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.