Regioselective Hydrothiolation of Terminal Alkynes using Half-Sandwich Ni(<sc>ii</sc>) Catalysts bearing Bidentate NHC-Carboxylate Ligands

A half-sandwich nickel complex containing an NHC-carboxylate chelate ligand (i. e., [Ni(eta 5-Cp)(kappa 2-C,O-NHC)]) derived from the (S)-leucine has been identified for the selective hydrothiolation of terminal acetylenes toward challenging Markovnikov-type alpha-vinyl thioethers, even with aryl alkynes. The activity and selectivity exhibited by the nickel complex are comparable, if not superior, to those of complexes of rhodium reported to be the best catalysts to date for the Markovnikov addition in the thiol-yne reaction. The experimental data are consistent with the participation of the coordinated carboxylate group in the catalytic reaction as an intermolecular acid-base co-catalyst, favoring the formation of nickel-thiolate intermediates.