The Ph2PC(H)CPh ligand in [Ir4(CO)9(μ3-η3-Ph 2PC(H)CPh)(μ-PPh2)] (1) undergoes selective P-C bond scission upon thermolysis in toluene at 70 °C, to give [Ir4(CO)8(η1-Ph)(μ 4-η3-PhPC-(H)CPh)(μ-PPh2)] (2; 60%), in addition to unreacted 1. 31P{1H}, 13C{1H}, and 1H NMR studies indicated the presence of two isomers in solution in a 3.2:1 ratio. The minor isomer 2b was fully characterized by single-crystal X-ray diffraction and exhibits a flat butterfly of metal atoms, with the PhPC(H)CPh ligand interacting with all four Ir atoms. The η1-Ph ligand is located on a wingtip Ir, on a radial site, trans to an Ir-Ir bond and cis to the P of the vinylidene ligand. A structure was proposed for the major isomer 2a, on the basis of multinuclear NMR spectroscopy, in which the η1-Ph ligand is located on an axial site, trans to the P of the vinylidene ligand. VT 31P{1H} NMR (25-90 °C) did not show interconversion of 2a and 2b. Carbonylation of the mixture of the two isomers yielded the CO inserted-products 3a and 3b (1:1.3), together with unreacted 2a. The molecular structure of [Ir4-(CO)8(η1-C(O)Ph)(μ 3-η3-PhPC(H)CPh)(μ-PPh2)] (isomer 3b), established by an X-ray analysis, is similar to that of 2b, except for the acyl group that remains bound to the same Ir atom but occupies the neighboring radial site. Multinuclear NMR studies showed that the η1-C(O)Ph group in isomer 3a occupies the same axial position as η1-Ph in 2a. A mechanism involving migration of the η1-Ph group in 2a and 2b, upon carbonylation, to give 3b and 3a, respectively, has been proposed.162248334838Garrou, P.E., (1995) Chem. Rev., 85, p. 171Deeming, A.J., Kimber, R.E., Underhill, M., (1973) J. Chem. Soc., Dalton Trans., p. 2589Brown, S.C., Evans, J., Smart, L.E., (1980) J. Chem. Soc., Chem. Commun., p. 1021Deeming, A.J., Kabir, S.E., Powell, N.I., Bates, P.A., Hursthouse, M.B., (1987) J. Chem. Soc., Dalton Trans., p. 1529Briard, P., Cabeza, X.A., Llamazares, A., Ouahab, L., Riera, V., (1993) Organometallics, 12, p. 1006. , and references thereinBergougnou, C., Bonnet, J.J., Fompeyrine, P., Lavigne, G., Lugan, N., Mansilla, F., (1986) Organometallics, 5, p. 60Deeming, A.J., Hardcastle, K.I., Kabir, S.E., (1988) J. Chem. Soc., Dalton Trans., p. 827Lugan, N., Bonnet, J.J., Ibers, J.A., (1988) Organometallics, 7, p. 1538Colbran, S.B., Irele, P.T., Johnson, B.F.G., Lahoz, F.J., