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

Abstract

Four triosmium carbonyl clusters bearing terminal pyrazines, bridging hydroxy and methoxycarbonyl ligands of general formula [Os 3(CO) 9(μ-OH)(μ-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 [Os 3(CO) 12] with the corresponding pyrazine derivatives and water in the presence of a methanolic solution of Me 3NO in moderate yields. Compounds [Os 3(CO) 9(μ-OH)(μ-OMeCO)L] react with a series of two electron donor ligands, L′ at ambient temperature to give [Os 3(CO) 9(μ-OH)(μ-OMeCO)L′] ( 5, L′ = PPh 3; 6, L′ = P(OMe) 3; 7, L′ = t BuNC; 8, L′ = C 5H 5N) 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.