Homogeneous Nickel Catalysts for the Selective Transfer of a Single Arylthio Group in the Catalytic Hydrothiolation of Alkynes

A novel homogeneous catalytic system has been developed for the regioselective hydrothiolation of
alkynes based on CpNi(NHC)Cl complexes (NHC = N-heterocyclic carbene). The designed catalyst
was efficient for the selective addition of a single ArS group to an alkyne and was suitable for the
synthesis of vinylsulfides, without side reactions leading to bis(arylthio)alkenes. Furthermore, this catalytic
system allowed for the S−H bond addition to alkynes to be performed with high regioselectivity (up to
31:1) and in good yields (61−87%). A mechanistic study showed that this reaction involved three steps: 
(1) a nickel-based substitution of chloride for the ArS group, (2) alkyne insertion into the Ni−S bond,
and (3) protonolysis of the Ni−C bond. The intermediate CpNi(NHC)(SAr) complexes were unambiguously characterized by X-ray analysis.