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

Abstract

Catalytic pathwaysfor 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 an eutral aqueous solution follows as tepwise 4e À /4 H + pathway,inwhich H 2 O 2 is formed as adetectable intermediate and subsequently reduced to H 2 Oi nt wo 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.F urthermore,e lectrochemical studies of the reaction kinetics revealed ah igh turnover frequency of 1.5 10 5 s À1 ,the highest reported for any molecular copper catalyst.

Influence of Ligand Denticity and Flexibility on the Molecular Copper Mediated Oxygen Reduction Reaction

“…This is not in line with the higher E 1/2 values of 0.31 and 0.30 V vs RHE for Cu - terpy and Cu - bmpa , respectively, compared to the reported E 1/2 of 0.21 V vs RHE for Cu - tmpa . 37 …”

“…At diluted concentrations, however, a first order dependence in copper was observed. 37 Noteworthy is that the onset potential and activity of the ORR with respect to the reduction of hydrogen peroxide lie in favor of the first reaction resulting in a buildup of hydrogen peroxide under conditions where the reaction is not run under mass-transport limitations of dioxygen. The overpotential of an optimized catalyst therefore is probably limited by the equilibrium potential of hydrogen peroxide at 0.68 V versus RHE.…”

Electrocatalytic Oxygen Reduction at Multinuclear Metal Active Sites Inspired by Metalloenzymes

“…Redox-active metal centers give one electron to O 2 , yielding superoxo (O−O •− ) intermediates and two-electron transfer produces peroxo intermediates [28−30]. For most of the mononuclear transition metal complexes, the ORR proceeds via end-on (η 1 ) superoxo intermediates [30,31]. Only a few examples of catalysis via side-on (η 2 ) peroxo complexes were reported [30, 32−34].…”

“…Homogeneous ORR catalysts based on dinuclear copper complexes can give mechanistic insights into ORR intermediates. Even in the case of mononuclear copper complexes such as [Cu(tmpa)(L)] 2+ (tmpa = tris(2-pyridylmethyl)amine, L = solvent), peroxo-bridged dinculear intermediates can be involved for the ORR depending on the experimental condition [31,[52][53][54][55][56]. For example, a dinuclear copper complex with a −(CH 2 ) 3 -linked bis[2-(2-pyridyl)ethyl]amine ligand selectively reduces O 2 to H 2 O in acetone that contains decamethylferrocene (Fc*) as the electron source and trifluoroacetic acid as the proton source [57].…”

Fully oxygen-tolerant atom transfer radical polymerization triggered by sodium pyruvate

“…[9][10][11][12] Even trace amounts of oxygen can inhibit polymerization by rapidly oxidizing the activator form of the catalyst Cu I /L to the inactive Cu II /L complex. 13 Furthermore, oxygen molecules can react with the propagating carbon-based radicals, thus terminating the polymerization process. 14 The sensitivity of ATRP to oxygen necessitates the use of specialized equipment or deoxygenation by inert gas sparging before the polymerization (Scheme 1).…”