X-ray molecular structures and multinuclear NMR studies of the tetranuclear iridium clusters [Ir4(CO)7(m4-h3-PhCC(H)CCPh)(m-PPh2)3] and [Ir4(CO)7(m3-h2-HCCPh)(h1-CCPh)(m-PPh2)3]

The reaction of [HIr4(CO)10(m-PPh2)] with two equiv. of Ph2PC.tplbond.CPh produced [HIr4(CO)8(Ph2PC.tplbond.CPh)2(m-PPh2)] (1) in quant. yield. Mild thermolysis of 1 gave [Ir4(CO)7(m4-h3-PhCC(H)CCPh)(m-PPh2)3] (2) and [Ir4(CO)7(m3-h2-HCCPh)(h1-CCPh)(m-PPh2)3] (3) in good yields. These compds. were characterized with anal. and spectroscopic data including 1H, 13C and 31P NMR (1 and 2D) spectroscopy, and their mol. 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 compd. 2 contains a butadienyl chain, m4-h3-PhCC(H)CCPh, interacting with all four iridium atoms, whereas compd. 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 compd. 2, they do not undergo condensation under thermolytic conditions.