Highly efficient NHC-iridium(I) catalyzed disulfide bond forming reaction

The N-heterocyclic carbene (NHC) iridium(I) complex [IrCl (COD)(IMes)] [IMes = 1,3-bis(2,4,6-trimethylphenyl) imidazole-2-ylidene] showed an excellent catalytic activity in the reactions of the aerobic oxidative coupling of thiols into disulfides. The use of oxygen of air as a green oxidant allows the thiols to be quantitatively converted into the corresponding disulfides under mild conditions and in a short reaction time. The replacement of chloride ligand on the iridium by the strong-donating thiolate ligand yielded an electron-rich and sensitive-to-oxygen active species [Ir(S-R)(COD)(IMes)] at room light and subsequently promoting the catalytic oxidative coupling reactions. This active species was successfully isolated and characterized by X-ray diffraction and found also to be essential in revealing a plausible mechanism for this Ir-catalyzed transformation. The Density Functional Theory (DFT)-calculated free energy profile of the proposed mechanism of our developed catalyst system can reasonably account for the key role of air in pursuing the catalytic reaction. Overall, the obtained computational and the experimental results of this study are in good agreement.