Synthesis and application of α-diimine Ni(II) and Pd(II) complexes with bulky steric groups to polymerization of ethylene and methyl methacrylate

Abstract

A series of α-diimine Ni(II) and Pd(II) complexes containing bulky steric groups, {[(4-R-2,6-Ph2C6H2NC)2Nap]MX2} (Nap: 1,8-naphthdiyl, MX2=NiBr2, R=F (4a); R=Cl (4b); R=Me (4c); R=n-Bu (4d) and MX2=PdCl2, R=F (5a); R=Cl, (5b); R=Me (5c); R=n-Bu (5d)), {[4-F-2,6-Ph2C6H2NC(Me)]2PdCl2}(5e), were synthesized and characterized. The crystal structures of ligands 3d, 3e and complexes 4a, 4b, 5a, 5b, 5e were determined by X-ray crystallography. These complexes, when activated with diethylaluminum chloride (DEAC), were used to catalyze polymerization of ethylene and methyl methacrylate (MMA) under mild conditions. The introduction of an electron-withdrawing group to the ligand framework improves the catalytic activity significantly. The Ni(II) catalysts 4a–d exhibited high catalytic activity in the polymerization of ethylene (up to106g PE/(molNihbar)) and produced highly branched polyethylenes at high temperature. Interestingly, complex 4a could produce syndiotactic-rich PMMAs at low temperature (0°C, up to 77.2% of rr triads).