Cuboidal Mo3S4 clusters as a platform for exploring catalysis: A three-center sulfur mechanism for alkyne semihydrogenation.

We report a trinuclear Mo3S4 diamino cluster that promotes the semihydrogenation of alkynes. Based on experimental and computational results, we propose an unprecedented mechanism in which only the three bridging sulfurs of the cluster act as the active site for this transformation. In the first step, two of these μ-S ligands react with the alkyne to form a dithiolene adduct; this process is formally analogous to the olefin adsorption on MoS2 surfaces. Then, H2 activation occurs in an unprecedented way that involves the third μ-S center, in cooperation with one of the dithiolene carbon atoms. Notably, this step does not imply any direct interaction between H2 and the metal centers, and directly results in the formation of an intermediate featuring one (μ-S)–H and one C–H bond. Finally, such half-hydrogenated intermediate can either undergo a reductive elimination step that results in the Z-alkene product, or evolve into an isomerized analogue whose subsequent reductive elimination generates the E-alkene p...