Olefin epoxidation reaction promoted by internal oxygen transfer: research on the oxygen transfer mechanism based on the Mn(Salen)-POM system

Abstract

Epoxidation reactions with hydrogen peroxide serving as the oxidant play a crucial role in the realm of organic chemistry. Herein, five inorganic–organic hybrid compounds ([Mn(Salen-X)]₄[SiW₁₂O₄₀], namely 1 X = H, 2 X = Me, 3 X = tBu, 4 X = Cl, and 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.