Synthesis and Reactivity of High Oxidation State Tungsten and Molybdenum Olefin
Metathesis Catalysts Bearing New Imido Ligands
By
MASSACHUSETTS INSTITUTE
OF TECHNOLOLOY
Jonathan Clayton Axtell
JUN 24 2015
B.S. (magna cum laude) in Chemistry (2010)
Villanova University, Villanova, PA
LIBRARIES
Submitted to the Department of Chemistry
in Partial Fulfillment of the Requirements for the Degree of
Doctor of Philosophy
at the
of Technology
Institute
Massachusetts
June 2015
C 2015 Massachusetts Institute of Technology. All rights reserved
Signature of Author
Signature redacted
(
Depar tment of Chemistry
May 14, 2015
Certified by
Signature redacted
Richard R. Schrock
Frederick G. Keyes Professor of Chemistry
Thesis Supervisor
Accepted
Signature redactedby_
Robert W. Field
Haslam and Dewey Professor of Chemistry
Chairman, Departmental Committee on Graduate Students
This doctoral thesis has been examined by a Committee of the Department as follows
Signature redacted
7
Psor
Mircea Dinca
Chairman
Signature redacted
Professor Richard R. Schrock
Thesis Supervisor
Signature redactedProfessor Yogesh Surendranath
2
Synthesis and Reactivity of High Oxidation State Tungsten and Molybdenum Olefin
Metathesis Catalysts Bearing New Imido Ligands
By
Jonathan Clayton Axtell
Submitted to the Department of Chemistry on May 14, 2015
in Partial Fulfillment of the Requirements for the
Degree of Doctor of Philosophy in Chemistry
ABSTRACT
-
Chapter 1 details the synthesis of tungsten imidoalkylidene compounds bearing strongly
electron-withdrawing imido ligands. An alternative synthesis involving the treatment of
WCl6 with 4 equivalents of N-trimethylsilyl-substituted anilines and subsequent workup
with 1,2-dimethoxyethane (DME) has been employed to form complexes of the type
W(NAr) 2C12(dme); syntheses employing WO 2C 2(dme) as the tungsten precursor were
unsuccessful. Alkylation with neopentylmagnesium chloride (ClMgNp) and subsequent
treatment with trifluoromethanesulfonic acid (HOTf) affords imidoalkylidene species
W(NAr)(CHCMe 3)(OTf) 2(dme)
(OTf =
trifluoromethanesulfonate);
analogous
neophylidene ([W]CHCMe 2Ph) species could not be made under these conditions.
Treatment of these compounds with two equivalents of LiO(2,6-(CHCPh 2)C6 H 3)-Et 2O
affords the bisaryloxide complexes of the type W(NAr)(CHCMe3 )(OR) 2 . Ring-Opening
Metathesis Polymerization (ROMP) studies using a series of these bisaryloxides show
that rates of ROMP increase as the electron-withdrawing power of the substituents on the
imido ligand increase if steric bulk about the metal center is held constant. A similar
trend between two bisaryloxides is observed for anti-to-syn alkylidene rotation rates at
50*C in toluene-d8 . Difficulties synthesizing bis-pyrrolide complexes of the type
W(NAr)(CHCMe 3)(pyr) 2 precluded their use as catalyst precursors; some MAP species
containing the more sterically encumbering 2,5-dimethylpyrrolide ligand are presented
and the metathesis activity of MAP species bearing the 2,5-dimethylpyrrolide ligand is
discussed.
Chapter 2 introduces Mo and W complexes bearing the current extreme in sterically
bulky imido ligands, the NHIPT (HIPT = 2,6-(2,4,6-iPr 3 CH 2 )CH3 ) ligand, in an effort to
generate all anti alkylidene species. A non-traditional synthetic route is employed in
order to install this ligand first as an anilide, and after subsequent proton transfer, as an
imido ligand to form a mixed imido species of the type M(NHIPT)(N'Bu)(NH'Bu)Cl.
Addition of one equivalent of 2,6-lutidinium chloride, followed by alkylation affords
dialkyl species M(NHIPT)(N'Bu)Np 2 , and treatment with three equivalents of pyridinium
3
chloride yields all anti imidoalkylidene dichloride species as mono-pyridine adducts,
M(NHIPT)(CHCMe 3)C 2(py) (M = Mo, W). General reactivity, including strategies for
removal of the pyridine adduct as well as substitution and metathesis chemistry, are
discussed. ROMP of MPCP (MPCP = 3-methyl-3-phenylcyclopropene) by a Mo-based
MAP species bearing the NHIPT ligand yields predominantly cis,syndiotactic
poly(MPCP) and in the homo-metathesis of 1 -octene yields ~81% cis-7-tetradecene. The
possible source of trans olefinic product is addressed.
Chapter 3 presents the synthesis of the first (1-adamantyl)imido species of tungsten. The
functional equivalent of common bisimido precursors for other Mo/W alkylidene species,
[W(NAd) 2C 2(AdNH 2)1 2, is shown to be a dimer stabilized by hydrogen-bonding
interactions between adamantylamine protons and adjacent chlorides bound to the second
metal of the dimer. Subsequent alkylation with ClMgNp affords the expected dialkyl
species, and treatment with three equivalents of 3,5-lutidinium chloride affords
imidoalkylidene complex W(NAd)(CHCMe 3)(C) 2(lut)2 (lut = 3,5-dimethylpyridine).
The most desirable synthetic route toward monoalkoxide pyrrolide (MAP) species
monochloride
intermediate
proceeds
through
a
monoaryloxide
W(NAd)(CHCMe 3)(Cl)(OAr)(lut) (Ar = 2,6-(2,4,6-Me 3)C6 H3 , 2,6-(2,4,6-'Pr 3)C6 H 3).
Removal of lutidine with B(C6 F5 ) 3 and subsequent treatment with lithium pyrrolide
affords W(NAd)(CHCMe 3 )(pyr)(OAr) (pyr = pyrrolide); 2,5-dimethylpyrrolide analogues
(W(NAd)(CHCMe3 )(Me 2pyr)(OAr) can be accessed via protonolysis by HOAr from
W(NAd)(CHCMe 3 )(Me 2pyr) 2(lut).
Thesis Supervisor: Richard R. Schrock
Title: Frederick G. Keyes Professor of Chemistry
4
TABLE OF CONTENTS
Title Page
1
Signature Page
2
Abstract
3
Table of Contents
5
List of Figures
8
List of Schemes
10
List of Tables
12
List of Charts
12
List of Abbreviations
13
Dedication
15
General Introduction
16
Chapter 1: Synthesis and Reactivity of Tungsten Alkylidene Complexes Bearing
Electron-Withdrawing Imido Ligands
34
Introduction
35
Results and Discussion
35
I. Synthesis of Electron-Withdrawing Bisimido Precursors
35
A. Attempts to synthesize bisimido complexes through traditional methods 36
B. WCl 6 -based synthesis of W(NR) 2C1 2(dme) (R = electron-withdrawing
aryl)
C. Synthesis of W(NR) 2(CH 2CMe 3)2 Complexes
38
38
II. Synthesis of Tungsten Alkylidene Complexes Containing an ElectronWithdrawing Imido Ligand
41
A. Synthesis of Bistriflate Species
41
B. Synthesis of Tungten Bis-Alkoxides
43
C. ROMP Studies of Tungsten Bis-Alkoxides
44
5
D. Study of syn/anti Interconversion Rates of Tungsten Catalysts Bearing
Electron-Withdrawing Imido Ligands
46
E. Synthesis of Bis-Pyrrolide, MAP, and Other Bis-Alkoxide Tungsten
Species
48
Conclusions
51
Experimental
53
References
71
Chapter 2: Synthesis and Reactivity of Molybdenum and Tungsten Alkylidene
Complexes Bearing the 2,6-bis(2,4,6-triisopropylphenyl)phenylimido
Ligand
74
Introduction
75
Results and Discussion
76
I. Synthesis of Molybdenum and Tungsten NHIPT Mixed-Imido Complexes
77
A. Installation of the NHIPT Ligand
77
B. Dialkyl Complexes Bearing the NHIPT Ligand
79
C. Syntheses of Molybdenum and Tungsten Complexes Containing the
NHIPT Ligand
80
II. Preliminary Metathesis Reactions of Molybdenum Species Containing the
NHIPT Ligand
86
Conclusions
89
Experimental
90
References
110
Chapter 3: Synthesis of Tungsten Adamantylimido Alkylidene Species
112
Introduction
113
Results and Discussion
114
I. Synthesis of Adamantylimido Precursors
114
II. Synthesis of Adamantylimido Alkylidene Complexes
116
A. Formation of Adamantylimido Alkylidenes Using Pyridinium Chloride
Salts
116
6
B. Functionalization of Adamantylimido Alkylidene Species
117
C. Attempts to Chemically Remove Lewis Base Adducts
120
D. Synthesis and Reactivity of Adamantylimido Alkylidene Species Bearing
2,5-Dimethylpyrrolide Ligands
122
Conclusions
124
Experimental
126
References
141
Publications/Presentations
143
Acknowledgements
145
7
List of Figures
Figure 0.1: Various applications of olefin metathesis.
Figure 0.2: The four regular microstructures of poly(norbornadiene)-type polymers
generated through ROMP.
Figure 0.3: Overlay of W0 2 Cl 2 samples prepared in lab (purple trace) and purchased
from Sigma Aldrich (red trace). The peak at 1256 cm' indicates a siloxy impurity
reported by Gibson.
Figure 0.4: Generic high oxidation state catalysts and distinct catalyst "generations."
Figure 0.5: Rotational isomers of high oxidation state alkylidene complexes.
Figure 0.6: dn-pr interactions in imido-alkylidene (or oxo-alkylidene) species.
Figure 0.7: Alkylidene rotation is stabilized by the interaction of a metal-based orbital
with a iT-based orbital of the carbene (charge on metal not shown).
Figure 0.8: u-agostic interaction in the syn isomer of an imidoalkylidene complex.
Figure 1.1: Generic Schrock-type metathesis catalyst.
Figure 1.2: Electron-deficient aryl groups chosen as imido ligand targets.
Figure 1.3: Desirable comparison for the isolation of electronic effects of the imido
ligand in metathesis.
Figure 1.4: Variable-temperature 'H NMR spectra of 2d showing fluxional behavior in
solution. At low temperatures in CD 2 C1 2 , aryl and CH 2 resonances broaden (see arrows);
at high temperatures in C7D8 , these peaks sharpen (see inset).
Figure 1.5: Thermal ellipsoid plot of 2d.
Figure 1.6: Solid-state structure of 3a.
Figure 1.7: Solid-state crystal structure of 4a.
Figure 1.8: Trend of enhanced ROMP activity as imido ligand substituents becoming
more electron-withdrawing.
Figure 1.9: Rotational isomerism of the alkylidene ligand in high oxidation state
metathesis catalysts.
8
Figure 1.10: Electron-withdrawing imido ligands stabilize localization of lone pair on
nitrogen during anti-to-syn alkylidene isomerization.
Figure 1.11: 'H NMR spectrum of cis,isotactic poly(DCMNBD) produced by 10.
Individual polymer microstructure regions, are integrated.
Figure 2.1: Syn/anti isomerism for MovI/WvI alkylidene complexes. The syn isomer is
generally favored due to a stabilizing cc-agostic interaction.
Figure 2.2: Concept for sterically enforcing an anti alkylidene.
Figure 2.3: Proposed method for using a terphenylimido ligand to enforce anti
alkylidenes and maintain Z-selectivity in metathesis.
Figure 2.4: Desymmetrization of 1 m, by heating in pyridine to form 2 m..
Figure 2.5: Thermal ellipsoid drawing (50%) of Mo(NHIPT)(N-t-Bu)(CH 2-t-Bu) 2 (4m).
.
Figure 2.6: Interconversion of cis-5 m. and trans-5M. in C6 D6
Figure 2.7: Solid-state structure of anti-6w.
Figure 2.8: Thermal ellipsoid plot of syn-6w.
Figure 2.9: 'H NMR spectrum of product generated from the addition of 2 equivalents of
TMS-Br to 5w. Two new products, both with anti alkylidenes, are generated.
Figure 3.1: a) HMTO and HIPTO ligands, respectively; b) Proposed nature of Zselectivity in catalysts bearing large phenoxides and comparatively small imido ligands.
Figure 3.2: Solid state structure of 1. Hydrogen bonding interactions are proposed to
stabilize this dimer towards dissociation.
Figure 3.3: Solid state structure of 2b.
Figure 3.4: X-ray crystal structure of 3a.
-
Figure 3.5: 3C NMR (left, alkyl region) and 'H NMR (right, olefinic region) spectra of
poly(DCMNBD) generated by 8 in CDC1 3
Figure 3.6: Solid-state structure of 11.
9
List of Schemes
Scheme 0.1: Original report of "olefin disproportionation."
Scheme 0.2: Chauvin Mechanism for olefin metathesis.
Scheme 0.3: Incorrect mechanistic proposals for the olefin metathesis reaction.
Scheme 0.4: Reaction to produce the first well-defined "alkylcarbene" complex.
Scheme 0.5: Synthesis of the first well-defined Group VI alkylidene metathesis catalyst.
Scheme 0.6: Synthesis of imidoalkylidene species via neopentylidyne intermediate.
Scheme 0.7: Alternative tungsten imidoalkylidene synthesis.
Scheme 0.8: Alternative synthesis of molybdenum imidoalkylidenes using
akylation/abstraction strategy.
Scheme 0.9: General synthesis for M(NR)(CHCMe 2R)(OTf) 2(dme) (M = Mo, W; R =
Me, Ph).
Scheme 0.10: Revised synthesis for tungsten oxo-alkylidene precursors.
Scheme 0.11: Proposed nature of Z-selective metathesis by MAP catalysts bearing bulky
phenoxide ligands and small imido ligands.
Scheme 0.12: Nature of syndiotactic polymer microstructure using MAP catalysts.
Scheme 0.13: Borane activation of [W]=O ligand.
Scheme 1.1: Standard synthesis for tungsten-based bisimido species.
Scheme 1.2: N-sulfinylamine synthesis used to install imido ligands on Mo and W.
.
Scheme 1.3: Synthesis of tungsten bisimido species starting from WCl 6
Scheme 1.4: Synthesis of tungsten dineopentyl bisimido species.
Scheme 1.5: Proposed monomer-dimer equilibrium of 2d.
Scheme 1.6: Synthesis of tungsten imidoalkylidene complexes.
Scheme 1.7: Synthesis of tungsten bis-alkoxide catalysts.
10
Scheme 1.8: Generic reaction of metathesis catalyst with ROMP monomer to produce
poly(DCMNBD) (one of four possible polymer microstructures is shown).
Scheme 1.9: Synthesis of bis-alkoxide catalysts.
Scheme 1.10: Synthesis of bis-pyrrolide complexes.
Scheme 1.11: Synthesis of MAP species bearing the ArcI3 imido ligand.
Scheme 1.12: Results of DCMNBD polymerization by initiators 8 and 9.
Scheme 1.13: Synthesis of a bis-terphenoxide by protonolysis.
Scheme 2.1: Synthesis of mixed imido precursor after base-catalyzed proton shuttling.
Scheme 2.2: Addition of "HCl" and subsequent alkylation to generate mixed imido
dineopentyl complexes.
Scheme 2.3: Alkylidene formation to give M(NHIPT)(CHCMe 3)C 2(py), which show
only anti alkylidenes in solution.
Scheme 2.4: Removal of pyridine ligands to generate 4-coordinate imidoalkylidenes 6m.
and 6w.
Scheme 2.5: Syntheses of Mo-based bispyrrolide and MAP adduct species.
Scheme 2.6: Polymerization of MPCP by 8m..
Scheme 2.7: Nature of cis,syndiotactic poly(MPCP) in MAP complexes with large imidc
ligands.
Scheme 2.8: Homometathesis of I -octene by 8 m..
Scheme 3.1: Synthesis of first Wv1 adamantylimido complex.
Scheme 3.2: Synthetic scheme for adamantylimido dialkyl and neopentylidene species o f
tungsten.
Scheme 3.3: Attempted synthesis of bispyrrolide species 4, which maintains both
lutidine adducts from 3a.
Scheme 3.4: Synthesis of mono-chloro, mono-terphenoxide species.
Scheme 3.5: Synthesis of adamantylimido MAP adduct 7.
.
Scheme 3.6: Possible decomposition pathway of 7 under 1 atm C 2H4
11
-
Scheme 3.7: Removal of lutidine adduct from 5 using B(C 6 F5 ) 3
Scheme 3.8: Synthesis of 4-coordinate adamantylimido MAP complex.
Scheme 3.9: Insertion of MeCN into W=C bond of 9.
Scheme 3.10: Synthesis of W(NAd)(CHCMe 3)(Me 2pyr) 2(lut).
Scheme 3.11: Synthesis of lutidine-free MAP species
W(NAd)(CHCMe 3)(Me 2pyr)(OHMT).
List of Tables
.
Table 1.1: Polymerization of DCMNBD with Initiators 4a-h in CDC1 3
List of Charts
Chart 1.1: Measurement of the decay of anti-5 and anti-6 in C7 D8 at -50*C.
12
List of Abbreviations
anti = alkylidene orientation in which the CHR group points away from the imido/oxo
ligand
Ad = 1-adamantyl
Ar = 2,6-iPr2C6 H4
Ar(CF3)2 = 3,5-(CF 3) 2C6 H3
ArBr 3 = 2,4,6-Br3C6 H 2
ArCl 2 CF3
=
2,6-C1 2-4-(CF3)-C6 H2
ArCI 3 = 2,4,6-Cl 3C6 H 2
DCMNBD = 2,3-dicarbomethoxynorbornadiene
DME = 1,2-dimethoxyethane
Et 2O = Diethyl ether
HIPT = 2,6-(2,4,6-'Pr3C6 H 2) 2C6 H3
HMT = 2,6-(2,4,6-Me 3CH 2) 2C6 H 3
)
'Pr = isopropyl (-CH(CH 3) 2
k = rate constant
lut = 3,5-dimethylpyridine
MAP = MonoAlkoxide (Mono)Pyrrolide
)
Me = Methyl (-CH 3
Me 2pyr = 2,5-dimethylpyrrolide
MeCN = CH3CN
Mes = 1,3,5-Trimethylphenyl
Min = Minutes
MPCP = 3-methyl-3-phenylcyclopropene
"JAB = NMR coupling constant of atoms A and B through n number of bonds
)
Np = Neopentyl (-CH 2C(CH3) 3
OTf = Trifluoromethanesulfonate/Triflate
Ph = Phenyl
Py = Pyridine (C 5HN)
)
Pyr = Pyrrolide/Pyrrolyl (-NC 4H 4
RCM = Ring Closing Metathesis
13
ROCM = Ring-Opening Cross-Metathesis
ROMP = Ring-Opening Metathesis Polymerization
Syn = alkylidene orientation in which the CHR group points toward from the imido/oxo
ligand
)
'Bu = Tert-butyl (-C(CH 3)3
THF = Tetrahydrofuran
TMS = Trimethylsilyl/Tetramethylsilane
TRIP = 2,4,6-Triisopropylphenyl
Tol = Toluene
14
This Thesis Is Dedicated to the Life and Memory of
Clayton M. Axtell, III:
Without whose example of hard work and dedication such a degree would not
have been possible.
15
General Introduction
16
Carbon-carbon bond-forming
reactions are some of the most important
transformations in chemistry. Over the past century, much progress has been made in
understanding the intricacies of these reactions, a particular subset of which involves
those that are catalyzed by transition metals.
The olefin metathesis reaction falls into this category and over the past several
decades has seen progress both in the understanding of the mechanism as well as its
application to various areas of chemical and materials science. It was a reaction that was
discovered largely by accident and was first documented in the late 50's and early 60's
by Eleuterio' and first reported in the literature in 1964 independently by Banks and
Bailey 2 and Natta.3 In an effort to develop new catalysts for olefin polymerization, it was
found that passing propylene over MoO 3/A1 20 7 resulted in the disproportionation of the
starting olefin to ethylene and 2-butenes (Scheme 0.1).
MoO 3/A120 7
++
-_
+ other olefins
High T
42
55
3
Scheme 0.1: Original report of "olefin disproportionation."
This observation sparked interest and research in the mechanism of this reaction and the
active species behind this (C=C bond forming) process. Over the next several decades,
several possible mechanisms of this reaction were proposed by Chauvin and others
(Scheme 0.2, Scheme 0.3).4
R
R
M[2+2]
R
'/
R
RI
R'
R'
[M]
[M]=CH 2
Scheme 0.2: Chauvin Mechanism for olefin metathesis.
Chauvin hypothesized that a M=C bond was the reactive fragment that enabled this
transformation.
Species bearing M=C bonds were known at the time, called "Fisher
carbenes,"5 and were later shown to display reactivity 6 similar to systems shows in
Scheme 0.2, but often required cocatalysts
(02,
alkylating agents, etc.) or strained olefins
in the absence of cocatalysts in order to proceed; the carbenes in these complexes were
17
found to be electrophilic versus those in high oxidation state alkylidenes, which bear
nucleophilic character (vide infra).6a,7
A
B
A
[M]
C
D
/
LD
\
[M]_
[M]
A
[M]
_
AB
B__
M__
D
C
C
D
A
B
C
[M]
[MI
B
D
C
___
D
+
D
B
M
A>
A
B
M
B
+
D
B
C
M
+
A
M ' C _D
A
B
A
[M
B
D
C
,I
Scheme 0.3: Incorrect mechanistic proposals for the olefin metathesis reaction.
It was not until 1974 when Schrock showed not only that a different type of species
bearing M=C bonds could be synthesized and isolated but that these compounds, unlike
Fisher carbenes, were competent olefin metathesis catalysts. This discovery lent further
credibility to the mechanism proposed by Chauvin. As shown in Scheme 0.4, treatment of
Np 3TaCl 2 with two equivalents of neopentyllithium resulted not in TaNp 5 but a
decomposition product of this sterically over-crowded molecule through an a-hydrogen
abstraction9 reaction, Np 3Ta(CHCMe 3). The mechanism of this reaction is not clear but it
is likely the metal assists in the activation of the a-hydrogen, which is then formally
removed as a proton.
Subsequent research by Schrock, Grubbs, and others into
complexes of this type culminated in this area of research being the subject of the 2005
Nobel Prize in Chemistry "for the development of the metathesis method in organic
synthesis."'
18
2 LiCH 2CMe
3
- 2 LiCI
TaC
T
11
TaC
2 LiCH 2CMe3
F~
- 2 LiCI
1.
F~
qBu H
Ta
q~uH
Hj
u
>TaA
B
H
Overcrowded
coordination sphere
Scheme 0.4: Reaction to produce the first well-defined "alkylcarbene" complex.
Olefin metathesis has been applied to various areas of chemical and materials
science and takes several different forms, despite the fact that the reaction itself proceeds
through similar intermediates. Examples of these different areas of olefin metathesis are
shown in Figure 0.1.
R'
+
R
[M]
,
R'
R
+
Homo-metathesis (R = R')
Cross-metathesis (R t R
=
)
=1
+
R
[M]
_
R
+
R
Ethenolysis
[M]
Ring-Closing Metathesis
+
R
R
[M]
R
0
Ring-Opening Cross
Metathesis (ROCM)
Figure 0.1: Various applications of olefin metathesis.
19
In the absence of a cross metathesis partner, (poly)cyclic olefins can be polymerized by
ring-opening
metathesis
The four
(ROMP).
polymerization
possible
regular
microstructures based on ROMP of norbornadiene-type monomers are shown in Figure
0.2.
R
R
R
R
R
R
cis,isotactic
R
ts Ring-Opening Metathesis
-n
R
R
R
]
-
trans,syndiotactic
[M]
R
R
R
Polymerization (ROMP)
R
R
R
R
R
R
R
R
"
cissyndiotactic
R
trans,isotactic
Figure 0.2: The four regular microstructures of poly(norbornadiene)-type polymers generated through ROMP.
It was eventually found that Ta-based carbene species were not especially active for
metathesis due in large part to competitive decomposition of metallacyclobutanes via
1-
hydride elimination." Work on high oxidation state olefin metathesis catalyst shifted to
Group VI metals, specifically Mo and W, with the serendipitous discovery of the first
Group VI alkylidene complex, a tungsten oxo complex synthesized by Wengrovius and
Schrock,
12
a
which
formed
Ta(CHCMe 3)C 3(PEt 3)2
and
W(O)(CHCMe 3)C 2(PEt3)2
13
via
a
complex
W(O)(O'Bu) 4
ligand
(Scheme
exchange
0.5)
to
between
generate
Related oxo complexes were synthesized in the same
manner. 2 The mechanism of this reaction is still unknown but the driving force likely
resides in the higher oxophilicity of Tav versus WvT. In order to prevent intermolecular
bridging of oxo ligands and decomposition, the isoelectronic imido substituent was
employed in its place.
20
EtP Et3P,,~
C,
Ta
C1C1
~
''
+
I
'e
_
j.Et3P
.%0~C
,W -%
3P.
'Et
______
0
,*0
C1
PEt3
0.5 [Ta(OtBu) 4C] 2
+
C-W
PEt3
Scheme 0.5: Synthesis of the first well-defined Group VI alkylidene metathesis catalyst.
The first syntheses of Mo- and W-based imidoalkylidene species began from
either
MoO 2 Cl 2
or
W(OMe) 3 C 3 , which
were
treated
with
6
equivalents
of
neopentylmagnesium chloride to afford trineopentyl neopentylidyne species in low yields
(M
4
4
= Mo bc, W1 a)
(Scheme 0.6). Subsequent treatment with HCl in the presence of 1,2-
dimethoxyethane (DME) gave M(CCMe 3)C1 3(dme) (M = Mol 4b, W 4 a).
Addition of
RN(H)TMS followed by NEt3 to induce proton transfer from the amide fragment to the
alkylidyne furnishes the desired imidoalkylidene product (M = Mo 15 , W 16).
-
EMC
R
R
-
R
CI ,.CI
CIs I ''
RNHTMS
.MM
Et 2 0
CI,,II. CI
3 HCI
6 CIMgCH 2CMe 3
Et 20
W(OMe) 3C 3
or MoO 2CI 2
R
N
C,,
.,NH
NEt 3 (cat.)
CL,
C1
I 0
Et 2 0
0<"
CI 1I O
'
3
M
_
CN
'o-I I
0-M
C
00
+ isomers
Scheme 0.6: Synthesis of imidoalkylidene species via neopentylidyne intermediate.
Despite the utility of this synthetic route, so other synthetic pathways were explored.
Treatment of WCl 6 with hexamethyldisiloxane ((SiMe 3) 2 0) to give WOCl4 , followed by
treatment with an arylisocyanate furnishes W(NR)C
4
in good yield." Addition of two
equivalents of LiO'Bu followed by two equivalents of neopentylmagnesium chloride
affords the mixed alkyl-alkoxide imido species. Subsequent treatment with PC 5 in the
presence of DME gives the desired M(NR)(CHCMe 3)C 2(dme) (Scheme 0.7).
21
R
R
0
(SiMe 3 )2 0,
CH 2CI 2
R-NCO
CI, 11, CI
CI ' 'CI
C8H18
N
CI, i1 ICI
2 LiOtBu_
Ci
TH F/Et 20
'*CI
N
C1
NII~CI
0w
OIC
0
R
2 CIMgCH 2CMe 3 _
I
-0 ,,. I
0,
Et 20
.
*
R
PC15
DME
0
01
CI
Scheme 0.7: Alternative tungsten imidoalkylidene synthesis.
An analogous method proceeding through a monoimido species of Mo was
developed by Pilyugina and Schrock, whereby an azide adds to MoIVCl 4(THF)2 to give
M(NR)C1 4(THF) (Scheme
0.8).
18
Alkylation
with neopentylmagnesium
chloride,
followed by treatment with stronger alkylating agent, neopentyllithium, resulted in aabstraction to give Mo(NR)(CHCMe 3)Np 2 , but this method proved not to be general for a
range of desired imido ligands.
Furthermore, both neopentyl ligands could not be
substituted to give more useful catalysts/precursors, so this method was not pursued.
Finally, the synthesis of isocyanates and azides on larges scales are potentially hazardous,
despite their convenience in certain cases shown here.
R
R
3 CIMgCH 2CMe 3
C0 1 'CI
Et20I
Mo
E2
N
MIMo
'
N
CI,. II .Cl
*
MoCI 4(THF) 2
RN 3
CH 2CI 2
C1
R
R
N
N
Mo
LiCH 2CMe 3
C 5 H 12 or C 7H 8
R = 2,6-iPr2C6 H 3 or CPh 3
Scheme 0.8: Alternative synthesis of molybdenum imidoalkylidenes using akylation/abstraction strategy.
The most general strategy that is still currently in use for the synthesis of most
catalysts proceeds through bisimido intermediates (M = Mo19, W17 ):
treatment of
22
Na 2 MoO 4 or W0 2 C 2 (dme) 2 0 with 2 equivalents of RNH 2 yields bisimido complex
M(NR) 2C1 2(dme) (Scheme 0.9). Alkylation with 2 equivalents of ClMgCH 2R' (R' = Me
When treated with trifluoromethanesulfonic acid
or Ph) affords M(NR) 2(CH 2R') 2.
yields the desired
of Et2 O and DME, a-abstraction
(HOTf) in the presence
imidoalkylidene precursors M(NR)(CHR')(OTf) 2(dme).
This bistriflate serves as a
convenient "universal precursor" to catalytically active 14-electron species, which are
accessible via substitution of triflate ligands and loss of DME (vide infra).
R
2RNH 2
xs TMSCI
C1
W0 2C1 2(dme)
xsNEt3
0
Na2MoO4
DME, 80'C
R
R
N
N
-
CF
2CIMgCH 2CMe 2R'
CN
H0
M
- 2 MgCI 2
'
0
R
R'
N
'T
CF 3HO 0_
Et 20/DME
-RNH 30Tf
R
MTf
Scheme 0.9: General synthesis for M(NR)(CHCMe 2R)(OTf) 2(dme) (M = Mo, W; R = Me, Ph).
We recently renewed our interest in employing oxo-alkylidene species as
initiators in olefin metathesis reactions. The original motivation for moving away from
oxo species lay in the likelihood of bimolecular interactions (e.g. bridging oxo ligands),
but with the applicaton of sterically encumbering terphenol-based ligands, 2 1 these species
were more closely examined. W0 2C12(dme), when treated with 2,2'-bipyridine (bipy),
affords W0 2C 2(bipy).22 Subsequent treatment with 3.8 equivalents of ClMgCH2 CMe 2R
(R = Ph or Me) and workup with airand water affords W0 2(CH 2R)2 (bipy).
When this
and
phosphine,
complex
is
charged
with
excess
ZnCl 2(dioxane),
TMSC1,
W(O)(CHR)C 2(PR' 3) 2 is generated in good yield (Scheme 0.10);24 analogous Mo-based
oxo-alkylidene species are not currently known.
It should also be noted that there are some reports of tungsten oxo- and
imidoalkylidene species being synthesized from reduced (W" and W'v) precursors that
involve formal oxidative addition of ketones 25 , imines 25 , strained cyclic olefins 26 , and
These methods did not prove to be general or encountered similar
phosphoranes.
synthetic difficulties as noted above, and were likely not pursued for these reasons.
R
2 TMSCI
ZnCI 2(dioxane),
-
W 21k1U
2,2'-bipy
W0 2C1 2(bipy)
3.7 CIMgCH 2CMe 2R
THF
\
1
N2
N
=O-
R'3P. I __
Toluene, 100*C
/
N
PR'
2______
T"'
SR
C
ci'
-
C PR
3
R
R
=Ph orMe
PR'3 = PPh2Me or PPhMe2
Scheme 0.10: Revised synthesis for tungsten oxo-alkylidene precursors.
23
Worth mention here is the nature of the W-based starting material for the
synthesis of tungsten oxo and imido compounds. Several reports"",8 in the literature exist
for the preparation of W0 2 C1 2 , and it has been noted in our group that the success and
yield of many reactions employing W0 2C1 2, particularly for tungsten imido compounds,
is highly variable, depending on the particular crop of W0 2 C1 2 , which ranges in color
from yellow to gray. It was therefore undertaken to resolve this ambiguity. W0 2 Cl 2 was
synthesized according to Ref. 28b and in comparison to commercially available W0 2C1 2
by IR spectroscopy (and referenced to IR data reported in Ref. 28a), it was found that the
former contained siloxide impurities reported by Gibson2,8 (Figure 0.3). Unfortunately,
scaling up Gibson's synthesis of W0 2 C1 2 past -3 grams was unsuccessful, so from this
point forth W0 2Cl 2 (dme), which has been synthesized previously 20 , has been used as the
starting material, the purity of which can be confirmed by 'H NMR and IR.
