Air- and Water-Stable Sulfide Radical Cations Supported by Cyclic (Alkyl)(amino)carbenes

Stable organic radicals have attracted significant attention owing to their key role in understanding reactive intermediates and their diverse applications as functional materials. Sulfide radical cations, in particular, serve as crucial intermediates in various fields such as organic chemistry, biochemistry, and polymer/materials science. However, the development of air- and water-stable sulfide radical cations has remained a significant challenge. In this study, highly stable sulfide radical cations supported by two cyclic (alkyl)(amino)carbene (CAAC) moieties have been synthesized. In addition to demonstrating high air- and water stability, these radical cations can withstand harsh conditions, including exposure to reactive chemicals such as sulfuric acid and hydrogen peroxide, as well as elevated temperatures. Combined experimental and computational studies reveal that the sulfur-centered unpaired electron is stabilized through electronic delocalization and steric protection provided by the CAAC substituents. These findings establish a new class of exceptionally stable sulfur-based radicals and pave the way for their potential applications as functional materials.