Immobilized chiral Mn(III) salen complexes on co-condensed imidazole-functionalized mesoporous materials: Effective catalysts for asymmetric epoxidation of olefins

• Functionalized imidazolate mesoporous supports were prepared by co-condensation.
• Immobilized chiral Mn(III) salen catalysts showed excellent catalytic performance.
• Notably high TOF values (up to 165 h−1) were obtained for olefin epoxidation.
• Co-condensed supports were better than the post-functionalized materials.
• Bigger support pore sizes gave better catalytic performance.

The heterogeneous chiral Mn(III) salen catalysts with ordered hexagonal mesostructure were prepared based on mesoporous materials functionalized by imidazole groups through a co-condensation procedure. These catalysts were highly active and enantioselective for the asymmetric epoxidation of olefins. Within a short reaction time, comparable conversion and enantiomeric excess to those of the homogeneous counterpart were obtained even with a very low catalyst dosage (0.60 mol%). Thus notably high turnover frequencies (up to 165 h−1) were provided by these catalysts, attributed in part to the homogeneous distribution of the active centers as well as the strong electron-donating ability of imidazole groups. Comparison experiments showed that these catalysts were twice more active than the catalysts supported on the mesoporous material graft-modified with imidazole. Furthermore, the nanopore size of mesoporous hybrid supports was found to have a considerable effect on the catalytic performance.

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