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

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.