Comparison of liquid-phase olefin epoxidation catalysed by dichlorobis-(dimethylformamide)dioxomolybdenum(VI) in homogeneous phase and grafted onto MCM-41

Abstract A mesoporous silica-supported molybdenum oxide catalyst with a loading of 0.17 Mo/nm 2 was prepared by liquid phase deposition of MoO 2 Cl 2 (dmf) 2 ( 1 ) onto MCM-41 (dmf = dimethylformamide). Powder X-ray diffraction and N 2 adsorption studies of Mo-MCM-41 indicate that the texture properties of the support were preserved during the grafting experiment. On the basis of evidence from FTIR spectroscopy, 13 C and 29 Si MAS NMR, and Mo K-edge EXAFS, the Mo atoms in this catalyst are mainly present as isolated {MoO 2 [(–O) 3 SiO] 2 (dmf) 2 } species, with a small contribution from oxo-bridged dimers. Catalysis tests show that complex 1 and Mo-MCM-41 are highly active oxidation catalysts for liquid-phase epoxidation of unfunctionalised olefins using tert -butylhydroperoxide as oxidant, from ambient to 55 °C. The high stability and recyclability of the heterogeneous Mo-MCM-41 catalyst is attributed to the strong metal oxide–support interaction. With cyclooctene, 1-octene, trans -2-octene and norbornene substrates, the corresponding epoxides were the only observed reaction products. The reactions of the other substrates gave by-products such as 8,9- p -menthen-1,2-diol from ( R )-(+)-limonene, campholenic aldehyde from α-pinene, and benzaldehyde from styrene. The addition of dichloromethane as a co-solvent had a beneficial effect on catalytic performance, and in the case of ( R )-(+)-limonene allowed the epoxide to be formed as the only reaction product.