.94; H, 8.56; N, 5.87.
W(N-t-Bu)(CHCMe3)C2(py)2
(3 w).
W(N-t-Bu)2(CH 2-t-Bu) 2 (0.70 g, 1.49 mmol) was
dissolved in ether (15 mL) and the solution was chilled at -30 *C for 2 h. Pyridinium chloride
(0.52 g, 4.46 mmol) was added and the mixture was allowed to stir at room temperature for 15 h.
The color of the solution turned from yellow to brown and a precipitate formed. All volatile
components were removed from the reaction mixture and the residue was extracted with a
mixture of toluene and methylene chloride. The extract was filtered through a pad of Celite on a
glass frit and all solvents removed from the filtrate to yield a yellow residue. Pentane was added
and the yellow solid was collected; yield 0.53 g (64%): 'H NMR (500 MHz, C 6D 6) 6 11.86 (s,
1H, W=CH), 9.63 (d, 4H, py), 6.69 (t, 2H, py), 6.39 (t, 4H, py), 1.38 (s, 9H, Me), 1.34 (s, 9H,
Me); 13 C NMR (125 MHz, C 6D 6) 6 297.03, 156.69, 138.08, 123.78, 68.94, 43.70, 34.31, 30.98.
The 'H NMR spectrum in C 6D 6 showed traces of [W(N-t-Bu)(CHCMe 3)Cl2(py)] 2 . A pure
sample of [W(N-t-Bu)(CHCMe 3)Cl 2(py)] 2 was obtained by recrystallization from methylene
chloride and pentane at -30 'C and an X-ray diffraction study was carried out: 'H NMR (500
MHz, CD2 Cl 2 ) 6 10.86 (s, 1H, W=CH), 8.78 (d, 2H, py), 7.98 (t, 2H, py), 7.54 (t, 2H, py), 1.34 (s,
9H, Me), 1.30 (s, 9H, Me);
13 C
NMR (125 MHz, CD 2 Cl 2 ) 6 282.20, 154.72, 139.91, 125.98,
56
70.54, 44.02, 32.29, 30.78. Anal. Caled for C2 8 H4 8 Cl4 N4W2: C, 35.39; H, 5.09; N, 5.90. Found C,
35.46; H, 5.15; N, 5.90.
W(NAr')(CHCMe2Ph)C2(bipy) (5w). W(NAr') 2 (CH2CMe2Ph)2 (420.3 mg, 0.61 mmol) and
2,2'-bipyridine (95.3 mg, 0.61 mmol) were dissolved in Et 2 0 (20 mL)/DME (-1.5 mL) and the
solution was chilled at -30 'C for 2 h. An ethereal solution of HCl (1.0 M, 1.22 mL, 1.22 mmol)
was added dropwise to the chilled suspension and the reaction mixture was allowed to stir at
room temperature overnight. The solution slowly turned pink and a precipitate formed. The
reaction mixture was filtered, and the resulting pink powder was washed with ether and dried in
vacuo; yield 367 mg (91%). The compound is a mixture of cis and trans isomers in a ratio of 4:3.
'H NMR (500 MHz, CD2Cl 2 ) 6 11.27 (s, 1H, W=CH, cis), 10.46 (s, 1H, W=CH, trans), 9.65 (dd,
lH, cis Ar), 9.48 (dd, 1H, trans Ar), 8.73 (dd, 1H, cis Ar), 8.61 (dd, 1H, trans Ar), 8.07-8.29
(overlapping peaks, 8H, Ar), 6.77-7.68 (overlapping peaks, 20H, Ar), 2.88 (s, 3H, cis CHMe2),
2.61 (s, 9H, trans and cis CHMe2), 1.75 (s, 3H, cis CHCMe2Ph), 1.66 (s, 6H, trans CHCMe2Ph),
1.62 (s, 3H, cis CHCMe2Ph). A
3C
NMR spectrum could not be obtained due to the insolubility
of 5w. Anal. Calcd for C 2 8 H 2 9Cl 2 N 3W: C, 50.78; H, 4.41; N, 6.34. Found C, 50.61; H, 4.53; N,
6.44.
W(NAr)(CHCMe2Ph)C2(bipy) (7w). Compound 7w was prepared as described for 5w from
W(NAr)2(CH2CMe2Ph)2 (200 mg, 0.25 mmol), 2,2'-bipyridine (39mg, 0.25 mmol), and an
ethereal solution of HCl (1.0 M 0.5 mL, 0.5 mmol). The reaction mixture was filtered, and the
resulting yellow powder (107.5 mg, 60%) was washed with Et20 and dried in vacuo: 1H NMR
(500 MHz, CDCl 3) 6 11.48 (s, 1H, W=CH, major isomer, cis), 9.74 (dd, 1H, Ar), 8.62 (dd, 1H,
Ar), 8.18 (d, 1H, Ar), 8.08-8.13 (overlapping peaks, 2H, Ar), 8.04 (t, 1H, Ar), 7.61 (t, 1H, Ar),
7.54 (d, 2H, Ar), 7.36 (t, 2H, Ar), 7.19 (t, 2H, Ar), 7.10 (d, 1H, Ar), 6.98 (t, 1H, Ar), 6.90 (d, 1H,
Ar), 4.39 (m, 1H, i-Pr CH), 2.83 (in, 1H, i-Pr CH), 1.79 (s, 3H, CHCMe2Ph), 1.62 (s, 3H,
CHCMe2Ph), 1.26 (d, 3H, i-Pr Me), 1.17 (d, 3H, i-Pr Me), 1.01 (d, 3H, i-Pr Me), 0.04 (d, 3H, iPr Me). A 13C NMR spectrum could not be obtained due to insolubility of 7w. Anal. Caled for
C32H 3 7 Cl2 N 3 W: C, 53.50; H, 5.19; N, 5.85. Found C, 53.13; H, 5.17; N, 5.78.
57
W(NArcI 2)(CHCMe2Ph)C
2 (bipy)
(9w). Compound 9w was prepared as described for 5w from
W(NArcI 2)2 (CH2 CMe 2Ph) 2 (128.8 mg, 0.17 mmol), 2,2'-bipyridine (26.1mg, 0.17 mmol), and an
ethereal solution of HCl (3.82 M 0.088 mL, 0.33 mmol). The solution slowly turned yellow and
a precipitate formed. The reaction mixture was filtered, and the resulting yellow powder (63 mg,
54%) was washed with Et20 and dried in vacuo: 'H NMR (500 MHz, CD2Cl 2 ) 6 11.10 (s, IH,
W=CH, major isomer), 9.66 (dd, 1H, Ar), 8.95 (dd, 1H, Ar), 8.25 (d, 1H, Ar), 8.16 (m, 2H, Ar),
8.06 (t, 1H, Ar), 7.63 (t, 1H, Ar), 7.58 (d, 2H, Ar), 7.35 (t, 1H, Ar), 7.27 (t, 2H, Ar), 7.07 (t, 3H,
Ar), 6.80 (t, 1H, Ar), 1.74 (s, 3H, CHCMe2Ph), 1.67 (s, 3H, CHCMe2Ph). A 13C NMR spectrum
could not be obtained due to the insolubility of 9 w. Anal. Calcd for C26H23Cl4N3W: C, 44.41; H,
3.30; N, 5.98. Found C, 44.33; H, 3.32; N, 6.02.
W(NAr'j')2(CHCMe2Ph)2 (10w). An ether solution of PhMe2CCH2MgCl (0.5 M, 9.59 mL, 4.80
mmol) was added to a -30 'C solution of W(NAriPr) 2Cl 2(3,5-lut) 2 (3,5-lut = 3,5-lutidine) (1.764
g, 2.398 mmol) in 50 mL of diethyl ether. The reaction mixture was stirred for 12 h at room
temperature. A white precipitate formed and the yellow solution turned darken. The mixture was
filtered through a pad of Celite and the solvent was removed from the filtrate in vacuo to yield a
yellow powder. The compound was extracted with toluene, the mixture filtered through a pad of
Celite, and the solvent was removed from the filtrate in vacuo. Pentane was added and the
product was filtered off (1.173 g, 68%): 'H NMR (500 MHz, C 6D 6) 6 7.35 (m, 4H), 7.14 (m,
,
6H), 7.05 (tt, 2H), 6.98 (dd, 2H), 6.94 - 6.87 (m, 4H), 3.62 (septet, 2H, i-Pr), 1.64 (s, 4H, CH2
2
JWH=
9 Hz), 1.43 (s, 12H, Me), 1.17 (d, 12H, Me,
3
JHH=
7 Hz); 13C NMR (125 MHz, C 6D 6) 6
154.13, 151.48, 141.78, 128.72, 126.83, 126.40, 126.32, 126.23, 126.11, 125.42, 125.31, 89.05,
41.25, 33.47, 28.21, 23.52. Anal. Calcd for C 3 8H4 8N 2 W: C, 63.69; H, 6.75; N, 3.91. Found C,
63.76; H, 6.68; N, 3.90.
W(NAri')(CHCMe2Ph)C2(bipy) (11w).
Compound 11w was prepared as described for 5w
from W(NArPr)2(CH 2 CMe 2Ph) 2 (100 mg, 0.14 mmol), 2,2'-bipyridine (21.8mg, 0.14 mmol), and
ethereal HCl (1.0 M 0.28 mL, 0.28 mmol). The reaction mixture was then filtered, and the
resulting pink powder (53.4 mg, 57%) was washed with Et20 and dried in vacuo.
The
)
compound is a mixture of cis and trans isomers in a ratio of 1:1.2: 'H NMR (500 MHz, CD 2 Cl2
6
11.20 (s, 1H, W=CH, cis), 10.46 (s, 1H, W=CH, trans), 9.62 (dd, 1H, cis Ar), 9.48 (dd, 1H,
58
trans Ar), 8.62 (dd, 1H, trans Ar), 8.59 (dd, 1H, cis Ar), 8.03-8.29 (overlapping peaks, 8H, Ar),
6.95-7.70 (overlapping peaks, 22H, Ar), 3.98 (m, 1H, trans i-Pr CH), 3.35 (m, 1H, cis i-Pr CH),
1.81 (s, 3H, cis CHCMe2Ph), 1.68 (s, 6H, trans CHCMe2Ph), 1.63 (s, 3H, cis CHCMe2Ph), 1.23
(d, 6H, trans i-Pr Me), 1.00 (d, 3H, cis i-Pr Me), 0.77 (d, 3H, cis i-Pr Me). A 13C NMR spectrum
could not be obtained due to the insolubility of l1w. Anal. Calcd for C 2 9H 3 1 Cl2 N 3 W: C, 51.50; H,
4.62; N, 6.21. Found C, 51.50; H, 4.70; N, 6.23.
W(N-t-Bu)(CHCMe3)(2,5-Me2pyr)2 (1 2 w).
Solid Li-2,5-Me2pyr (0.182 g, 1.80 mmol) was
added portion-wise to a -30 'C solution of W(N-t-Bu)(CHCMe3)Cl2(py)2(0.499 g, 0.90 mmol)
in toluene (40 mL). The reaction mixture was stirred for 15 h at room temperature. The solution
became dark yellow. The reaction mixture was filtered through a pad of Celite on a glass frit and
the solvents were removed from the yellow filtrate in vacuo to give a brown oil. Pentane was
added and the yellow precipitate was filtered off. The filtrate was concentrated, cooled to -30 'C
and a second crop was collected; total yield 0.270 g (58%): 'H NMR (500 MHz, C 6D 6) 6 10.12
(s, 1H, syn-W=CH, IJCH
=
110 Hz), 5.95 (br, 4H, NC4H2 ), 2.26 (s, 12H, Me), 1.28 (s, 9H, Me),
1.20 (s, 9H, Me); "C NMR (125 MHz, C6 D 6 ) 6 273.0, 107.1, 70.22, 45.05, 34.20, 33.29, 32.33,
18.73. Anal. Calcd for C 2 1H 3 5N 3 W: C, 49.13; H, 6.87; N, 8.19. Found C, 49.25; H, 6.89; N,
8.08.
W(N-t-Bu)(CHCMe3)(pyr)2(bipy) (13w). W(N-t-Bu)(CHCMe 3 )Cl2(py)2 (1 g, 1.804 mmol) was
suspended in toluene (50 mL) and the suspension was chilled at -30 'C for 1 h. Lipyr (0.264 g,
3.61 mmol) was added in one portion and the mixture was allowed to stir at room temperature
for 3 h, during which time salts precipitated out. The precipitate was filtered off on a pad of
Celite on a glass frit and washed with toluene. 2,2'-Bipyidine (0.268 g, 1.72 mmol) was added to
the solution and the mixture was allowed to stir at room temperature overnight. The resulting
precipitate was collected by filtration and dried in vacuo to give a red powder (0.876 g, 83%). A
sample of this red powder was used for elemental analysis. At room temperature, three isomers
were observed.
(Alkylidene peaks in 'H NMR spectrum: 500 MHz, CD 2 Cl 2 , 6 11.08, 10.85,
10.46) Heating the NMR sample to 100 'C overnight generated one major isomer: 'H NMR
(500 MHz, CD 2 Cl2) 6 10.27 (s, 1H), 9.20 (d, 1H, bipy), 8.24 (d, 1H, bipy), 8.19 (d, 1H, bipy),
8.05 (q, 2H, bipy), 7.59 (d, 1H, bipy), 7.51 (t, 1H, bipy), 7.45 (t, 1H, bipy), 6.80 (in, 2H, NC 4 H2 ),
59
6.19 (in, 2H, NC 4H2), 6.07 (br, 2H, NC 4H2 ), 1.52 (s, 9H, Me), 1.17 (s, 9H, Me). A
13 C
NMR
spectrum could not be obtained due to insolubility of the sample. Anal. Calcd for C2 7H 3 5N 5 W: C,
52.86; H, 5.75; N, 11.42. Found C, 53.01; H, 5.82; N, 11.34.
W(N-t-Bu)(CHCMe3)(2,5-Me2pyr)(OHMT)
(1 4 w). A J. Young NMR tube was charged with a
solution of W(N-t-Bu)(CHCMe3)(2,5-Me2pyr)2 (65 mg, 0.127 mmol) and HMTOH (42 mg,
0.126 mmol) in a total of 1.2 mL C 6D 6 . The NMR tube was heated at 60 'C until the starting
material was consumed (~3h).
Formation of W(N-t-Bu)(CHCMe3)(2,5-Me2pyr)(OHMT) was
observed by 'H NMR spectroscopy. The volatiles were removed in vacuo and the residue was
extracted with pentane to yield a light yellow powder (63 mg, 67%): 'H NMR (500 MHz, C 6D6)
6 8.34 (s, 1H, syn-W=CH,, IJCH = 110 Hz,
2
JWH =
15 Hz), 6.96-6.91 (m, 3H, Ar), 6.86 (s, 2H, Ar),
6.77 (s, 2H, Ar), 6.11 (s, 2H, NC 4H2), 2.23 (s, 6H, OHMT Me), 2.16-2.13 (br, 12H, OHMT Me
+ pyr Me), 2.00 (s, 6H, OHMT Me), 1.24 (s, 9H, Me), 1.05 (s, 9H, Me);
13 C
NMR (125 MHz,
C6 D 6) 6 259.11, 157.92, 136.90, 136.53, 135.24, 131.96, 130.20, 129.37, 128.54, 122.97, 109.81,
70.59, 43.75, 33.97, 32.00, 21.42, 21.22, 20.19.
Anal. Calcd for C 3 9H 52N 2 0W: C, 62.57; H,
7.00; N, 3.74. Found C, 62.43; H, 6.84; N, 3.67.
W(N-t-Bu)(CHCMe3)(pyr)(OHIPT) (15w). W(N-t-Bu)(CHCMe3)(pyr)2(bipy) (200 mg, 0.326
mmol), ZnCl2(dioxane) (73.2 mg, 0.326 mmol) and HIPTOH (136.6 mg, 0.274 mmol) were
dissolved in toluene (- 40 mL) in a 100 mL Schlenk bomb. The bomb was sonicated for 16 h
(water bath reached 60 C) and the mixture was filtered through a pad of Celite on a glass frit.
All solvents were removed from the filtrate in vacuo. The residue was extracted with minimal
pentane and the extract was filtered through a pad of Celite on a glass frit. All solvents were
removed in vacuo to generate a yellow foam (163.7 mg, 67%): 'H NMR (500 MHz, C 6D 6) 6
9.11 (s, 1H, syn-W=CH, JCH = 110 Hz, 2 JWH = 20 Hz), 7.24 (d, 2H, Ar), 7.20 (d, 2H, Ar), 7.07
(dd, 2H, Ar), 6.86 (tt, 1H, Ar), 6.66 (in, 2H, NC4H2), 6.37 (in, 2H, NC 4H2 ), 3.02 (sept, 2H,
MeCHMe), 2.95-2.84 (in, 4H, MeCHMe), 1.37-1.33 (m, 18H, OHIPT Me), 1.21 (s, 9H, Me),
1.20 (d, 6H, OHIPT Me), 1.33 (d, 6H, OHIPT Me), 1.04 (s, 9H, Me), 1.03 (s, 9H, Me); "C NMR
(125 MHz, C6 D6) 6 259.05, 159.30, 148.59, 147.59, 147.54, 135.66, 134.23, 132.32, 131.53,
122.46, 122.04, 121.82, 111.43, 71.06, 43.94, 35.01, 34.32, 32.45, 31.70, 25.44, 25.20, 24.92,
60
24.86, 24.68, 23.59. Anal. Caled for C 4 9H 72 N 2 0W: C, 66.20; H, 8.16; N, 3.15. Found C, 66.31;
H, 8.20; N, 3.09.
9.5
9.0
8.5
8.0
7.5
7.0
6.5
6.0
5.5
5.0
4.5
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
Figure 1.6. 1H NMR spectrum of W(N-1-Bu)(CHCMe3)(pyr)(OHIPT) (in C6D6, 500 MHz).
W(N-t-Bu)(CHCMe3)(pyr)(OHMT)
(16w). W(N-t-Bu)(CHCMe3)(pyr)2(bipy) (200 mg, 0.326
mmol), ZnCl2(dioxane) (73.2 mg, 0.326 mmol) and HMTOH (90.5 mg, 0.274 mmol) were
dissolved in toluene (- 25 mL) in a 100 mL Schlenk bomb. The bomb was sonicated for 15 h,
(the water bath reached 60 'C) and the mixture was filtered through a pad of Celite on a glass frit.
All solvents were removed from the filtrate in vacuo. The residue was extracted with minimal
pentane and the mixture was filtered through a pad of Celite on a glass frit to yield a yellow
powder (197.3 mg, 99%): 'H NMR (500 MHz, C 6D 6) 6 8.34 (s, lH, syn-W=CH, IJCH = 115 Hz,
2
JWH =
15 Hz), 6.95-6.84 (m, 7H, Ar), 6.69 (m, 2H, NC 4H2), 6.40 (m, 2H, NC 4H2), 2.24 (s, 6H,
OHMT Me), 2.14 (s, 6H, OHMT Me), 1.97 (s, 6H, OHMT Me), 1.15 (s, 9H, Me), 1.04 (s, 9H,
Me); 13C NMR (125 MHz, C 6D 6 ) 6 255.02, 157.80, 136.97, 136.84, 136.75, 135.40, 133.98,
132.13, 130.05, 129.51, 128.71, 123.23, 111.06, 70.48, 43.41, 33.38, 31.76, 21.23, 21.03, 20.17.
Anal. Caled for C3 7 H 4 8N20W: C, 61.67; H, 6.71; N, 3.89. Found C, 61.33; H, 6.68; N, 3.84.
61
8.5
Figure 1.7.
8.0
7.5
7.0
6.5
6.0
5.5
5.0
4.5
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.!
IH NMR spectrum of W(N-t-Bu)(CHCMe3)(pyr)(OHMT) (in C 6D6 , 500 MHz).
W(N-t-Bu)(CHCMe3)(pyr)(ODFT)(py)
(17w). W(N-t-Bu)(CHCMe3)C 2(py) 2 (158.8 mg, 0.287
mmol) was suspended in toluene (20 mL). Lipyr (0.043 g, 0.587 mmol) was added in one portion
and the mixture was allowed to stir at room temperature for 2 h, during which time salts
precipitated out. The precipitate was filtered off on a pad of Celite on a glass frit and washed
with toluene.
DFTOH (0.104 g, 0.244 mmol) was added to the solution and the mixture was
allowed to stir at room temperature overnight. All solvents were removed from the filtrate in
vacuo. Pentane was added and removed in vacuo a couple of times to remove excess toluene.
The resulting precipitate was collected by filtration in pentane and dried to an grey powder (159
mg, 73%): 'H NMR (400 MHz, C6 D 6) 6 10.79 (s, IH, syn-W=CH, IJCH = 112 Hz, 2 JWH = 9.6 Hz),
8.47 (d, 2H, Ar), 6.81 (t, 1H, Ar), 6.89 (t, 1H, Ar), 6.43 (in, 4H, pyr), 6.32 (m, 2H, Ar), 1.08 (s,
9H, Me), 1.06 (s, 9H, Me); '9F NMR (376.5 MHz, C 6D 6) 6 -137.81, -138.83, -157.77, -161.48,
-162.92; "C NMR (100.61 MHz, C 6D 6) 6 281.31 (WCHCMe 3 , 'Jcw
=
178 Hz), 160.02, 152.02,
146.07, 143.29, 141.54, 139.04, 138.42, 133.29, 131.29, 124.67, 119.72, 118.18, 114.30, 108.81,
62
69.61, 43.92, 32.53, 31.43. Anal. Calcd for C 36H 3 iFioN 30W: C, 48.29; H, 3.49; N, 4.69. Found
C, 48.03; H, 3.66; N, 4.96.
10.5
9.5
9.0
8.5
8.0
7.5
7.0
6.5
6.0
5.5
5.0
4.5
4.0
Figure 1.8. 'H NMR spectrum of W(N-t-Bu)(CHCMe3)(pyr)(ODFT)(py)
Mo(N-t-Bu)(CHCMe3)[OCH(CF3)22(NH2-t-Bu)
3.5
3.0
2.5
2.0
1.5
1.0
0.5
(in C 6D6 , 400 MHz).
(3 mo). Mo(N-t-Bu)2(CH2-t-Bu)2 (0.52 g, 1.38
mmol) was dissolved in diethyl ether (15 mL) and the solution was chilled at -30 'C for 2 h.
Hexafluoro-2-propanol (0.32 mL, 3.04 mmol) was added and the mixture was stirred at room
temperature for 23 h. The solvents were removed in vacuo. Pentane was added to off-white
solid and the solid was collected via filtration. The filtrate was concentrated and cooled to -30
'C to give a second crop of product; total yield 0.23 g (26%): 1H NMR (500 MHz, C 6 D6 ) 6 12.81
(s, 1H, Mo=CH), 6.00 (m, 1H, (CF3) 2 CH), 4.48 (m, 1H, (CF3 )2CH), 2.67 (d, 1H, H2N-tBu), 2.45
(d, 1H, H2N-tBu), 1.12 (s, 9H, Me), 1.07 (s, 9H, Me), 0.7 (s, 9H, Me); ' 9F NMR (300 MHz,
C 6D 6) 6 -74.61, -75.20, -76.08; 13C (125 MHz, C 6 D 6) 6 302.03, 83.91 (quintet), 74.11 (quintet),
71.49, 71.33, 50.71, 45.65, 45.43, 31.83, 30.75, 30.22. Anal. Calcd for C 19H 32F 12N202MO: C,
35.41; H, 5.01; N, 4.35. Found C, 35.40; H, 5.01; N, 4.34.
63
ill I
I
13
12
11
10
9
8
7
6
5
4
3
2
1
1
Figure 1.9. H NMR spectrum of Mo(N-t-Bu)(CHCMe3)[OCH(CF 3)21 2(NH 2-t-Bu) (in C6 D6, 500 MHz).
Mo(N-t-Bu)(CHCMe3)(OC6F)2(NH2-t-Bu)
(4 mo).
Mo(N-t-Bu)2(CH 2-t-Bu) 2 (1.96
g, 5.16
mmol) was dissolved in diethyl ether (30 mL) and the solution was chilled to -30 'C.
Pentafluorophenol (1.99 g, 10.83 mmol) was added and the mixture was allowed to stir at room
temperature for 4 h. The solvents were removed in vacuo. Pentane was added and the off-white
precipitate was collected; yield 2.93 g (84%): 'H NMR (500 MHz, C 6 D 6) 8 13.21 (s, lH,
Mo=CH), 2.64 (d, 1H, H2N-t-Bu), 2.50 (d, 111, H2N-t-Bu), 1.23 (s, 9H, Me), 0.93 (s, 9H, Me),
0.67 (s, 9H, Me); 1 9F NMR (300 MHz, C 6D 6 ) 6 -162.71, -164.18, -168.06, -168.67, -174.76; 13C
(125 MHz, C 6D6) 6 340.94, 145.73, 142.29, 141.97, 140.40, 139.99, 139.55, 137.61 (overlapping
aryl resonances are split due to fluorine coupling), 72.43, 50.96, 45.82, 30.84, 30.44, 30.07.
Anal. Calcd for C2 5H 3oFioN 2 02Mo: C, 44.39; H, 4.47; N, 4.14. Found C, 44.29; H, 4.48; N, 4.06.
64
14
13
12
11
10
9
8
7
6
5
4
Figure 1.10. 'H NMR spectrum of Mo(N-t-Bu)(CHCMe)(OC6F)2(NH2-t-Bu)
Mo(N-t-Bu)(CHCMe3)(Pyr)2(bipy)
3
2
1
0
(in C6D6, 500 MHz).
(5 Mo). Mo(N-t-Bu)(CHCMe3)(OC6F5)2(NH2-t-Bu) (0.53 g,
0.79 mmol) was suspended in toluene (20 ml) and the mixture was chilled to -30 *C. LiPyr
(0.115 g, 1.58 mmol) was added in one portion and the mixture was allowed to stir at room
temperature for 3 h, during which time LiPyr salts precipitated out. The mixture was filtered
through a pad of Celite on a glass frit, and the salts were washed with toluene. 2,2'-Bipyridine
(0.111 g, 0.71 mmol) was added to the solution and the mixture was allowed to stir at room
temperature overnight. The resulting red precipitate was collected by filtration and dried in
vacuo; yield 0.526 g (61%). At room temperature, three isomers were observed in NMR spectra:
1H NMR (500 MHz, CD2Cl2) 8 14.03 (s, 1H, Mo=CH), 13.46 (s, 1H, Mo=CH), 13.01 (s, 1H,
Mo=CH), 9.55 (d, 1H, bipy), 9.49 (d, 1H, bipy), 9.21 (d, 1H, bipy), 9.00 (d, 1H, bipy), 8.71 (d,
1H, bipy), 8.55 (d, 1H, bipy), 8.10-7.94 (m, 12H, bipy), 7.65-7.49 (m, 6H, bipy), 6.83 (m, 2H,
NC 4 H2), 6.66 (m, 2H, NC4H2), 6.28 (m, 2H, NC 4H2), 6.15 (m, 4H, NC 4H2), 6.11 (m, 2H, NC 4H2),
65
6.06 (in, 2H, NC4H2 ), 6.04 (m, 2H, NC 4H2), 5.65 (in, 4H, NC 4H2), 5.59 (m, 2H, NC 4H2), 1.56 (s,
9H, Me), 1.52 (s, 9H, Me), 1.44 (s, 9H, Me), 1.34 (s, 9H, Me), 1.21 (s, 9H, Me), 1.00 (s, 9H, Me).
The product was too insoluble to purify readily through recrystallization, and several elemental
analyses produced variable results. Therefore Mo(N-t-Bu)(CH-t-Bu)(Pyr)2(bipy) was employed
without purification in the synthesis of Mo(N-t-Bu)(CH-t-Bu)(Pyr)(OHMT) (see below).
14
13
12
11
10
9
8
7
6
5
Figure 1.11. 1H NMR spectrum of Mo(N-t-Bu)(CHCMe3)(pyr)2(bipy)
Mo(N-t-Bu)(CH-t-Bu)(Pyr)(OHMT)
4
3
2
1
(in CD 2 C2, 500 MHz).
(6 mo). Mo(N-t-Bu)(CH-t-Bu)(Pyr)2(bipy) (200 mg, 0.381
mmol), ZnC12(dioxane) (85.4 mg, 0.381 mmol), and HMTOH (105.6 mg, 0.320 mmol) were
dissolved in toluene (40 mL) in a 100 mL Schlenk bomb. The bomb was placed in a sonicator for
21 h. The mixture was filtered through a pad of Celite on a glass frit and solvents were reinived
from the filtrate in vacuo. The residue was extracted with a small amount of pentane.
The
extract was filtered through a pad of Celite, and the solvents were removed in vacuo to give a
yellow solid; yield 189.8 mg (94%): 'IH NMR (500 MHz, C 6D 6) 6 11.07 (s, 1H, Mo=CH), 6.986.86 (m, 7H, aryl), 6.64 (in, 2H, NC 4 H2 ), 6.46 (in, 2H, NC 4H2), 2.24 (s, 6H, OHMT methyls),
2.15 (s, 6H, OHMT methyls), 1.99 (s, 6H, OHMT methyls), 1.11 (s, 9H, Me), 0.99 (s, 9H, Me);
66
"C NMR (125 MHz, C6 D 6) 6 287.72, 158.31, 136.90, 136.87, 136.67, 136.15, 132.55, 131.83,
129.95, 129.44, 128.62, 122.44, 109.78, 73.92, 44.84, 31.36, 30.89, 21.22, 21.00, 20.18. Anal.
Caled for C3 7H 4 SN2OMo: C, 70.23; H, 7.65; N, 4.43. Found C, 69.93; H, 7.93; N, 4.35.
liii
I
11
12
10
9
8
7
L__
6
5
4
3
2
1
0
1
Figure 1.12. H NMR spectrum of Mo(N-t-Bu)(CH-t-Bu)(pyr)(OHMT) (in C6D6, 500 MHz).
Crystal data and structure refinement (Performed by Dr. Peter Muller)
Low-temperature diffraction data were collected on a Bruker-AXS X8 Kappa Duo
diffractometer coupled to a SMART Apex2 CCD detector with Mo Ka radiation (A = 0.71073 A)
from an IuS micro-source, for the structures of 1w, 3w, and 16w and on a Siemens Platform
diffractometer coupled to a SMART Apex detector with graphite-monochromated Mo Ka
radiation (A = 0.71073 A) for the structure of 6 mo, performing
#-and
wv-scans. The structures
were solved by direct methods using SHELXS 43 and refined against F2 on all data by full-matrix
least squares with SHELXL-974 4 following established refinement strategies.
All non
hydrogen atoms were refined anisotropically. Except when noted otherwise below, all hydrogen
atoms were included into the model at geometrically calculated positions and refined using a
riding model. The isotropic displacement parameters of all hydrogen atoms were fixed to 1.2
67
times the U value of the atoms they are linked to (1.5 times for methyl groups). Details of the
data quality and a summary of the residual values of the refinements are listed in tables below.
[W(N-t-Bu)2C1(u-C1)(t-BuNH2)]2 (1w) crystallizes in the triclinic space group P-1 with
2.5 molecules of 1w and five molecules of dichloromethane per asymmetric unit. The half
molecule is completed by the crystallographic inversion center and each unit cell contains thus 5
molecules of 1w and 10 molecules of CH 2 C12.
Two of the t-Bu groups in the molecule
containing tungsten atoms W3 and W4 as well as two of the solvent molecules are disordered
over two positions. Those disorders were refined with the help of similarity restraints on 1-2 and
1-3 distances and displacement parameters as well as rigid bond restraints for anisotropic
displacement parameters. Coordinates for the nitrogen bound hydrogen atoms were taken from
the difference Fourier Synthesis. The hydrogen atoms in question were subsequently refined
semi-freely with the help of distance restraints (target N-H distance 0.91(2) A, while
constraining their Uis0 to 1.2 times the value of the Ueq of the nitrogen atom to which they bind.
[W(N-t-Bu)(CHCMe3)C2(py)]2
(3w) crystallizes in the monoclinic space group P21/c
with half a molecule 3w of in the asymmetric unit.
The second half is generated by the
crystallographic inversion center. The crystallographically independent alkylidene ligand (Cl to
C5) is disordered over two positions and disorder was refined with the help of similarity
restraints on 1-2 and 1-3 distances and displacement parameters as well as rigid bond restraints
for anisotropic displacement parameters.
The ratio between the two components was refined
freely and converged at 0.744(14).
W(N-t-Bu)(CHCMe3)(pyr)(OHMT)
(16w) crystallizes in the monoclinic space group
P21/n with one molecule 16w of in the asymmetric unit. The alkylidene and the N-t-Bu ligand
are engaged in a disorder that makes them swap places. The disorder was refined with the help
of similarity restraints on 1-2 and 1-3 distances and displacement parameters as well as rigid
bond restraints for anisotropic displacement parameters. The ratio between the two components
In spite of this disorder, coordinates the two
was refined freely and converged at 0.552(5).
independent hydrogen atoms on Cl and CIA (the carbon atoms binding directly to tungsten)
could be taken from the difference Fourier Synthesis. The hydrogen atoms in question were
subsequently refined semi-freely with the help of distance restraints (target C-H distance
0.95(2)
A,
while constraining their Uis0 to 1.2 times the value of the Ueq of the carbon atom to
which they bind.
68
Mo(N-t-Bu)(CHCMe3)(pyr)(OHMT)
( 6 mo) crystallized in the monoclinic space group
P21/n with one molecule in the asymmetric unit. The pyrrole and HMTO ligands of the central
Mo atom were well behaved, but the two t-butyl-containing ligands were disordered over
multiple positions. First, the positions of the alkylidene (CHCMe3) and N-t-Bu ligands were
swapped with respect to the Mo in a two-part disorder having a ratio that converged to 0.563(3).
The minor component of the alkylidene ligand was then further disordered over two positions,
with the major component converging to 0.310(4) of the remaining 0.437(3) occupancy. The N-tBu was thus disordered over two independent positions, and the alkylidene ligand was disordered
over three independent positions. The occupancies of the three alkylidene components were
restrained to sum to 1.0000(1). Rigid bond restraints and similarity restraints were employed on
the displacement parameters, and similarity restraints were used for the 1-2 and 1-3 distances for
all equivalent atoms involved in the disorders. In the two minor components of the alkylidene
ligand, the equivalent carbon atoms bound to the Mo (CIA and ClB) as well as the equivalent
neighboring carbon atoms (C2A and C2B) were constrained to have identical anisotropic
displacement parameters.
69
Table 1.3. Crystal data and structure refinement for [W(N-t-Bu) 2C1(p-Cl)(t-BuNH 2)] 2 (Iw).
Identification code
X8_12060
Empirical formula
C 26 H 6 2 Cl 8 N6 W 2
Formula weight
1110.12
Temperature
100(2) K
Wavelength
0.71073 A
Crystal system
Triclinic
Space group
P-I
Unit cell dimensions
a = 12.5147(14)
a = 98.741(2)0
b= 19.130(2)A
8= 93.348(2)'
A
y = 99.364(2)0
c = 22.909(3)
A3
5329.1(10)
Z
5
Density (calculated)
1.730 Mg/M 3
Absorption coefficient
5.918 mm-'
F(000)
2720
Crystal size
0.30 x 0.28 x 0.18 mm 3
Theta range for data collection
0.90 to 31.00'
Index ranges
-18<=h<= 18, -27<=k<=27, -33<=l<=33
Reflections collected
504483
Independent reflections
33880 [Ri,, = 0.0395]
Completeness to theta = 3 1.000
99.8
Absorption correction
Semi-empirical from equivalents
Max. and min. transmission
0.4155 and 0.2733
Refinement method
Full-matrix least-squares on
Data / restraints / parameters
2
%
Volume
33880 / 590 / 1132
Goodness-of-fit on P
1.052
Final R indices [I>2-(I)]
RI = 0.0259, wR2 = 0.0660
R indices (all data)
RI
Largest diff. peak and hole
2.379 and -0.995 e.A-3
=
0.0320, wR2
70
=
0.0709
F2
Table 1.4. Crystal data and structure refinement for [W(N-t-Bu)(CHCMe 3)Cl 2(py)] 2 (3w).
Identification code
X8_12031
Empirical formula
C 28 H 48 Cl 4 N 4 W 2
Formula weight
950.20
Temperature
100(2) K
Wavelength
0.71073 A
Crystal system
Monoclinic
Space group
P21/c
Unit cell dimensions
a = 13.9455(13) A
b = 9.6269(9)
a=900
A
/8= 107.163(2)0
y= 900
c = 14.1894(13) A
3
Volume
1820.1(3) A
Z
Density (calculated)
2
Absorption coefficient
6.631 mm-1
F(000)
920
Crystal size
0.28 x 0.25 x 0.06 mm 3
Theta range for data collection
1.53 to 30.510
Index ranges
-19<=h<= 19, -13<=k<==13, -20<=l<=20
Reflections collected
115442
Independent reflections
5555 [Ri,, = 0.0496]
Completeness to theta = 30.5 1
100.0%
Absorption correction
Semi-empirical from equivalents
Max. and min. transmission
0.6918 and 0.2582
Refinement method
Full-matrix least-squares on F2
1.734 Mg/m3
Data / restraints / parameters
2
5555 / 194 / 218
Goodness-of-fit on F
1.130
Final R indices [I>20 (J)]
RI = 0.0443, wR2
R indices (all data)
RI
Largest diff. peak and hole
4.900 and -4.241 e.A-3
=
=
0.1040
0.0458, wR2 = 0.1048
71
Table 1.5. Crystal data and structure refinement for W(N-t-Bu)(CHCMe 3 )(pyr)(OHMT) (1
6
w).
