Mo Insertion into the H2 Bond in MoxSy- + H2 Reactions

A combined experimental and computational study of H-2 reactions with small (MoxSy-)-Mo-98 clusters ranging from subsulfide (x similar to y) to hypersulfide (y > 2x) is presented. Results suggest that the subsulfides react with H-2 primarily by insertion of a more reduced Mo center into the H-H bond, forming a dihydride product. We find that this reaction occurs up to Mo oxidation states of +4. For the subsulfides containing a second metal in a sufficiently low oxidation state, a second insertion of H-2 occurs, leading to a tetrahydride product. The reaction mechanisms of the sulfides are found to be very similar, albeit slightly higher energetically to those of the analogous oxosulfides that are also observed at low abundances in the experiments. In addition, the experimental results show an overall reduction of hypersulfides in the presence of H-2, suggesting loss of H2S neutral molecules.