Transcript JonesSpr11
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.