Cobalt(II) imino pyridine assisted ethylene polymerization: A quantum-mechanical/molecular-mechanical density functional theory investigation

We investigate the new family of late-transition-metal bis(imino)pyridine ( BIMP) catalysts discovered by Brookhart's (J. Am. Chem. Soc. 1998, 120, 404 9) and Gibson's (Chem. Commun. 1998, 849) groups by means of theoretical mo del calculations. Reaction pathways and energetics for chain propagation an d chain termination reactions are located. Quantum-mechanical/molecular-mec hanical coupling is used to expose the differences between the original [2, 6-bis(1-((2,6-isopropylphenyl)imino)ethyl)pyridine]cobalt(II) catalyst and its "generic" pendant, [2,6-bis(iminomethyl)pyridine]cobalt(II). We show th at the activity of the [2,6-bis(1-((2,6-diisopropylphenyl)imino)ethyl)pyrid ine]cobalt(II) catalyst is inhibited by steric crowding that imposes barrie rs on olefin capture and internal rearrangements, while at the same time in creasing its activity by lowering the insertion barrier and increasing the chain termination barriers.