100 -w
Axtell
g0Aldrich
75
70-
45
20
10:
0
4000
3500
3000
2500
2000
1500
1000
Wavenumbers (cm-i)
Figure
0.3: Overlay of W0 2C1 2 samples prepared in lab (purple trace) and purchased from Sigma Aldrich (red
trace). The peak at 1256 cm' indicates a siloxy impurity reported by Gibson.
A generic schematic of a "Schrock-type" catalyst, along with notable generations
of these catalysts, is shown in Figure 0.4. Generation I catalysts2 emplo tw
lkoxide
or phenoxide ligands ("bis-alkoxides"), the most well-known of which is likely
24
Mo(NAr)(CHCMe 2R)(OC(CF 3)2Me) 2 (Ar = 2,6-'Pr 2C6 H 3, R = Me 2 9a or Ph 2 9b), whose
reactivity is attributed to the electron-withdrawing nature of the alkoxide.s 3
1c,3O
Generation I catalysts are generally applied in polymer chemistry but have also found use
'
in organic synthesis. 3
R
-R'= Me, Ph
- M = Movi, WvI
x
- R = Oxo or imido
M1
O
0
R
R'
CF 3
R'
N
0
0
Mes
Mes
-
F 3C
R'
ItBu R
/
F 3C ,
XN = Anionic ligand
Generation I
Bis-alkoxide
Generation II
Chiral Diolate
Generation III
Stereogenic-at-Metal
Highly Reactive
Enantioselective
Z-Selective
Figure 0.4: Generic high oxidation state catalysts and distinct catalyst "generations."
Stereo- and enantio-enriched metathesis products became achievable through
Generation II catalysts, which employ a chiral diolate (e.g. binaphtholate, biphenolate)
ligand. Furthermore, highly (cis) isotactic polymers became accessible by employing
these catalysts which direct monomer insertion to the same face of the catalyst upon each
insertion and dictate polymer structure through "enantiomorphic site control."32 Highly
tactic polymers are usually the most sought-after structures as highly regular polymers
often exhibit the most desirable properties 32 (crystallinity, melting point, etc.)
Generation III catalysts employ both a pyrrolide ligand and a phenoxide or
alkoxide ligand, rendering the metal center of these MAP (MonoAlkoxide Pyrrolide)
catalysts chiral. These species often exhibit enhanced reactivity with respect to their bisalkoxide
or alkoxide/alkyl
counterparts.
enhancement is proposed to be twofold:
The nature
of this observed
activity
a) the pyrrolide ligands, as a result of the
nitrogen being more electronegative than carbon, increases the energetic barrier for Phydride elimination, a well-known decomposition pathway for metallacyclobutane
species (vide supra), relative to productive cycloreversion and metathesis; b) the
increased o-donor power of the pyrrolide ligand relative to alkoxides favors the
metathesis pathway along the reaction coordinate. 3 3 Unsubstituted or 2,5-dimethyl-
25
substituted pyrrolides are those most commonly used, but other variations have been
employed within our group.3424a
The use of bulky terphenoxide ligands 21 within the MAP scaffold has given rise to
Z-selective olefin methathesis catalysts. 32s It has been suggested3 6 that the nature of this
Z-selectivity arises as a result of the bulky phenoxide forcing substituents on the
metallacyclobutane intermediate to point towards the comparably smaller imido (or oxo)
ligand (Scheme 0.11); upon productive cycloreversion, Z olefins are generated.
R'
SMALL
G
Rsmall
Rsmal
N
G
I10G R1
==/
[2+2]
N
|
N M.:
4
0
RbigOrM zCH2
[2+2]
U
N
Rbig
BIG
Scheme 0.11: Proposed nature of Z-selective metathesis by MAP catalysts bearing bulky phenoxide ligands and
small imido ligands.
The chiral nature of the metal center also gives rise to catalysts the produce (cis)
syndiotactic polymers as a consequence of "stereogenic metal control": 32a computational
studies have shown that the catalyst stereochemistry inverts with each productive
metathesis step, a process required by the principle of microscopic reversibility if
productive metathesis is to occur. As such, monomer will insert trans to the pyrrolide
ligand for both R and S chiralities of the metal, giving rise to syndiotactic polymers
(Scheme 0.12).24b37
R
R"xLl4R
"'
R
R,
.
Nt
Addtio to Rt
Productive cycloreversion
R Inversion of configuration
I
Addition to
C/X/O face
N
R"~I
, XIx.
R'
xx
C
X
R
R
X
R
NN
ac nversion of configuration R F
t/ / N-
0.12:
Nature
of syndiotactic
R
R
Productive cycloreversion
SR
Scheme
R
R"
'
X
R
R
R"
polymer microstructure
using
MAP catalysts.
26
The most recent advances of these Generation III catalysts have been in the realm
of tungsten oxo-alkylidene species, which have shown to be some of the most reactive
and Z-selective catalysts known, particularly those which are activated through the oxo
ligand by a Lewis acid such as B(C6 F5 ) 3 (Scheme 0.13).
Activation of the oxo
2435c,37d
ligand using such Lewis acids has been experimentally shown to increase ROMP rates by
approximately two orders of magnitude relative to the unactivated catalyst with a
"
concomitant increase in the regularity of the polymer.2 4
F5
B
0
-Ph
0
16
B(C6F5)3
0
- Ph
0
Scheme 0.13: Borane activation of [W]=O ligand.
A unique and defining characteristic of high oxidation state alkylidene species is
the interconversion of alkylidene isomers - syn and anti - which have been observed
experimentally and treated computationally (Figure 0.5).9a,38
Z
syn
Z
H
Z = NR', O
Y
anti
Figure 0.5: Rotational isomers of high oxidation state alkylidene complexes.
Syn isomers are defined as those in which the alkylidene substituent is pointing toward
the imido or oxo ligand; the anti isomer adopts the opposite configuration, where the
alkylidene substituent faces away from the imido or oxo ligand. The two isomers are
formed through rotation about the M=C bond, which for Mov' and WV' species has been
measured to be on the order of 15-22 kcal/mol. In both isomers, R is coplanar with
Z/M/C, which results from the tendency of the metal to maximize dn-p7t interactions with
the Z (NR' or 0) and carbene ligands (Figure 0.6).
27
R
R
R
N
z
RH
C
R'
H
Metal-nitrogen a-interactions
Metal-carbon
n-interaction
Figure 0.6: dx-px interactions in imido-alkylidene (or oxo-alkylidene) species.
Considering the canonical metal-based orbitals, the Z ligand exhibits a-overlap with the
d and dy orbitals, and the alkylidene fragment shows a-overlap with the dx, orbital,
giving rise to only two rotational isomers (both in which Z, M, C, and R/H are coplanar)
in which such a-interactions are maximized. In order for synlanti interconversion to take
place, the M=C bond must break and the M=Z pseudo triple bond (X 2 L) character must
decrease, as the rotation of the alkylidene fragment is stabilized by interaction of the
singly occupied n-orbital with the metal dxz orbital (Figure 0.7).
R
R
R
N'
hv
C
H
R
LCH
H
R'
Figure 0.7: Alkylidene rotation is stabilized by the interaction of a metal-based orbital with a i-based orbital of
the carbene (charge on metal not shown).
This simplistic model is supported experimentally and computationally by, e.g.,
significantly higher barriers of alkylidene rotation in isolobal Rev" alkylidyne alkylidene
-
species, where one would expect reducing the bond order of a covalent triple bond (X 3
ligand) and placing charge on the less electronegative carbon atom would be much more
energetically demanding; indeed, interconversion rates in these systems have been shown
to be on the order of ~ 25-35 kcal/mol .38d39 The barrier of this rotation for Mo and W
systems is also dependent upon the metal itself. Work within this group has shown that
rates of interconversion of otherwise isostructural catalysts are systematically faster for
W than Mo, despite the fact that agostic interactions (see below) for isostructural
catalysts differing only in metal are stronger for W. 3 M,3 9 The nature of this difference was
28
not discussed, though possible causes could lie a) in the more diffuse 5d orbitals of W
compared to the 4d orbitals of Mo, allowing for greater orbital overlap in the transition
state, b) the greater polarization of the W=C bond relative to the Mo=C bond, giving the
W=C bond less covalent (more ionic) character. 3
'40
It might also be assumed that the
electronic effects of the imido group would modulate this rotational barrier if sterics were
held constant; such effects have not been previously studied in depth but will be
addressed herein.
The syn isomer is generally present in solution in the
R
NI
concentration,
highest
owing
to
the
presence
of an
electronically favorable cc-agostic interaction 4 ' of the cc-CH
bond of the alkylidene with a M-NR or M-O o* orbital (Figure
0.8). This interaction is manifested both crystallographically
R
and spectroscopically:
M=C-R bond angles for Mo and W
species have been shown to be on the order of 140, much
H
2
this
larger than expected for a typical sp -hybridized carbon;
effect is much more pronounced for Group V metals such as
Figure 0.8: a-agostic
interaction in the syn isomer of Ta and Nb, where analogous angles have been measured
to be
an imidoalkylidene complex.
nearly linear (~170).41
In addition, syn isomers show a
characteristically reduced JCH value relative to their anti isomers. VJCH values are related
to the amount of s-character in a bond, since only s-orbitals have non-zero electron
density at the nucleus; as the M=CR angles increases due to this interaction (sterics may
also play a synergistic role in "pushing" the R substituent down to increase this angle),
the s-character of the carbon increases, resulting in an increase in the p-character of the
carbon-based orbital to which the proton is bound. The JCH value is therefore reduced.
In neutral, 4-coordinate Mo/W systems the JCH values for syn alkylidenes are typically
~ 115 - 125 Hz;38,4 2 for Ta/Nb systems, these values have been measured to be as low as
75 - 80 Hz. 4 1,43 Furthermore, 1VCH values have also correlated with C-H bond lengths. In
a
neutron
diffraction
study
it was
shown
that
the
C-H
bond
length
in
[Ta(CHCMe 3)C 3(PMe 3)b2 (1.131 A) is elongated from the average C-H bond distance of
an methyl group (1.083 A); the
'JCH
is likewise reduced in this complex. 1 Similar studies
of analogous Group VI alkylidene species have not been conducted, however, one
29
neutron diffraction study of Mo(NAr) 2(Me) 2 (Ar = 2,6-Pr 2C6 H3 ) has been conducted."
Based on characteristic Mo --H and Mo-C distances and significant distortions from ideal
metal-ligand bond angles for a complex with a tetrahedral metal center, agostic
interactions are strongly implicated in this complex and, by extension, complexes of this
type.
The focus of the following chapters will center largely on the modification of the
imido substituent for both Mo- and W-based catalysts.
Chapter 1 will outline new
synthetic protocols for installing electron-withdrawing imido ligands on tungsten, and the
effects of these imido ligands on metathesis will be discussed. Chapter 2 will detail the
synthesis of sterically encumbering terphenyl-based imido ligands for both Mo and W. A
brief disclosure of catalyst reactivity will be given. Chapter 3 will introduce the first
examples of tungsten adamantylimido species.
30
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36 a) Kress, J.; Aguero, A.; Osborn, J. A. J. Mol. Catal. 1986, 36, 1; b) Ibrahem, I.; Yu,
M.; Schrock, R. R.; Hoveyda, A. H. J. Am. Chem. Soc. 2009, 131, 3844.
3 a) Flook, M. M.; Jiang, A. J.; Schrock, R. R.; Muller, P.; Hoveyda, A. H. J. Am. Chem.
Soc. 2009, 131, 7962; b) Flook, M. M.; Gerber, L. C. H.; Debelouchina, G. T.; Schrock,
R. R. Macromolecules 2010,43,7515; c) Flook, M. M.; Ng, V. W. L.; Schrock, R. R. J.
Am. Chem. Soc. 2011, 133, 1784; d) Forrest, W. P.; Weis, J. G.; John, J. M.; Axtell, J. C.;
Simpson, J. H.; Swager, T. M.; Schrock, R. R. J. Am. Chem. Soc. 2014, 136, 10910.
38 a) Oskam, J. H.; Schrock, R. R. J. Am. Chem. Soc. 1993, 115, 11831; b) Schrock, R. R.;
Crowe, W. E.; Bazan, G. C.; DiMare, M.; O'Regan, M. B.; Schofield, M. H.
Organometallics,1991, 10, 1832; c) Oskam, J. H.; Schrock, R. R. J. Am. Chem. Soc.
1992, 114, 7588; d) Jeong, H.; John, J. M.; Schrock, R. R.; Hoveyda, A. H. J. Am. Chem.
Soc. 2015, 137, 2239; e) Poater, A.; Solans-Monfort, X.; Clot, E.; Coperet, C.;
Eisenstein, 0. Dalton. Trans. 2006, 3077; f) Fox, H. H.; Schofeld, M. H.; Schrock, R. R.
Organometallics1994, 13,2804.
39 a) Toreki, R.; Schrock, R. R.; Davis, W. M. J. Am. Chem. Soc. 1992, 114,3367.
40 Cundari, T. R.; Gordon, M. S. Organometallics1992, 11, 55.
41 a) Goddard, R. J.; Hoffman, R.; Jemmis, E. D. J. Am. Chem. Soc. 1980, 102,7667; b)
Brookhart, M.; Green, M. L. H.; Wong, L. Prog. Inorg. Chem. 1988,36, 1; c) Schultz, A.
J.; Williams, J. M.; Schrock, R. R.; Rupprecht, G. A.; Fellmann, J. D. J. Am. Chem. Soc.
1979, 101, 1593; d) Boncella, J. M.; Cajigal, M. L.; Abboud, K. A. Organometallics
1996, 15, 1905.
42 a) Pedersen, S. F.; Schrock, R. R. J. Am. Chem. Soc. 1982, 104, 7483; b) SolansMonfort, X.; Eistenstein, 0. Polyhedron 2006, 25, 339; Schrock, R. R. Chem. Rev. 2009,
109, 3211; Schrock, R. R. Chem. Rev. 2002, 102, 145.
43 Freundlich, J. S.; Schrock, R. R.; Cummins, C. C.; Davis, W. M. J. Am. Chem. Soc.
1994, 116,6476.
44Cole, J. M.; Gibson, V. C.; Howard, J. A. K.; McIntyre, G. J.; Walker, G. L. P. Chem.
Commun. 1998, 1829.
33
Chapter 1
Synthesis and Reactivity of Tungsten Alkylidene Complexes Bearing
Electron-Withdrawing Imido Ligands
Portions of this chapter have appeared in print:
Axtell, J. C.; Schrock, R. R.; Muller, P.; Smith, S. J.; Hoveyda, A. H. "Synthesis of
Tungsten Imido Alkylidene Complexes that Contain an Electron-Withdrawing Imido
Ligand" Organometallics2014, 33, 5342.
Autenreith, 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
doi: 10.1021/acs.macromol.5b00123.
34
INTRODUCTION
Since their advent in the 1980's, much of the steric and electronic ligand variation
in Schrock-type metathesis catalysts (oxo and imido) has centered around the monoanionic ligands (X and Y, Figure 1.1; see Introduction).
R
x..
-
M =MovI, WVI
-R = Oxo or imido
R'= Me, Ph
- X/Y = Anionic ligand
Figure 1.1: Generic Schrock-type metathesis catalyst.
Substitutions of these positions are carried out at late stages of catalyst synthesis and
involve simple salt metathesis or protonolysis protocols:
from bistriflate or dihalide
precursors, Generation I-III Schrock type catalysts can be synthesized (see Introduction).
Much less time has been spent on imido ligand variation, likely due to the fact
that these substituents are installed in the first step of the traditional synthesis.1 Within
this imido framework, relatively electron-rich phenylimido ligands are most commonly
used; alkylimido ligands (see Chapter 3) and imido ligands with strongly electronwithdrawing substituents (see below) have been far less explored. It has been clearly
established through experiment that the electronic contribution of alkoxide ligands can
drastically affect catalyst reactivities and alkylidene rotation rates.2 It therefore became
of interest to examine the electronic effect of the imido ligand in metathesis. A closer
look at previously reported imido ligands of this catalyst type revealed a general lack of
electron deficient arylimido ligands.e
Recent work within the Schrock group has shown
that Mo and W species containing a pentafluorophenylimido ligand are highly reactive
for the metathesis of olefins; 4 collaborative efforts with the Hoveyda group have also
shown that molybdenum and tungsten alkylidene species bearing electron-withdrawing
imido ligands are highly useful catalysts within the realm of natural product synthesis.'
More sterically varied and electron-deficient aryl substituents were therefore chosen for
evaluation in metathesis.
RESULTS AND DISCUSSION
I. Synthesis of Electron-Withdrawing Bisimido Precursors
35
A. Attempts to synthesize bisimido complexes through traditional methods
Beside the pentafluorophenylimido (NC6 F5 ) ligand, very few reports exist for
tungsten (alkylidene) species that contain electron-withdrawing imido ligands. Previous
work in this area has been carried out with molybdenum and was directed towards the
synthesis of imido species containing a 2,4,6-X 3C6 H2 (X = F (Ar'3), Cl (Arc 3), Br (Arr
3
))
substitution pattern, 6 as well as C6F and 3,5-(CF 3)2C6 H 3 (Ar(CI) 2) arylimido complexes.7
While two precursors of the type Mo(NR) 2C12(dme) (R = ArC13 , ArBr3 ) could be
synthesized, subsequent alkylation products Mo(NR) 2 (CH2 CMe 2 R') 2 (R = ArC13 , ArBr3 ; R'
= Me, Ph) were found to be unstable toward decomposition, even in the solid state. It is
unclear why these species decompose, since Mo(NC6 F5 ) 2 (CH2 CMe 2 Ph) 2 is known to be
stable indefinitely under inert conditions.'
Efforts toward the synthesis of tungsten
analogues were not reported.
We hypothesized that tungsten species bearing strongly electron-withdrawing
imido ligands could be made, given the well-known trend of stronger metal-ligand bonds
for 5d versus 4d transition metals. Four electron-deficient imido candidates were chosen
to explore this new area of ligand modification (Figure 1.2)
C1
Br
CF 3
F 3C
CI
Cl
ArC
13
Br
Br
Ar3r3
CI
F3
CI
ArC12CF3
Ar(CF3)2
Figure 1.2: Electron-deficient aryl groups chosen as imido ligand targets.
These relatively cheap and commercially available anilines presented interesting aspects
for comparison with known imido ligands, in particular those which bear 2- and 6-chloro
substituents, which along with 2,6-Cl 2 C6 H 3 (Arc', imidoalkylidene complexes of which
are known) ,3cs vary in only at the para position and make a purely electronic variation of
catalyst structure possible (Figure 1.3).
36
CI
CF 3
-Steric conservation at 2- and 6-positions
CVC1
.
CI C1 v. C1 C1 eSignificant electronic variation at distal position
~ relative to metal center
~ ~
Arc'
13
ArC12CF3
ArC
Figure 1.3: Desirable comparison for the isolation of electronic effects of the imido ligand in metathesis.
The standard synthesis employs the protocol shown in Scheme 1.1.
Treatment of
W0 2C12(dme) 9 with aniline, TMSC1, and base should afford bisimido complex
W(NR) 2C12(dme). We found, however, that this reaction was not amenable to strongly
electron-deficient anilines. We propose that only one oxo ligand (if any) is displaced,
rather than the requisite two, as a result of the poor nucleophilicity of the parent aniline.
W02C 2(dme)
2RNH 2
xs TMSCI
xs NEt3
Ci
I
R
N
N.
O-W=N-R
DME, 80C
,0\
CI
Scheme 1.1: Standard synthesis for tungsten-based bisimido species.
Similar observations were made for the NC 6 F5 ligand." Variations of this reaction,
including employing stronger neutral donors such as pyridine or 2,4-lutidine, stronger
non-nucleophilic bases, or more forcing thermal conditions were also unsuccessful.
Sundermeyer and co-workers reported the synthesis of W(NC6 F 5)2C12(dme) and
Mo(NArBr 3 )2 Cl2(dme) using an N-sulfinylamine under conditions of refluxing toluene and
a flow of argon gas through the solution (Scheme 1.2).1o
R
M02C 2(L)
Toluene, reflux
Bubbling Ar(g)
CI N
NI
N-.I
0 M=N-R
|
0
-2SO 2
M = Mo, R
L = dme
=
C
2,4,6-Br3 C6 H 2
,
2 R-NSO
M = W, R = C6 F 5
Scheme 1.2: N-sulfinylamine synthesis used to install imido ligands on Mo and W.
This reaction proved unsuccessful for the imido candidates of choice for tungsten and
prompted a shift away from metathetical-type ligand exchanges with very strong W=O
bonds."
37
B. WCl 6 -based synthesis of W(NR) 2C 2(dme) (R = electron-withdrawing aryl)
WCl 6 is a cheap and reactive starting material amenable for the synthesis of
tungsten-based compounds. Nielson previously reported the synthesis of tungsten tertbutylimido
species using WCl 6 and 4 equivalents
of
tBuN(H)SiMe
3
to
form
[W(NBu) 2C 2(NH 2t Bu)] 2 '12 We viewed this strategy as a promising alternative route to
[W]=NR compounds for the electron-withdrawing imido targets at hand. Treatment of
aniline with nBuLi (or KH in the case of ArBr3 ) followed by chlorotrimethylsilane
afforded the SiMe 3-substituted anilines in good yield.
Subsequent treatment of WCl 6
-
with 4 equivalents of these silylanilines in C H6, followed by addition of DME after 24
36h cleanly affords species of the type W(NR) 2C1 2(dme) 1 (Scheme 1.3). The reaction is
proposed to proceed via extrusion of TMSC to form W-NHR linkages, followed by
intramolecular proton transfer between two anilide ligands to afford a W=NR bond and
-
RNH 2
R
N
'_.=N-R
O-W=N-R
1. 4 RNHTMS, C6 H, 36h
WCI 6 W~e 2. DME
0 I CI
R = 2,4,6-C 3C 6H 2 (1a) 82%
2,4,6-Br3C6 H 2 (1 b) 74%
2,6-C 2-4-(CF 3 )C 6 H 2 (1c) 47%
3,5-(CF 3)2 C6 H 3 (1d) 65%
.
Scheme 1.3: Synthesis of tungsten bisimido species starting from WC1 6
Whereas Nielson reported a dimer in the tert-butylimido system (incorrectly
presumed to be bridging through the imido ligands, see Chapter 3), no clean dimeric
species could be isolated in these cases; addition of DME is proposed to break up the
presumed dimers to form the 6-coordinate, 18-electron products. Free aniline is observed
in solution only after treatment with DME, suggesting the aniline is part of some complex
prior DME addition.
Compounds la-d are obtained cleanly and in good yield by
isolation from pentane or recrystallization from DME.
C. Synthesis of W(NR) 2(CHCMe) 2 Complexes
38
Subsequent treatment of la-d with 2 equivalents of neopentylmagnesium chloride
cleanly affords W(NR) 2Np 2 , which for 2a-2c can be isolated in analytically pure form
from acetonitrile; 2d is soluble in MeCN and can instead be precipitated from pentane
(Scheme 1.4)
R
R
N
CI '. 11
O-W=N-R
0
CI
N
2.05 CIMgCH 2 CMe 3
W
Et 20, -30C
N
R
la-id
R
=
2,4,6-C 3C 6 H 2 (2a) 75%
2,4,6-Br3 C6 H 2 (2b) 65%
2,6-C 2 -4-(CF 3 )C6 H 2 (2c) 78%
3,5-(CF 3) 2C6 H 3 (2d) 72%
Scheme 1.4: Synthesis of tungsten dineopentyl bisimido species.
Complexes bearing the closely related 2-methyl-2-phenylpropyl (neophyl) alkyl ligand
can also be made, but were not pursued (vide inrJIa).
2d proved to be a unique case among these dialkyl species. Whereas the a-CH 2
protons for 2a-c are well-defined in solution by 'H NMR, for 2d only a broad, ill-defined
signal was observed at room temperature. Cooling of this species in CD 2Cl 2 resulted in
further broadening of the a-CH 2 signal; heating 2d in CD8 resulted in the sharpening of
all peaks to the point where '8W satellites became visible flanking the u-CH 2 singlet
(Figure 1.4). X-ray quality crystals were grown from a concentrated CH2 Cl 2 solution and
revealed the species to be a dimer in the solid state (Figure 1.5).
39
t
W-CH2 Bu
70'C
1.33
1;0
1;4i.
1.6
3i
1.73
1.13
171.4
17;2
113
IU
1I3
-30-C
-20-C
-101C
O'C
101C
Figure 1.A: Variable-temperature 'H NMR spectra of 2d showing fluxional behavior in solution. At low
temperatures in CD 2CI 2, aryl and CH2 resonances broaden (see arrows); at high temperatures in CD,, these
peaks sharpen (see inset).
Figure 1.5: Thermal ellipsoid plot of 2d. Selected bond distances (A) and angles (deg): W1-N1 = 1.888(2),
W1-N2 = 1.756(7), W1-C1 = 2.135(2), W1-C6 2.126(2), Wi-NIA 2.262(2); W1-N1-C1 = 127.0(7),
W1-N2-C21 = 179.2(7), W1-C1-C2 = 128.7(9), W1- C6-C7 = 129.1(9), Wi-Ni-WIA = 104.3(0).
40
We therefore conclude that an equilibrium exists between monomeric and dimeric forms
of 2d in CD 2 Cl 2 : at lower temperatures, equilibrium favors the dimeric species and at
higher temperatures, the monomer and dimer interconvert readily on the NMR timescale
(Scheme 1.5).
F 3C
F3
F 3C
N
2
F3
Low T
N
N N
FF3C
F3
Scheme 1.5:
CF 3
F3
NN
N
F3C
HighT
F3
.
CF3
F3 C
F3
Proposed monomer-dimer equilibrium of 2d.
Complexes 2a-d are stable indefinitely under an inert atmosphere. This contrasts
previous observations of the Mo analogues (specifically those bearing ArC13 and ArBr3
imido ligands) synthesized previously, which were found to decompose in the solid state
to aniline and uncharacterized metal-based products.'
II.
Synthesis of Tungsten Alkylidene
Complexes
Containing an Electron-
Withdrawing Imido Ligand
A. Synthesis of Bistriflate Species
The next step in the synthesis requires treatment of the dialkyl intermediate with
trifluoromethanesulfonic
acid
(HOTf)
to
generate
complexes
of
the
type
W(NR)(CHCMe 3)(OTf) 2(dme) 3.' Treatment of the neophyl analogues of 2a-d with
HOTf under the same conditions resulted in complex mixtures with no evidence of any
alkylidene-bearing species; only 2a-d could be successfully converted to the desired
alkylidene species (Scheme 1.6).
41
R
R
N
NTfN
3 TfOH
11.1
W
Do__'IN_____II____+_isomer__s)
N
O-w+
1'OTf
Et 2 0/DME, -30C
R
isomer(s)
R = 2,4,6-C 3C 6 H 2 (3a) 88%
2,4,6-Br3C6 H 2 (3b) 69%
2,6-C12-4-(CF 3)C6 H 2 (3c) 49%
3,5-(CF 3 )2C6 H 3 (3d) 84%
Scheme 1.6: Synthesis of tungsten imidoalkylidene complexes.
The reason for this divergent reactivity is not currently understood. Similar behavior has
been observed with W-based (but not Mo-based) complexes bearing the NC6 F5 ligand.a
Since more electron-rich arylimido species of tungsten bearing neophylidene ligands
have been synthesized, it seems that the electronic profile of the imido group is an
important factor in determining the success of this reaction for tungsten-based species.
Compounds 3a-c exist as a mixture of cis and trans triflate isomers, whereas 3d
exists exclusively as the trans isomer. An X-ray diffraction study was carried out on 3a
in an effort to examine any potential differences from other imidoalkylidene speces. The
bond lengths and angles in 3a do not vary dramatically from values normally observed in
complexes of this type."
0(2)
0013)
0(23)
l
CO) C(2)
Figure 1.6: Solid-state structure of cis-3a. Select bond distances (A) and angles (): Wi-N1 = 1.736(11), WI-Cl
= 1.1983(15), Wl-01 = 2.3122(10), W1-02 = 2.1031(10), Wl-013 = 2.0561(10), Wl-023 = 2.1710(10); W1-N1C31 = 170.71(11), WI-C1-C2 = 141.39(11), N1-W1-Cl = 100.41(6).
42
B. Synthesis of Tungsten Bis-Alkoxides
Ultimately, the purpose of this project was to evaluate tungsten-based
imidoalkylidene catalysts in order to extract information about the role of imido
electronics on metathesis (cf. Figure 1.3). Therefore, compounds 3a-d were treated with
2 equivalents of LiODBMP-Et 2O (ODBMP = O-2,6-(DiBenzhydril-4-Methyl)Phenyl) to
afford bisalkoxides W(NR)(CHCMe 3)(ODBMP) 2 4a-d, which are isolated cleanly in
moderate yield; catalysts for comparison (4e-h) were synthesized in an analogous manner
(Scheme 1.7).
2
R
TfO N
Ph''
Ph
/
I
O-W
Et 2 O
R
'Ph
Ph
h
CHh21
Ph 2HC
Et20, rt
1OTf
/
OLI
0
Ph2HC
R
=
CHPh 2
2,4,6-CI 3C6 H 2 (4a) 57%
2,4,6-Br3C6 H 2 (4b) 69%
2,6-C 2-4-(CF 3)C 6 H 2 (4c) 61%
3,5-(CF 3)2C6 H 3 (4d) 65%
2,6-CI 2C 6H 3 (4e) 63%
C6 F 5 (4f) 59%
2,6-Me 2C6 H 3 (4g) 75%
3,5-Me 2C6 H 3 (4h) 79%
R'= Me, 4a-g; Ph, 4h
Scheme 1.7: Synthesis of tungsten bis-alkoxide catalysts.
An X-ray crystal diffraction study was carried out on crystals of 4a, grown from a
concentrated CH2 Cl 2 solution (Figure 1.7). The bond angles and distances are typical for
imidoalkylidene complexes."
43
Figure 1.7: Solid-state crystal structure of 4a. Selected bond distances (A) and angles (deg): Wi-N1 = 1.741(2),
Wi-Cl = 1.897(3), Wl-01 = 1.906(0), W1-02 = 1.907(2); W1-N1-C11 = 175.4(2), W1-C1-C2 = 144.8(4),
Wl-01-C21 = 138.1(1), W1- 02-C61 = 140.8(9).
C. ROMP Studies of Tungsten Bis-Alkoxides
Ring-opening metathesis polymerization (ROMP) of 2,3dicarbomethoxynorbornadiene (DCMNBD) was chosen as the test reaction for catalysts
4a-h (Scheme 1.8)."
R
CHPhR
Ph2HC
R
R
R
R
R
R
tR
0
CHPh 2
CDCI 3, rtR = CO 2 Me
-
P h 2H C
n
Scheme 1.8: Generic reaction of metathesis catalyst with ROMP monomer to produce poly(DCMNBD) (one of
four possible polymer microstructures is shown).
Reactions were carried out under identical conditions with a monomer-to-catalyst ratio of
50:1 in CDC1 3 . The results of the polymerizations of DCMNBD with 4a-h are shown in
Table 1.1. In general, the resulting polymers contained a predominantly cis,isotactic
microstructure, as has been observed before for bis-alkoxide initiators: the pseudo mirror
44
symmetry of the catalyst should render each face of the catalyst equal in energy for
approach of the monomer, leaving the double bond geometry and tacticity of the polymer
under chain end control.4.d Interestingly, catalysts with imido ligands containing 3,5disubstitution
a much smaller percentage
gave polymers with
of cis,isotactic
microstructure, where x% cis,isotactic refers to x% of the entire integrated area for all
polymeric products.
Table 1.1: Polymerization of DCMNBD with Initiators 4a-h in CDCl 3 ".
