X-ray molecular structures and multinuclear NMR studies of the tetranuclear iridium clusters [Ir4(CO)7(μ4-η3-PhCC(H)CCPh)(μ-PPh2)3] and [Ir4(CO)7(μ3-η2-HCCPh)(η1-CCPh)(μ-PPh2)3]

The reaction of [HIr4(CO)10(μ-PPh2)] with two equiv. of Ph2PCtriple bond; length of mdashCPh produced [HIr4(CO)8(Ph2PCtriple bond; length of mdashCPh)2(μ-PPh2)] (1) in quantitative yield. Mild thermolysis of 1 gave [Ir4(CO)7(μ4-η3-PhCC(H)CCPh)(μ-PPh2)3] (2) and [Ir4(CO)7(μ3-η2-HCCPh)(η1-CCPh)(μ-PPh2)3] (3) in good yields. These compounds were characterized with analytical and spectroscopic data including 1H, 13C and 31P NMR (1 and 2D) spectroscopy, and their molecular structures were established by X-ray diffraction studies. The metal frameworks of 2 and 3 are similarly constituted of a spiked metal triangle; in both clusters the seven CO ligands are terminally bound and the three –PPh2 ligands span two consecutive Ir–Ir bonds and an open edge. The difference between the two structures is that compound 2 contains a butadienic chain, μ4-η3-PhCC(H)CCPh, interacting with all four iridium atoms, whereas compound 3 bears two fragments of this ligand, i.e. a phenylacetylene capping a triangular face and a terminally bound phenylacetylide bonded to the fourth atom of the cluster. Although these two fragments are directed in the appropriate fashion to interact further and generate the chain of compound 2, they do not undergo condensation under thermolytic conditions.