Identification code
X8_12105
Empirical formula
C3 7 H48 N 2 0 W
Formula weight
720.62
Temperature
100(2) K
Wavelength
0.71073 A
Crystal system
Monoclinic
Space group
P2i/n
Unit cell dimensions
a= 11.8827(14) A
a= 900
b= 16.2588(19)A
,8= 92.693(2)-
c = 18.144(2) A
y= 900
A3
Volume
3501.4(7)
Z
4
Density (calculated)
1.367 Mg/m3
Absorption coefficient
3.327 mm-1
F(000)
1464
Crystal size
0.18 x 0.12 x 0.08 mm 3
Theta range for data collection
1.68 to 31.30'
Index ranges
-1 7<=h<= 16, -23<=k<=23, -26<=l<=26
Reflections collected
274022
Independent reflections
11466 [Rint = 0.0335]
Completeness to theta = 31.30'
100.0%
Absorption correction
Semi-empirical from equivalents
Max. and min. transmission
0.7767 and 0.5857
Refinement method
Full-matrix least-squares on F2
Data / restraints / parameters
11466 / 370 / 473
Goodness-of-fit on F2
1.083
Final R indices [I>2o(l)]
RI = 0.0201, wR2 = 0.0456
R indices (all data)
RI
Largest diff. peak and hole
1.705 and -1.335 e.A-3
=
0.0232, wR2
72
=
0.0470
Table 1.6. Crystal data and structure refinement for Mo(N-t-Bu)(CHCMe 3)(pyr)(OHMT) (6 mo).
Identification code
x12178
Empirical formula
C37 H48 Mo N2 O
Formula weight
632.71
Temperature
100(2) K
Wavelength
0.71073
Crystal system
Monoclinic
Space group
P2(1)/n
Unit cell dimensions
a= 11.8579(5)A
a = 900
b = 16.2400(7) A
P = 92.5340(10)
c = 18.1978(8)A
y=
A
9 00
Volume
3501.0(3) A 3
Z
4
Density (calculated)
1.200 Mg/m3
Absorption coefficient
0.403 mm-1
F(000)
1336
Crystal size
0.22 x 0.22 x 0.20 mm 3
Theta range for data collection
1.68 to 31.64'
Index ranges
-17<=h<=17, -23<=k<=23, -25<=l<=26
Reflections collected
97895
Independent reflections
11674 [R(int)
Completeness to theta = 31.640
99.0
Absorption correction
Semi-empirical from equivalents
Max. and min. transmission
0.9237 and 0.9166
Refinement method
Full-matrix least-squares on F 2
Data / restraints / parameters
Goodness-of-fit on F
2
0.0328]
%
=
11674 / 624 / 520
1.036
Final R indices [I>2sigma(I)]
RI = 0.0293, wR2 = 0.0736
R indices (all data)
RI = 0.0357, wR2
Largest diff. peak and hole
0.939 and -0.907 e.A-3
73
=
0.0773
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76
Chapter 2
Z-selective Ring-Opening Metathesis Polymerization of 3-Substituted
Cyclooctenes
Portions of this chapter have appeared in print:
Jeong, H.; Kozera, D. J.; Schrock, R. R.; Smith, S. J.; Zhang, J.; Ren, N.; Hillmyer, M. A. ZSelective
Ring-Opening
Metathesis
Polymerization
of 3-Substituted
Cyclooctenes
by
Monoaryloxide Pyrrolide Imido Alkylidene (MAP) Catalysts by Molybdenum and Tungsten.
Organometallics,2013, 32, 4843 - 4850.
77
INTRODUCTION
The physical properties of polymers are highly related to their primary structure, so
For
precise control of polymer structure has been pursued in the field of polymer chemistry.
example, it has been shown that the tacticity of hydrogenated poly(DCPD) (DCPD =
1
Dicyclopentadiene) has a huge impact on its thermal and crystalline properties. Although the
Diene
synthesis of highly stereo- or regioregular polymers is highly challenging, Acyclic
Metathesis (ADMET) and Ring-Opening Metathesis Polymerization (ROMP) have been
effective tools to achieve this goal. For example, synthesis of precise ethylene/vinyl chloride
polymers containing a chlorine substituent on every ninth carbon atom has been performed by
2
Wagener et al. through ADMET. In addition, a recent report from the Hillmyer group showed
that highly trans,HT 3-substituted cyclooctene (3-RCOE) polymer has been achieved using
Grubbs nd generation catalysts; the substituents are positioned on every eighth carbon atom.
2
These polymers were hydrogenated with tosylhydrazide to form linear low-density polyethylene
on the
(Scheme 2.1).3 By selectively putting additional pendant groups on carbon atoms
cyclooctene backbone, sequence-specific polymers can be obtained. The Hillmyer group has
shown that trisubstituted cyclooctene (at 3,4,5-positions) can be polymerized in a highly regio4
and stereoregular fashion, but 3-substitution is required for highly regular polymers.
Mes-N,..
N-Mes
R
R=Ph
CI,T
RR
R
Cro
R
C
P(CY)
__________
3
60 C, 20h, CHCI 3
4300 equiv.
R
TsNHNH 2
f
n
140 *C, 6h, xylenes
Trans, HT
Linear LDPE
R = H, Me, Et, Hex, Ph
Scheme 2.1. Synthesis of
trans,HT-selective 3-substituted cyclooctenes by a Ru catalyst.
In the Schrock group, the development of Mo- and W-based MonoAlkoxide Pyrrolide
(MAP) catalysts has led to the Z-selective formation of polymers from a variety of monomers.
Mo(NAd)(CHCMe2Ph)(pyr)(OHIPT) (1, Figure 2.1; NAd = adamantylimido, OHIPT
=
0-2,6-
polymers
(2',4',6'-i-Pr 3C6H2)2C6H3) is a highly effective catalyst for generating cis,syndiotactic
2,3-dicarbomethoxynorbomadiene, cis-cyclooctene, and
of the
cis- 1 ,5-cyclooctadiene 6 (Figure 2.2). The Z selectivity arises due to the syn addition
monomer such that its substituents point toward the imido group and away from the large
5
of 3-methyl-3-phenylcyclopropene,
78
aryloxide group. Chirality at the metal center allow syndiotactic and alternating enantiomer
structures to form. 7
Ph
1
NI.
0
Figure 2.1. Mo(NAd)(CHCMe2Ph)(pyr)(OHIPT) (1).
COOMe
MeOOC
/
MeOOC
COOMe
2%, 1
/
COOMe
COOMe
0.6M, rt
COOMe
MeOOC
>99% cis, >99% syndiotactic
Ph
,Ph
Ph.
.-
Ph
1%, 1
0.5M, rt
n
>99% cis, >99% syndiotactic
0.3%, 1
n
rt
98% cis
0.3%, 1
n
rt
>98% cis
Figure 2.2. Generation of cissyndiotactic polymers from various monomers using catalyst 1.
The driving force for polymerization of norbornene or norbornadiene monomers comes
from the release of their high ring strain. Therefore, low-ring-strain monomers such as 5-, 6-, 7-,
and 8-membered cycloalkenes might show lower propensity to polymer than high-ring-strain
monomers. This is because low-ring-strain monomers is known to form cyclic oligomers through
backbiting by the catalyst onto the propagating chain. 8 As a consequence, chain-transfer
reactions lead to broad molecular weight distributions and higher polydispersities of the
79
polymer. 9 In order to understand whether Z-selective ROMP using MAP catalysts can be
extended to 3-RCOE monomers, polymerization studies of several 3-RCOE substrates with
various Mo and W MAP catalysts were undertaken. Part I of this chapter discusses stereo- and
regioselective formation of polymers employing libraries of catalysts and monomers, as well as
cyclooctene monomer without 3-substitution to determine the effect of 3-substitution on
regiochemistry. Part II will be a detailed analysis of the system in terms of the origin of
selectivity and kp/ki studies.
RESULTS AND DISCUSSION
I. Polymerization of 3-RCOEs by Various MAP Catalysts
Investigation
of
polymerization
Mo(NAd)(CHCMe2Ph)(pyr)(OHMT) (la; OHMT
of
=
3-RCOEs
began
with
2,6-dimesitylphenoxide) because it had
been shown to be highly Z-selective for the ROMP of substituted norbornadienes. 7 In addition,
molybdenum tert-butylimido MAP catalyst Mo(N-t-Bu)(CHCMe 3)(pyr)(OHMT) (1b) and
tungsten tert-butylimido MAP catalyst W(N-t-Bu)(CHCMe3)(pyr)(OHMT) (1c) (Figure 2.3)
were chosen for this study since these are newly developed alkylimido-based catalysts, and Mo
and W catalysts could be compared directly for polymerization of 3-RCOEs. Three 3-RCOE
monomers (R = methyl, n-hexyl, phenyl) were chosen for polymerization.
Ph
N 1
N
<CN
N
N,
0
0
0
la
1b
1c
Figure 2.3. The three catalysts for ROMP of 3-RCOEs.
A. Formation of Z-selective Poly(3-RCOEs)
Polymerization of 3-RCOEs was initially performed at various temperatures at low
concentration ([3 -RCOE] = 0.6-1.1 M) and with 15-100 equivalents of monomer (-1 -7 mol%) by
80
Daniel Kozera. Polymerization was slow and cyclic oligomers appeared to form based on 'H
NMR spectroscopy. In order to confirm that cyclic oligomer species were formed in dilute
condition through backbiting, 5 equivalents of 3-HexCOE were treated with 1c in C6 D6 solution
at 60 'C for 18 h. The 'H NMR spectrum showed mainly the starting catalyst, residual monomer,
and some new olefinic signals (Figure 2.4). Cyclic dimer (MW=388.71) was detected via
GC/MS, so it is plausible that the new olefinic signals are from the cyclic oligomers (Figure 2.5).
oligomer
polymer
polymer
oligomer
3-HexCOE
5.85
5.65
5.75
5.55
5.45
5.35
fl (ppm)
5.25
5.15
4.85
4.95
5.05
1
Figure 2.4. Olefinic region of the H NMR spectrum of W(N-t-Bu)(CHCMe3)(pyr)(OHMT) with 5 equivalents
of 3-HexCOE (C6D6, 500 MHz).
Hex
Hex
20 mol % lc
starting catalyst + cyclic oligomers_
C6 D 6
0.25 M
Hex
60 C, 15 h
(b)
(a)
cyclic dimer
(b)
Figure 2.5. (a) Reaction of 3-HexCOE with Ic formed uninitiated catalyst along with cyclic oligomers.
Observed cyclic dimer species with GC/MS.
However, when the polymerization reaction was performed in neat monomer, >98%
cis,HT-poly(3-RCOE) (HT = head to tail) could be achieved at room temperature by all three
catalysts. In neat monomer, polymerization was fast and formation of cyclic oligomers decreased
substantially. The list of catalysts, monomers, and conversions are shown in Table 2.1. The bulk
polymerization was performed with 0.02 mol% loading for R = Me, Hex and 0.1 mol% for R =
Ph (Scheme 2.2). The conversion was monitored after 4 and 24 hours and the listed numbers are
each an average of two runs. The reaction was quenched with benzaldehyde and the polymer was
isolated by precipitation of the reaction mixture in methanol.
81
R
Mo/W cat
R
n
neat, RT
1000 equiv. (R = Ph)
5000 equiv. (R = Me, Hex)
Scheme 2.2. Polymerization of 3-substituted cyclooctenes where R substituents are methyl, n-hexyl, and
phenyl groups.
Table 2.1. Summary of ROMP reactions in bulk 3-RCOE to give >98% cis,HT polymer. a
la
lb
1c
R
nb
time
conv (%)
time
conv (%)
time
conv (%)
Me
5000
Hex
5000
Ph
1000
30m
4h
4h
Id
4h
Id
48
97
10
42
1
22
5m
lh
4h
Id
4h
47
98
19
35
24
86
5m
lh
4h
Id
4h
80
>99
25
70
36
87
Id
a All
Id
polymerization were carried out at 22 'C. Conversions are reported as the average of two runs.
monomer to initiator.
bRatio
of
The fastest initiator is ic in all three polymerization reactions. This is quite interesting
given that molybdenum MAP complexes are faster than tungsten analogs in some metathesis
studies such as Z-selective homocoupling of terminal olefinsi0 or dienes." For the case of
M(NAr)(C3H 6)(OBitet)(Me2Pyr)
Me2NC4H2,
OBitet
is
the
(M = Mo, W) (NAr = N-2,6-i-Pr2C 6H 3 , Me2Pyr = 2,5anion
from
(R)-3,3'-Dibromo-2'-(tert-butyldimethylsilyloxy)-
5,5',6,6',7,7',8,8'-octahydro-1,1'-binaphthyl-2-ol),
the rate of cleavage of an unsubstituted
molybdacycle to an ethylene/methylidene intermediate at 20 'C is 4500 times faster than
cleavage of the analogous tungstacyclobutane complex,1 2 consistent with Mo catalysts being
faster than W analogs in many olefin metathesis reactions. The two metal complexes might have
different rate-determining steps in ROMP of 3-RCOEs, or the substituted metallacyclobutanes
necessary for ROMP may behave differently than unsubstituted metallacyclobutane species.
Proton and 13 C NMR spectra of isolated polymers display the number of resonances
expected for a cis,HT structure, i.e. eight backbone resonances (two olefinic and six aliphatic)
and one, six, and four side-chain resonances for R = Me, Hex, and Ph, respectively. Head-to-tail
regioregularity was confirmed employing 'H- 1H COSY NMR methods; the olefinic protons were
82
found to be coupled with a
3
JHH
of ~10 Hz, consistent with formation of cis,HT linkages (Figure
2.6).
Ph
(a)
Hex
(b)
(C)
.___Me
__
5.65
5.45
5.55
5.35
5.25
5.15
4.95
5.05
4.85
(d)
Ph
(e)
Hex
(f) _Me
150
148
146
144
142
140
138
136
134
132
130
128
126
124
Figure 2.6. Olefinic (1H) and olefinic and aryl ('3C) regions of the 'H (top) (500 MHz in CDC3) and 1 3C
(bottom) (125 MHz in CDC3) NMR spectra of isolated >98% cis,HT-poly(3-RCOE) (R = Ph (a,d), Hex (b,e),
Me (c,f)) prepared using la.
For all catalysts, 3-MeCOE is polymerized most rapidly of three monomers followed by
3-HexCOE and 3-PhCOE which is most likely a consequence
of the steric demand
(phenyl>hexyl>methyl) of the R group. When initiators lb and Ic were employed for 3-MeCOE,
some olefinic impurities (1% intensity compared to the major cis,HT polymer product) were
observed by 'H NMR spectroscopy. The NMR signals of the impurities did not match with trans
polymer peaks reported by Hillmyer. 3 They are likely either cyclic oligomers (from backbiting
83
processes) or regioisomeric polymers having HH, TT geometries. In order to better understand
the nature of the impurities, the ROMP of 3-MeCOE with 0.02 mol% 1c was run for 42 hours.
Note that the polymerization reaction is finished within 1 h, but it was postulated that longer
reaction time might produce more impurities due to the remaining active catalyst species. Indeed,
at longer reaction times, more olefinic impurities were observed by
1H
NMR spectroscopy
(Figure 2.7). 1H-1H COSY was performed in order to see if the impurities had HT or HH, TT
linkages. If olefinic cross peaks were observed, the impurities would likely have HT linkages.
Besides major HT correlations from the desired polymer, there is also a correlation between
signals at 5.31 and 5.21 ppm, which can be assigned as the correlation between olefinic
impurities. Some impurities appear to have HT linkages, but the low intensity of the signals
hinders exact assignment (Figure 2.8).
(a)
(b)
s.40
s.35
5.30
5.25
S.20
S.A
s
.10
5.05 s
.00
4.95
4.9
Figure 2.7. Proton NMR spectra of the olefinic region of cis,HT poly(3-MeCOE) prepared from Ic after (a) I
h and (b) 42 h (C6D6, 500 MHz).
84
r2
4.9j
5.0-
5.5
5.4
5.3
5.2
5.1
5.0
4.9
n1 (pf)
prepared from 1c
1
Figure 2.8. The 1H- H COSY spectrum of the olefinic region of cis,HT-poly(3-MeCOE)
after 42 h.
For 3-HexCOE, 1c proved the most active among three catalysts; 70% conversion of 3HexCOE (5000 equiv) to cis,HT-poly(3-HexCOE) was achieved after 1 day at room temperature,
whereas 3 days at room temperature gave 78% conversion with la (0.02 mol%) as the initiator.
the
The ROMP reaction of 3-HexCOE employing 1c was also performed at 60 'C to determine
more than
temperature effect on the rate of reaction. The conversion was 46 % after 4 h, which is
at
observed at room temperature (25 % after 4 h). The high cis,HT selectivity is also maintained
60 'C, according to 'H NMR spectroscopy.
The ROMP of 3-PhCOE was much slower at 0.02% catalyst loading than it was for 3-Me
1c
and 3-HexCOE, so the conversion of 3-PhCOE was monitored at 0.1% loading. Catalyst
that of the
appears to be the most active at first, but conversion after 24 h was similar to
also
molybdenum analogue 1b. For the case of 3-PhCOE, minor olefinic impurities were
the
observed with lb and 1c. GC/MS measurements were performed in order to see whether
product mixtures contained any cyclic dimer, but the dimer was not observed. When 1% catalyst
1c was employed, >99% of the monomer was converted to cis,HT-poly(3-PhCOE) after 4 hours
and the ratio of cisHT-poly(3-PhCOE) to impurities was found to be 8:1. After 24 h, impurities
were largely consumed and the ratio of cis,HT-poly(3-PhCOE) to impurities increased to 27:1;
therefore, it appears that the impurities are consumed to yield cis,HT-poly(3-PhCOE). A 1H-1H
85
COSY spectrum was taken after 4 hours in order to check for correlation peaks between olefinic
impurities. However, there was no correlation for an observed major impurity peak at 5.58 ppm.
A 'H NMR spectrum (500 MHz, CDCl 3 ) of a mixture of cis,HT-poly(3-HexCOE)
(prepared employing la as the initiator) and trans,HT-poly(3-HexCOE) (prepared by the
Hillmyer group employing Grubbs' 2 "d generation catalyst) shows four distinct resonances of the
olefinic protons in the mixture of two polymers (Figure 2.9).
H1
C 6H 13
cis
Poly(31 exCOC)
trans
trans
HI
H2
5.25
5.35
7
cis
n
H2
6
5.15
5
4.95
5.05
3
4
ppm
2
1
0
Figure 2.9. 'H NMR spectrum of a mixture of cis,HT-poly(3-HexCOE) prepared using Ia and trans,HTpoly(3-HexCOE) prepared using Grubbs' 2 "dgeneration catalyst (CDC13, 500 MHz).
B. Molecular Weight Determination of Poly(3-RCOEs)
The isolated polymers were analyzed by size exclusion chromatography (SEC) using
CHCl3 eluent at room temperature. At first, number-average molecular weights (M.) were
obtained using a one-column SEC setup by comparison to polystyrene standards. The obtained
Mn values for poly(3-PhCOE) were found to be 57-97% of the calculated molecular weights for
an ideal living polymerization system. However, for the case of poly(3-MeCOE) and poly(386
HexCOE), the Mn values were found to be only 10-15% of the calculated molecular weights. The
observed polydispersity indices (PDI = Mw/M.) are found to be between 1.2 and 1.5, indicating
that this is not a highly living polymerization system (PDI = 1 for a perfect living
polymerization). These PDI values stand in contrast to the low PDI values (close to 1) obtained
for
polymers
prepared
from
3,3-disubstituted
cyclopropenes' 3
and
dicarbomethoxynorbornadienes1 4 with various Mo/W MAP initiators. Low PDI values are
expected given the high ring strain of cyclopropenes and norbornadienes.
The large discrepancies between obtained Mn and calculated Mn for poly(3-MeCOE) and
poly(3-HexCOE) might be due to the following reasons: the physical properties of poly(3MeCOE) and poly(3-HexCOE) might be very different from those of polystyrene standards, or
the one-column SEC setup may not have enough pore volume to guarantee successful separation.
In order to test whether the relative Mn values (using polystyrene dn/dc = 0.16 at RT in THF) are
within a good range, refractive index increment (dn/dc) values of poly(3-MeCOE) and poly(3HexCOE) were calculated using differential refractive index (dRI) detector. The dn/dc describes
the change of the refractive index of a polymer solution with change of the polymer
concentration. Each polymer has its own dn/dc value in a given solvent system. Five samples of
poly(3-MeCOE), each having a different concentration in chloroform, were prepared and
injected to the dRI detector at 40 'C using a syringe pump (Figure 2.10). The ASTRA software
was used to fit and plot the data to determine the slope, which is the dn/dc value of the polymer
in chloroform (Figure 2.11). The slope was found to be 0.0683 ml/g, where R2 is 0.995. When
this dn/dc value is used to interpret the previous GPC data, the obtained Mn is found to be 2023% of the calculated molecular weight. The same procedure is applied to poly(3-HexCOE), and
its dn/dc is found to be 0.0707 ml/g, where R2 is 0.983. Similarly, the obtained Mn of poly(3HexCOE) is found to be 27-32% of the calculated molecular weight. Although applying dn/dc
value gives more reliable molecular weights, the results are still quite far off from the calculated
molecular weights for a living polymerization system.
SEC data for several polymers prepared with 1c were conducted by the Hillmyer group
which are shown in Table 2.2. Mn for poly(3-MeCOE) and poly(3-HexCOE) samples still did not
match well with calculated values, likely due to backbiting and rate differences of propagation
versus initiation steps. In all cases, polydispersity values for the polymers are between ~1.7 and
1.9. However, when the same polymer sample was analyzed both on the one-column SEC setup
87
in our laboratory and also on a multi-column SEC setup in the Hillmyer group (both used
polystyrene standard), the former setup showed 161 kgmol- whereas the latter setup showed 375
kgmol-'. Therefore, it is necessary to have multi-column SEC to determine Mn values.
r -s
1.0
Define Peaks
r uv -
e
a
-
I
.
.
L
.3
0.5
0.0
10.0
15.0
10.0
15.0
ie (min)
a
a,
5.0
0.0
25.0
200
am
a'
I
30.0
25-0
20.0
Figure 2.10. Concentration detection of five different concentrations of poly(3-MeCOE) using dRI detector
(CHCL3, 40 *C).
Determine dn/dc from Ri
51.0x10
-
1.5x104
0.0000.005 .000 0015
002
5.0x10-
0.0,.
0.0000
0.0-500010
0.0015
coadnceftv
0.0020
(..i)
Figure 2.11. Differential refractive index versus concentration for poly(3-MeCOE).
Table 2.2. Characterization Data for cis,HT-poly(3-RCOE) Prepared using 0.02 mol% initiator 1c at 22 *C.
Mn (calcd)a
612
636
Mn (SEC LS)b
4995
4884
conv (%)
99
67
430
Mn (SEC PS)c
706
416
4884
63
598
480
375
R
Me
Hex
nb
Hex
PDI
1.9
1.7
1.8
aM.(calcd) = (mol wt of 3-RCOE) x [3-RCOE]o/[initiator]o x conversion in units of kg mol-. b Determined by SEC
using THF as eluent as 25 0C and a multiangle light scattering detector. c Determined by SEC using THF as eluent
as 25 0C and refractive index detector relative to PS standards. d This sample had been stored for several weeks in
air.
88
C. Catalyst Screenings in ROMP of 3-RCOEs
Various MAP and bisalkoxide Mo and W catalysts have been screened in the ROMP of
3-HexCOE.1 5 For example, W(N-2,6-Me 2C 6H3 )(CHCMe2Ph)(pyr)(OHMT)"
cis,HT-poly(3-HexCOE),
polymerization
of
forms >98%
but the polymerization rate is lower than half the rate of
3-HexCOE
Mo(NC 6 F5 )(CHCMe2Ph)(ODFT)2
by
la,
1b,
or
The
1c.
bisalkoxide
catalysts,
2,6-bis-(pentafluorophenyl)phenoxide)16,
(ODFT
and
Mo(NAd)(CHCMe2Ph)(OCMe(CF 3)2)21 7 form significant amounts of trans,HT polymer. In
addition, catalysts bearing 2,5-dimethylpyrrolide do not give any conversion of 3-HexCOE. For
example,
W(N-t-Bu)(CHCMe3)(2,5-Me2pyr)(OHMT),1
8
W(NAd)(CHCMe3)(2,5-
Me2pyr)(OTript) (OTript = OTriptycene), and W(NArCI3 )(CHCMe 3)(2,5-Me 2 pyr)(OHMT) (the
last two developed by Jonathan Axtell) showed no ROMP activity. It is interesting to note that a
drastic difference in ROMP activity is observed for compound 1c with a parent pyrrolide ligand
versus the analogous 2,5-dimethylpyrrolide-bearing compound.
W(O)(CHCMe3)(Me2Pyr)(OHMT)(PMe2Ph) was found to be a poor catalyst in ROMP of
3-HexCOE (after 24 h, <2 % conversion at 22'C). Coordination of the phosphine to tungsten
would create a five-coordinate species that could be too sterically congested to form propagating
species. However, it was shown that two equivalents of B(C 6Fs) 3 could activate the catalyst: one
equivalent is to remove PMe 2Ph ligand by forming PMe 2Ph-B(C6FS) 3 as a precipitate, and
another equivalent of B(C6F5 )3 to coordinate to the oxo ligand so that the electrophilicity of W
increases
significantly.
The
X-ray
crystal
structure
of
W(O)(B(C 6F5 )3)(CHCMe3)(Me2Pyr)(OHMT) was reported in the literature.1 9 Activation of the
oxo ligand with the lewis acid B(C 6F5 )3 increases the rate of homocoupling of terminal olefins as
well as ROMP of dicarbomethoxynorbornadiene 2 ' by approximately a factor of 50.
Several experiments were carried out by varying B(C 6F5 ) 3 equivalents in the ROMP of 3HexCOE with W(O)(CHCMe3)(Me2Pyr)(OHMT)(PMe2Ph) catalyst. 1.77, 2.06, 3.82, 4.00, 5.88,
and 8.24 equivalents were used in separate runs. The results are shown on Table 2.3. As shown,
the general trend is that while some B(C6F5 )3 is required for ROMP, excess B(C 6Fs) 3 appears to
limit conversion.
A test reaction was conducted in order to determine whether B(C 6F5 )3 affects the speed of
polymerization for a catalyst having an imido moiety. One equivalent of B(C 6 F5 ) 3 was added to a
3-HexCOE ROMP experiment with 1b. Surprisingly, the conversion was observed to be 68%
89
after 4 hours. It should be noted that in the absence of B(C 6F5 ) 3 , the conversion was 19% after 4
hours. It appears that B(C 6Fs) 3 activates lb for ROMP as well.
Table 2.3. Variation of B(C6Fs)3 equivalents for ROMP of 3-HexCOE (5000 equiv, neat, 22 0 C) using
W(O)(CHCMe3)(Me2Pyr)(OHMT)(PMe2Ph) catalyst.
Entry
1
2
3
4
5
6
Equiv of B(C 6F5)3 Time (h)
1.77
4
48
2.06
3
24
4
3.82
48
4
4
24
5.88
4
24
4
8.24
conv (%)
35
64
53
50
27
27
5
21
<2
<2
<2
Also, W(N-t-Bu)(CHCMe3)(Me2Pyr)(OHMT) was treated with 2 equivalents of B(C 6F5 )3
and tested for ROMP reactivity with 5000 equivalents of 3-HexCOE. Surprisingly, 99%
conversion was observed after 4 hours. It was known that various dimethylpyrrolide-containing
MAP catalysts were inactive in ROMP of 3-HexCOE (vide supra). It remains unclear how
B(C6F5)3 interacts with imido catalysts to increase catalytic activity, but presumably B(C 6F5 )3
might distort the catalyst geometry so that the dimethylpyrrolide-containing MAP catalyst can
also ROMP 3-HexCOE.
D. Expansion of Monomer Scope in ROMP of Substituted Cyclooctenes
Besides 3-Me, 3-Hex, and 3-Ph substituted cyclooctenes, the more sterically crowded 3-iPrCOE was attempted in ROMP reactions. However, there was no conversion of 3-i-PrCOE to
polymer by any catalyst employed in the same conditions, indicating the steric sensitivity in this
system. Attention has been shifted to heteroatom-containing monomers. 3-AcetoxyCOE was not
polymerized
in
neat
monomer
Mo(NAr)(CHCMe2Ph)(OCMe(CF3)2)2.
at
0.1%
catalyst
loading
of
la,
1b,
1c,
or
It was postulated that the catalysts were perhaps not
stable toward the acetoxy functionality, or impurities in the monomer (such as hydrolyzed acid)
might kill the catalyst. For the case of 3BrCOE, catalyst decomposition was observed at 5%
loading in neat monomer. When a stoichiometric amount (1.8 eq) of 3-BrCOE was added to lb
90
in chloroform-d solution, a new alkylidene signal was observed by 'H NMR, but no new olefinic
signals arose. These results indicates that 3-BrCOE interacts with the catalyst to lead to
undesirable decomposition products.
According to a paper from the Hillmyer group4 , a 3-substituent is required to generate
highly trans- and regioselective polymer. It would be interesting to see whether Mo and W MAP
catalysts also require 3-substituted monomers in order to generate high Z or regioselectivity. In
addition, more challenging substrates that contain oxygen functional groups could be good
candidates in terms of testing functionality tolerance and modification after polymerization.
Therefore, a few monomers were selected for polymerization: 3-epoxycyclooctene21 (1), 5epoxycyclooctene 22 (2), 3-methoxycyclooctene 2 3 (3), and 5-methoxycyclooctene 24 (4). Syntheses
of monomers were achieved as reported in the literature and shown in Scheme 2.3.
1.36 eq m-CPBA
Br
0
NaOMe
O*C to rt, 17 h, CHC1 3
rt, 2 d, MeOH
1(69%)
3(13%)
1. Hg(OAc) 2
2. 3M NaOH
3. 0.5M NaBH 4 in 3M NaOH
0.8 eq m-CPBA
0 C to rt, 16 h, THF/CHC
OMe
-
rt, 5 h, MeOH
3
0
2 (36%)
OMe
4 (33%)
Scheme 2.3. Synthesis of 3,4- and 5,6-substituted cyclooctene monomers.
Addition of 0.8 equivalents of m-chloroperbenzoic acid (m-CPBA) in chloroform
solution to cis-1,5-cyclooctadiene (COD) in THF solution with stirring generated 2. However,
1% of 1,5-COD remaining in the product mixture creates difficulty in isolating the product
cleanly, even after multiple distillations. Addition of excess m-CPBA in chloroform solution to
1,3-COD makes a clean product 1. The polymerization of monomers was performed under
various conditions. In general, polymerization of 2 and 4 was successful whereas that of 1 and 3
was not. The summary of the results is shown in Scheme 2.4.
91
cat. lb or cat.1c
OMe
S
No reaction
1
No reaction
3
0.3 mol% cat. lb
0
2
cat. lb or cat.Ic
__________
0.3 mol% cat. Ic
n
rt, 1 h, 2.2M C6 H 6
rt, 1 h, neat
OMe
OMe
Poly 2
4
Poly 4
Scheme 2.4. Polymerization of oxygen-containing cyclooctene monomers.
When 300 equivalents of 2 were added to a 2.2 M C 6H6 solution of catalyst lb at room
temperature, gel immediately formed as the monomer was added. After 5 min, an aliquot was
taken and complete conversion was observed by 'H NMR spectroscopy. The speed of
polymerization of monomer 2 is much faster than that of 3-substituted cyclooctene derivatives.
As shown in Scheme 2.4, the symmetrical monomer 2 forms single, regioregular polymer. Based
on 'H NMR spectroscopy, 95% cis-selective polymer (5.46 ppm, triplet) was observed and the
yield was 71%. '3 C NMR showed cis (129.57 ppm) and trans (130.10 ppm) olefinic signals. The
assignment of NMR peaks was done by comparison with a previous report, 24 which shows a
mixture of cis and trans polymers. The signals for trans polymer grew in over a longer period of
time; it seems that the catalyst isomerizes double bonds to a mixture of cis and trans.
Monomer 4 was polymerized at 0.3 mol% catalyst lc in neat monomer at room
temperature. 40% conversion was observed after 24 hours, and the cis selectivity of the polymer
was >95%. In the case of asymmetrically substituted monomer, HH, HT, and TT isomerism can
be found based on 'H and 13C NMR spectroscopy. Therefore, Z selectivity maintained for 5substituted cyclooctene monomer, but regioselectivity was not achieved.
For the cases of monomers 1 and 3, polymerization was not successful under various
conditions. Conversion was not observed at 0.1 and 0.3 mol% catalyst loading, both at room
temperature and at 60 0C. It is possible that oxygen-atom-containing functional groups at allylic
positions might interact with the catalyst so as to shut down catalytic activity. This hypothesis
can also be applied to the case of 3-acetoxyCOE. It was reported that 2,5-diheptyloxy-1,4divinylbenzene was more difficult to polymerize than 2,5-diheptyl-1,4-divinylbenzene because
of the oxygen atom coordinating to molybdenum, leading to a stabilization of catalytic
intermediates.2 5
92
11. Determination of the Origin of Selectivity
With the promising results from Part 1 showing formation of cis,HT-poly(3-RCOEs), we
next undertook a systematic study of catalyst 1c with three 3-RCOE monomers (R = Me, Hex,
Ph) to observe the propagating species and explore how monomer approaches the catalyst.
A. Nature of Propagating Species
As shown above, high head-to-tail (HT) selectivity was observed in ROMP of 3-RCOEs.
Given this, there are two possible orientations in which the monomer may approach the metal
center. The 3-RCOE monomer can approach such that the R substituent is either far away from
the metal center or close to it. The first type has the R substituent group on the C7 carbon atom
of the alkylidene chain (P1) whereas the second type has the R substituent group on the C2
carbon atom (P2) (Scheme 2.5).
NR'
pyro~.. py
I.
IIpyro,,
I P
pyr',,, M
R
TMHR'
R
__
_
_
_
TMH
R
TMHO
P1
NR'
pyr
TMHO
R
NR'
I
P
NR'
pyro' "M
TTMHO
pyrI'.M
TMHO~
TMHO
R
R
P2
Scheme 2.5. Two possible 3-RCOE monomer approach to MAP catalyst (P = polymer chain).
Since the metal center of a MAP catalyst has chirality, each type can have two
diastereomers. Therefore, given a single configuration at the metal center, four possible
propagating alkylidenes are shown in Scheme 2.6.
NR'
pyr
NR'
pyr,,,, M
.
TMHO
R
NR'
py I
prIM~
TMHOO
TMHO
P
R
,,,I
RP
R
NR'
pyrII,.M
TMHO
P
P
R
P
Scheme 2.6. Four possible propagating alkylidenes for a given configuration at the metal center.
93
If monomer approaches to form a first type (P1), the alkylidene proton of the propagating
metal complex should show a triplet in the 'H NMR spectrum, as opposed to a doublet if the R
group is closer to the metal center (P2). In addition, both syn and anti alkylidene isomers of the
MAP could be present, but 14e alkylimido MAP complexes used in this study have been found
to contain syn alkylidene isomers at room temperature, so we will exclude the anti cases.1 8 Only
sterically demanding arylimido species such as Mo/W 2,6-dimesitylphenylimido
bis(2,4,6-triisopropylphenyl)phenylimido
27
26
or W 2,6-
complexes are shown to contain significant anti
alkylidene isomers in 14e species.
In the Hillmyer paper,3 it was shown that the 3-RCOE monomers approach to the catalyst
such that the R substituent is farther away from the Ru center. This was demonstrated by
studying the stoichiometric reaction between monomer and catalyst. Therefore, a stoichiometric
reaction between monomer and catalyst has performed in our system. Initially, 1c was treated
with 5 equivalents of 3-HexCOE in C 6D6 solution at 60'C for 18 h. The 'H NMR spectrum
showed mainly the starting catalyst, residual monomer, and some new olefinic signals. In the
alkylidene region, although the new alkylidene peak was observed, its intensity was very small
compared to the starting neopentylidene peak (20:1 based on integration). Based on the result, it
is likely that the rate of propagation (kp) is much faster than the rate of initiation (ki), so that most
of the catalyst remains unreacted and the metal complexes having propagating chains might
backbite to form cyclic oligomers.
Since poor catalyst initiation makes it hard to observe the first insertion product, a
catalyst bearing a methylidene moiety should be a better candidate because it would be more
reactive
toward
3-RCOE
monomers.
The
known
methylidene
complex
Mo(NAr)(CH2)(pyr)(OHIPT) has been synthesized from Mo(NAr)(C3H 6)(pyr)(OHIPT).1
2
1.24
equivalents of 3-HexCOE were added to the Mo methylidene toluene-d solution at -78 'C.
After 30 minutes, a 1H NMR spectrum obtained at room temperature showed that there is a
major clear triplet signal in the alkylidene region, which means the major insertion occurred in
the orientation where the R group is farther away from the metal center. It seems likely that
sterics around the metal center favors this orientation. There were some other peaks in the
alkylidene region; some arose from unreacted methylidene and others presumably from insertion
in the other orientation. However, their low intensity made them hard to assign. Since the
94
methylidene species used above has a different ligand environment from the initiator in our
previous study, attention shifted back to the original initiator 1c.
