A new synthetic route for the preparation of [Os(CO)(μ-OH)(μ-H)] and its reaction with bis(diphenylphosphino)methane (dppm): syntheses and X-ray structures of two isomers of [Os(CO)(μ-OH)(μ-H)(μ-dppm)] and [Os(CO)(μ-CO)(μ-O)(μ-dppm)].

The triosmium cluster [Os(CO)(μ-OH)(μ-H)] containing bridging hydride and hydroxyl groups at a common Os-Os edge was obtained in good yield ( 75%) from the hydrolysis of the labile triosmium cluster [Os(CO)(NCMe)] in THF at 67 °C. [Os(CO)(μ-OH)(μ-H)] reacts with dppm at 68 °C to afford the isomeric clusters 1 and 2 with the general formula [Os(CO)(μ-OH)(μ-H)(μ-dppm)] that differ by the disposition of bridging dppm ligand. Cluster 1 is produced exclusively from the reaction of [Os(CO)(μ-OH)(μ-H)] with dppm in CHCl at room temperature in the presence of added MeNO. Heating cluster 1 at 81 °C furnishes 2 in a process that likely proceeds by the release of one arm of the dppm ligand, followed by ligand reorganization about the cluster polyhedron and ring closure of the pendent dppm ligand. The oxo-capped [Os(CO)(μ-CO)(μ-O)(μ-dppm)] (3) has been isolated starting from the thermolysis of either 1 or 2 at 139 °C. Reactions of [Os(CO)(μ-dppm)] with ROH (R = Me, Et) in the presence of MeNO at 80 °C furnish [Os(CO)(μ-OH)(μ,η,κ-OCOR)(μ-dppm)] (4, R = Me; 5, R = Et). Clusters 1-5 have been characterized by a combination of analytical and spectroscopic studies, and the molecular structure of each product has been established by X-ray crystallography. The bonding in these products has been examined by electronic structure calculations, and cluster 1 is confirmed as the kinetic product of substitution, while cluster 2 represents the thermodynamically favored isomer.