Polymer Microstructurec
84% cis,iso
71% cis,iso
85% cis,iso
(M's')
0.59
0.075
1.1
Imido substituent
2,4,6-Cl 3C6 H 2 (4a)
2,4,6-Br3C6 H 2 (4b)
2,6-Cl 2-4-(CF3)C6 H2 (4c)
kobs
3,5-(CF 3) 2C6 H3 (4d)
>4.1 (est)b
53% cis,iso
2,6-Cl 2C6 H 3 (4e)
0.51
88% cis,iso
C6 F5 (4f)
2,6-Me 2C6 H 3 (4g)
>4.1 (est)b
85% cis,iso
3,5-Me 2C6 H 3 (4h)
>4.1 (est)b
75% cis,iso (10% trans)
0.005
55% cis,iso
initiator.
"Monomer and initiator concentrations were held constant at 0.1M and 0.002M across three trials for each
Reactions were >95% complete at 5min. ' Unless otherwise noted, <5% trans polymer sequences is observed.
More interesting, however, is how the values of
kob,
b
change as the imido ligands for
otherwise isostructural catalysts are varied. The most obvious trend is how
kObs
tracks
with the size of the imido ligand: catalysts bearing small imido ligands (4d, 4f, 4h)
polymerize 50 equivalents DCMNBD before a sufficient number of measurements can be
taken to reliably calculate
kabs;
on the other hand, those bearing large imido ligands (4b,
4g) are slow to polymerize DCMNBD.
Second, and more importantly, those catalysts
which vary only in the identity of the 4-substituent on the arylimido ligand (4a, 4c, 4e)
show an increase in the rate of ROMP as the electron-withdrawing power of this 4substituent increases (Figure 1.8). This result is consistent with other reports 2 that more
electron-deficient metal centers show enhanced metathesis activity, though this is the first
example of such a concept being definitively shown as a result of imido ligand
electronics.
45
/\,
ka/s
+1
H
Cl
CI
CI
CI
CF 3
CI
CI
C
ArC1 2CF 3
Arc 13
ArcI
Increasing ROMP kobs
Figure 1.8: Trend of enhanced ROMP activity as imido ligand substituents becoming more electronwithdrawing.
D. Study of synlanti Interconversion Rates of Tungsten Catalysts Bearing ElectronWithdrawing Imido Ligands
A cornerstone of high oxidation state olefin metathesis chemistry lies in the
existence of and interconversion between syn and anti alkylidene rotational isomers
(Figure 1.9).
z
z
II
R
X1--Mu
ks/a
II
X I.X. M:
|
syn
H
Z=NR',0
anti
H
R-R'
Figure 1.9: Rotational isomerism of the alkylidene ligand in high oxidation state metathesis catalysts.
A large volume of research from our own group has been published on this equilibrium
and resulting reactivity (see Introduction for references).
In these studies, the primary
focus centered on the equilibrium constants and rotation rates with respect to the
electronic profile of the alkoxide ligands (X and Y in Figure 1.9). However, far less has
been done to evaluate the role of the imido group in this isomerization. Therefore, with
electronically varied imido groups that have a distinct influence on metathesis activity
(vide supra), a brief exploration into the role of imido electronics on alkylidene
isomerization was undertaken.
In line with previous studies, simple bis-alkoxides were chosen as target
complexes.
The two new imido ligands that showed drastically different metathesis
activities - NArI 3 and NArC2CF3 - but conserved the steric profile near the metal center
were also selected. Treatment of 3a and 3c with 2 equivalents of LiOC(CF 3) 3 (LiORF 9) in
46
toluene
at
room
temperature
the
afforded
bis
expected
alkoxide
species
W(NR)(CHCMe 3)(ORF 9) 2 (R = ArC 3, 5; ArC1 2CF3, 6) (Scheme 1.9).
R
R
Cl
C,
CI
CI
N
N
Tf,
0'
2LiOC(CF
3)3 F3C
o-w-
N Tf
II
>
F 3C
C 7DA, rt
*F 3
F3 C '"
CF3 F3
R = CI (5) 81%
CF 3 (6) 69%
Scheme 1.9: Synthesis of bis-alkoxide catalysts.
Photolysis of alkylidene complexes at ~366nm at low temperature has been
shown to generate -20-40% of the anti alkylidene isomer in solution.2es
The decay of
the anti isomer back to the syn isomer can be measured over time by 'H NMR and a rate
constant from this interconversion can be extracted. Samples of 5 and 6 in toluene-d.
were irradiated for -4h at -78*C and inserted into the 'H NMR spectrometer, and the
decay of anti to syn was measured at -50*C. The data is shown in Chart 1.1.
Decay of anti isomers of 5 and 6 at -50'C
2.5
y=0.000861x-0.131726
R 2 =0.981785
2
9
y = 0.00025lx + 0.068724
R 2 =0.985551
*6
.5
-0.5
- 0 .5 j
500
1000 1500 2000 2500 3000 3500 4000 4500
Time (s)
Chart 1.1: Measurement of the decay of anti-5 and anti-6 in C.D. at -50'C.
47
This difference in rotation rate - 2.5x10-4 s-' for 5 and 8.61x10-4 S- for 6 - clearly shows
that the electronic profile of the imido ligand influences the energetic barrier of
alkylidene rotation. In order for anti to convert back to syn, competition for a metalbased orbital between the imido ligand and the rotating alkylidene must take place
(Figure 1.10).
R
R
R
C 1_H
-*
R'
H
R'
C ' R 'I
H
Figure 1.10: Electron-withdrawing imido ligands stabilize localization of lone pair on nitrogen during anti-tosyn alkylidene isomerization.
We propose that the more electron-withdrawing imido ligand in 6 reduces the interaction
of the nitrogen lone pair with the metal (relative to 5) to form a pseudo triple bond,
lowering the kinetic barrier to alkylidene rotation.
This finding is significant, given the continued importance of alkylidene isomers,
and the rates at which they interconvert, in metathesis. Oskam and Schrock found that
based upon the electronic profile of alkoxide ligands in Mo(NAr)(CHCMe 3)(OR') 2 (R =
2,6-iPr 2 C6 H3 ; R' = 'Bu or C(CF3 ) 3 ), two completely different polymer microstructures
were produced in the polymerization of 2,3-bis(trifluoromethyl)norbornadiene.-" This
difference was ascribed to fast and slow rate of alkylidene isomerization with respect to
monomer insertion for the bis(tert-butoxide) and bis(perfluoro-tert-butoxide) catalysts,
respectively.
More recently, AB copolymers of hindered norbornadienes with less
strained cycloolefins was demonstrated, a result made possible through a delicate balance
of monomer insertion rates and alkylidene rotation rates.' 6 Imido ligand electronics have
now been shown to influence this process and can now be used, in concert with other
ancillary ligands, to generate complexes with varying alkylidene rotation rates.
E. Synthesis of Bis-Pyrrolide, MAP, and Other Bis-Alkoxide Species
MAP (MonoAlkoxide MonoPyrrolide) species of Mo and W have been shown to
be highly active in metathesis. 5 14',17 Therefore, with a new synthetic route to alkylidene
48
complexes with electron-withdrawing imido ligands in hand, we chose to pursue the
synthesis of bis-pyrrolide and MAP complexes.
Treatment of 3a-d with two equivalents of LiMe 2pyr in either toluene or Et2 O
afforded complexes of the type W(NR)(CHCMe 3)(Me 2pyr) 7a-c (Scheme 1.10).
R
R
NN
T~fO'_
__
2 LiMe 2pyr
0 7 D8 , rt
0 'OTf
R = 2,4,6-C3C 6 H 2 (7a) 84%
2,4,6-Br3C6 H 2 (7b) 83%
3,5-(CF 3 )2C6 H 3 (7c) 87%
Scheme 1.10: Synthesis of bis-pyrrolide complexes.
While originally prepared to provide an intermediate that gave milder access to
biphenolate and binaphtholate complexes through protonolysis via addition of the diol,'"
addition of a single equivalent of an alcohol affords the stereogenic-at-metal MAP
species.
9
Treatment of 7a with HO-2,6-Mes 2C6 H3 (HMTOH) or HO-2,6-(C6 F5 ) 2 C6 H 3
(DFTOH) afforded the expected MAP species 8 and 9, respectively (Scheme 1.11).
CI
CI
OH
CI I
C
R
R
CI
Et20, rt
CI
0
R
R
=
R
Mes (8) 35%; C 6F 5 (9) 74%
Scheme 1.11: Synthesis of MAP species bearing the Arc1 imido ligand.
MAP species 8 and 9 were tested for the polymerization of DCMNBD.
Catalyst 8
polymerizes 100 equivalents of DCMNBD in -2h to give 94% cis and 90% syndiotactic
poly(DCMNBD); 9 polymerizes 50 equivalents of monomer in under 90 minutes to give
-99% cis and 94% syndiotactic polymer, as identified by the characteristic olefinic
resonance at 5.35 ppm in CDC1 3 (Scheme 1.12).2o Polymerization under "stereogenic
metal control,," which is operative due to the stereogenic nature of the metal center and
49
the inversion of chirality after each productive metathesis step, is proposed to be the
source of these syndiotactic-biased polymers."'d 8 and 9 have also been tested for the
polymerization of endo-dicyclopentadiene (DCPD).2 ' 8 polymerizes 50 equivalents of
DCPD in 1 minute, yielding 85% cis and 90% syndiotactic poly(DCPD); under the same
conditions, 9, in 30 seconds, affords >98% cis and 66% syndiotactic poly(DCPD).
CI
CI
CI
CO 2Me
N
d
CDCI, rt
0n
R
R
R
R
R
COM
R
R
R
R = CO 2Me
8: 94% cis, 90% syndiotactic (x= 100)
9: 99% cis, 94% syndiotactic (x = 50)
R
=
Mes (8); C6 F5 (9)
Scheme 1.12: Results of DCMNBD polymerization by initiators 8 and 9.
The reproducible synthesis of bispyrrolide and MAP species containing unsubstituted
pyrrolide ligands has yet to be achieved. The success of these reactions so far appears to
be highly dependent on solvent and temperature. Further work needs to be conducted to
address these problems in order to gain access to MAP catalysts of this type, since the
smaller size of the unsubstituted pyrrolide should make these complexes more reactive
than the dimethylpyrrolide analogues.
Given the success of bis-terphenoxides in the realm of tungsten oxoalkylidenebased metathesis,"" 7c - which bears the smallest of the new imido groups presented
here - was charged with two equivalents of 2,6-bis(pentafluorophenyl)phenol (DFTOH)
(Scheme 1.13). Compound 10 was obtained in 85% yield.
F 3C
F3
F 3C
F3
.,
OH
C6F 5
C 6F5C
2
C
W
N
10
Et 20, rt
PF
C6F5
F
-
F
0
F
F
F
( 5 F
F
|
F
F
7c
10m(85%)
Scheme 1.13: Synthesis of a bis-terphenoxide by protonolysis.
50
10 was tested for metathesis activity in the ROMP of 50 equivalents of DCMNBD. The
reaction was allowed to stir for -12h, and approximately 89% of the monomer was
consumed.
Approximately 95% cis,isotactic
poly(DCMNBD) was produced, as
characterized by the olefinic resonance at 5.41 ppm in CDCl 3 -l4 a The 'H NMR of the
olefinic region is shown in Figure 1.11. This is an encouraging result given that few bisterphenoxide complexes bearing imido ligands are known, some of which are unreactive
even towards ethylene at elevated temperatures.
It is also interesting to note the high
degree of isotacticity, which is not generally observed for bis-alkoxides (vide supra; see
Chart 1.1), since in these cases polymerization is proposed to be under chain-end
control.
44cd
Figure 1.11: 'H NMR spectrum of cis,isotactic poly(DCMNBD) produced by 10. Individual polymer
microstructure regions are integrated.
CONCLUSIONS
A new synthetic route has been established to access bis-imido species of tungsten
for strongly electron-withdrawing imido ligands beginning from WCl 6 .
Previous
attempts to access this precursor through W=O bond cleavage were unsuccessful, likely
due
to
the
poor
nucleophilicity
of the
aniline
reactants.
Alkylation
with
neopentylmagnesium chloride and treatment with HOTf affords the desired bistriflate
51
products; analogous Mo-based bisalkyl complexes are unstable towards decomposition.
Bis-phenoxide complexes bearing these imido groups have been synthesized and tested in
the ROMP of DCMNBD. If sterics are conserved in the immediate coordination sphere
of the metal (i.e. 2- and 6-positions of the arylimido ligand are held constant), the rate of
ROMP has been shown to increase as the electron-withdrawing power of the imido
substituents increases; a similar trend is observed in the kg, of two simple bis-alkoxides,
in which the ku, increases as the electron-withdrawing power of the imido substituents
increases.
Bis-2,5-dimethylpyrrolide, MAP, and one bis-terphenoxide species have also
been synthesized. The MAP and bis-terphenoxide species have been tested in the ROMP
of DCMNBD and afford highly cis,syndiotactic and cis,isotactic polymers, respectively.
Further research to develop synthetic routes to bispyrrolide and MAP species containing
unsubstituted pyrrolide ligands is still needed and could provide access to more
interesting and highly reactive catalysts.
52
EXPERIMENTAL
General Details.
All manipulations of air-sensitive compounds or reactions were
performed under nitrogen in a drybox or using Schlenk techniques. All glassware was
oven-dried and allowed to cool under vacuum or nitrogen before use. Diethyl ether,
pentane, benzene, methylene chloride, THF, DME, and toluene were sparged with
nitrogen and passed through activated alumina. All solvents were stored over molecular
Deuterated solvents were also stored over
(4A) sieves in a nitrogen atmosphere.
molecular sieves (4A). NMR spectra were obtained on Varian spectrometers operating at
300 MHz or 500 MHz.
NMR chemical shifts are reported as ppm relative
tetramethylsilane, and were referenced to the residual proton or '3C signal of the solvent
('H CDCl 3: 7.260 ppm; 'H C 6D6 : 7.160 ppm; 'H CD 2Cl 2 : 5.320 ppm;
ppm;
3
C CDCl 3 :
77.160 ppm;
13 C
53.840 ppm).
CD 2 Cl 2 :
referenced with respect to C6H5F (-113.15 ppm).
3
C CD6 : 128.06
19F NMR spectra are
Lithium pyrrolide and 2,5-
dimethyllithium pyrrolide were synthesized by addition of 1 equivalent of n-BuLi to an
ethereal solution of the neutral pyrrole and were isolated by filtration and washed
thoroughly with pentane.
HMTOH, 22 DFTOH,4a W(NArF)(CHCMe 3)(OTf) 2(dme)
W(NAr 2,6Me2)(CHCMe 3)(OTf)2(dme),
W(NAr3,sMe 2)(CHCMe 2Ph)(OTf) 2(dme)
23
W(NArcI)(CHCMe 3)(OTf)2(dme) ,3 N-trimethylsilyl-2,4,6-tribromoaniline,
trimethylsilyl-2,6-dichloro-4-trifluoromethylaniline
reported procedures.
25
were
24
and
17d
N-
synthesized according to
LiODBMP was synthesized by the addition of n-BuLi to
DBMPOH 26 in Et 2O at -30'C. Unless otherwise noted, all other reagents were obtained
from commercial sources and used as received.
N-(trimethylsilyl)-2,4,6-trichloroaniline:
Et2O (50 mL) was added to a Schlenk flask
under argon containing 2,4,6-trichloroaniline that had been recrystallized from hot
hexane). The solution was chilled to -78'C and n-butyllithium (2.OM in cyclohexane,
4.03mL, 8.06 mmol) was added via syringe under an argon flow and the resulting white
slurry was allowed to stir for 2 h; the slurry acquired a reddish tint over time.
Trimethylsilylchloride (1.86mL, 14.6 mmol) was added by syringe and the solution was
allowed to warm to room temperature. Solvent was removed and the orange residue was
charged with CH2 C 2 . The mixture was filtered over Celite, the Celite washed with
53
CH 2 Cl 2 , and the filtrate concentrated under reduced pressure to give an analytically pure
orange oil in 90% yield (1.776g, 6.61mmol): 'H NMR (C6 D6 ,20*C) 6 6.95 (s, 2H, Ar),
3.76 (s, 1H, NH), 0.16 (s, 9H, SiMe 3);
C NMR (CD6 , 20 0 C) 8 179.5, 141.3, 124.8,
3
1
123.6, 1.8. Anal. Calcd for C9 H12Cl 3NSi: C, 40.24; H, 4.50; N, 5.21. Found: C, 40.01;
H, 4.39; N, 5.22.
N-(trimethylsilyl)-2, 6-dichloro-4-trifluoromethylaniline:
Diethyl ether (200mL) was
added to a Schlenk flask under nitrogen containing 2,6-dichloro-4-trifluoromethylaniline
(14.39g, 62.6 mmol) and was cooled to -78*C.
n-butyllithium (2.5M in henxane,
26.3mL, 65.7 mmol) was added over 15 min to the stirred solution. The solution was
stirred at -78*C for 2h and then taken out of the cold bath, during which time a dark
red/brown color evolved. Trimethylsilylchloride (15.9mL, 125 mmol) was then added
dropwise to afford a light yellow slurry. This mixture was allowed to warm to room
temperature and was filtered through Celite. The yellow filtrate was concentrated under
reduced pressure to give an analytically pure orange oil; yield 18.90g, (98%): 'H NMR
200 C): 6 145.7, 125.4 (m), 123.9 (q,
(m);
19F
'JCF =
NMR (C6 D, 200 C): 8 -61.8.
271 Hz), 123.4, 121.3 (q,
2
3
1C
JCF =
NMR (C6 D6
,
(CD6 , 20-C) 6 7.24 (s, 2H, Ar), 4.21 (bs, IH, NH), 0.16 (s, 9H, TMS);
33.8 Hz), 2.2
Anal. Calcd for C1 0H1 2Cl 2F3NSi: C, 39.75; H,
4.00; N, 4.64; Found: C, 40.06; H, 3.84; N, 4.42.
W(NAr 3) 2 C12 (dme) (la). WCl 6 (0.568g, 0.143 mmol) was added to toluene (25mL) in
a round bottom flask. A solution of N-trimethylsilyl-2,4,6-trichloroaniline (1.539g, 0.572
mmol) in toluene was added to the stirred WCl 6 solution. The red/orange mixture was
stirred for two days, after which the solvent was removed in vacuo. Pentane (20mL) and
2mL DME were added to the viscous residue and the mixture was stirred.
The
precipitated orange solid was isolated by filtration; 82% yield (757mg, 0.118 mmol): 'H
NMR (C6 D6 , 20-C) 6 6.93 (s, 4H, Ar), 3.61 (s, 6H, CH3), 3.16 (s, 4H, CH2 );
3
1
C NMR
(C 6D 6 , 200 C) 6 149.0, 132.9, 130.4, 127.8,71.5, 64.9. Anal. Calcd for C,6 H1 4 ClN2 0 2W:
C, 26.19; H, 1.92; N, 3.82. Found: C, 26.26; H, 1.96; N, 3.75.
54
W(NArCI 3 ) 2 (CH2 CMe3 ) 2 (2a). W(NArCI 3) 2(dme)C
2
(l0g, 13.6 mmol) was charged to a
round bottom flask with 200mL Et 2 0 and chilled at -30C for lh. Neopentylmagnesium
chloride (1.68M, 16.6mL, 27.9 mmol) was added dropwise by syringe. The resulting
mixture was allowed to stir overnight. The suspension was filtered over Celite and the
Celite cake was washed thoroughly with Et2 O. The volatiles were removed from the
filtrate under vacuum to afford a red oil. Acetonitrile and minimal diethyl ether were
added to the viscous residue and the mixture was stirred. The precipitated yellow solid
'H NMR (C6 D6
,
was filtered off and rinsed once with acetonitrile; yield 75% (7.322g):
20*C) 6 9.94 (s, 4H, Ar), 2.19 (s, 4H, CH2), 1.16 (s, 18H, CMe3 ); 13C NMR (C 6D 6 , 200 C)
6 149.7, 131.4, 129.5, 127.9,95.6, 35.4, 34.1. Anal. Calcd for C 22H 26Cl 6N 2W: C, 36.96;
H, 3.67; N, 3.92. Found: C, 37.11; H, 3.78; N, 4.02.
W(NArCI 3)(CHCMeC)(OTf) 2(dme) (3a). W(NArCI 3)(CH 2 CMe 3 ) 2 (7.15g, 10.0 mmol) was
charged to a flask with 50mL Et 2 O and 25mL DME and chilled at -30'C for 2h. A
solution of triflic acid (4.50g, 30.0 mmol) in 5mL chilled Et 2O was added dropwise to the
stirred mixture. The resulting mixture was stirred for 1.5h and allowed to warm to room
temperature. The solvents were removed in vacuo from the resulting mixture and CH 2Cl2
was added. The salts were removed by filtration through Celite and the filtrate taken to
'H NMR (CD 2 Cl 2
,
dryness in vacuo to give the desired product; yield 7.37g (88%):
20*C) (major isomer) 6 11.51 (s, 1H, W=CH), 7.47 (s, 2H, Ar), 4.58 (s, 3H, CH3),4.39
(m, LH, CH), 4.31 (m, 1H, CH), 4.11 (m, 1H, CH) 3.72 (s, 3H, CH3), 3.72 (m, 1H, CH),
1.22 (s, 9H, CMe 3 );
3
C NMR (C6D6, 20 0C) 8 (2 isomers) 302.6 ('Jwc = 169 Hz), 294.7
1
('Jwc = 169 Hz), 147.6, 147.4, 135.2,133.5, 132.9, 128.4, 128.3, 120.6 (q, 'JCF = 315 Hz),
119.8 (q,
'JCF =
315 Hz), 119.7 (q,
'JCF =
315 Hz), 81.3, 78.4, 74.4,70.6, 70.2, 67.2, 63.0,
61.3, 48.4, 48.2, 33.3, 33.1; '9F NMR (CD 2Cl 2 , 20*C) (major isomer) 6 -77.4, -78.2.
Anal. Calcd for C 17H 22 Cl 3 F 6No8 S 2 W: C, 24.40; H, 2.65; N, 1.67. Found: C, 24.25; H,
2.32; N, 1.59.
W(NArc' 3)(CHCMe)(ODBMP) 2 (4a). Compound 3a (95mg, 0.114 mmol) was charged
with LiODBMP-Et 2O (101mg, 0.227 mmol) in lOmL Et2 O at room temperature. The
mixture was stirred for 2h to yield an orange solution with precipitate. The solvent was
55
removed in vacuo and CH 2Cl 2 was added to the residue. The mixture was filtered through
a Celite plug and solvents were removed from the filtrate in vacuo. Pentane was added to
the orange residue and the mixture was stirred for lh to give a yellow solid, which was
isolated by filtration. Analytically pure product was obtained by recrystallization from
toluene; yield 86 mg (57%): 'H NMR (CD 2Cl 2 , 20C) 8 9.29 (s, 1H, W=CH), 7.12 (m.
14H, Ar), 6.89-6.78 (m, 28H, Ar), 6.56 (s, 4H, Ar), 5.84 (s, 4H, CHPh 2), 2.11 (s, 6H,
CH3), 1. 13 (s, 9H, CMe3 );
13C
NMR (CD 2Cl 2 , 20 0 C) 6 255.0, 159.5, 149.8, 144.4, 143.5,
133.3, 133.3, 131.5, 130.4, 130.1, 130.1, 129.9, 128.5, 128.4, 127.6, 126.5, 126.4, 50.1,
45.9, 34.5, 21.3. Anal. Calcd for C 77HesCl 3 NO 2 W: C, 69.66; H, 5.01; N, 1.06. Found: C,
69.52; H, 4.81; N, 1.04.
W(NArWr 3 ) 2C12(dme) (1b). WC1 6 (3.51 g, 8.87 mmol) was added to benzene (150mL) in
a round bottom flask. N-trimethylsilyl-2,4,6-tribromoaniline (19.26 g, 35.5 mmol) was
added and the dark red mixture was stirred for 36 h, after which the solvent was removed
in vacuo. Minimal DME was added to the red viscous solid and the resulting yellow
solid was isolated by filtration and washed twice with minimal DME; yield 6.53g (74%):
'H NMR (C 6 D6 , 20 0 C) 6 7.37 (s, 4H, Ar), 3.60 (s, 6H, CH3), 3.07 (s, 4H, CH2 ); 13C NMR
(CD6 , 200C)
6
151.8,
134.2,
122.1,
118.5, 71.4,
65.0.
Anal.
Calcd for
C1 6H,4 Br6 Cl 2 N 2O 2 W: C, 19.21; H, 1.41; N, 2.80. Found: C, 19.65; H, 1.26; N, 2.86.
W(NArBr 3 ) 2 (CH 2 CMe 3 ) 2 (2b).
A solution of W(NArBr 3 ) 2C 2(dme) (6.0g, 6.0 mmol) in
diethyl ether was chilled for lh, after which neopentylmagnesium chloride (1.55M in
Et2O, 7.91mL, 12.3 mmol) was added. After 2h, 2mL of dioxane was added. The
mixture was stirred for 20 min and filtered through Celite. The Celite pad was washed
thoroughly with dichloromethane and the solvents were removed from the filtrate in
vacuo. Acetonitrile was added to the residue and the resulting yellow solid was isolated
by filtration; yield 3.81g (65%): 'H NMR (C6D6 ,200 C) 6 7.36 (s, 4H, Ar), 2.27 (s, 4H,
CH2), 1.21 (s, 18H, CMe3);
13C
NMR (CD 2 Cl 2 , 125 MHz) 6 152.6, 134.1, 121.6, 116.9,
97.3, 34.9, 34.1. Anal. Calcd for C2 2 H 2 6Br 6N 2 W: C, 26.92; H, 2.67; N, 2.85. Found: C,
27.27; H, 2.50; N, 2.96.
56
W(NArBr 3)(CHCMeC)(OTf) 2(dme) (3b). W(NArBr 3 ) 2 (CH2 CMe 3 ) 2 (3.67 g, 3.74 mmol)
was added to a mixture of 30 mL of Et2 O and 20 mL of DME and the solution was cooled
at -30*C for lh. A solution of trifluoromethanesulfonic acid (1.68g, 11.2 mmol) in ~4
mL of Et 2O was added dropwise to yield a deep red/orange solution. The solution was
stirred for one hour, after which the volatiles were removed in vacuo. The residue was
dissolved in CH 2 Cl 2 and the solution was filtered through Celite. The solvents were
removed from the filtrate in vacuo. The residue was triturated with pentane and the
resulting yellow solid was isolated by filtration; yield 2.50g (69%). (Repeated isolations
'H NMR (CD 2 Cl 2
,
may be necessary in order to remove all anilinium triflate salts.):
20'C) 6 (major isomer) 11.47 (s, IH, W=CH), 7.48 (s, 2H, Ar), 4.59 (s, 3H, CH3), 4.44
(m, 1H, CH), 4.31 (m, 1H, CH), 4.06 (m, 1H, CH), 3.75 (s, 3H, CH3), 3.73 (m, 1H, CH),
1.24 (s, 9H, CMe 3 );
13C
NMR (CD 2Cl 2, 20'C) 6 (major isomer) 303.2 (W=C), 150.4,
135.2, 124.0, 121.5, 120.0 (q,
JCF =
316 Hz), 119.0 (q,
'JCF
=
316 Hz), 82.0, 79.2, 71.8,
62.3, 48.5, 32.9; '9F NMR (CD 2Cl 2, 20*C) 6 -77.3 (major), -77.4 (minor), -77.1 (major).
Anal. Calcd for C, 7H 22 Br 3 F6 NO8 S 2 W: C, 21.05; H, 2.29; N, 1.44. Found: C, 21.00; H,
2.15; N, 1.23.
W(NArBr 3)(CHCMe 3)(ODBMP)2 (4b).
Solid LiODBMP-Et 2O (144mg, 0.276 mmol)
and 3b (134mg, 0.138 mmol) were added to lOmL of Et 2O at room temperature. Workup
and isolation of the product followed the same procedure as 4a.
Analytically pure
product was obtained by recrystallization from toluene/pentane; yield 139 mg (69%): 'H
NMR (CD2CI 2, 200 C) 6 9.82 (s, 1H, W=CH), 7.50 (s, 2H, Ar), 7.13 (m, 12H, Ar), 6.94
(m, 12H, Ar), 6.86 (m, 8H, Ar), 6.80 (m, 8H, Ar), 6.62 (s, 4H, Ar), 6.01 (s, 4H, CHPh 2 ),
2.14, (s, 6H, CH3), 1.13 (s, 9H, CMe 3 ); 13 C NMR (CD 2Cl 2 , 200 C) 6 260.6, 159.8, 144.4,
143.6, 134.2, 133.6, 133.4, 131.5, 130.2, 130.1, 130.0, 128.5, 128.4, 126.5, 126.4, 123.6,
50.2, 46.0, 34.4, 21.3.
Anal. Calcd for C7 7H66Br3 NO 2 W: C, 63.31; H, 4.55; N, 0.96.
Found: C, 63.63; H, 4.56; N, 0.89.
W(NArCl 2CF3 2 Cl 2(dme) (1c):
N-trimethylsilyl-2,6-dichloro-4-(trifluoromethyl)aniline
(44.65g, 148 mmol) was added to a solution of WC1 6 (14.6g, 36.9 mmol) in 400mL
benzene. The mixture was stirred for 48h and all solvents were removerd in vacuo.
57
The precipitate was
isolated on a glass frit and washed with pentane; yield 24.98g (85%):
'H NMR (C6 D6
,
Minimal DME was added to the residue, followed by pentane.
200 C) 6 7.21 (s, 4H, Ar), 3.54 (s, 6H, CH3), 3.05 (s, 4H, CH2 ); 13C NMR (C6 D6 , 200 C) 6
132.7, 127.0, 125.1 (q), 124.6, 121.0, 71.4, 64.9. Anal. Calcd for C18 HI 4 N 2 F6 C1 4 02 W: C,
26.99; H, 1.76; N, 3.50. Found: C, 26.92; H, 1.72; N, 3.23.
W(NArCl 2CF3 )2(CHCMe3 )2 (2c). A solution of ic (4.21g, 5.25 mmol) in 150mL of Et2O
was chilled for lh. Neopentylmagnesium chloride (1.555M in Et 20, 6.93mL, 10.8 mmol)
was added dropwise to the mixture. After 2h, the suspension was filtered through Celite
and the Celite pad was washed with Et2O until the filtrate ran colorless. The solvents
were removed from the filtrate in vacuo. A small quantity of acetonitrile was added to
the residue and the resulting yellow solid was isolated by filtration; yield 3.21g (78%):
'H NMR (C 6D6 , 20 0C) 6 7.27 (s, 4H, Ar), 2.25 (s, 4H, CH2), 1.15 (s, 18H, CMe3 );
3
1C
NMR (CD 2Cl 2 , 20-C) 6 153.2, 131.7, 126.5, 125.3, 123.4, 97.4, 35.6, 34.1; '9F NMR
(CD6 , 20-C) 6 -62.5. Anal. Calcd for C 24 H 2 6Cl 4 F6N 2 W: C, 36.86; H, 3.35; N, 3.58.
Found: C, 37.26; H, 3.28; N, 3.53.
W(NArCl 2CF 3 )2(CHCMe3)(OTf) 2(dme) (3c).
A solution of W(NArC1 2 CF3) 2 (CH 2 CMe 3 ) 2
(2.23g, 2.85 mmol) in a mixture of 30mL Et2O and 15mL DME was chilled at -30'C
overnight. HOTf (1.28g, 8.55 mmol) in 5mL of cold Et 2O was added dropwise to the red
solution. After 1.5h, the volatiles were removed in vacuo and minimal dichloromethane
was added to the residue. The mixture was filtered through Celite and the solvents were
removed from the filtrate in vacuo. Pentane was added to the residue and the insoluble
product was isolated by filtration; yield 1.22g (49%): 'H NMR (CD 2Cl 2 , 200 C) 6 11.52
(s, 1H, W=CH), 7.72 (s, 2H, Ar), 4.61 (s, 3H, CH3), 4.38 (m, 2H, CH), 4.16 (m, 1H, CH),
3.73 (s, 3H, CH3), 3.73 (m, 1H, CH), 1.23 (s, 9H, CMe3);
303.8 (W=C, 'JwC = 170 Hz), 150.9, 135.7, 129.8 (q,
= 315 Hz), 119.2 (IJCF = 315Hz), 119.1
('JCF =
2
JCF =
3C
NMR (CD 2Cl 2 , 20 0C) 6
34.4 Hz), 126.2, 120.0 (q, 'JCF
315Hz), 82.4, 79.6, 71.7, 62.2, 48.5, 33.0;
'9F NMR (CD 2 Cl 2 , 20 0C) 6 -77.4, -78.2. Anal. Calcd for C, 8 H2 2 Cl 2 F 9No8 S 2 W: C, 24.84;
H, 2.55; N 1.61. Found: C, 24.78; H, 2.38; N 1.47.
