Ni(II) Phenoxyiminato Olefin Polymerization Catalysis: Striking Coordinative Modulation of Hyperbranched Polymer Microstructure and Stability by a Proximate Sulfonyl Group

Abstract

The synthesis, structural characterization, and ethylene polymerization properties of two neutrally charged Ni(II) phenoxyiminato catalysts are compared and contrasted. Complex FI-SO2-Ni features a −SO2– group embedded in the ligand skeleton, whereas control FI-CH2-Ni has the −SO2– replaced by a −CH2– functionality. In comparison with FI-CH2-Ni, at 25 °C, FI-SO2-Ni is 18 times more active, produces polyethylene with 3.2 times greater MW and 1.5 times branch content, and is significantly more thermally stable. The FI-SO2-Ni-derived polymer is a hyperbranched polyethylene (148 branches 1000 C–1, MW = 3500g mol–1) versus that from FI-CH2-Ni (98 branches 1000 C–1, MW = 1100g mol–1). DFT calculations argue that the distinctive FI-SO2-Ni catalytic behavior versus that of FI-CH2-Ni is associated with nonnegligible OSO···Ni interactions involving the activated catalyst.