Synthesis, structures and reactivity of triosmium clusters containing terminal pyrazines, bridging hydroxy and methoxycarbonyl ligands

Four triosmium carbonyl clusters bearing terminal pyrazines, bridging hydroxy and methoxycarbonyl ligands of general formula [OS3(CO)(9)(mu-OH)(mu-OMeCO)L] (1, L = pyrazine; 2. L = 2-methylpyrazine; 3, L = 2,3-dimethylpyrazine; 4, L = 2,3,5-trimethylpyrazine) were synthesized by the reactions of [OS3(CO)(12)] with the corresponding pyrazine derivatives and water ill the presence of a methanolic solution of Me3NO in moderate yields. Compounds [OS3(CO)(9)(mu-OH)(mu-OMeCO)L] react with a series of two electron donor ligands, L' at ambient temperature to give [OS3(CO)(9)(mu-OH)(mu-OMeCO)L'](5,L'=PPh3; 6, L' = P(OMe)(3); 7, L' = 'BuNC; 8, L' = C5H5N) in good yields by the displacement of the pyrazine ligands. This implies that the pyrazine ligands in 1-4 are relatively labile. Compounds 2, 3, 4, and 8 were characterized by single crystal X-ray diffraction analyses. All the four compounds possess two metal-metal bonds and a non-bonded separation of two osmium atoms defined by Os(1)Os-...(3), which are simultaneously bridged by OH and MeOCO ligands and a heterocyclic ligand is terminally coordinated to one of the two non-bonded osmium atoms. (c) 2005 Elsevier Ltd. All rights reserved.