Synthesis, Electronic Structure, and Ethylene Polymerization Activity of Bis(imino)pyridine Cobalt Alkyl Cations

摘要

The independent discovery of ethylene polymerization by MAO-activated (MAO = methylaluminoxane) aryl-substi-tuted bis(iraino)pyridine iron and cobalt dihalide complexes (~(Ar)TDI)MCl2 by Brookhart, Gibson, and their respective co-workers has attracted both academic and industrial attention and renewed interest in base-metal catalysis. Despite the numerous studies on catalyst optimization by ligand substituent modification, much remains to be learned about the active species formed upon treatment with MAO, and the propagating species responsible for monomer enchainment. The possibility of different oxidation and spin states of both iron and cobalt, coupled with the ability of the bis(imino)pyridine ligand to directly participate in the electronic structure and undergo chemical modification such as alkylation, presents challenges in understanding the mechanism of polymerization and the identity of the propagating species.