Alternating copolymerization of carbon dioxide with alicyclic epoxides using bimetallic nickel(II) complex catalysts containing benzotriazole-based salen-type derivatives: Catalysis and kinetics

A series of dinuclear nickel complexes based on hexadentate bis(benzotriazole iminophenolate) derivatives with the 1,4-butylene diimine bridging backbone have been synthesized and characterized by single crystal x-ray crystallography. Dinickel complex 1 was demonstrated to be an efficient catalyst for alternating copolymeriza-tion of carbon dioxide (CO2) with cyclohexene oxide (CHO) or 4-vinyl-1,2-cyclohexene oxide (VCHO), affording CO2-based polycarbonates with >99% carbonate linkages under the optimized conditions. Particularly, not only the effective catalytic property of binickel complex 1 for CO2-copolymerization of alicyclic epoxides is enabled, but also 1 has been demonstrated to reveal an "immortal" manner in the CO2/VCHO copolymerization. Using the dinickel catalyst 1 in combination with excess diol derivatives as the chain transfer agents could produce very narrowly distributed poly(vinylcyclohexene carbonate) polyols having molecular weights ranging from 5000 to 12000 g/mol. In addition, detailed kinetic studies of the CO2/CHO copolymerization by Ni catalyst 1 were investigated. The results showed that such copolymerization follows a first-order kinetics on both catalyst 1 and CHO concentrations.