Catalysis and kinetics for alternating copolymerization of carbon dioxide with epoxides using dinuclear nickel catalysts of pyrazolyl based diamine-bisphenolate ligands

Abstract

The synthesis of structurally well-characterized dinuclear nickel complexes bearing a new type of pyrazolyl based diamine-bisphenolate ligand was reported for the first time. Catalysis towards nickel-catalyzed copolymerization of CO2 with cyclohexene oxide (CHO) by these newly prepared bimetallic complexes was systematically investigated. Particularly, dinickel complex 4 supporting 2-nitrophenoxide coligands was demonstrated to effectively catalyze CO2-copolymerization of CHO, 4-vinyl-1,2-cyclohexene oxide or cyclopentene oxide, generating the corresponding CO2-based polycarbonates with >99% carbonate linkages under optimal conditions. Kinetic studies of CO2/CHO copolymerization revealed that such copolymerization catalysis is first-order in dinickel complex 4 and second-order in CHO concentration.