58
W(NArC1 2CF3)(CHCMe 3)(ODBMP) 2 (4c).
A mixture of 3c (112mg, 0.129 mmol) and
LiODBMP-Et 2O (134mg, 0.257 mmol) in IOmL Et 2O was stirred overnight. Workup and
isolation followed that of 4a. Analytically pure product was obtained by recrystallization
from a mixture of toluene and pentane; yield 106mg (61%): 'H NMR (CD2Cl 2 , 20 0C) 6
9.31 (s, 1H, W=CH), 7.38 (s, 2H, Ar), 7.15-7.09 (m, 12H, Ar), 6.93-6.86 (m, 12H, Ar),
6.84-6.74 (m, 16H, Ar), 6.57 (s, 4H, Ar), 5.85 (s, 4H, CHPh 2), 2.11 (s, 6H, CH3 ), 1.11 (s,
9H, CMe3 );
3
C NMR (CD 2Cl 2, 20 0C) 6 256.4, 144.3, 143.5, 133.3, 133.3, 131.8, 130.0,
129.9, 129.7, 128.9, 128.6, 128.5, 128.4, 126.5, 126.5, 124.9
= 270 Hz), 50.1, 45.9, 34.5, 21.3;
'9F
NMR (CD6 ,
20 0 C)
( 2 jCF
=
3.75Hz), 123.3 (OJCF
6 -62.5.
Anal. Calcd for
C 78H66Cl 2 F3 NO 2 W: C, 68.83; H, 4.89; N, 1.03. Found: C, 69.08; H, 4.82; N 1.00.
W(NArcF 3) 2)2C12(dme) (1d).
N-trimethylsilyl-3 ,5-bis(trifluoromethyl)aniline (65g, 215
mmol) was added over 10 minutes to a solution of WCl6 (21.33g, 53.8 mmol) in 400mL
of benzene in a round bottom flask. The red-orange mixture was stirred for 36h and the
mixture was filtered through a glass frit. The solid was washed with minimal DME and
,
pentane to give a yellow-orange solid; three crops totaled 30.2g (70%): 'H NMR (C6 D6
20 0 C) 6 7.52 (s, 2H, Ar), 7.29 (s, 1H, Ar), 3.29 (s, 6H, CH3), 2.93 (s, 4H, CH2 ); 13C NMR
(C 6D6 , 20*C) 6 156.2, 132.4 (q,
2
JCF =
33.8 Hz), 123.8, 123.6 (q,
71.5, 64.6; '9 F NMR (CD6 , 20 0C) 6 -63.6.
JCF =
271 Hz), 119.0,
Anal. Calcd for C 2 0HI 6 Cl 2 FI 2 N 2 0 2 W:
C,
30.06; H, 2.02; N, 3.51. Found: C, 29.98; H, 2.09; N, 3.38.
W(NAr(CF 3) 2)2 (CH2CMe3 ) 2 (2d). A solution of W(NAr(CF3) 2 )Cl2 (dme) (1-.g, 1.25 mmol)
in Et 2O was chilled for lh. Neopentylmagnesium chloride (1.06mL, 2.57mmol, 2.42M in
Et2O) was added dropwise and the mixture was stirred overnight. The solvents were
removed from the mixture. Diethyl ether was added to the residue and the mixture was
filtered through Celite. Toluene was added to the filtrate and all volatiles were removed
in vacuo. Pentane was added to the resulting yellow solid and the solid was filtered off to
give the product.
Analytically pure product was obtained by recrystallization from
CH2Cl 2/pentane; yield 699mg (72%): 'H NMR (C6D6 , 20 0 C) 6 7.49 (s, 4H, Ar), 7.45 (s,
2H, Ar), 1.75 (s, 4H, CH2), 0.99 (s, 18H, CMe3 ); 13 C NMR (CD2Cl 2, 20 0 C) 6 157.5, 132.4
(q,
2
JCF =
33.8 Hz), 124.7, 123.5 (q,
'JCF
= 271 Hz), 118.5, 97.2, 37.3, 34.3;
19F
NMR
59
(C 6D6 , 200 C) 6 -63.5. Anal. Calcd for C 2 6 H28FI 2 N2 W: C, 40.02; H, 3.62; N, 3.59. Found:
C, 39.93; H, 3.57; N, 3.43.
W(NAr(CF 3 )2)(CHCMe 3)(OTf)2(dme) (3d). A solution of 2d (289mg, 0.370 mmol) in a
mixture of 7mL DME and 7mL Et 2O was chilled at -30'C for 2h. A chilled solution of
HOTf (166 mg, 1.11 mg) in 4mL of Et 2O was added dropwise. After stirring the reaction
mixture overnight, the solvent was removed in vacuo. Toluene was added to the residue
and the mixture was filtered through Celite. The solvents were remived from the filtrate
in vacuo and pentane was added to the residue. The yellow product was isolated on a
glass frit; yield 321mg (84%): 'H NMR (C6D6 , 20*C) 6 10.45 (s, 1H, W=CH), 8.40 (s,
2H, Ar), 7.53 (s, IH, Ar), 3.07 (s, 3H, CH3), 2.96 (t, 2H, CH2), 2.80 (s, 3H, CH3), 2.43 (t,
2H, CH2), 1.35 (s, 9H, CMe3 ); 13 C NMR (C6D6 , 20 0C) 6 291.2 (W=C), 154.9, 133.0 (q,
2
jCF =
33.8 Hz), 128.5 (m), 123.3 (q,
74.5, 69.8, 64.5, 62.3, 48.8, 33.7;
'9F
IJCF =
272 Hz), 121.5 (m), 119.8 (q,
NMR (C6 D6
, 20 0C)
JCF =
376 Hz),
6 -63.5, -77.2. Anal. Calcd for
C, 9 H23F 2 NO8 S 2 W: C, 26.25; H, 2.67; N, 1.61. Found: C, 25.86; H, 2.45; N, 1.50.
W(NAr(CF 3 )2)(CHCMe 3)(ODBMP) 2-2 DME (4d). Compound 3d (75mg, 0.086 mmol)
and LiODBMP-Et 2O (90mg, 0.173 mmol) were added to 10mL of Et 2O at room
temperature and the mixture was stirred overnight.
Solvents were removed from the
mixture in vacuo. The residue was dissolved in toluene and the mixture was filtered
through Celite. The solvents were removed from the filtrate in vacuo and ~1mL of DME
was added and the mixture was cooled at -30'C overnight to give a yellow-orange
crystalline product. The mother liquor was drawn off, the solid washed once with cold
DME, and the solid was dried in vacuo; yield 86mg, (65%): 'H NMR (CD 2Cl 2, 20 0C) 6
7.13-7.03 (m, 25H, Ar + W=CH), 6.98-6.88 (m, 17H, Ar), 6.75 (s, 2H, Ar), 6.59 (s, 4H,
Ar), 5.94 (s, 4H, CHPh 2), 3.47 (s, 8H, CH2), 3.32 (s, 12H, CH3 ), 2.12 (s, 6H, CH3), 0.83
(s, 9H, CMe3);
131.4, 131.3 (q,
3C
2
NMR (CD 2Cl 2 , 200 C) 6 248.0, 158.3, 156.5, 144.1, 143.4, 132.6,
JCF
= 33.75 Hz), 130.0, 129.9, 129.7, 128.68, 128.65, 126.8, 126.7,
126.2 (m), 123.6 (q, IJCF = 271 Hz), 118.0 (m), 72.2, 59.1, 50.5, 45.2, 33.5, 21.3; '9F
(CD 2Cl 2 , 20-C) 6 -65.4. Anal. Calcd for C 87H87F 6NO 6W: C, 67.83; H, 5.69; N, 0.91.
Found: C, 68.04; H, 5.37; N, 1.06.
60
W(NArc')(CHCMe 3 )(ODBMP) 2 (4e). A mixture of W(NArC)(CHCMe 3)(OTf) 2(dme)
(97mg, 0.121 mmol) and LiODBMP-Et 2O (126mg, 0.242 mmol) in lOmL Et2O at room
temperature was stirred overnight.
Workup and isolation followed the procedure
employed for 4a. Analytically pure product was obtained by recrystallization from a
mixture of toluene and pentane; yield 99mg (63%): 'H NMR (CD 2C 2 , 20'C) 6 9.32 (s,
LH, W=CH), 7.16-7.08 (m, 14H, Ar), 9.94 (t, IH, Ar), 6.90-6.76 (m, 28H, Ar), 6.54 (s,
3
1C
NMR (CD 2 Cl 2
,
4H, Ar), 5.84 (s, 4H, CHPh 2), 2.10 (s, 6H, CH 3), 1.13 (s, 9H, CMe3 );
20-C) 6 254.6, 159.5, 150.9, 144.5, 143.6, 133.4, 133.0, 131.3, 130.1, 130.0, 129.9,
128.4, 128.3, 127.7, 126.5, 126.4, 126.1, 50.0, 45.9, 34.5, 21.3. Anal. Calcd for
C77 H 67Cl 2 NO 2 W:
C, 71.52; H, 5.22; N, 1.08. Found: C, 71.38; H, 5.15; N 0.86.
W(NArF)(CHCMe 3 )(ODBMP) 2 (4f). A mixture of W(NArF)(CHCMe 3)(OTf)2(dme)
(126mg, 0.153 mmol) and LiODBMP-Et 2O (159mg, 0.306 mmol) in lOmL Et2O was
stirred for 2h.
Workup and isolation followed the procedure employed for 4a; yield
118mg (59%): 'H NMR (C6 D 6 , 20*C) 6 7.20 (m, 14H, Ar), 7.05-6.85 (30H, Ar), 6.32 (s,
4H, CHPh 2), 1.83 (s, 6H, CH3), 1.14 (s, 9H, CMe3 ); 13C NMR (CD 2Cl 2, 20 0 C) 6 251.7,
144.6, 144.1, 144.0, 143.3, 142.7, 138.8, 136.5, 132.8, 130.00, 129.98, 129.7, 128.9,
128.57, 128.55, 126.7, 126.5, 50.1, 45.3, 33.7, 21.3; '9F NMR (C6 D6 ,20 0C) 6 -147.1 (t,
2F), -160.3 (d, 2F), -164.6 (s, IF). Anal. Calcd for C77 HMF 5NO 2 W: C, 70.37; H, 4.91; N,
1.07. Found: C, 70.13; H, 4.83; N 0.98.
W(NAr 2,6Me 2)(CHCMe)(ODBMP)
2
(4g): A mixture of W(NAr')(CHCMe 3)(OTf) 2(dme)
(133mg, 0.175 mmol) and LiODBMP-Et 2O (182mg, 0.349 mmol) in 10 mL Et2O was
stirred for 2h.
Workup and isolation followed the procedure employed for 4a; yield
164mg (75%): 'H NMR (CD 2Cl 2 , 200 C) 6 9.12 (s, 1H, W=CH), 7.15-7.08 (m, 12H, Ar),
6.90-6.74 (m, 31H, Ar), 6.56 (s, 4H, Ar), 5.82 (s, 4H, CHPh 2), 2.10 (s, 6H, CH3 ), 1.86 (s,
6H, CH3), 1.07 (s, 9H, CMe3 ); 13C NMR (CD 2Cl 2 , 20 0 C) 6 249.7, 159.3, 155.3, 144.5,
143.6, 135.2, 133.3, 131.1, 130.10, 130.05, 129.7, 128.4, 128.3, 127.4, 126.5, 126.4,
125.9, 50.0, 46.1, 34.6, 21.2, 19.8. Anal. Calcd for C7 9H 73 NO 2 W: C, 75.77; H, 5.88; N,
1.12. Found: C, 76.16; H, 6.00; N, 0.93.
61
W(NAr 3,sMe 2)(CHCMe 2Ph)(ODBMP)2
W(NAr 3,sMe 2)(CHCMe 2Ph)(OTf) 2(dme)
(4h).
(93mg, 0.123
A
mmol)
mixture
and
of
LiODBMP-Et 2O
(127mg, 0.244 mmol) in 10mL Et20 was stirred 2h. Workup and isolation followed the
procedure employed for 4a; yield 118mg (79%): 'H NMR (CD 2Cl 2 , 20'C) 6 7.11-6.81
(m, 39H, W=CH + Ar), 6.74 (d, 2H, Ar), 6.68 (s, IH, Ar), 6.60 (s, 4H, Ar), 6.12 (s, 2H,
Ar), 5.90 (s, 4H, CHPh2), 2.16 (s, 6H, CH3), 2.01 (s, 6H, CH3), 1.33 (s, 6H, CMe 2Ph); 13C
NMR (CD 2Cl, 20-C) 6 242.8, 158.7, 156.0, 152.1, 144.4, 143.7, 137.7, 133.0, 131.0,
130.1, 130.0, 129.5, 128.6, 128.5, 128.0, 127.9, 126.6, 126.6, 126.5, 125.6, 124.6, 51.7,
50.3, 34.2, 21.3, 21.1. Anal. Caled for C8Hj
75
NO 2 W: C, 76.76; H, 5.75; N, 1.07. Found:
C, 77.13; H, 5.90; N, 0.76.
Procedure for polymerization using W(R)(CHMe 2R')(ODBMP) 2 as the initiator.
From a 0.2M stock solution in CDC1 3 , ImL (50 equiv) of dicarbomethoxynorbornadiene
.
(DCMNBD) was charged with lmL of a 0.004M stock solution of catalyst in CDC1 3
Aliquots were taken out of the reaction vial approximately every 6-9 minutes for three to
four cycles, brought outside the glovebox in a capped vial, and quenched with wet
CDC1 3. Integrations of polymer were measured with respect to the monomer peak at 6.92
ppm in CDC1 3. The rate constants were determined by plotting ln[([M]+[P])/[M] v. time,
where [M] and [P] represent integration of monomer peak and all polymer peaks (approx.
5.50 ppm - 5.20 ppm), respectively, and where time is measured in seconds. The slope
of this curve was divided by the concentration of catalyst to give polymerization rate
constant.
W(NArcI 3)(CHCMe3)(OC(CF 3)3)2 (5). 3a (100mg, 0.120 mmol) in ~8mL toluene was
charged with LiOC(CF 3)3 (58mg, 0.240 mmol) and was stirred overnight. The mixture
was then filtered through Celite and dried to give a yellow powder (88mg, 81%). 'H
NMR (C6 D 6 , 500 MHz): 6 9.46 (s, 1H, W=CH), 6.78 (s, 2H, Ar), 1.06 (s, 9H, CMe 3 ); 13 C
NMR (C6 D 6 , 125 MHz, 20'C): 266.37 (W=CH, Jve = 189 Hz), 149.09, 133.94, 133.28,
122.35, 120.03, 106.72, 47.09, 33.07; 19F NMR (282 MHz): -73.48. Anal. Calcd for
C,9 H, 2 Cl 3 Fi 8NO 2 W: C, 24.85; H, 1.32; N, 1.53. Found: C, 24.97; H, 1.31; N, 1.55.
62
W(NArC1 2CF 3)(CHCMe 3 )(OC(CF 3)3)2 (6). 3c (173mg, 0.199 mmol) in ~8mL toluene was
charged with LiOC(CF 3)3 (96mg, 398 mmol) and was stirred overnight. The resulting
mixture was filtered through Celite, dried, and precipitated from cold pentane and
isolated by filtration (13 1mg, 69%). 'H NMR (C6 D 6 , 500 MHz): 6 9.43 (s, 1H, W=CH),
7.12 (s, 2H, Ar), 1.03 (s, 9H, CMe3 );
129.54 (q, 2 'CF
84.62
(m),
=
13
C NMR (C6 D6 , 125 MHz) 266.79, 151.97, 133.94,
34 Hz), 125.16 (m), 122.77 (q,
46.82,
32.78;
'9F NMR
'JCF =
271 Hz), 120.95 (q,
(282 MHz)
-72.89.
'JCF=
290 Hz),
Anal. Calcd for
C2 0HI2 Cl 2 F2 1NO 2 W: C, 25.23; H, 1.27; N, 1.47. Found: C, 25.35; H, 1.86; N, 1.72.
W(NArCI 3)(CHCMe3 )(2,5-Me 2pyr)2 (7a). 10 (1.0g, 1.20 mmol) was charged to a flask
with 4OmL toluene and -1mL DME. The resulting solution was chilled at -30'C for 2h.
LiMe 2pyr (254mg, 2.51 mmol) was then added to the stirred solution and the resulting
mixture was allowed to stir for 1.5h. Solvent was removed under vacuum and the residue
was charged with CH 2 Cl 2 . The mixture was filtered through Celite and washed with
CH2 C 2 . The filtrate was dried under vacuum to give an orange solid (641mg, 84%). 'H
NMR (C6 D6 , 500 MHz) 6 11.02 (bs, 1H, W=CH), 6.81 (s, 2H, Ar), 6.03 (bs, 4H, pyr),
2.26 (bs, 12H, pyr), 1.21 (s, 9H, Me 3 ); 13C NMR (125 MHz): 288.14 (W=C), 148.89,
132.52, 130.21, 128.48, 128.34, 107.62, 48.42, 33.83, 18.62.
C23H2,Cl 3 N 3 W:
Anal. Calcd for
C, 43.39; H, 4.43; N, 6.60. Found: C, 43.11; H, 4.31; N, 6.41.
W(NArBr 3)(CHCMe 3 )(Me 2pyr)2 (7b). 3b (400mg, 0.412 mmol) in ~10mL toluene was
charged with LiMe 2pyr (83mg, 0.825 mmol) and was stirred overnight. The resulting
mixture was filtered through Celite and washed with CH2 C 2 . The filtrate was dried,
charged with pentane, and the resulting solid was isolated on a glass frit. The filtrate was
taken up in pentane and dried 2-4 times, and upon more thorough drying, more solid can
be isolated from pentane. Yield: 285mg, 83%. 'H NMR (500 MHz, C6D6) 6 10.92 (bs,
IH, W=CH), 7.27 (s, 2H, Ar), 6.05 (bs, 4H, Me 2pyr), 2.27 (bs, 12H, Me 2pyr), 1.22 (s, 9H,
CMe3 );
3
C NMR: Even at high concentrations in varying solvents, the spectrum is too
broad to obtain a reliable
3
1C
NMR. Anal. Calcd for C23H 2 8Br 3 N3W: C, 35.87; H, 3.67; N,
5.46. Found: C, 36.11; H, 3.48; N, 5.17.
63
W(NArCF 3 )2 )(CHCMe 3 )(Me 2 pyr)2 (7c). 3d (100mg, 0.115 mmol) was dissolved in 8mL
toluene and was charged with LiMe 2pyr (23.3mg, 0.230 mmol) at room temperature.
After 5h, the suspension was filtered over Celite and washed with CH 2 C 2 . The filtrate
was dried under vacuum and charged with pentane and stirred. The solvent was removed
under vacuum to give a yellow/brown foam (67mg, 87%). 'H NMR (300 MHz, C6D6 ) 6
10.67 (s, LH, W=CH), 7.47 (s, 3H, Ar), 5.84 (s, 4H, pyr), 2.12 (s, 12H, pyr), 1.13 (s, 9H,
CMe 3 ); 13C NMR (125 MHz, CD 2 Cl 2 ) 286.84 (W=CH), 157.08, 132.46 (q, JCF
125.84, 123.90 (JCF
=
=
33.25),
146.25 Hz), 119.03, 186.84, 106.02, 49.10, 34.42, 18.05; '9F NMR
(282 MHz, C 6D6) -63.20.
W(NArCI 3)(CHCMe 3)(Me 2pyr)(OHMT) (8). 7a (250mg, 0.393 mmol) was charged to a
flask with 4OmL Et2 O, and the resulting solution was chilled for lh. HMTOH (130mg,
0.393 mmol) was added and the solution was allowed to stir and warm to room
temperature overnight. The solution was dried under vacuum and the resulting residue
was charged with minimal pentane to give a yellow solid (119mg, 35%). The filtrate was
again concentrated and put in the freezer to isolate a pure second crop of product. 'H
NMR (C 6D6 , 500 MHz) 8.40 (s, 1H, W=CH,
IJCH
=
115Hz,
2
JWH =
17 Hz), 6.93 (m, 3H,
OHMT), 6.81 (s, 4H, OHMT), 6.80 (s, 2H, Ar), 6.06 (s, 2H, pyr), 2.14 (s, 12H, OHMT),
2.11 (s, 6H, pyr), 2.03 (s, 6H, OHMT), 1.13 (s, 9H, CMe 3 ); 13C NMR (125 MHz): 269.28
(W=CH), 157.98, 149.47, 137.18, 136.84, 136.51, 135.04, 132.27, 130.41, 129.71,
129.49, 128.65, 127.70, 123.80, 110.29,46.22, 33.10, 21.33, 21.21, 20.49.
W(NArcI 3)(CHCMe 3)(Me 2pyr)(ODFT) (9). 7a (304mg, 0.477 mmol) was charged to a
flask with 20mL Et2O and chilled for 45 min. DFTOH (203mg, 0.477 mmol) was added
to the stirred mixture in 2mL Et 2O dropwise. After lh, the volatiles were removed and
pentane was charged to the resulting residue to give 239mg; further recrystallization from
Et2O gave an extra 101mg. (340mg, 74%). 'H NMR (C6D6 , 500 MHz) 8.87 (s, 1H,
W=CH, 'JCH
=
110Hz,
2
JWH =
16 Hz), 7.09 (d, 2H, ODFT), 6.85 (t, 1H, ODFT), 6.61 (s,
2H, Ar), 5.87 (bs, 2H, Me 2pyr), 2.11 (bs, 6H, Me 2pyr), 0.93 (s, 9H, CMe 3 ); 13C NMR
(125 MHz):
270.46 (W=CH, 'Jwc = 190Hz), 163.07, 148.86, 145.67 (m), 143.71 (m),
64
142.26 (m), 140.44 (m), 139.25 (m), 137.26 (m), 133.73, 132.15, 131.21, 127.95, 123.09,
118.02, 111.67 (td), 110.98, 65.95, 46.77, 32.44; '9F NMR (282 MHz): -140.01 (d, 2F,
ortho), -140.54 (d, 2F, ortho), -153.09 (t, IF, para), -161.38 (m, 2F, meta); Anal. Caled
for C3 5 H23Cl 3 FION 2 OW: C, 43.44; H, 2.40; N, 2.89. Found: C, 43.50; H, 2.33; N, 2.73.
W(NAr(CF 3 )2)(CHCMe 3)(ODFT) 2 (10).
W(NAr(CF 3 )2 )(CHCMe 3)(Me 2pyr) 2 (85mg, 0.127
mmol) was charged with DFTOH (108 mg, 0.254 mmol) in benzene at room temperature.
The mixture was stirred for lh, after which the volatiles were removed under vacuum.
The residue was charged with pentane and stirred overnight to give the yellow product,
which was isolated by filtration. The filtrate was dried and charged with minimal Et2O
and set at -30'C. An extra 48 mg of product was obtained by filtration. Total: 144 mg,
85%. 'H NMR (500 MHz, C 6 D6 )
6
7.81 (s, 1H, W=CH), 7.39 (s, 1H, Ar), 7.15 (s, 2H,
Ar), 6.93 (d, 4H, DFTO), 6.73 (t, 2H, DFTO), 0.71 (s, 9H, CMe 3);
161.23, 155.91, 144.42 (d,
254), 137.98 (d, IJCF
=
'JCF =
243 Hz), 141.51 (d,
254), 133.66, 132.72 (q,
'JCF =
'JCF =
13C
NMR 253.82,
254 Hz), 138.34 (d,
IJCF
=
34 Hz) 125.07, 123.42, 122.17,
119.74, 117.76, 111.40, 45.46, 32.87; '9F NMR (282 MHz) -63.76 (s, 6F), -140.24 (d,
8F), -153.48 (t, 4F), -161.69 (dt, 8F); Anal. Calcd for C4 qH 1 F2 6NO 2 W: C, 44.20; H, 1.44;
N, 1.05. Found: C, 43.99; H, 1.57; N, 1.06.
65
X-ray crystal structure determination details (Performed by Dr. Peter Muller).
Low-temperature diffraction data (0-and o-scans) were collected on a Bruker-AXS
X8 Kappa Duo diffractometer coupled to a Smart APEX2 CCD detector with Mo Ku
radiation (X = 0.71073
A)
from an IgS micro-source for the structures of compounds 3a
and 4a, and on a Siemens Platform three-circle diffractometer coupled to a Bruker-AXS
Smart Apex CCD detector with graphite-monochromated Mo Ka radiation (A = 0.71073
A) for the structure of compound 2d. Absorption and other corrections were applied
using SADABS. 2 7 All structures were solved by direct methods using SHELXS 28 and
refined against F2 on all data by full-matrix least squares with SHELXL-97 (structure of
X8_3a) or SHELXL-2013
29
(structures of 4a and 2d) using established refinement
approaches.3 0 Coordinates for hydrogen atoms bound to carbon directly attached to the
central metal atoms were taken from the difference Fourier synthesis and those hydrogen
atoms were subsequently refined semi-freely with the help of distance restraints. All
other 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 Uq value of the atoms they are linked to (1.5 times for
methyl groups).
Compound 3a crystallizes in the monoclinic centrosymmetric space group P21/n
with one molecule of 3a and one molecule of dichloromethane per asymmetric unit.
There is no disorder and except for the Cl-H1 distance restraint, no restraints were
applied. Compound 4a crystallizes in the triclinic centrosymmetric space group PI with
one molecule of 4a and one half Et 2O molecule per asymmetric unit. The half Et2 O
molecule is located near a crystallographic inversion center and was refined as over two
independent sites, resulting in a four-fold disorder of the full Et 2O molecule in the unit
cell with two of the four disorder components pairwise related to the other two by the
crystallographic inversion center.
In addition, the alkylidene ligand was found to be
disordered over two positions, approximately corresponding to a slight rotation about the
WI-Cl and a stronger rotation about the Cl -C2 bond. 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. The
circumstance that the structure contains only half a molecule of diethyl ether for every
66
full molecule of 4a results in a non-integer number for the element oxygen in the
empirical Formula in Table S3.
Compound 2d crystallizes in the monoclinic centrosymmetric space group P2 1/n
with one half molecule of 2d per asymmetric unit. The other half of the molecule is
generated by a crystallographic inversion center. Two of the four crystallographically
independent CF3 groups were refined as disordered over two positions, corresponding to
a rotation about the respective C-C bonds. All C-F bonds and all F-C-F angles in
the structure were refined to be equivalent. For one of the two disordered CF3 groups the
disorder was found to correspond to a rotation of approximately 600 about the C-C bond
and fluorine atoms located on opposite sides of the disorder axis were pairwise
constrained to have identical anisotropic displacement parameters as described in section
4.2 in reference 4. In addition, similarity and rigid bond restraints were applied to the
anisotropic displacement parameters of all atoms involved in the disorders.
The diffractometer used for data collection for the structures of compounds 3a and
4a was purchased with the help of funding from the National Science Foundation (NSF)
under Grant Number CHE-094672 1.
67
Table Si. Crystal data and structure refinement for 3a
Identification code
x12199
Empirical formula
C18 H24 C15 F6 N 08 S2 W
Formula weight
921.60
Temperature
100(2) K
Wavelength
0.71073 A
Crystal system
Monoclinic
Space group
P2(1)/c
Unit cell dimensions
a = 9.7487(7)
a= 900
b = 20.1371(14)
3= 92.5210(10)0
c = 15.5354(11)A
y = 900
A3
Volume
3046.8(4)
Z
4
Density (calculated)
2.009 Mg/m3
Absorption coefficient
4.446 mm-i
F(000)
1792
Crystal size
0.21 x
Theta range for data collection
1.66 to 31.500.
Index ranges
- 14<=h<=
Reflections collected
212424
Independent reflections
10153 [R(int) = 0.04141
Completeness to theta = 31.500
100.0
Absorption correction
Semi-empirical from equivalents
Max. and min. transmission
0.5749 and 0.4553
Refinement method
Full-matrix least-squares on F2
Data / restraints / parameters
Goodness-of-fit on F
2
0.16
x 0.14 mm
3
%
14, -29<=k<=29, -22<=l<=22
10153 / 1 / 378
1.030
Final R indices [I>2sigma(I)]
RI = 0.0 148, wR2 = 0.0345
R indices (all data)
RI = 0.0164, wR2 = 0.0350
Largest diff. peak and hole
1.548 and -0.685 e.A-3
68
Table S2. Crystal data and structure refinement for 2d.
Identification code
14011
Empirical formula
C52 H56 F24 N4 W2
Formula weight
1560.70
Temperature
100(2) K
Wavelength
0.71073
Crystal system
Monoclinic
Space group
P 2 1/n
Unit cell dimensions
a = 13.8640(19)
A
A
14.478(2) A
c= 900
b = 14.775(2)
p= 97.329(2)0
c=
y = 900
2941.6(7) A3
Z
2
Density (calculated)
1.762 Mg/m3
Absorption coefficient
4.022 mm-'
F(000)
1520
Crystal size
0.460 x 0.440 x 0.130 mm 3
Theta range for data collection
1.915 to 30.505'.
Index ranges
-19<=h<=19, -21<=k<=21, -20<=l<=20
Reflections collected
82838
Independent reflections
8967 [R(int) = 0.0376]
Completeness to theta = 25.2420
100.0
Absorption correction
Semi-empirical from equivalents
Refinement method
Full-matrix least-squares on F 2
Data / restraints / parameters
Goodness-of-fit on F
2
%
Volume
8967 / 617 / 422
1.050
Final R indices [I>2sigma(I)]
RI = 0.0195, wR2 = 0.0462
R indices (all data)
RI = 0.0228, wR2 = 0.0482
Extinction coefficient
n/a
Largest diff. peak and hole
1.069 and -0.774 e.&-3
69
Table S3. Crystal data and structure refinement for 4a.
Identification code
x13201
Empirical formula
C79 H71 C13 N 02.50 W
Formula weight
1364.56
Temperature
100(2) K
Wavelength
0.71073
Crystal system
Triclinic
Space group
P1
Unit cell dimensions
a = 12.8493(l[8) A
A
b = 13.6749(19)
A
c = 20.269(3)
a= 87.484(3)
@= 88.749(3)*
y = 69.065(3)0
Volume
3323.2(8) A3
Z
2
Density (calculated)
1.364 Mg/m3
Absorption coefficient
1.907 mm-1
F(000)
1394
Crystal size
0.060 x 0.050 x 0.015 mm 3
Theta range for data collection
1.596 to 30.5080
Index ranges
-
Reflections collected
108220
Independent reflections
20238 [R(int) = 0.0787]
Completeness to theta = 25.2420
100.0
Absorption correction
Semi-empirical from equivalents
Refinement method
Full-matrix least-squares on F2
Data / restraints / parameters
20238 / 358 / 887
Goodness-of-fit on F2
1.027
Final R indices [I>2sigma(I)]
RI = 0.0367, wR2 = 0.0686
R indices (all data)
RI = 0.0553, wR2 = 0.0750
Extinction coefficient
n/a
Largest diff. peak and hole
2.112 and -1.159 e.A-3
%
18<=h<= 18, -19<=k<= 19, -28<=l<=28
70
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Betz, P. Organometallics 1990, 9, 2262; b) Schrock, R. R.; Murdzek, J. S.; Bazan, G.;
Robbins, J.; DiMare, M.; O'Regan, M. J. Am. Chem. Soc. 1990, 112, 3875; c) Fox, H. H.;
Yap, K. B.; Robbins, J.; Cai, S.; Schrock, R. R. Inorg. Chem. 1992, 31, 2287; d) Gibson,
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Knoll, K.; Feldman, J.; Murdzek, J. S.; Yang, D. C. J. Mol. Catal. 1988,46,243; c)
Schrock, R. R.; Feldman, J.; Cannizzo, L. F.; Grubbs, R. H. Macromolecules 1987,20,
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R. R.; Crowe, W. E.; Bazan, G. C.; DiMare, M.; O'Regan, M. B.; Schofield, M. H.
