Monooxo complexes of ruthenium(V) as homogeneous redox catalysts for the electrooxidation of benzyl alcohol

Abstract

The electrochemical behavior of three Ru(IV)-monooxo complexes, trans-[RuIV(TMC)O(X)]ClO4 (TMC = 1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane; X- = Cl-, NCO-, N3 -), in acetonitrile is described. The formal potentials of the Ru(V)/Ru(IV) couples decrease in the order Cl- > NCO- > N3 -. The electrochemically generated Ru(V)-monooxo complexes are active catalysts for the oxidation of benzyl alcohol to benzaldehyde. The rate of benzyl alcohol oxidation decreases in the same order as the formal potentials. The second-order rate constants for reaction between the Ru(V) complexes and benzyl alcohol were evaluated by rotating disk voltammetry. The values obtained were 2.1 × 102 and 1.4 × 102 M-1 s-1 for X- = Cl- and NCO-, respectively. The catalysts gradually lose their activity during the course of the electrooxidation of benzyl alcohol because of what appears to be decomposition of the catalysts during the period that they are in the Ru(V) oxidation state. © 1987 American Chemical Society.