P. Margl et al., Cobalt(II) imino pyridine assisted ethylene polymerization: A quantum-mechanical/molecular-mechanical density functional theory investigation, ORGANOMETAL, 18(26), 1999, pp. 5701-5708
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.