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Arndt, S.; Schrock, R. R.; Miller, P. Organometallics2007, 26, 1279; d) Cefalo, D. R.;
Kiely, A. F.; Wuchrer, A.; Jamieson, J. Y.; Schrock, R. R.; Hoveyda, A. H. J. Am. Chem.
Soc. 2001, 123, 3139.
4 a) Yuan, J.; Schrock, R. R.; Mfler, P.; Axtell, J. C.; Dobereiner, G. E. Organometallics
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Organometallics2013, 32, 2983.
5 a) Mann, T. J.; Speed, A. W. H.; Schrock, R. R.; Hoveyda, A. H. Angew. Chem., Int.
Ed. 2013, 52, 8395; b) Wang, C.; Yu, M.; Kyle, A. F.; Jakubec, P.; Dixon, D. J.; Schrock,
R. R.; Hoveyda, A. H. Chem. Eur. J. 2013, 19, 2726; c) Wang, C.; Haeffner, F.; Schrock,
R. R.; Hoveyda, A. H. Angew. Chem. Int. Ed. 2013, 52, 1939.
6 Jamieson, J. Y. Ph.D. Thesis, Massachusetts Institute of Technology, Cambridge, MA,
2002.
7 Pilyugina, T. S.; Schrock, R. R.; Hock, A. S.; Mffller, P. Organometallics2005, 24,
1929.
8 Krieckmann, T.; Arndt, S.; Schrock, R. R.; Mfller, P. Organometallics2007, 26, 5702.
9 Dreisch, K.; Andersson, C.; Stalhandske, C. Polyhedron 1991, 10, 2417.
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10
a) Rufanov, K. A.; Kipke, J.; Sundermeyer, J. Dalton Trans. 2011, 40, 1990; b)
Rufanov, K. A.; Zarubin, D. N.; Ustynyuk, N. A.; Gourevitch, D. N.; Sundermeyer, J.;
Churakov, A. V.; Howard, J. A. K. Polyhedron 2001, 20, 379.
" Tucci, G. C.; Donahue, J. P.; Holm, R. H. Inorg. Chem. 1998,37, 1602.
12 Nielson, A. J. Polyhedron 1987, 6, 1657
13 Schrock, R. R. In Handbook of Metathesis, 2n Ed.; Grubbs, R. H.; O'Leary, D. J., Ed.;
Wiley: Weinheim, Germany, 2015.
14 a) McConville, D. H.; Wolf, J. R.; Schrock, R. R. J. Am. Chem. Soc. 1993, 115,4413;
b) Schrock, R. R.; Lee, J.-K.; O'Dell, R.; Oskam, J. H. Macromolecules 1995,28,5933;
c) Schrock, R. R. Dalton Trans. 2011, 40, 7484; d) Schrock, R. R. Acc. Chem. Res. 2014,
47, 2457; e) Forrest, W. P.; Weis, J. G.; John, J. M.; Axtell, J. C.; Simpson, J. H.;
Swager, T. M.; Schrock, R. R. J. Am. Chem. Soc. 2014, 136, 10910; f) Forrest, W. P.;
Axtell, J. C.; Schrock, R. R. Organometallics2014, 33, 2313.
" a) Oskam, J. H.; Schrock, R. R. J. Am. Chem. Soc. 1993, 115, 11831.
Jeong, H.; John, J. M.; Schrock, R. R.; Hoveyda, A. H. J. Am. Chem. Soc. 2015, 137,
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Am. Chem. Soc. 2011, 133,20754; c) Marinescu, S. C.; Levine, D. S.; Zhao, Y.; Schrock,
R. R.; Hoveyda, A. H. J. Am. Chem. Soc. 2011, 133, 11512; d) Marinescu, S. C.;
Schrock, R. R.; MUller, P.; Takase, M. K.; Hoveyda, A. H. Organometallics2011, 30,
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18 Hock, A. S.; Schrock, R. R.; Hoveyda, A. H. J. Am. Chem. Soc. 2006, 128, 16373.
Singh, R.; Schrock, R. R.; Muller, P.; Hoveyda, A. H. J. Am. Chem. Soc. 2007, 129,
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20 Flook, M. M.; Jiang, A. J.; Schrock, R. R.; MUller, P.; Hoveyda, A. H. J. Am. Chem.
19
Soc. 2009, 131,7962.
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M. R.; Schrock, R. R. Macromolecules 2015, doi: 10.1021/acs.macromol.5b00123.
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Lopez, L. P. H.; Schrock, R. R. J. Am. Chem. Soc. 2004, 126,9526.
24 Storozhenko, P. A.; Belyakova, Z. V.; Starikova, 0. A.; Nosova,
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27 Sheldrick, G. M. SADABS; University of Gttingen: Germany,
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30 MUller, P. Crystallography Reviews 2009,
15, 57-83.
73
Chapter 2
Synthesis and Reactivity of Molybdenum and Tungsten Alkylidene Complexes Bearing
the 2,6-Bis(2,4,6-triisopropylphenyl)phenylimido Ligand
Portions of this chapter have appeared in print:
Axtell, J. C.; Schrock, R. R.; Muller, P.; Smith, S. J.; Hoveyda, A. H. "Synthesis of Molybdenum
and
Tungsten
Alkylidene
triisopropylphenyl)phenylimido
Complexes
(NHIPT)
that
Ligand"
Contain
the
Organometallics
2,6-Bis(2,4,62015,
doi:
10.1021/om501213x.
74
INTRODUCTION
The syn/anti alkylidene isomerism in Movi and WV1 alkylidene species (Figure 2.1) has
been a central focus since its identification in well-characterized olefin metathesis catalysts.! A
great body of work, both experimental and theoretical, has been published in an effort to
understand the mechanism of this interconversion as well as the differing reactivity profiles of
these two isomers (See Introduction).
Z
II
Xo-.M
Y,
.. R
syn
|
H
Z
11
ks/a
H
X11.M-2
\
/
kais
R
anti
M = Movi, WvI
Z= O, NR'
Figure 2.1: Syn/anti isomerism for MovI/WV" alkylidene complexes. The syn isomer is generally favored due to a
stabilizing a-agostic interaction.
Recent work within our group has shown that in certain cases, the anti alkylidene can be
orders of magnitude more reactive,2 even though this is generally not the thermodynamically
preferred isomer:
an electronically favorable a-agostic interaction' is present in the syn
alkylidene conformation, rendering this isomer lower in energy.
Given the low concentrations of anti in solution, it was hypothesized that a (phenyl)imido
ligand with a sufficiently bulky steric profile could override this electronic stabilization on steric
grounds. This would enforce an anti disposition of the alkylidene and provide access to the more
reactive anti isomer (Figure 2.2).
LARGE
N
II
M R
N
I
?I
R
Figure 2.2: Concept for sterically enforcing an anti alkylidene.
The success of MAP species bearing terphenoxide ligands in generating Z olefin
metathesis products prompted an investigation into the use of terphenyl groups on imido ligands.
The nature of Z-selectivity in these MAP species resides in a mutually cis orientation of
metallacyclobutane
substituents
in order to
avoid
unfavorable
interactions
with the
75
terphenoxide. 4 As an imido group, this same principle was predicted to be operative in order to
generate all-anti alkylidene species (Figure 2.3).
"large"
R small
N
II
RI
IMI
R
\R
R
R,
R
R
"large"
Z-selective
syn initiator
>
R
5rR"-'
R
-
R
N
II
IM]
R
R small
Z-selective?
anti initiator?
Figure 2.3: Proposed method for using a terphenylimido ligand to enforce anti alkylidenes and maintain Z-selectivity in
metathesis.
An additional benefit to this framework is the greater steric protection of the alkylidene
ligand by the imido substituent. Whereas [MI-OR bonds in these systems are generally on the
order of ~1.9 - 2.1A, [M]=NR bond distances are usually much shorter (-1.70 - 1.75A), which
is expected given the pseudo triple bond character of the metal-nitrogen bond. This enhanced
steric protection should further prevent bimolecular decomposition of alkylidene complexes, a
well-known mode of catalyst deactivation, 6 thereby increasing catalyst longevity.
Finally, with
the absence of an a-agostic interaction in the anti alkylidene isomer, the alkylidene proton
should be rendered much less acidic (as yet an untested aspect of alkylidene species) and
therefore less susceptible to deprotonation inter- or intramolecularly to form alkylidynes.7
Pioneering work using this model has been carried out by our group utilizing the 2,6dimesitylphenylimido (NHMT) ligand.8 Employing a "mixed imido" synthetic route first
introduced by Gibson and co-workers,9 alkylidene complexes bearing this imido ligand were
synthesized. However, equilibrium mixtures only slightly favoring anti (Ke = kJ/k/a ~ 2-20; see
Figure 2.1) were obtained in most cases. Therefore, in an effort to generate complexes in which
only anti alkylidene isomers would be observed, syntheses of Mo and W species bearing the 2,6bis(2,4,6-triisopropylphenyl)phenylimido (NHIPT) ligand, first introduced by Gavenonis and
Tilley,' 0 were undertaken.
RESULTS AND DISCUSSION
76
I. Synthesis of Molybdenum and Tungsten NHIPT Mixed-Imido Complexes
A. Installation of the NHIPT Ligand
Consistent with the initial formulations of the NHMT system mentioned above,
proceeding through a bisimido intermediate (in which the two imido groups are the same) is
likely not possible due to the steric bulk of the NHIPT ligand. Therefore, the NHIPT fragment is
instead introduced as an anilide.
The syntheses of HIPT-NH 2 and LiN(H)HIPT have been
reported previously.lOc Treatment of Mo(N'Bu) 2C12(dme) or W(Nt Bu)C 2(py) 2 (py = pyridine)
with HIPTN(H)Li in Et2O resulted in dark yellow mixtures and the formation of anilide
complexes of the type M(N t Bu)2(N(H)HIPT)Cl (1m).
As single tBu resonance is observed,
indicating 1mhas mirror symmetry and contains two tert-butylimido ligands.
HIPT
IN
N
N
11
L-M=N
I I
C--L
M = Mo, L = dme
M = W, L = C 5H 5N
LiNH(HIPT)
Et2 O 2h
Et20, 2h
1
"|.aCI
N
C 6H 5N
650C, 4h
NNH
HIPT
-
Ci-.M
1 Nt..
HN
-
C1,
M = Mo (IMo)
M = W (1w)
M = Mo (2 mo, 70%)
M = W (2w, 93%)
Scheme 2.1: Synthesis of mixed imido precursor after base-catalyzed proton shuttling.
In Tilley's initial report of the NHIPT ligand on tantalum, the imido was generated from
the anilide by addition of 20 equivalents of base and stirring for three days."4 An adaptation of
this protocol was used in the NHMT system in which the base behaved as a proton shuttle,
chaperoning the anilide proton to the more basic tert-butylimido nitrogen to form the mixed
imido target. In both of these systems, triethylamine was the base of choice, but with analogous
NHIPT complexes it was found that little or no reaction proceeded over 1-2 hours to generate the
desired mixed imido species. After 24 hours at room temperature, the only other product besides
the starting reactants is free HIPT-NH 2 - We hypothesized that a stronger or sterically less
encumbering base (or both) may be required to allow this reaction to proceed. Treatment of 1m
77
with approximately 0.1 equivalents of DBU (DBU = 1,8-diazabicycloundec-7-ene) results in the
immediate formation of M(NHIPT)(N'Bu)(NH'Bu)Cl
by 'H NMR, but after 1-2 hours a
significant amount of HIPT-NH 2 is observed. We suggest that since DBU is a stronger base than
tert-butylamine, the proton shuttling reaction is reversible, and that the full protonation of the
NHIPT nitrogen (and likely also the tert-butyl nitrogen) serves as the sink in this reaction.
Therefore a slightly weaker base - comparable to that of an aniline - and one with a slim steric
profile was pursued.
Gratifyingly, we found that heating
1m for
3-4 hours in neat pyridine
resulted in the clean formation of mixed imido species M(NHIPT)(NtBu)(NH'Bu)Cl (2m) with
little or no formation of HIPT-NH 2 (Scheme 2.1).
The 'H NMR spectrum clearly shows a desymmetrization of the metal complex after
heating in pyridine. The 'H NMR spectra of 1m. and 2 m. are shown in Figure 2.4. From one tert-
butyl resonance and three iso-propyl resonances in 1m., two tert-butyl peaks, six iso-propyl
peaks, in addition to an upfield shift in the NH resonance, are produced in the spectrum of 2m..
HIPT
N
N
CeHN
"II
N
ci -.N
65-C, 4h
H
HN
HIPT
N()4u
NQIE)HIPT
_
S
8
7.
7
7.7
70
70
7A
70
7
71
7
8
7
1.7
1
1
IA
Figure 24: Desymmetrization of 1mo (lower spectrum) by heating in pyridine to form
2
12
____
12
1.
1.0
0U
mo (upper spectrum).
The NHIPT complexes presented herein show incredibly high solubility in most solvents,
including alkanes.
As a result, some chemical transformations are carried out in sequence
without isolation of the intermediate. For example, 1m. and 1w are not isolated upon formation.
78
Rather, they were extracted into pentane and the solution was filtered to remove the LiCl
byproduct. These species are then dissolved in pyridine and converted directly to 2m.
B. Dialkyl Complexes Bearing the NHIPT Ligand
In order for an alkylidene to be generated via c-abstraction, two alkyl ligands bound to
Mo/W are required. From 2m, one equivalent of HCl must be added to the metal so that two
chloride ligands can subsequently be substituted for alkyl ligands.
The proton should
preferentially migrate to the tert-butyl amide ligand to generate the amine adduct of the "mixed
imido" species. Addition of one equivalent of 2,6-lutidinium chloride to 2m affords 3 m(Scheme
2.2). Whereas full conversion is observed in the case of 3mo, some 2w is always observed in
addition to 3w after the addition of the lutidinium salt. Similar behavior was observed for the
analogous tungsten NHMT species." Addition of more an excess of lutidinium chloride to 2w
results in the formation of undesired products rather than full conversion to 3w.
HIPT
- HCI
N
NloH/N N
HN15h
N
N
C 7H 8, 50C
HIPT
HIPT
N
N
CliM
H2N
H2 N
C
N
L
M = Mo (3 mo)
M = W (3w)
2 t-BuCH 2MgCI
N-
Et 20, -30C
15h
M = Mo (4 mo, 81%)
M = W (4w, 84%)
Scheme 2.2: Addition of "HOl" and subsequent alkylation to generate mixed imido dineopentyl complexes.
Both 3m. and the mixture of 2w and 3w are extracted into pentane and filtered through
Celite to remove excess salts. These compounds are then treated with alkylating agent without
isolation.
Even in the presence of acidic protons on the amine adduct, alkylation proceeds
smoothly to produce 4m(Scheme 2.2). These dialkyl complexes are extracted into pentane and
filtered through Celite. The resulting solutions are dried in vacuo. 4m. and 4w precipitate upon
addition of acetonitrile. They exhibit magnetically inequivalent u-CH 2 protons, which appear as
two sets of doublets in the 'H NMR spectrum.
Both 4m. and 4w crystallize in large blocks from concentrated solutions of toluene, so 4m.
was chosen for an X-ray diffraction study (Figure 2.5).
79
CA
C6MOO1) NO1)
U11
C0 7)
C47
Figure 2.5: Thermal ellipsoid drawing (50%) of Mo(NHIPT)(N-t-Bu)(CH 2-t-Bu) 2 (4m(). Selected bond distances (A) and
angles ('): Mol-N1 = 1.7477(17), Mol-N2 = 1.7641(17), Mol-NI-CI1 = 156.88(15), Mol-N2-C21 = 162.53(14).
4m.
crystallizes in a PT space group and contains one molecule of toluene in the asymmetric
Bond angles and distances are similar to those observed in other imido and alkyl
11
complexes of Movi and WVI.9,
unit.
C. Syntheses of Molybdenum and Tungsten Alkylidene Complexes Containing the NHIPT
Ligand
Treatment of 4 m with three equivalents of finely ground pyridinium chloride cleanly
affords the desired alkylidene complexes, M(NHIPT)(CHCMe 3)C 2(py) (5m) through selective
protonation of the more basic tert-butylimido and concomitant cc-abstraction by a neopentyl
ligand (Scheme 2.3).
80
HIPT
iPr
3
N
-HC/
[
Nr
M
'Pr
N
Et2, 22 -C
15h
o
'Pr N 'Pr
'Pr-
Pr
C
+ isomer (Mo only)
C,
M = Mo (5 Mo, 57%)
M = W ( 5 w, 86%)
Scheme 2.3: Alkylidene formation to give M(NHIPT)(CHCMe)Cl 2 (Py), which show only anti alkylidenes in solution.
5w is obtained as a single isomer which we propose to contain cis chlorides, evidenced by the six
independent iso-propyl peaks shown in the proton NMR spectrum. In contrast, two alkylidene
peaks are observed for
5 M.
in approximately a 1:1 ratio.
containing cis and trans chlorides, since one (similar to
the other has mirror symmetry.
5
We propose these to be isomers
w) shows six iso-propyl doublets and
For all three alkylidene peaks observed, each has a
-
characteristically large 'JCH value - 147 Hz ( 5 w), 148 Hz (cis-5m.), and 158 Hz (trans- 5 m.)
indicating the presence of anti alkylidenes and validating the design principle behind the
sterically encumbering NHIPT imido ligand (vide supra). No syn alkylidene can be observed in
solution for 5 w or 5 m..
The isomerism of 5 m. was confirmed by variable temperature (VT) 'H NMR experiments.
Heating of a sample of 5. in C6D 6 resulted in the broadening of both peaks (Figure 2.6).
Whereas the trans isomer appears to be preferred at room temperature, the cis isomer appears to
be slightly favored at higher temperatures (e.g. ~1 : 2.5 cis:trans at 500 C).
The addition of
pyridine at room temperature to a sample of 5 m. results in the sharpening of the peaks for cis-5.
and trans-5., but no new peaks are observed, indicating that a six coordinate complex
containing two pyridine ligands cannot be formed. The broadening of the peaks for the cis and
trans isomers of 5 m. in the presence of excess pyridine is much less pronounced at higher
temperatures, suggesting that these isomers interconvert through the loss of pyridine.
81
Cis-5Mo
trans-mo
30'C
40'C
60'C
70'C
70'C
13.0
12.9
12.8
12.7
12.6
12.5
12.4
12.3
12.2
12.1
12.0
11.9
.
Figure 2.6: Interconversion of cis-5 ,,, and trans-5,
11 in C6 D 6
After a few trial experiments it became clear that sterically inducing the dissociation of
the pyridine adduct for both 5m. and 5w would be difficult simply by adding larger ligands (e.g.
pyrrolides or alkoxides) to the metal. Therefore, the chemical removal of the pyridine ligand
was pursued (Scheme 2.4). Treatment of 5m. with three equivalents of ZnCl 2 in Et 2O over lh
afforded a red mixture containing the pyridine-free Mo(NHIPT)(CHCMe)C
2
(6mo), which is
isolated in 94% yield. Treatment of 5w with ZnCl 2 did not result in conversion to the analogous
dichloride complex. Instead, one equivalent of B(C6 F,)3 was charged to 5w in THF to afford
W(NHIPT)(CHCMe)Cl 2(THF), which can be dissolved in toluene and dried to afford
W(NHIPT)(CHCMe)C
2 (6w)
in 84% yield. Symmetric 'H NMR spectra are observed for both
-
6m. and 6w, and the 'JCH values of the alkylidene peaks - 158 Hz ( 6 m.) and 155 Hz (6w)
indicate the anti isomer is present in solution. Again, no syn isomers are observed.
82
'Pr
'Pr
I
Pr N P
~
Cl"I
'Pr
'Pr
Pr
Mo "CI
3 ZnC 2 (anhyd.)
Et 20, 1h
_
'Pr
Pr
-iPr
'Pr N Pr
C,
MP
Cl"
6mo, 94%
(cis plus trans)
Pr
Pr
Pr
'Pr
1. B(C 6F 5)3, THF, 1h
'Pr
-
'Pr NPr
Cl CIIII
wW .'1c
-"Ci
'Pr
2. C7H 8 , vacuum
Pr
-
'iPr N Pr
II0C'',..
C
-
"
iPr
6w, 84%
Scheme 2.4: Removal of pyridine ligands to generate 4-coordinate imidoalkylidenes 6, and 6,.
X-ray quality crystals of 6w were grown from a concentrated CH 2Cl 2 solution.
The
structure demonstrated whole molecule disorder, with contributions from anti-6w (-86%) and
syn-6w (~14%) (Figure 2.7).
C11
C12
C11
Figure 2.7: Solid-state structure of anti-6w. Selected bond distances (A) and angles (*): Wi-Cl 1.892, W1-N1 1.702, WiC11 2.274, Wl-Cl2 2.272; Wi-Ci-C2 126.88, Wi-N1-C11 17837, N1-W1-C1 98.31.
The geometry of anti-6w is pseudotetrahedral about the metal, with bond angles and distances
typical of imidoalkyidene species.7" The structure of syn-6w resembles that of anti-6w, but the
standard deviations for bond lengths and distances are much larger (Figure 2.8).
83
W1A
Cl1A
C2A
CI2A
Figure 2.8: Thermal ellipsoid plot of syn-6,. Select bond distances (A) and angles (): W1A-N1A = 1.760(14), WiA-ClA
= 1.879(18), WIA-CIlA = 2.256(11), W1A-Cl2A = 2.233(10); WIA-NiA-Cli = 179(8), W1A-C1A-C2A = 149(2), N1AWLA-ClA = 114(3).
The N1-WL-Cl-C2 dihedral angle in syn-6w is 17(6) and suggests that within experimental error
the alkylidene is not twisted out of this plane, despite likely unfavorable steric interactions of the
tert-butyl group with the TRIP rings of the imido ligand. Although syn-6w is found in the solid
state, no 6w has been observed in solution, even upon cooling a solution of 6w to -80C. If syn6w is found in the solid state it is reasonable to assume that it is present in solution, but given the
size of the imido ligand the equilibrium between the two isomers must greatly favor anti-6w.
To the best of our knowledge, 6 w and
6m.
(which we assume to be isostructural with 6 w)
are the only examples of 14-electron imidoalklyidene dihalide complexes reported in the
literature.
We suggest that the large size of the imido ligand enables the isolation of these
compounds as monomeric species and prevents dimerization or oligomerization via bridging
halide ligands. Attempts to make analogous pyridine-free species in the NHMT system using
B(C6 F5 ) 3 were unsuccessful due to the similar solubilities of the desired product and the Lewis
.
acid/base adduct, B(C6 F5) 3 -NC5 N5
Treatment of 5w with 2 equivalents of TMSBr affords two new species by NMR with 'JCH
values of 145 Hz and 150 Hz (Figure 2.9), which we suggest to be the cis and trans isomers of
the dibromide. We propose that the comparatively larger bromide ligands labilize the pyridine
adduct, making both cis and trans isomers accessible. Treatment of a solution of this product
with ZnBr2 results produces a red solution and a symmetric 1H NMR spectrum is obtained,
84
analogous to that of 6m. and 6w. As expected, this compound, obtained in 71% yield, analyzes as
W(NHIPT)(CHCMe 3)Br2 (6
Br).
____J
150
H
145 Hz
111 1 5
410
1056
40
50.6
104
506
0.
7 t 0.i O0p5.0
05"06 00 54
Figure 2.9: 'H NMR spectrum of product generated from the addition of 2 equivalents of TMS-Br to 5,. Two new
products, both with anti alkylidenes, are generated.
Given the success of MAP species in metathesis, and the absence of pyridine-free MAP
species that contain an unsubstituted pyrrolide ligand in the NHMT system,8 b the syntheses of
such compounds were pursued. Treatment of 6mo with two equivalents of Kpyr in Et2 O resulted
in the formation of Mo(NHIPT)(CHCMe 3 )(pyr) 2 (7M) in 77% yield. Treatment of 6w with either
Lipyr or Kpyr in a variety of solvents give species that appear to be the desired bispyrrolide
complex by 'H NMR but with very broad peaks, possibly due to '- f isomerization of one of
the pyrrolide ligands.
',r
rt FO
DME
So far no clean tungsten-based bispyrrolide has been isolated.
iPr
'Pr
Pr
2
N 'r
'62Pr
'P C'
2
Pr
C
0H
6F
5 P NCCH
3
"
C*
KA
N
I
'Pr
Pr N'r
'ro
Mo
Pr
i
'Pr N'Pr
-p
'Pr
E
4h
6
Pr
'Pr
'Pr
then CH 3CN
7
Mo
77%
CF
F
\I
F
F
8
MO,
72%
Scheme 2.5: Syntheses of Mo-based bispyrrolide and MAP adduct species.
85
Slow addition of pentafluorophenol to a solution of 7m. in DME at room temperature
affords the desired MAP complex, but the high solubility of this complex has precluded
isolation. Only after addition of acetonitrile can the MAP complex be cleanly isolated as an
acetonitrile adduct (Scheme 2.5). The 'H NMR spectrum suggests the acetonitrile is labile in
solution, but attempts to completely remove acetonitrile in vacuo in the presence of a higher
boiling solvent has so far been unsuccessful; in addition, isolation of the adduct-free MAP
species from more weakly binding adducts such as tetrahydrofuran (THF) or tetrahydropyran
(THP) have also been unsuccessful.
II. Preliminary Metathesis Reactions of Molybdenum Species Containing the NHIPT
Ligand
While it has been established that predominantly anti species can be synthesized by
employing a sterically encumbering imido ligand (vide supra), a remaining question is whether
this framework would give rise to Z-selectivity in metathesis.
With one MAP catalyst in hand,
we tested the hypothesis that Z-olefins should be generated.
Despite the inability to isolate
8m,
without acetonitrile bound, this complex serves a
functional equivalent of acetonitrile-free 8m., which can be generated in situ and observed by 1H
NMR. A test reaction with 50 equivalents of 3-methyl-3-phenylcyclopropene (MPCP) in CDCl 3
showed that both 8., and the acetonitrile-free complex generated in solution gave identical
results. Therefore, subsequent metathesis experiments were carried out using 8m.. Treatment of
this catalyst with 50 equivalents of MPCP in CDC1 3 resulted in the polymerization of the
monomer and production of ~71 % cis,syndiotactic poly(MPCP)
3 (Scheme
2.6). The integration
of cis,syndiotactic polymer with respect to all polymer peaks in the 'H NMR remains unchanged
if the reaction is run at -30C.
i
'Pr
Pr
,Ph
\
Pr
Pr
i~rrN NCC3P
'P
IPr
11-m
2NI~
F
F
0
_
_
_
_
.PhPh
_
-Ph-
_
CDC1
n
3
rt or -30*C
\/
F
V
50
50
-71% cissyndiotactic poly(MPCP)
F
F
8mo
Scheme 2.6: Polymerization
of MPCP by 8m.
86
This result supports our proposition that Z-selectivity should be maintained using this ligand
framework. In the metallacyclobutane intermediate, the substituents on the metallacycle should
point away from the large imido ligand and toward the smaller pentafluorophenoxide ligand
(Scheme 2.7).
ROD,
R Mo
pyr
HIPT
HIPT
Ph
HIPT
NN
----Do
pyr -
R
R
'Pha
pyr-Mool
OR RIPh
N
P111RO,
P 'M
R0'O
HIPT
Ph
Isotactic
N1
pyr
y
MoR
Syndiotactic
Scheme 2.7: Nature of cis,syndiotactic poly(MPCP) in MAP complexes with large imido ligands.
Consistent with chiral-at-metal MAP framework, the monomer should insert trans to the
pyrrolide and the stereochemistry of the metal should invert with each productive metathesis
step, giving rise to poly(MPCP) with a syndiotactic microstructure.
Mo(NHIPT)(CHCMe 3 )(pyr)(OC6 F5 )(MeCN) was tested for the homometathesis of 1As expected, -80% cis-7-tetradecene is produced from this reaction at 5 minutes
octene.
Aliquots were taken at during the course of the reaction at 5 minutes and 30
(Scheme 2.8).
minutes. The ratio of trans:cis 7-tetradecene clearly varies at these different time points, with
the cis content eroding over time (-80% cis at 5 min, -69% cis at 30min). This suggests that
post-metathesis isomerization" of the product olefin is operative and gives rise to the increased
Furthermore, despite the size of the imido ligand, a
trans content at the later time point.
significant amount of trans product is produced early on in the reaction (-20%), which may
implicate the presence and reactivity of a syn alkylidene.
'Pr
N
'Pr N 'Pr
Pr
50
I .'NCCH 3
0
F
CDC1 3
F
F
F
-
--
'Pr
'Pr
~80% cis
rt or -30*C
F
8mo
Scheme 2.8: Homometathesis
of 1-octene
by 8mo.
87
The possibility of the syn isomer being metathetically active is suggested by the
observation of syn-6, in the solid state, despite the fact that no syn- 6 w can be observed in
solution. The alkylidene region of 8m. is too broad to determine
'JCH
values (likely due to the
dissociation of the MeCN ligand on the timescale of the NMR) and definitively verify the
presence of the more likely anti alkylidene isomer, but this does not rule out the reactivity of the
syn isomer. Furthermore, the reacting alkylidene that eventually generates a molecule of 7tetradecene must be a heptylidene, which is much smaller than the starting neopentylidene (CH 2(n-alkyl) group instead of C(CH 3)3); as such, the steric stress felt by the heptylidene in a syn
orientation will be much smaller than that of the neopentylidene and could allow for a greater
concentration of the electronically favored syn rotational isomer in solution.
In order to determine whether the syn isomer is accessible, 8m. was treated with a slight
excess of cis-3-hexene and cis-4-octene such that a propylidene or butylidene, which are closely
related to the reacting heptylidene in the aforementioned homometathesis experiment, could be
observed in solution. Unfortunately, only broad signals are observed in the alkylidene region in
addition to starting material. These broad peaks neither suggest nor rule out the presence of
(interconverting) syn and anti isomers. Eventually, decomposition of the catalyst is observed. It
is unclear at this time why the catalyst decomposes, since through the addition of an internal
olefin no ethylene is generated that could catalyze the decomposition of the catalyst. This,
however, still does not rule out the presence of syn and anti alkylidene isomers: both species
could still competent in these reactions, but their interconversion may not proceed at the
alkylidene stage.
Rather, pseudo-rotation-type rearrangements are possible and have been
invoked in certain cases to explain unexpected polymerization results, specifically with a catalyst
that contains a large phenoxide ligand and a small imido ligand." If the rate of this turnstile
rearrangement is competitive with the rate of olefin insertion, both cis and trans olefinic linkages
are still possible.
It has also been established through experiment that metathesis reactions run at different
temperatures can give rise to drastically different metathesis products due to the high sensitivity
of alkylidene rotation rate to temperature." Interestingly, treatment of 8m. with 50 equivalents
of MPCP at -30'C does not result in poly(MPCP) with a greater or lesser degree of regularity.
Similar results are observed with the homo-metathesis of 1-octene:
approximately the same
degree cis content is observed at the same time point for reactions run both at room temperature
88
and -30'C. Further experimentation, in particular low temperature experiments, will be required
in order to elucidate the nature of the trans metathesis products and determine any possible role
of a syn isomer in these metathesis reactions.
CONCLUSIONS
Using a mixed imido synthetic strategy, molybdenum and tungsten complexes bearing
the NHIPT imido ligand have been synthesized. Imidoalkylidene complexes can be generated
from dialkyl precursors through the addition of pyridinium chloride to give anti alkylidenes as
the only observable alkylidene-containing species in solution. Chemical removal of the pyridine
ligands with either ZnCl 2 or B(C6 F5 ) 3 furnish the 14-electron imidoalkylidene dihalide
complexes, which also display anti alkylidenes by proton NMR. An X-ray crystal study of 6w
showed the presence of a syn alkylidene isomer in addition to the anti isomer, although the syn
isomer cannot be observed in 1H NMR spectra, even at low temperatures.
