The tricarbonyl complex CpMo(CO)(3)C1 was found to act as a precatalyst for the reaction of tert-butyl hydroperoxide and olefins to yield the corresponding epoxides and diols. Under the reaction conditions, oxidative decarbonylation leads to the formation of the dioxo complex CpMoO2Cl. The catalytic recyclability and the effect of temperature on the catalytic results have been examined, and a reaction mechanism proposed, supported by kinetic modelling.