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

Abstract

New neutral nickel(II) complexes bearing asymmetric β-ketoiminato (N,O) ligands ( 5a − c ), [(2,6- i Pr 2 C 6 H 3 )NC(R 2 )C(H)C(R 1 )O]Ni(Ph)(PPh 3 ), 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.