A Kinetic Study on the Reactivity of a cis-Dioxoruthenium(VI) Complex. Oxidation of Alcohols, Aromatic Hydrocarbons, and Alkenes by cis-(2+)

Article abstract of DOI:10.1021/jo00126a038

The kinetics of oxidation of alcohols, aromatic hydrocarbons, and alkenes by cis-(2+) (Tet-Me6 = N,N,N',N'-tetramethyl-3,6-diazaoctane-1,8-diamine) have been studied.In general, the oxidation chemistry of cis-(2+) is similar to those of trans-dioxoruthenium(VI) compounds such as trans-(2+) (N2O2 = 1,12-dimethyl-3,4:9,10-dibenzo-1,12-diaza-5,8-dioxacyclopentadecane) and trans-(2+) (pytn = N,N'-dimethylbis(2-pyridylmethyl)propylenediamine).The oxidation is first-order with respect to cis-(2+) and organic substrates and is accompanied by large and negative ΔS(excit.).Large k_H/k_D values were found for the oxidation of alcohols.A linear Hammett plot for the oxidation of para-substituted benzyl alcohols with a slope of -1.0 was obtained.For alcohol oxidation, a charge-transfer mechanism involving hydride abstraction has been proposed.Oxidation of toluene, ethylbenzene, and cumene by cis-(2+) gave benzaldehyde, acetophenone/sec-phenylisopropyl alcohol, and 2-phenylisopropyl alcohol, respectively.A k_H/k_D value of 11 has been found for the oxidation of ethylbenzene.In the oxidation of these aromatic hydrocarbons, the key step likely involves C-H bond activation in the transition state.Allylic oxidation is the major reaction pathway in the cyclohexene oxidation.In the oxidation of alkenes, both C=C bond cleavage product(s) and epoxides were found.The Hammett plot for the oxidation of para-substituted styrenes is linear with a slope of -2.0.The oxidation likely proceeds through a charge-transfer mechanism.