New nickel(II) diimine complexes bearing phenyl and sec‐phenethyl groups: synthesis, characterization and ethylene polymerization behaviour

Abstract

A series of nickel(II) catalysts containing phenyl and chiral sec‐phenethyl groups, {[(4‐R1‐2‐R2C6H2NC)2Nap]NiBr2} (Nap: 1,8‐naphthdiyl, R1 = Me, R2 = Ph (3a); R1 = Me, R2 = sec‐phenethyl (3b); R1 = Cl, R2 = sec‐phenethyl (3c); R1 = Me, R2 = Me (3d) were synthesized and characterized. All organic compounds were fully characterized by FT‐IR and NMR spectroscopy and elemental analysis. The single crystal for X‐ray crystallography was isolated from 3a in CH2Cl2/n‐hexane under air; the crystal structure showed a binuclear complex 3a′, in which each nickel atom was six‐coordinate. The two nickel atoms together with two bromine atoms form a planar four‐membered ring, with a bromine and H2O axial ligands. These complexes, activated by diethylaluminum chloride and chiral nickel pre‐catalysts rac‐3c, exhibited good activities (up to 2.85 × 106 g PE (mol Ni h bar)−1) for ethylene polymerization, and produced polyethylene products with a high degree of branching (up to 117 branched per 1000 carbons) at high temperature. The type and amount of branches of the polyethylenes obtained were determined by 1H and 13C NMR spectroscopy. Copyright © 2014 John Wiley & Sons, Ltd.