Heterogenisation of Os species on MCM-41 structure for epoxidation of trans-stilbene Original Research Article

Metal organic chemical vapour deposition technique (MOCVD) has been used to immobilise Os species onto the internal porous structure of MCM-41. Evidence suggests that volatile Os3(CO)12 cluster reacts with surface silanol groups of the MCM-41 via an oxidative addition reaction to yield a trinuclear HOs3(CO)10(OSi) surface species. After heat treatment in air or at their very low surface coverage, these triangular sites break up to partially oxidised mononuclear surface species. In the presence of tert-butyl hydroperoxide (TBHP) as an oxidant, we demonstrate that the mononuclear species form extremely active species that catalyse the oxidation of trans-stilbene selectively to the corresponding epoxide. By carefully controlling the parameters of the MOCVD method (loading and calcination temperature), we report a new class of optimised MCM-41 porous heterogeneous catalysts carrying isolated but active Os sites for the selective oxidation of trans-stilbene in liquid phase. The reaction selectivity of the solid supported Os is apparently higher than the soluble homogeneous Os3(CO)12 cluster. It is envisaged that our solid supported catalysts not only facilitate separation from products but also offer an excellent utilisation of Os for catalysis.