Dinuclear Nickel Complexes Using Hexadentate Benzothiazole-Based Diamine-Bisphenolate Ligands: Highly Active Catalysts for Copolymerization of Carbon Dioxide with Epoxides

We reported for the first time the utilization of hexadentate benzothiazole-based diamine-bisphenolate ligands to synthesize structurally well-characterized dinickel dicarboxylate complexes and studied their catalysis for copolymerization of carbon dioxide with epoxides. Dinickel carboxylate complexes having a 1,3-diamine-bridged backbone were demonstrated to be high-performance catalysts for alternating copolymerization of CO2 and cyclohexene oxide (CHO) with high product selectivity. Particularly, acetate-supported nickel complex 2 enabled us to promote such CO2-copolymerization of this kind with a maximum turnover frequency of up to 2600 h-1 and gave good molecular weight controllability under high-pressure conditions. It is worth noting that bimetallic Ni catalyst 2 was also capable of mediating the catalytic CO2-polymerization of alicyclic epoxides at atmospheric pressure. Kinetic investigations of CO2/CHO copolymerization by 2 allowed us to determine the rate equation of-d[CHO]/dt = kp[2]1[CHO]1, and such catalysis exhibited a first-order dependence on both dinickel complex and CHO concentrations.