A surface-confined OMnV(salen) oxene catalyst and high turnover values in asymmetric epoxidation of unfunctionalized olefins

Abstract

Given the widespread importance of chiral epoxides in chemical, biochemical and agricultural fields, an efficient synthesis that avoids wasteful use of the catalyst and assures its total recovery and reuse and high turnover values is highly desirable. We report on a thermally and temporally robust covalent monolayer of (salen)Mn(III) molecules on silica functionalized substrates that resulted in an active heterogeneous catalyst for enantioselective epoxidation of 6-ciano-2,2-dimethyl-chromene, chosen as a model alkene, in high yields and high turnover numbers. No catalyst leaching was observed thus allowing continuous recycling. Experimental XPS evidence for the formation of the surface confined OMn^V(salen) oxene species has been obtained.