Cationic Selenuranes – Bench‐Stable Sources of Se(III) Radicals

Abstract Radicals are often considered unstable and synthetically unpredictable. Stable radicals, defined as species that can be stored and handled under ambient conditions, serve as valuable reagents for redox and radical‐mediated transformations. We report the multigram‐scale synthesis, isolation, and characterization of cationic selenuranes–formally λ 4 ‐selane species–as bench‐stable reservoirs of one‐center/one‐electron selenium radical cations. Solid‐state stability arises from a selective, reversible head‐to‐head Se–Se oligomerization, with the salts remaining stable under air and moisture for over a month. In solution, electrostatic repulsion weakens the Se─Se σ‐bond (Δ H 298 = 29.9 kcal·mol −1 ), enabling dissociation into radical cations without external activation. The resulting Se(III) radicals promote oxidation and substitution reactions with hydrazines, alcohols, sulfinates, borates, silanes, and stannanes, including functionalizations of complex molecules.