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

摘要

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.