In order to drive reaction more so that more initiated alkylidene could be observed,
various equivalents of neat 3-HexCOE monomer were applied to 1c. After some time, CDCl3
was added, and the mixture was observed by 1H NMR spectroscopy. When 1 to 100 equivalents
of bulk 3-HexCOE were treated with 1c, the same new alkylidene species were observed in all
cases, but addition of 100 equivalents produced the largest amount of propagating species. 100
equivalents of bulk 3-HexCOE were treated with Ic for 4h 30min, and then the sample was
dissolved in CDCl 3 . The monomer was mostly consumed (>95%) and the proton NMR spectrum
of the resulting alkylidene region is shown in Figure 2.12a. Two major doublet peaks are
observed for the propagating alkylidene(s). The clear doublet indicates that the major coupling is
with the hydrogen on C2 and thus that the R group is at the C2 position. The hydrogen on C2
appeared at 3.73 ppm; its identity can be confirmed by a coupling to the propagating alkylidene
peak with 'H-1H COSY. The other two monomers, 3-MeCOE and 3-PhCOE, were also treated
with initiator 1c, and two doublets were observed in both cases (Figure 2.12c and 2.12b). The
two doublets probably come from diastereomers generated by the chiral centers both on the metal
and at the C2 position. Each peak is a doublet where
2
JHW
2
JHH =
~10 Hz and has
18 3 W
satellites with
= ~20 Hz. For the case of 3-MeCOE, two sets of hydrogens on C2 gave resonances at 3.81
and 3.77 ppm, which can be observed by 1H-'H COSY.
95
(a)
(b)
(c)
8.55
8.50
8.45
8.40
8.35
830
8.25
8.20
8.15
8.10
8.05
Figure 2.12. Proton NMR spectra of the alkylidene region of poly(3-RCOE) in CDC 3 prepared through
polymerization of bulk 3-RCOE treated with lc (500MHz) : (a) R = Hex, 100 quiv; (b) R = Ph, 100 equiv; (c)
R = Me, 200 equiv. A peak at 8.16 ppm indicates the remaining initiator alkylidene proton.
As mentioned earlier, the opposite is observed when Mo(NAr)(CH2)(pyr)(OHIPT) is
treated with 1.2 equivalents of 3-HexCOE in toluene-d8 solution at -78 'C. In the methylidene
system, the major alkylidene peak observed was a triplet due to coupling with two Hp protons.
The steric bulk of the terphenoxide and imido groups might force the R substituents to occupy
the C7 position. However, the polymerization of 3-HexCOE with either 0.02 or 0.1 mol%
Mo(NAr)(CH2)(pyr)(OHIPT) was not achieved.
In order to mimic the alkylidene moiety where the R group (R = Me) is at the C2 position,
three equivalents of 3-methyl-i-pentene were added to 1c at room temperature in benzene
solution and all volatiles were removed in vacuo. Two diastereotopic doublets were observed by
'H NMR spectroscopy: -8.20 ppm and -8.32 ppm with
2
JHW
(20 Hz),
3
JHH
(10Hz) couplings
(Figure 2.13a). The two sets of Hp protons on the C2 carbon are observed at 3.74 ppm (coupled
to the 8.32 ppm alkylidene peak) and 3.66 ppm (coupled to the 8.20 ppm alkylidene peak). The
coupling of the alkylidene proton and the Hp proton is observed by 1H-1H COSY (Figure 2.14).
96
In addition, homo-decoupling of the signals at 3.74 and 3.66 ppm led to the collapse of the
doublet signals to singlets at 8.32 and 8.20 ppm, respectively. This confirms that the major
doublet comes from the
3
JHH
coupling between alkylidene proton and Ho proton. The alkylidene
region of the homo-decoupling experiment at 3.74 ppm is shown at Figure 2.13b.
(a)
8.50
8.45
8.40
8.35
8.30
6.35
6.30
8.25
8.20
8.15
8.1
8.05
8.10
(b)
8.46
1.48
6.25
6.10
6.16
6.10
6.08
Figure 2.13. (a) Proton NMR spectrum of the alkylidene region of W(N-t-Bu)(CHCHMeEt)(pyr)(OHMT)
of volatiles
prepared as follows: 3 equivalents of 3-methyl-1-pentene was treated with Ic followed by removal
W(N-tof
region
alkylidene
the
in vacuo (CDCb, 500 MHz). (b) Proton NMR spectrum of
MHz).
500
(CDCb,
3.74ppm
Bu)(CHCHMeEt)(pyr)(OHMT) after homodecoupling at
72
N
H
Has*
9
0
7
6
5
4
3
2
1
-0
VI (PPM)
Figure 2.14. 1H-1H COSY spectrum of W(N-t-Bu)(CHCHMeEt)(pyr)(OHMT) (CDCb, 500 MHz).
97
,
When excess 3-methyl-1-pentene was treated with ic at room temperature in CDCl 3
alkylidene resonances for W(N-t-Bu)(CHCHMeEt)(pyr)(OHMT) are broadened which suggests
excess 3-methyl-1-pentene is exchanging with W(N-t-Bu)(CHCHMeEt)(pyr)(OHMT)
in a
degenerate metathesis. Therefore, 3 equivalents of 3-methyl-i-pentene were added at room
temperature to a J-Young tube where le was dissolved in CDCl 3, and the tube was immediately
injected into a pre-chilled -20 'C NMR probe. The proton NMR spectrum at -20 'C showed
formation of a metallacyclobutane. The two Hx protons appeared at 4.31 and 4.25 ppm, and two
Hp protons appeared at -0.09 and -1.02 ppm (Figure 2.15). Based on chemical shifts, the
resultant species is assigned as a trigonal bipyramidal metallacycle having two substituents on
each of the a and a' carbons. As the temperature was increased by increments of 10 'C, breakup
of the metallacyclobutane species and formation of alkylidene were observed in the range from
-20 to 20 'C.
Based on the results shown here, the polymerization reaction proceeds such that the R
substituent is on C2 of the propagating alkylidene chain (P2 pathway, Scheme 2.5). This result
was somewhat surprising, since it could be thought that monomer comes in the orientation where
the R substituent is on C7 (P1) in order to avoid steric congestion around the metal center.
However, based on a paper reported by the Hillmyer group where they performed DFT studies
on polymerization of 3-MeCOE with ic initiator, pathways in which the propagating chain
contains a C2 substituent have lower free energy than those in which the propagating chain
contains a C7 substituent.28 This result is consistent with our observation by 'H NMR
spectroscopy. The rate determining step is the breakdown of the metallacyclobutane species, and
the P1 pathway is not preferred because there is a steric repulsive interactions between the
methyl group (or allylic substituent) and the tert-butyl alkylidene (or growing polymer chain)
(Figure 2.16).
98
-
3
N
Benzene
0
.-
0
,,.-
I
Ha
(a)
r. 20 min
<
N
N
CHEtMe
HEtMe
vacuum
(b)
4.5
3.5
0.5
1.5
2.5
-0.5
-1.5
Figure 2.15. Proton NMR spectrum (-20 *C) in the tungstacyclobutane region after addition of 3-methyl-ipentene to 1c (CDCb, 500 MHz).
steric repulsion
N
N
vvJ
HofI
H3C
OHMT
OHMT
P1 approach
P2 approach
Figure 2.16. TBP metallacyclobutane intermediate of both P1 and P2 approach with 3-MeCOE monomer and
ic. The pyrrolide ligand was omitted for clarity.
B. Determination of kp/ki
Based on various results mentioned above, it is known that the rate of propagation (kp) is
much higher than the rate of initiation (ki) in ROMP of 3-RCOE. We are interested in the
tentative kp/ki ratio (r), which can be determined using the following equation2 9 ,30 : M-Mo = (1r)/(I-Io) + rloln(IIo), if I
0, where Mo and M are the initial and final concentration of monomers
and Io and I are initial and final concentration of initiator, respectively. When the concentration
99
of monomer reaches 0 (M -* 0), r can be calculated by measuring the amount of remaining
initiator (I). An accurate r value can be obtained when I is significantly less than lo, but greater
than zero. For the 3-MeCOE case, r is found to be 630 when Mo/Io = 200 and I/Io = 0.40. For 3HexCOE, r is found to be 280 when Mo/Io = 100 and I/Io = 0.37. For 3-PhCOE, r is 140 when
Mo/Io = 100 and I/Io = 0.23. The trend of r values follows the order of Ph<Hex<Me, which fits
according to the decreasing steric bulk of the R groups. This relationship is demonstrated by
comparison to the A values of the substituents, which are a measure of the energy difference
between the higher energy conformation and the lower energy conformation for various
substituents on a monosubstituted cyclohexane ring. A-values can help predict the steric effect of
a substituent: the larger a substituent's A-value, the larger the steric effect of that substituent.
.
The A values for methyl, ethyl, and Ph are 1.7, 1.75, and 3 kcal/mol, respectively3 1
CONCLUSIONS
Mo and W alkylimido MAP complexes have proven to be valuable catalysts in
generating highly stereo- and regioselective polymers (>98% cisHT) of 3-substituted
cyclooctenes. While dilute conditions generated mixtures of polymers and cyclic oligomers,
reactions in neat monomers at room temperature went to much higher conversions and resulted
in clean formation of >98% cis,HT polymers. All three catalysts proved to be highly selective,
and the W MAP catalyst W(N-t-Bu)(CHCMe3)(pyr)(OHMT) was faster than analogous Mo
catalyst Mo(N-t-Bu)(CHCMe3)(pyr)(OHMT), which had not been previously observed in other
olefin metathesis reactions. Through the size exclusion chromatography studies, it was found that
the obtained polymers had molecular weights with a range of 370 ~ 710 kgmol' and
polydispersity indices with a range of 1.7 ~ 1.9, which are not indicative of a living
polymerization system. Also, the refractive index increment indicates that physical properties of
poly(3-MeCOE) and poly(3-HexCOE) are different than that of polystyrenes. Some other Mo/W
MAP and Mo bisalkoxide catalysts were screened in ROMP of 3-RCOEs. Some catalyst were
able to generate >98 cis,HT polymers but their rate was much lower than that of the Mo/W
alkylimido
MAP
catalysts,
and
some
catalysts
proved
to
be
not
as
selective.
W(O)(CHCMe3)(Me2Pyr)(OHMT)(PMe 2 Ph) was not as active, but with the addition of the
Lewis acid B(C 6Fs) 3, the polymerization rate increased significantly and highly cis,HT polymers
were formed. By monitoring alkylidene regions during polymerization, it was found that
100
monomer approaches the R substituent is on the C2 carbon on the propagating alkylidene (the
alternative pathway leads to R substituents on the C7 carbon on the propagating chain). This
mechanism was corroborated by the DFT calculation studies of the Hillmyer group, as the
pathway where the propagating alkylidene contains the R substituent on C2 is lower in energy
than the pathway wherein the R substituent is in the C7 position at room temperature in
chloroform. As expected through SEC studies, rate of propagation versus rate of initiation (kp/ki)
ranges from 140 - 630, indicating much faster propagation than initiation. As the size of the R
substituent increases (Me<Hex<Ph), kp/ki decreases significantly because as bulkier R
substituent is, increased steric hindrance in the propagating species makes lower differences kp
versus ki.
EXPERIMENTAL
General Considerations
All manipulations of air- and moisture-sensitive materials were conducted under a
nitrogen atmosphere in a Vacuum Atmospheres glovebox or on a dual-manifold Schlenk line.
The glassware, including NMR tubes, were oven-dried prior to use. Diethyl ether, pentane,
toluene, THF, dichloromethane, and benzene were degassed and passed through activated
alumina columns and stored over 4
A Linde-type
molecular sieves prior to use. Dimethoxyethane
was dried from dark purple solution of sodium benzophenone ketyl, and degassed by the freezepump-thaw technique. The deuterated solvents were dried over 4 A Linde-type molecular sieves
prior to use.
Materials. Cyclooctene (95%) was purchased from Alfa Aesar and distilled before use. 3BrCOE, 3-MeCOE, 3-HexCOE, 3-PhCOE, and 3-iPrCOE were synthesized as reported 3 and
were degassed by a minimum of three freeze-pump-thaw cycles and dried over 4A Linde-type
molecular
sieves
prior
to
use.
HMTOH32
Mo(NAd)(CHCMe2Ph)(pyr)(OHMT) 7,
(HMT
=
2,6-(2,4,6-Me3C6H2)2C6H3),
Mo(N-t-Bu)(CHCMe3)(pyr)(OHMT)
33 ,
W(N-t-
W(N-t-Bu)(CHCMe3)(pyr)(OHMT) 1 8,
Bu)(CHCMe3)(2,5-Me2pyr)(OHMT),
Mo(NAd)(CHCMe 2 Ph)(OC(CF3)2Me)217,
and Mo(NAr)(CH2)(pyr)(OHIPT)1
2
were prepared
according to literature procedures. W(NAr')(CHCMe2Ph)(pyr)(OHMT) 1" (Ar' = 2,6-Me2C6H3),
Mo(NC 6F5 )(CHCMe2Ph)(ODFT)2
(ODFT
=
101
2,6-bis(pentafluorophenyl)phenoxide)
16,
and
W(O)(CHCMe3)(Me2pyr)(PMe 2 Ph)(OHMT)1 9 were gifts from Erik Townsend, Jian Yuan, and
Dmitry Peryshkov respectively. Unless otherwise noted, all other reagents were obtained from
commercial sources and used as received.
Instrumentation. 'H, and
3
1
C
spectra were acquired at room temperature using 300MHz
and 500MHz spectrometers. Chemical shifts for 'H and '3 C spectra are reported as parts per
million relative to tetramethylsilane and referenced to the residual H/1 3 C resonances of the
deuterated solvent ('H (6) : benzene 7.16, chloroform 7.26, methylene chloride 5.32; "C (6):
benzene : 128.06, chloroform 77.16, methylene chloride 53.84). Chemical shifts for 1 9F are
reported as parts per million relative to trichlorofluoromethane, and referenced using an external
standard of fluorobenzene (6 -113.15). Refractive index increment (dn/dc) at 690 nm was
measured in chloroform at 40 'C using a Wyatt Optilab differential refractometer. Numberaverage molar masses (Mn) were determined by size exclusion chromatography (SEC) using
tetrahydrofuran (THF) as the mobile phase (25 'C, 1 ml/min flow rate).
This instrument is
equipped with 3 Waters Styragel columns, together with a Wyatt DAWN Heleos II light
scattering detector and Wyatt OPTILAB T-rEX refractive index detector (658nm wavelength).
General procedure: ambient-temperature polymerizations, neat monomer
In the glovebox, the Mo or W initiator was added as a stock solution in benzene to an 8 mL vial
containing a stir bar. The benzene was frozen and removed by sublimation, and the monomer
(250 ptL, 5000 equiv.) was added via syringe. The vial was capped and the mixture stirred at
ambient temperature.
Aliquots were removed from the box and quenched with wet CDCl3
(stored under air without desiccant).
The polymerization reactions were quenched either by
addition of 5 mL wet CHCl 3 (stored under air without desiccant) or addition of benzaldehyde,
followed by sonication for 30 min. The polymers were precipitated by addition of this solution
to 50 mL methanol. The precipitated polymers were freeze-dried overnight from frozen benzene
solutions.
General procedure: elevated-temperature polymerizations, neat monomer
Polymerizations at elevated temperatures were performed identically to those at ambienttemperature with the following exceptions: a small Schlenk tube with PTFE plug was used
102
instead of a vial and, once the monomer was added, the tube was sealed, removed from the box,
and heated with stirring in an oil bath. Aliquots were taken for monitoring in the glovebox.
cis,HT-poly(3-MeCOE)
'H NMR (500 MHz, CDCl 3) 6 5.27 (dt,
Hz, 1H), 2.40 (m, 1H), 2.00 (m, 2H,
3
JHH=
6.7 Hz, 3H);
13C
3
3
JHH
JHH =
10.8, 7.3 Hz, 1H), 5.09 (apparent t,
3
NMR (125 MHz, CDC1 3) 6 136.5, 128.5, 37.7, 31.8, 30.1, 29.7, 27.7,
n
7.0
6.5
6.0
-~-~~t
5.5
~~~-.-
--------------
5.0
4.5
4.0
3.5
3.0
2.5
2.0
Figure 2.17. 1H NMR spectrum of cis,HT-poly(3-MeCOE) (CDC 3 , 500 MHz).
103
-
1.5
-.--
1.0
-,---
-
5.05
5.15
5.25
- - ~-~~~-'
7.5
10.3
7.2 Hz), 1.38-1.10 (overlapping peaks, 8H), 0.91 (d,
27.6, 21.6.
5.35
JHH
0.5
n
g~i~
I
.
140
130
90
100
110
120
~
80
70
60
20
30
40
50
Figure 2.18. 13C NMR spectrum of cis,HT-poly(3-MeCOE) (in CDC13, 125 MHz).
I
n
hj-2-152-Hc_2D
STANDARD PROTON PARAMETERS
-1.0
,
to
-1.5
-2.0
6.e
i*
I
lk
2.5
-3.0
-3.5
-4.0
-4,5
-5,0
-. 5
5.5
5.0
4.5
4.0
3.5
3.0
f2 (ppm)
2.5
2.0
Figure 2.19 IH-'H COSY spectrum of cis,HT-poly(3-MeCOE) (in CDC3, 500 MHz).
104
1.5
1.0
E
cis,HT-poly(3-HexCOE)
'H NMR (500 MHz, CDCl 3 ) 6 5.34 (dt,
3
JHH =
10.9, 7.2 Hz, 1H), 5.00 (apparent t,
Hz, 1H), 2.25 (m, 1H), 1.98 (m, 2H), 1.40-1.05 (overlapping peaks, 18H), 0.88 (t,
3H);
13 C
3
JHH =
3
JHH =
5.35
5.15
5.25
5.05
P~IK
-I
I
7.1 Hz,
NMR (125 MHz, CDCl3) 6 135.2, 129.7, 37.4, 36.2, 36.2, 32.1, 30.2, 29.9, 29.8, 28.0,
27.5, 27.5, 22.9, 14.3.
7.5
10.5
-,- , - -
7.0
-
6.5
------ 1- - - - - - ---- T-
---
6.0
5.5
5.0
---
-- T -
4.5
---
,
- - --
4.0
-r
3.5
3.0
2.5
2.0
1.5
Figure 2.20. 'H NMR spectrum of cis,HT-poly(3-HexCOE) (in CDC3, 500 MHz).
105
1.0
0.5
0.0
n
30
70
60
50
40
90
80
120 110 100
150 140 130
Figure 2.21. 13C NMR spectrum of cis,HT-poly(3-HexCOE) (in CDC3, 125 MHz).
20
aj
A,i
10
L-o
hj-2-225-2D
STANDARD PROTON PARANETERS
C,
4' j
-1
-2
-3
.4
Pt
a
~
.7
I
.8
8.0
7.5
7.0
6.5
6.0
5.5
5.0
4.0
4.5
f:? (ppm)
35
3.0
2.5
2.0
15
1.0
Figure 2.22. 1H- 1H COSY spectrum of cis,HT-poly(3-HexCOE) (in CDCb, 500 MHz).
106
0.5
0.0
E
cis,HT-poly(3-PhCOE)
'H NMR (500 MHz, CDCl 3) 6 7.27-7.24 (overlapping peaks, 2H), 7.16-7.13 (overlapping peaks,
3H), 5.46 (apparent t,
3
JHH =
3
JHH =
10.3 Hz, 1H), 5.36 (dt,
3
JHH =
10.7, 7.1 Hz, 1H), 3.48 (apparent q,
7.8 Hz, 1H), 2.03 (m, 2H), 1.66-1.60 (m, 1H), 1.57-1.51 (m, 1H), 1.32-1.21 (overlapping
peaks, 5H), 1.18-1.12 (m, 1H);
13
C NMR (125 MHz, CDCl 3 ) 6 146.1, 129.8, 128.5, 127.4, 127.4,
125.9, 43.6, 37.1, 29.7, 29.5, 27.7, 27.6.
n
5.7
7.5
7.0
6.5
6.0
5.5
5.0
4.5
5.6
4.0
5.5
5.4
3.5
5.3
3.0
5.2
2.5
2.0
Figure 2.23. 'H NMR spectrum of cis,HT-poly(3-PhCOE) (in CDC 3 , 500 MHz).
107
1.5
1.0
0.5
n
r
I~a~I
K~
30
40
50
60
70
80
160 150 140 130 120 110 100 90
Figure 2.24. 13C NMR spectrum of cis,HT-poly(3-PhCOE) (in CDC13, 125 MHz).
ii
20
A
A
hj-2-122-2D-full
STANDARD PROTON PARMvETERS
-1.0
S
*
S.
-1.5
4
of
-2.0
-2.5
-3.0
S
I
0
-3.5
-4.0
-4.5
-5.0
S
W
-5.5
-6.0
-6.5
*
-7.5
7.5
7.0
6.5
6.0
5.5
5.0
4.5
4.0
f2 (ppm)
3.5
3.0
2.5
2.0
Figure 2.25. 1H- 1H COSY spectrum of cisHT-poly(3-PhCOE) (in CDC3, 500 MHz).
108
1.5
1.0
3-epoxy-1-cyclooctene.
To a 500-mL round-bottom flask equipped with a stir bar was added cis
-1,3-cyclooctadiene (5.77 mL, 46 mmol). The flask was chilled in an ice bath, and it was fitted to
a dropping funnel which contained 3-chloroperoxybenzoic acid (10.84 g, 63 mmol) in
chloroform (120 mL). The solution was added slowly to the round-bottom flask over 3 h. The
reaction was allowed to stir at room temperature 19 h, then filtered. The mixture was washed
with 20%(w/v) aqueous NaHSO4 (40 mL), 10%(w/v) aqueous NaHCO 3 (40 mL), and then brine.
The organic layer was dried over MgSO4, filtered, and the filtrate was dried in vacuo. The
product was isolated by fractional vacuum distillation using a Vigreaux column (4 Torr, 42 0C).
The compound was transferred into a Schlenk bomb and was freeze-pump-thawed three times
before being brought inside the glovebox, affording 3.93 g (69% yield). The measured density at
room temperature was 1.01 g/ml. The 'H NMR spectrum was matched with a previously
reported spectrum.2 1
5-epoxy-1-cyclooctene.
To a 250-mL round-bottom flask equipped with a stir bar was added cis-
1,5-cyclooctadiene (13.6 mL, 111 mmol) and THF (20 mL). The flask was chilled in an ice bath,
and 3-chloroperoxybenzoic acid (15.3 g, 89 mmol) in chloroform (140 mL) was transferred
through a cannula. The solution was added slowly to the round-bottom flask. The reaction was
allowed to stir at room temperature 4 h, then filtered. The mixture was washed with 20%(w/v)
aqueous NaHSO 3 (40 mL), 10%(w/v) aqueous NaHCO3 (40 mL), and then brine. The organic
layer was washed a couple of times with saturated Na2CO3, dried over MgSO4, and the filtrate
was dried in vacuo. The product was isolated by fractional vacuum distillation using a Vigreaux
column (2.6 Torr, 40 "C). The compound was transferred into a Schlenk bomb and was freezepump-thawed three times before being brought inside the glovebox, affording 3.96 g (36% yield).
The measured density at room temperature was 1.01 g/ml. The 1H NMR spectrum was matched
with a previously reported spectrum.2 2
3-methoxy-1-cyclooctene.
To a 250-mL round-bottom flask equipped with a stir bar was added
3-bromo-1-cyclooctene (4.44 g, 24 mmol) and methanol (30 mL). 25 wt% NaOMe in methanol
(5.08 g, 24 mmol) was added via syringe. The reaction mixture was stirred at room temperature
for 2 days. The mixture was poured into an ice/water bath (100 mL), and extracted with ether (5
x 20 mL). The organic layer was dried over MgSO4, and the filtrate was dried in vacuo. The
109
product was isolated by fractional vacuum distillation using a Vigreaux column (3 Torr, 38 C).
The compound was transferred into a Schlenk bomb and was freeze-pump-thawed three times
before being brought inside the glovebox, affording 0.42 g (13% yield). The 'H NMR spectrum
was matched with a previously reported spectrum. 23
5-methoxy-1-cyclooctene. To a 500-mL round-bottom flask equipped with a stir bar was added
cis-1,5-cyclooctadiene (13 mL, 106 mmol) and methanol (100 mL). Hg(OAc)2 (33.8 g, 106
mmol) was added in portions, and the reaction mixture was stirred at room temperature for 2 h.
3M NaOH in water (80 mL) was added slowly using a dropping funnel, and then 0.5 M NaBH4
in 3M NaOH (100 mL) was added and the mixture was stirred for 2 h. The mixture was filtered,
and the solid was extracted with dichloromethane. The combined organic layer was dried over
MgSO4 and dried in vacuo. The product was isolated by fractional vacuum distillation using a
Vigreaux column (4.2 Torr, 36 'C). The compound was transferred into a Schlenk bomb and was
freeze-pump-thawed three times before being brought inside the glovebox, affording 4.95 g
(33% yield). The measured density at room temperature was 0.94 g/ml. The 'H NMR spectrum
was matched with a previously reported spectrum. 24
Cis,poly(5-epoxycyclooctene)
1H
NMR (500 MHz, CDCl 3) 6 5.51 (trans, m, 2H), 5.46 (cis, m,
2H), 2.93 (in, 2H), 2.25 (m, 4H), 1.58 (m, 411); "C NMR (125 MHz, CDCl 3 ) 6 130.10 (trans),
129.57 (cis), 56.90, 28.09, 24.52.
Cis,poly(5-methoxycyclooctene)
'H NMR (500 MHz, CDCl 3) 6 5.37 (cis, m, 2H), 3.31 (s, 3H),
3.15 (m, 1H), 2.09-2.04 (m, 6H), 1.51-1.37 (in, 4H);
13 C
NMR (125 MHz, CDCl 3) 6 130.14-
129.59 (cis), 80.38, 56.57, 33.65, 33.13, 29.85, 27.47, 25.46, 23.20.
110
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R.; Schrock, R. R. Macromolecules 2015, 48, 2480-2492.
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Boz, E.; Nemeth, A. J.; Ghiviriga, I.; Jeon, K.; Alamo, R. G.; Wagener, K. B.
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(3)
Kobayashi, S.; Pitet, L. M.; Hillmyer, M. A. J Am. Chem. Soc. 2011, 133, 5794-5797.
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Flook, M. M.; Gerber, L. C. H.; Debelouchina, G. T.; Schrock, R. R. Macromolecules
2010, 43, 7515-7522.
(6)
Flook, M. M.; Jiang, A. J.; Schrock, R. R.; Miller, P.; Hoveyda, A. H. J Am. Chem. Soc.
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Flook, M. M.; Ng, V. W. L.; Schrock, R. R. J. Am. Chem. Soc. 2011, 133, 1784-1786.
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Bielawski, C. W.; Grubbs, R. H. Prog. Polym. Sci. 2007, 32, 1-29.
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Khosravi, E.; Szymaiska-Buzar, T. Ring Opening Metathesis PolymerisationAnd Related
Chemistry; NATO Science Series II. Mathematics, Physics and Chemistry, 2000.
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Jiang, A. J.; Zhao, Y.; Schrock, R. R.; Hoveyda, A. H. J. Am. Chem. Soc. 2009, 131,
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Townsend, E. M.; Schrock, R. R.; Hoveyda, A. H. J. Am. Chem. Soc. 2012, 134, 1133411337.
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Schrock, R. R.; Jiang, A. J.; Marinescu, S. C.; Simpson, J. H.; Muller, P. Organometallics
2010, 29, 5241-5251.
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Singh, R.; Czekelius, C.; Schrock, R. R. Macromolecules 2006, 39, 1316-1317.
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Kozera, D. J. Ring-opening metathesis polymerization of 3-substituted cyclooctenes
initiated by group 6 alkylidene complexes, Master Dissertation, Massachusetts Institute of
Technology, 2012.
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Yuan, J.; Schrock, R. R.; Muller, P.; Axtell, J. C.; Dobereiner, G. E. Organometallics
2012, 31, 4650-4653.
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Organometallics2013, 32, 4843-4850.
112
Chapter 3
Synthesis and Reactivity Studies of Tungsten Alkylidene Complexes
Containing a tert-butylimido Ligand
113
INTRODUCTION
After their initial discovery in 2007,1 various molybdenum and tungsten imido alkylidene
monoalkoxide pyrrolide (MAP) complexes have been shown to be highly successful Z-selective
catalysts in a number of metathesis reactions such as ring-opening metathesis polymerization
(ROMP), 23 ethenolysis,4 ring-opening cross metathesis, 5 and homocoupling of terminal olefins. 6
Since molybdenum adamantylimido MAP complexes are some of the most selective catalysts in
ROMP of substituted norbornadienes or cyclopropenes,2, 7 synthesis of alkylimido W MAP
complexes was desirable. Through several synthetic modifications, several new Mo and W tertbutylimido or adamantylimido MAP complexes have been successfully synthesized (see Chapter
1).8 9 Among them, W(N-t-Bu)(CHCMe3)(pyr)(OHMT) (HMT = 2,6-(2,4,6-Me 3C6H2)2C6H3) has
been found to be not only highly Z-selective but also faster in ROMP of 3-substituted cyclooctenes
than that of Mo analogs (See Chapter 2).10
In order to further understand the effects of ligands in olefin metathesis reactions, various
types of ligand modifications of W-based tert-butylimido complexes are presented in this chapter.
Among hundreds of derivatives of high-oxidation-state Mo- and W-based olefin metathesis
catalysts, relatively few variations of the alkylidene ligand have been reported compared to those
on imido and anionic ligands. Several chelating alkylidene complexes were reported in the early
1990s by Grubbs and Schrock which were installed either by alkylidene transfer from
phosphoranes" or through a reaction of neophylidene or neopentylidene with terminal olefins
(Scheme 3. 1).12 The synthesis of chelating alkylidenes of Mo and W tert-butylimido complexes
will be discussed and basic metathesis reactivity will be discussed in Part I of this chapter.
R'
RO. NCI
Ro W C
RC
Ph 3 P=CH(o-MeOC 6 H 4 )
R'
R'
Na/Hg
benzene, THF
- PPh 3, - 2 NaCl
R = CMe(CF 3)2 R' = Me, H, i-Pr
114
,
R
O
R
OMe1
OMe
MeO
N
ROI-.MO'
RO
N
RO , I I
Mo-
I
- H2 C=CHCMe 3
/
~MeO/
R = CMe(CF 3)2
RO
OMe
OMe
Scheme 3.1. Previously reported synthesis of Mo and W chelating alkylidene complexes.
Mo and W arylimido complexes bearing a chelating biphenolate or binaphtholate ligand
have shown to initiate formation of cis,isotacticpolymers. 13 1 4 In addition, bisaryloxide complexes
of
Mo
and
W
tend
complexes
to
dicarbomethoxynorbornadiene (DCMNBD).
form
5 "6
cis,isotactic-biased polymers
of
2,3-
Part II of this chapter focuses on the exploratory
synthesis and characterization of W tert-butylimido biphenolate and bisaryloxide complexes.
Since ethylene is a byproduct of the metathesis of terminal olefins, understanding the stability of
the catalysts in the presence of ethylene is needed. Fundamental reactivity of several W tertbutylimido catalysts with ethylene will be discussed in Part III of this chapter.
RESULTS AND DISCUSSION
I. Synthesis and Reactivity Studies of Mo and W tert-butylimido Species Containing
Chelating Alkylidenes
A. Synthesis of Chelating Alkylidene Complexes
Substitution reactions of neopentylidene complexes with terminal olefins has been carried
out to form chelating alkylidenes for Mo and W tert-butylimido complexes. When 2methoxystyrene
was
added
to
Mo(N-t-Bu)(CHCMe3)(OCF5)2(t-BuNH2)
and
W(N-t-
Bu)(CHCMe3)(Cl)2(py)2, Mo(N-t-Bu)(CH-o-MeOC6H 4)(OC6F 5)2(t-BuNH2) (1mo) and W(N-tBu)(CH-o-MeOC6H4)(Cl)2(py) (1w) form cleanly with loss of tert-butylethylene (Scheme 3.2).
Formation of iMo does not require heating, whereas formation of 1w requires heating.
115
C 6 F 50,, N
Mo
H2 N 0
OC6 F 5
H2
benzene, r.t.
3 h
,'OC6F5
Mo-
C 6F5 O 1 I
- H 2C=CHCMe 3
1
Mo (68%)
NIN
Wbenzene, 604C
2h
N
C
Wl
7
/
CI
C
'I N
CN
IN
1w (96%)
Scheme 3.2.
Synthesis of Mo(N-t-Bu)(CH-o-MeOC6H 4)(OC6 F) 2(t-BuNH 2) (1mo)
and W(N-t-Bu)(CH-o-
MeOC6H4)(CI)2(py) (1w).
Given the straightforward formation of 1m, we conducted whether Grignard reagents
containing alkyl groups with pendant chelating moieties form diimido dialkyl complexes, the
common presursors to alkylidene complexes. 17 In order to test this idea, two equivalents of 2methoxybenzylmagnesium
chloride was added to diimido dichloride complexes M(N-t-
Bu)2(Cl)2L 2 (M = Mo, L = dme; M = W, L = py). The expected di(tert-butylimido) dialkyl
complexes M(N-t-Bu)2(CH2-o-MeOC 6H 4) 2 (M = Mo ( 2 mo), W ( 2 w)) form cleanly. For the
synthesis of
2 w,
the known dimer, [W(N-t-Bu)2(p-Cl)Cl(t-BuNH 2 )] 2, also can be used in this
reaction. Compound 2 mo is obtained as a yellow solid whereas 2w is a brown liquid (Scheme 3.3).
02
MgC
Ii.
N
0/ 0 11 N N
/
K
CI
t 'ci
Mo
Diethyl ether
-30 OC to r.t.
5h
0N
2
Mo (71%)
116
OMgCI
2
C
II. N
0__:
__
N CI
C1
w
__1
Diethyl ether, THF\./
-30 OC to r.t.
0
19 h
2
or 1/2 [W(N-t-Bu) 2C1 2(t-BuNH 2 )21 2
Scheme 3.3. Synthesis
w (84%)
of Mo(N-t-Bu)2(CH2-o-MeOC6H 4 )2 ( 2 mo) and W(N-1-Bu)2(CH2-o-MeOC6H4)2 (2 w).
Treatment of 2 mo with 2.2 equivalents of either pentafluorophenol or perfluoro-tert-butanol
forms Mo(N-t-Bu)(CH-o-MeOC6H 4)(OR)2(t-BuNH 2 ) (R = C6F5 (Imo), R = C(CF 3)3 (3 mo))
(Scheme 3.4). It is worth noting that neopentylidene analogue of 3 mo did not form upon treatment
of Mo(N-t-Bu)2(CH2CMe3)2 with perfluoro-tert-butanol (See Chapter 1). This could be ascribed
due to the smaller size of chelating benzyl groups compared to neopentyl ligand. One equivalent
of pentafluorophenol was added to Nuo in order to remove the tert-butylamine ligand from the
metal. A mixture containing Nuo and new alkylidene complexes was obtained, but separation of
the new species from Nuo was not successful.
0l- N 2.2 ROHH2N
OR
MON
MoN
\/
0
2
1
R0o
Diethyl ether
-30O0 Cto r.t.
/0
IMo R C6 F5 (55%)
3
Mo R = C(CF 3)3 (64%)
mo
Scheme 3.4. Synthesis of Mo(N-t-Bu)(CH-o-MeOC6H4)(OR)2(t-BuNH2)
(R = C6F5, C(CF3)3).
Complexes Nuo and 3 mo both showed IJCH values of 145 Hz for the alkylidene proton in
C 6D6. 1JCH
values in the range of 135 - 155 Hz are indicative of anti alkylidenes. 18 The proposed
structure involves the coordination of oxygen from the chelating benzylidene in a position trans
to the imido group thereby enforcing the anti alkylidene orientation. An X-ray crystallographic
study of 3 mo confirmed this ligand orientation (Figure 3.1). Compound 3 mo crystallizes in a Pcba
space group from a chilled Et 2O solution. One of perfluoro-tert-butoxide groups is disordered over
three positions. The Mo(l) - N(2) distance (1.7039 A) is longer than the Mo=N bond distance in
the 4-coordinate Mo tert-butylimido MAP complex Mo(N-t-Bu)(CHCMe 3 )(pyr)(OHMT),
117
but is
possibly due to the trans influence of methoxy group bound trans to imido ligand,
9
Mo(1)
comparable to the Mo=N distance in Mo(NAd)(CHCMe3)(pyr)(OHIPT) (1.707 A).' The
on tert- O(1) distance (2.3675 A) indicates a bonding interaction. In addition, two protons
perfluorobutylamine are found to form two hydrogen bonds with one CF3 group on one of the
tert-butoxide ligands. The H --F distances (2.456(17) and 2.467(17) A) are within the sum of the
20
van der Waals radii (ca. 2.55 A) and can be regarded as weak hydrogen bonds. ,21 Another
example of intramolecular H- -F hydrogen bonding was reported in Mo(CCMe 2Ph)(HNC6F4-p-
CF 3 )(OC 6F5 )2(t-BuNH2).
22
The protons on the tert-butylamine are hydrogen bonded to the ortho
F
F atom on the OC6F5 ligand in Mo(CCMe 2Ph)(HNC 6F 4-p-CF3)(OC6F5)2(t-BuNH2). The H -.distances were found to be 2.305(18) and 2.258(18) A through an X-ray crystallographic study.
