Iridium cluster chemistry: The synthesis and the solid state structures of[HIr5(CO)(12)](2-) and [HIr4(CO)(10)PPh3](-)

The cluster [HIr5(CO)(12)](2-) (1) was prepared by condensation of [HIr4(CO )(11)](-) and [Ir(CO)(4)](-) (molar ratio 1:1) in refluxing THF, with almos t quantitative yields. Its solid state structure was determined by X-ray di ffraction at low temperature on the salt [PPh3CH2Ph](2)[HIr5(CO)(12)]. The metal atoms define a trigonal bipyramidal arrangement. The hydride ligand w as located indirectly as a bridge between apical and equatorial metal atoms . The phosphine-substituted cluster [HIr4(CO)(10)PPh3](-) (2) was synthetiz ed by CO displacement on [HIr4(CO)(11)], in THF at room temperature. This r eaction is selective, with no traces of polysubstitution products. In the s olid state, the hydride and the triphenylphosphine are axially bound on bas al iridium atoms; the terminal hydrogen atom was directly located by X-ray analysis at a Ir-H distance of 1.57(9) Angstrom. On the contrary, two isome rs are present in THF solution, and they interconvert tepidly at room tempe rature, as shown by H-1 and P-31 NMR spectra.