A hemilabile and cooperative N-donor functionalized 1,2,3-triazol- 5-ylidene ligand for selective and base-free rhodium(I) catalyzed alkyne hydrothiolation reactions

Abstract

A series of novel cationic and neutral Rh-complexes with an N-donor functionalized 1,2,3-triazol-5-ylidene (TRZ) ligand (where pendant N-donor is NHBoc, NH2 or NMe2 respectively) is described. Their catalytic activity was evaluated towards the hydrothiolation of alkynes. Among the catalysts, a neutral dicarbonyl complex featuring the tethered-NBoc amido-TRZ ligand proved very selective for alkyne hydrothiolation with an aryl thiol. Remarkably, the reaction could be carried out in the absence of pyridine or base additive. In addition, during the reaction course, no evidence for oxidative addition of the thiol S-H was observed, strongly suggesting a reaction pathway whereby a bifunctional ligand is involved. Experimental and theoretical mechanistic investigations suggest a ligand-assisted deprotonation of substrate thiol, hemilabile dissociation of amine from metal and thiolate coordination, which is indicative of a different reaction mechanism to those previously reported for related alkyne hydrothiolation reaction.