Intramolecular hydrogen bonding in transition metal clusters: NMR evidence for an Os–H⋯H–S interaction in H(μ-H)Os3(CO)10(HSR) (R=ethyl, cyclopentyl)

The reaction of H2Os3(CO)10 with RSH (R=CH2CH3, cyclopentylthiol) at low temperatures in CD2Cl2 affords three H(μ-H)Os3(CO)10(RSH) adducts, where, by the 13C NMR carbonyl spectrum, it can be shown that the thiol ligand occupies an axial position. The presence of an intermolecular MH⋯HS interaction in the main isomer has been determined by longitudinal relaxation time measurements. The isolation of the H,H dipolar contribution to the terminal hydride relaxation affords a value of 1.97 Å for the ‘unconventional’ hydrogen–hydrogen interaction in H(μ-H)Os3(CO)10(RSH) (R=cyclopentylthiol). An intramolecular proton transfer from the thiol ligand RSH to the terminal hydride, via a dihydrogen bonded species, ultimately losing an H2 molecule. leading to the formation of the stable product (μ-H)Os3(CO)10(μ-SR) is proposed.