Titanocene perfluorobutanesulfonate catalyzed reduction of disulfides in the presence of zinc to synthesize unsymmetrical sulfides

Abstract

Titanocene perfluorobutanesulfonate Cp2Ti(OH2)2(OSO2C4F9)2·H2O·THF (1·H2O·THF) was successfully synthesized by treatment of Cp2TiCl2 with C4F9SO3Ag, and was found to have the nature of air-stability, water tolerance, high thermal stability and strong Lewis acidity. In the presence of 10 mol% 1·H2O·THF, reductive cleavage SS bond by zinc dust at room temperature led to nucleophilic sulfur anion species, which reacted with alkyl halides to afford unsymmetrical sulfides in good to excellent yield using commercial THF as solvent. Activated chlorides, organic iodides and bromides underwent the reactions efficiently. The possible reaction mechanism is that zinc dust reduces Cp2TiIV(OPf)2 (Pf = SO2C4F9) to generate Cp2TiIIIOPf, which reacts with diaryl disulfides to form Cp2TiIVSAr(OPf) by oxidative addition. Further reaction of Cp2TiIVSAr(OPf) with alkyl halides to afford unsymmetrical sulfides. This method provides an efficient and mild protocol for the synthesis of unsymmetrical sulfides.