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(mu-H)Os-3(CO)(10)(RSH) adducts, where, by the C-13 NMR carbonyl spectrum, it can be shown that the thiol ligand occupies an axial position. The presence of an intermolecular (MHHS)-H-... interaction in the main isomer has been determined by longitudinal relaxation time measurements. The isolation of the 14,14 dipolar contribution to the terminal hydride relaxation affords a value of 1.97 Angstrom for the 'unconventional' hydrogen-hydrogen interaction in H(mu-H)Os-3(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 H, molecule. leading to the formation of the stable product (mu-H)Os-3(CO)(10)(mu-SR) is proposed. (C) 2003 Elsevier Science B.V. All rights reserved.