SYNTHESIS AND X-RAY STRUCTURE OF THE HETERONUCLEAR CLUSTER, (MU-H)2(ETA-5-C5H5)IROS3(CO)10

(Mu-H)2(eta-5-C5H5)IrOs3(CO)10 was prepared in 21% yield by reaction of (mu-H)2Os3(CO)10 with (eta-5-C5H5)Ir(CO)2. The cluster was characterized by IR, H-1 and C-13 NMR, and mass spectrometry and by X-ray crystallography. The structure of (mu-H)2(eta-5-C5H5)IrOs3(CO)10 consists of a tetrahedral cluster core with a semi-bridging carbonyl from Ir to Os. It closely resembles the other members of the series (mu-H)2(eta-5-C5H5)MOs3(CO)10 (M = Co, Rh). The semi-bridging carbonyl has greater bridging character as M = Ir < Rh < Co. This is reflected in the relative intensities and shapes of the semi-bridging CO stretching bands in the IR spectra and in the C-13 NMR chemical shifts of the semi-bridging carbonyl signals of the compounds. The semi-bridging carbonyl C-13 resonance is shifted to higher field from cobalt to iridium.