SYNTHESIS, STRUCTURE AND REACTIVITY OF TRIOSMIUM CLUSTERS DERIVED FROM THE REACTIONS OF [OS-3(CO)(10)(MU-DPPM)] (DPPM = PH2PCH2PPH2) AND [OS-3(MU-H)(CO)(8)(PH2PCH2P(PH)C6H4)] WITH PHPH2

The reaction of [Os-3(CO)(10)(mu-dppm)] 1 with diphenylphosphine in re fluxing taluene led to the substituted cluster [Os-3(CO)(9)(mu-dppm)(P HPh2)] 3 and the phosphido-bridged dihydride [Os3H(mu-H)(CO)(7)(mu-dpp m)(mu-PPh2)(2)] 4. The cluster 4 exists as three isomeric forms in sol ution. The 46-electron compound [Os-3(mu-H)(CO)(8){Ph2PCH2PCH2P(Ph)-C6 H4}] 2 reacted with an excess of PHPh2 at room temperature to yield [O s-3(mu-H)(CO)(8){Ph2PCH2P(Ph)C6H4}-(PHPh2)] 5 and [Os-3(CO)(8)(mu-dppm )(PHPh2)(2)] 6 in 16 and 62% yields respectively. Thermolysis of 6 in refluxing toluene gave 4 and two stereoisomeric compounds 7 and 8 with stoichiometry [Os-3(mu-H)(2)(CO)(6)(mu-dppm) (mu-PPh2)(2)]. The clust er 3 decarbonylated at 110 degrees C to give the phosphido-bridged mon ohydride cluster [Os-3(mu-H)(CO)(8)-(mu-dppm)(mu-PPh2)] 9 which exists as two isomers in solution. Compound 4 converts into 7 and 8 on therm olysis in toluene. All the compounds have been characterized by infrar ed, H-1 and P-31-{H-1} NMR spectroscopy and elemental analysis and in the case of 3, 4, 6 and 7 also by X-ray crystallography.