Chiral salen Mn(iii) complexes immobilized onto crystalline aluminium oligo-styrenyl phosphonate-hydrogen phosphate (AlSPP) for heterogeneous asymmetric epoxidation

Abstract

A novel type of organic polymer–inorganic hybrid material layered crystalline aluminium oligo-styrenyl phosphonate-hydrogen phosphate (AlSPP) was designed and prepared in the absence of any template. The chiral salen Mn(III) complex immobilized onto alkoxy-modified AlSPP was synthesized and characterized by FT-IR, diffusion reflection UV-vis, AAS, N₂ volumetric adsorption, SEM, TEM, XRD, TG and AFM. The supported catalysts displayed superior catalytic activities in the asymmetric epoxidation of α-methylstyrene and indene with m-CPBA as an oxidant. Delightfully, the heterogeneous catalysts afforded a remarkable increase in conversion and ee values without the expensive O-coordinating axial bases for the asymmetric epoxidation of olefins. The catalysts can be easily recovered and reused with a slight decrease in activity and enantioselectivity after ten cycles. Furthermore, they could also be efficiently used in large-scale reactions with the enantioselectivity being maintained at the same level, which provided the potentiality for application in industry.