Electrocatalytic reduction of organic and small molecule substrates offers a promising approach to harness renewably sourced energy to synthetize value-added products and fuels. However, these reductive transformations usually require harsh reduction potentials which, in the presence of proton sources to generate the desired products, predominantly lead to hydrogen evolution reaction (HER) at the electrode. The latter hinders the widespread development of efficient and viable electrochemical technologies for the reduction of a number of industrially relevant substrates such as olefins, ketones or N<sub>2</sub>; new approaches suppressing HER are essential. In this context, concerted proton-electron transfer (CPET) reactions have emerged as an exciting opportunity to bypass high energy intermediates otherwise generated via stepwise electron and proton transfers, opening up new reaction pathways at milder reduction potentials. The increasing interest in CPET strategies has led to the discovery of several systems that can act as efficient CPET donors for chemical and photochemical transformations where initial electron transfer is thermodynamically inaccessible. However, they are employed as stoichiometric reagents or rely on stoichiometric amounts of exogenous reductant; adaption to electrochemical means has proven challenging. This work describes the design of a molecular CPET mediator via synthetic integration of a redox mediator and a Brønsted base, where spatial isolation of the proton and electron relays is key to store a highly reactive H-atom equivalent preventing catalyzed HER. This net H-atom can be further delivered via an electrocatalytic CPET (eCPET) cycle that operates at potentials sufficiently mild to also outcompete electrode mediated HER, allowing to explore its potential application to reduction unsaturated organic substrates and small molecules such as nitrogen.

Orchestrating protons and electrons for selective electrocatalytic reduction

ACS Spring 2022

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.