Reactions of Radical Anions with Hydrides: Supercharging Electron Upconversion for Electron Catalysis

Radical anions are well known to react with proton donors, yet their reactivity with hydrides remains largely unexplored. Here, we investigate the reactions of five stable radical anions with B-H and Si-H hydrides (pinacolborane, diphenylsilane, and triphenylsilane) and uncover a new class of chemical reactions. Ketyl radical anions react with main-group hydrides, forming C-E and O-H bonds (E = B, Si) through a process in which the radical anion acts both as a Lewis base and as a H atom acceptor. The resulting radical anions of the hydroelementation products are substantially stronger reductants than the original radical anions, with an estimated increase of ∼1.1 V, bringing their overall reducing power into the range of alkali metals (∼3 V). This allows electron transfer from the product radical anion to neutral substrate molecules, propagating a single-electron-transfer chain and achieving efficient electron catalysis with turnover numbers exceeding 300. These reactions are scalable and do not require conventional catalysts: Either electric current or substoichiometric chemical reductants are sufficient as the source of catalytic electrons. Analogous electron-catalyzed silylation and borylation are also demonstrated with quinone radical anions and inorganic radical anions such as superoxide. This work highlights a new reactivity mode of radical anions, broadens the scope of electron upconversion, and establishes a versatile platform for catalytic single-electron transformations.