Synthesis, Structures and Ethylene Oligomerization Reactivity of Transition
Metal Complexes Supported by Multidentate Amidine-Based Ligands
†
T. C. Jones, S. A. Bender, M. J. Carney, J. A. Halfen, B. L. Small , and O. L. Sydora
†
†
Department of Chemistry, University of Wisconsin-Eau Claire, Eau Claire, Wisconsin 54702 and Chevron Phillips
Chemical Company, 1862 Kingwood Drive, Kingwood, TX 77339
Goals and Objectives
Multidentate Amidine-Based Ligands and Chromium Complexes: Synthesis and Structures
Synthesize new families of multidentate ligands and exploit their ability
to coordinate transition metals
Develop new transition metal catalysts for olefin polymerization,
including the oligomerization of ethylene to high purity a-olefins
Develop new tridentate ligands to serve as analogues of Sasol-type
catalysts
Examine the impact of ligand structure (type, number and position of
substituents) on catalyst performance
Chromium Complexes
Substituent Variation
Catalyst performance attributes include the following: catalyst productivity,
purity of a-olefins and overall a-olefin selectivity
Background Information
Tridentate ligands figure prominently in recent chromium catalyzed
olefin polymerization studies.
Cr-P
2.394 Å
Cr-N(2) 2.011 Å
Cr-O
2.077 Å
Chromium pyridinebis(imine) complexes display high activities for ethylene
oligomerization or polymerization, with polymer products being highly
dependent on the ligand substituents.
N(1)
S
N(2)
N(1)
Cl
P
Cl
R'
N
N
R'
N
Cr
Cl
MMAO
Cl
H
H
Me
C 2H 4
R ''
R''
H
Me
Me
R'''
t
Bu
H
H
P
Product properties
Cr
N(3)
N(2)
Cr
1-butene, 99 % purity
distribution of a-olefins
polyethylene
Cl
Cl
O
Cr-P
2.424 Å
Cr-N(2) 2.024 Å
Cr-N(3) 2.237 Å
Cl
Cl
O
R '''
Small, Carney, et. al., Macromolecules 2004, 37, 4375-4386
Sasol has demonstrated that chromium complexes supported by tridentate
PNP and SNS ligands display high activities for ethylene oligomerization,
including the uncanny ability to selectively produce 1-hexene and 1-octene
(the highest value a-olefins).
H
N
N(2)
Cl
Cr
Cl
PR2
or
RS
Cr
Cl
Cl
Cl
PNP
SNS
SR
1 -h e x e n e a n d /o r 1 -o cte n e
C 2H 4
N(3)
Cl
McGuinness, et. al., J. Am. Chem. Soc. 2003, 125, 5272
Cl
N(2)
P
Transition metal complexes were isolated as greenish-blue to royal
blue solids. Slow recrystallization provided samples suitable for x-ray
analysis.
Polymerizations (MMAO co-catalyst) were performed in a 500 mL
autoclave in using the reactor conditions indicated in the table.
Oligomeric products were analyzed by GC using the polymerization
solvent as an internal standard.
X-Ray crystallography and NMR spectroscopy of ligands and metal
complexes confirm successful synthesis.
Cl
Cl
Cr-P
2.438 Å
Cr-N(2) 2.010 Å
Cr-N(3) 2.143 Å
Cl
Cr-P
2.423 Å
Cr-N(2) 2.129 Å
Cr-N(3) 2.068 Å
R
R
R
T ( C)
Activity
(g/g cat-hr)
CH2CH2NC4H8O
Ph
Ph
60
0
C6 fraction
% a-olefin
nd
CH2CH2PPh2
Ph
Ph
60
0
nd
CH2CH2NMe2
Ph
Ph
60
0
nd
CH2CH2NMe2
Ph
Ph
90
1000
92.9
C6H4-o-SPh
Ph
Ph
Ph
90
10400
98.0
p-MeC6H4
Ph
60
4100
28.2
2,6-Me2C6H4
p-MeC6H4
Ph
60
75100
96.2
2,6-Me2C6H4
p-MeC6H4
i
Pr
60
108000
99.3
2,6-Me2C6H4
p-MeC6H4
i
Pr
90
301200
99.4
2,6-Me2C6H4
p-t BuC6H4
i
60
481000
99.5
1
2
3
Pr
o
Surprisingly, chromium complexes supported by tridentate ligands
(Sasol analogues) are not active polymerization catalysts.
However, chromium complexes supported by bidentate N-phosphino
amidine ligands yield catalysts with high activity and product purity.
Selected Polymerization Data
Experimental Details
N-phosphino amidine ligands were isolated as solids or viscous oils
and characterized by 1H and 13C NMR spectroscopy.
P
N(3)
McGuinness, et. al., J. Am. Chem. Soc. 2004, 126, 14712
Amidine ligand precursors were purified by crystallization or vacuum
distillation and characterized by 1H and 13C NMR spectroscopy.
Ligand synthetic methods are modular and versatile, allowing for a
large array of substituent combinations.
Cr
Cr
MMAO
Cl
N(1)
N(1)
H
N
Cl
R 2P
Conclusions and Future Work
Polymerizations w ere performed for 30 minutes at 900 psi (850 psi ethylene, 50 psi hydrogen) in
cyclohexane using MMAO as cocatalyst (Al:Cr = 1000)
Continuing Work:
Examine other ligand substituents and their effect on catalyst performance
Prepare other transition metal (V, Fe, Ni, Pd, etc.) complexes using Nphosphino amidine ligands and examine their catalytic performance
Conduct theoretical studies (DFT computations/molecular modeling) to help
predict the impact of ligand modifications on metal complex geometry and
catalytic behavior
Acknowledgements
The authors thank the UW-Eau Claire Office of Research and
Sponsored Programs (ORSP) and Chevron Phillips Chemical
Company for their generous financial support of this work.