Effects of backbone substituent and intra-ligand hydrogen bonding interaction on ethylene polymerizations with α-diimine nickel catalysts

Abstract

The design of transition metal catalysts and the development of new catalyst design strategies for olefin polymerization have received substantial attention in the field of polyolefin research. In this paper, we initially reported backbone substituent effects on ethylene polymerizations with α-diimine nickel catalysts and intra-ligand hydrogen bonding interactions operating ethylene polymerizations. A series of α-diimine nickel catalysts with electron-donating/withdrawing groups (OMe, H, Cl, Br, and I) on the dibenzobarrelene backbone were synthesized and employed in ethylene polymerization. Halogen substituents simultaneously showed steric and electronic effects on ethylene polymerization, and catalyst 5 with diiodo (I) substituent showed the highest activity and produced the highest molecular weight polyethylene. The intra-ligand hydrogen bonding interactions (CH···OMe) were initially observed in the methoxy-substituted dibenzobarrelene α-diimine nickel complex, and the weak noncovalent interactions enhanced the catalyst thermal stability and living fashion of ethylene polymerization at high temperatures up to 80 °C.