Overview of outer-sphere electron transfer mediators for electrosynthesis

This review provides a summary of redox mediators that have been used in organic electrosynthesis, supplemented by other redox active molecules that may find application in electrosynthesis. The redox-active species described herein are considered only in the context of outer-sphere electron transfer (ET) mechanisms. Molecular electrocatalysts that participate in inner-sphere mechanisms, such as hydrogen-atom transfer (HAT), hydride transfer, or organometallic pathways, are not discussed. Graphical summaries are presented to show structurally related families of mediators, with their redox potentials. These summaries include structures that may not have yet been used for electrosynthesis. For example, some of the molecules have been used in other fields of research where redox chemistry plays a vital role, (e.g., photredox catalysis, energy storage/bateries, organic electronics, and photovoltaics). The aim of this chapter is to provide the reader with an accessible guide to possible redox-active molecules that could be considered as mediators for electrochemical screening, when pursuing the discovery or optimization of redox reactions. The chapter concludes with a summary of gaps and opportunities for the development of new mediators.