Fast Oxygen Reduction Catalyzed by a Copper(II) Tris(2-pyridylmethyl)amine Complex through a Stepwise Mechanism.

Catalytic pathways for the reduction of dioxygen can either lead to the formation of water or peroxide as the reaction product. We demonstrate that the electrocatalytic reduction of O by the pyridylalkylamine copper complex [Cu(tmpa)(L)] in a neutral aqueous solution follows a stepwise 4 e /4 H pathway, in which H O is formed as a detectable intermediate and subsequently reduced to H O in two separate catalytic reactions. These homogeneous catalytic reactions are shown to be first order in catalyst. Coordination of O to Cu was found to be the rate-determining step in the formation of the peroxide intermediate. Furthermore, electrochemical studies of the reaction kinetics revealed a high turnover frequency of 1.5×10  s , the highest reported for any molecular copper catalyst.