Spin-Crossing in the ()-Selective Alkyne Semihydrogenation Mechanism Catalyzed by MoS Clusters: A Density Functional Theory Exploration.

Semihydrogenation of internal alkynes catalyzed by the air-stable imidazolyl amino [MoSCl(ImNH)] cluster selectively affords the ()-alkene under soft conditions in excellent yields. Experimental results suggest a sulfur-based mechanism with the formation of a dithiolene adduct through interaction of the alkyne with the bridging sulfur atoms. However, computational studies indicate that this mechanism is unable to explain the experimental outcome: mild reaction conditions, excellent selectivity toward the ()-isomer, and complete deuteration of the vinylic positions in the presence of CDOD and CHOD.