A bispyrrolide and solvent-bound MAP complex of Mo have been synthesized. The MAP
species produces predominantly cis,syndiotactic polymer when treated with excess MPCP and
gives mostly cis-7-decene when treated with 1-octene. This cis content eroded over time to
trans, suggesting post-metathesis isomerization of the product olefin by the catalyst is operative.
Attempts to observe a closely analogous active species (propylidene or butylidene) in solution to
determine if any syn alkylidenes are accessible during the course of the metathesis of 1-octene
through the addition of either cis-3-hexene or cis-4-octene have so far been inconclusive.
Further experimentation, likely low temperature 'H NMR studies, is needed to further understand
these metathesis results. In addition, more research is needed develop the tungsten system and to
address difficulties isolating four-coordinate MAP complexes.
89
EXPERIMENTAL
General Details. All manipulations of air- and moisture-sensitive materials were performed
either in a Vacuum Atmospheres glovebox (N 2 atmosphere) or on a dual-manifold Schlenk line.
All solvents were sparged with nitrogen, passed through activated alumina, and stored over
activated 4
A
molecular sieves. HIPTNHLi,'4 Mo(N'Bu) 2C 2(DME), 9a and W(NBu) 2 C 2 (py) 2 16
were prepared according to reported procedures. All other reagents were used as received unless
otherwise noted. Methylene chloride-d 2 and benzene-d6 were stored over 4
A molecular
sieves.
NMR measurements of air- and moisture-sensitive materials were carried out in Teflon-valvesealed J. Young NMR tubes. NMR spectra were recorded using spectrometers at 500 or 300
MHz ('H), 125 MHz (13C), and 282 ('9F) MHz, reported in 6 (parts per million) relative to
tetramethylsilane ('H,
3
1 C)
or PhF (19F) and referenced to residual 'H/ 3 C signals of the deuterated
solvent ('H (6), benzene 7.160, methylene chloride 5.320);
3
1C
(6), benzene 128.06, methylene
chloride, 53.84. Elemental analyses were carried out by the CENTC Elemental Analysis Facility
at the University of Rochester.
Mo(NHIPT)(N'Bu)(NH'Bu)Cl
(2m.).
This product can be made without isolating 1..
A
solution of HIPTNHLi (3.40g, 6.74 mmol) in ~15mL Et2O was added to a solution of
Mo(Nt Bu) 2C1 2(dme) (2.69g, 6.74 mmol) in ~15mL Et2O and the mixture was stirred for 2h,
during which time a yellow-orange mixture with precipitate was formed. The solvents were
removed in vacuo, pentane was added to the residue, and the mixture was filtered through Celite.
All solvents were removed from the filtrate in vacuo and the residue was dissolved in pyridine.
The red solution was heated to 65'C for 4h in a Schlenk bomb and then all pyridine was removed
in vacuo. The red residue was extracted with pentane, and all volatiles were removed from the
filtrate in vacuo. Minimal Et2O was added to give some yellow precipitate, and to this stirred
mixture was added acetonitrile to encourage further precipitatation of the yellow product. This
mixture was stirred for an additional 6h and the yellow product was isolated by filtration and
washed with acetonitrile; yield 3.61g (70%): 'H NMR (C6 D6 , 500MHz) b 7.71 (s, 1H, NH), 7.27
(overlapping singlets, 2H, Ar), 7.25 (overlapping singlets, 2H, Ar), 7.06 (d, 2H, Ar), 6.84 (t, 1H,
Ar), 3.12 (sept, 4H, CHMe 2), 2.88 (sept, 2H, CHMe 2 ), 1.52 (d, 6H, 'Pr), 1.46 (d, 6H, 'Pr), 1.31 (d,
6H, 'Pr), 1.29 (d, 6H, 'Pr), 1.20 (d, 6H, 'Pr), 1.13 (d, 6H, 'Pr), 1.09 (s, 9H, tBu), 1.06 (s, 9H, tBu);
3C
1
NMR (CD 2Cl 2 , 500 MHz, 20'C) 155.37, 148.16, 147.52, 147.08, 136.15, 135.75, 131.16,
90
124.04, 121.41, 121.30, 71.11, 58.22, 34.56, 32.20, 31.46, 31.15, 31.08, 25.85, 25.33, 24.28,
24.06, 24.05, 23.83. Anal. Calcd for C4H68 ClMoN 3: C, 68.59; H, 8.90; N, 5.45. Found: C,
68.23; H, 8.65; N, 5.04.
TIP
&0
7's
7 0
3 0
2 5
40
1 S
110
0,5
W(Nt Bu)(NHIPT)(NH'Bu)CI (2w). This product can be made without isolating 1w. A solution
of HIPTNHLi (3.59g, 7.13 mmol) in -15mL Et 2O was added to a solution of W(N'Bu) 2Cl 2py 2
(3.96g, 7.13 mmol) in -50mL Et2O. The resulting yellow-brown mixture was stirred for 4h. The
suspension was then filtered through a Celite plug, which was rinsed with Et2 O. The volatiles
were removed from the filtrate in vacuo. Pyridine was added to the residue and the solution was
transferred to a Schlenk bomb. The Schlenk bomb was heated at 65*C for 4h. The solvent was
then removed in vacuo, pentane was added, and the solvent was again removed in vacuo.
Minimal Et 2O was added to give some yellow precipitate, and to this stirred mixture was added
acetonitrile to further precipitate the yellow product. This mixture was stirred for an additional
6h and the yellow product was isolated by filtration and washed with acetonitrile; yield 5.70g
(93%): 'H NMR (C6 D6 , 500 MHz) 6 7.26 (s, 2H, Ar), 7.25 (s, 2H, Ar), 7.12 (d, 2H, Ar), 6.82 (t,
91
LH, Ar), 6.56 (s, 1H, NHBu), 3.10 (overlapping sept, 4H, CHMe 2), 2.88 (sept, 2H, CHMe 2), 1.51
(d, 6H, 'Pr), 1.46 (d, 6H, 'Pr), 1.32 (d, 6H, 'Pr), 1.30 (d, 6h, 'Pr), 1.21 (d, 2H, 'Pr), 1.14 (d, 6H,
'Pr), 1.11 (s, 9H, tBu), 1.05 (s, 9H, 'Bu);
3
1C
NMR (C 6 D 6 , 125 MHz) 154.57, 148.05, 147.73,
147.28, 137.17, 136.21, 130.73, 123.53, 121.31, 121.17, 67.99, 56.82, 34.63, 32.69, 32.58, 31.26,
31.16, 25.85, 25.17, 24.44, 24.34, 24.18, 24.11. Anal. Calcd for C14H6ClN 3 W: C, 61.57; H,
7.99; N, 4.90. Found: C, 61.91; H, 7.95, N, 4.73.
IN
N~
Mo(NHIPT)(N'Bu)(CH 2CMe)
Lutidinium
chloride
(677
2
(4m.). This product can be made without isolating 3 m.. 2,6-
mg,
4.71
mmol)
was
added
to
a
solution
of
Mo(N'Bu)(NHIPT)(NH'Bu)C (3.63g, 4.71 mmol) in ~75mL toluene. The resulting mixture was
stirred for 15h at 50*C in a Schlenk bomb. The orange mixture was filtered and the solvents
were removed from the filtrate in vacuo. The residue was extracted with pentane and filtered
through Celite into a tared vial. All solvent was removed in vacuo, diethyl ether was added, the
mixture was chilled at -30*C for lh, and 2.05 equivalents of neopentylmagnesium chloride
(2.42M, 3.88 mL) was then added dropwise to the stirred solution. The resulting mixture was
92
stirred for 16h. The mixture was filtered and the solvents removed from the filtrate in vacuo. A
small amount of CH 3CN was added and the mixture was stirred for 2h. The yellow product was
then isolated by filtration; yield 728 mg (81%): 'H NMR (C6D6 , 500MHz) 6 7.24 (s, 4H, Ar),
7.09 (d, 2H, Ar), 6.83 (t, 1H, Ar), 3.21 (sept, 4H, CHMe 2), 2.92 (sept, 2H, CHMe 2), 2.27 (d, 2H,
CH2), 1.52 (d, 12H, 'Pr), 1.40 (s, 9H, 'Bu), 1.35 (d, 12H, 'Pr), 1.16 (d, 12H, 'Pr), 0.96 (s, 18H,
'Bu), 0.38 (d, 2H, CH2 );
3
C NMR:
156.24, 147.88, 147.29, 136.79, 135.37, 132.12, 123.01,
121.16, 81.07, 69.81, 34.67, 33.59, 33.52, 32.83, 31.04, 26.30, 24.48, 24.42. Crystals of 4m.
obtained from toluene were found to contain one toluene of crystallization. Anal. Calcd for
C57H,8MoN 2 : C, 76.30; H, 9.89; N, 3.12. Found: C, 76.12; H, 9.84; N, 3.07.
W(N'Bu)(NHIPT)(CH 2CMe)
2
(4 w). This compound can be made without isolating 3w. 2,6-
lutidinium chloride (878mg, 6.11 mmol) was added to W(N'Bu)(NHIPT)(NH'Bu)Cl (5.00g, 5.82
mmol) in -75mL toluene and the mixture was heated to 50'C for 15h in a Schlenk bomb. All
solvents were removed in vacuo, the residue was extracted with pentane, and the mixture was
filtered through Celite. The volatiles were removed in vacuo and the residue was redissolved in
93
-75mL Et2O. The solution was chilled for lh in a freezer kept at -30'C. Neopentylmagnesium
chloride (2.42M, 4.57 mL) was added and the resulting mixture was stirred overnight. The
solvent was removed under vacuum and the residue was extracted with pentane. The suspension
was filtered through Celite and the solvents were removed from the filtrate in vacuo.
Acetonitrile was added to the residue and the resulting tan product was isolated by filtration;
yield 4.38g (84%): 'H NMR (C6D6 , 500 MHz) 6 7.24 (s, 4H, Ar), 7.12 (d, 2H, Ar), 6.82 (t, 1H,
Ar), 3.18 (sept, 4H, CHMe 2), 2.92 (sept, 2H, CHMe 2), 2.13 (d, 2H, CH2), 1.51 (d, 12H, 'Pr), 1.43
(s, 9H,'Bu), 1.35 (d, 12H,'Pr), 1.16 (d, 12H,'Pr), 0.96 (s, 18H, 'Bu), 0.08 (d, 2H, CH2 ); 3 C NMR
(CD2 Cl 2 , 125 MHz) 156.07, 147.60, 147.26, 136.70, 135.34, 131.75, 121.78, 121.07, 89.88,
68.15, 34.45, 34.04, 33.80, 33.45, 30.88, 25.94, 24.45, 24.19. Crystals of 4w obtained from
toluene contain one molecule of toluene. Anal. Calcd for C5 7HN
2
W:
C, 69.49; H, 9.00; N,
2.84. Found: C, 69.04; H, 8.98; N, 2.90.
I
I
\/
'
I I
\
Mo(NHIPT)(CHCMe)Cl 2(py) (5m.). Pyridinium chloride (1.26g, 10.9 mmol) was added to a
solution of Mo(NHIPT)(N'Bu)(CH 2CMe) 2 (2.92g, 3.63 mmol) in ~175 mL Et2O and the mixture
94
was stirred for 12h. The solvents were removed in vacuo and the residue was extracted with
pentane. The mixture was filtered through Celite, washed with pentane, and the filtrate taken to
dryness in vacuo. A small amount of acetonitrile was added to the residue and a yellow solid
was isolated by filtration; yield 1.69g (57%) as a mixture of isomers:
'H NMR (CD 2C 2 , 500
MHz, Major (cis) isomer) 6 12.55 (s, 1H, Mo=CH), 7.74 (tt, 1H, py), 7.54 (d, 2H, py), 7.30 (t,
IH, Ar), 7.22 (s, 2H, Ar), 7.19 (d, 2H, Ar), 7.16 (t, 2H, py), 7.11 (s, 2H, Ar), 3.01 (sept, 2H,
CHMe 2), 2.86 (sept, 2H, CHMe 2), 2.50 (sept, 2H, CHMe 2), 1.37 (d, 6H, CHMe2 ), 1.35 (d, 6H,
CHMe2 ), 1.28 (d, 6H, CHMe2), 1.05 (d, 6H, CHMe2), 0.95 (d, 6H, CHMe2), 0.94 (s, 9H, t Bu),
0.71 (bs, 6H CHMe2);
3
1
C NMR 331.54,156.38, 155.53, 148.96, 147.80, 147.73, 139.36, 134.94,
131.36, 127.31, 125.18, 125.17, 121.79, 121.26,45.40, 34.79, 31.10, 30.95, 28.78, 25.82, 25.72,
24.62, 24.22, 23.11, 23.04.
C, 68.05; H, 7.95; N,
Anal. Calcd for C6H4Cl 2 N 2 Mo:
3.45. Found: C, 67.99; H, 8.09; N, 3.32.
IL
CY! q
9.5
W(NHIPT)(CHCMe)C 2(py) (5w).
8.0
7.5
0
ri C pl c
7.0
6.5
10
2 5
2,0
I'S
1.0
0.5
Pyridinium chloride (1.16g, 10.1 mmol) was added to a
solution of W(NHIPT)(NBu)(CH 2CMe 3)2 (3.00g, 3.36 mmol) in -75 mL Et2 O and the resulting
95
mixture was stirred for 18h.
The mixture was filtered through Celite and the solvents was
removed from the filtrate in vacuo. A small amount of pentane was added to precipitate a yellow
solid which was isolated by filtration; yield 2.60g (86%): 'H NMR (C6D 6 , 500 MHz) 6 10.65 (s,
1H, W=CH, IJCH
=
147Hz), 7.81 (d, 2H, py), 7.37 (s, 2H, Ar), 7.19 (s, 2H, Ar), 7.18 (d, 2H, Ar),
6.86 (t, 1H, Ar), 6.79 (t, 1H, py), 6.53 (t, 2H, py), 3.21 (sept, 2H, CHMe 2 ), 2.90 (sept, 2H,
CHMe 2), 2.82 (sept, 2H, CHMe 2), 1.54 (d, 6H, 'Pr), 1.34-1.31 (m, 12H, 'Pr), 1.19 (s, 9H, tBu),
1.13 (d, 6H, 'Pr), 1.06 (d, 6H, 'Pr), 0.91 (br s, 6H, 'Pr);
3
1C
NMR (C6 D, 125 MHz) 298.90
(W=CH), 156.63, 155.30, 148.61, 148.05, 147.84, 138.60, 138.40, 135.81, 130.87, 125.67,
124.97, 121.72, 121.01, 41.04, 34.86, 31.72, 31.20, 30.98, 26.04, 25.83, 24.83, 24.32, 23.44,
23.43. Anal. Calcd for C4,HCl 2 N 2 W: C, 61.41; H, 7.17; N, 3.11. Found: C, 61.72; H, 7.51; N,
2.95.
\l
1'\
I
ui
J
"
I
JJL~1I
J
-
x
I
I
Mo(NHIPT)(CHCMe)Cl
2
(6m.).
s
60
0
4 S
4 0
1s
Mo(NHIPT)(CHCMe)C 2(py) (281mg, 0.346 mmol) was
charged with 25mL Et2 O, followed by ZnCl 2 (142mg, 1.04 mmol). The resulting red mixture
was stirred for lh, then dried under vacuum, extracted with pentane, and filtered through Celite.
96
The filtrate was dried to afford a red/orange solid; yield 238mg (94%):
'H NMR (C6 D 6 , 500
MHz) 6 11.85 (s, 1H, Mo=CH, IJCH = 158 Hz), 7.26 (s, 4H, Ar), 7.09 (d, 2H, Ar), 6.92 (t, 1H,
Ar), 2.97 (sept, 4H, CHMe 2), 2.84 (sept, 2H, CHMe 2), 1.42 (d, 12H, 'Pr), 1.28 (d, 12H, 'Pr), 1.16
(d, 12H, 'Pr), 1.07 (s, 9H, tBu); 13C NMR (C6 D6 , 125 MHz) 317.76, 158.16, 149.64, 147.39,
138.09, 133.55, 130.53, 127.44, 121,56, 44.98, 34.82, 31.54, 28.15, 25.64, 24.36, 23.54. Anal.
Calcd forC 4 ,H59 Cl 2MoN: C 67.20; H, 8.12; N, 1.91. Found: C, 67.08; H, 8.41; N, 1.75.
ILL
I
W(NHIPT)(CHCMe 3)C
2
(6w).
A!I
J~IL~
B(C6 F5 ) 3 (285mg, 0.556 mmol) was added to a solution of
W(NHIPT)(CHCMe 3)C 2(py) (500mg, 0.556 mmol) in 20mL THF. The orange solution was
stirred for 30 minutes and all volatiles were removed in vacuo. The resulting solid was then
extracted with pentane and the mixture was filtered through a Celite plug. The volatiles were
removed from the filtrate in vacuo. Toluene (~AOmL) was added and removed again in vacuo to
give the red product; yield 384mg (84%): 'H NMR (C6 D6 , 500MHz) 6 9.93 (s, 1H, W=CH,
2
JWH
= 40.5 Hz, 'JCH = 155 Hz), 7.25 (s, 4H, Ar), 7.16 (d, 2H, Ar), 6.93 (t, 1H, Ar), 2.96 (sept, 4H,
CHMe 2), 2.86 (sept, 2H, CHMe 2), 1.40 (d, 12H, 'Pr), 1.29 (d, 12H, 'Pr), 1.17 (d, 12H, 'Pr), 1.08
97
(s, 9H, 'Bu);
3
C NMR (C6 D 6 , 125MHz) 284.06 (W=CH), 155.51, 149.26, 147.33, 137.82,
134.11, 130.21, 126.45, 121.38, 40.21, 34.84, 31.43, 30.96, 25.61, 24.41, 23.60. Anal. Calcd for
C 4 ,H59 Cl 2 NW: C, 60.01; H, 7.25; N, 1.71. Found: C, 59.94; H, 7.05; N, 1.56.
I
I
W(NHIPT)(CHCMe)C
2
(6wBr).
irnJL
W(NHIPT)(CHCMe 3)C 2(py) (130mg, 0.144 mmol) was
dissolved in -8mL Et 2O and charged with bromotrimethylsilane (38[LL, 0.289 mmol).
The
mixture was stirred for 15 minutes, after which time ZnBr 2 (65mg, 0.289 mmol) was added. The
mixture was stirred for lh, dried in vacuo, and extracted with pentane. The mixture was filtered
through Celite and the solvent was removed under vacuum to give W(NHIPT)(CHCMe 3)Br 2
(93mg, 71%): 'H NMR (C6 D6 , 500 MHz) 6 10.28 (s, 1H, W=CH,
'JCH
=
153 Hz), 7.24 (s, 4H,
Ar), 7.15 (d, 2H, Ar), 6.95 (t, 1H, Ar), 2.96 (sept, 4H, CHMe 2), 2.86 (sept, 2H, CHMe 2), 1.41 (d,
3
C NMR (125 MHz, C6D6
)
12H, 'Pr), 1.30 (d, 12H, 'Pr), 1.16 (d, 12H, 'Pr), 1.12 (s, 9H, tBu);
289.62, 155.93, 149.28, 147.27, 137.70, 134.18, 130.55, 126.45, 121.39, 40.61, 34.84, 31.38,
30.77,25.70, 24.44, 23.80. Anal. Calcd for C 4,H 59Br2NW: C, 54.14; H, 6.54; N, 1.54. Found: C,
54.38; H, 6.73; N, 1.67.
98
10.0
9.5
.0
8.5
80
7.5
7.0
6.5
Mo(NHIPT)(CHCMe 3)(pyr) 2 (7mo).
-OmL
6.0
5.5
5.0
4.5
4.0
3.5
Mo(NHIPT)(CHCMe 3)C
3.0
2
2.5
2.0
1,5
1.0
0.5
0.
(132mg, 0.180 mmol) in
Et2O was treated with Kpyr (38mg, 0.360 mmol) and was allowed to stir for 4h. The
resulting mixture was then filtered through a Celite plug, washed with Et 2 O, and dried under
vacuum to afford the desired product; yield 110mg (77%): 'H NMR (C6D 6 , 500 MHz) 6 12.35
(s, 1H, Mo=CH), 7.25 (s, 4H, Ar), 7.01 (d, 2H, Ar), 6.83 (t, 1 H, Ar), 6.59 (t, 4H, pyr), 6.22 (t,
4H, pyr), 2.90 (m, 6H, CHMe 2), 1.34 (d, 12H, CHMe2), 1.15 (d, 12H, CHMe2), 1.10 (d, 12H,
CHMe2 ), 1.04 (s, 9H,'Bu); 13 C NMR (125 MHz) 314.29, 156.16, 148.78, 147.41, 137.16, 135.16,
131.19, 129.97, 125.28, 121.82, 109.47, 48.46, 34.78, 31.52, 25.71, 24.39, 22.91. Anal. Calcd
for C4 9H 67MoN 3 : C, 74.12; H, 8.51; N, 5.29. Found: C, 73.88; H, 8.79; N, 5.06.
99
Mo(NHIPT)(CHCMe)(pyr)(OC 6 F5 )(CH 3CN) (8m). 7m. (50mg, 0.0630 mmol) in -5mL DME
was charged with C 6F 5OH (11mg, 0.0630 mmol) in -3mL DME.
After one hour the volatiles
were removed in vacuo. The residue was charged with MeCN and stirred for 3h to precipitate a
yellow solid. The volatiles were removed in vacuo to yield the desired product; yield 43mg
(72%): 'H NMR (500 MHz, C6D6 ~0.01M):
6
12.57 (bs, 1H, Mo=CH), 7.28 (s, 2H, Ar), 7.27
(s, 2H, Ar) 7.06 (d, 2H, Ar), 6.84 (t, 1 H, Ar), 6.44 (bs, 2H, pyr), 6.42 (bs, 2H, pyr), 2.99 (m, 4H,
CHCMe 2), 2.80 (sept, 2H, CHCMe 2), 1.41 (d, 6H, CHCMe2), 1.38 (d, 6H, CHCMe2), 1.21 (d,
6H, CHCMe2), 1.15 (d, 6H, CHCMe2), 1.12 (d, 6H, CHCMe2), 1.06 (s, 9H, 'Bu), 0.97 (d, 6H,
CHCMe2);
140.02 (JCF
13 C
=
NMR (125 MHz, ~0.09M) 334.19 (Mo=CH), 155.27, 148.91, 147.10, 146.49,
240Hz), 140.00 (m), 138.37 ('JCF
=
244 Hz), 138.18, 134.82, 133.45 (1JCF = 241
Hz), 131.00, 130.85, 128.35, 125.61, 121.98, 121.65, 107.72, 47.36, 34.84, 31.45, 31.20, 30.15,
-
26.08, 26.02, 24.69, 24.00, 23.28, 22.66, 0.93; '9F NMR (282 MHz, ~0.09M) -157.92 (d, 2F),
167.30 (t, 2F), -174.01 (bs, IF). Anal. Calcd for C 53HesF5 MoN3 O: C, 66.86; H, 6.99; N, 4.41.
Found: C, 66.87; H, 6.93; N, 4.30.
100
I I
IM\
.5
13.0
125
120
11.5
11.0
10.5
10.0
9.5
9.0
a.5
8.0
7.5
7
6.5
0i 44")
6.0
.
5.5
5.0 ' . '
5.0 4.5
4.0
3.5
1.5
3.0
2.5
2.0
1.5
1.0
0.5
Procedure for the Polymerization of MPCP and Metathesis of 1-octene by 8.: 200pL of a
0.01M stock solution of 8m. in CDC1 3 was charged to 50 equivalents of either MPCP or 1-octene
in 200pL of CDCl 3 . For reactions run at -30*C, both the catalyst stock solution and the substrate
solution were chilled for 1 hour at -30*C prior to mixing. Homometathesis reactions were run
with a loose vial cap to permit the escape of ethylene outside of the reaction vial.
101
80
7.S
7.0
6.s
60
S.5
5.0
4.5
40
5
10
2
2.0
1.5
1.0
.
8bH
H NMR spectrum of I %, before treatment with pyridine.
102
8'0
75
7.0
e 6R0
o
55
45
yG 4.0
3Sb
2
20
1p
O'e
H NMR spectrum of lw before treatment with pyridine.
103
I
'H NMR spectrum of 3 mo before treatment with ClMgCH 2 -t-Bu.
104
7
Li
iU\~L~JiJ
LL
'H NMR spectrum of 3 w before treatment with ClMgCH 2 -t-Bu.
105
X-ray crystal structure determination details. (Performed by Dr. Peter Mfller)
Low-temperature diffraction data (#-and w-scans) were collected on a Siemens Platform
three-circle diffractometer coupled to a Bruker-AXS Smart Apex CCD detector with graphitemonochromated Mo Ka radiation (A = 0.71073 A) for the structure of 4 mo and on a Bruker-AXS
X8 Kappa Duo diffractometer coupled to a Smart APEX2 CCD detector with Mo Ka radiation (k
= 0.71073 A) from an IpS micro-source for the structure of compound 6 w. Absorption and other
corrections were applied using TWINABS1 7 for the structure of 4 mo and SADABS1 8 for the
structure of 6 w. All structures were solved by direct methods using SHELXT' 9 and refined
against F2 on all data by full-matrix least squares with SHELXL-201320 using established
refinement methods.2 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 Uq 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.
4 mo
crystallizes in the triclinic centrosymmetric space group P~1 with one molecule of 4 mo
and one molecule of toluene per asymmetric unit. The crystal was non-merohedrally twinned;
two independent orientation matrices for the unit cell were found using the program
CELLNOW , and data reduction taking into account the twinning was performed with
SAINT 2. The program TWINABS' was used to set up the HKLF5 format file for structure
refinement. The twin ratio was refined freely and converged at a value of 0.3988(6). Advanced
rigid bond restraints 24 were applied to all atoms in order to counteract correlation effects caused
by the twinning. Coordinates for hydrogen atoms bound to carbon directly attached to the
central molybdenum atom (carbon atoms C1 and C6) were taken from the difference Fourier
synthesis and those hydrogen atoms were subsequently refined semi-freely with the help of
distance restraints.
6w
crystallizes in the orthorhombic centrosymmetric space group Pbca with one molecule of
per asymmetric unit. The structure shows substantial disorder and the refinement was
challenging. Most importantly, the structure is a mixture of the of syn and anti isomers. Because
the geometries of the two isomers are significantly different, the best description of this mixture
would be a whole molecule disorder (WMD). Probably owing to additional disorders in the
NHIPT ligand that are independent of the syn-anti disorder, a complete WMD model was not
stable. Therefore, only the positions of the tungsten, chlorine and alkylidene carbon atoms (Cl
to C 10) were included in this "partial whole-molecule disorder". The ratio between syn and any
isomers was refined freely and converged at 0.860(3), corresponding to ca. 14% syn and 86%
anti. Due to the much lower occupancy of the syn isomer, the anti molecule is described
6w
106
significantly better and the structural parameters obtained for the syn isomer are therefore much
less precise that those of the anti isomer. This is evident from the higher standard uncertainties
for all structural parameters of the syn isomer. In addition, it should be noted that the NHIPT
ligand position belongs to the anti isomer, as the coordinates of this ligand could not be included
in the syn-anti disorder. As mentioned above, the NHIPT ligand shows disorders unrelated to
the described syn-anti disorder. Namely one full tri-isopropyl-phenyl group and two of the three
iPr groups on the other tri-isopropyl-phenyl moiety were independently refined as disordered
over two positions. All disorders were refined with the help of similarity restraints on 1-2 and 13 distances and displacement parameters as well as rigid bond restraints for anisotropic
displacement parameters.
107
Table Si. Crystal data and structure refinement for 4 mo.
Identification code
14012_t5
Empirical formula
C 57 H8 8 Mo N 2
Formula weight
897.23
Temperature
100(2) K
Wavelength
0.71073
Crystal system
Triclinic
Space group
PI
Unit cell dimensions
a= 11.366(2)
A
a = 88.474(4)0
b = 13.229(3)
A
P#= 89.275(3)0
c = 18.298(3)
A
y = 72.197(3)0
A
A3
Volume
2618.6(8)
Z
2
Density (calculated)
1.138 Mg/m3
Absorption coefficient
0.286 mm- 1
F(000)
972
Crystal size
0.380 x 0.250 x 0.120 mm 3
Theta range for data collection
1.113 to
Index ranges
-16<=h<= 16, -18<=k<= 18, 0<=/<=26
Reflections collected
16197
Independent reflections
16197 [R,,, = 0.0537]
Completeness to theta = 25.242'
100.0
Absorption correction
Semi-empirical from equivalents
Refinement method
Full-matrix least-squares on F2
Data / restraints / parameters
16197 / 473 / 576
Goodness-of-fit on F2
1.042
Final R indices [1>2-(J)]
RI = 0.0359, wR2 = 0.0952
R indices (all data)
RI
Largest diff. peak and hole
%
30.5080
=
0.0417, wR2
=
0.1001
0.538 and -0.732 e.A-3
108
Table S2. Crystal data and structure refinement for 6W.
Identification code
X14136
Empirical formula
C4 , H 59 Cl2 N W
Formula weight
820.64
Temperature
100(2) K
Wavelength
0.71073 A
Crystal system
Orthorhombic
Space group
Pbca
Unit cell dimensions
a= 19.2637(18)A
b = 16.7591(18)
A
c = 24.480(3) A
a
=
90'
#3= 900
y = 900
A3
Volume
7903.2(14)
Z
8
Density (calculated)
1.379 Mg/m3
Absorption coefficient
3.086 mm-1
F(000)
3360
Crystal size
0.170
Theta range for data collection
1.813 to 30.5060
Index ranges
-13<=h<=27, -23<=k<=23, -34<=1<=34
Reflections collected
141820
Independent reflections
12060 [R,,,
Completeness to theta = 25.2420
100.0
Absorption correction
Semi-empirical from equivalents
Max. and min. transmission
0.4942 and 0.3487
Refinement method
Full-matrix least-squares on F2
Data / restraints / parameters
2
0.110 x 0.075 mm 3
=
0.0966]
%
x
12060 / 2343 / 622
Goodness-of-fit on F
1.103
Final R indices [I>2-(1)]
RI
R indices (all data)
RI = 0.0823, wR2 = 0.1428
Largest diff. peak and hole
=
0.0587, wR2 = 0.1315
2.382 and -2.089 e.A-3
109
REFERENCES
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R. R. Acc. Chem. Res. 1979, 12,98.
2 Oskam, J. H.; Schrock R. R. J. Am. Chem. Soc. 1993, 115, 11831.
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Brookhart, M.; Green, M. L. H.; Wong, L. Prog. Inorg. Chem. 1988,36, 1; c) Schultz, A. J.;
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5Schrock, R. R. In Handbook of Metathesis, 2nd Ed.; Grubbs, R. H.; O'Leary, D. J., Ed.; Wiley:
4 a)
Weinheim, Germany, 2015.
6 a) Schaverein, C. J.; Dewan, J. C.; Schrock, R. R. J. Am. Chem. Soc. 1986, 108, 2771; b)
Schrock, R. R.; DePue, R.; Feldman, J.; Schaverein, C. J.; Dewan, J. C.; Liu, A. H. J. Am. Chem.
Soc. 1988, 110, 1423; c) Mowat, W.; Wilkinson, G. J. Chem. Soc., Dalton Trans. 1973, 10,
1120; d) Zue, Z.-L., Morton, L. A. J. Organomet. Chem. 2011, 696, 3924.
7a) Schrock, R. R. In Reactions of CoordinatedLigands; Braterman, P. R., Ed.; Plenum: New
York, 1986; p 221; b) Schrock, R. R. Chem. Rev. 2002, 102, 145; c) Lichtscheidl, A. G.; Ng, V.
W. L.; Muller, P.; Takase, M. K.; Schrock, R. R.; Malcolmson, S. J.; Meek, S. J.; Li, B.;
Kiesewetter, E. T.; Hoveyda, A. H. Organometallics2012,31,4558; d) Schrock, R. R.;
Guggenberger, L. J. J. Am. Chem. Soc. 1975, 97, 6578.
8 a) Gerber, L. C. H.; Schrock, R. R.; Miller, P.; Takase, M. K. J. Am. Chem. Soc. 2011, 133,
18142; b) Gerber, L. C. H.; Schrock, R. R.; Miller, P. Organometallics2013, 32, 2373.
9 a) Bell, A.; Clegg, W.; Dyer, P. W.; Elsegood, M. R. J.; Gibson, V. C.; Marshall, E. L. J. Chem.
