The site preference for PPh3 substitution in HOs3(CO)10(PPh3)2(μ-1,2-N,C-η1,κ1-C7H4NS) (1) has been investigated.

The reaction of the electron-deficient 6-methoxyquinolinate-substituted triosmium cluster [Os3(CO)9{μ3-η 1 ,κ 1-C9H5N(6-OMe)}(μ-H)] (1) with PPh3 proceeds readily at room temperature to afford the electron-precise adduct [Os3(CO)9(PPh3){μ-η 1 ,κ 1-C9H5N(6-OMe)}(μ-H)] (2), in which the PPh3 ligand is bound to the osmium that serves as the coordination site for the hydride and the metallated-carbon atom of the benzoheterocycle. This reaction also leads to a change in the hapticity of the 6-methoxyquinolinate ligand from μ3-η 1 ,κ 1 to μ-η 1 ,κ 1 as confirmed by X-ray crystallography. Thermolysis of 2 in boiling toluene furnishes five new triosmium clusters (3-7) as a result of ligand isomerization, decarbonylation and orthometallation of the ancillary PPh3 ligand. Clusters 3 and 4 are isomers of 2 and the location of the metal-bound hydride and PPh3 with respect to 6methoxyquinolinate moiety is the only difference between these isomers. Control experiments show that 5 is a decarbonylation product of 4 which converts in to 6 as a result of further decarbonylation with concomitant orthometallation of one of the phenyl rings of the coordinated PPh3 ligand, whilst 7 is formed from 6 through replacement of an equatorial 2 carbonyl of the nitrogen-bound osmium by PPh3 ligand. All the new clusters have been characterized by a combination of analytical and spectroscopic methods as well as by X-ray crystallography in the case of 2, 3, 6 and 7.

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