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.