Mechanistic studies on oxidation of hydrogen peroxide and hydrazine by a metal-bound superoxide

Abstract

In aqueous acetate buffer, hydrogen peroxide and hydrazine reduce the bridging superoxide in [(en)(dien)Co III(O 2)Co III(en)(dien)](ClO 4) 5 ( 1) to the corresponding hydroperoxo complex [(en)(dien)Co III(μ-O 2H)Co III(en)(dien)] 5+ ( 2). In the presence of excess [H 2O 2] and [N 2H 5 +] over [ 1], both the reactions obeyed first-order kinetics and exhibited inverse proton dependence. Protonation of 1 at equilibrium generates [(en)(dien)Co III(μ-O 2H)Co III(en)(dien)] 6+ ( 1H), the conjugate acid from 1, which appears to be a kinetic dead-end and that accounts for the observed inverse proton dependence on rate. Reaction rates significantly decrease with increasing proportion of D 2O replacing H 2O in the solvent and an H-atom transfer (HAT) from the reducing species to the bridging superoxide in 1 seems reasonable at the rate step.