3
The two diastereotopic protons (HIA and HIB) on the tert-butylamine ligand for mo appear as
doublets (2 JHH = 12.5 Hz) by 'H NMR spectroscopy, presumably due to germinal coupling with
each other, but do not show observable coupling to the fluorine on the NMR time scale. Only two
tertpeaks are observed by '9 F NMR spectroscopy at room temperature, supporting that perfluoro
butoxide groups are rotating in the timescale of NMR.
3
of disorders are
Figure 3.1. Thermal ellipsoid plots shown at 50% probability level of mo. Minor component
- N(1) =
Mo(1)
1.7039(11),
=
N(2)
Mo(1)
omitted for clarity. Selected bond distances (A) and angles(*):
- 0(3) =
Mo(1)
2.0452(9),
=
0(2)
Mo(1)
2.3675(9),
=
2.2551(10), Mo(1) - C(1) = 1.9611(12), Mo(1) - 0(1)
C(21)148.07(9),
=
C(15)-0(3)-Mo(1)
144.01(8),
=
1)-0(2)-Mo(1)
C(1
122.00(9),
2.1421(9), C(2)-C(1)-Mo(1) =
N(1)-Mo(1) = 134.48(8), C(25)-N(2)-Mo(1) = 177.20(10).
118
In the case of W di(tert-butylimido) dialkyl complex, 1w was formed upon treatment of
2w with 3 equivalents of pyridinium chloride in Et 2 0. Compound 1w showed a IJCH value of 145
Hz for the alkylidene proton in C 6D 6, which is indicative of an anti alkylidene. We therefore
assume 1w to have an analogous structure to iNo.
0W
N
3 pyHCI
N
Diethyl ether
-30 C to r.t.
19 hb
C
I
0
iw (79%)
2w
Scheme 3.5. Synthesis of W(N-t-Bu)(CH-o-MeOC6H4)(CI)2(py)
(iw).
Since Mo and W tert-butylimido complexes with chelating benzylidene ligands can be
formed upon treatment of the diimido dialkyl precursor with acid sources, we decided to test this
synthetic route for arylimido complexes. Mo(NAr) 2 (CH2-o-MeOC 6H4)2 (4 mo) and W(NAr)2(CH2o-MeOC6H4)2 (3w) form upon treatment of M(NAr)2(Cl) 2 (dme) (M = Mo, W) with two equivalents
of the Grignard reagent. However, attempts to form alkylidene species using various acids were
not successful for either the Mo or the W case. In the case of 4 mo, protonation of the benzyl group
occurred upon treatment with acids (C 6F5OH, TfOH, CH 3 SO2H, HC1, and pyHCl). The expected
byproduct 2-methoxytoluene was observed by 1H NMR spectroscopy. Compound 3w was also
treated with various acid sources (TfOH, HC1, pyHCl, and CH 3(CF 3)2COH), but alkylidene
formation was not successful.
B. Studies of Chelating Alkylidene Complexes for W tert-butylimido MAP Species
The same procedures for forming W(N-t-Bu)(CHCMe3)(pyr)2(bipy)
from W(N-t-
Bu)(CHCMe3)(py)2CI2 8 were adapted to form W(N-t-Bu)(CH-o-MeOC 6H4)(pyr)2(bipy) (4 w) from
the reaction of 1w with 2 equivalents of Lipyr followed by addition of 2,2'-bipyridine. It is
proposed that the methoxy group on the chelating alkylidene is not bound to the W in the presence
of
strongly
chelating
2,2'-bipyridine
ligand.
The
synthesis
of
W(N-t-Bu)(CH-o-
MeOC 6 H4)(pyr)(OHMT) (5w) is successful upon treatment of 4 w with ZnCI2(dioxane) and
HMTOH in toluene at 75 'C for 24 hours (Scheme 3.6).
119
..
N,
CI
CI'
/l10
1
2 Lipyr
0.9 (2,2'-bipy)
Toluene
-30 C to r.t.
Toluene
r.t., 12 h
0.85 HMTOH
ZnCI 2(dioxane)
N
OMe
N_
N
;,io II''\
Toluene
75 00, 24 h
N
3h
/
IN
4w(81%)
1w
Scheme 3.6. Synthesis of W(N-t-Bu)(CH-o-MeOC6H4)(pyr)(OHMT) (5w).
In order to compare the reactivity of 5w with its neopentylidene analogue W(N-tBu)(CHCMe3)(pyr)(OHMT), 1 -octene homocoupling experiment was performed. Each reaction
was carried out with ~4 mg W complex (2 mol%) in neat 1 -octene. Conversion was monitored
after 1, 4, 8, and 24 hours. The results are shown in Table 3.1. Compound 5w showed slightly
better Z selectivity but lower reactivity than W(N-t-Bu)(CHCMe3)(pyr)(OHMT).
Table 3.1.Reactivity tests of W(N-t-Bu)(CHCMe3)(pyr)(OHMT) and 5 w in
1-octene homocoupling.
2 mol% cat
"Vea
4t ,
I.L.
W(N-t-Bu)(CHCMe 3)(pyr)(OHMT)
W(N-t-Bu)(CH-o-MeOC 6H 4)(pyr)(OHMT) (5w)
Time
Conv (%)
cis (%)
Conv (%)
cis (%)
I h
42
80
32
90
4h
68
72
63
88
8h
81
60
73
84
24h
81
48
75
76
I1. Synthesis of Tungsten tert-butylimido Bisaryloxide Species
A. Synthesis of Bisterphenoxide Complexes
Among
various
Mo
and
W
four-coordinate
bisaryloxide
species,
W(O)(CHCMe 2 Ph)(OHMT) 2 and Mo(NR)(CHCMe2Ph)(ODFT) 2 (R =C 6F5 , 2,6-Me2C6H3; ODFT
= 2,6-bis-(pentafluorophenyl)phenoxide)
complexes are relatively selective in ROMP of
DCMNBD. BisOHMT species have shown to form >90% cis,syndiotacticpolymers23 whereas >98%
cis,isotactic polymers were formed from bisODFT species.
120
6
Therefore, in order to test whether
this selectivity can be applied to tungsten tert-butylimido species, synthesis of W(N-tBu)(CHCMe 3)(OHMT) 2 and W(N-t-Bu)(CHCMe 3)(ODFT)2 complexes were targeted.
The first attempt to form W(N-t-Bu)(CHCMe3)(OHMT)2 consisted of treating W(N-tBu)(CHCMe3)(pyr)(OHMT) with 1 equivalent of HMTOH. However, heating the reaction mixture
at 100 'C for 12 hours in C 6D 6 did not lead to any conversion to a new product. Therefore, an
anionic route was sought. When 1 equivalent of HMTOLi was added to a benzene solution of
W(N-t-Bu)(CHCMe3)(Cl)2(py)2 and the mixture was heated to 70 'C, a monoHMTO species W(Nt-Bu)(CHCMe3)(Cl)(OHMT)(py) (6w) was formed cleanly in 79% yield (Scheme 3.7). However,
when 1 equivalent of HMTOLi was added to 6w, a bisHMTO species was not observed even after
heating the reaction mixture to 100 'C for 48 hours in toluene-d. It is likely that the five-coordinate
starting material is sterically congested and prevents the second HMTO ligand from coordinating
to tungsten. Note that synthesis of W(O)(CHCMe 2Ph)(OHMT) 2 was reported by the reaction of
W(O)(CHCMe3)(Cl)2(PPh2Me)2 with 2.4 equivalents of HMTOLi in toluene at 100 0 C for 48
hours. 23 Therefore, a higher steric demand of a tert-butylimido ligand compared to an oxo ligand
likely inhibits formation of bisHMTO species using this route.
N
1.1 HMTOLI
N
C
benzene, 70 C
19 h
C1
N
0
6w (79 %)
Scheme 3.7. Synthesis of W(N-t-Bu)(CHCMe3)(CI)(OHMT)(py)
also
W(O)(CHCMe 2Ph)(OHMT)2
(6 w).
can
be
formed
from
W(O)(CHCMe 2Ph)(Cl)(OHMT)(PMePh2) and 1 equivalent of HMTOLi in the presence of 1.1
equivalents of B(C6F5 )3 at room temperature for 3 hours. 24 It is proposed that B(C 6F5 ) 3 removes
the PMePh2 ligand to form MePh 2P-B(C6F5 )3 so that the second HMTOLi can be added without
heating. However, when 1 equivalent of both HMTOLi and B(C6F5 )3 were added to a benzene
solution of 6w, partial conversion to W(N-t-Bu)(CHCMe 3)(Cl)(OHMT) (6w') was observed by 'H
NMR spectroscopy. When 2 equivalents of B(C6F5 )3 were added to 6w along with 1 equivalent of
HMTOLi,
the
starting
materials
were
consumed.
A
mixture of 6w'
and
W(N-t-
Bu)(CHCMe 3)(OHMT)2 (7w) was observed by 'H NMR spectroscopy. Heating the reaction
121
mixture at 60 'C led to formation of a new alkylidene with a 'H NMR signal at 9.77 ppm. This
signal is a triplet (J= 4.5 Hz) with W satelites
( 2 JWH =
14.5 Hz). It is postulated that a C 6F5 from
B(C 6FS)3 might have exchanged with a chloride ligand, but the isolation of this side product
unfortunately was not successful.
A stepwise synthetic route was therefore devised: 1.1 equivalents of B(C 6F5 ) 3 was added
to 6w to form 6w' and py-B(C6Fs)3. Then 6w' was isolated from most of py-B(C6Fs)3 by extraction
with pentane, and treated with 1.1 equivalents of HMTOLi at 130 'C for 5 hours in toluene. After
the reaction, 7 w was separated out by stirring the reaction mixture in acetonitrile for 30 minutes.
Since
7w
is not soluble in acetonitrile, it could be isolated cleanly by filtration. The reaction
overview is shown in Scheme 3.8.
1.1 B(C6 F5)3
_9)
N
\~'o
benzene
r.t., 30 min
I
1.1 HMTOLI
_
ll!-
_
\
I__
I
_
toluene
0
130 C, 17 h
\ /
6w'
--
o
7
w (31 %)
Scheme 3.8. Synthetic route to form W(N-t-Bu)(CHCMe3)(OHMT)2 (7w).
With the new bisHMTO complex 7w in hand, metathesis reactivity for ROMP was tested
using DCMNBD. When 7w was treated with 50 equivalents of DCMNBD in CDCl 3 solution, no
ROMP reactivity was observed even at 60 'C. In addition, a degassed solution of 7w did not react
with ethylene either at room temperature or at 60 'C in C 6D 6 . Apparently 7w is so sterically
crowded that it does not react with ethylene or DCMNBD. Note that W(O)(CHCMe3)(OHMT)2
was found to react with I atm of ethylene to form W(O)(C 3H6 )(OHMT) 2 and W(O)(CH2)(OHMT)
2
species.
In contrast, when in situ generated
6 w'
was treated with 50 equivalents of DCMNBD in
CDCl 3 solution, >98% cis,syndiotacticpoly(DCMNBD) 2 was formed after 1 h. Generation of high
cis,syndiotactic poly(DCMNBD)
Bu)(CHCMe3)(pyr)(OHMT).
from this catalyst was comparable to that of W(N-t-
Compound
6w'
slightly
reacted
faster
than
W(N-t-
Bu)(CHCMe3)(pyr)(OHMT). Both catalysts generated >98% cis,syndiotactic poly(DCMNBD)
(Table 3.2).
122
Table 3.2. Reactivity tests of W(N-t-Bu)(CHCMe3)(pyr)(OHMT) and 6 w' in ROMP of DCMNBD.
W(N-t-Bu)(CHCMe 3)(pyr)(OHMT)
W(N-t-Bu)(CHCMe 3)(Cl)(OHMT) ( 6 w')
Time
Conv (%)
Cis,syndio (%)
Conv (%)
Cis,syndio (%)
2 min
47
>98
70
>98
5 min
79
>98
87
>98
10 min
>99
>98
98
>98
All polymerization were carried out at 22 'C. 2 mol% catalyst was added to a solution of [DCMNBD]o = 0.12 M.
Next, attention shifted towards the synthesis of W(N-t-Bu)(CHCMe3)(ODFT)2. Previously,
when
synthesis
of
was
W(N-t-Bu)(CHCMe3)(pyr)(ODFT)
attempted
from
W(N-t-
Bu)(CHCMe3)(pyr)2(bipy) with 1 equivalent of ZnCl2(dioxane) and 0.9 equivalents of DFTOH, a
major byproduct was proposed to be W(N-t-Bu)(CHCMe 3)(ODFT) 2 ( 8 w). Therefore, W(N-tBu)(CHCMe3)(pyr)2(bipy) was treated with 1 equivalent of ZnCl2(dioxane) along with 1.9
equivalents of DFTOH in toluene at 75 C for 2 hours; 8w was be formed cleanly in 47% yield
(Scheme 3.9).
F
F
F
1.9 DFTOH
ZnCI 2 (dioxane)
N
N
N 4J
\
Toluene
75 OC, 2 h
F
NF
F
F
FI
FF
\F
F
F
FF
F
F
8W (47 %)
Scheme 3.9. Synthesis of W(N-t-Bu)(CHCMe3)(ODFT)2 (8 w).
When 8w was treated with 50 equivalents of DCMNBD
polymerization
was
much
slower
compared
to
the
in CDCl3, the rate of
reaction
with
W(N-t-
Bu)(CHCMe3)(pyr)(OHMT) or 6w' (Table 3.2) with DCMNBD. Full consumption of monomer
was not observed even after 1 day, and isolated poly(DCMNBD) contained a cis,syndiotactic
biased microstructure (cis selectivity 88%; syndiotactic selectivity 67%).
B. Synthesis of Chelating Diolate Complexes
Complexes that contain chelating biphenolates or binaphtholates have been shown to form
high cis,isotacticpolymers of substituted norbomadienes
123
26
and endo-dicyclopentadiene
27
through
enantiomorphic site control. 28 However, W chelating diolate complexes are relatively scarce
compared to Mo analogs, so reactions of chelating diolates with tungsten tert-butylimido species
has been pursued. BiphenCF3 and Biphenme were chosen as the diolate ligands (Figure 3.2).
R
OH
OH
R
(rac)
R = Me = [BiphenMe]H 2
R = CF 3 = [BiphenCF 3]H 2
Figure 3.2. [BiphenMe]H2 and jBiphencF3JH2 ligands.
Reaction of [BiphenCF3]H2 with one equivalent of W(N-t-Bu)(CHCMe 3)(Me2pyr)2(py) in
benzene at 70 'C for 12 hours formed W(N-t-Bu)(CHCMe3)(BiphenCF3)(py) (9w). The 'H NMR
spectrum of 9w contains two alkylidene resonances in a 57:43 ratio. Both isomers of 9w were
found to have the neopentylidene in a syn orientation on the basis of 1JCH values (112 Hz for both
isomers) compared to a typical value for
in an anti isomer (~135-155 Hz). 18 The pyridine
'JCH
ligand is bound to tungsten on the NMR time scale at 20 'C in each isomer. In order to remove
pyridine, one equivalent of B(C 6F5 )3 was added to a benzene solution of 9w at room temperature
for 30 min. Formation of a new product along with py-B(C6F5)3 were observed by 'H NMR
spectroscopy. The new product did not contain any alkylidene signals but two sets doublets (at
3.53 ppm and 2.24 ppm both with 2 JHH = 16 Hz) were observed (Figure 3.3). We postulated that a
C-H bond in one tert-butyl group on the biphen ligand adds across the W=C bond to form a new
alkyl compound. The two alkyl proton signals (at 3.53 ppm and 2.24 ppm) did not contain a
correlation peak with respect to each other based on 'H- 1 H gCOSY NMR spectroscopy, suggesting
each from two distinct W-CH2 ligands. The other two protons of W-CH 2 ligands were shown at
1.66 ppm (correlated with a peak at 2.24 ppm) and 1.36 ppm (correlated with a peak at 3.58 ppm)
observed by 1H-1H gCOSY NMR spectroscopy.
124
N
/I
B(C 6 F 5)3
H 2[BiphenCF 3]
N"
0
Benzene
Benzene
70 C, 12 h
F3 C
F 3C
CF 3
CF 3
9
low
w (56 %)
Scheme 3.10. Synthesis of W(N-t-Bu)(CHCMe3)(BiphenCF3)(py)
(9 w) and its alkylidene C-H activation.
W=CH
W=CH
iA hi
II
il II.
I
I
W-CH2
W-CH 2
-11
L1.0
10.5
10.0
9.5
9.0
8.5
8.0
7.5
jI
a
7.0
6.5
6.0
5.5
5.0
4.5
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
Figure 3.3. IH NMR spectra of W(N-t-Bu)(CHCMe3)(BiphenCF3)(py) and W(N-t-Bu)(CH2CMe3)(BiphenCF3).
Top: 'H NMR spectra of W(N-t-Bu)(CHCMe3)(BiphenCF3)(py) in C6D6. Bottom: 1H NMR spectrum of W(N-tBu)(CH2CMe3)(BiphenCF3) obtained in situ in C6D6.
The new compound W(N-t-Bu)(CH2CMe3)(BiphenCF3) (10w) recrystallizes from toluene
and Et2 0 mixture, and the structure was confirmed by X-ray analysis. (Figure 3.4). Compound
10w crystallizes in the monoclinic space group P21/n and refines as a two-component nonmerohedral twin. The W atom is five coordinate. This compound has T= 0.81 (where -= 0 for a
square pyramid andr = 1 for a trigonal bipyramid), 29 indicating it is close to a trigonal bipyramidal
geometry where the imido ligand and 01 are occupy axial sites. Bond lengths and angles are as
expected for W imido alkyl species. 8 Intramolecular addition of the CH bond across the metal
125
carbon double bond has been observed in tantalum complexes in which activation of one tert-butyl
30
group leads to a 6-membered metallacycle and alkyl species. In addition, CH activation from
tungsten alkylidyne complexes bearing a 2,6-ditert-butylphenoxide to form a cyclometalated
31
alkylidene species was reported in our group.
17
Figure 3.4. Thermal ellipsoid (50 %) drawing of W(N-t-Bu)(CH2CMe3)(BiphencF3) (10w). Selected bond
length (A) and angles (0): W1-N1 = 1.7525(16), Wi-Cl = 2.1239(20), Wi-01 = 2.0084(13), WI-02 =
1.9315(13), W1-C18 = 2.1383(19). Ni-Wi-Ci = 92.18(8), Ci-Wl-02 = 125.55(7), 02-WI-01 = 85.92(5), W1C18-C17 = 121.22, 01-Wl-C18 = 83.39(6), C18-Wl-Nl = 91.42(7), NI-Wi-01 = 174.32(6).
In order to see whether 9w can be regenerated from 10w, two equivalents of pyridine were
added to a C6D 6 solution of 10w. At room temperature, no reaction was observed after two hours.
However, upon heating the reaction mixture at 60 'C for 2.5 hours, formation of 9w was observed
by 'H NMR spectroscopy. Along with 9w, new alkylidenes at 11.13 ppm and 9.59 ppm were
observed, and it is postulated a-hydrogen elimination occurred to form an alkylidene on biphen
ligand extruding neopentane (Scheme 3.11).
NNN
benzene,11o
pyridine
W
/
F 3C
,N
6
0
benzene, 80 IC
0
+
0
N
F3 C
F 3C
CF3
CF 3
9
low
9
Scheme 3.11. Regeneration of w from 1Ow.
126
w
\
CF 3
a possible product
Compound 9w was tested for ROMP of endo-dicyclopentadiene (DCPD) by Dr. Benjamin
Autenrieth.2 7 100 equivalents of monomer was added to a catalyst in dichloromethane at room
temperature, and the reactions were monitored by 1H NMR spectroscopy. Three ROMP reactions
were carried out: 9w, 9w with one equivalent of B(C 6F5 ) 3, and 9w with one equivalent of B(C6H5)3.
The results of the polymerization runs, including cis selectivity and tacticity data, are shown in
Table 3.3. When 9w was used, full conversion was achieved after 90 min. The polymers were
highly cis, but the degree of isotacticity is approximately 60%. When 9 w was first treated with one
equivalent of B(C 6F5 )3, full conversion to polymer was observed within 3 minutes. However, its
polymer structure is not regular in terms of olefin stereochemistry and tacticity. It could be
postulated that B(C 6F5 )3 removes pyridine effectively, but as shown above, the alkylidene ligand
C-H activates upon pyridine removal so identity of the active species on this ROMP reaction is
,
not known. When ROMP was carried out with 9 w first treated with one equivalent of B(C 6Hs) 3
full conversion was observed after 60 min, giving >98% cis and >80% isotactic polymer.
1 mol% catalyst
CH2 CI2 , r.t.
Scheme 3.12. ROMP of DCPD with catalyst 9 w and 9 w in the presence of B(C6FS)3 or B(C6H5)3.
Table 3.3. Polymerization of DCPD by W(N-I-Bu)(CHCMe)(BiphenCF3)(py) (9W) in the presence of Lewis
acid.
Catalyst
% cis
Tacticity
9w
>98%
60% iso
9w + B(C 6F5 )3
50%
Atactic
9w + B(C 6H5 )3
>98%
>80% iso
To see whether intramolecular C-H activation occurs for complexes only with
[BiphenCF3]H2 ligand, the synthesis of W(N-t-Bu)(CHCMe 3)(Biphenme)(py) (l1w) was attempted.
The synthetic procedure was adapted from a previous report, 32 W(N-t-Bu)(CHCMe3)(Cl)2(py)2
was added to a THF solution of K2(Biphenme), generated in situ from the reaction of benzyl
potassium and [Biphenme]H2 (Scheme 3.13). 11w was found to be a pyridine adduct, and two
alkylidene resonances at 10.56 ppm and 9.27 ppm were observed in a ratio of 51:49 by 1H NMR
spectroscopy in C 6D 6 . When 1 equivalent of B(C 6F5 ) 3 was added to a C 6D6 solution of 11w, a
127
mixture of pyridine-free 11w' with an alkylidene peak at 7.59 ppm and the C-H activation product
were observed in a ratio of about 50:50.
2 benzyl-K
N
H2 [BiphenMel
C-
THF
r.t., 19 h
C1
N
W
B(C6F5)3
0
N
N
W
W
0
Benzene
11
11w (7 6 %)
00
w
Scheme 3.13. Synthesis of W(N-t-Bu)(CHCMe3)(BiphenMe)(py) (11w).
In order to see whether the C-H activation is assisted by B(C6 F5)3, a pyridine-free synthetic
route was attempted to form 11w' directly. W(N-t-Bu)(CHCMe3)(pyr)2(bipy) was sonicated with
1 equivalent of ZnCl2(dioxane) along with 0.9 equivalents of [BiphenMe]H2 in toluene for 4.5 hours.
Again, a mixture of 11w' with the C-H activated product were observed by 1H NMR spectroscopy,
indicating both species are thermodynamic products.
I1. Synthesis of Tungsten tert-butylimido Metallacyclobutane Species
Reaction of new alkylidene species with ethylene were conducted to determine whether
they form methylidene or unsubstituted metallacyclobutane complexes. 2 Previously, when the
synthesis
of
W(N-t-Bu)(CHCMe3)(pyr)(ODFT)
was
attempted
from
W(N-t-
Bu)(CHCMe3)(pyr)2(bipy) with 1 equivalent of ZnCl2(dioxane) along with 0.9 equivalents of
DFTOH, clean formation of W(N-t-Bu)(CHCMe3)(pyr)(ODFT) was not successful due to
contamination with inseparable minor products. However, when a degassed solution of this
reaction mixture in pentane was treated I atm of ethylene at room temperature for 30 min, yellow
precipitate was formed. The reaction mixture was filtered off to isolate the pale white solid of
metallacyclobutane W(N-t-Bu)(C3H6)(pyr)(ODFT) (1 2 w). Based on 'H NMR spectroscopy, it is
likely to be a TBP metallacyclobutane. 33 ,34 Similarly, metallacycle W(N-t-Bu)(C 3H6 )(ODFT)2
(1 3 w) can be generated from from W(N-t-Bu)(CHCMe3)(pyr)2(bipy) with 1.9 equivalents of
DFTOH. The electron withdrawing abilities of ODFT ligand might stabilize formation of
metallacyclobutane species for these W tert-butylimido ligand (Scheme 3.14).
128
N1
0.9 DFTOH
ZnCI 2(dioxane)
N
F
sonication, 15 h
F
N
[
F
I
F
F
0
F
L
I
F
1.9 DFTOH
ZnCI 2 (dioxane)
F
N
NN
sonication, 19 h
F
F
F
w (3 1 %)
F
F
FF
F
F
F
F
F
F
F
F
12
F
F
O
F
F
F
F
F
F
pentane
r.t., 30 min
F
-
N
N
F
FF
F '
F
F
F
FF
F
F
F
\F
F
F
FF
pentane
r.t., 30 min
F
F F
F
F
0N
FF
F
FF
F
0
F
F
F
F
1 3w (29 %)
3
Scheme 3.14. Synthesis of W(N-t-Bu )(C3H 6)(pyr)(ODFT) (1 2 w) and W(N-t-Bu)(C 3H 6)(ODFT)2 (1 w).
CONCLUSIONS
Various ligand modifications on tungsten tert-butylimido complexes have been studied in
this chapter for further understanding their effect on olefin metathesis reactions. Chelating
alkylidenes for both Mo and W tert-butylimido complexes can be installed either by substitution
reaction with styrene derivatives or by traditional synthetic route in forming alkylidenes from
ditert-butylimido compounds with substituted benzyl ligands. The use of a mild acid for tertbutylimido species can be applied for chelating alkylidene species; triflic acid could not generate
alkylidene complexes from Mo and W diarylimido dialkyl species of this type. MAP complex
W(N-t-Bu)(CH-o-MeOC6H4)(pyr)(OHMT) was synthesized and its basic metathesis reactivity in
1 -octene was tested. The reactivity was comparable to that of W(N-t-Bu)(CHCMe3)(pyr)(OHMT)
catalyst, but deterioration of Z-selectivity over time is slower than that of W(N-tBu)(CHCMe3)(pyr)(OHMT).
Two bisterphenoxide species containing W tert-butylimido ligand have been synthesized:
W(N-t-Bu)(CHCMe3)(OHMT)2
W(N-t-Bu)(CHCMe 3)(ODFT) 2.
and
W(N-t-
Bu)(CHCMe3)(OHMT)2 complex was inactive towards ethylene and DCMNBD, likely due to
129
crowded steric environment. W(N-t-Bu)(CHCMe3)(ODFT)2 was not highly selective in ROMP of
DCMNBD unlike Mo(NC 6F 5)(CHCMe2Ph)(ODFT)2.
Two biphenolate ligands were employed to form W tert-butylimido biphenolate complexes.
Although the pyridine adduct of five-coordinate species formed cleanly on both cases, the
chemical removal of pyridine induces C-H activation of tert-butyl group on the biphen ligand,
forming alkyl complexes. Considering the fact that analogous Mo adamantylimido complexes
have been reported, this C-H activation seems to be unique for W species.
Two TBP metallacyclobutane complexes containing W tert-butylimido ligand have
synthesized. Both complexes contain the ODFT ligand. The electron withdrawing abilities of
ODFT ligand might help in forming a stable metallacyclobutane species.
EXPERIMENTAL
General Considerations
All air and moisture sensitive materials were manipulated under a nitrogen atmosphere in a
Vacuum Atmospheres glovebox or on a dual-manifold Schlenk line. All glassware, including
NMR tubes, was dried in an oven prior to use. Diethyl ether, toluene, dichloromethane, 1,2dimethoxyethane, and benzene were degassed, passed through activated alumina columns, and
stored over 4 A Linde-type molecular sieves prior to use. Pentane was washed with H2SO4,
followed by water, and saturated aqueous NaHCO3, and dried over CaCl2 pellets over at least two
weeks prior to use in the solvent purification system. Deuterated solvents were dried over 4 A
Linde-type molecular sieves prior to use. 'H (500 MHz) and 'C NMR (125 MHz) spectra were
obtained on Varian 500 MHz spectrometers, and 'H (400 MHz), "C (100.61 MHz), and 1 9 F (376.5
MHz) NMR spectra were obtained on Bruker 400 MHz spectrometer. Chemical shifts for 'H and
13 C spectra are reported as parts per million relative to tetramethylsilane and referenced to the
residual 'H or
13 C
resonances of the deuterated solvent ('H (6) : benzene 7.16, chloroform 7.26,
methylene chloride 5.32; 19F(6) external PhF standard -113.15; 13 C (6) : benzene 128.06,
chloroform 77.16, methylene chloride 53.84). 'H-'H gCOSY NMR experiments were conducted
on a Varian Inova 500 MHz spectrometer. Sonications were performed on a Bransonic Ultrasonic
Cleaner 151 OR-MT purchased from Branson Ultrasonics Corporation. Benzaldehyde was distilled
and stored under nitrogen. Pyridinium chloride was purchased from Sigma-Aldrich or Alfa Aesar
130
and sublimed before use. Lipyr and HMTOLi were prepared by addition of one equivalent of nbutyllithium to a cold pentane or ether solution of pyrrole or HMTOH, and the solids were
collected on a frit, washed with pentane and dried in vacuo. Endo-dicyclopentadiene was
purchased from Sigma-Aldrich and was distilled before use. 1 -octene and were dried over CaH2
and vacuum transferred. Ethereal solutions of HCl were prepared by bubbling HCl gas into diethyl
ether and were titrated before use. Mo(N-t-Bu)(CHCMe3)(OC6F 5)2(NH 2 -t-Bu),10 [W(N-tBu)2(Cl)2(t-BuNH2)2]2, 8 W(N-t-Bu)(CHCMe 3)(Cl)2(py)2, 8 W(N-t-Bu)(CHCMe 3)(pyr)(OHMT), 8
2-methoxystyrene, 3 5
benzyl
potassium, 36
DCMNBD
,3
[Biphenme]H2, 38
[BiphenCF3]H2, 38
neopentyl Grignard, 3 9 HMTOH, 40 DFTOH, 4 1 and ZnCl2(dioxane)42 were prepared according to
literature procedures.
All other reagents were used as received. CENTC Elemental Analysis
Facility at the University of Rochester provided the elemental analysis results.
W(N-t-Bu)(CH-o-MeOC6H4)(C)2(py)
(1w) Pyridinium chloride (0.354 g, 3.06 mmol) was added
portion-wise to a cold (-30 'C) solution of W(N-t-Bu) 2 (CH2-o-MeOC6H4)2 (2 w) (0.580 g, 1.02
mmol) in 20 mL of ether. The reaction mixture was stirred for 19 h at room temperature. The
reaction mixture was dried in vacuo. Dichloromethane was added and the mixture was filtered
through a pad of Celite on a glass frit and the filtrate was dried in vacuo. Ether was added to
precipitate yellow powder, and the solid was collected by filtration (0.423 g, 79%): 'H NMR (500
MHz, C6D6) 6 11.96 (s, iH, W=CH,
'JCH =
145 Hz), 8.65 (d, 2H, py), 6.96 (t, iH, Ar), 6.59 (d,
IH, Ar), 6.45 (in, 3H, Ar and py), 6.10 (t, 2H, py), 4.35 (s, 3H, OMe), 1.44 (s, 9H, CMe3);
13
C
NMR (125 MHz, C6D6) 6 260.87, 160.77, 156.67, 152.25, 138.45, 134.62, 129.48, 128.59, 125.88,
124.55, 122.42, 120.90, 110.31, 71.15, 59.55, 29.72. Anal. Caled for C 17 H 2 2 Cl2 N 2 0W: Theory C,
38.88; H, 4.22; N, 5.33. Found C, 39.20; H, 4.30; N, 5.42.
131
12.0
11.0
10.0
9.0
8.0
7.0
6.0
5.0
Figure 3.5. 'H NMR spectrum of W(N-t-Bu)(CH-o-MeOC6H4)(C)2(py)
Mo(N-t-Bu)(CH-o-MeOC6H4)(OC6F)2(t-BuNH2)
4.0
3.0
2.0
1.0
(in C6D6, 500 MHz).
(Imo) Pentafluorophenol (85.3 mg, 0.463
mmol) was added portion-wise to a cold (-30 C) solution of Mo(N-t-Bu)2(CH2-o-MeOC 6H4)2
(2 mo) (0.101 g, 0.211 mmol) in 6 mL of ether. The reaction mixture was stirred for 2 h at room
temperature. The reaction mixture was dried in vacuo. Pentane was added to precipitate and the
yellow solid was isolated by filtration (0.084 g, 55%): 'H NMR (500 MHz, C 6D6) 6 13.31 (s, 1H,
Mo=CH), 6.60 (m, 2H, Ar), 6.48 (m, 1H, Ar), 6.09 (m, 1H, Ar), 4.10 (s, 3H, OMe), 3.06 (d, 1H,
NH 2), 2.20 (d, 1H, NH2), 1.51 (s, 9H, CMe3), 0.45 (s, 9H, CMe3); '9F NMR (300 MHz, C 6D 6) 6
-166.23 (d, 2F), -161.92 (d, 2F), -188.69 (t, 2F), -169.62 (t, 2F), -176.41 (m, 2F); '3 C NMR
(125 MHz, C 6D6) 6 281.31, 158.18, 146.19, 143.11, 141.74, 139.89, 138.90, 137.91, 136.99,
134.63, 134.03, 132.08, 130.09, 122.66, 122.07, 109.47, 75.19, 56.46, 51.72, 29.99, 28.57. Anal.
Calcd for C 28H 28FioN2O3Mo: Theory C, 46.29; H, 3.88; N, 3.86. Found C 46.28, H 3.91, N 3.74.
132
14
13
12
11
10
9
8
7
6
5
4
Figure 3.6. 'H NMR spectrum of Mo(N-t-Bu)(CH-o-MeOC6H4)(OC6Fs)2(t-BuNH2)
W(N-t-BU)2(CH2-o-MeOC6H4)2
3
2
1
0
(in C6D6,500 MHz).
(2w) 2-methoxybenzylmagnesium chloride (9.76 mL, 0.25 M,
2.44 mmol) was added to a cold (-30 C) solution of W(N-t-BU)2(Cl)2(py)2 (0.677 g, 1.22 mmol)
in 50 mL of ether/THF. The reaction mixture was stirred for 19 h at room temperature. The mixture
was filtered through a pad of Celite on a glass frit and the filtrate was dried in vacuo. Benzene was
added and the mixture was filtered through a pad of Celite on a glass frit and the filtrate was dried
in vacuo. Pentane was added and the brown liquid product was separated by filtration (0.580 g,
84%): 1H NMR (500 MHz, C6D6)
7.20 (d, 2H, Ar), 6.86 (m, 4H, Ar), 6.30 (d, 2H, Ar), 3.43 (s,
6H, OMe), 2.76 (s, 4H, CH2), 1.33 (s, 18H, CH3); 13 C NMR (125 MHz, C6D6) 6 160.63, 138.17,
131.75, 124.98, 122.18, 110.93, 67.41, 57.64, 39.34, 32.66. Anal. Caled for C24H36N202W: Theory
C, 50.71; H, 6.38; N, 4.93. Found C, 50.88; H, 6.43; N, 4.81.
133
7.5
7.0
6.5
6.0
5.5
5.0
4.5
4.0
3.5
3.0
2.5
2.0
1.5
1.0
Figure 3.7. 'H NMR spectrum of W(N-t-Bu)2(CH2-o-MeOC 6H 4)2 (in C6D 6 , 500 MHz).
Mo(N-t-Bu)2(CH2-o-MeOC6H4)2 ( 2 mo) 2-methoxybenzylmagnesium chloride (21.9 mL, 0.25 M,
5.48 mmol) was added to a cold (-30 C) solution of Mo(N-t-Bu)2(Cl) 2(dme) (1.09 g, 2.74 mmol)
in 50 mL of ether. The reaction mixture was stirred for 5 h at room temperature. The mixture was
filtered through a pad of Celite on a glass frit and the filtrate was dried in vacuo. Pentane was
added and the mixture was filtered through a pad of Celite on a glass frit and the filtrate was dried
in vacuo. Minimum amount of pentane was added and the yellow product was collected by
filtration (0.934 g, 71%): 'H NMR (500 MHz, C 6D 6 ) 6 7.05 (d, 2H, Ar), 6.99 (t, 2H, Ar), 6.79 (t,
2H, Ar), 6.42 (d, 2H, Ar), 3.39 (s, 6H, OMe), 2.59 (s, 4H, CH 2), 1.28 (s, 18H, CH3 );
13C
NMR
(125 MHz, C6 D6) 6 158.73, 131.93, 130.34, 125.74, 121.56, 110.88, 67.15, 55.45, 32.70, 31.93.
Anal. Calcd for C 24H 36N 20 2MO: Theory C, 59.99; H, 7.55; N, 5.83. Found C, 60.04; H, 7.62; N,
5.70.
134
7.0
6.5
6.0
5.5
5.0
4.0
4.5
3.5
Figure 3.8. 1H NMR spectrum of Mo(N-t-Bu)2(CH2-o-MeOC6H 4) 2 (in
Mo(N-t-Bu)(CH-o-MeOC6H4)(OC(CF3)3)2(t-BuNH2)
3.0
C6D6, 500
2.5
2.0
1.5
1.C
MHz).
