Synthesis and Structural Characterization of [Ir4(mu-CO)(CO)7{mu4-eta3-Ph2PC(H)C(Ph)PCBu t}(mu-PPh2)]: Alkyne-Phosphaalkyne Coupling and Formation of a Novel 2-phosphabutadienylphosphine Ligand

reaction of [ir4(m-h)(co)9(ph2pcocph)(m-pph2)] 1 with pocbut in ch2cl2, at 35 °c, for 4 h yields the novel compound [ir4(m-co)(co)7{m4-h3-ph2pc(h)c(ph)pcbut}(m-pph2)] 2, which contains the 2-phosphabutadienylphosphine chain. compound 2 is also formed upon thermolysis of [ir4(co)10(ph2pcocph)(pph2h)] 3 in the presence of pocbut in thf, at 40 °c, for 48 h. small amounts of [ir4(m-co)(co)7(m3-h2-hccph)(m-pph2)2] 4 are always obtained from both reactions, because of the competing rates of the transformations of 1 and 3 into 4 and of their reactions with pocbut. compound 2 was characterized by analytical and spectroscopic studies such as fab ms, 1h, 31p, 13c, 2d 31p-1h hetcor, noe difference and dept nmr experiments, which led to its formulation and established the coupling between the coordinated ph2pcocph and pocbut and the migration of the hydride to the ca of the ph2pcocph ligand. however, it was impossible to establish unambiguously if cleavage of the p-csp bond of the ph2pcocph ligand had occurred and the mode of interaction of the organophosphorus chain. an x-ray diffraction study of compound 2 established a butterfly arrangement of iridium atoms with the new ligand interacting with the metal framework via four s bonds and the pph2 phosphorus lone pair.