Bimetallic Nickel Complexes as Effective and Versatile Catalysts for Copolymerization of Epoxides with Carbon Dioxide or Phthalic Anhydride: Catalysis and Kinetics.

This study reported three novel structurally well-characterized dihalide dinuclear nickel complexes containing benzotriazole-based 1,3-diamine-linked bisphenolate ligands, which were high-performance catalysts for ring-opening copolymerization (ROCOP) of cyclohexene oxide (CHO) and carbon dioxide (CO 2 ). The dinickel diiodo 3 was shown to catalyze CO 2 copolymerization of CHO with high activity (turnover frequency up to 2250 h -1 ), excellent selectivity (>99% polycarbonates, >99% carbonate repeated units), and good molecular weight controllability. Apart from CO 2 /CHO copolymerization, the most active complex 3 was found to effectively catalyze ROCOP of CHO with phthalic anhydride (PA). Not only has the controllable manner of 3 for PA/CHO copolymerization been proven but also a broad substrate scope for PA copolymerization of epoxides by the same complex has been achieved. Diverse terminal or internal epoxides were demonstrated to copolymerize PA by 3 , producing the corresponding semiaromatic polyesters with good activity and excellent product selectivity. Kinetic studies for CHO copolymerization of CO 2 or PA mediated by 3 were systematically investigated. For kinetics of PA/CHO copolymerization, it allowed us to propose the rate equation of -d[CHO]/d t = k p [ 3 ] 1 [PA] 0 [CHO] 1 , and such catalysis displayed a first-order dependence on both dinickel complex and CHO concentrations as well as a zero order for PA. This work offers a bimetallic dihalide nickel complex as an efficient and versatile catalyst for two different types of copolymerization catalysis.