(3 Mo) Perfluoro-t-butanol (150 pL, 1.08
mmol) was added to a cold (-30 C) solution of Mo(N-t-Bu)2(CH 2 -o-MeOC6H4 )2 (2 mo) (0.259 g,
0.540 mmol) in 20 mL of ether. The reaction mixture was stirred for 2 h at room temperature. The
reaction mixture was dried in vacuo. Pentane was added to precipitate and the reaction mixture
was chilled to -30 'C. The green solid was isolated by filtration (0.287 g, 64%): 'H NMR (500
MHz, C 6D6) 6 13.28 (s, 1H, Mo=CH), 6.81 (t, 1H, Ar), 6.69 (t, 1H, Ar), 6.47 (d, 1H, Ar), 6.30 (d,
1H, Ar), 3.96 (s, 3H, OMe), 2.97 (d, 1H, NH2), 2.550 (d, 1H, NH2), 1.37 (s, 9H, CMe3), 0.51 (s,
9H, CMe3);
19F
NMR (300 MHz, C 6D 6 ) 6 -72.13 (s, 9F), -73.16 (s, 9F); 13 C NMR (125 MHz,
C 6D6) 8 282.5, 159.04, 135.18, 130.00, 122.69, 121.10, 109.37, 84.66, 75.75, 56.56, 52.07, 30.13,
28.26. Anal. Calcd for C24H2 8FI 8N 2 O3Mo: Theory C, 34.71; H, 3.40; N, 3.37. Found C, 34.95; H,
3.43; N, 3.26.
135
Mo(NAr)2(CH2-o-MeOC6H4)2
( 4 mo) 2-methoxybenzylmagnesium chloride (5.64 mL, 0.25 M,
1.41 mmol) was added to a cold (-30 'C) solution of Mo(NAr)2(Cl) 2 (dme) (428 mg, 0.705 mmol)
in 10 mL of ether. The reaction mixture was stirred for 12 h at room temperature. The mixture was
filtered through a pad of Celite on a glass frit and the filtrate was dried in vacuo. Pentane was
added and stirred to collect orange solid. The orange solid was dissolved in benzene (10 mL) and
the mixture was filtered through a pad of Celite on a glass frit and the filtrate was dried in vacuo.
Pentane was added and and the resulting orange solid was collected by filtration (380 mg, 78%):
'H NMR (500 MHz, C6D6) 6 7.17 (d, 2H, Ar), 7.01 (d, 4H, Ar), 6.93 (t, 2H, Ar), 6.84 (t, 2H, Ar),
6.78 (t, 2H, Ar), 6.22 (d, 2H, Ar), 3.87 (m, 4H, i-Pr), 3.36 - 3.34 (s, IOH, CH2 and OMe), 1.17 (d,
24H, CH3); 13C NMR (125 MHz, C 6D6)
5
159.11, 153.94, 142.81, 134.46, 131.17, 125.85, 124.80,
122.74, 121.73, 110.45, 56.55, 39.94, 28.18, 24.10. Anal. Calcd for C4oH52N202Mo: Theory C,
69.75; H, 7.61; N, 4.07. Found C, 69.42; H, 7.55; N, 3.93.
LJ-I
I
7.0
6.5
6.0
5.5
5.0
4.5
4.0
3.5
3.0
2.5
Figure 3.9. 'H NMR spectrum of Mo(NAr)2(CH2-o-MeOC6H4)2 (in C6D6, 500 MHz).
136
2.0
1.5
1.0
Observation of W(NAr)2(CH2-o-MeOC6H4)2 (3w) 2-methoxybenzylmagnesium chloride (9.40
mL, 0.25 M, 2.35 mmol) was added to a cold (-30 C) solution of W(NAr)2(Cl)2(dme) (817 mg,
1.175 mmol) in 15 mL of ether. The reaction mixture was stirred for 16 h at room temperature.
The mixture was filtered through a pad of Celite on a glass frit and the mixture was washed with
THF. The filtrate was dried in vacuo. Benzene/dichloromethane was added and the mixture was
filtered through a pad of Celite on a glass frit and the filtrate was dried in vacuo. Pentane was
added and the resulting yellow solid was collected by filtration (886 mg, crude yield 97%): 1H
NMR (500 MHz, C6D6) 6 7.17 (d, 2H, Ar), 7.11 (d, 4H, Ar), 6.95 (t, 2H, Ar), 6.79 (t, 2H, Ar), 6.72
(t, 2H, Ar), 5.99 (d, 2H, Ar), 3.96 (in, 4H, i-Pr), 3.42 (s, 6H, OMe), 3.32(s, 4H, CH 3 ), 1.22 (d, 24H,
CH3).
W(N-t-Bu)(CH-o-MeOC6H4)(pyr)2(bipy)
(4 w) 1w (0.626 g, 1.192 mmol) was suspended in
toluene (50 ml) and the suspension was chilled at -30 'C for 1 h. Lipyr (0.183 g, 2.502 mmol)
was added in one portion and the mixture was allowed to stir at room temperature for 2 h, during
which time salts precipitated out. The precipitate was filtered off on a pad of Celite on a glass frit
and washed with toluene. 2,2'-Bipyidine (0.168 g, 1.072 mmol) was added to the solution and the
mixture was allowed to stir at room temperature overnight. The resulting precipitate was collected
by filtration and dried in vacuo to give a red powder (0.574 g, 81%). At room temperature, two
isomers were observed. 1H NMR (500 MHz, CD 2 Cl2) 6 11.87 (s, 1H, W=CH), 10.94 (s, lH,
W=CH), 9.91 (d, iH, bipy), 9.61 (d, IH, bipy), 9.50 (d, 1H, bipy), 8.63 (d, 1H, bipy), 8.18 - 7.55
(m, 18H, Ar), 7.01 - 6.50 (in, IOH, Ar), 6.31 (in, 4H, pyr), 6.17 (in, 2H, pyr), 5.97 (in, 2H, pyr),
5.75 (m, 2H, pyr), 5.67 (in, 4H, pyr), 5.32 (in, 4H, pyr), 3.93 (s, 3H, OMe), 3.66 (s, 3H, OMe),
1.37 (s, 9H, Me), 1.34 (s, 9H, Me); A
13
C NMR spectrum could not be obtained due to insolubility
of the sample. Anal. Calcd for C 30H33N 50W: Theory C, 54.31; H, 5.01; N, 10.56. Found C, 54.50;
H, 5.02; N, 10.16.
W(N-t-Bu)(CH-o-MeOC6H4)(pyr)(OHMT)
(5w)
4w
(338.1 mg, 0.510 mmol), ZnCl2(dioxane)
(114.3 mg, 0.510 mmol). and HMTOH (143 mg, 0.433 mmol) were suspended in toluene (- 25
mL) in a 100 mL Schlenk bomb. The solution was stirred for 24 h at 75 'C, and filtered through a
pad of Celite on a glass frit and the filtrate was dried in vacuo. The compound was extracted with
minimum amount of pentane, filtered through a pad of Celite on a glass frit, and dried, generating
137
orange powder; 324 mg (97%): 'H NMR (500 MHz, C 6D 6) 6 10.83 (s, 1H, anti-W=CH, IJCH
152 Hz), 7.04 - 6.98 (m, 3H, Ar), 6.92 (t, 1H, Ar), 6.85 (s, 2H, Ar), 6.54 (t, 2H, Ar), 6.42 - 6.37
(m, 2H, Ar), 6.26 (m, 4H, pyr), 3.20 (s, 3H, OMe), 2.24 - 2.07 (two s, one br, 18H, Me), 1.25 (s,
9H, Me);
13 C
NMR (100.61 MHz, C 6D6) 232.19, 159.32, 156.04, 136.50, 136.26, 135.51, 135.45,
134.76, 130.89, 129.84, 129.07, 128.60, 128.47, 125.11, 123.67, 122.00, 121.04, 109.70, 107.67,
70.12, 56.03, 32.83, 30.44, 21.65, 21.34, 21.17. Anal. Calcd for C4 0H 46N 2 02 W: Theory C, 62.34;
H, 6.02; N, 3.64. Found C, 62.07; H, 5.90; N, 3.49.
I
11.0
lill iii
10.0
9.0
8.0
7.0
--6.0
5.0
4.0
3.0
2.0
1.0
Figure 3.10. 'H NMR spectrum of W(N-t-Bu)(CH-o-MeOC6H 4)(pyr)(OHMT) (in C6D6, 500 MHz).
W(N-t-Bu)(CHCMe3)(OHMT)(C)(py)
(6w) Solid LiOHMT-THF (398.4 mg, 0.975 mmol) was
added portion-wise to a solution of W(N-t-Bu)(CHCMe3)(Cl)2(py)2 (491.3 mg, 0.887 mmol) in
benzene (20 mL). The reaction mixture was stirred for 19 h at 70 'C. The mixture was filtered
through a pad of Celite on a glass frit and the filtrate was dried in vacuo. Pentane was added and
removed in vacuo a couple of times to remove excess benzene. The resulting precipitate was
collected by filtration in pentane and dried to an ivory powder (541 mg, 79%). 1H NMR (500 MHz,
138
C 6D 6) 6 9.67 (s, 1H, W=CH), 8.05 (m, 2H, py), 7.24 (d, 1H, Ar), 7.17 (d, 1H, Ar), 7.08 (s, IH, Ar),
7.01 (m, 2H, Ar), 6.92 (s, 1H, Ar), 6.74 (m, 2H, py and Ar), 6.41 (m, 2H, py), 2.76 (s, 3H, Me),
2.74 (s, 3H, Me), 2.31 (s, 3H, Me), 2.27 (s, 3H, Me), 1.95 (s, 3H, Me), 1.65 (s, 3H, Me), 1.22 (s,
9H, CMe3), 1.14 (s, 9H, CMe3); 13C NMR (125 MHz, C 6D6) 6 278.23, 160.82, 153.75, 139.13,
138.99, 138.12, 138.02, 137.54, 137.07, 135.81, 135.50, 132.04, 131.47, 130.01, 129.90, 129.47,
129.24, 127.49, 127.23, 124.44, 119.81, 67.85, 43.11, 32.68, 31.88, 31.10, 22.41, 22.23, 21.44,
21.24, 20.91, 20.86. Anal. Calcd for C 3 8H 4 9CN20W: Theory C, 59.34; H, 6.42; N, 3.64. Found C,
58.27; H, 6.17; N, 3.75. Other attempts for elemental analysis produced variable results. Therefore,
W(N-t-Bu)(CHCMe3)(OHMT)(Cl)(py) was employed in the next step without further purification.
LLL
---------
10.0
9.5
9.0
8.5
8.0
-T
- - ----T--
7.5
7.0
6.5
6.0
5.5
5.0
4.5
4.0
Figure 3.11. IH NMR spectrum of W(N-t-Bu)(CHCMe3)(OHMT)(Cl)(py)
Observation of W(N-t-Bu)(CHCMC3)(OHMT)(CI)
3.5
(in
3.0
C6D6,
2.5
2.0
1.5
1.0
500 MHz).
(6w') B(C 6F5 ) 3 (66 mg, 0.129 mmol) was
added portion-wise to a solution of W(N-t-Bu)(CHCMe3)(OHMT)(Cl)(py) (99 mg, 0.129 mmol)
in benzene (5 mL). The reaction mixture was stirred for 30 min at room temperature and the
mixture was dried in vacuo. Pentane was added and removed in vacuo a couple of times to remove
139
benzene. Pentane was charged and the mixture was filtered through a pad of Celite on a glass frit.
The filtrate was dried in vacuo, leaving orange sticky solid. 'H NMR (500 MHz, C 6D 6) 6 8.21 (s,
1H, W=CH), 6.98 - 6.90 (m, 7H, Ar), 2.22 (s, 6H, Me), 2.19 (s, 6H, Me), 2.17 (s, 6H, Me), 1.16
(s, 9H, CMe3), 1.05 (s, 9H, CMe3).
W(N-t-Bu)(CHCMe3)(OHMT)2 (7w) B(C 6F5 ) 3 (96.4 mg, 0.19 mmol) was added portion-wise to
a solution of W(N-t-Bu)(CHCMe3)(OHMT)(Cl)(py) (132 mg, 0.17 mmol) in benzene (6 mL). The
reaction mixture was stirred for 30 min at room temperature and the mixture was dried in vacuo.
Pentane was added and removed in vacuo a couple of times to remove benzene. Pentane was
charged and the mixture was filtered through a pad of Celite on a glass frit. The filtrate was dried
in vacuo and dissolved in toluene-d8. It was transferred into a J-Young tube along with HMTOLi
(69 mg, 0.21 mmol). The mixture was placed in a 130 'C oil bath for 17 h and the mixture was
filtered through a pad of Celite on a glass frit. The mixture was washed with benzene and the
filtrate was dried in vacuo. The resulting mixture was stirred with acetonitrile for 30 min, and light
yellow powder was filtered, affording (52.6 mg, 3 1%): 1H NMR (500 MHz, C 6 D6 ) 6 7.64 (s, 1H,
W=CH), 6.92 (s, 4H, Ar), 6.89 (s, 4H, Ar), 6.86 - 6.79 (m, 6H, Ar), 2.27 (s, 12H, Me), 2.18 (s,
12H, Me), 2.05 (s, 12H, Me), 0.94 (s, 9H, CMe3), 0.92 (s, 9H, CMe3);
6
241.61 ('Jcw
=
13
C NMR (125 MHz, C 6D6)
192.5 Hz), 160.33, 137.00, 136.82, 136.34, 136.29, 131.88, 131.24, 128.91,
128.80, 121.63, 70.44, 41.63, 34.72, 32.78, 32.04, 22.12, 21.55, 21.36. Anal. Calcd for
C 57H 69 NO 2 W:
Theory C, 69.57; H, 7.07; N, 1.42. Found C, 69.77; H, 6.99; N, 1.29.
140
8.0
7.5
7.0
6.5
6.0
5.0
5.5
4.5
4.0
3.5
Figure 3.12. 1H NMR spectrum of W(N-t-Bu)(CHCMe3)(OHMT)
3.0
2
2.5
2.0
1.5
1.0
0.5
0.0
(in C6D6, 500 MHz).
W(N-t-Bu)(CHCMe3)(ODFT)2 (8 w) W(N-t-Bu)(CHCMe3)(pyr)2(bipy) (197.3 mg, 0.322 mmol),
ZnCl2(dioxane) (72.2 mg, 0.322 mmol) and DFTOH (260.5 mg, 0.611 mmol) were dissolved in
toluene (20 mL) in a 100 mL Schlenk bomb. The mixture was heated for 2 h at 75 'C. The solution
was filtered through a pad of Celite on a glass frit and filtrate was dried in vacuo. The compound
was triturated with a minimum amount of pentane, isolated by filtration. Yellow solid was filtered
off (179.2 mg, 47%): 1H NMR (400 MHz, C 6D 6) 6 7.86 (s, 1H, W=CH), 6.97 (d, 4H, Ar), 6.73 (t,
2H, Ar), 0.84 (s, 9H, CMe3), 0.73 (s, 9H, CMe3); 19F NMR (300 MHz, C 6 D6 ) 6 -130.37 (in, 4F),
-144.38 (t, 2F), --151.46 (m, 4F);
3
C NMR (100.62 MHz,C 6 D6)6 248.95, 161.99, 145.75, 143.22,
142.70, 139.74, 138.19, 133.62, 122.23, 117.82, 112.16, 71.96, 42.56, 33.45, 31.61. Anal. Caled
for C 4 5H 2 5F2 0NO2W: Theory C, 45.98; H, 2.14; N, 1.19. Found C, 45.69; H, 1.81; N, 1.41.
141
8.0
7.5
7.0
6.5
6.0
5.5
5.0
4.5
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0.0
Figure 3.13. 'H NMR spectrum of W(N-t-Bu)(CHCMe3)(ODFT)2 (in C6D6, 400 MHz).
W(N-t-Bu)(CHCMe3)(BiphencF3)(py)
(9w) W(N-t-Bu)(CHCMe3)(Me2pyr)2(py)
(173.5 mg,
0.314 mmol), and [biphenCF3]H2 (145 mg, 0.314 mmol) were dissolved in benzene (10 mL) in a
20 mL Schlenk bomb. The mixture was heated at 70 'C for 12 h, and the solvent was removed in
vacuo. The mixture was triturated with pentane, and the resulting suspension was filtered off to
give a off-white solid. The filtrate contained some product, W(N-t-Bu)(CHCMe3)(Me2pyr)2(py),
and some free [biphenCF3]H2, so the mixture was dissolved in benzene (5 mL) in a 20 mL Schlenk
bomb and heated at 70 'C for 12 h. After the same workup, two crops were combined (153.2 mg,
56%). Two isomers were present in a 56:44 ratio. 'H NMR (500 MHz, C 6 D 6) 6 10.66 (s, 1H,
W=CH, IJCH = 112 Hz, 2 JHw = 15 Hz, major), 9.37 (s, 1H, W=CH, IJCH = 112 Hz, 2 JHW = 15 Hz,
minor), 8.36 - 8.44 (dd, 4H, Ar), 7.85 - 7.95 (m, 4H, Ar), 6.66 (in, 2H, Ar), 6.31 (t, 2H, Ar), 6.24
(t, 2H, Ar), 2.47 (s, 3H, Me), 2.41 (s, 3H, Me), 2.06 (s, 3H, Me), 2.01 (s, 3H, Me), 1.59 (d, 18H,
CMe3), 1.38 (s, 18H, CMe3), 1.15 (s, 9H, CMe3), 1.06 (s, 9H, CMe3), 0.85 (s, 9H, CMe3), 0.78 (s,
9H, CMe3); 1 9 F NMR (300 MHz, C6D6) 6 -58.41 (in, 3F), -58.45 (m, 6F), -58.62 (in, 3F);
142
13 C
NMR (125 MHz, C6D6 ) 6 276.84, 271.98, 170.78, 167.59, 164.66, 164.30, 154.64, 153.84, 138.61,
137.81, 135.88, 135.86, 135.79, 135.42, 134.74, 134.61, 133.72, 131.87, 131.18, 130.44, 130.27,
128.60, 125.97, 125.90, 125.62, 125.50, 125.21, 124.58, 124.51, 124.39, 123.98, 123.58, 121.05,
120.82, 120.66, 120.43, 119.70, 119.47, 119.36, 119.13, 69.61, 69.12, 44.06, 43.75, 35.92, 35.50,
34.56, 34.13, 33.52, 32.34, 32.31, 31.58, 31.54, 31.53, 30.09, 30.00, 16.47, 16.25, 16.19, 16.02.
Anal. Calcd for C 3 8H 50 F6N 2 0 2 W: Theory C, 52.79; H, 5.83; N, 3.24. Found C, 52.46; H, 5.64; N,
3.02.
I
11
I
11.5
10.5
9.5
9.0
8.5
8.0
11
7.5
7.0
6.5
11
6.0
5.5
5.0
4.5
Figure 3.14. 1H NMR spectrum of W(N-t-Bu)(CHCMe3)(BiphenCF3)(py)
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
(in C6D6, 500 MHz).
W(N-t-Bu)(CH2CMe3)(BiphencF3) (10w) In a 20 mL vial, W(N-t-Bu)(CHCMe3)(BiphenCF3)(py)
(35.5 mg, 0.041 mmol) was dissolved in benzene (3 mL). B(C 6F5 )3 (21.0 mg, 0.041 mmol) was
added portion-wise and the mixture was stirred at room temperature for 30 min before the solvent
was removed in vacuo. The product was extracted into pentane, and the mixture was filtered
through a bed of Celite to remove py-B(C6Fs)3. Pentane was dried in vacuo to yield an orange solid,
and recrystallized from a mixture of Toluene and Et20. Residual py-B(C6F5)3 was observed by 1H
143
NMR spectroscopy: 'H NMR (400 MHz, C6 D 6) 6 7.95 (br, py-B(C 6 F5 )3), 7.89 (s, 1H, Ar), 7.75 (s,
IH,
Ar), 6.57 (t, py-B(C 6 Fs) 3), 6.23 (t, py-B(C6Fs)3), 3.58 (d, 1H, WCH 2 , 2Jiw
=
16 Hz, other
WCH 2 signal is at 1.36 ppm) 2.45 (d, 3H, Me), 2.25 (d, 1H, WCH2 , 2 JHw = 15.2 Hz, other WCH 2
signal is at 1.66 ppm), 2.08 (d, 3H, Me), 1.66 (s, 3H, Me), 1.41 (s, 3H, Me), 1.37 (s, 9H, CMe3),
1.18 (s, 9H, CMe3), 0.95 (s, 9H, CMe3).
-iL-J
8.0
7.5
7.0
I
JULJdi
II
6.5
6.0
5.5
5.0
4.5
4.0
Figure 3.15. 1H NMR spectrum of W(N-t-Bu)(CH2CMe3)(BiphencF3)
2.5
2.0
C6D6, 400
MNz).
3.0
3.5
(in
1.5
1.0
O.
W(N-t-Bu)(CHCMe3)(Biphenme)(py) (11w). Benzyl potassium (145 mg, 1.114 mmol) was added
to a solution of [BiphenMe]H2 (197.4 mg, 0.557) in THF (20 mL) and stirred for 20 min at room
temperature. A solution of W(N-t-Bu)(CHCMe3)(py)2(C)
2
(308.5 mg, 0.557 mmol) in THF was
added to this reaction mixture and stirred 19 hours at room temperature. The reaction mixture was
dried in vacuo and pentane was charged and dried in order to remove excess THF. The product
was extracted with benzene and the mixture was filtered through a bed of Celite to remove KCl.
After concentration in vacuo, the product was triturated with pentane, and the resulting suspension
was filtered off to give an off-white solid, affording (318.9 mg, 76%). Two isomers were present
144
in a 51:49 ratio: 'H NMR (500 MHz, C 6D6) 6 10.56 (s, 1H, W=CH,
(s, 1H, W=CH,
2
JHW =
2
JHw =
11.2 Hz, major), 9.27
12.8 Hz, minor), 8.61 - 8.55 (dd, 4H, Ar), 7.38 (s, 1H, Ar), 7.36 (s, 1H,
Ar), 7.30 (d, 2H, Ar), 6.66 (m, 2H, Ar), 6.32 (t, 2H, Ar), 6.25 (t, 2H, Ar), 2.41 (s, 3H, Me), 2.35
(s, 3H, Me), 2.30 (s, 3H, Me), 2.24 (s, 3H, Me), 2.22 (s, 3H, Me), 2.18 (s, 3H, Me), 1.79 (d, 21H,
Me and CMe 3), 1.75 (s, 3H, Me), 1.45 (s, 18H, CMe3), 1.35 (s, 9H, CMe3), 1.26 (s, 9H, CMe3),
0.94 (s, 9H, CMe3), 0.90 (s, 9H, CMe3);
13C
NMR (100.61 MHz, C 6D 6) 6 273.50, 268.81, 164.80,
160.96, 160.45, 160.01, 154.76, 153.88, 138.01, 137.19, 135.15, 134.87, 134.81, 134.63, 134.54,
133.79, 133.66, 133.06, 131.17, 130.92, 130.31, 129.76, 127.57, 127.46, 126.86, 126.74, 126.30,
126.10, 125.77, 124.17, 124.12, 69.05, 68.32, 43.66, 43.33, 35.88, 35.47, 34.44, 34.00, 33.81,
32.77, 32.51, 32.41, 32.35, 31.79, 30.89, 30.84, 29.87, 22.73, 20.76, 20.67, 20.33, 20.24, 17.48,
17.26, 17.05, 16.81, 14.28. Anal. Calcd for C 3 8H 56N 2 0 2 W: Theory C, 60.32; H, 7.46; N, 3.79.
Found C, 60.68; H, 7.80; N, 3.40.
JLJL--A
10.5
9.5
9.0
8.5
8.0
7.5
7.0
6.5
6.0
5.5
5.0
4.5
4.0
3.5
3.0
2.5
2.0
Figure 3.16. 'H NMR spectrum of W(N-t-Bu)(CHCMe3)(Biphenme)(py) (in C6D6 , 400 MHz).
145
1.5
1.0
0.5
W(N-t-Bu)(C3H6)(pyr)(ODFT) (12w) W(N-t-Bu)(CHCMe3)(pyr)2(bipy) (270 mg, 0.440 mmol),
ZnCl2(dioxane) (98.7 mg, 0.440 mmol) and DFTOH (169 mg, 0.396 mmol) were dissolved in
toluene (20 mL) in a 100 mL Schlenk bomb. The mixture was sonicated for 15 h, filtered through
a pad of Celite on a glass frit and filtrate was dried in vacuo. The compound was extracted with
pentane (20 mL), filtered through a pad of Celite on a glass frit, and dried until pentane is about 2
mL. The mixture was transferred to a Schlenk bomb. The solution was degassed via three freezepump-thaw cycles, and it was exposed to 1 atm of ethylene for 30 min. Off white solids precipitated
out and filtered off, affording (98.1 mg, 31%). 'H NMR (500 MHz, C 6D 6) 6 7.36 (m, 2H, pyr),
7.08 (d, 2H, Ar), 6.79 (t, 1H, Ar), 6.47 (in, 2H, pyr), 4.00 (in, 2H, WCHa), 3.10 (m, 2H, WCHa),
0.66 (s, 9H, CMe3), -1.55 (m, 1H, WCHp), -1.84 (in, 1H, WCHfi);
-137.61 (in, 4F), -156.06 (t, 2F), -161.57 (m, 4F);
13 C
19F
NMR (300 MHz, C 6D 6) 6
NMR (125 MHz, C6D6 ) 6 159.17, 145.72,
143.76, 142.00, 139.99, 138.74, 136.76, 133.16, 132.52, 119.68, 118.65, 113.98, 110.32, 96.12,
65.96, 29.00, -6.47. Anal. Calcd for C 2 9H 2 2 F 1oN 2 0W: Theory C, 44.18; H, 2.81; N, 3.55. Found
C, 44.29; H, 2.87; N, 3.42.
7.5
-
-
U
7.0
6.5
6.0
5.5
5.0
4.5
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0.0
Figure 3.17. 'H NMR spectrum of W(N-t-Bu)(C 3H6)(pyr)(ODFT) (in C6D6, 500 MHz).
146
-0.5
-1.0
-1.5
-2.0
-2.5
W(N-t-Bu)(C3H6)(ODFT)2
(13w) W(N-t-Bu)(CHCMe3)(pyr)2(bipy) (160 mg, 0.260 mmol),
ZnCl2(dioxane) (58.5 mg, 0.260 mmol) and DFTOH (211 mg, 0.495 mmol) were dissolved in
toluene (10 mL) in a 100 mL Schlenk bomb. The mixture was sonicated for 19 h, filtered through
a pad of Celite on a glass frit and filtrate was dried in vacuo. The compound was extracted with
pentane (20 mL), filtered through a pad of Celite on a glass frit, and dried until pentane is about 2
mL. The mixture was transferred to a Schlenk bomb. The solution was degassed via three freezepump-thaw cycles, and it was exposed to 1 atm of ethylene for 30 min. Off white solids precipitated
out and filtered off, affording (85.5 mg, 29%): 'H NMR (500 MHz, C6D6) 6 6.98 (d, 4H, Ar), 6.74
(t, 2H, Ar), 2.72 (m, 2H, WCHa), 1.87 (in, 2H, WCHa), 0.53 (s, 1OH, CMe3 and WCHfi), -0.20 (in,
IH, WCHfl); '9F NMR (300 MHz, C 6D 6 ) 6 -138.72 (m, 4F), -154.76 (m, 2F), -162.22 (in, 4F);
13C
NMR (125 MHz, C 6D6) 6 161.04, 145.71, 143.74, 142.11, 140.10, 139.13, 137.13, 133.88,
121.27, 118.59, 113.65, 70.48, 68.85, 28.50, 5.99. Anal. Calcd for C 4 3 H2 lF 2 oNO2W: Theory C,
45.01; H, 1.84; N, 1.22. Found C, 45.13; H, 1.92; N, 1.10.
A
7.5
7.0
6.5
6.0
5.5
5.0
4.5
4.0
3.5
3.0
2.5
2.0
1.5
Figure 3.18. 'H NMR spectrum of W(N-t-BU)(C3H6)(ODFT)2 (in C6D6, 500 MHz).
147
1.0
05
0.0
-0.5
-1.0
General procedure for polymerization reactions
In a 20 ml vial in the glovebox was placed 50 equivalents of monomer with a stir bar and solvents
(C 6D6 , dichloromethane, or CDCl3). In a 4 ml vial, 1 equivalent of catalyst was dissolved in
appropriate solvents, and catalyst solution was added dropwise to the monomer solution. The
reaction progress was monitored by 'H NMR spectroscopy by taking aliquots in wet CDCl 3 outside
box.
General procedure for 1-octene homocoupling experiments
In a 0.5 dram vial in the glovebox was placed 5 tmol solid catalyst (2 mol%) and 43 p.L 1-octene
(0.272 mmol, 50 equiv) was injected. The vial was capped with a septum with a hole and the
mixture was stirred at room temperature. The aliquots were taken after 1 h, 2 h, 8 h, and 24 h and
wet chloroform-d was added outside box. The conversion of 1 -octene to 7-tetradecene was
measured with 'H NMR spectroscopy.
Crystal data and structure refinement (Performed by Dr. Peter Muller)
Low-temperature diffraction data (#-and w-scans) were collected on a Bruker-AXS X8 Kappa
Duo diffractometer coupled to a Smart APEX2 CCD detector with Mo Ka radiation (X = 0.71073
A) from an IpS micro-source for the structure of compound 3 mo and on a Siemens Platform threecircle diffractometer coupled to a Bruker-AXS Smart Apex CCD detector with graphitemonochromated Mo Kcc radiation (A = 0.71073
A)
and other corrections were applied using SADABS
for the structure of compound 10w. Absorption
43 for the
structure of 3 mo and TWINABS 4 4 for
the structure of lOw. All structures were solved by direct methods using SHELXT 4 5 and refined
against F2 on all data by full-matrix least squares with SHELXL-2012 (3 mo) or SHELXL-2014
(10w) 46
using established refinement approaches. 4 7 Unless noted otherwise below, all hydrogen
atoms were included into the model at geometrically calculated positions and refined using a riding
model. The isotropic displacement parameters of all hydrogen atoms were fixed to 1.2 times the
Ueq value of the atoms they are linked to (1.5 times for methyl groups). Details about crystal
properties, diffraction data and crystal structures can be found in the tables below.
Compound 3 mo crystallizes in the orthorhombic centrosymmetric space group Pbca with one
molecule of 3 mo per asymmetric unit. One of the two O-C(CF 3)3 ligands was refined as disordered
148
over three positions corresponding to a rotation about the O-C bond. The fractional occupancies
of the three disorder components were refined freely while restraining the sum of the three
occupancies to unity within 0.0001. The fractional occupancies refined to 0.4950(16), 0.4397(17),
and 0.0652(11), respectively. The disorder was refined with the help of similarity restraints on 12 and 1-3 distances and displacement parameters as well as advanced rigid bond restraints 48 for
anisotropic displacement parameters. Coordinates for the hydrogen atoms on nitrogen NI and on
the alkylidene carbon C1 were taken from the difference Fourier synthesis and those hydrogen
atoms were subsequently refined semi-freely with the help of distance restraints.
Compound 10w crystallizes in the monoclinic centrosymmetric space group P21/n with one
molecule of 10w per asymmetric unit.
The crystal was non-merohedrally twinned; two
independent orientation matrices for the unit cell were found using the program CELLNOW,4
and data reduction taking into account the twinning was performed with SAINT. 50 The program
TWINABS 43 was used to set up the HKLF4 format file for structure refinement. Coordinates for
hydrogen atoms bound to carbon directly attached to the central tungsten atom (carbon atoms CI
and C18) were taken from the difference Fourier synthesis and those hydrogen atoms were
subsequently refined semi-freely with the help of distance restraints.
149
Table 3.4. Crystal data and structure refinement for 3 mo.
Identification code
x13120
Empirical formula
C24 H28 F18 Mo N2 03
Formula weight
830.42
Temperature
100(2) K
Wavelength
0.71073 A
Crystal system
Orthorhombic
Space group
Pbca
Unit cell dimensions
a = 16.5372(8)A
b = 17.6547(9)
X= 900
A
P = 90
c = 21.0898(1l)A
y = 900
Volume
6157.4(5) A 3
Z
8
Density (calculated)
1.792 Mg/m3
Absorption coefficient
0.566 mnv 1
F(000)
3312
Crystal size
0.500 x 0.400 x 0.300 mm 3
Theta range for data collection
1.931 to 31.301'.
Index ranges
-24<=h<=24, -25<=k<=25, -30<=l<=30
Reflections collected
133122
Independent reflections
10068 [R(int) = 0.0394]
Completeness to theta = 25.242'
100.0%
Absorption correction
Semi-empirical from equivalents
Max. and min. transmission
0.7463 and 0.6800
Refinement method
Full-matrix least-squares on F 2
Data / restraints / parameters
2
10068 / 3442 / 644
Goodness-of-fit on F
1.038
Final R indices [I>2sigma(I)]
RI
0.0249, wR2
=
0.0593
R indices (all data)
RI = 0.0314, wR2
=
0.0627
Extinction coefficient
n/a
Largest diff. peak and hole
0.483 and -0.425 e.A-3
=
150
Table 3.5. Crystal data and structure refinement for 10w.
Identification code
14018_t4
Empirical formula
C33 H45 F6 N 02 W
Formula weight
785.55
Temperature
100(2) K
Wavelength
0.71073 A
Crystal system
Monoclinic
Space group
P21/n
Unit cell dimensions
a = 12.8518(11) A
a
=
900
b = 17.2888(16)A
p
=
97.0070(10)0
c = 15.1767(14) A
y= 900
Volume
3347.0(5) A3
Z
4
Density (calculated)
1.559 Mg/m3
Absorption coefficient
3.514 mm-1
F(000)
1576
Crystal size
0.380 x 0.340 x 0.190 mm 3
Theta range for data collection
1.984 to 30.034'.
Index ranges
-18<=h<= 18, 0<=k<=25, 0<=l<=22
Reflections collected
175483
Independent reflections
9799 [R(int)= 0.0364]
Completeness to theta = 25.2420
100.0%
Absorption correction
Semi-empirical from equivalents
Max. and min. transmission
0.746156 and 0.473130
Refinement method
2
Full-matrix least-squares on F
Data / restraints / parameters
2
9799 / 85 / 413
Goodness-of-fit on F
1.058
Final R indices [I>2sigma(I)]
RI
R indices (all data)
RI = 0.0191, wR2 = 0.0373
Extinction coefficient
n/a
Largest diff. peak and hole
0.787 and -0.480 e.A-3
=
0.0158, wR2
151
=
0.0363
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154
Chapter 4
Synthesis and Mechanistic Studies of Alternating trans-AB Copolymers
by Molybdenum Alkylidenes
Portions of this chapter have appeared in print:
Jeong, H.; John, J. M.; Schrock, R. R.; Hoveyda, A. H. Synthesis of Alternating trans-AB
Copolymers through Ring-Opening Metathesis Polymerization Initiated by Molybdenum
Alkylidenes. J. Am. Chem. Soc. 2015, 137, 2239 - 2242.
155
INTRODUCTION
Over the past 20 years, development of more efficient and selective olefin metathesis
catalyst has enriched the field of organic and polymer chemistry. In polymer chemistry, ringopening metathesis polymerization (ROMP) has provided a great tool for controlling polymer
structure. 1 Highly regio- or stereoregular polymers have been prepared from norbomene or
norbornadiene 2 , cyclopropene 3, or cyclooctene-based monomers.4 5 Although examples are rare
compared to their homopolymers, alternating copolymers bearing two different AB monomers
have been prepared through ROMP. Typically, the two AB monomers employed were norbornene
and cyclooctene, but the cyclobutene/cyclohexene combination was also reported in the
literature.6-1 0 In all cases, ruthenium-based Grubbs catalysts were used. Copolymer formation from
methyl cyclobut- 1 -ene- 1 -carboxylate and cyclohexene is a particularly interesting case (Scheme
4.1).6 Methyl cyclobut- 1 -ene- 1 -carboxylate forms a first insertion product bearing a disubstituted
alkylidene which is unreactive toward a second monomer insertion. Instead, a cyclohexene reacts
with the disubstituted alkylidene and alternating insertion of two monomers is followed. Since the
free energy for polymerization of cyclohexene is 6.2 kJ/mol, homolinkages of polycyclohexene
are unlikely to be formed in this system."
N-Mes
Cl,
0
R
Ph
Br
O'Br
R
[Ru]
rt, CD 2 C
R = CH 3 or Ph
7R
OR
[Ru]-
O
R 1 = R2 = H
2
R, = H,
Ph
R2
0OR
O
R,R
1
2
-
Mes-N'
R2
= CH20CH3
Ph
Scheme 4.1. Alternating copolymerization of 1-subsitutted cyclobutene and cyclohexene.
Two examples of alternating copolymerization containing two enantiomers have been
reported. First, racemic 1-methylbicyclo[2.2.1]-hept-2-ene was polymerized by ReCls catalyst to
yield a polymer having a cis, syndiotactic,alternating (cis,syndio,alt) structure.1 2 Second,
Mo(NAd)(CHCMe2Ph)(pyr)(OHMT) (NAd = adamantylimido, pyr = pyrrolide, OHMT = 0-2,6(2',4',6'-Me 3C 6 H2)2C6H3) is a highly effective catalyst for generating cis,syndio,alt polymers from
each
endo,exo-5,6-dicarbomethoxynorbornene
and
1 -methyl-5,6-dicarbomethoxy-7-
oxanorbornadiene (Scheme 4.2)." Cis selectivity results from formation of an all cis
156
metallacyclobutane intermediate as a consequence of the steric demand of OHMT ligand.
