Zirconium phosphonates-supported chiral Mn (III) Salen complexes for the asymmetric epoxidation of unfunctionalized olefins

Abstract

Abstract The mesoporous zirconium phosphonates-supported Mn (III) Salen complexes ( 1a–e ) with the different lengths of alkylsulfonic linkage ( n = 2–6) and the loading amount of 0.041–0.059 mmol g −1 (based on Mn) were prepared and used as heterogeneous catalysts in the asymmetric epoxidation of styrene, α-methylstyrene and indene. The ee values significantly increased with the linkage length ( n ) from 2 to 6 only in the case of indene with the m- CPBA/NMO as an oxidant system, in all other shown cases the ee values are not significantly influenced by the linkage length ( n ). In m -CPBA/NMO system, the comparable ee values to the homogeneous Mn (III) Salen complex 1 were achieved. Due to the confined effect originating from the nanopores of zirconium phosphonates, the heterogeneous Mn (III) Salen complexes ( 1a–e ) gave twice (84–88%ee) as many as ee values of homogeneous Mn (III) Salen complex 1 (49%ee) in the NaClO/PPNO system.