Molecular Catalysis of Electrochemical Reactions: Competition between Reduction of the Substrate and Deactivation of the Catalyst by a Cosubstrate Application to N₂O Reduction

Abstract

In the context of molecular catalysis of electrochemical reactions, the competition between reduction of the substrate and deactivation of the catalyst by a cosubstrate is investigated. It is a frequent situation because proton donors are ubiquitous cosubstrates in reductive electrochemical reactions and molecular catalysts, either transition metal complexes or organic aromatic molecules, and are often prone to electrohydrogenation. We provide a formal kinetic analysis in the framework of cyclic voltammetry, and we show that the response is governed by two parameters and that the competition does not depend on the scan rate. From this analysis a methodology is proposed to analyze such systems and then illustrated via the study of N2O to N2 electroreduction catalyzed by 4‐cyanopyridine in acetonitrile electrolyte with water as proton donor. Incidentally, new insights into the mechanism of 4‐cyanopyridine radical anion protonation are revealed.

Electrochemical Reduction of N2O with a Molecular Copper Catalyst

“…It has previously been shown that some organic radicals are competent outer-sphere redox catalysts for the electrochemical reduction of N 2 O in MeCN, and we were particularly inspired by catalysis using 4-cyanopyridine . We were interested in investigating a pyridine donor that could be used as an effective electron shuttle for Cu-catalyzed N 2 O reduction (Figure b).…”

“…It has previously been shown that some organic radicals are competent outer-sphere redox catalysts for the electrochemical reduction of N 2 O in MeCN, 47 and we were particularly inspired by catalysis using 4-cyanopyridine. 49 We were interested in investigating a pyridine donor that could be used as an effective electron shuttle for Cu-catalyzed N 2 O reduction ( Figure 1 b). Since demetalation of Cu(I) is a common deactivation pathway in Cu Z * synthetic models, we rationalized that polydentate chelates with strong N donors could minimize the loss of this labile metal.…”

Electrochemical Reduction of N2O with a Molecular Copper Catalyst

“…It has previously been shown that some organic radicals are competent outer-sphere redox catalysts for the electrochemical reduction of N2O in MeCN, 47 and we were particularly inspired by catalysis using 4-cyanopyridine. 49 We were interested in investigating a pyridine donor that could be used as an effective electron shuttle for Cu-catalyzed N2O reduction (Figure 1b). Since demetallation of Cu(I) is a common deactivation pathway in CuZ* synthetic models, we rationalized that polydentate chelates with strong N-donors could minimize the loss of this labile metal.…”