Design and synthesis of binuclear Co-salen catalysts for the hydrolytic kinetic resolution of epoxides

Three binuclear Co(III)-salen complexes have been synthesized based on a series of hydrophilic cyclic frameworks with different ring sizes. The catalytic performance of Co-salen complexes have further been evaluated in the hydrolytic kinetic resolution of racemic epoxides. And kinetic studies reveal that the binuclear Co-salen catalysts show a higher reactivity and better enantioselectivity in comparison to monometallic reference complex, indicating the two Co-salen units on the cyclic framework may work in a cooperative manner. Specifically, Co3, with the most flexible cyclic framework exhibits the best catalytic performance among the three catalysts, due to the efficient cooperative interactions between two cobalt centers.