Chemists release free electrons into solution to bypass decades-old selectivity barrier

Researchers at the University of Wisconsin–Madison, Colorado State University, and the University of Colorado Boulder have demonstrated a catalyst that releases electrons directly into the surrounding solution rather than transferring them to a specific substrate. The work, published in Nature, addresses a long-standing limitation in single-electron transfer chemistry where electrons preferentially flow to the molecule easiest to reduce, blocking access to other potentially useful reaction pathways.

The catalyst, developed over five years by the group of UW–Madison chemistry professor Zachary Wickens, ejects an electron into the solvent, creating what the researchers describe as an extremely aggressive reductant. Because a free electron in solution is highly unstable, it attaches rapidly to the first molecule it encounters, even if that molecule would not normally be favored based on thermodynamic reduction potential.

Computational studies led by Robert Paton at Colorado State University and spectroscopic analysis by Niels Damrauer’s group at CU Boulder revealed why the approach yields unexpected selectivity. Their findings indicate that the crucial selection occurs after the initial electron transfer: the desired reactant proceeds toward product while the molecule that is easier to reduce is recycled back to its starting material, effectively sidestepping the usual thermodynamic preference.

The technique could make a wide range of previously inaccessible coupling reactions possible, expanding the toolkit for building complex molecules used in pharmaceuticals, advanced materials, and the study of biological processes. Wickens characterized the advance as a new framework for designing redox reactions rather than simply another synthetic method.

The research was supported by the National Science Foundation-funded Center for Sustainable Photoredox Catalysis (SuPRCat). The team included Joseph Edgecomb, Matthew Resmini, and Alissia Meyer of UW–Madison; Niket Manoj of CSU; and Arindam Sau of CU Boulder.