Mechanistic Studies on Rh-Catalyzed Ligand-Controlled Chemoselective Hydrothiolation of Cyclopropenes

Recently, it has been reported that Rh-catalyzed ligand-controlled hydrothiolation of cyclopropenes leads to cyclopropyl or allylic sulfides with high regiocontrol. However, there has yet to be any previous research investigating the detailed mechanism of this reaction. Therefore, density functional theory calculations were performed to provide mechanistic insight into the hydrothiolation of cyclopropenes. The study results show that when L5 is the ligand, cyclopropyl sulfide 3 is the main product, and reductive elimination is the rate-determining step. However, allylic sulfide 4 becomes the primary product when L8 is employed. The reaction follows the carbene formation pathway instead of the initially proposed cyclopropene π bond activation pathway. The chemoselectivity is determined by the competition with Rh−Cγ insertion and reductive elimination. When L5 as the ligand, the origin of the chemoselectivity can be attributed to the electronic effect, steric hindrance effect, and C–H…π interaction. Additionally, the distortion/interaction analysis shows that the allylic sulfide originated predominantly due to the lower distortion energy of the substrate fragment in the reductive elimination transition state under the L8 ligand.