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.

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.

Transition-metal catalyzed coupling reactions of carbonyl compounds using simple chemical feedstocks have become a cornerstone of modern synthetic organic chemistry. The mechanisms and origins for ligand-controlled palladium-catalyzed regioselective α- and γ-arylation of α,β-unsaturated ketones with aryl halides have been investigated by density functional theory (DFT) calculations. Computational results have confirmed our proposed catalytic cycle, which includes four steps: oxidative addition, transmetallation, deprotonation/protonation, and reductive elimination. The Heck-type mechanism for α-arylation of α,β-unsaturated ketones is proved to be less feasible due to the high energy barrier for the insertion step. While reductive elimination is the rate-determining step (RDS), the critical process responsible for the regioselectivity depends upon the direction of protonation step, where the base function as a proton shuttle to facilitate H migration. Distortion/interaction analysis, natural bond orbital (NBO) analysis, and bur-ied volume calculations indicate that the regioselectivity is primarily controlled by the steric hindrance at the region of the ligand close to the enone. The indole ring of the phosphine ligand lay upward or downward, varying the space crowding in the region, thus leading to different protonation products followed by corresponding reductive elimination. The phenomenon of [1,5]-H trans-fer discovered in the γ-arylation of β-alkoxy cyclohexenones is also well rationalized by the proton shuttle model.