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.