Use of Base Control To Provide High Selectivity between Diaryl Thioether and Diaryl Disulfide for C-S Coupling Reactions of Aryl Halides and Sulfur and a Mechanistic Study

Previous studies have reported that S-arylation produces diaryl disulfide when the precursors include sulfur powder and aryl halide using CuI as the catalyst. However, our research has revealed that the use of different bases in the above S-arylation process results in the coproduction of diarylsulfane and diaryldisulfane. In addition, we have demonstrated that the ratio of the two products can be controlled by selecting the alkalinity of the bases. H-1 NMR spectra showed that diaryldisulfane was the first product, which became the reagent in a reaction with aryl halide to form diarylsulfane through CuI catalysis. Various aryl halides were tested to enhance the selectivity between diarylsulfane and diaryldisulfane using various different bases, leading to the following principles. A weak base, such as metal carbonate or acetate, results in the production of only diaryldisulfane; a strong base, such as metal hydroxide, results in the production of both diaryldisulfane and diarylsulfane. According to DFT calculations, hydroxide ions, which were exchanged for iodide and bonded with Cu, affected Cu electrons more strongly to reduce diaryl disulfide.