Theoretical investigation of the mechanism of gold(i)-catalyzed hydrothiolation of alkynes and alkenes with phenthiol

Abstract

The mechanisms of the gold-catalyzed hydrothiolation of alkynes and alkenes with phenthiol have been investigated using density functional theory calculations done at the B3LYP/6-31G (d,p) (SDD for Au) level of theory. The solvent effect was taken into account by B3LYP/6-311++G (d,p) (SDD for Au) single-point calculations with the integral equation formalism polarizable continuum model (IEFPCM) and solvation model (SMD) in toluene. The calculations indicated that the reactions of the gold-catalyzed hydrothiolation proceed through two competing pathways and lead to Markovnikov-type sulfides or anti-Markovnikov-type products. The process of forming anti-Markovnikov-type products is more favored kinetically with barriers of 21.9 and 23.6 kcal mol⁻¹ for alkyne and olefin versus >27.0 kcal mol⁻¹ for the pathway of forming Markovnikov-type products. The computational results are consistent with the experimental observations of Corma and co-workers. Furthermore, comparing the different metal catalysts of silver and copper for the activity and regioselectivity of the hydrothiolation, the results indicate that the silver catalyst has a relatively high catalytic activity, but the regioselectivity is not satisfactory compared to the gold catalyst and the regioselectivity of copper catalysts is the worst.