Olefin Epoxidation Reaction Promoted by Internal Oxygen Transfer: Research on Oxygen Transfer Mechanism Based on Mn(Salen)-POM System

Epoxidation reactions with hydrogen peroxide serving as the oxidant have a crucial position in the realm of organic chemistry. Here in, the five inorganic-organic hybrid compounds ([Mn(Salen-X)]4[SiW12O40], namely 1 X=H, 2 X=Me, 3 X=tBu, 4 X=Cl, 5 X=Br) were employed as catalysts in the epoxidation of cyclohexene, with hydrogen peroxide serving as the oxidant. Cyclohexene exhibited a conversion of 72.0% and a selectivity of 99.3% toward cyclohexene oxide under mild conditions (20 °C) and in a short reaction time (60 min). The results of UV-vis spectroscopy and electrochemical analyses indicated that the Mn(Salen) moiety acts as the catalytic centre, and the [SiW12O40]4−(SiW12) polyanion promotes electron transfer, thereby guaranteeing the stable catalytic activity of the Mn(Salen) moiety. Thorough characterization studies elucidated the mechanism responsible for the catalytic activity of Mn(Salen) and polyoxometalate-based inorganic-organic hybrid materials. This study provides important theoretical foundations and practical experience for the development of more efficient Mn(Salen)-POM-based catalysts for the green epoxidation of cyclohexene, and offers theoretical basis for the development of efficient and environmentally-friendly olefin epoxidation processes..