A N-bridged strategy enables hemilabile phosphine–carbonyl palladium and nickel catalysts to mediate ethylene polymerization and copolymerization with polar vinyl monomers

Abstract

Hemilabile phosphine–carbonyl (P^O) Pd(II) and Ni(II) catalysts usually feature ethylene oligomerization due to the weakly coordinated nature of the carbonyl CO group. In this contribution, with the aim of designing a new structural P^O catalyst for the improvement on olefin (co)polymerization, we developed a N-bridged strategy to overcome this issue. Therefore, a novel family of N-bridged phosphine–carbonyl Pd(II) catalysts Pd1–Pd6 and Ni(II) catalysts Ni1–Ni6 bearing various electronic nature and steric bulk were prepared and studied for ethylene polymerization. Compared with the previously reported C-bridged phosphine-ketone Pd(II) and Ni(II) catalysts as references, these N-bridged phosphine-amide catalysts showed obviously enhanced molecular weights, which reach a 200 times higher value of 83.2 kg mol⁻¹ that is comparable to those using pioneering bisphosphine-monoxide P^O catalysts. More significantly, not only preferred cationic Pd(II) catalysts but also the more challenging Ni(II) catalysts enabled ethylene copolymerizations with challenging polar vinyl monomers such as methyl acrylate, acrylic acid, and n-butyl vinyl ether with good catalytic activities, molecular weights (14.1 kg mol⁻¹), and comonomer incorporation (3.3 mol%). This work adds a new and effective member to the electronically asymmetric P^O-type late transition metal catalyst family applied in olefin (co)polymerization.