Nitrogen Donor Ligand (<i>α</i>‐Diamine vs. <i>α</i>‐Diimine) Makes Big Differences in Palladium‐Catalyzed Ethylene (Co)Polymerization

The nitrogen donor atom is widely used in the design and synthesis of olefin polymerization catalysts, while the amine donor featured sp³ hybridized N is less applied in the ligand design than the imine donor featured sp² hybridized N. We have herein reported the synthesis and characterization of α-diamine palladium complexes with two sp³ hybridized N donors and their catalytic properties toward homopolymerization of ethylene and copolymerization of ethylene with methyl acrylate (MA). The X-ray crystallographic analyses identify that the α-diamine palladium complexes have a significantly distorted chelate ring (N─C─C─N─Pd), which is distinct from conventional α-diimine palladium complexes with a planar chelate ring. Ethylene polymerization results elucidate that bulky steric hindrance of the α-diamine palladium catalyst is required to achieve high activity and high molecular weight polymer. Comparisons of ethylene (co)polymerization results between the α-diamine palladium catalyst and the classic α-diimine palladium analogue disclose that the variation from imine donor to amine donor makes a decreasing change in catalytic activity and polymer molecular weight but an increase in the degree of linearity of polymeric product and MA incorporation in EMA copolymer.