Novel bis-Salen Mn(III) chiral complexes of rigid structure axially coordinated with bis-diphenolate and bis-diamine for epoxidation of unfunctionalized olefins

A series of bis-Salen Mn(III) chiral complexes of rigid structure axially coordinated with bis-diphenolate and bis-diamine ligands were synthesized and their catalytic performances in asymmetric epoxidation of indene and α-methylstyrene were investigated in detail. Compared with Jacobsen’s catalyst and the corresponding monomer salen Mn(III) catalyst, bis-Salen Mn complex showed higher activity and enantioselectivity under the same reaction conditions. A point worth emphasizing was that the bis-diphenolate axially coordinated bis-Salen Mn catalysts afforded remarkable increases of ee values in the absence of axial base NMO for the asymmetric epoxidation of olefins, especially for the epoxidation of indene (ee: from 55% to 100%), however, the axial base is indispensable for the bis-diamine axially coordinated bis-Salen Mn(III) catalysts, these performance might attribute to the rigid difference of the structure. Furthermore, the catalyst could be conveniently recovered and reused at least five times without significant losses of both activity and enantioselectivity. Specially, it could also be efficiently used in large-scale reactions with superior catalytic disposition being maintained at the same level, which possessed the potentiality for application in industry.