Syndiotacticity results from inversion of configuration at the metal center (R, S) in each productive
metathesis step. Furthermore, one enantiomer of the monomer is preferred for each configuration
of the metal center so that one alternating enantiomer sequence in the polymer chain is formed.
This unique selectivity deteriorates with other racemic monomers and catalysts.14
R
R
1%, [Mo]
R
(IraR
R
f
R= COOMe
-
R
RR
R
-
/ /0
P
N
n
(rac)
Mo
R
R
R
1%, [Mo]-
R
R/
R =COOMe
R
(rac)
n[O
Scheme 4.2. Synthesis of cis,syndio,alternating polymers employed by Mo(NAd)(CHCMe2Ph)(pyr)(OHMT).
Recently we reported a highly stereoselective polymerization of 2,3-dicarbomethoxy-7isopropylidenenorbornadiene (B) with W(O)(CHCMe3)(Me2Pyr)(OHMT)(PMe2Ph) (Me2Pyr =
2,5-Me2NC4H2) (Scheme 4.3).15 ROMP of B was particularly interesting because ROMP could
not be achieved employing either Mo and W imido-substituted catalysts or Grubbs catalysts (G2
and
G3).
When
B
was
added
to
Mo(NAr)(CHCMe3)(O-t-Bu)2
=
(NAr
2,6-
diisopropylphenylimido), a first insertion product was formed but no polymer was generated
(Scheme 4.4).16
0
PhMe2P
0
R
R
R
R
R
R
R
R
1lM01%-
n
CDC13
cis, isotactic
R = COOMe
Scheme
4.3.
Polymerization
of
2,3-dicarbomethoxy-7-isopropylidenenorbornadiene
W(O)(CHCMe3)(Me2pyr)(PMe2Ph)(OHMT).
157
(B)
with
NN
1
0N
oi
0
-
0
0
0-~
0
0'
0
Scheme 4.4. Formation of a first insertion product of B with Mo(NAr)(CHCMe3)(O-t-Bu)
2
.
0
1"M + I:(/Toluene, 8 h
Therefore, addition of a less reactive and small monomer partner might lead to copolymer
formation. We chose to begin our investigations with 7-isopropylidenenorbornadienes and
cyclooctene monomers and molybdenum arylimido complexes as initiator.
RESULTS AND DISCUSSION
I. Formation of trans-AB Alternating Copolymers
Two molybdenum bisalkoxide catalysts 1 and 2 in Figure 4.1 were chosen initially in this
study for the following reasons: a Mo adamantylimido MAP complex has shown higher selectivity
in ROMP of racemic monomers for forming cis,syndio,alt polymers than that W tert-butylimido
MAP analog.'7 In addition, Mo(NAr)(CHCMe3)(0-t-Bu) 2 is known to form a clean first insertion
product with B, 16 so formation of polyB will be minimized.
F3C
N
'''Mo~
N
Ph
F3 C
F3C
Ph
Mo
F3C 0F
0
0
CF 3
'CF3
CF3
CF3
1
2
Figure 4.1. The two catalysts for ROMP of alternating copolymerizations.
A. Stereoselective ROMP of Four AB Alternating Copolymers with a Molybdenum Catalyst
When C6D6 solution of 1 was added to a mixture of 50 equivalents of 2,3-dicarbomethoxy7-isopropylidenenorbornadiene (B) and 50 equivalents of cis-cyclooctene (A) at room temperature,
full consumption of both monomers were observed by 'H NMR spectroscopy after 1 h and 15 min.
The reaction was quenched through addition of benzaldehyde and the polymer was isolated
158
through precipitation in methanol. The isolated polymer contains two major olefinic protons with
trans linkages. A double doublet for Hi (at 5.27 ppm) and a double triplet for H 2 (at 5.48 ppm) are
observed in the 'H NMR spectrum in CDCl 3 (Scheme 4.5). Formation of trans double bonds is
consistent with a coupling constant between Hi and H2 of
3
JHH =
15.5 Hz, as well as IR
spectroscopy (presence of a strong absorption at 967 cm-1). Two minor peaks around 5.35 ppm in
the 'H NMR spectrum were confirmed to be cis and trans AA linkages via control experiments
(See Experimental Section). Proton and carbon NMR peaks were fully assigned with the aid of
'H-1H COSY and 'H-13C HSQC. Based on the integration values of the 'H NMR spectroscopy,
>90% of the polymer contains alternating AB linkages (Figure 4.2).
0
I
/
/
1
C63
6D, 1.25
hH2
0
RT, 2 h
0
trans-AB
A (50 eq)
B (50 eq)
Scheme 4.5. Formation of trans-poly[A-alt-B] by 1.
H,
H3
OMe
H12
n
H1,
0
0
7
H 10
H2
-
0
AB linkages
0 0
\
o
Me
AA linkages
5.65
5.55
5.45
5.15
5.25
5.35'
CDC1 3
7.5
7.0
6.5
6.0
5.5
5.0
4.5
4.0
,H
HHiH
H2
3.5
3.0
2.5
2.0
1.5
Figure 4.2. 1H NMR spectrum of isolated >90% trans-poly[A-alt-B] using 1 (500 MHz, CDC3).
159
1.0
Typically, when a catalyst solution (4 pM) was added to a stirred solution containing both
A (0.2 - 0.36 M) and B (0.2 - 0.36 M) in various organic solvents (benzene, toluene, THF, or
chloroform), >90% trans-poly[A-alt-B] (typically 92 - 94%) was generated. The polymerization
was finished within 2 hours in all solvents except THF, which took 24 hours to reach full
conversion. It was thought that THF coordinates to molybdenum and slows the polymerization
reaction. There was no precedent in the literature to have both highly stereoselective and
chemoselective (>90% alternating incorporation) A,B-copolymerization through ROMP. When a
2:1 ratio of B:A was employed, the isolated polymer contained 94% trans-poly[A-alt-B], which
was a slight improvement than 1:1 addition of B:A (Figure 4.3b). When initial concentration of A
was twice that of B, the isolated polymer contained more AA linkages, and olefinic peaks of transpoly[A-alt-B] are less sharp as a consequence of the reduced regularity in the polymer (Figure
4.3a). When the ratio of B:A was 1:1 at 65 'C, mainly polyA linkages were formed (Figure 4.3c).
When the polymerization was performed at 0 'C with the ratio of B:A:1 (50:50:1), the isolated
polymer contained 90% trans-poly[A-alt-B] by 'H NMR spectroscopy, which was essentially the
same as the sample prepared at room temperature. When 50 equivalents of A were added via a
syringe pump over 5 or 20 minutes to a stirred mixture of 50 equivalents of B and 1, the isolated
polymer from both experiments contained 96% AB linkages by 'H NMR spectroscopy, a slight
improvement compared to the simultaneous addition of A and B.
160
(a) B:A = 1:2, r.t.
(b) B:A = 2:1, r.t.
(c) B:A = 1:1, 65 *C
AAAA
I
(d) B:A = 1:1, r.t.
5.80
5.75
5.70
5.65
5.60
5.55
5.50
5.45
5.40
5.25
5.30
5.35
5.20
5.15
5.10
5.05
5.00
4.95
Figure 4.3. Olefinic regions of the 'H NMR spectra of poly[A-alt-B] using various conditions prepared from 1:
(a) B:A = 1:2, r.t. (50:100 equivalents to 1; 500 MHz in CDC3) (b) B:A = 2:1, r.t. (100:50 equivalents to 1; 400
MHz in CDC3) (c) B:A = 1:1, 65 *C (50:50 equivalents to 1; 500 MHz in CDC3) (d) B:A = 1:1, r.t. (50:50
equivalents to 1; 400 MHz in CDCb).
Cis-cycloheptene
(A')
and
spiro[bicyclo[2.2. 1 ]hepta-2,5-diene-2,3-
dimethyl
dicarboxylate-7,1'-cyclopropane] (B')1 8 were explored as monomers. A catalyst solution of 4 pM
of 1 was added to a stirred solution of A' (50 equivalents, 0.36 M) and B' (50 equivalents, 0.36 M)
in benzene or toluene. The reaction was found to be complete after 2 hours and the isolated polymer
contained >90% trans-poly[A'-alt-B']. With two types of A (A and A') and two types of B (B and
B'), four alternating copolymers were synthesized from 1 (Scheme 4.6).
0
A =
D
A' =
B' =
/
/
0
161
0
0
BO
O
0
O
B =0
O
/
n
00
/
0
0
I-
0 0
0
trans-AB
A
B
0
0
//
-n
0-
0
0
0 0
0
trans-A'B
A'
B
0
S0
n
0
0
0~
0 0
0
trans-AB'
A
B'
0
0
//
7
n
o
0.
00
0
B'
0
trans-A'B'
A'
Scheme 4.6. Synthesis of four >90% trans-poly[A-alt-B
using 1.
All isolated polymers were readily soluble in common organic solvents (chloroform, THF,
acetone, DMSO, toluene, and benzene). Two isolated polymers were subjected to GPC (relative
to polystyrene, in THF) in order to determine number average molecular weight. trans-poly[A-altB] showed Mn = 30.3 kDa (PDI = 2.04, Mn(calculated) = 17.9 kDa) and trans-poly[A-alt-B']
showed Mn = 36.8 kDa (PDI = 1.74, Mn(calculated) = 17.2 kDa), indicating that these polymers
do not fall under the classification of living polymerization (PDI = 1).
When catalyst 2 was employed for four monomer combinations, >90% trans-poly[A-altB'] and trans-poly[A'-alt-B'] were generated. However, combinations of A/B/2 and A'/B/2 did
not lead to >90% transaltpolymer, but only 80% transalt polymer linkages along with 20%
polyA (or polyA') based on 1H NMR spectroscopy (See Experimental Section).
In some cases, "sequence editing" polymerization has been reported in the literature where
cyclooctene was polymerized (reversibly) first followed by insertion of norbornene to form AB
162
alternating copolymers. 8,19 However, this possibility was ruled out in our system via addition of
polyA to B. To a polyA (25 equiv) initiated by 1, addition of B (25 equiv) was subsequently
followed. However, even after 5 days, trans-poly[A-alt-B] formation was not observed. Therefore,
sequence editing is not a competitive pathway on the time scale of in a copolymerization system
of A/B/1.
B. Determination of Rate Constants for trans-poly[A-alt-B] in Various Solvents
In order to compare the copolymerization reactivity of 1, rates were followed in various
solvents. Since A reacts with a MB (M is the metal and B is the last inserted monomer) to form
alternating propagating chain, the rate could be simplified to kobs[A]. The rate could be simplified
to kobs[B] which must equal to kos[A]. However, not all plots fit a perfect first order consumption
of A or B and different data were acquired at different stages during the reactions; kobs values are
used for comparisons. Consumption of [A] and [B] were measured versus an internal standard by
'H NMR spectroscopy (Scheme 4.7).
rate = k[MB][A]
F 3C
IL
P
rate = kobs[A]
n
N
C
F3
CF 3
F3
MA
MB
0
F 3C
F3C
0____0_
0K 00,0
rate
=
k[MA][B]
rate
=
kobs[B]
P
1 Mo
n
N
F3 C
F
-K
F 3 C CF 3
FO
/
F 3C CF 3
MB
MA
Scheme 4.7. Kinetic studies of reactions between MB with A and MA with B in a pseudo-first-order regime.
163
Table 4.1. List of
kobs values
of monomer A/B or A'/B' using catalyst 1.
Combinations
Equivalents
of A/B/cat
of A/B/cat
A/B/1
50/50/1
A/B/1
Solvent
Concentration of kbs (A)
kobs (B)
Monomer (M)
(x 105 s-1)
(x 10-5 S-)
CDC1 3
0.12
29
20
50/50/1
THF-d
0.16
3.4
3.3
A'/B'/1
50/50/1
Toluene-d
0.20
23
16
A'/B'/1
100/100/1
Toluene-d
0.20
26
16
A'/B'/2
50/50/1
Toluene-d
0.20
3.1
2.7
In all cases, consumption of A is slightly faster than that of B; the difference can be ascribed
to the formation of AA linkages. When the reaction was carried out in THF, rate constants for both
A and B were ~1 order of magnitude slower than the reaction in chloroform. When the ratio of A
and B was doubled (100/100/1), rate constants for both A and B remained almost the same as those
formed for 50/50/1 ratio. This indicates that rate constants are not highly dependent on the
concentration of the catalyst. As mentioned in Section 4.1 .A, 2 can form >90% trans-poly[A'-altB'], but the rate constants for both A' and B are ~1 order of magnitude slower than rate constants
for consumption of monomers by 1.
C. Kinetic Studies of Alkylidene Rotation for Mo(NAr')(CHCMe2Ph)(OCMe(CF3)2)2
It has been proposed that the rate of interconversion of syn and anti alkylidene isomers can
affect the stereochemistry of the polymer generated. 20 Therefore, in order to determine the origin
of trans selectivity in AB alternating copolymerization, the kinetics of alkylidene rotation was
studied.
N
CF 3
F3CH
0
Ph
hv -350 nm, -78 OC
higher temperature
F3C
N
F3 C
CF 3
0
F3CF3
syn
anti
Scheme 4.8. Anti and syn alkylidene isomers of 1.
164
Ph
Syn and anti alkylidene isomers are distinguished on the basis of values for IJCH coupling
constants. The syn isomer typically shows a IJCH of 110~120 Hz, while the anti isomer shows a
and
140-155 Hz. 2 0 The syn alkylidene has a CHa agostic interaction, which stabilizes it
lowers the coupling constant with respect to the anti isomer. At room temperature,
OR = tM(NAr)(CHCMe2Ph)(OR)2 (NAr = 2,6-diisopropylimido or 2,6-dimethylphenylimido;
butoxide, and partially fluorinated t-butoxide) complexes are mainly syn isomers, but photolysis
'JCH of
at low temperature generates a significant amount of anti isomer. A sample of complex 1 was
photolyzed at 350 nm for 3 h at -78 'C in toluene-d8 and the sample was placed in a 500 MHz
NMR spectrometer at -50 'C. A new peak at 13.02 ppm (IJCH = 156 Hz, 45%) was observed via
'H NMR spectroscopy. This peak was a downfield of syn-1 (12.02 ppm, IJCH = 122 Hz) and was
to
assigned to anti-1. Anti-i decayed back to syn-1 upon warming the sample. The decay of anti-1
was
syn-I was followed at several temperatures over a 15 'C range. The concentration of anti
recorded relative to internal standards. According to ln(co/c) = kt (co = initial concentration of anti,
c = concentration of anti at time t, t = time in seconds), kais (rate constant from anti to syn isomer)
is an
values were obtained from the slope of the respective graphs in Figure 4.4. Since this process
intramolecular process, kais can be obtained from a first-order log plot. A slight curvature from
linearity was observed and the reason is not clear.
2100
1600
1100
W-
,
600
100
0
500
1000
1500
2500
2000
3000
time (s)
-400
90 deg 0
-5 deg @ -10 deg
Figure 4.4. Measurement of ka/s at various temperatures.
165
-15 deg
3500
4000
4500
Table 4.2. Determined rate constants for 1 at various temperatures.
T (*C)
ka/s (s-)
-15
4.25 x 104
-10
9.00 x 10 4
-5
18.0 x 104
0
27.5 x 10 4
Using the above data, values for AH and ASt can be calculated from the Eyring plot (Figure
4.5). AHt was found to be 17.1 kcal/mol from the slope of the graph and ASI was found to be -7.4
eu from the y-intercept. AG'298 at room temperature was found to be 19.3 kcal/mol. From the linear
extrapolation of the Eyring plot, ka/s at room temperature was found to be 0.045 s-. Since Keq (=
ka/s / ks/a) value was determined to be 1400, ks/a at room temperature was calculated to be 3.2 x 105 s-1. ka/s for complex 2 at room temperature is reported to be 0.10 s-I and ks/a is 7 x 10-5 S-1.20 (eq
values for both 1 and 2 was the same but both ka/s and ksia for 1 were half the values formed for 2.
-11
0.0037
-11.5
0.0038
0.00375
0.00385
0.0039
-
0.00365
-12
-12.5
-13
y = -8594.6x + 20.032
R 2 = 0.9906
..
-13.5
1/T
Figure 4.5. Construction of the Eyring Plot for 1.
D. Stoichiometric Reactions of B with Mo(NAr')(CHCMe2Ph)(OCMe(CF3)2)2
There are four possible geometries that result from the reaction of B with 1 (Scheme 4.9).
When B adds to a syn face of the alkylidene (enesyn), syn-MBjs (syn-MB with cis olefin) or synMBtrans (syn-MB with trans olefin) species are formed. However, when B adds to an anti face of
166
the alkylidene (eneanti), anti-MBeis (anti-MB with cis olefin) or anti-MBtran (anti-MB with trans
olefin) species are formed.
Ar'
Ar'
N
N
R
R0
SR
0
R'01, -
MoC
Ar'
N R
A'0
S+Mo
syn, cis or syn, trans
--
R'OI .Mo__
C
R'R0'M
Roz
I_
R'O
0
syn or anti
0
Ar'
Ar'
R'O0
\NO
R
0
B addition to syn face (enesy)
syn or anti
ArI
R',
R'0 01
/11RO
1
= CMe 2 Ph R' 0R' = CMe(CF 3 )2
Ar'
N
Mo
/
R'o:=
0
R =CMe 2Ph
R' = CMe(CF 3 )2
R-00
--
0
0
R
0,
B addition to anti face (eneant)
anti, cis or anti, trans
Scheme 4.9. Four possible geometries from the first insertion product.
The stoichiometric reaction of B with 1 has been studied in order to determine whether the
first insertion product is formed and if so, what isomer is obtained. If 1 can serve a model for MA,
this experiment will give information as to how B reacts with MA in the actual alternating
copolymerization.
When 0.7 - 0.8 equivalents of B were added to a toluene solution of 1 at room temperature,
full consumption of B was observed within 20 minutes by 'H NMR spectroscopy (Figure 4.6).
Two doublets with different coupling constants (3JHH of 3.3 Hz and 7.5 Hz) were observed in the
alkylidene region. In the olefinic region, two sets of peaks were observed as well, both isomers
had cis stereochemistry ( 3JHH = 12 Hz). With the aid of 1H-1H COSY and 'H-'"C HSQC, individual
olefinic peaks were assigned and found to be from two isomers of the first insertion product. Since
the two isomers contain cis olefinic peaks, the two isomers should have a syn,cis or anticis
geometry (Scheme 4.10). Different 3JHH values for syn and anti isomers of the first insertion
product were reported previously, 21 22 due to a different dihedral angle between Ha and Hb by
rotation about Ca-Cb bond. The major isomer ( 3JHH of 3.3 Hz) showed 1JCH = 157 Hz, therefore
smaller 3JHH peak was assigned to be anti-MBcis, whereas the minor isomer ( 3 JHH of 7.5 Hz) was
assigned to be syn-MBci,. At room temperature, two isomers reach equilibrium in the absence of
B and Keq (= [syn-MBis]/[anti-MBis]) was found to be 0.05. Rate constant of interconversion
167
from syn-MB to anti-MB by 1 was measured over time and was found to be 0.00035 s- at 20 *C
in toluene-d8. Note that rate constant of syn-MB' to anti- MB' by 2 in toluene-d8 was found to be
23
0.0003 s-' at 22 0 C, which was measured by Dr. Jeremy John.
Ar'
N
a
\
b
Re
/
RO,,
c
0
0
anti-MB
Hb
Hd
He
He
Ho
syn-1
12.23
12.24
12.20
1214
12.12
syn-MB
12.08
5.50
12.04
5.75s 5.70
5.65
5.60
5.55
5.50
5.45
5.40
5.'35
5.30 5.'25
5.20
5.'15
5.10
5.05
5.00
4.95
4.85
4.90
4.90 4.75
Figure 4.6. 1H NMR spectrum (left, alkylidene region; right, olefinic region) of the first insertion product of
1
with B (500 MHz, toluene-ds).
0
F3Cr
0'
Ph11R'__
I
0
ACF'CF
3
0.
N
NP
F 3C,
Ar'
Ph
Ar'
,
+ R'O..Mo-
m-,,/-hMo
--
R'/
0
R'0#
..,
Tol-d8
3
Ph
R'= CMe(CF 3)2
syn, cis
anti, cis
Scheme 4.10. Two isomers of the first insertion product.
The observation of a cis isomer was surprising because a crystallographically characterized
first insertion product of B with Mo(NAr)(CHCMe3)(O-t-Bu)2 has a syn, trans geometry (Scheme
4.4).16 In our case, clean isolation of the first insertion product was not successful due to multiple
insertion of B as a minor product in the mixture. Indeed, complex 1 could polymerize 50
equivalents of B, as opposed to Mo(NAr)(CHCMe3)(0-t-Bu)2. Polymerization of B was slow
compared to the timescale of alternating copolymerization, where >96% conversion was observed
after 24 hours and an isolated polymer was not stereoregular (Figure 4.38 in Experimental Section).
Syn and anti isomers were shown to exhibit different reactivities in some cases. For
example, 5,6-bistrifluoromethylnorbornadiene (NBDF6) reacts only with anti-2 isomer in a
168
2
oC. O
mixture of syn-2 and anti-2 at -30
3-Methyl-3-phenylcyclopropene (MPCP) reacts only with
a syn isomer of Mo(NAr)(CHCMe2Ph)(pyr)(OTPP) (OTPP
=
2,3,5,6-tetraphenylphenoxide) at
-60 C. 24 Therefore, the reactivity of syn-1 and anti-1 towards B was tested by reacting a mixture
of 55% syn-1 and 45% anti-i at -50 *C.
In a NMR tube, B (0.45 equiv) in a toluene-d8 solution was added to a mixture of syn-1
and anti-i at -78 'C. When the sample was injected to a prechilled -50
0C
'H NMR probe,
complete consumption of anti-1 was observed after 10 minutes. Note that 30% of anti-1 was
0
converted back to syn-1 after 10 minutes at -15 'C, so complete consumption of anti-1 at -50 C
is mainly from the reaction of anti-1 with B. In the alkylidene region, the syn-MBrans isomer of
the first insertion product was formed. Its stereochemistry was consistent with the coupling
constants of the alkylidene and the olefinic protons. When the temperature was raised to -40 'C,
syn-1 started to react with B to form syn-MBeis. At -10 "C, the two alkylidene peaks of syn-MBe1 s
and syn-MBtrans were resolved by 'H NMR spectroscopy. The assignment of both isomers was
elucidated with the aid of 'H-'H COSY. The olefinic 'H NMR spectrum at -10 'C with the
assignment of both isomers was shown in Figure 4.7.
N
R
Ar'
Ar, -
Ar'
o M-b
R1O0
RO
c d0o e
,,
R0
0-
\
I
R9
R
- 1-
0
fh
e
N
/
0O
0
:-ge
090
g
0
/
0Q
syn-MBtrans
syn-M~cis
Hh
He
He
Hg
6.3
6.2
6.1
6.0
5.9
5.8
5.7
Hf
Hd
Hb
Hc
5.6
5.5
5.4
5.3
5.2
5.1
5.0
4.9
4.8
4.7
4.6
4.5
4.4
4.3
4.2
4.1
4.0
3.9
3.E
Figure 4.7. Proton NMR spectrum of a mixture of syn-MBeas and syn-MBrans at -10 OC (500MHz, toluene-ds)
(* is the residual B).
Upon warming up the mixture to 20 'C, both syn-MBeis and syn-MBtrans were converted to
3
anti-MBeis and anti-MBtrans, respectively, and each had a JHH of 3.3 Hz. From the photolysis
169
experiment, the following information can be deducted. First, anti-1 is more reactive toward B
than is syn-1. Secondly, B approaches consistently with its substituents pointing towards the imido
ligand (enesyn) in both syn-1 and anti-1. Third, reaction of B with 1 produced only syn-MB whereas
anti-MB is formed through rotation of the alkylidene. Finally, anti-MB is the more
thermodynamically stable isomer (Scheme 4.11).
NN
RO,,
Ph
0
R
01
00
o
0'
-
'Ar'
Ar'
0\
Ph
syn-MBcis
anti-MBcis
Ar'
Ar'
N
N
Ph1"
0
M'
0
0
11
R-0Ph
Ph
ORh
0
anti-MBtrans
syn-MBtrans
Scheme 4.11. Four possible isomers of B insertion to 1.
E. Reaction of B with in situ Generated Cyclooctene Linkages
Since syn-1 reacts with B to form syn-MBeis instead of syn-MBtrans at room temperature,
syn-1 is not a model for the alkyl-substituted alkylidene formed during the actual copolymerization.
Therefore, efforts has been initiated to form MA linkages in order to investigate how MA reacts
with B. Stoichiometric reaction of A with syn-1 in toluene-d8 did not form a first insertion product.
Rather, polyA is formed with no observable syn-1 consumption because kp is significantly larger
than ki in this system. 4 However, when 15 equivalents of A were added to a THF-d solution of
1, two new alkylidenes each with triplet were observed by 'H NMR spectroscopy after 15 h. One
is formed at 13.49 ppm (3JHH = 9 Hz), and the other is formed at 13.07 ppm (3JHH = 7 Hz, IJCH =
125.5 Hz). Based on IJCH values, the downfield one is assigned to anti-MA whereas the upfield
one is assigned to syn-MA alkylidenes. Conversion to MA from 1 was 58% based on the
integration of 'H NMR spectrum (Figure 4.8a). B (0.5 equiv) was added to this mixture of 1 and
MA, and two syn-MB species were observed by 'H NMR spectroscopy. The two syn-MB
resonances were assigned to syn-MBjs and syn-MBtrans (Figure 4.8b). Therefore, syn-MA and antiMA react with B to form syn-MBei, and syn-MBtrans respectively, i.e., B approaches the enesyn face
to both syn-MA and anti-MA.
170
syn-1
syn-MA
anti-MA
(a)
-
anti-i
syn-MBeis and syn-MBtrans
j
(b)
13.8
13,7
13.6
13.5
13.4
13.3
13.2
13.0
13.1
12,9
12.8
12.7
12.6
12.5
12.4
I
12.3
12.2
12.1
12J
Figure 4.8. (a) In situ formation of MA upon reaction of A (15 equiv) with 1 (THF-d8, 500 MHz) (b) Addition
of B (0.5 equiv) to (a) (THF-d8, 500 MHz).
The stoichiometric reaction of B with 1 has been studied in THF-d in order to compare
results in toluene-d8 (Section 4.1 .D). When 1 equivalent of B was added to 1 in THF-d8 at room
temperature, a new alkylidene (26% conversion) was generated and assigned to syn-MBjs (12.38
ppm with 3JHH of 8 Hz) based on 'H NMR spectroscopy. Note that Keq (= syn-1/anti-1) of 1 in
THF-d8 at room temperature was determined to be 37. When a sample of 1 was photolyzed at 350
nm for 3 h at -78 'C in THF-d8 and the sample was placed in a 500 MHz NMR spectrometer at
-50 'C, 21% of anti-I was observed at 13.73 ppm. To this mixture, B (0.2 equiv) was added at
-78 'C and full consumption of B was observed at 10 'C. Syn-MBtrans (12.34 ppm with 3JHH of 8
Hz) was the only isomer formed and rotation to anti isomer was not observed for 30 minutes at
20 'C. Alkylidene rotation from syn-MBtrans to anti-MBtrans (12.46 ppm with 3JHH of 4.5 Hz) was
also observed in THF-d8 at room temperature after 1 day by 'H NMR spectroscopy. Note that the
half-life of rotation of syn-MB to anti-MB in toluene-ds was measure to be approximately 2000 s,
rotation of syn-MB to anti-MB in THF-ds is slower than that in toluene-d8.
F.
Proposed
Mechanism
for
the
Formation
Mo(NAr')(CHCMe2Ph)(OCMe(CF3)2)2
171
of
trans-poly[A-alt-B]
by
Four possible alkylidene species could be present during alternating copolymerization: synMB, anti-MB, syn-MA, and anti-MA. Based on the stoichiometric reaction of 1 with B in both
toluene-d8 or THF-d8 (see Section 4.1 .D and 4.1 .E), only syn-MB is formed from the reaction of
MA with B and anti-MB is formed through the rotation about the Mo=C bond. Therefore, it was
hypothesized that A has to approach eneanti side to syn-MB to form anti-MAtrans linkages in order
to form trans alternating polymer chain. To anti-MAtrans species, B approaches enesyn side to form
a new syn-MBrans species and the catalytic cycle can be repeated. The syn-MB and anti-MA are
proposed to comprise the active propagating species among four possible alkylidene species, and
the proposed mechanism is shown in Scheme 4.12. Formation of exclusive trans linkages in this
system can be attributed to the steric demand of the "big" monomer (B). "Small" monomer (A) is
thought to approach selectively on eneanti side to syn-MB and forms a trans metallacyclobutane
intermediate.
+A
eneanti
0 0
F 3 C,
N
0
,,i 11
0
0
O
F31
(CH 2 )(
F
P
0
,,
N
1
r
(CH2)
0
CF3
''CF3
CF 3
CF 3
synMB
if
0
/
0
\
antMA
enesyn
synMA
antiMB
Scheme 4.12. Proposed mechanism of forming trans-poly[A-alt-Bi by 1 (P = polymer).
When alkylidene species were monitored during the actual copolymerization in toluene-d, or
CDCl 3 , only syn-MB and anti-MB are observed by 1H NMR spectroscopy (Figure 4.9). In these
system, it is thought that reaction of MA with B is faster compared to the reaction of MB with A;
therefore MA is not observed during the reaction. In addition, the rate of rotation of syn-MB to
anti-MB in CDCl 3 or toluene-d is roughly the time scale of the reaction, so that the both species
can be observed. It is also observed that the ratio of syn-MB to anti-MB in CDCl 3 or toluene-d
172
decrease as the reaction progresses. This means that syn-MB dominates when the concentration of
monomer is high, but as the concentration of monomer decreases, more anti-MB is formed through
the rotation of the alkylidene. The reason of why there are two anti-MB species is not clear.
syn-MB
anti-MB
(c)
1265
1255
1245
1235
1215
1225
1205
11.95
1185
1175
Figure 4.9. Alkylidene regions of the 'H NMR spectra (500 MHz) of polymerization of AB by I (A:B:1 =50:50:1)
in Toluene-ds at three different conversions : (a) 48% conversion; (b) 75% conversion; (c) 94% conversion.
Assignment of syn-MB and anti-MB was based on 'JH coupling constants.
When the reaction was followed in THF-d8, syn-MB and one MA (assignment of syn or anti
not determined) are observed as reaction is progressed (Figure 4.10). The reason of why MA can
be observed in THF-d8 could be that MA can be stabilized by the coordination of THF-d to the
metal, and the reaction of MA with B is not much faster than reaction of MB with A. In addition,
rotation of syn-MB to anti-MB is slow in THF, so that anti-MB is not observed during the
timescale of the polymerization.
173
syn-MBtrans
syn-MBc15
(a)
(b)
12.65
12.75
12.85
12.95
12.05
12.15
12.25
12.35
12.45
12.55
Figure 4.10. Alkylidene regions (* = syn-1) of the 'H NMR spectra (500 MHz) of polymerization of AB by I
(A:B:1 = 50:50:1) in THF-d8 at three different conversions : (a) 9% conversion; (b) 15% conversion; (c) 72%
conversion.
II. Variation of Catalysts and Monomers in Alternating Copolymerization
A. Catalyst Variation for Alternating Copolymerization
A-1. Screening of Bisalkoxide Catalysts
The results presented above led us to question whether this new type of selectivity can be
when
achieved
species
bisalkoxide
Since
employed.
are
catalysts
other
(M(NR)(CHCMe2Ph)(OR)2) 1 and 2 have shown superior reactivity, we varied the identity of
imido and alkoxide ligands. All compounds were synthesized according to the literature2 5 except
for 3e and 3f, which are reported in the experimental section.
CF3
F
0''
F3C;'I~
1
Ph
00
SF
3a
F
"
F 3C~
CF
CF
/- Ph
-,,
FC"CA-CF,
3C
N
N
N
FF3
3b
F 3C
0.
FC1
F3C, ,,
F 3 C1,
0
CF
,
3
Ph
00
F 3C'
F3C-11
CF
CF 33
3d
3c
Figure 4.11. Variation of imido and alkoxide ligands in bisalkoxide framework.
174
N
O
-.
CE
CF 3 3
3e
Ph
5
CISF
Ph
6
I
F5
.AC
C 6,F
5
3f
Table 4.3. Summary of alternating copolymerization reactions with various bisalkoxide catalysts.
1
Monomers
Concentration (M)
Time (h)
Conversion (%)
Alt (%)
AB
[A]o=[B]o=0.36
1
95
93
[A]o=[B]o=0.36
4
13
---
[Mo]o = 0.0072
7.5
16
---
47
47
38
[A]o=[B]o=0.36
4
54
82
[Mo]o = 0.0072
7.5
73
80
[A]o=[B]o=0.3
15
58
---
[Mo]o = 0.006
36.5
70
---
[A]o=[B]o=0.1
1
95
90
28
68
---
17a
<2
[Mo]o = 0.0072
3a
3b
3c
3d
AB
AB
AB
A'B'
[Mo]o = 0.002
3e
AB
[A]o=[B]o=0.15
[W]o = 0.0031
3f
AB
[A]o=[B]o=0.17
[Mo]o = 0.0035
a All polymerization were carried out at 22 0C, but 3f at 50 OC. All polymerization were carried out with the ratio of
[A]o/[B]o/[I]o = 50/50/1. The first row is for the comparison.
As shown in Table 4.3, catalysts containing trifluoro-t-butoxide (3a) or perfluoro-tbutoxide ligands (3b) were not as selective or as fast as 1 in forming trans-poly[A-alt-B]. Besides
trans-poly[A-alt-B],polyA was observed by 'H NMR spectroscopy from 3a and 3b. When catalyst
3c was employed as described in Table 4.3, the reaction proceeded slowly and generated
significant amounts of polyA and polyB linkages compared to 1. In addition, new olefinic signals
at 5.2 ppm were observed by the 1H NMR spectroscopy, which could be cis-poly[A-alt-B] linkages
( 3JHH = 8.5 Hz) (Figure 4.12b). Catalyst 3d was tested with A'B' system. The rate of
polymerization in forming polyA'B' is comparable to that of 1, but significant amounts of cispoly[A'-alt-B'] linkages were observed by 'H NMR spectroscopy (3JHH = 10.5 Hz) (Figure 4.12c).
Another catalyst bearing ortho-substituted imido, Mo(NAriP)(CHCMe 2Ph)(OCMe(CF 3)2 )2
(NAr' = 2-isopropylphenylimido),
was tested by Dr. Jeremy John in A'B' system.
Mo(NArPr)(CHCMe 2Ph)(OCMe(CF 3)2)2 is also a fast catalyst but a mixture of cis and transpoly[A'-alt-B'] linkages (28:72) were formed. When tungsten analog of 1 (3e) was employed to a
175
mixture of AB, the generated product mainly contained polyA linkages leaving B monomer intact.
Catalyst 3f also proved to be unreactive in this system, where its conversion was <2% even after
heating the mixture at 50 'C for 12 hours. Portions of the 'H NMR spectra from the aliquot of the
reaction mixture or from the isolated polymers are presented in Figure 4.12.
(a) A/B/3b/7.5h
cis-AB
(b) A/B/3c/36.5h
cis-A B'
(c) A'/B'/3d/lh
5.80
5.70
\
5.60
5.50
5.40
fi (ppm)
5.30
5.20
5.10
5.00
Figure 4.12. Olefinic regions of IH NMR spectra (CDC1 3 , 500 MHz) of polyAB (various initiators and monomers
as indicated). Note that 'H NMR spectra are from reaction aliquots ((a) and (b)) or isolated polymers (c).
A-2. Screening of MAP and Biphen Catalysts
Next, several MAP and biphen-based catalysts were investigated in this study, these
catalysts are shown in Scheme 4.13. Catalysts 4a-4c, and 5a were synthesized according to the
literature procedures, 4,26- 2 8 and 4d was synthesized by Dr. Peter Sues. When Mo(N-tBu)(CHCMe 3)(pyr)(OHMT) (4a) was added to a mixture of A and B, both monomers were
consumed slowly (19% conversion after 16 h), but more cis-polyA linkages were formed than
polyAB formation. Steric demand of OHMT ligand might inhibit consumption of B and forming
polyA. A similar catalyst Mo(NAd)(CHCMe2Ph)(pyr)(OHIPT) is known to form >98% cispolyA. 2 When Mo(NAr')(CHCMe2Ph)(Me2Pyr)(OBr 2Bitet) (4b) (OBr2Bitet = the anion of (R)176
3,3'-Dibromo-2'-(tert-butyldimethylsilyloxy)-5,5',6,6',7,7',8,8'-octahydro- 1,1 '-binaphthyl-2-ol)
employed as catalyst and added to a mixture of A and B, consumption of B is observed mainly
after 2 hours. However, when the polymerization reaction was run for 5 days, formation of transpoly[A-alt-B], polyA, and polyB were observed by 'H NMR spectroscopy (Figure 4.13a). This
result is somewhat surprising because 4b is known to be a cis selective catalyst in ringopening/cross-metathesis reactions 2 8 but trans linkages were observed in AB copolymerization.
Mo(NAr)(CHCMe2Ph)(Me2Pyr)(OCMe(CF3)2) (4c) was tested in both the AB and AB' systems.
