A Persistent Phosphanyl-Substituted Thioketyl Radical Anion

Alkali metal salts, M⁺ [Ter(iPr)P-C(=S)-P(iPr)₂ S]^.- (M=Na, K; 2_M; Ter=2,6-bis-(2,4,6-trimethylphenyl)phenyl) containing a room-temperature-stable thioketyl radical anion were obtained by reduction of the thioketone precursor, Ter(iPr)P-C(=S)-P(iPr)₂ S (1), with alkali metals (Na, K). Single-crystal X-ray studies as well as EPR spectroscopy revealed the unequivocal existence of a thioketyl radical anion in the solid state and in solution, respectively. The computed Mulliken spin density within 2_M is mainly located at the sulfur (49 %) and the carbonyl carbon (33 %) atoms. Upon adding [2.2.2]-cryptand to the radical species 2_K to minimize the interionic interaction, an activation reaction was observed, yielding a potassium salt with a phosphanyl thioether based anion, [K(crypt)]⁺ [Ter(iPr)P-C(-S-iPr)-P(iPr)₂ S]^- (3) as the product of an intermolecular shift of an iPr group from a second anion. The products were fully characterized and application of the radical anion as a reducing agent was demonstrated.