A zwitterionic nickel-olefin initiator for the preparation of high molecular weight polyethylene

The reaction of the sodium 3-(2,6-diisopropylphenylimino)-but-1-en-2-olato with Ni(PMe₃)₂(η¹-CH₂C₆H₅)Cl provides 3-(2,6-diisopropylphenylimino)-but-1-en-2-olato(η¹-benzyl)(trimethylphosphine) nickel (1), which was structurally characterized. The addition of 2 equiv. of B(C₆F₅)₃ to 1 results in the formation of 2-tris(pentafluorophenyl)borate-3-(2,6-diisopropylphenylimino)-but-1-ene(η³-benzyl)nickel (2), in which the borane coordinates to the O site of the ligand and forces binding of the olefin unit to the nickel center. The solid-state structure of 2 shows a zwitterionic structure with substantial positive charge at the nickel center. Compound 2 can be used to initiate the homopolymerization of ethylene to yield high molecular weight polyethylene.