Synthesis of a new type of immobilized chiral salen Mn(III) complex as effective catalysts for asymmetric epoxidation of unfunctionalized olefins

Abstract

A new type of inorganic–organic hybrid materials—zirconium poly(styrene-phenylvinylphosphonate)-phosphate (ZPS-PVPA) was designed and synthesized. A series of new heterogeneous catalysts was obtained by grafting diamine or polyamine on ZPS-PVPA and subsequently axial coordination with chiral salen Mn(III) complexes. All the synthesized heterogeneous catalysts exhibited great activity and enantioselectivity in the asymmetric epoxidation of unfunctionalized olefins. Especially, in the epoxidation of α-methylstyrene, both the conversion and enantiometric excess (ee) could exceed 99%. Furthermore, the catalysts were conveniently separated from the reaction system by simple precipitation in hexane and could be reused at least ten times without significant loss of activity and enantioselectivity.