Dinuclear Nickel Complexes Containing Imidazole-Based Bis(iminophenolate) Derivatives: Highly Active Catalysts for Ring-Opening Copolymerization of Carbon Dioxide with Alicyclic Epoxides

We report the synthesis of a series of dinuclear nickel complexes based on triphenylimidazole-derived salen-type ligands bearing different substituents on the phenyl rings. These complexes were applied as single-component catalysts for the copolymerization of CO2 and alicyclic epoxides. All dinuclear Ni complexes exhibited high catalytic activity and excellent selectivity for the alternating copolymerization of CO2 and cyclohexene oxide (CHO). Among them, the methoxy-substituted bis(acetate) and dichloride complexes 2 and 6 showed the outstanding performance, achieving turnover frequencies (TOFs) exceeding 2000 h-1 and turnover numbers (TONs) over 9000. Notably, the dichloride complex 6 also enabled terpolymerization of different alicyclic epoxides, affording CO2-based polycarbonates bearing vinyl or acrylate functionalities. Kinetic analysis suggests that the copolymerization follows first-order dependence on both complex 6 and CHO concentrations.