Nanostructured Dioxomolybdenum(VI) Catalyst for the Liquid‐Phase Epoxidation of Olefins

Abstract

AbstractA new organosilica hybrid mesoporous material (HM) containing phosphane oxide surface groups was prepared via the “dual” organosilane templated co‐condensation of 4‐bis(triethoxysilyl)benzene and (diphenylphosphanyl)propyltriethoxysilane, followed by post‐synthesis oxidation of the phosphane surface groups. The HM material was used to immobilise the [Mo(O)2Cl2] complex. The resultant material (HM‐Mo) is an active and selective catalyst in the liquid‐phase epoxidation of olefins [cis‐cyclooctene, (R)‐(+)‐limonene, trans‐2‐octene, 1‐octene] with tBuOOH at 55 °C and gives comparable epoxide yields to those observed for the free complex [MoCl2(O)2{OP(CH2CH3)(Ph)2}2] (1), under similar reaction conditions: the crystal structure of complex 1 remains the same after reaction with tBuOOH. The oxidant is essentially consumed in the HM‐Mo or 1 catalysed epoxidation of the olefin. In the case of limonene (possesses endo‐ and exocyclic C=C bonds), the molar ratio of 1,2‐epoxy‐p‐menth‐8‐ene/1,2–8,9‐diepoxy‐p‐menthane at ca. 90 % conversion (reached after 24 h reaction) is ca. 5 and 10 for 1 and HM‐Mo, respectively, indicating a favourable regioselectivity towards the epoxidation of the endocyclic C1–C2 double bond, especially in the case of the heterogeneous catalyst.