Kinetics and mechanism of epoxidation of olefins by a novel ruthenium(IV)-oxo complex

[Ru-IV(tpy)(pic)(O)](+) (1) was synthesized by chemical oxidation of the corresponding aqua-complex [Ru-II(tpy)(pic)(H2O)](+) (2) and characterized by analytical, spectroscopic (UV-vis and IR) and magnetic moment studies. Complex 1 effected epoxidation of styrene and substituted styrenes, cis- and trans-stilbenes and cyclohexene, in CH3CN at room temperature. Epoxides were found to be the major product for styrenes and stilbenes, whereas, the oxidation of cyclohexene yielded allylic oxidation product. Detailed kinetic studies were performed under pseudo-first order conditions of excess alkene concentrations. A working mechanism in agreement with the rate and activation parameters is presented, and the results are discussed in reference to the data reported for the alkene oxidation by relevant Ru-IV=O system in CH3CN. (C) 2007 Elsevier B.V. All rights reserved.