Kinetics of oxidation of aromatic hydrocarbons and tetrahydrofuran by trans-dioxoruthenium(VI) complexes

Abstract

The kinetics of oxidation of aromatic hydrocarbons and tetrahydrofuran by trans-[Ru^VILO₂]²⁺{L = 2 bipy(bipy = 2,2′-bipyridine), L¹= 6,7,14,15,16,17,18,19-octahydro-14,18-dimethyl-13H-dibenzo[e,n][1,4,8,12]dioxadiazacyclopentadecine, L²=N,N′-dimethyl-N,N′-bis(2-pyridylmethyl)propylenediamine and L³=meso-2,3,7,11,12-pentamethyl-3,7,11,17-tetraazabicyclo[11.3.1]heptadeca-1(17),13,15-triene} has been studied. In acetonitrile the second-order rate constants follow the order: toluene < ethylbenzene < cumene. The kinetic isotope effects for the oxidation of ethylbenzene by trans-[RuLO₂]²⁺(L = L¹ or L²) are 16 and 12 : 1 respectively. In the oxidation of tetrahydrofuran by trans-[RuL¹O₂]²⁺, k₂ was found to be 0.170 mol^–1 dm³s^–1 at 298 K with a measured kinetic isotope effect of 20 : 1. A linear correlation between log(rate constant) and E°(Ru^VI–Ru^IV) for the oxidation of tetrahydrofuran has been observed. The activation parameters for the oxidation reactions have also been determined. A hydrogen-atom abstraction mechanism is suggested for the oxidation of C–H bonds by trans-dioxoruthenium(VI) complexes.