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-2 by the pyridylalkylamine copper complex [Cu(tmpa)(L)](2+) in a neutral aqueous solution follows a stepwise 4 e(-)/4 H+ pathway, in which H2O2 is formed as a detectable intermediate and subsequently reduced to H2O in two separate catalytic reactions. These homogeneous catalytic reactions are shown to be first order in catalyst. Coordination of O-2 to Cu-I 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 1.5x10(5) s(-1), the highest reported for any molecular copper catalyst.