Mesoporous material AlPS-BrPPAS derivatives supported chiral Mn(III) salen complex and highly efficient epoxidation of olefins as a recoverable catalyst

Abstract

A novel layered crystalline of organic–inorganic hybrid material aluminium 3-bromopropylphosphonate-phosphate (AlPS-BrPPAS) was synthesized and used as catalyst supports for immobilization of chiral salen Mn(III) with different types of diamine linkers. The heterogeneous salen Mn(III) catalysts were characterized by FT-IR, XRD, TG, SEM, and N2 sorption, and the results indicated the successful immobilization of the chiral Mn(III) salen complex. It was found that the structure of the catalysts was closely correlated with the linkers. The confinement effect of linkers on the catalytic performance of the heterogeneous catalysts was studied for the asymmetric epoxidation of unfunctionalized olefins with sodium hypochlorite as an oxidant. Moreover, the heterogeneous chiral salen Mn(III) catalysts can be recovered and reused up to nine times with retention of conversion and enantioselectivity. Interestingly, two heterogeneous chiral salen Mn(III) catalysts with different linkers also significantly alter the configuration of epoxide products for 6-cyano-2,2-dimethylchromene and 6-nitro-2,2-dimethyl-chromene.