This catalyst formed >90% trans-poly[A-alt-B'] and 80% trans-poly[A-alt-B], and its reactivity
was very similar to that of catalyst 2 (Figure 4.13b and 4.13c). This result led us to synthesize other
MAP
catalysts
bearing
smaller
imido
ligand than NAr with the
general
formula
Mo(NR)(CHCMe 2Ph)(Me 2 Pyr)(OCMe(CF3)2)(NR = NAr', NArCF 3 , NAd, and NArPr). However,
synthesis of MAP complexes with these imido ligands were not successful from the reaction of
Mo(NR)(CHCMe2Ph)(Me 2 Pyr)2 with one equivalent of HOCMe(CF3)2 in THF: a mixture of
bisalkoxide,
bispyrrolide,
and
MAP
species
formed.26
was
When
W(O)(CHCMe2Ph)(Me2Pyr)(PMe2Ph)(OCMe(CF3)2) (4d) was tested with AB system, formation
of polyA and polyB was observed by 'H NMR spectroscopy but formation of polyAB linkages
was not observed. One biphen catalyst Mo(NAr')(CHCMe2Ph)((S)-OBiphenme) ((S)-OBiphenMe
=
3,3'-di-tert-butyl-5,5',6,6'-tetramethyl-1,1'-biphenyl-2,2'-diolate) (5a) was tested with AB system,
but only polyB linkages were formed even after 17 h. All reaction conditions and results are shown
in Table 4.4.
~N
Mo
0
4a
/
0
PhtBu
-N
W/'MoY
0
Br
TBS
N
Br0/41F
Br
PhMe 2P
0CF3
CF 3
4b
4c
Scheme 4.13. Several MAP catalysts and a biphen catalyst used in this study.
177
\
Mo
/
O
CF 3
4d
tBu
5a
Ph
Table 4.4. Summary of alternating copolymerization reactions with various MAP and biphen catalysts.
4a
Monomers
Concentration (M)
Time
Conversion (%)
Alt (%)
AB
[A]o=[B]o= 0.33
16 h
19
---
5 day
86
21
29 h
62
80
3 h
57
90
24 h
48
---
17 h
6
---
[Mo]o = 0.0067
4b
AB
[A]o=[B]o= 0.17
[Mo]o =0.0033
4c
AB
[A]o=[B]o= 0.20
[Mo]o =0.0040
4c
AB'
[A]o=[B']o= 0.31
[Mo]o = 0.0061
[A]o=[B]o= 0.20
AB
4d
[Mo]o =0.0040
5a
[A]o=[B]o= 0.29
AB
[Mo]o = 0.0057
All polymerization were carried out at 22 0C with the ratio of [A]o/[B]o/[I]o
=
50/50/1.
(a) A/B/4b/5d
A/
(b) A/B/4c/29h
I
(c) A/B'/4c/3h
5.75
5.70
5.65
5.60
5.55
5.50
5.45
5.40
5.35
5.30
5.25
5.20
5.15
5.10
5.05
5.00
4.95
4.
Figure 4.13. Olefinic regions of 1H NMR spectra (CDC 3, 500 MHz) of polyAB (various initiators and monomers
as indicated). Note that 1H NMR spectra are from reaction aliquots (a) or isolated polymers ((b) and (c)).
178
0 FF 08
B. Expansion of Monomer Scope in Alternating Copolymerization
The copolymerization of AB monomers to form trans-poly[A-alt-B] represents a new
microstructure through ROMP, we are interested in extending this selectivity to other AB
monomers. Monomer variation of both A and B type is explored in the following section.
B-1. Monomer Scope in B Type
Several bridge carbon substituted norbornene monomers were copolymerized with
cyclooctene (A) (Scheme 4.14). All monomers were synthesized by Dr. Jeremy John. In all cases,
a stock solution of 1 was added to a mixture of 50 equivalents of B and 50 equivalents of A in
various solvents. The reaction progress was monitored by 'H NMR spectroscopy of the reaction
mixture aliquots (Table 4.5).
Ph
0
/
//0
0
/
0
F F
0
//0
/
/
0
0
?
8
0
0
(R)
B1
F
0-
0-0-.a.
0
0
/
/
O
B2
B3
B4
B5
B6
B7
B8
Scheme 4.14. B-type monomers for alternating ROMP.
Table 4.5. Summary of alternating copolymerization reactions with various B monomers with A.
Monomers
Solvents
Time
Conversion (%)
Alt (%)
AB1
CDCl 3
2h
47
<5
AB 2
Toluene
2 day 18 h
>98
75*
AB 3
C 6 D6
6h
94
94
A'B 3
C6 D 6
6h
87
93
AB 4
C 6 D6
4h
97
93
AB 5
C6 D 6
1.2 h
>98
85*
AB 6
C 6 D6
13 h
>98
90
AB 7
CDC1 3
3 h
52
<5
AB 8
CDC1 3
3 h
66
36
0
All polymerization were carried out at 22 C with the ratio of [A]o/[B]o/[I]o = 5/50/1
due to partial overlap of peaks.
179
*
shows a tentative percentage
When a CDCl 3 solution of 1 was added to a solution of 50 equivalents of each 7-(1phenylethylidene)-2,3-dicarbomethoxynorbomadiene (Bi) and A, polyA was observed leaving
unreacted Bi after 2 hours. Presumably steric bulk on 7-substitution was increased too much to
form alternating copolymer. When (R)-1,1,7-trimethylnorbomene (B2) was partnered with A,
-
formation of polyA was observed predominantly over formation of trans-poly[A-alt-B2] (3 JCH
15.5 Hz) after 2 hours. However, when the reaction mixture was stirred for two days, full
consumption of B2 was observed by 'H NMR spectroscopy. After the usual workup, a white
polymer was isolated and its 'H NMR spectrum showed mainly trans-poly[A-alt-B2] along with
some AA linkages. This result supports the possibility that sterically less hindered monomer A
forms polyA, followed by a ring-opening cross metathesis of B2 with polyA linkages. 7Cyclopentylidene-2,3-dicarbomethoxynorbomadiene (B3) produced >90% trans-poly[A-alt-B3]
or trans-poly[A'-alt-B3] with either A and A' (Figure 4.14a).
7-cyclohexylidene-2,3-
dicarbomethoxynorbomadiene (B4) also formed >90% trans-poly[A-alt-B4] with A (Figure 4.14b).
When a C 6D 6 solution of 1 was added to a mixture of 50 equivalents of 11isopropylidenebenzanorbornadiene (Bs) and 50 equivalents of A, full conversion of both
monomers were observed after 1.2 hours. The isolated polymer showed mainly trans-poly[A-altB5]
linkages (Figure 4.14c), but polyB5 linkages were also observed, presumably due to more
reactive nature of B5 than B. This result is consistent with the fact that polyB5 can be formed using
1 mol% Mo(NAr)(CHCMe 3 )(O-t-Bu)2 initiator 29 whereas only the first insertion product is formed
upon reaction of a stoichiometric amount of B with Mo(NAr)(CHCMe3)(0-t-Bu)2.1
6
When 11-
isopropylidene-tetrafluorobenzonorbornadiene (B6) was employed to the same condition to B5, the
polymerization reaction was slower than reaction with Bs, and the isolated polymer contained
>90% trans-poly[A-alt-B6] linkages (Figure 4.14d).
The
attempted
alternating
copolymerization
of
7-isopropylidene-2,3-
bis((menthyloxy)carbonyl)norbornadiene (B7) with A lead only formation of polyA linkages.
Similarly, when 50 equivalents of 7-isopropylidene-2,3-dicarbodecylnorbornadiene (Bs) and 50
equivalents of A were added to 1, only 36% trans-poly[A-alt-B8] was formed along with
predominant polyA linkages.
180
(a) A/B 3/1/6h
(b) A/B 4 /1/4h
(c) A/Bs/1/1.2h
(d) A/B6/1/13h
.80
5.75
5.70
5.65
5.60
5.55
5.50
5.45
5.40
5.35
5.30
5.25
5.20
5.15
5.10
5.05
5.00
4.95
4.90
4.85
4.8(
Figure 4.14. Olefinic regions of 1H NMR spectra (CDC13, 400 MHz) of polyAB (various B monomers as
indicated). Note that all 'H NMR spectra are from isolated polymers.
B-2. Monomer Scope in A Type
Besides cyclooctene and cycloheptene, several other cyclic monomers were used with B to
form alternating copolymers (Scheme 4.15). 5-Epoxycyclooctene (Ai) was synthesized according
to the literature report 30 while 1,5-cyclooctadiene (A2), cis-cyclodecene (A3), and cyclohexene
(A4) were purchased commercially. All were distilled before use. Reaction conditions are
summarized in Table 4.6.
0
A1
A2
A3
Scheme 4.15. A-type monomers for alternating ROMP.
181
A4
Table 4.6. Summary of alternating copolymerization reactions with various A monomers with B.
Monomers
Concentration (M)
Time
Conversion (%)
Alt (%)
AiB
[A1]o=[B]o= 0.19
14.5 h
>98
93
1h
88
---
3h
70
85
20 h
Full consumption of
82
[Mo]o = 0.0038
A2B
[A1]o=[B]o= 0.14
[Mo]o = 0.0028
A 3B
[A 3]o=[B]o= 0.53
[Mo]o =0.0011
A4B
[A 4]o=1.33, [B]o= 0.27
[Mo]o =0.0053
B observed
All polymerization were carried out at 22 'C with the ratio of [A]o/[B]o/[I]o = 50/50/1 except A 4B where the ratio was
[A]o/[B]o/[I]o = 250/50/1.
When 1 was added to a toluene solution of 50 equivalents of Al and 50 equivalents of B,
both monomers were consumed after 14.5 h according to 'H NMR spectroscopy. The isolated
polymer contained >90% trans-poly[Al-alt-B] linkages (Figure 4.15a). The reaction rate was
slower compared to the formation of trans-poly[A-alt-B] which was finished after 2 hours.
Formation of polyAi at the beginning was not observed, so sequence editing is ruled out in this
system. When A2 was partnered with B, A2 was consumed after 1.5 h, leaving unreacted B behind.
1H NMR olefinic signals of poly[A2-alt-B] and polyA2 overlapped and the resonances were not
sharp enough to determine the ratio of alternating copolymer formation. When A3 and B were
paired as described above in CD 2Cl 2 , 70% conversion after 3 h at room temperature was observed.
The isolated polymer contained 85% trans-poly[A3-alt-B] linkages (Figure 4.15b). No reaction
was observed from A4 (0.16 M, C 6D 6 ) with 14 mol% of 1 by 'H NMR spectroscopy. Therefore,
alternating copolymerization was attempted with 250 equivalents of A4 and 50 equivalents of B in
A4 as the solvent. Full consumption of B was observed after 20 h by 'H NMR spectroscopy. The
isolated polymer contained 80% trans-poly[A4-alt-B] linkages along with A4A4 linkages (Figure
4.15c).
182
(a) A 1/B/1/14.5h
(b) A3 /B/1/3h
(c) A4/B/1/20h
5.75
5.70
5.65
5.60
5.55
5.50
5.45
5.40
5.35
5.30
5.25
5.20
5.15
5.10
5.05
5.00
Figure 4.15. Olefinic regions of 'H NMR spectra ((a) CDCl3, 500 MHz; (b), (c) CDC3, 400 MHz) of polyAB
(various A monomers as indicated). Note that all 'H NMR spectra are from isolated polymers.
CONCLUSIONS
This chapter reports the synthesis of four trans-selective >90% AB alternating copolymers
employing Mo(NAr')(CHCMe2Ph)(OCMe(CF3) 2) 2 (1) as the initiator. The four monomers initially
used
are
2,3-dicarbomethoxy-7-isopropylidenenorbomadiene
spiro[bicyclo[2.2.1]hepta-2,5-diene-2,3-dicarboxylate-7,1'-cyclopropane]
(B),
dimethyl
(B'), cyclooctene (A),
and cycloheptene (A'). Mo(NAr)(CHCMe2Ph)(OCMe(CF 3) 2)2 (2) also forms >90% alternating
copolymer with the combinations of A/B' and A'/B', but combinations with A/B and A'/B yield
80% trans,altpolymers. Kinetic studies using 1 showed that the consumption of A is slightly faster
than that of B. The difference can be ascribed to the formation of AA linkages between B units.
The stoichiometric reaction of 1 with B revealed that the first insertion product was a syn-MB
species, but the more thermodynamically stable anti-MB is produced through alkylidene rotation
over time. It is proposed that the mechanism of alternating copolymerization involves the reaction
of MA with B to give syn-MB and then anti-MA is formed through the reaction of syn-MB with
A to give a trans linkage.
Various other catalysts were synthesized and tested for alternating copolymerization.
Increasing or decreasing the degree of fluorination on the tert-butoxide ligand, i.e. employing
Mo(NAr')(CHCMe2Ph)(OCMe2(CF3))2
and Mo(NAr')(CHCMe2Ph)(OC(CF 3) 3) 2, resulted in a
183
decrease in selectivity for formation of poly-[A-alt-B]. Increasing the size of the alkoxide also
decreases the extent of alternating copolymer formation. Changing the identity of metal from Mo
to W lead to consumption of A, leaving B behind. When ortho-substituted phenylimido initiators
were employed for polymerization of A' and B', high alternating copolymer formation was
observed, but substantially more cis-poly[A'-alt-B'] linkages were produced. Among other types
of catalysts that were screened, we found that Mo(NAr)(CHCMe2Ph)(Me2Pyr)(OCMe(CF 3)2 ) also
forms >90% trans-poly[A-alt-B'] and 80% trans-poly[A-alt-B], which is comparable to the result
observed employing 2.
Various steric or electronic modifications on B were also examined. 7-Cyclopentylidene2,3-dicarbomethoxynorbornadiene
(B3)
and
7-cyclohexylidene-2,3-
dicarbomethoxynorbornadiene (B4) also form >90% trans-poly[A-alt-B] copolymers. Finally, 5epoxycyclooctene, cis-cyclodecene, and cyclohexene also form >80% trans-poly[A-alt-B]
structures.
EXPERIMENTAL
General considerations
All air and moisture sensitive materials were manipulated under a nitrogen atmosphere in a
Vacuum Atmospheres glovebox or on a dual-manifold Schlenk line. All glassware, including
NMR tubes, was dried in an oven prior to use. 'H (500 MHz) and 13C NMR (125 MHz) spectra
were obtained on Varian 500 MHz spectrometers, and 'H (400 MHz), 13C (100.61 MHz), and
19F
(282 MHz) NMR spectra were obtained on Bruker 400 MHz spectrometer. All chemical shifts are
reported in 6 (parts per million), and referenced to residual 'H/1 3 C signals of the deuterated solvent
('H(6) benzene 7.16, chloroform 7.26, tetrahydrofuran 3.58, toluene 2.08;
chloroform 77.16, toluene 20.43; 19F(6) external PhF standard -113.15).
13 C(6)
benzene 128.06,
Low temperature 'H
NMR experiments were conducted on a Varian Inova 500 MHz spectrometer capable of a
temperature range of -100 'C to +150 'C. 'H-'H gCOSY, HSQC, and DEPT NMR experiments
were conducted on a Varian Inova 500 MHz spectrometer. Pentane was washed with H2SO4,
followed by water, and saturated aqueous NaHCO 3, and dried over CaCl2 pellets over at least two
weeks prior to use in the solvent purification system. HPLC grade diethyl ether, toluene,
tetrahydrofuran, pentane, and methylene chloride were sparged with nitrogen and passed through
184
activated alumina. In addition, benzene was passed through a copper catalyst. Organic solvents
were then stored over activated 4 A Linde-type molecular sieves. Deuterated solvents were
degassed and stored over activated 4 A Linde-type molecular sieves. Benzaldehyde was distilled
and stored under nitrogen. 2,3-Dicarbomethoxy-7-isopropylidenenorbomadiene
(B) 3 1 and
(B')1 8, were
dimethylspiro[bicyclo[2.2.1]hepta-2,5-diene-2,3-dicarboxylate-7,1'-cyclopropane
prepared according to published literature procedures. Cyclooctene (95%) (A) was purchased from
Alfa Aesar and distilled before use. Cycloheptene (>96%) (A') was purchased from TCI America
and distilled before use. Cyclodecene (>98.5%) was purchased from Sigma-Aldrich and distilled
before
use.
Mo(NAr')(CHCMe2Ph)(OCMe(CF 3 )2)
2
(1)25
and
Mo(NAr)(CHCMe2Ph)(OCMe(CF3)2)2, (2)32 (NAr'= 2,6-Me2C6H3N; NAr = 2,6-i-Pr2C6H3N) were
prepared according to literature procedures. Unless otherwise noted, all other reagents were
obtained from commercial sources and used as received. ATR-FT-IR spectra were acquired using
a Thermo Scientific Nicolet 6700 FT-IR with a Ge crystal for ATR and are reported in terms of
frequency of absorption (cm- 1). Midwest Microlabs, Inc., and the CENTC Elemental Analysis
Facility at the University of Rochester provided the elemental analysis results.
185
W(NAr')(CHCMe2Ph)(OCMe(CF3)2)2
W(2,6-Me2C6H3N)(CHCMe 2 Ph)(OTf)2(dme)
(3e).
(161.8 mg, 0.196 mmol, 1 equiv) was dissolved in Et20 (-8 mL). The yellow solution was cooled
to -30'C and added to a cold Et20 solution of LiOCMe(CF 3)2 (74 mg, 0.393 mmol, 2 equiv). The
solution was stirred for 2 h and all volatiles were removed in vacuo. The residue was taken up in
pentane and the solution was filtered through a pad of Celite. The solvent was removed in vacuo
to yield a yellow solid (113 mg, yield
W=CH,
2
JWH =
=
72.13%): 1H NMR (500 MHz, C6 D 6) 6 9.035 (s, 1H, syn-
15 Hz, IJCH = 115 Hz), 7.18-7.20 (m, 2H, Ar), 7.03-7.06 (m, 2H, Ar), 6.92-6.93
(m, 4H, Ar), 2.17 (s, 6H), 1.44 (s, 6H), 1.16 (s, 6H);
13 C
NMR (125 MHz, C6 D6 ) 6252.48, 154.41,
150.67, 136.14, 128.47, 128.35, 128.16, 127.97, 127.82, 127.19, 126.37, 125.92, 124.99, 122.71,
81.78, 51.74, 32.04, 18.76, 18.63; '9F NMR (282.3 MHz, C 6D 6) 6-77.62, -77.97. Anal. Calcd for
C 2 6H 2 7 F 12 NO 2 W: Theory C, 39.17; H, 3.41; N, 1.76. Found C, 39.36; H, 3.47; N, 1.89.
9.0
Figure 4.16.
8.5
8.0
7.5
7.0
6.5
6.0
5.5
5.0
4.5
4.0
3.5
3.0
2.5
2.0
1.5
IH NMR spectrum of W(NAr')(CHCMe2Ph)(OCMe(CF3)2)2 (in C6 D6, 500 MHz).
186
1.0
Mo(NAr')(CHCMe2Ph)(OCMe(C6F)2)2
(3f). Mo(NAr')(CHCMe2Ph)(OTf)2(dme) (218.9 mg,
0.298 mmol, 1 equiv) was dissolved in Et20 (~10 mL). The deep orange solution was cooled to
-30 'C and added to a cold Et20 solution of LiOCMe(C6F5)2 (240 mg, 0.625 mmol, 2.1 equiv).
The solution was stirred for 17 h and all volatiles were removed in vacuo. The residue was
extracted with benzene and the solution was filtered through a pad of Celite. Pentane was added
)
and the yellow solid was collected in filtration; yield 177.1 mg (54%): 'H NMR (500 MHz, C6 D6
6 14.43 (s, 1H, syn-Mo=CH, IJCH =120 Hz), 7.24 (d, 2H, Ar), 7.15 (d, 2H, Ar), 7.04 (m, 1H, Ar),
6.88-6.82 (m, 3H, Ar), 2.23 (s, 6H), 2.06 (s, 6H), 1.48 (s, 6H); 13C NMR (125 MHz, C 6D 6) 6276.73,
150.21, 148.58, 145.94, 143.45, 141.98, 139.46, 136.96, 136.01, 126.58, 125.75, 120.89, 120.02,
82.28, 53.37, 32.59, 31.13, 19.27.; '9F NMR (282.3 MHz, C 6D 6) 6-140.27 (dd), -153.81 (t),
-154.64 (t), -161.88 (dtd). Anal. Calcd for C46H2 7F2oNO2Mo: Theory C, 50.15; H, 2.47; N, 1.27.
Found C, 50.40; H, 2.48; N, 1.17.
I
11
11.5
10.5
9.5
8.5
7.5
6.5
5.5
4.5
3.5
2.5
Figure 4.17. 1H NMR spectrum of Mo(NAr')(CHCMe2Ph)(OCMe(C 6 F) 2) 2 (in C6D6, 500 MHz).
187
1.5
Polymerization of trans-poly[A-alt-B] by 1.
CC
C
0
C5=0
o
o
C6
Formation of trans-poly[A-alt-B]. A stock solution of Mo(NAr')(CHCMe2Ph)(OCMe(CF3)2)2
(4.7 mg, 6.6 pmol, 180 ptL) was added to a vigorously stirred solution of 2,3-dicarbomethoxy-7isopropylidenenorbornadiene (B) (81.5 mg, 0.33 mmol) in benzene (0.9 mL) and cyclooctene (A)
(43 pL, 0.33 mmol) was added via syringe. The solution was stirred for 1 h and 30 minutes. At
this point, the conversion was >97% by 'H NMR spectroscopy. Benzaldehyde (~0.2 mL) was
added to quench the polymerization and the mixture was stirred for 1 h. The mixture was poured
into MeOH and the precipitated polymer (107 mg, 0.30 mmol, 91% yield) was isolated by
centrifugation and dried in vacuo overnight: 'H NMR (500 MHz, CDCl3, 20 0C) 6 5.48 (dt,
=
15 and 7 Hz, 2H, H2), 5.27 (dd,
3
JHH =
15.5 and 8 Hz, 2H, H 1), 4.11 (d,
3
JHH
'JHH
= 8 Hz, 2H, H3),
3.75 (s, 6H, H 6), 1.98 (m, 4H, Hio), 1.63 (s, 6H, H 9), 1.30 (m, 8H, Hii and H1 2 ); 13C NMR (125
MHz, CDCl3, 20 C) 6 165.71 (Cs), 141.02 (C 4 ), 133.17 (C 7 or C8), 132.58 (Ci), 128.80 (C 7 or C8),
128.38 (C 2 ), 53.39 (C 3 ), 52.06 (C 6), 32.59 (C1 o), 29.65 (C
1
or C 12), 29.15 (Ci1 or C 12 ), 20.52 (C9).
IR (neat): 2924, 2854, 1721, 1641, 1435, 1323, 1270, 1208, 1133, 1098, 1023, 967 (trans), 919,
777 cm-1.
188
6
9
AA dyads
5.65
5.55
5.35
5.45
5.25
5.15
2 1
7.5
7.0
6.5
6.0
5.5
11,12
3_10
3
5.0
4.5
1
4.0
3.5
3.0
2.5
2.0
1.5
1.0
Figure 4.18. 'H NMR spectrum of trans-poly[A-alt-B] (in CDC13, 500 MHz).
9
6
12
5
1011,12
3
4
7or8
~miin~ininmmms'iinsmim~
-~
170
160
150
140
130
120
110
100
90
80
70
60
Figure 4.19. 13C NMR spectrum of trans-poly[A-alt-BI (in CDC3, 125 MHz).
189
50
40
'Sm
30
20
.1
AIM
*
F2
(ppm)
2-
3-
4-
59
60
7-
8
7
6
5
4
3
2
1
0
F1 (ppm)
Figure 4.20. 1H-'H gCOSY spectrum of trans-poly[A-alt-B] (in CDC3, 500 MHz).
101
99
97
G
95
E
I
93
91
89
4100
3600
3100
2600
2100
1600
Wave Number (cm-1)
Figure 4.21. IR spectrum of trans-poly[A-alt-B] (neat).
190
1100
600
Polymerization of trans-poly[A-alt-B'] by 1.
77/C8
C7 , I
C1CC9 CC11
"02
03
"010
/
n
C4
0
0
C6
Formation of trans-poly[A-alt-B'J. A solution of Mo(NAr')(CHCMe 2 Ph)(OCMe(CF3)2)2 (4.7
mg, 6.6 ptmol) was added to a vigorously stirred solution of dimethylspiro[bicyclo[2.2.1]hepta2,5-diene-2,3-dicarboxylate-7,1'-cyclopropane (B') (82.1 mg, 0.351 mmol) in benzene (0.9 mL).
Cyclooctene (A) (46 pL, 0.351 mmol) was added via syringe and the solution was stirred for 1 h
20 min at room temperature. After 1 h, conversion was 98% (monitored via 1H NMR). The
polymerization was quenched by addition of benzaldehyde (~0.2 mL). The entire mixture was
added to MeOH. The precipitated polymer was isolated by centrifugation and dried in vacuo
overnight (84 mg, 0.24 mmol, 70% yield). 'H NMR (CDCl 3 , 20 0 C) 6 5.32 (dt,
Hz, 2H, H2), 5.20 (dd,
3
JHH =
15 and 9.5 Hz, 2H, HI), 3.73 (s, 3H, H 6), 3.13 (d,
3
3
JHH =
JHH =
15 and 7
9 Hz, 2H,
H 3 ), 1.98 (m, 4H, H 9), 1.30-1.24 (m, 8H, Hio and Hi1), 0.57-0.46 (m, 4H, H8); 13C NMR (CDCl3,
20 'C) 6 165.8 (Cs), 141.9 (C 4 ), 133.4 (C 2 ), 129.1 (CI), 57.5 (C 3 ), 52.0 (C6), 32.5 (C 9), 29.6 (Cio
or Cii), 29.1 (Cio or Cii), 15.6 (C 8 ), 7.15 (C 7 ). IR (neat): 2926, 2854, 1721, 1642, 1435, 1323,
.
1206, 1126, 1101, 1098, 1021, 973 (trans), 905, 797, 754 cm-
191
6
C 7, C-1 C-Cg'
C1
03
C2
Cl
C4
0
05-0O
II
0
0
06
5.5
5.35
.5
5.25
5.15
5.05
3
10, 11
9
2 1
8.0
7.5
7.0
6.5
6.0
5.5
8
5.0
4.5
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0.0
Figure 4.22. 1H NMR spectrum of trans-poly[A-alt-B' (in CDC 3 , 500 MHz).
3
9
6
10,11
2
1
5
4
7
8
-
170
160
Figure 4.23.
-
150
~-
m
140
130
120
l- It
110
100
90
80
70
13
60
50
40
30
C NMR spectrum of trans-poly[A-alt-B'I (in CDC13, 125 MHz).
192
20
10
0
-0.5
I LA-
I
F2
(ppm)
3-
4-
5-
3
a
6-
7-
7
6
3
4
5
2
Fl (ppm)
Figure 4.24. 1H- 1H gCOSY spectrum of trans-poly[A-alt-B'i (in CDC3, 500 MHz).
101
99
97
a
93
91
89
3600
3100
1600
2100
2600
Wavenumber (cm-1)
Figure 4.25. IR spectrum of trans-poly[A-alt-B'] (neat).
193
1100
600
*
95
Polymerization of trans-poly[A'-alt-B'] by 1.
7>8
C2
C3
C1
n
C4
0)
C5=0
0
0
C6
Formation
of
of
trans-poly[A'-alt-B'].
A
stock
solution
of
Mo(NAr')(CHCMe2Ph)(OCMe(CF 3)2)2 (6.0 mg, 8.4 !Imol, 229 pL) was added to a vigorously
stirred
solution
of
dimethylspiro[bicyclo[2.2.1]hepta-2,5-diene-2,3-dicarboxylate-7,1'-
cyclopropane (B') (98.5 mg, 0.42 mmol) and cycloheptene (A') (49 pL, 0.42 mmol) in benzene
(0.9 mL). The solution was stirred for 1 h and 50 minutes. At this point, the conversion was
observed >96% by 'H NMR spectroscopy. Benzaldehyde (~0.2 mL) was added to quench the
polymerization and the mixture was stirred for 1 h. The mixture was poured into MeOH and the
precipitated polymer (81 mg, 0.245 mmol, 58% yield) was isolated by centrifugation and dried in
vacuo overnight. 'H NMR (500 MHz, CDCl 3, 20 C) 6 5.34 (dt,
(dd,
3
JHH =
3
JHH =
15 and 7 Hz, 2H, H2), 5.20
15.5 and 9 Hz, 2H, HI), 3.74 (s, 6H, H 6), 3.12 (d, 3 JHH = 9.5 Hz, 2H, H 3), 1.97 (m, 4H,
Hio), 1.36-1.25 (m, 6H, H1o and H, 1 ), 0.56-0.48 (m, 4H, H8); 13C NMR (CDC 3, 20 0C) 6 165.8
(Cs), 141.9 (C4 ), 133.4 (C 2 ), 129.1 (C 1), 57.4 (C3), 52.1 (C 6 ), 32.5 (C9), 29.5 (Cio or C 1 ), 28.7 (Cio
or Cii), 15.6 (C8), 7.17 (C 7 ). IR (neat): 2926, 2853, 1722, 1642, 1435, 1319, 1271, 1206, 1129,
1101, 1074, 1021, 969 (trans), 770 cm-.
194
03
'C2
/
'C1 0
C4
0
C5=0
0
/
6
5.6
5.5
5.4
5.3
52
5.1
8.0
7.5
7.0
6.5
6.0
5.5
5.0
3
4.5
4.0
C6
5.0
2 18
8.5
0
3.5
9
3.0
2.5
2.0
10,11
1.5
1.0
8
0.5
0.0
Figure 4.26. 'H NMR spectrum of trans-poly[A'-alt-B'I (in CDC13, 500 MHz).
6
2 1
9
310,11
5
170
160
Figure 4.27.
150
13C
140
130
120
110
100
90
80
70
60
50
40
30
NMR spectrum of trans-poly[A'-alt-B'l (in CDC13, 125 MHz).
195
20
10
0
-0.5
11I I
JA-
F2
(ppm):-0-
lp
*
A
.
3
2
34
5-
7-
8
91
1010
9
8
7
6
5
4
1
-0
-1
Fl (ppm)
Figure 4.28. 'H- 1H gCOSY spectrum of trans-poly[A'-alt-B'I (in CDC13, 500 MHz).
102
101
100
99
98
97
96
95
94
93
92
4000
3500
3000
1500
2000
2500
Wavenumber (cm-1)
Figure 4.29. IR spectrum of trans-poly[A'-alt-B'] (neat).
196
1000
500
a
Polymerization of trans-poly[A'-alt-B] by 1.
08
C Cn
C3 C CC
C1C12
C4
O
C5=0
0
0
/
\o
C6
Formation of trans-poly[A'-alt-B]. A stock solution of Mo(NAr')(CHCMe2Ph)(OCMe(CF3)2)2
(4.5 mg, 6.4 upmol, 200 pL) was added to a vigorously stirred solution of 2,3-dicarbomethoxy-7isopropylidenenorbornadiene (B) (79.2 mg, 0.32 mmol) and cycloheptene (A') (37 pL, 0.32 mmol)
in benzene (0.9 mL). The solution was stirred for 1 h and 45 minutes. At this point, the conversion
was >98% by 'H NMR spectroscopy. Benzaldehyde (~0.2 mL) was added to quench the
polymerization and the mixture was stirred for 1 h. The mixture was poured into MeOH and the
precipitated polymer (95 mg, 0.28 mmol, 86% yield) was isolated by centrifugation and vacuum
dried overnight. 'H NMR (500 MHz, CDCl 3 , 20 C) 6 5.48 (dt,
5.26 (dd, 3JHH
=
15 and 8 Hz, 2H, HI), 4.11 (d,
3
JHH =
3
JHH =
15.5 and 6.5 Hz, 2H, H 2 ),
7.5 Hz, 2H, H 3), 3.75 (s, 6H, H6 ), 1.97 (m,
4H, Hio), 1.63 (s, 6H, H9), 1.30 (m, 6H, HI 1, H1 2 ); 13C NMR (125 MHz, CDCl 3 , 20 C) 6 165.71
(C 5), 141.03 (C 4 ), 133.16 (C 7 or C8), 132.57 (Ci), 128.87 (C 7 or C8), 128.40 (C 2), 53.41 (C 3 ), 52.07
(C6),
32.58 (Cio), 29.59 (C 1 or C 12), 28.83 (CIi or C 12), 20.54 (C9). IR (neat): 2924, 2853, 1722,
.
1642, 1434, 1324, 1270, 1207, 1134, 1097, 1024, 966 (trans), 919, 775 cm-
197
C9
C8
6
II
C3
C2
C
1
C4
0
C5-0
0
0
polv(cvclohepten e)
C6
e)
9
IF
NO
5.65
v
VI,
5.45
5.55
5.35
5.15
5.25
7.5
7.0
6.0
6.5
5.5
5.0
4.5
11,12
10
3
2
4.0
3.0
3.5
2.5
2.0
1.0
1.5
0.5
Figure 4.30. 1H NMR spectrum of trans-poly[A'-alt-B] (in CDC13, 500 MHz).
9
6
2
1
10
3
5
11 or 12
7 or 8
4
180
170
11 c r 12
150
160
Figure 4.31.
140
130
120
110
100
90
80
13
70
60
50
40
C NMR spectrum of trans-polylA'-alt-Bi (in CDC3, 500 MHz).
198
30
20
10
F2
(ppm)_
*
2
3-
4--
5-
6-
7-
8-
8
7
6
4
5
1
2
3
Fl (ppm)
Figure 4.32. 'H- 1H gCOSY spectrum of trans-poly[A'-alt-Bi (in CDC13, 500 MHz).
102
100
98
96
94
E
VI
92
90
88
86
4000
3500
3000
2000
2500
Wavenumber (cm-1)
1500
Figure 4.33. IR spectrum of trans-poly[A'-alt-B] (neat).
199
1000
500
1'
ROMP of cycloheptene:
A 1 mL C 6D 6 solution of Mo(NAr)(CHCMe2Ph)(OCCH3(CF3)2)2 (15.9 mg, 20.0 pmol) was added
to a rapidly stirred solution of cis-cycloheptene (100 mg, 1.00 mmol) in 4 mL of C 6D6. The
resulting yellow solution that was formed was stirred for 12 h. The polymerization was then
quenched by addition of the solution to stirring MeOH (40 mL). The precipitated polymer was
isolated by centrifugation and vacuum dried. Isolated yield was 50.4 mg or 50.4%. 'H NMR of the
waxy solid showed a 18:82 mixture of cis- and trans-poly(cycloheptene).
cis-poly(cycloheptene):
'H NMR (CDCl 3 , 500.43 MHz, 20 C): 6 5.36 (t, 3 JHH = 4.5 Hz, 2H), 2.03 (bm, 4H), 1.31 (bm,
6H). 13C NMR (CDCl 3 , 125.79 MHz, 20
C): 6 130.00 (=CH), 28.87 (=CHCH2), 27.34
(CH 2CH 2CH2).
trans-poly(cycloheptene):
'H NMR (CDCl 3 , 500.43 MHz, 20 C): 6 5.39 (t, 3 JHH = 4.5 Hz, 2H), 1.97 (bm, 4H), 1.35 (bm,
6H). "C NMR (CDCl 3 , 125.79 MHz, 20
C): 6 130.46 (=CH), 32.74 (=CHCH2), 29.68
(CH 2CH2CH2).
ROMP of cyclooctene:
In a J-Young NMR tube, a 0.2 mL solution of Mo(NAr')(CHCMe2Ph)(OCCH 3(CF 3 )2)2 (2.4 mg,
3.4 pimol) was added to cis-cyclooctene (22 pL, 0.169 mmol) in a 0.4 mL of C 6D 6 . After 1 h, the
complete consumption of monomer was observed, and the polymerization was quenched by
addition of benzaldehyde. The mixture was poured into stirring MeOH (5 mL) and the precipitated
polymer was isolated by centrifugation and vacuum dried (5 mg). IH NMR of the polymer showed
a 20:80 mixture of cis- and trans-poly(cyclooctene).
cis-poly(cyclooctene):
'H NMR (CDCl3, 500 MHz, 20 'C): 6 5.34 (t,
3
JHH =
4.8 Hz, 2H), 2.00 (m, 4H), 1.33 -1.27 (m,
8H). 13C NMR (CDCl 3, 125.79 MHz, 20 'C): 6 130.02 (=CH), 29.90 (=CHCH2), 29.34
(CH 2 CH2CH2), 27.37 (CH 2 CH 2 CH 2 ).
200
trans-poly(cyclooctene):
'H NMR (CDCl3, 500 MHz, 20 'C): 8 5.38 (t, 3 JHH
8H).
13 C
NMR (CDCl3, 125.79 MHz, 20
=
3.4 Hz, 2H), 1.96 (m, 4H), 1.33 -1.27 (m,
C): 6 130.48 (=CH), 32.76 (=CHCH2), 29.79
(CH2CH2CH2), 29.20 (CH2CH 2CH 2).
Comparison of four trans copolymers formed from 1 and that formed from 2
Polymerization reactions employing catalyst 2 were analogous as those of catalyst 1 (vide supra),
but the mixtures were stirred overnight to complete the polymerization.
Comparison of trans-poly(A-alt-B') formed from 1 and that formed from 2
1~
/11 1\~
~
"p1
52
5.
.4
5.4
305. 25 5. 20 5.1 5. 10 '5 5.05 5.0
5.
5.50
5.45
5.40
5.35
5.30
5.25
5.15
5.20
5.10
5.05
5.00
Figure 4.34. Comparison of the olefinic region IH NMR spectrum of trans-poly(A-alt-B') formed from 1 (left)
and 2 (right) in CDC3.
