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 H 2 O 2 is formed as a detectable intermediate and subsequently reduced to H 2 O 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 1.5×10 5 s −1 , the highest reported for any molecular copper catalyst.