Control of Chain Transfer by Tailored Metal–Phenyl π ‐Interactions in Bis(Imino)Pyridyl Cobalt‐Catalyzed Ethylene Polymerization

Abstract

ABSTRACT In bis(imino)pyridyl iron/cobalt‐catalyzed ethylene polymerization, broad and bimodal molecular weight distributions of polyethylenes (PEs) are often produced because of two different chain transfer pathways. In this paper, a combined theoretical and experimental study demonstrates how weak attractive metal–phenyl π ‐interactions can favor β ‐H transfer to ethylene over chain transfer to Al to achieve a unimodal distribution. A series of bis(imino)pyridyl cobalt complexes with a substituted 8‐( p ‐R‐phenyl)naphthylamine (R = OMe, Me, CF 3 ) were designed and synthesized for ethylene polymerization. The intramolecular Co–phenyl π ‐interactions between the capping aryl groups and the cobalt metal are clearly identified in “half‐sandwich” bis(imino)pyridyl cobalt complexes. Ethylene polymerization results show that bis(imino)pyridyl cobalt catalyst with an electron‐donating methoxy group can produce low‐molecular‐weight polyethylene with a unimodal distribution. This control of β ‐H transfer to ethylene monomer is promoted by weak Co–phenyl interactions, operative only for the case of sufficiently electron‐rich aryls (R = OMe) and low temperatures (−10°C–30°C).