Comparison of trans-poly(A'-alt-B') formed from 1 and that formed from 2
,AJ\j\i
5.50
5.45
5.40
5.35
~A
5.30
5.25
5.20
h'kI\
LI
I
5.15
5.10
5.05
5.50
5.00
5.45
5.40
5.35
5.30
5.25
5.20
5.15
5.10
5.05
5.00
Figure 4.35. Comparison of the olefinic region IH NMR spectrum of trans-poly(A'-alt-B') formed from 1 (left)
and 2 (right) in CDCb.
201
Comparison of trans-poly(A'-alt-B) formed from 1 and that formed from 2
.60
s.55
S.50
S.4S
S.4
5.35
5.30
5.25
S.20
S.S
5.55
5.10
5.45
5.50
5.40
S.35
5.30
5S
5.20
5.10
5.15
Figure 4.36. Comparison of the olefinic region 1H NMR spectrum of trans-poly(A'-alt-B) formed from 1 (left)
and 2 (right) in CDCb.
Comparison of trans-poly(A-alt-B) formed from 1 and that formed from 2
5.55
5
25
5.45
5.20
5.15s
5.5s
5.10
5.50
5.45
5.40
5.3S
S.30
5.2S
S
.20
.S
5.10
.
1
Figure 4.37. Comparison of the olefinic region H NMR spectrum of trans-poly(A-alt-B) formed from 1 (left)
and 2 (right) in CDC 3
Kinetic Studies of Conversion of anti-i to syn-1. Samples were irradiated at 350 nm at -78 'C
in a Rayonet photolysis apparatus in Teflon-stoppered NMR tubes. The sample was kept at -78
'C until it was placed in a 500 MHz 1H NMR spectrometer preequilibrated to -50 'C. Data were
collected over at least 2 half-lives by observing the disappearance of the anti-1 resonance with the
respect to an internal standard (mesitylene or tetramethylsilane).
Observation of anti-MBeis and syn-MBeis by 1
In a J-Young NMR tube, 0.7 equivalents of B (5.7 mg, 23 tmol) were added to a 0.7 mL toluened8 solution of catalyst 1 (22.8 mg, 32 [tmol) at room temperature. After 2 hours, a 'H NMR
spectrum was taken. The major species was anti-MBis and the minor species was syn-MBeis. The
assignment of major olefinic peaks were confirmed by gCOSY and HSQC experiments. The
sample was left in solution for 3 days to reach equilibrium. Keq (= [syn-MBis]/[anti-MBis]) was
found to be 0.05.
202
'H NMR spectrum of alkylidene region:
anti-MBeis
'JHH=
Hz
3.3
syn-1
syn-MBeis
anti-MBBcis
\JHH= 7.5
12.25
12.30
12.15
12.20
12.10
12.05
Hz
12.00
11.95
Photolysis of 1 and addition of B by varying the temperature.
In a Wilmad screw-cap NMR tube, Mo(NAr')(CHCMe2Ph)(OCMe(CF 3)2)2 (32.5 mg, 45.8 ptmol)
was dissolved in 0.6 mL of toluene-d. The sample was closed with a PTFE/silicon septum cap
and irradiated at -78 'C in a Rayonet photolysis apparatus at 350 nm for 3 h. The sample was kept
at -78 'C until it was placed in a 500 MHz NMR spectrometer preequalibrated to -50 *C. 45% of
anti-i was generated.
1H
NMR spectrum of the alkylidene region at -50 'C:
anti-1
1
JCH
.3.7
13.6
13.5
1 34
13.3
13.2
13.1
13 0
1
.9
syn-1
=156 Hz
12.8
12.7
12.6
12.5
12.4
12.3
12.2
12.1
12.0
1CH =
122 Hz
11.9
11.7
11.8
11.6
11.5
11.4
11.2
After observation at -50 'C, the sample was returned to a -78 'C bath and 0.5 equivalents of B
(5.1 mg, 20.5 ptmol) in 0.1 mL of toluene-ds was added via a syringe. The consumption of B was
monitored as the temperature was changed by +10 'C.
203
'H NMR spectrum of the alkylidene region at -40 'C:
syn-1
syn-MBrans
13.6
13.5
134
13.3
13.1
13.2
12.9
13.0
12.6
12.7
12.6
12.5
12.4
12.3
12.2
12.1
12.0
11.9
11.7
11.B
11.6
11.4
11.5
11.3
At -10 'C, both syn-MBtrans and syn-MBeis species are resolved and olefinic peaks were assigned
by gCOSY.
'H NMR spectrum of the alkylidene region at -10 'C:
syn-1
syn-MBrans
syn-MBCi-s
12.15
12.20
12.05
11.90
11.95
12.00
11.85
NMR spectrum of the olefinic region at -10 'C:
Ar'
Ar'
N
N
R'O"o
R'0/
..-
0
0
d
R'0 11
R'O/
e
204
h
e.
-
0
0
0\s
Syn-MBcis
\
-
/
1H
12.10
0
0,
Syn-MBtrans
Hh
He
He
Hf
Hd
Hg
He
Hb
6.3
6.2
6.0
6.1
5.9
5.8
5.7
5.6
5.5
5.4
5.3
5.2
5.0
5.1
4.9
4.8
4.7
4.G
4.5
4.4
4.3
4.2
4.1
4.0
3.9
3.A
'H-'H gCOSY spectrum of the olefinic region at -10 'C:
F2
(ppm)
0
4.4
-
4.2
4.6
4.8
5.0
5.2
5.4
5.6-
5.8
6.0
6.0
5.8
5.6
5.4
5.2
5.0
4.8
4.6
4.4
4.2
4.0
Fl (Ppm)
'H- 1 H gCOSY spectrum of the olefinic region of syn-MBe1 s and syn-MBtran at -10 'C
205
Rate of interconversion of syn-MB to anti-MB by 1 in toluene-d8.
In a Wilmad screw-cap NMR tube, Mo(NAr')(CHCMe2Ph)(OCMe(CF3)2)2 (16.1 mg, 22.7 pmol)
was dissolved in 0.5 mL of toluene-d8. The sample was closed with a PTFE/silicon septum cap
and irradiated at -78 'C in a Rayonet photolysis apparatus at 350 nm for 3 h. The sample was kept
at -78 'C until it was placed in a 500 MHz NMR spectrometer preequalibrated to -50 'C. The
generation of anti-1 along with syn-1 was observed at -50 'C, the sample was returned to a -78
'C bath and 0.45 equivalents of B (2.5 mg, 10.2 pmol) in 0.1 mL of toluene-d8 was added via a
syringe. Temperature was raised to 20 'C and interconversion from syn-MB to anti-MB was
monitored over 2 half lives.
ln([syn-MB])
Time (s)
207
-1.436
507
807
1107
1407
1707
2007
2307
2607
2907
3207
3507
3807
4107
-1.498
-1.609
-1.748
-1.925
-2.018
-2.176
-2.274
-2.355
-2.477
-2.549
-2.580
-2.655
-2.733
0.000
-0.500
-1.000
y = -0.00035x - 1.39004
R = 0.98051
-1.500
-2.000
Ti---...
-2.500
-3.000
Time (s)
Slope (kobs) = 3.5 x 10-4 s-1
206
-9.....
Polymerization of B by 1.
In a J-Young NMR tube, Mo(NAr')(CHCMe 2Ph)(OCMe(CF3)2)2 (1.15 mg, 1.6 pmol) was added
to B (20.1 mg, 0.081 mmol) in a 0.5 mL of toluene-d. After 24h, >96% consumption of monomer
was observed, and the polymerization was quenched by addition of benzaldehyde. The mixture
was poured into stirring MeOH (5 mL) and the precipitated polymer was isolated by centrifugation
and vacuum dried.
7.5
7.0
6.5
6.0
5.5
5.0
4.5
4.0
3.5
Figure 4.38. 'H NMR spectrum of polyB formed from
3.0
2.5
2.0
1.5
1 (in CDC3, 500 MHz).
207
1.0
Rate of consumption of A and B by 1 in CDCb.
In a J-Young NMR tube, 50 equivalents of B (0.102 mmol, 25.4 mg) and 50 equivalents of A
(0.102 mmol, 13 ptL) in 0.85 mL of chloroform-d were added and consumption of each monomer
were monitored over 2 half lives.
Time (s)
ln([A]/[A]o)
ln([B]/[B]o)
1392
-1.111
-0.743
1650
-1.245
-0.830
1906
-1.310
-0.913
2162
-1.409
-0.975
2508
-1.551
-1.068
2718
-1.608
-1.107
3027
-1.715
-1.178
3452
-1.833
-1.257
4142
-2.010
-1.363
5260
-2.234
-1.502
0.000
0
1000
2000
4000
3000
5000
6000
-0.500
-1.000
y = -0.00029x - 0.77812
R2 = 0.98133
1.500
-2.000
0
-2.500
Time (s)
Slope (kobs)
=
2.9 x 10-4 s-
208
0.000
-0.200
0
1000
2000
3000
4000
5000
6000
-0.400
-0.600
-0.800
y = -0.00020x - 0.54117
R2 = 0.96654
-1.000
C
-1.200
-1.400
-1.600
-1.800
Time (s)
Slope (kobs)
=
2.0 x 10-4 s-1
Rate of consumption of A' and B' by 1 in toluene-ds.
In a J-Young NMR tube, 50 equivalents of B' (0.119 mmol, 27.8 mg) and 50 equivalents of A'
(0.119 mmol, 14 pL) in 0.6 mL of toluene-d8 were added and consumption of each monomer were
monitored over 2 half lives.
Time (s)
ln([A']/[A']o)
ln([B']/[B']o)
1336
-0.905
-0.676
1667
-1.015
-0.758
1937
-1.105
-0.827
2237
-1.174
-0.861
2569
-1.264
-0.933
2887
-1.355
-0.994
3203
-1.433
-1.061
3507
-1.517
-1.092
3873
-1.604
-1.153
4245
-1.697
-1.208
4624
-1.740
-1.240
5048
-1.861
-1.333
5480
-1.943
-1.394
5894
-2.022
-1.450
209
6342
-2.117
-1.502
6758
-2.184
-1.553
7220
-2.226
-1.608
0.000
0
2000
1000
3000
4000
6000
5000
7000
8000
-0.500
0
' -1.000
y = -0.00023x - 0.67869
R2 = 0.99043
-1.500
-2.000
0
-2.500
Time (s)
Slope (kobs) = 2.3
x
10-4 S-
0.000
-0.200
0
1000
2000
3000
4000
5000
6000
7000
8000
-0.400
-0.600
b
0
-0.800
-1.000
y = -0.00016x - 0.52504
R2 = 0.99202
-1.200
-1.400
-1.600
-1.800
Time (s)
Slope (kobs) = 1.6 x 10-4s-1
210
Rate of consumption of A and B by 1 in THF-d8.
In a J-Young NMR tube, 50 equivalents of B (0.0987 mmol, 24.5 mg) and 50 equivalents of A
(0.0987 mmol, 13 pL) in 0.6 mL of THF-d8 were added and consumption of each monomer were
monitored over 3 half lives.
ln([A]/[A]o)
Time (s)
ln([B]/[B]o)
463
0.000
0.000
1104
2287
9256
-0.035
-0.037
-0.346
-0.030
-0.151
-0.373
13487
21060
29340
-0.456
-0.671
-1.012
-0.470
-0.726
-0.990
0.000
0
5000
10000
15000
20000
25000
-0.200
-0.400
-0.600
C
-0.800
-1.000
-1.200
y = -0.000034x + 0.01321
R2 = 0.994844
Time (s)
Slope (kobs) = 3.4 x 10-5 s-'
211
30 )00
35000
0.000
0
5000
10000
15000
25000
20000
-0.200
-0.400
co
-0.600
-0.800
y = -0.000033x - 0.02523
R2 = 0.991656
-1.000
-1.200
Time (s)
Slope
(kobs)=
3.3 x 10- s-1
212
30000
35000
Polymerization of trans-poly[A-alt-B31 by 1.
011
03
02
012
n
C4
05=0
0
0
0
C6
Formation of trans-poly[A-alt-B31. A stock solution of Mo(NAr')(CHCMe2Ph)(OCMe(CF3)2)2
(1.4 mg, 2.0 pmol) was added to a vigorously stirred solution of 7-cyclopentylidene-2,3dicarbomethoxynorbornadiene (B3) (27.4 mg, 0.10 mmol) and cyclooctene (A) (13 ptL, 0.10
mmol) in C 6 D 6 (0.5 mL). The solution was stirred for 6 h. At this point, the conversion was 94%
by 'H NMR spectroscopy. Benzaldehyde (~0.2 mL) was added to quench the'polymerization and
the mixture was stirred for 1 h. The mixture was poured into MeOH and the precipitated polymer
(29 mg, 0.075 mmol, 76% yield) was isolated by centrifugation and dried in vacuo overnight. 'H
NMR (400 MHz, CDCl3, 20 'C) 6 5.48 (dt,
and 8.4 Hz, 2H, HI), 3.99 (d,
3
JHH =
3
JHH
=14.8 and 7.2 Hz, 2H, H2), 5.20 (dd,
8.4 Hz, 2H, H3 ), 3.74 (s, 6H,
H6),
3
JHH =
15.2
2.19 - 1.98 (m, 8H, H 9 and
Hii), 1.62 (m, 4H, Hio), 1.32 - 1.27 (m, 8H, H1 2 and H13); 13C NMR (100.61 MHz, CDC13, 20 0 C)
6 165.75, 141.29, 140.48, 132.78, 129.96, 127.64, 54.42, 52.01, 32.52, 30.46, 29.67, 29.15, 26.53.
213
5.7
8.0
5.5
5.6
7.5
5.4
5.3
fI (ppm)
6.5
7.0
5.2
I ~
170
160
Figure 4.40.
150
13
140
4.9
5.0
5.5
6.0
Figure 4.39. 1H NMR spectrum
5.1
3.0
2.5
2.0
1.5
40
30
of trans-polyIA-alt-B3] (in CDCI3, 400 MHz).
H
130
3.5
4.5
4.0
fu (ppm)
5.0
~
120
110
100
90
80
Ru ~
70
60
50
C NMR spectrum of trans-polyA-alt-B31 (in CDC3, 100.61 MHz).
214
1.0
Polymerization of trans-poly[A'-alt-B31 by 1.
010
IIC
C7
C2 -
03
C11 CC13
C2
012
n
C4
0
0
C6
Formation of trans-poly[A'-alt-B31. A stock solution of Mo(NAr')(CHCMe2Ph)(OCMe(CF 3)2)2
(1.1 mg, 1.6 pmol) was added to a vigorously stirred solution of 7-cyclopentylidene-2,3dicarbomethoxynorbornadiene (B3) (21.9 mg, 0.080 mmol) and cycloheptene (A') (9.3 pL, 0.080
mmol) in C 6D 6 (0.4 mL). The solution was stirred for 6 h. At this point, the conversion was 87%
by 'H NMR spectroscopy. Benzaldehyde (~0.2 mL) was added to quench the polymerization and
the mixture was stirred for 1 h. The mixture was poured into MeOH and the precipitated polymer
(21 mg, 0.057 mmol, 71% yield) was isolated by centrifugation and dried in vacuo overnight. 'H
NMR (400 MHz, CDCl 3, 20 'C) 6 5.49 (dt,
and 8.4 Hz, 2H, HI), 3.98 (d,
3
JHH =
3
JHH =
14.8 and 6.8 Hz, 2H, H2), 5.20 (dd,
3
JHH =
14.8
8Hz, 2H, H 3 ), 3.75 (s, 6H, H6), 2.19 - 1.98 (m, 8H, H9 and
H11 ), 1.62 (m, 4H, Hio), 1.32 (m, 6H, H 12 and H1 3 );
13
C NMR (100.61 MHz, CDCl3, 20 'C) 6
165.75, 141.29, 140.55, 132.79, 129.93, 127.64, 54.43, 52.03, 32.51, 30.48, 29.61, 28.85, 26.54.
215
A~x
__
5.8
5.7
5.6
5.5
5.4
5.3
f1 (ppm)
_
5.2
5.1
5.0
_
8.0
7.5
7.0
6.5
4.9
4.8
I
_
6.0
5.5
5.0
4.5
4.0
fI (ppm)
3.5
3.0
2.5
2.0
1.5
1.0
Figure 4.41. 1H NMR spectrum of trans-poly[A'-alt-B3] (in CDC3, 400 MHz).
h1
I
170
160
150
140
130
~r IA
s~
120
110
100
90
80
70
60
50
Figure 4.42. "C NMR spectrum of trans-poly[A'-alt-B3] (in CDC 3, 100.61 MHz).
216
40
30
~u
20
Polymerization of trans-poly[A-alt-B41 by 1.
011
C10
II
C8C
11
0T7 ,-0,-. C12
C3
C2
/
-C14
C13
n
C4
O
0
C5=0
o
050
C6
Formation of trans-poly[A-alt-B4]. A stock solution of Mo(NAr')(CHCMe2Ph)(OCMe(CF3)2)2
(1.4 mg, 2.0 pmol) was added to a vigorously stirred solution of 7-cyclohexylidene-2,3dicarbomethoxynorbomadiene (B4) (63.6 mg, 0.221 mmol) and cyclooctene (A) (28.7 pL, 0.221
mmol) in C 6D 6 (1.1 mL). The solution was stirred for 4 h. At this point, the conversion was 97%
by 'H NMR spectroscopy. Benzaldehyde (~0.2 mL) was added to quench the polymerization and
the mixture was stirred for 1 h. The mixture was poured into MeOH and the precipitated polymer
(77 mg, 0.193 mmol, 88% yield) was isolated by centrifugation and dried in vacuo overnight. 'H
NMR (400 MHz, CDCl3, 20 'C)
and 7.6 Hz, 2H, HI), 4.14 (d,
H12),
3
5.48 (dt,
JHH =
3JHH =
15.2 and 6.8 Hz, 2H, H2), 5.30 (dd,
3
JHH
=15.2
7.6 Hz, 2H, H 3), 3.74 (s, 6H, H 6), 2.11 - 1.94 (m, 8H, H9 and
1.54 - 1.25 (m, 14H, Hio, Hii, H13, H14);
13C
NMR (100.61 MHz, CDCl3, 20 C) 6 165.73,
140.94, 136.61, 132.13, 129.87, 129.05, 52.62, 52.01, 32.58, 30.95, 29.64, 29.13, 27.67, 26.61.
217
5.7
8.0
5.6
5.5
5.4
5.3
5.2
5.1
5.0
7.5
7.0
6.5
6.0
5.5
5.0
4.5
4.0
3.5
3.0
2.5
2.0
1.5
1.0
40
30
20
Figure 4.43. 1H NMR spectrum of trans-poly[A-alt-B4] (in CDC3, 400 MHz).
170
160
150
140
130
120
110
100
90
80
70
60
50
Figure 4.44. 3C NMR spectrum of trans-poly[A-alt-B4] (in CDC1 3 , 100.61 MHz).
218
Polymerization of trans-poly[A-alt-B6] by 1.
08
C CC
30
2
11
04
F
C5-F
F
C6
F
Formation of trans-poly[A-alt-B6]. A stock solution of Mo(NAr')(CHCMe2Ph)(OCMe(CF3)2)2
(5.0 mg, 7.1
pmol) was added to a vigorously stirred solution of 11-isopropylidene-
tetrafluorobenzanorbornadiene (B6) (90.3 mg, 0.355 mmol) and cyclooctene (A) (46.3 pL, 0.355
mmol) in C 6 D 6 (1.6 mL). The solution was stirred for 13 h. At this point, the conversion was >98%
by 1H NMR spectroscopy. Benzaldehyde (~0.2 mL) was added to quench the polymerization and
the mixture was stirred for 1 h. The mixture was poured into MeOH and the precipitated polymer
(107 mg, 0.294 mmol, 83% yield) was isolated by centrifugation and dried in vacuo overnight. 'H
NMR (400 MHz, CDCl 3, 20 C) 6 5.49 (dt, 3JHH = 15.6 and 6.4 Hz, 2H, H2), 5.34 (dd, 3JHH
1.25 (m, 8H, HII and
H12);
=
6.8Hz, 2H, H 3), 1.97 (m, 4H, Hio), 1.74 (s, 6H, H9), 1.32
-
and 7.2 Hz, 2H, H 1 ), 4.49 (d, 3JHH
15.2
'9F NMR (282.3 MHz, C 6D 6) 6 -144.45 ( d), -150.26( d).
13 C
NMR
(100.61 MHz, CDCl 3 , 20 'C) 6 144.93, 142.50 (d, IJCF = 245 Hz), 141.14, 138.60 (d, IJCF = 256
Hz), 134.72, 131.61, 129.38, 128.68, 127.48, 49.15, 32.42, 29.52, 29.07, 20.77.
219
5.5
5.6
7.5
7.0
5.4
5.5
6.0
6.5
5.3
5.2
5.1
4.5
5.0
4.0
fl (ppm)
5.0
3.5
2.0
2.5
3.0
1.0
1.5
Figure 4.45. 'H NMR spectrum of trans-poly[A-alt-B61 (in CDC13, 400 MHz).
145
135
Figure 4.46.
3
1C
125
115
105
95
90
85 80
fi (ppm)
75
70
65
60
55
50
45
40
35
NMR spectrum of trans-poly[A-alt-B] (in CDC3, 100.61 MHz).
220
30
25
20
15
Polymerization of trans-poly[Ai-alt-BJ by 1.
080
03
0C2
C11-
---
/
-04
0
n
C5-0
o
o
C6
Formation of trans-poly[Ai-alt-B]. A stock solution of Mo(NAr')(CHCMe 2Ph)(OCMe(CF3)2)2
(2.5 mg, 3.5 pmol) was added to a vigorously stirred solution of 2,3-dicarbomethoxy-7isopropylidenenorbornadiene (B) (42.8 mg, 0.172 mmol) and cis-5-epoxycyclooctene (Ai) (21.4
mg, 0.172 mmol) in toluene (0.9 mL). The solution was stirred for 14.5 h. At this point, the
conversion was >98% by 'H NMR spectroscopy. Benzaldehyde (~0.2 mL) was added to quench
the polymerization and the mixture was stirred for 1 h. The mixture was poured into MeOH and
the precipitated polymer (54 mg, 0.145 mmol, 84% yield) was isolated by centrifugation and dried
in vacuo overnight. 'H NMR (500 MHz, CDCl 3, 20 C) 6 5.55 - 5.52 (m, 2H, H2), 5.34 (dd,
=
15 and 8 Hz, 2H, HI), 4.11 (d,
3
JHH
=
7.5Hz, 2H, H 3 ), 3.73 (s, 6H, H9), 2.90 (s, 2H,
(m, 4H, H1o), 1.62 - 1.52 (m, 1OH, H9 and H11);
13 C
H12),
3
JHH
2.19
NMR (125 MHz, CDCl 3 , 20 0 C) 6 165.52
(C 5), 140.89 (C 4 ), 132.67, 131.69, 130.52, 130.02, 129.30, 128.77, 57.27 (C 12 ), 55.89, 53.84 (C 3 ),
52.67 (C 6), 51.50, 50.34, 30.63, 29.58, 27.92, 26.94, 20.20, 19.99.
221
5.4
6.0
6.5
7.0
7.5
5.5
5.6
5.7
5.3
5.5
5.2
5.1
5.0
4.5
3.5
4.0
3.0
1.0
1.5
2.0
2.5
Figure 4.47. 1H NMR spectrum of trans-poly[Ai-alt-B] (in CDC3, 500 MHz).
-
L Ill. 1170
160
Figure 4.48.
1;0
13
140
130
120
110
100
90
80
70
60
50
40
C NMR spectrum of trans-poly[Ai-alt-B] (in CDC13, 125 MHz).
222
30
20
10
Polymerization of trans-poly[A3-alt-B] by 1.
C8
C7C -C,
- C/
C4
o
-C-C1o C-C12
03 C2
011
013
n
n
C5=0
0
0
C6
Formation of trans-poly[A3-alt-B]. A stock solution of Mo(NAr')(CHCMe2Ph)(OCMe(CF 3)2)2
(3.1 mg, 4.4 pmol) was added to a vigorously stirred solution of 2,3-dicarbomethoxy-7isopropylidenenorbornadiene (B) (53.5 mg, 0.215 mmol) and cis-cyclodecene (A3) (34 pL, 0.215
mmol) in CD 2 Cl 2 (0.41 mL). The solution was stirred for 3 h. At this point, the conversion was
70% by 1H NMR spectroscopy. Benzaldehyde (~0.2 mL) was added to quench the polymerization
and the mixture was stirred for 1 h. The mixture was poured into MeOH and the precipitated
polymer (55 mg, 0.142 mmol, 66% yield) was isolated by centrifugation and dried in vacuo
overnight. 'H NMR (400 MHz, CDCl 3, 20 'C)
(dd,
3
JHH =
15.2 and 8 Hz, 2H, H1), 4.12 (d,
3
5.51 (dt,
JHH =
3
JHH =
15.2 and 6.8 Hz, 2H, H2 ), 5.30
7.6 Hz, 2H, H 3), 3.77 (s, 6H, H6), 1.99 (m, 4H,
Hio), 1.67 (s, 6H, H9), 1.34 - 1.27 (m, 12H, H11, H12 and H1 3 ); 13C NMR (125 MHz, CDC1 3, 20
0C)
6 165.70, 140.01, 133.16, 132.58, 128.73, 128.31, 53.34, 52.03, 32.57, 29.66, 29.64, 29.25,
20.49.
223
5.7
8.0
7.5
5.6
5.5
7.0
6.5
-
A
5.4
5.3
6.0
5.2
5.5
5.1
5.0
5.0
4.5
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
Figure 4.49. 'H NMR spectrum of trans-polyIA3-alt-B] (in CDC1 3, 400 MHz).
"Mi
170
IIj
.1
PfItIW~
160
Figure 4.50.
150
140
130
a
120
110
100
90
80
13
70
60
50
C NMR spectrum of trans-poly[A3-alt-B] (in CDC 3 , 125 MHz).
224
Ij
I
40
30
20
0.0
1H
NMR spectra (olefinic regions, CDCLb) of polymers prepared from indicated initiators
.;
S.;o
%.I
5
5
50
4.9 4.
505 L005.60
5 5.05.65
PPM)FL
5.70
$IS -10 .05ti
51 S M$A5A5.%s.34 .25 MC
5.55
5.50
5.45
5.40
5.35
AB/7.5 h
5.75
5.70
5.5
5.60
5.55
5.5
5.45
ft
5.40 535
(Pm)
5.30
5.25
5.0
5.15
5.10
5.05
50
5.90
S.75 5.70 5.65
5,60 5-55
5.50
5.55
5.50
5.45
5.40 535
.0
50
.0
49
5.45 5.40 5.35 5.30 5.25
5.20
1.15
5.10 5.05 5.W0
AB/16 h
_______A'
/
5.60
51
Mo(N-t-Bu)(CHCMe3)(pyr)(OHMT) (4a)
AB/28 h
5.65
5.20
AB'/2h
W(NAr')(CHCMe2Ph)(OCMe(CF3)2)2 (3e)
5.70
5.25
Mo(NArCF 3)(CHCMe 2 Ph)(OCMe(CF 3 ) 2) 2 (3d)
Mo(NAr')(CHCMe 2Ph)(OCMe2(CF3))2 (3a)
5.80
5.30
.
and monomers:
5.30
5.25
5.20
5.15
5.10
5.80
5.05 5.00
W(O)(CHCMe 2Ph)(Me 2Pyr)(PMe 2Ph)(OCMe(CF3)2)
5.75
5.70
5.65
rn
~.1
5.60 5.55
5.50 5.45 5.40
225
125
5.20 5.15
5.10
Mo(NAr')(CHCMe 2Ph)((S)-OBiphenMe)(5a)
AB/12 h
(4d) AB/29 h
535 5.30
5.70
5.65
5.60
5.55
5.50
5.45
5.40 5.35
5.30
5.25
5.20 5.60 5.55 5.50 5.45 5.40 5.35 5.30 5 5 5.20 5.15
Mo(NAr')(CHCMe2Ph)(OCMe(CF 3)2)2 (la)
5.55
5.50
5.45
5.40
5.35
A'B3/6 h
5.30 525
5.20
5.15
5.10
5.70
Mo(NAr')(CHCMe2Ph)(OCMe(CF 3)2) 2 (la)
5.65 5.60
5.55 5.50
5.60
5.55
5.50
5.45
5.40
5.45
5.40 5.35
5.30
5.25
5.20
Mo(NAr')(CHCMe2Ph)(OCMe(CF 3)2 )2 (la)
AB5/1.2 h
5.65
5.00
Mo(NAr')(CHCMe 2Ph)(OCMe(CF 3 )2 )2 (la)
ABi/2 h
5.60
5.10 5.05
AB7/3 h
5.35
5.30
5.25
5.20
5.15
580
5.75
Mo(NAr')(CHCMe2Ph)(OCMe(CF3)2)2 (la)
5.70 5.65
5.60 5.55
5.50
5.45
540
535
530 5.25
5.20
55
5.10 5.05
Mo(NAr')(CHCMe2Ph)(OCMe(CF 3)2)2 (la)
A2B/1.5 h
AB8/3 h
226
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228
Hyangsoo Jeong
Massachusetts Institute of Technology
Department of Chemistry
77 Massachusetts Avenue, Cambridge, MA 02139
EDUCATION
Massachusetts Institute of Technology, Cambridge, MA
2010 -2015
Ph.D. Candidate in Inorganic Chemistry
Relevant Coursework: Principles of Inorganic Chemistry II & III, Principles of Organometallic
Chemistry, Physical Inorganic Chemistry, Organometallic Compounds in Catalytic Reactions
Korea Advanced Institute of Science and Technology, Daejeon, South Korea
2005 -2010
Bachelor's Degree in Department of Chemistry, Summa Cum Laude
2008
Georgia Institute of Technology, Atlanta, GA
Exchange student in Department of Chemistry and Biochemistry
EXPERIENCE
Massachusetts Institute of Technology, Graduate Research
2010 - Present
Advisor: Prof. Richard R. Schrock
*
*
"
"
Designed catalysts for olefin metathesis using synthetic organometallic techniques
Developed new synthetic routes for olefin metathesis catalysts allowing for less harsh reaction
conditions
Optimized catalyst structure for highly stereoselective and regioselective in ring-opening
metathesis polymerization
Collected and analyzed characterization data including NMR (1 D and 2D), GC/MS, GPC, and Xray crystal structures
Korea Advanced Institute of Science and Technology (KAIST), Undergraduate Research
2009
Advisor: Prof. Youngkyu Do
*
*
Studied and synthesized iridium-based phosphorescent OLED materials using Salen-Al systems
Presented research at Undergraduate Research Participation Program symposium
Korea Institute of Science and Technology (KIST), Undergraduate Research
2008
Advisor: Dr. Young Whan Cho
"
*
Studied alkaline earth metal borohydride compounds for use in hydrogen storage materials
Became proficient in a variety of techniques including ball milling and powder x-ray diffraction
Korea Advanced Institute of Science and Technology (KAIST), Undergraduate Research
Advisor: Prof. Hee Yoon Lee
229
2007
0
Synthesized phenylpyrazole-containing I,4-disubstituted piperazine derivatives
TEACHING EXPERIENCE
MIT, Department of Chemistry
2010-2011
Principles of Chemical Science, Principles of Inorganic Chemistry I. Teaching Assistant
Helped faculty to prepare teaching materials including problem sets and exams. Supervised and
proctored students' exams. Led recitation classes while addressing individual students' questions
and needs.
AWARDS
National Science Scholarships, KAIST (2005 - 2009), Departmental Scholarships, KAIST (2006 - 2009)
PUBLICATIONS AND PRESENTATIONS
Autenrieth, B.; Jeong, H.; Forrest, W. P.; Axtell, J. C.; Ota, A.; Lehr, T.; Buchmeiser, M. R.; Schrock, R.
R. Stereospecific Ring-Opening Metathesis Polymerization (ROMP) of endo-Dicyclopentadiene by
Molybdenum and Tungsten Catalysts Macromolecules 2015, 48, 2480 - 2492.
Jeong, H.; Ng, V. W. L.; Birner, J.; Schrock, R. R. Stereoselective Ring-Opening Metathesis
Polymerization (ROMP) of Methyl-N-(1-phenylethyl)-2-azabicyclo[2.2.1]hept-5-ene-3-carboxylate
by
Molybdenum and Tungsten Initiators Macromolecules 2015, 48, 2006 - 2012.
Jeong, H.; John, J. M.; Schrock, R. R.; Hoveyda, A. H. Synthesis of Alternating trans-AB Copolymers
through Ring-Opening Metathesis Polymerization Initiated by Molybdenum Alkylidenes. J Am. Chem.
Soc. 2015, 137, 2239 - 2242.
Jeong, H.; Synthesis of new Mo/W tert-butylimido metathesis catalysts and their reactivity in Ring-Opening
Metathesis Polymerization (ROMP). Oral Presentation, 2014 Gordon Research Seminar, Newport, July,
2014
Jeong, H.; Synthesis of Mo/W tert-butylimido olefin metathesis catalysts for cis-selective ROMP. Poster
Presentation, 2014 Gordon Research Conference, Newport, July, 2014
Jeong, H.; Synthesis of new Mo/W tert-butylimido metathesis catalysts and their reactivity in Ring-Opening
Metathesis Polymerization (ROMP). Chemistry Student Seminar, Massachusetts Institute of Technology,
April, 2014
Jeong, H.; Kozera, D. J.; Schrock, R. R.; Smith, S. J.; Zhang, J.; Ren, N.; Hillmyer, M. A. Z-selective RingOpening Metathesis Polymerization of 3-Substituted Cyclooctenes by Monoaryloxide Pyrrolide Imido
Alkylidene (MAP) Catalysts of Molybdenum and Tungsten. Organometallics,2013, 32, 4843 - 4850.
Jeong, H.; Axtell, J. C.; Tbr$k, B.; Schrock, R. R.; Mfller, P. Synthesis of Tungsten tert-Butylimido and
Adamantylimido Alkylidene Complexes Employing Pyridinium Chloride As the Acid. Organometallics,
2012, 31, 6522 - 6525.
230
Acknowledgements
Many people have contributed to this thesis during the past five years and obtaining my
degree would not have been possible without them. First, I would like to thank my advisor
Professor Richard Schrock for the opportunity to work in his group. He was always available to
discuss results and I am thankful for all his guidance whenever it was needed. I learned a lot from
him and he definitely helped me to think deeply about any problem. I hope to embody some traits
of his enthusiasm toward chemistry and qualities of work as a chemist. I also would like to thank
my thesis committee chair, Professor Kit Cummins. Discussions with him during annual meetings
were valuable and he has given new insights into my projects. I would thank the rest of the
inorganic faculty, Prof. Lippard, Dinca for classes and Prof. Surendranath for serving as my thesis
committee member. I thank Dr. Jeff Simpson from DCIF and Dr. Peter MUller from X-ray Facility
for their help over the years with characterization and their answers from my occasional pestering
questions. Before MIT, I thank Prof. Hyunjoon Song and Prof. Youngkyu Do at KAIST for classes
and research opportunities and Prof. E. Kent Barefield for organometallic class at Georgia Tech.
Those experiences have led me to be interested in inorganic and organometallic chemistry.
Every Schrock group members has helped me in some ways during my time and I thank
you for a friendly environment to share ideas and chemicals. Alejandro Lichtscheidl was an
awesome office mate in 6-428 and I really enjoyed chemistry discussions with him. He was always
helpful when I had difficult months at the beginning. I owe a big thank you to Erik Townsend who
has been a great friend and also a great English teacher. I thank Laura Gerber for all advice for
every step in graduate school. Graham Dobereiner and Matthew Cain have provided examples of
talented postdocs and I thank them for the help for my third-year proposals and encouragements
when I was in doubt of my projects. I was lucky to work with Jeremy John who showed me hard
work and perseverance. I thank Benjamin Autenrieth for help with polymerization reactions in
Chapter 3 of this thesis. Jonathan Axtell has been a wonderful friend and I appreciate his help,
from opening old valves of liquid nitrogen tank to all our chemistry discussions. My gratitude goes
to Smaranda Marinescu, Victor Ng, Jian Yuan, Dmitry Peryshkov, William Forrest, Peter Sues,
Jonathan Lam, and Jakub Hyvl for their knowledge. Erik Townsend, Jonathan Axtell, Jonathan
Lam, and Jeremy John also deserve special appreciation for reading and editing this thesis.
Outside of the lab, I would like to thank Grace Han, Bon Jun Koo, Sungjae Ha, and Sarah
Lee for being great friends. They have been always available and we shared lots of up and down
moments during graduate school. I really appreciate our friendship and moments when we shared
laughs. Mike Huynh was a great guitar teacher and I enjoyed guitar jamming sessions with him. I
thank Tom Teets of his critiques for my third-year proposals. I thank friends from Korea, Hyejin
Lee and Boram Won, for their keep warm gifts which helped me to survive long winters in Boston.
I would like to thank Yong Seok Choi for his support and love. His cheers have helped me to get
through challenges and I look forward our time together in near future.
Finally, I would like to thank my family for their support and love. They have been a
constant source for me to keep moving forward. My grandparents, mom, dad, younger brother
Seokheon and younger sister Heesoo have supported me for my whole life with unconditional love.
I cannot express how much I am thankful to my parents, Jeomdeok Woo and Hyowoon Jeong for
all the trust you have given me. Lastly, I acknowledge and miss the memories of my grandma.
231