New molybdenum(VI) catalysts for the epoxidation of cyclohexene: synthesis, reactivity and crystal structures

Compounds 1–6 of the type MoO2X2L2 (X=F, Cl, Br; L=OPMePh2, OPPh3) have been prepared in order to investigate the variation in catalytic activity with changes in electronic and steric properties. All six complexes catalyze the epoxidation of cyclohexene with tert-butylhydroperoxide, and the species with X=Cl and L=OPMePh2 (2) displays the best activity with 83% conversion and 90% selectivity in one hour at ambient atmosphere. These inexpensive and easily prepared dioxo catalysts are stable to air and water. Reactions of the dioxo compounds with H2O2 and t-BuOOH have also been carried out. The structures of MoO2F2(OPMePh2)2 (1) and the product of its reaction with H2O2, MoO(O2)2(OPMePh2)2 (7) have been solved by single crystal X-ray diffraction.