Reactivity comparison of epoxidation of unfunctionalized olefins with different oxidants catalyzed by mesoporous silica supported unsymmetric chiral Mn(III) salen complexes in heterogeneous condition

• Unsymmetric chiral Mn(III) salen complexes were immobilized on mesoporous silica.
• Great difference in reactivity was observed with different oxidants.
• UV–vis spectra and reaction kinetics were employed to analyze the difference.

Unsymmetric Mn(III) salen complexes were synthesized through a facile method and grafted on several mesoporous silica (MCM-41, MCM-48 and SBA-15). The spectra of FT-IR and DR UV–vis indicated that the Mn(III) salen complexes were immobilized successfully and the characterization of XRD and N2 sorption proved that the mesoporous structures of supports were kept well after grafting of Mn(III) salen complexes. These heterogeneous catalysts were evaluated by the asymmetric epoxidation of unfunctionalized olefins. Comparable activity and enantioselectivity to the homogeneous catalysts were obtained. Two kinds of oxidants were employed and great difference was observed in the catalytic performance of heterogeneous epoxidation of olefins, although in homogeneous conditions m-CPBA and NaClO almost obtained the same reactivity in this reaction. The heterogenization of Mn(III) salen complexes gave different influence for two oxidation systems. Compared with m-CPBA (m-chloroperbenzoic acid), the reaction oxidated by NaClO exhibited higher conversions in heterogeneous conditions, and the reason was discussed with the aid of UV–vis spectra and reaction kinetics.

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