Mechanism and Modeling of Brookhart-Type Polymerization Catalysts
Dean M. Philipp, Richard P. Muller, and William A. Goddard, III.
Materials and Process Simulation Center, California Institute of Technology
Mark McAdon, Michael Mullins, and Joey Storer
The Dow Chemical Company
We used first principles density functional theory (B3LYP/6-31G**) to investigate the energetics of the chain propagation steps in olefin polymerization by Brookhart-type homogeneous olefin polymerization catalysts. In particular we considered:
but with the mesityl ligands simplified. For the Fe and Co pyridine-bis(imine) cases, we also did full quantum mechanics (QM) calculations for catalysts including the bulky mesityl sidegroups. Full QM calculations on such large molecules are very costly and time-consuming, and thus the impending implementation of mixed quantum mechanics/molecular mechanics (QM/MM) methods to do such calculations will be briefly discussed.
We find that the mechanism generally proceeds as follows for pyridine-bis(imine) systems:
We have also investigated trends in the catalytic behavior of these systems as the metals, coordinating ligands, and monomer units (ethylene or propylene) are varied. Finally, we considered the regioselectivity and stereo-selectivity of the propylene catalytic pathways.
This research was funded by the Dow Chemical Company, NSF (95-22129), and by the MSC.