Two isomeric products [Os3(μ-H)(C14H9N4)(CO)9] formed by orthometallation of the cluster [Os3(C14H10N4)(CO)10] containing the chelating ligand 2,3-bis(2-pyridyl)pyrazine

Treatment of the labile compound [Os3(CO)10(CH3CN)2] with 2,3-bis(2-pyridyl)pyrazine (C14H10N4) in dichloromethane at room temperature gave the cluster [Os3(C14H10N4)(CO)10] (1), which contains the chelating ligand co-ordinated axially through one of the pyridine rings and equatorially through a pyrazine nitrogen atom while one of the pyridine rings remains unco-ordinated. Thermolysis of 1 leads to loss of CO and yields two structural isomers of [Os3(μ-H)(μ,η3-C14H9N4)(CO)9] (2) and (3). Isomer 2 contains an orthometallated 2-pyridyl group and a co-ordinated 2-pyridyl which is not orthometallated. A seven-membered chelate ring is formed and the pyrazine ring is uncoordinated. On the other hand, isomer 3 contains a 2-pyridyl-1,4-pyrazine fragment metallated in the pyrazine ring to form a five-membered chelate ring with the one pyridine ring remaining unco-ordinated. The molecular structures of 1–3 were confirmed by X-ray crystallographic studies.