Soc., Chem. Commun. 1994,2547; b) Bell, A.; Clegg, W.; Dyer, P. W.; Elsegood, M. R. J.;
Gibson, V. C.; Marshall, E. L. J. Chem. Soc., Chem. Commun. 1994, 2247.
10
a) Gavenonis, J.; Tilley, T. D. J. Am. Chem. Soc. 2002, 124, 8536; b) Gavenonis, J.; Tilley, T.
D. Organometallics2002, 21, 5549; c) Gavenonis, J.; Tilley, T. D. Organometallics2004,23,
31.
" a) Gibson, V. C.; Redshaw, C.; Walker, G. L. P.; Howard, J. A. K.; Hoy, V. J.; Cole, J. M.;
Kuzmina, L. G.; De Silva, D. S. J. Chem. Soc., Dalton Trans. 1999, 161; b) Cole, J. M.; Gibson,
V. C.; Howard, J. A. K.; McIntyre, G. J.; Walker, G. L. P. J. Chem. Soc., Chem. Commun. 1998,
1829.
12 a) Hock, A. S.; Schrock, R. R.; Hoveyda, A. H. J. Am. Chem. Soc. 2006, 128, 16373; b) Singh,
R.; Schrock, R. R.; Muller, P.; Hoveyda, A. H. J. Am. Chem. Soc. 2007, 129, 12654; (c)
110
Lichtscheidl, A. G.; Ng, V. W. L.; Mfller, P.; Takase, M. K.; Schrock, R. R. Organometallics
2012,31,2388.
13 Flook, M. M.; Gerber, L. C. H.; Debelouchina, G. T.; Schrock, R. R. Macromolecules 2010,
43,7515.
14
a) Wang, C.; Yu, M.; Kyle, A. F.; Jakubec, P.; Dixon, D. J.; Schrock, R. R.; Hoveyda, A. H.
Chem. Eur. J. 2013, 19,2726; b) Townsend, E. M.; Schrock, R. R.; Hoveyda, A. H. J. Am.
Chem. Soc. 2012, 134, 11334; c) Schrock, R. R.; Feldman, J.; Cannizzo, L. F.; Grubbs, R. H.
Macromolecules 1987, 20, 1169.
15 Flook, M. M.; Borner, J.; Kilyanek, S. M.; Gerber, L. C. H.; Schrock, R. R. Organometallics
2012,31,6231.
16 Rische, D.; Baunemann, A.; Winter, M.; Fischer, R. A. Inorg. Chem. 2006,45,269.
7
1 Sheldrick, G. M., TWINABS; University of Gttingen: Germany, 2008.
18 Sheldrick, G. M., SADABS; University of Gbttingen: Germany, 1996.
19 Sheldrick, G. M., A cta Cryst. 2015, A 71, accepted.
Sheldrick, G. M., Acta Cryst. 2008, A64, 112-122.
21 Miller, P., CrystallographyReviews 2009, 15,
5 7-83.
22 Sheldrick, G. M CELLNOW; University of Gdttingen: Germany,
2008.
23 Bruker SAINT, Bruker-AXS Inc., Madison, Wisconsin, USA,
2010.
24 Thorn, A., Dittrich, B. & Sheldrick, G. M., Acta Cryst. 2012, A68,
448-451.
20
111
Chapter 3
Synthesis of Tungsten Adamantylimido Alkylidene Species
Portions of this chapter have appeared in print:
Jeong, H.; Axtell, J. C.; Tor6k, B.; Schrock, R. R.; Muller, P. "Syntheses of Tungsten
tert-Butylimido and Adamantylimido Alkylidene Complexes Employing Pyridinium
Chloride as the Acid" Organometallics2012, 31, 6522.
112
INTRODUCTION
Over the past decade, Z-selective olefin metathesis catalysts have been developed.
Early examples of Z-selective polymerizations through ROMP, for example, have been
reported' but the selectivity in these cases was largely ascribed to rates of alkylidene
isomerization relative to the rate of monomer insertion, and generally speaking,
polymerization by chain-end control. However, in cases where these reactions are not
completely under kinetic control (i.e. those in which isomerization to thermodynamically
favored olefins is possible), Z-selectivity - which in this case would require the nature of
-
the substrate to dictate olefin geometry toward the energetically disfavored Z isomer
often will not predominate; rather, mixtures of E and Z isomers or an excess of the
generally undesired E isomer are to be expected. 2
In the early to mid 2000's, 2,6-terphenyl-based ligands were introduced and have
since been employed as phenoxide/alkyl ligands for the isolation of coordinatively
unsaturated and inherently reactive main group and transition metal centers. 3 The utility
of the extreme bulk of these and other phenoxides has been applied over the last several
years to the high oxidation state metathesis catalyst scaffold in order to generate Zselective catalysts.
It was ultimately found that catalysts which employ the sterically encumbering
HMTO (2,6-dimesitylphenoxide, or HexaMethylTerphenoxide) or HIPTO (2,6-bis(2,4,6triisopropylphenyl)phenoxide, or HexalsoPropylTerphenoxide) ligands (Figure 3.1a)
with comparatively small imido or oxo ligands (which adopt mutually trans positions at
the
axial
sites
of
intermediate
metallacyclobutanes)
unprecedented geometric control (Figure 3.1b).
cis,syndiotactic 5 or cisisotactic"
6
polymers
generate
Z-olefins
with
It was also later found that ~100%
were
accessible
using this ligand
combination.
G
SuALL
R'
Rsml
Rsmj
'Pr
'Ki1'
Pr
'P
'Pr0
N
NN-NM
ZZ1 R'
4
'Pr
G
-Ch-N
N
G
[C
-A
[2+2]
N
12+2]
bg"-zH
r
BIG
a)
b)
Figure 3.1: a) HMTO and HIPTO ligands, respectively; b) Proposed nature of Z-selectivity in catalysts bearing
large phenoxides and comparatively small imido ligands.
113
Of the small imido ligands used, the adamantyl group proved to be one of the
most successful for Z-selective olefin metathesis, in particular Z-selective ROMP of
norbornadiene- and cyclopropene-derived monomers, as well as for enantioselective
ROCM
and
RCM
reactions.2,sab
'
Of
note,
one
such
catalyst,
Mo(NAd)(CHCMe 2Ph)(pyr)(OHMT), stands as one of only two examples thus far that
selectively generates alternating AB copolymers via ROMP.5c
8
It therefore became of interest to synthesize tungsten analogues to compare
reactivity and overall Z-selectivity, given that tungsten is generally the less reducible of
these Group 6 metals and tends not to engage in post-metathesis isomerization to the
extent of
Mo 2
4
,a
(despite one report in the literature with W9).
Though adamantylimido
species of molybdenum have been known for many years, no tungsten analogues have
ever been synthesized. Indeed, the only tungsten bisalkylimido complexes known were
[W(NBu) 2C 2(NH 2 Bu)1 2 , reported by Nielson'0 and synthesized by the treatment of WCl 6
with 4 equivalents of tBuNHSiMe 3 , along with related complexes supported by strong
Lewis bases. Given this success and the utility of this synthetic protocol for other areas
of metathesis catalyst chemistry where imido installation proved challenging (see Chapter
1), this method was employed to synthesize adamantylimido complexes of tungsten.
RESULTS AND DISCUSSION
I. Synthesis of Adamantylimido Precursors
The synthesis of AdNHSiMe 3 has been reported previously." Treatment of WCl 6
in benzene with 4 equivalents of AdNHSiMe 3 gives rise to a brown/purple mixture
(Scheme 3.1).
WC 6
+
4 AdNHSiMe 3
"W(NAd) 2 C1 2 (NH 2Ad)"
C6H6,
36h
Scheme 3.1: Synthesis of first WVI adamantylimido complex.
Filtration
through Celite and isolation
from
pentane
affords dimeric
species
[W(NAd) 2C 2(AdNH 2)1 2 1, which was also confirmed by X-ray crystallography (Figure
3.2).
1 shows three chemically independent adamantyl moieties, which explains the
rather complex 'H NMR spectrum: a close examination of the
W-Nimido
bond distances
114
reveals that the cis imido substituents on each tungsten are inequivalent and that therefore
1 must be viewed as a Ct-symmetric dimer with inequivalent adamantylimido fragments
rather than a species with C 2 symmetry.
Each half dimer can be viewed as a square
pyramidal fragment with one apical and one basal imido ligand. The remaining axial
interaction is supplied by the bridging chloride from the other half of the dimer.
N4)
\~
/<~
AdC
N
MW
C1
N
Ad
.N
H N(H)Ad
N
Ad('
---
C1 e
N
Ad
' CI
Figure 3.2: Solid state structure of 1. Hydrogen bonding interactions are proposed to stabilize this dimer
towards dissociation. Selected distances (A) and angles (*) : W(1)-N(1) = 2.206(2), W(1)-N(2) = 1.732(2), W(1)-
N(3) = 1.762(2), W(1)-CI(1) = 2.4048(7), W(1)-CI(3) = 2.6023(7), W(1)-CI(4) = 2.8155(7), W(2)-N(4) = 2.212(2),
W(2)-N(5) = 1.739(2), W(2)-N(6) = 1.764(2), W(2)-CI(2) = 2.4001(7), W(2)-Cl(3) = 2.8172(6), W(1)-CI(4) =
2.5997(7), W(1)-N(1)-C(10) = 128.80(16), W(1)-N(2)-C(20) = 172.53(18), W(1)-N(3)-C(30) = 153.22(18), W(1)CI(3)-W(2) = 105.81(2), W(1)-Cl(4)-W(2) = 105.93(2), W(2)-N(4)-C(40) = 126.86(16), W(2)-N(5)-C(50)=
171.01(19), W(2)-N(6)-C(60) = 152.40(19).
The adamantylamine ligands show a characteristically off-axis ligation with tungsten;
based on the distance of the adamantylamine nitrogens with the adjacent chlorides
(3.355k and 3.301A), a hydrogen bonding interaction is proposed to be operative. 2 A
close examination of the 'H NMR spectrum supports this conclusion, as in certain
solvents (CH2Cl 2 , e.g.), two distinct AdNH 2 proton resonances are observed.
This
complex is incredibly stable, neither dissociating to the monomer or decomposing even at
120*C in DME.
Under atmospheric conditions, however, this complex gradually
decomposes.
Despite it's dimeric nature and the presence of acidic protons on the
adamantylamine
ligand,
alkylation
with
neopentyl
or
2-methyl-2-
phenylpropylmagnesium chloride cleanly affords the expected, monomeric dialkyl
complexes W(NAd) 2 (CH 2 CMe 2 R) 2 2 (R = Me 2a, Ph 2b; Scheme 3.2).
The neophyl
analogue was also studied by X-ray crystallography (Figure 3.3). The bond angles and
distances resemble those of other species of this type."
115
C2
N1
40
0--21
C12
Figure 3.3: Solid state structure of 2b. Selected bond distances (A) and angles ("): W-N1: 1.751, W-N2: 1.757,
W-C1: 2.147, W-C11: 2.126; W-N1-C21: 159.83, W-N2-C31: 162.86, W-C1-C2: 119.72, W-C11-C12: 127.92.
II. Synthesis of Adamantylimido Alkylidene Complexes
A. Formation of Adamantylimido Alkylidenes Using Pyridinium Chloride Salts
Synthesis of molybdenum adamantylimido complexes requires the treatment of
Mo(NAd) 2(CH 2CMe 2R) 2 (R = Me, Ph) with 3 equivalents of HOTf in DME/Et2O to
generate the desired imidoalkylidene complex; 4 this method proved unsuccessful for the
tungsten analogue.
Instead, treatment of W(NAd) 2 (CH 2 CMe 2 R) 2 (R = Me, Ph) with
either pyridinium chloride or 3,5-lutidinium chloride affords W(NAd)(CHCMe 3)Cl 2L2 (L
= py or 3,5-lutidine) 3 (Scheme 3.2). The lutidine adduct of the neopentylidene analogue
was selected for further study due to its greater ease of isolation. The X-ray crystal
structure of 3a is shown in Figure 3.4.
Rt
"W(NAd) 2C1 2(NH 2 Ad)"
1
2 ClMgCH 2CMe 2R'
2
Et 2O
RK'~
R'
N
11
3 3,5-R 2-Py-HCI
Nf
R
I,
Et 2O
CR
R
R' = Me, 2a; Ph, 2b
R = Me, 3a; H, 3b
Scheme 3.2: Synthetic scheme for adamantylimido dialkyl and neopentylidene species of tungsten.
The lutidine ligands are disposed trans to each other, and the two chlorides are trans to
the imido and alkylidene fragments.
In bis-triflate complexes the DME often orients
116
itself trans to the L2- ligands, though (oxo)alkylidene complexes bearing phosphine
ligands contain phosphines trans to one another.15 The bond angles and distances,
however, are typical for what is expected in an imidoalkylidene complex.
C(16)
C(12)
C(17)
C
(1)
C(5)
C(2322(2
N(2)
C(3)
CM1
C(24
C(25)
/
CI(2)
31)
N(
32)
C(35)
CI()
(33)
C(4
Figure 3.4: X-ray crystal structure of 3a. Selected distances (A) and angles (*): W(1)-C(1) = 1.957, W(1)-N(1) =
1.736, W(1)-N(2) = 2.221, W(1)-N(3) = 2.213, W(1)-CI(1) = 2.512, W(1)-Cl(2) = 2.259; W(1)-C(1)-C(2) = 137.07,
W(1)-N)1)-C(11) = 164.74, N(1)-W(1)-C(1) = 99.78, N(2)-W(1)-N(3) = 166.36, N(1)-W(1)-Cl(1) = 172.60, CI(2)W(1)-C(1) = 168.97, N(1)-C(11)-[C(12,16,17) average] = 109.85, N(1)-W(1)-C(1)-C(2) = 12.64.
B. Functionalization of Adamantylimido Alkylidene Species
Ultimately the goal of this project was to synthesize NIAP complexes for
evaluation in metathesis.
The first step toward this end requires the installation of
pyrrolide ligands via a salt metathesis with the coordinated halides. Treatment of 3a with
two equivalents of Lipyr yields a complex which by 'H NMR appears to be
W(NAd)(CHCMe 3)(pyr) 2(lut)2 4 with one strongly abound and one weakly bound lutidine
ligand (Scheme 3.3), based on the sharpening of the broad set of lutidine peaks at low
temperature.
117
2 Lipyr
C -WW~-
C 7H 8 , -30C
-
NW
| \
4
3a
Scheme 3.3: Attempted synthesis of bispyrrolide species 4, which maintains both lutidine adducts from 3a.
The extreme difficulty of isolating this complex in pure form, likely due to the lability of
one of the lutidine ligands in solution, prompted investigation of an alternative synthetic
strategy in order to make MAP species bearing an unsubstituted pyrrolide ligand. Given
the persistence of the lutidine adduct(s), it was hypothesized that a stable mono-chloride,
mono-terphenoxide complex could be made. It was presumed that one lutidine ligand
would be forced to dissociate due to unfavorable steric interactions but that the other
would be retained and would provide additional stability to the complex. Treatment of
3a
with
one
equivalent
of
HMTOLi
or
affords
HIPTOLi
complexes
W(NAd)(CHCMe 3 )(Cl)(OR)(lut) (R = HMT, 5; HIPT, 6) (Scheme 3.4).
LiOAr
60-C
CI-C6H6,
CIN
3
C--
-6R
/R
R RR
C
R
C1
R = Me, 5; iPr, 6
Scheme 3.4: Synthesis of mono-chloro, mono-terphenoxide species.
We hoped that treatment with lithium pyrrolide, in addition to replacing the chloride
ligand, would also introduce enough bulk around the metal center to force the
dissociation of the lutidine ligand. However, treatment of 5 with one equivalent of Lipyr
affords MAP adducts W(NAd)(CHCMe 3)(pyr)(OHMT)(lut) in which the lutidine is
retained (Scheme 3.5).
118
-N
.1Lipyr
o.
\
CAH, 70/C
CI
VV
/
N
7
5
Scheme 3.5: Synthesis of adamantylimido MAP adduct 7.
Unfortunately, the steric bulk around the metal is insufficient to force dissociation of the
lutidine ligand in any meaningful concentration.
Bulk chemical analysis and the
sharpness of the lutidine peaks in the 'H NMR spectra of 7 supports this conclusion.
Preliminary results suggest that the OHIPT analogue of 7 also contains a lutidine adduct,
so this compound was not pursued. Despite the persistent solvent adduct, this complex
was tested for metathesis activity. As expected, 7 only very sluggishly promotes the
homometathesis of 1 -octene and ROMP of DCMNBD.
Several
cases
have
now
been
reported
for
isolating
tungsten-based
metallacyclobutane species,7"' generated through the addition of 1 atm of ethylene to a
solution containing the tungsten alkylidene. We proposed that if a metallacyclobutane
could be generated from 7, a 5-coordinate metallacyclobutane species could be isolated
and separated from dissociated lutidine. Treatment of 7 with 1 atm of ethylene resulted
in a complex 'H NMR spectrum.
Despite the presence of tert-butyl ethylene, the
necessary metathesis product of 7 with ethylene, no new alkylidene signals or
metallacyclobutane peaks are observed. We suggest that 7 decomposes in the presence of
ethylene via P-H elimination and reduction to Wv1 (Scheme 3.6). Such reductions have
been observed previously, particularly in the presence of a Lewis base.
17
119
P-H elimination
xs C 2H 4
-W
I
1CH_
N'H
4
N
0
N/0,
N
7
1 atm C
2
H4
.
Scheme 3.6: Possible decomposition pathway of 7 under
C. Attempts to Chemically Remove Lewis Base Adducts
It became clear at this point that chemical removal of the lutidine adduct would be
Treatment of 5 with
required in order to isolate a 4-coordinate MAP species.
ZnCl 2(dioxane),, which has previously been used to remove nitrogen-derived Lewis
bases,"gives a new product which appears to have peaks corresponding to a new MAP
species, but under these reaction conditions other products are observed, in particular,
one that results from pyrrolide/halogen exchange to regenerate 5.
An alternative
approach involves the treatment of 5 with one equivalent of B(C6 F,)3 , which gives rise to
a deep red solution and the production of adduct-free complex 8 (Scheme 3.7). B(C6F5)3
has similarly been used within our group to remove Lewis bases from tungsten
centers.-5e'9
N
B(C 6F 5)3
0
"*
CI
CH 2C 2, rt
5
0'
8
.
Scheme 3.7: Removal of lutidine adduct from 5 using B(CF,) 3
Filtration of the pentane-soluble 8 through Celite removes the sparingly pentane-soluble
borane-lutidine Lewis acid/base pair. Subsequent treatment of 8 with one equivalent of
Lipyr in THF affords 9-THF. Dissolution of 9-THF in toluene and removal of solvent in
vacuo affords 4-coordinate MAP complex 9 (Scheme 3.8).
9 can also be accessed
directly from 8 by treatment of 8 with Lipyr in toluene.
120
I
vacuu
Lipyr
THF, rt
/
N
N
8
CH8, vacuum0
9-THF
9
Scheme 3.8: Synthesis of 4-coordinate adamantylimido MAP complex.
Given the pentane-solubility of 9 and purification difficulties, initial isolation
attempts were made using MeCN, which has proven very convenient for highly soluble
species (e.g. those bearing HIPT-based ligands; see also Chapters 1 and 2) and in general
complexes in these systems which form MeCN adducts. ' Dissolution of 9 in MeCN
followed by stirring for 1-2 hours results in the precipitation of an off-white solid. Upon
isolation of this solid and redissolution in C6D, the MeCN adduct appears to have
formed. Over time, however, a new product grows in the 'H NMR spectrum with a
diagnostic shift at ~ 5.06 ppm with concomitant loss of the alkylidene resonance. We
propose this to be the insertion product of MeCN into the W=C bond of 10 (Scheme 3.9).
Similar reactivity has been observed for Group 5 alkylidenes.2 0 Attempts to remove the
MeCN adduct from 9-MeCN under vacuum in the presence of a higher boiling solvent
were only partially successful: some 10 is always observed in the reaction mixture along
with 9. The isolation of 9 via crystallization from THF, therefore, is the preferred method
(see above).
observed
Interestingly, similar reactions of MeCN insertion into W=C bonds are
for
both
8
and
W(N t Bu)(CHCMe3 )(pyr)(OHMT);
for
the
tert-butylimido
however, no such
analogue
of
9,
reactions are observed for
Mo(NR)(CHCMe 2R')(pyr)(OHMT) (R = Ad, R' = Ph; R = tBu, R' = Me).
1. MeCN, isolation
2.C6 1D 6
S--------
N
N'N
N
Hour
------
N
9
N
9-MeCN
10
Scheme 3.9: Insertion of MeCN into W=C bond of 9.
121
With crude 9 in hand, polymerization attempts were carried out to evaluate the Zselective nature of this catalyst and to see if similar results to the Mo analogue were
obtained. Treatment of 9 with excess DCMNBD affords nearly 100% cis,syndiotactic
poly(DCMNBD), which is identified by characteristic C 1 , C,, and Ha chemical shifts5a in
CDCl 3 (Figure 3.5). Though 9 awaits complete characterization, given the precedent set
by the Mo analogue it is reasonable to conclude that 9 is the only metathetically active
species present, especially in light of the high regularity of the polymer generated.
C1
M.O1C
COM.
C7
.
Figure 3.5: "C NMR (left, alkyl region) and 'H NMR (right, olefinic region) spectra of poly(DCMNBD)
generated by 9 in CDC 3
D. Synthesis and Reactivity of Adamantylimido Alkylidene Species Bearing 2,5Dimethylpyrrolide Ligands
We were also interested to see if MAP complexes bearing 2,5-dimethylpyrrolde
ligands could be synthesized and if similar procedures of adduct removal were required.
Treatment of 3a with two equivalents of LiMe 2pyr in a toluene/DME solution affords
bispyrrolide complex 11 (Scheme 3.10).
122
1
2 LiMe 2pyr;N
N
C 7D 8 /DME
1"N
11
3a
Scheme 3.10: Synthesis of W(NAd)(CHCMe3)(Me 2pyr)2(lut).
The 'H NMR spectrum of this complex suggests only one lutidine is retained and based
on the broadened peaks is somewhat labile. X-ray quality crystals were grown from Et 2O
and the diffraction study revealed that the lutidine adduct is bound under the
crystallization conditions. The solid-state structure is shown in Figure 3.6. This example
makes clear, as well, that in order to generate a 4-coordinate bis-pyrrolide species,
chemical removal of the lutidine adduct is necessary.
The sterically-induced dissociation of one lutidine ligand from 3a to form 11 was
still encouraging given the ultimate goal of generating Z-selective catalysts, which
typically employ very bulky phenoxide ligands.
C(51
6C(8)
61)
(6)
(67)
N(5)
-CM
C(9)
W(2)
C(6)
C(10)
CH72)
NM7
NO8
C(82
C(85)
C(75
Figure 3.6: Solid-state structure of 11. Selected distances (A) and angles (*): W(2)-C(6)= 1.893, W(2)-N(5)=
1.733, W(2)-N(6) = 2.267, W(2)-N(7) = 2.140, W(2)-N(8) = 2.100, N(5)-C(51) = 1.457; W(2)-N(5)-C(51) = 169.91,
W(2)-C(6)-C(7) = 144.84, N(5)-W(2)-C(6) = 103.73, N(6)-W(2)-N(8) = 163.74, N(7)-W(2)-C(6) = 121.96, N(5)C(51)-[a-CH2(average)] = 109.86, N(5)-W(2)-C(6)-C(7) = 13.00.
123
It was hypothesized that the treatment of 11 with a phenol such as HMTOH would yield
4-coordinate W(NAd)(CHCMe 3)(Me 2pyr)(OHMT) and free 3,5-lutidine as a consequence
of the considerable steric bulk of the OHMT ligand. Indeed, charging HMTOH to 11 in
C7 H and heating to 80'C for ~5h affords 4-coordinate 12 (Scheme 3.11).
N
Y N
HMTOH
11
N-
C 7H8 , 80*C
N
\0
0
-
_
/
N
12
Scheme 3.11: Synthesis of lutidine-free MAP species W(NAd)(CHCMe 3 )(Me 2pyr)(OHMT).
-
As expected, 12 proved to be somewhat sluggish in the ROMP of DCMNBD
only -75% conversion after 24h - likely due to the larger pyrrolide ligand compared to
the unsubstituted congener, though the structure of the polymer, as expected, is mostly
cis,syndiotactic.
The utility of 12 and related 2,5-dimethylpyrrolide-containing MAP
catalysts in other areas of metathesis (ROCM, RCM, etc.) has yet to be studied. It also
remains to be seen whether smaller terphenols such as 2,6-diphenylphenol and 2,6bis(pentafluorophenyl)phenol would be sterically encumbering enough to force the
dissociation of the lutidine adduct from 11 yet small enough to perform metathesis with
reasonable rates and selectivities. In addition, given the lability of the lutidine ligand
(judged by the broadened in the proton NMR), chemical removal using a Lewis base (e.g.
ZnCl 2) should be possible.
CONCLUSIONS
Other comparisons of [W](NAd) and [Mo](NAd) would be potentially interesting
and could provide further understanding of the reactivities of both alkylimido species and
the differences between Mo and W within these systems. A recent report from our group
detailed the success of Mo and W alkylimido species in the ROMP of cyclooctene
(COE).21 It was clear from this study that the tert-butyl and adamantylimido groups
124
differed greatly, and that the tert-butylimido complexes of Mo and W also differed, with
W giving greater conversion than Mo under identical conditions and with a high degree
of selectivity for head-to-tail ROMP.
Further effort is still needed within the tungsten adamantylimido system to tease
out potential uses and troubleshoot the synthetic pitfalls presented here. However, the
facts remain that a) the installation of the adamantylimido group on tungsten(VI) is
possible via an alternative synthetic route and b) that alkylidene complexes that bear this
imido ligand can be generated and do behave as high oxidation state metathesis catalysts.
125
EXPERIMENTAL
General Details.
All air-sensitive compounds or reactions were manipulated under
nitrogen in a drybox or using Schlenk techniques. All glassware was oven-dried and
allowed to cool under vacuum or nitrogen before use. Diethyl ether, pentane, benzene,
methylene chloride, THF, DME, and toluene were sparged with nitrogen and passed
through activated alumina. All solvents were stored over molecular (4A) sieves in a
nitrogen atmosphere. Deuterated solvents were also stored over molecular sieves (4A).
NMR spectra were obtained on Varian spectrometers operating at 300 MHz or 500 MHz.
NMR chemical shifts are reported as ppm relative tetramethylsilane, and were referenced
to the residual proton or 13 C signal of the solvent (H CDCl 3: 7.260 ppm; 'H C6 D6 : 7.160
ppm; 'H CD 2 Cl 2 : 5.320 ppm;
CD 2 Cl 2 :
53.840 ppm).
13
C C6D 6 :
128.06 ppm;
13
C CDCl 3: 77.160 ppm; "C
N-trimethylsilyl(1 -adamantyl)amine"
has been reported
previously; our preparation involved the use of n-BuLi and chlorotrimethylsilane
Lithium pyrrolide and 2,5-dimethyllithium pyrrolide were synthesized by addition of 1
equivalent of n-BuLi to an ethereal solution of the neutral pyrrole and were isolated by
filtration and washed thoroughly with pentane. Pyridinium chloride was purchased from
Sigma Aldrich or Alfa Aesar, sublimed, and ground with mortar and pestle before use.
3,5-lutidinium chloride was synthesized through the addition of 1 equivalent of ethereal
hydrogen
chloride
to
a
chilled
(-30'C)
ether
solution
of
3,5-lutidine.
Neopentylmagnesium chloride22, HMTOH 3 a, and ZnCl 2(dioxane) 2 3 were synthesized
according to reported procedures. Unless otherwise noted, all other reagents were
obtained from commercial sources and used as received.
[W(NAd) 2Cl(p-Cl)(AdNH 2)] 2 (1). N-trimethylsilyl(1-adamantyl)amine
(28.2 g, 126
mmol) was added to a stirred suspension of WCl 6 (12.51 g, 31.6 mmol) in benzene (400
mL) in a roundbottom flask. After 24 h, the mixture was filtered through Celite and the
Celite pad was washed with methylene chloride. All volatile components were removed
from the filtrate in vacuo. The resulting tan solid (16.68 g, 75%) was washed on a glass
frit with cold Et2O and dried in vacuo. A sample for elemental analysis was isolated from
a concentrated solution in Et2 O at -30 0 C: 'H NMR (500 MHz, C6D6 ) 6 2.61 (s, 4H, NH 2 ),
2.26 (br s, 24H, CH 2), 2.07 (br s, 12H, CH), 1.94 (br s, 6H, CH), 1.86 (br s, 12H, ax/eq
126
CH2 ), 1.54 (m, 24H, ax/eq CH2 ), 1.46 (br s, 12H, CH); 13 C NMR (125Hz, CD 2 Cl 2 ); 49.83,
45.32, 45.12, 43.58, 36.49, 36.41, 35.90, 30.20, 30.18, 30.00. Anal. Calcd for
C60H, 4 Cl 4 N6 W2 : C, 51.15; H, 6.72; N, 5.96. Found: C, 50.86; H, 6.47; N, 6.01.
W(NAd) 2(CH2 -t-Bu) 2 (2a).
[W(NAd) 2C1(U-Cl)(AdNH 2)
2
(3.62 g, 2.57 mmol) was
added to 60 mL of diethyl ether and the solution was to -30'C for 1 h.
Ethereal
Me 3CCH 2MgCl (2.32 M, 4.98 mL, 11.6 mmol) was added to the stirred mixture and the
whole was stirred for 6 h. The solvent was removed in vacuo, the residue was extracted
with benzene, and the extract was filtered through Celite. Solvents were removed from
the filtrate in vacuo. Cold ether was added to the product, and the pale product (1.71 g,
53%) was isolated by filtration: 'H NMR (500 MHz, C6D6 ) 6 2.11 (d, 12H, CH 2), 2.05
(br s, 6H, CH), 1.66 (s, 4H, WCH2, 2 jWH
=
10.5 Hz), 1.58 (m, 12H, ax/eq CH2 );
(125 MHz, C6 D 6 ) 84.42, 67.05, 47.40, 36.70, 34.79, 34.35, 30.51.
C30 H5 2 N 2 W:
13C
NMR
Anal. Calcd for
C, 57.69; H, 8.39; N, 4.49. Found: C, 57.66; H, 8.14; N, 4.39.
W(NAd) 2(CH2CMe 2Ph)2 (2b). A solution of [W(NAd) 2Cl(p-Cl)(AdNH 2) 2 (6.0 g, 8.18
mmol) in 60 mL of diethyl ether was chilled at -30 'C for 1 h.
Ethereal
ClMgCH 2CMe 2 Ph (0.5 M, 33.5 mL, 16.8 mmol) was added to the stirred mixture and the
resulting mixture was allowed to stir for 6 h. The suspension was filtered over Celite and
washed with ether. The filtrate was dried under vacuum and pentane was added to the
residue. The resulting pale yellow solid (3.82 g, 56%) was isolated by filtration: 'H
NMR (500 MHz, C6 D6 ) 6 7.42 (d, 4H, Ar), 7.24 (t, 4H, Ar), 7.09 (t, 2H, Ar), 2.04 (br s,
6H, CH), 1.95 (d, 12H, CH2 ), 1.58 (m, 6H, ax/eq CH 2 ), 1.57 (s, 4H, WCH 2), 1.56 (s, 12H,
CMe2Ph); ' 3 C NMR (125 MHz, C6 D6 ) 152.84, 128.51, 126.35, 125.78, 83.26, 67.07,
47.00, 40.41, 36.69, 34.07, 30.48. Anal. Calcd for C4OH5 6N2 W:
C 64.17; H, 7.54; N,
3.74. Found: C, 64.27; H, 7.57; N, 3.62.
W(NAd)(CHCMe3 )C 2(3,5-Me 2CH 3N) 2 (3a). W(NAd) 2 (CH 2 CMe 3 ) 2 (4.67g, 7.48 mmol)
was charged to a flask, followed by 3,5-dimethyllutidine hydrochloride (3.22g, 22.4
mmol) and -70mL Et 2O. The resulting mixture was stirred at room temperature for 24h.
