Cooperatively Halide- and Benzhydryl-Modified Bis(imino)pyridylcobalt Complexes for Linear α-Olefin-Type Polyethylenes

Abstract

This work investigates the influence of electronic properties of cobalt catalysts on key polymerization steps, including monomer insertion rate, chain propagation, and chain termination, which in turn affect catalytic activity, polymer molecular weight, and chain-end structures. Herein, a series of electronically (─Cl and ─F substituents) and sterically (Ph₂CH) modified bis(imino)pyridylcobalt complexes, each appended with an N-2-benzhydryl-4-fluoro-6-chlorophenyl group, has been prepared and fully characterized. Upon activation with either MAO or MMAO, all cobalt complexes exhibited high activities in the range of 7.20 × 10⁶–11.78 × 10⁶ g mol⁻¹ h⁻¹ for ethylene polymerization and produced vinyl-terminated linear polyethylenes (CH₂═CH(CH₂)_nCH₃: 92%–100%) with molecular weights ranging from 12.9 to 118.0 kg mol⁻¹ and controlled dispersities (in most cases Ð < 2). The peak activity of 11.78 × 10⁶ g mol⁻¹ h⁻¹ at elevated temperature of 80°C, together with polymer molecular weight of 28.1 kg mol⁻¹ and moderately narrow dispersity (Ð = 1.75), places these complexes among the most effective cobalt precatalysts reported to date for ethylene polymerization. Additionally, chain termination occurs predominantly via β-H elimination, resulting in α-olefin-type polyethylenes (almost up to 100%). These polyethylenes with terminal vinyl functionality provide valuable opportunities for post-functionalization of otherwise inert polyethylene backbones.