Ethylene Polymerization Characteristics of an Electron-Deficient Nickel(II) Phenoxyiminato Catalyst Modulated by Non-Innocent Intramolecular Hydrogen Bonding

The synthesis and characterization of the neutrally charged electron-deficient nickel(II) phenoxyiminato catalyst {2-(hydroxydiphenylmethyl)-4-tert-butyl-[6-(2,6-diisopropylphenyl)]salicylaldiminato}methyl(trimethylphosphine)nickel(II) (1b) with an intramolecular hydrogen bond directed toward the active catalytic site is reported. At room temperature, catalyst 1b exhibits 2.5× greater ethylene polymerization activity and 2× greater polyethylene product branching than an analogous catalyst without the hydrogen bond (2b). Furthermore, catalyst 1b produces substantially greater polyethylene yields in the presence of polar additives such as ethyl ether, acetone, and water than does 2b under identical conditions. This enhanced polymerization activity in the presence of polar additives suggests that the hydrogen bonding proximate to the metal center significantly modifies the relative rates of competing enchainment and chain transfer processes.