Mechanistic Study on the Ruthenium-Catalyzed Terminal Alkyne Hydrochlorination

Vinyl chlorides can be effectively prepared via alkyne hydrochlorination catalyzed by the [Cp*­RuCl­(cod)]/​PPh3 system. The reaction mechanism has been elucidated by density functional theory calculations. Different from the previously proposed pathway (oxidative addition, alkyne coordination, H-/Cl-transfer via inner addition, and reductive elimination), the calculation results indicate that HCl favorably attacks the alkyne stepwise from the outer coordination sphere of the Ru center. The reaction is essentially the electrophilic addition of HCl to alkyne. Therefore, the proton tends to attack the more negatively charged carbon of the C–C triple bond, leading to the Markovnikov product.