Migratory Insertion into a Hafnium–Phenyl Bond and a Ligand-Assisted Mechanism for Reversible Chain Transfer in the Living Coordinative Polymerization of Olefins

Abstract

Results of a combined experimental and computational investigation are presented that (1) document phenyl group exchange and migratory insertion (MI) within neutral and cationic CPAM hafnium complexes bearing a Hf–Ph bond that are relevant to the living coordinative (chain transfer) polymerization of olefins to produce phenyl-terminated polyolefins, (2) establish that ΔG⧧ (initiation) < ΔG⧧ (propagation) for initial and subsequent MIs of ethene into a Hf–Ph bond of an ion pair initiator for living coordinative polymerization, and (3) support an alternative stepwise, ligand-assisted mechanism for reversible chain transfer that resolves problematic issues with the often-invoked direct chain exchange process proceeding through a four-membered-ring bis(μ-bridging chain) intermediate.