Synthesis, reactivities and electrochemistry of trans-dioxoruthenium(VI) complexes of π-aromatic diimines

Abstract

The synthesis and electrochemistry of trans-[Ru^III(L)₂(OH)(H₂O)][CIO₄]₂[L = 1,10-phenanthroline (phen) or 5,5′-dimethyl-2,2′-bipyridine(dmbipy)] are described. Oxidation of trans-[Ru^III(L)₂(OH)(H₂O)]²⁺ by Ce^IV in water gave trans-[Ru^VI(L)₂O₂]²⁺ which were isolated as the yellow perchlorate salts. The complex trans-[Ru^VI(dmbipy)₂O₂][CIO₄]₂ is a powerful oxidant with E°(Ru^VI–Ru^IV)= 1.0 V vs. saturated calomel electrode at pH 1.0. In acetonitrile or acetone, it oxidizes alcohols to ketones/aldehydes, tetrahydrofuran to γ-butyrolactone, alkenes to epoxides and saturated or aromatic hydrocarbons to alcohols/ketones. Oxidation of saturated alkanes occurs preferentially at the tertiary C–H bond. In the presence of CCl₄, cyclohexane is oxidized to cyclohexyl chloride instead of cyclohexanone. The mechanisms of alcohol and cyclohexane oxidation were investigated by kinetic experiments and by isotope labelling studies.