Ru(III) analogue of model methane monooxygenase in the effective catalytic oxidation of cyclohexane by molecular oxygen

Abstract The catalytic oxidation of cyclohexane to cyclohexanol by Ru(III) analogue of the model methane monooxygenase (MMO) system, involving complex [Ru 2 O(Py) 6 –μ–(AcO) 2 (PF 6 ) 2 1 (pyridine, Py; acetate, AcO) as a catalyst and molecular oxygen as the oxidant was investigated in a 60:40 (v/v) mixture of acetone and water. In typical experiments at 303 K and p O 2 =5 atm, 5×10 −2  M of cyclohexanol was found to be formed in 7 h with 4.54×10 −4  M of the catalyst from oxidation of 8.84×10 −2  M of cyclohexane. Spectrophotometric, electrochemical, NMR, gas chromatographic and kinetic techniques were used to study the catalytic species and the oxidation reactions in solution. The kinetic studies indicated first order dependence in terms of the concentrations of the catalyst (complex 1 ), cyclohexane and molecular oxygen. On the basis of kinetics and experimental results, a non-radical, ionic mechanism is suggested for oxidation of cyclohexane. The activation parameters for oxidation of cyclohexane evaluated from temperature dependence are: E a =33.98 kJ mol −1 , Δ H # =31.48 kJ mol −1 , Δ S # =−215.86 J (° mol) −1 and Δ G # =96.90 kJ mol −1 .