Copolymerization of Ethylene with Methyl Methacrylate with Neutral Nickel(II) Complexes Bearing β-Ketoiminato Chelate Ligands

New neutral nickel(II) complexes bearing asymmetric β-ketoiminato (N,O) ligands (5a−c), [(2,6-iPr2C6H3)NC(R2)C(H)C(R1)O]Ni(Ph)(PPh3), have been synthesized. X-ray crystal
structures reveal that each of complexes 5a−c adopts a near square-planar coordination
geometry and the triphenylphosphine group is always trans to the arylamine group. With
modified methylaluminoxane (MMAO) as a cocatalyst, complexes 5a−c can promote the
polymerization of methyl methacrylate (MMA) in excellent yields (>98%), producing
syndiotactic-rich PMMAs (rr around 70%). It is very exciting that the 5a−c/MMAO catalyst
systems exhibit highly catalytic activities for the copolymerization of ethylene with MMA,
producing high molecular weight functionalized polyethylenes with up to 16.7 mol % of
methacrylate units built into the moderately branched polyethylene backbone. Further
mechanistic studies have shown that PMMAs and copolymers obtained using these complexes
possibly arise from a coordination−insertion mechanism rather than a radical mechanism.