The volatiles were removed in vacuo and the residue was charge with toluene. The
127
suspension was filtered through Celite and washed thoroughly with toluene and once with
benzene. The filtrate was dried under vacuum and the resulting solid was charged with
pentane and isolated as a pale yellow solid (3.22g, 74%). 'H NMR (C6 D 6 , 500 MHz): 6
(major isomer) 11.92 (s, 1H, W=CH), 9.54 (s, 4H, lutidine), 6.38 (s, 2H, lutidine), 2.32
(s, 6H, lutidine), 1.94 (s, 3H, CH), 1.71 (s, 12H, CH 2 ), 1.50 (s, 9H, Me3 ), 1.45 (m, 6h,
ax/eq CH 2 );
13
C NMR (CD 2 Cl 2 , 125 MHz): 298.27, 154.10, 140.03, 133.76,70.58,43.39,
36.15, 33.92, 29.64, 29.33, 18.37. Anal. Calcd for C 2 9 H4 3 Cl 2 N 3 W: C, 50.60; H, 6.30; N,
6.10. Found: C, 50.89; H, 6.38; N, 5.62.
W(NAd)(CH-t-Bu)C
2(PY) 2
(3b). A solution of W(NAd) 2 (CH2 CMe 2 Ph) 2 (3.84 g, 6.15
mmol) in ether was chilled to -30 C. Pyridinium chloride (2.13 g, 18.4 mmol) was
added and the mixture was stirred for 24 h. The resulting suspension was filtered through
Celite and the filter cake was washed with toluene and methylene chloride. The filtrate
was concentrated in vacuo and pentane was added in order to precipitate the yellow
product (2.12 g, 75%): 'H NMR (500 MHz, C6 D6 ) 6 11.88 (s, 1H, WCH), 9.70 (d, 4H,
py), 6.68 (t, 2H, py), 6.41 (t, 4H, py), 2.20 (br s, 6H, CH 2 ), 1.90 (br s, 3H, CH), 1.42 (in,
6H, ax/eq CH 2 ), 1.40 (s, 9H, -t-Bu);
3
1C
NMR (125 MHz, CD 2 Cl 2 ) 299.21 ('Jwe = 155
Hz), 156.58, 138.93, 124.41, 70.63, 43.32, 43.25, 35.91, 33.79, 29.48. Anal. Calcd for
C 2 5 H 3 5 Cl 2 N 3 W: C, 47.49; H, 5.58; N, 6.65. Found: C, 47.49; H, 5.79; N, 6.54.
Observation
of
W(NAd)(CHCMe 3)(pyr)2(3,5-Me 2 CH3N) 2
(4):
3
(278mg,
0.404mmol) was charged to a flask with 10mL toluene and chilled at -30'C for lh.
Lithium pyrrolide (59mg, 0.808 mmol) was added and the mixture was stirred for lh.
The solvent was removed under vacuum and the residue was charged with CH 2 Cl 2 . The
suspension was filtered over Celite.
The filtrate was dried under vacuum and the
resulting solid was charged with pentane. A yellow solid was isolated by filtration. 'H
NMR (CD 2 Cl 2 , 500 MHz, -10'C): 10.63 (s, 1H, W=CH), 8.12 (bs, 2H, lutidine), 7.92 (s,
2H, lutidine), 7.53 (s, 1H, lutidine), 7.35 (bs, 1H, lutidine), 6.67 (t, 2H, pyr), 6.19 (d, 2H,
pyr), 6.06 (in, 4H, pyr), 2.28 (s, 6H, lutidine), 2.27 (s, 6H, lutidine), 2.04 (s, 3H, CH),
1.83 (in, 6H, ax/eq CH2 ), 1.54 (s, 6H, CH2 ), 1.30 (s, 9H, Me 3).
Due to purification
difficulties this compound was not characterized further.
128
-
Observation of 4 at -10 C in CD 2 Cl 2
Neopentyl
Lutbdine
Adamanlyl
Lutidine
Pyrrolide
W=CH
1.0
10.5
10.0
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
20
15
10
0!
.
'H NMR spectrum of 4 at -10'C in CD 2 Cl 2
W(NAd)(CHCMe)(Cl)(OHMT)(3,5-Me
2CH 3N)
(5).
3a (500mg, .726 mmol) and
LiOHMT (259mg, .770 mmol) were added to a Schlenk bomb followed by 30mL
benzene.
The resulting dark yellow solution was heated at 600 C overnight.
The
suspension was filtered over Celite and washed with benzene. The filtrate was dried
under vacuum and the residue was charged with minimal pentane. The resulting pale
yellow solid (210mg, 63%), was isolated by filtration on a glass frit. 'H NMR (C6 D 6 , 500
MHz) 6 9.75 (s, 1H, W=CH,
2
jWH=
5Hz), 7.96 (s, 2H, lutidine), 7.26 (d, 1H, OHMT),
7.21 (d, 1H, OHMT), 7.10 (s, 1H, OHMT), 7.06 (s, 1H, OHMT), 7.01 (t, 1H, OHMT),
6.93 (s, LH, OHMT), 6.73 (s, lH, OHMT), 6.46 (s, 1H, lutidine), 2.77 (s, 6H, lutidine),
2.33 (s, 3H, o-Me), 2.32 (s, 3H, o-Me), 1.96 (bs, 3H, CH), 1.94 (s, 3H, o-Me), 1.88 (m,
3H, p-Me), 1.82 (m, 3H, p-Me), 1.81 (s, 6H, CH2 ), 1.61 (s, 3H, o-Me), 1.51 (m, 6H, ax/eq
CH2 ), 1.28 (s, 9H, Me 3 );
3
1C
NMR: 278.4 (W=C, 'Jwc = 168 Hz), 161.05, 151.71, 139.17,
129
139.13, 138.30, 137.96, 137.56, 137.22, 135.81, 135.17, 133.98, 132.00, 131.44, 130.07,
129.59, 129.49, 129.41, 128.88, 127.31, 126.96, 119.62, 68.82, 44.77, 42.85, 36.59,
32.84, 30.12, 22.50, 22.12, 21.47, 21.27, 20.86, 20.52, 17.89.
Anal. Calcd for
C,4H5 9 ClN 2 OW: C, 63.12; H, 6.79; N, 3.20. Found: C, 62.77; H, 6.80; N, 3.22.
W(NAd)(CHCMe)(Cl)(OHIPT)(3,5-Me
2CH3N)
(6).
3a (500mg, .726 mmol) and
LIOHIPT (366mg, .726 mmol) were charged to a Schlenk bomb, followed by 30mL
benzene.
The resulting dark yellow solution was heated overnight at 60 C.
The
resulting suspension was filtered over Celite, and the filtrate was dried under vacuum.
The residue was charged with pentane and a pale solid (288mg, 38%) was isolated by
filtration on a glass frit. 'H NMR (C6D 6 , 500 MHz) 6 10.02 (s, 1H, W=CH,
2
jWH =
5Hz),
7.64 (s, 2H, lutidine), 7.46 (d, 1H, HIPTO), 7.41 (dd, IH, HIPTO), 7.40 (d, IH, HIPTO),
7.37 (dd, 1H, HIPTO), 7.05 (d, 1H, HIPTO), 7.01 (t, 1H, HIPTO), 6.47 (s, 1H, lutidine),
3.96 (sept, 1H, CH), 3.87 (sept, 1H, CH), 3.17 (sept, IH, CH), 3.01 (sept, 1H, CH), 2.93
(sept, 1H, CH), 2.80 (sept, 1H, CH), 1.92 (bs, 3H, CH), 1.87 (bd, 3H, eq CH2), 1.85 (s,
6H, lutidine), 1.81 (d, 3H, HIPTO), 1.70 (bd, 3H, ax CH2), 1.67 (d, 3H, HIPTO), 1.46 (m,
6H, CH2 ), 1.41 (d, 3H, HIPTO), 1.39 (d, 3H, HIPTO), 1.38 (d, 3H, HIPTO), 1.37 (d, 3H,
HIPTO), 1.29 (d, 3H, HIPTO), 1.26 (s, 9H, Me 3), 1.25 (d, 3H, HIPTO), 1.06 (d, 3H,
HIPTO), 1.05 (d, 3H, HIPTO), 1.05 (d, 3H, HIPTO), 0.63 (d, 3H, HIPTO).
3
1
C NMR:
277.96 ('Jwc = 171 Hz), 161.71, 152.42, 149.37, 249.30, 147.97, 147.49, 147.37, 146.81,
139.41, 137.22, 137.03, 133.92, 132.00, 131.77, 131.42, 130.68, 122.86, 121.28, 120.02,
119.45, 118.70, 68.91, 44.51, 42.93, 36.52, 35.05, 34.62, 33.88, 31.18, 30.61, 30.35,
29.96, 27.90, 27.51, 26.08, 25.53, 25.30, 24.88, 24.66, 24.52, 24.49, 24.44, 24.02, 22.64,
21.57, 18.07.
Anal. Calcd for Ca,,H 83 ClN 2 OW: C, 66.75; H, 8.02; N, 2.68. Found: C,
66.55; H, 7.96; N, 2.87.
W(NAd)(CHCMe)(pyr)(OHMT)(3,5-Me
2CH3N)
(7).
5 (322mg, .368 mmol) and
lithium pyrrolide (29.4mg, .403mmol) were charged to a Schlenk bomb, followed by
30mL of benzene. The reaction was stirred at 700 C overnight. The mixture was filtered
over Celite, washed with benzene and concentrated under vacuum.
The residue was
charged with minimal pentane to give brown precipitate. This mixture was chilled at -30*
130
C and filtered to give a pale brown solid (210mg, 63%). 'H NMR (C6 D 6 , 500 MHz) 6
9.92 (s, LH, W=CH), 8.08 (s, 2H, lutidine), 7.13, (d, 1H, OHMT), 7.10 (br s, 2H,
OHMT), 7.06 (d, 1H, OHMT), 6.96 (s, 1H, OHMT), 6.91 (t, LH, OHMT), 6.75 (s, 1H,
OHMT), 6.73 (t, 2H, pyr), 6.52 (s, 1H, lutidine), 6.51 (t, 2H, pyr), 2.58 (s, 3H, OHMT),
2.36 (s, 3H, lutidine), 2.34 (s, 3H, lutidine), 1.96 (br s, 6H, OHMT), 1.88 (br s, 9H,
OHMT + adamantyl CH), 1.58 (m, 6H, ax/eq CH 2 ), 1.49 (s, 3H, OHMT), 1.42 (m, 6H,
CH2 ), 1.23 (s, 9H, Me 3 );
3
1C
NMR (C6 D6 , 125MHz): 279.98 ('Jwc = 172.5 Hz), 160.34,
151.89, 140.20, 138.82, 138.18, 137.83, 137.55, 137.44, 136.60, 136.19, 135.62, 133.66,
133.33, 131.78, 130.62, 130.14, 130.01, 129.80, 129.39, 128.70, 128.59, 127.35, 127.27,
119.40, 107.73, 69.45, 45.02, 43.29, 36.53, 33.32, 30.12, 21.64, 21.48, 21.40, 21.27,
20.85, 20.39, 14.31; Anal. Caled for C5OH6 3 N 3 0W: C, 66.29; H, 7.01; N, 4.64. Found:
C, 66.28; H, 7.09; N, 4.57.
W(NAd)(CHCMe)(Cl)(OHMT)
(8). 5 (185mg, .211 mmol) was taken up in CH 2 Cl2
and charged with B(C6 F5 ) 3 (108 mg, .211 mmol) and was stirred for lh. The resulting
solution was dried in vacuo and was charged with tetramethylsilane and stirred
vigorously for 48h. The resulting suspension was then filtered through Celite and dried.
The complex is carried forward without isolation, but the crude 'H NMR is shown below.
131
Neopentyl
*TMS
HMTO
Methyls
Adamantyl
HMTO
W=CH
9.5
9.0
8.5
8.0
7.5
7.0
6.5
6.0
55
5.0
4.5
4.0
3.5
3.0
2.5
2.0
15
1.0
0.5
0.0
.
'H NMR spectrum of 8 in C 6D6
Observation of W(NAd)(CHCMe 3)(pyr)(OHMT) (9).
8 (55mg, .0716 mmol) was
taken up in C 7H8 and charged with Lipyr (5.2mg, .0716 mmol) and stirred overnight. The
resulting mixture was filtered through Celite and dried under vacuum to give a reddish
foam. 'H NMR (C6 D 6 , 500 MHz) 6 8.39 (s, lH, W=CH), 6.95-6.87 (m, 7H, HMTO),
6.75 (s, 2H, pyr), 6.42 (s, 2H, pyr), 2.25 (s, 6H, HMTO), 2.16 (s, 6H, HMTO), 1.99 (s,
6H, HMTO), 1.86 (bs, 3H, Ad), 1.61 (m, 6H, Ad), 1.43 (m, 6H, Ad), 1.20 (s, 9H, CMe 3)-
132
Neopenty
HMTO
Methyls
Adamantyl
Pyrrolide
HMTO
1
W=CHJ
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
1.0
1.5
.
'H NMR spectrum of 9 in C6 D6
W(NAd)(CHCMe,)(2,5-Me 2pyr)2(3,5-Me 2CH3N) (11).
3a (894mg, 1.30 mmol) was
charged to a flask with lOmL toluene and ~2mL DME and chilled at -30 0C for lh.
Lithium 2,5-dimethylpyrrolide (276mg, 2.73 mmol) was added and the mixture was
stirred for lh. The solvent was removed under vacuum and the residue was charged with
CH 2 Cl 2 . The suspension was filtered over Celite. The filtrate was dried under vacuum
and the resulting solid was charged with pentane. The yellow product (438mg, 48%) was
isolated by filtration. 'H NMR (C6D6 , 500 MHz) 6 10.07 (W=CH), 8.23 (s, 2H, lutidine),
6.66 (s, 1H, lutidine), 6.08 (s, 4H, pyr), 2.34 (s, 12H, pyr), 1.98 (s, 6H, lutidine), 1.88 (s,
3H, CH), 1.80 (s, 6H, CH2 ), 1.42 (m, 6H, ax/eq CH2 ), 1.31 (s, 9H, CMe3 );
3
C NMR
(CD, 125 MHz): 280.90 (very broad), 149.61, 138.10, 136.44, 133.39, 108.38, 72.11,
45.70, 45.27, 36.27, 33.61, 30.17, 19.26, 18.05; Anal. Calcd for C 34H5ON 4W: C, 58.45; H,
7.21; N, 8.02. Found: C, 58.80; H, 7.60; N, 7.82.
133
W(NAd)(CHCMe)(Me 2pyr)(OHMT) (12).
11 (276mg, .395 mmol) was taken up in
C7 H. in a Schlenk bomb. HMTOH (131mg, .395 mmol) was added and the mixture was
heated to 80 0C for 5h. The mixture was then dried in vacuo, extracted with pentane, and
filtered through Celite. The filtrate was concentrated, cooled to -30'C overnight, and a
.
pale yellow solid was filtered off. 2 crops were obtained (178mg, 54%). 'H NMR (C6 D 6
500 MHz) 8.41 (s, 1H, W=CH), 6.94 (overlapping peaks, 3H, OHMT), 6.88 (s, 2H,
OHMT), 6.80 (s, 2H, OHMT), 6.14 (s, 2H, pyr), 2.24 (s, 6H, OHMT), 2.19 (overlapping
singlet/broad singlet, 12H, OHMT + Me2pyr), 2.03 (s, 6H, OHMT), 1.87 (m, 3H, Ad),
1.65 (m, 6H, Ad), 1.44 (m, 6H, Ad), 1.29 (s, 9H, CMe3 ); 3C NMR (125 MHz) 259.36
('Jwc = 189 Hz), 158.06, 136.83, 136.64, 136.60, 135.41, 131.94, 130.37, 129.32, 128.57,
122.94, 109.82, 71.58, 45.35, 43.61, 36.10, 34.15, 30.23, 21.51, 21.31, 20.22, 18.33.
Multiple attempts to pass elemental analysis have failed.
The 'H NMR spectrum is
shown below.
8.5
8.0
7.5
7.0
8.5
6.0
5.5
5.0
4.5
4.0
3.5
3.0
2.5
2.0
1.5
.
'H NMR spectrum of 12 in C 6D6
134
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 K, radiation (A =
0.71073 A) from an IpS micro-source for the structure of 1, 3a and 11 and on a Siemens
Platform diffractometer coupled to a SMART Apex detector with graphitemonochromated Mo K, radiation (A = 0.71073
A) for the structure of 2b, performing
b-
and o-scans. The structures were solved by direct methods using SHELXS24 and refined
against F2 on all data by full-matrix least squares with SHELXL-97 25 or SHELXL-201426
following established refinement strategies 27 . 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 times the
Uq 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(NAd) 2Cl(p-Cl)(AdNH 2)] 2 (1) crystallizes in the triclinic space group P T with
1.5 molecules of lb and 7.5 molecules of dichloromethane in the asymmetric unit. The
half molecule is completed by the crystallographic inversion center and the half-occupied
solvent molecule is located near a crystallographic inversion center and disordered over
four positions (that is two independent positions); thus the unit cell contains 3 target
molecules and 15 solvent molecules. Besides the solvent molecule near the inversion
center, one further dichloromethane molecule is disordered over two positions. Those
solvent 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. The crystal was non-merohedrally twinned. Two independent
orientation matrices for the unit cell were found using the program CELLNOW 28 , and
data reduction taking into account the twinning was performed with SAINT 2 9 . The
program TWINAB S 30 was used to perform absorption correction and to set up a
detwinned HKLF4 format file for structure refinement. Coordinates for the nitrogen
bound hydrogen atoms were taken from the difference Fourier Synthesis. The hydrogen
135
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 Ui,, to 1.2 times the
value of the Uq of the nitrogen atom to which they bind.
W(NAd) 2(CH 2 CMe 2Ph)2 (2b) crystallizes in the triclinic space group PT with 1
molecules of 2b in the asymmetric unit. The crystal was split (domain 2 is rotated from
-
domain 1 by 3.4 degrees about reciprocal axis 1.000 -0.466 0.568 and real axis 1.000
0.637 0.260) and treated as non-merohedrally twinned as described above.
W(NAd)(CHCMe)C
2(lut) 2 (3a)
crystallizes in the triclinic centrosymmetric
space group P I with one target molecule and two molecules of benzene (C6 D6 treated as
CH6 ) in the asymmetric unit. Similar ADP and rigid-bond restraints were applied to the
solvent atoms. Coordinates for the hydrogen atom on the carbon atom bound directly to
the metal (Cl) were taken from the difference Fourier synthesis and the hydrogen atom
was subsequently refined semi-freely with the help of a C-H distance restraint (target
value 0.95(2)
A)
while constraining its Ui,, to 1.2 times the value of Uq of Cl. No
further restraints were applied.
W(NAd)(CHCMe)(Me 2pyr)2(lut) (11) crystallizes in the monoclinic
centrosymmetric space group P21/c with two target molecules as well as 1.5 molecules of
diethyl ether in the asymmetric unit. The half occupied ether is disordered involving the
crystallographic inversion center. In addition the target molecules contain two disordered
moieties: The adamantyl group in the molecule containing W1 is disordered over two
positions and the tert-butyl group on the alkylidene on W2 is disordered over two
positions. Those two disorders were refined with the help of similarity restraints on 1,2and 1,3-distances. In addition, similar ADP and rigid-bond restraints were applied to all
atoms involved in the disorders as well as the solvent molecules. The circumstance that
one of the ether molecules is only half occupied results in a non-integer value for the
atom types oxygen and hydrogen in the empirical formula.
136
Table 1. Crystal data and structure refinement for 1.
Identification code
x12067_t4
Empirical formula
C65 H 104 Cl14 N6 W2
Formula weight
1833.54
Temperature
100(2) K
Wavelength
0.71073
Crystal system
Triclinic
Space group
PT
Unit cell dimensions
a = 16.100(2) A
a= 95.280(3)*.
b = 19.006(3) A
= 110.896(3).
c = 19.600(3) A
y = 94.619(4)*
5537.7(13) A3
Z
3
Density (calculated)
1.649 Mg/m 3
Absorption coefficient
3.663 mm-1
F(000)
2766
Crystal size
0.25 x 0.20 x 0.15 mm 3
Theta range for data collection
1.08 to 31.00
Index ranges
-23<=h<=21, -27<=k<=27, 0<=l<=28
Reflections collected
35319
Independent reflections
35319 [R(int) = 0.0000]
Completeness to theta = 31.000
99.9
Absorption correction
Semi-empirical from equivalents
Max. and min. transmission
0.6095 and 0.4611
Refinement method
Full-matrix least-squares on F2
Data / restraints / parameters
2
%
Volume
35319 / 229 / 1263
Goodness-of-fit on F
1.037
Final R indices [I>2sigma(I)]
RI = 0.0326, wR2 = 0.0816
R indices (all data)
RI = 0.0399, wR2 = 0.0851
Largest diff. peak and hole
3.249 and -2.347 e.A-3
137
Table 2. Crystal data and structure refinement for 2b.
Identification code
12033
Empirical formula
C40 H56 N2 W
Formula weight
748.72
Temperature
100(2) K
Wavelength
0.71073
Crystal system
Triclinic
Space group
PT
Unit cell dimensions
a = 12.451(2)
a= 89.600(2)*.
b = 12.881(2)A
3= 66.785(2)0.
c = 12.923(2)
y = 65.290(2)0.
1699.2(5) A3
Z
2
Density (calculated)
1.463 Mg/m3
Absorption coefficient
3.429 mm-1
F(000)
768
Crystal size
0.20 x 0.20 x 0.10 mm 3
Theta range for data collection
1.77 to 30.030
Index ranges
-17<=h<=15, -18<=k<=18, -18<=l<=0
Reflections collected
9892
Independent reflections
9892 [R(int) = 0.04741
Completeness to theta = 30.030
99.5
Absorption correction
Semi-empirical from equivalents
Max. and min. transmission
0.7255 and 0.5471
Refinement method
Full-matrix least-squares on F2
Data / restraints / parameters
9892/4/404
Goodness-of-fit on F2
1.044
Final R indices [I>2sigma(I)]
RI = 0.0 195, wR2 = 0.0434
R indices (all data)
RI = 0.0227, wR2 = 0.0444
Largest diff. peak and hole
0.813 and -0.864 e.A-3
%
Volume
138
Table 3. Crystal data and structure refinement for 3a.
Identification code
x12145
Empirical formula
C41 H55 C12 N3 W
Formula weight
844.63
Temperature
100(2) K
Wavelength
0.71073 A
Crystal system
Triclinic
Space group
PT
Unit cell dimensions
a = 10.2134(9) A
c= 93.782(2)0.
b = 14.1021(13)A
3= 108.766(2)*.
c = 14.2847(13)A
y = 92.576(2)*.
Volume
1939.0(3)
Z
2
Density (calculated)
1.447 Mg/m3
Absorption coefficient
3.148 mm-1
F(000)
860
Crystal size
0.30 x 0.25 x 0.22 mm 3
Theta range for data collection
1.45 to 31.510
Index ranges
-14<=h<= 15, -20<=k<=20, -20<=l<=21
Reflections collected
140432
Independent reflections
12898 [R(int) = 0.0382]
Completeness to theta = 31.510
99.9
Absorption correction
Semi-empirical from equivalents
Max. and min. transmission
0.5483 and 0.4519
Refinement method
Full-matrix least-squares on F2
Data / restraints / parameters
2
%
3
12898 / 97 / 434
Goodness-of-fit on F
1.098
Final R indices [I>2sigma(I)]
RI = 0.0238, wR2 = 0.0603
R indices (all data)
RI = 0.0259, wR2 = 0.0617
Largest diff. peak and hole
2.369 and -1.526 e.A-3
139
Table 4. Crystal data and structure refinement for 11.
Identification code
x13006
Empirical formula
C37 H57.50 N4 00.75 W
Formula weight
754.22
Temperature
100(2) K
Wavelength
0.71073
Crystal system
Monoclinic
Space group
P2(1)/c
Unit cell dimensions
a = 16.2605(8) A
c= 90*.
b = 21.1628(10)
3= 90.0190(10)*.
c = 20.7847(10)
Y = 900.
A
7152.4(6) A3
Z
8
Density (calculated)
1.401 Mg/m3
Absorption coefficient
3.262 mm-1
F(000)
3100
Crystal size
0.12 x 0.10 x 0.08 mm 3
Theta range for data collection
1.37 to 30.520.
Index ranges
-23<=h<=23, -30<=k<=30, -29<=l<=29
Reflections collected
470008
Independent reflections
21839 [R(int) = 0.0534]
Completeness to theta = 30.520
99.9
Absorption correction
Semi-empirical from equivalents
Max. and min. transmission
0.7803 and 0.6956
Refinement method
Full-matrix least-squares on F2
Data / restraints / parameters
Goodness-of-fit on F
2
%
Volume
21839 / 549 / 941
1.066
Final R indices [I>2sigma(I)]
RI = 0.0219, wR2 = 0.0530
R indices (all data)
RI = 0.0294, wR2 = 0.0564
Largest diff. peak and hole
1.410 and -0.772 e.A-3
140
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Organometallics2015, doi: 10.1021/om501213x
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143
PUBLICATIONS AND PRESENTATIONS
Axtell, J. C.; Thai, S. D.; Mortan, L. A.; Kassel, W. S.; Dougherty, D. G.; Zubris, D. L.
"Syntheses of rac/meso-{PhP(3-t-B-C 5H3) 2}-Zr{RN(CH 2)3NR}, structural analyses
of rac-{PhP(3-t-Bu-C 5H3) 2}Zr{RN(CH 2)3NR} (where R is SiMe3 or Ph),
and meso to rac isomerization" J. Organomet. Chem. 2008, 693, 3741.
Yuan, J.; Schrock, R. R.; Muller, P.; Axtell, J. C.; Dobereiner, G. E.
"Pentafluorophenylimido Complexes of Molybdenum and Tungsten" Organometallics
2012,31,4650.
Jeong, H.; Axtell, J. C.; Tor6k, B.; Schrock, R. R.; Muller, P. "Syntheses of
Tungsten tert-Butylimido and Adamantylimido Alkylidene Complexes Employing
Pyridinium Chloride As the Acid" Organometallics2012, 31, 6522.
Forrest, W. F.; Axtell, J. C.; Schrock, R. R. "Tungsten Oxo Alkylidene Complexes as
Initiators for the Stereoregular Polymerization of 2,3-Dicarbomethoxynorbornadiene"
Organometallics2014, 33, 2313.
Forrest, W. F.; Weis, J. G.; John, J. M.; Axtell, J. C.; Simpson, J. H.; Swager, T. M.;
Schrock, R. R. "Stereospecific Ring-Opening Metathesis Polymerization of
Norbornadienes Employing Tungsten Oxo Alkylidene Initiators" J. Am. Chem. Soc.
2014, 136, 10910.
Axtell, J. C.; Schrock, R. R.; Muller, P.; Smith, S. J.; Hoveyda, A. H. "Synthesis of
Tungsten Imido Alkylidene Complexes that Contain an Electron-Withdrawing Imido
Ligand" Organometallics2014, 33, 5342.
Axtell, J. C.; Schrock, R. R.; Muller, P.; Hoveyda, A. H. "Synthesis of Molybdenum and
Tungsten Alkylidene Complexes That Contain the 2,6-Bis(2,4,6triisopropylphenyl)phenylimido (NHIPT) Ligand" Organometallics2015, doi:
10.1021/om501213x.
Autenreith, B.; Jeong, H.; Forrest, W. F.; Axtell, J. C.; Ota, A.; Lehr, T.; Buchmeiser, M.
R.; Schrock, R. R. "Stereospecific Ring-Opening Metathesis Polymerization (ROMP)
ofendo-Dicyclopentadiene by Molybdenum and Tungsten Catalysts" Macromolecules
2015, doi: 10.1021 /acs.macromol.5b00 123.
Poster: Axtell, J.C.; Schrock, R. R.; Muller, P. 1St Annual Oliver G. Ludwig Alumni
Symposium, Villanova University, Villanova, PA, March 14,2014. "New Catalysts for
Tungsten-Based Olefin Metathesis"
Poster: Axtell, J.C.; Schrock, R. R.; Muller, P. Organometallic Chemistry, Gordon
Research Seminar, Newport, RI, July 4-5, 2014. "Syntheses of New Catalysts for
Tungsten-Based Olefin Metathesis"
144
Poster: Axtell, J.C.; Schrock, R. R.; Muller, P. Organometallics Chemistry, Gordon
Research Conference, Newport, RI, July 6-11, 2014. "Syntheses of New Catalysts for
Tungsten-Based Olefin Metathesis"
Oral: Axtell, J.C.; Schrock, R. R.; Mfller, P. Professional Development Seminar,
Villanova University Villanova, PA, February 24,2015. "Electron-Withdrawing Imido
Ligands in Olefin Metathesis"
145
ACKNOWLEDGEMENTS
This degree would not have been possible without the support of many around
me. I must first thank Prof. Schrock, who twice - first in college and second in graduate
school - has given me the opportunity to research under his direction. He has given me
generous latitude to explore our chemistry and has shown what might be considered
undue patience with the unforeseeable setbacks in most of my projects. I would to thank
the rest of the inorganic faculty (Lippard, Cummins, Dinca, and Surendranath) as well as
Prof. Dan Nocera, my original thesis chair and whose advice led to my appreciation of
the strength of W=O bonds and helped steer my experiments toward alternate strategies
for imido installation. A thank you goes to the Department staff, in particular Dr. Jeff
Simpson, for keeping the DCIF operational, and Dr. Peter Muller for dealing with my alltoo-frequent visits to look at preliminary structures. My mentors from Villanova are also
to thank, especially Prof. W. Scott Kassel and my undergraduate research advisors Prof.
Deanna Zubris (Nova) and Prof. Kevin Minbiole (JMU/Nova). I would also like to
acknowledge Mrs. Linda Garbade, who somehow made learning about electron
configurations in 7 th grade interesting enough to spark my interest in chemistry from then
onward.
I am indebted to many old graduate student and post-docs for being support
systems, sounding boards, gym partners, teammates, etc. To Prof. Smaranda Marinescu,
who was my mentor in this group in 2009 and to Dr. Brian Hanna, with whom I shared a
glovebox and an office during 2009 and up until he left in 2010, thank you for your
patience when I was a rookie and for your mentorship during that time. Dr. Jian Yuan
and Prof. Dmitry Peryshkov, with whom I also shared 6-427 for many great chemical
conversations. To all former grad students and post-docs with whom I overlapped for
helpful advice and being great lab mates over the years. To members of the current
group and in particular, a thank you to Hyangsoo Jeong, the other of the final two from
our lab, who has been a wonderful labmate and served as my thesis reader.
A special thank you to Prof. Graham Dobereiner, Prof. Matt Cain, and Dr.
William Forrest who have constantly been voices of reason and insight and helped bear
me through my darkest days of graduate school. Thanks Matt for Sundays, Mondays,
Tuesdays (etc) at the Muddy and Will and Kerry for the hospitality and an interesting
adventure from Franklin to Danbury to Freehold.
I have been very fortunate to have overlapped with a great many people outside
our lab, and for every 30 minute chat in the hall or 30 second chat in the elevator, I am
thankful. A special thank you goes to particular Prof. Alex Spokoyny, Prof. Nate Jui, Dr.
Aaron Sather, Katya Vinogradova, Carl Brozek, Miller Li, and Jon Weis.
My friends have put up with a lot from me over these years and I am greatly
indebted in particular to Ryan Mancino, Eric Madden, Brendan Ricciardelli, Chris
Harrington, Pete Siemenski, Dr. Vince Calleo, and Nick Rotella for keeping me from
flying off the handle and bearing with me when I did.
Family has always been there for me, and to all the Axtells and Zemanicks I am
grateful for support. In particular, the Berg family for constant support and always
offering a place of refuge during my trips home. To my brothers, Chris and Mike, in
their own ways having my back through this process, and to my mom, Catherine, whose
compassion, support, and understanding knows no bounds. I cannot thank you enough.
146
This thesis is dedicated to the memory of Clayton M. Axtell, III, who through
both example and instruction instilled in me a profound appreciation of hard work for
hard works sake, a curiosity of all things, and the importance of fundamentals and
thoroughness. Thanks Chief.
147