Kinetic Study and Nonlinear Phenomenon during the Copolymerization of CO2 with meso‐Epoxides Catalyzed by Various Bimetallic CoIII Complexes

Abstract

AbstractThe privileged salen ligands coordinated with a metal center have demonstrated their successful applications in many challenging reactions. Moreover, their relatively straightforward preparations and an ease of structural modifications are also very attractive. The CoIII–salen complex has demonstrated to be one of the most efficient catalysts for the copolymerization of CO2 with epoxides. Especially, the elaborate combination of two or more CoIII–salen units into one single molecule may enforce an intramolecular, cooperative reaction pathway, resulting in enhanced reaction rates or/and higher selectivities. Otherwise, the reactivity and/or selectivity will be reduced, or some side reactions may occur. Herein, various bimetallic CoIII complexes based on different linking groups are reported to bridge two salen planes, including flexible and rigid structures, together with their reactivities and selectivities toward copolymerization of CO2 with meso‐epoxides. The asymmetric depletion in copolymerization CO2 with cyclohexene oxide mediated by monometallic CoIII complex 2 is first observed, demonstrating the bimetallic mechanism; especially, the comparative kinetic measurements are performed as a function of reaction temperature to assess the activation barrier for production of copolymers for bi‐ and monometallic CoIII complexes. This study is expected to be instructive and meaningful to design more efficient bimetallic catalyst and to improve the copolymerization selectivity.