Dirhodium(II)-Catalyzed Sulfide Oxygenations: Catalyst Removal by Coprecipitation with Sulfoxides

The dirhodium(II) carboxylate complex Rh-2(esp)(2) (esp = alpha,alpha,alpha',alpha-tetramethyl-1,3-benzenedipropanoate) was shown to catalyze the sulfoxidation of organic sulfides using tert-butyl hydroperoxide as the oxidant. Due to the unique structure of Rh-2(esp)(2) and its stable Rh-2(II,II) catalyst resting state, the rhodium catalyst is able to precipitate as a Rh-2(esp)(2)-sulfoxide complex following the reaction which makes separation of the catalyst from the products very convenient. The precipitated Rh-2(esp)(2)-sulfoxide complexes could be reused to catalyze sulfide oxygenation reactions without considerable loss of activity. Mechanistic studies suggest that the axial ligands fine-tune the redox potential of the dirhodium(II,II) compounds and determine the predominant catalyst species in the oxidation reaction.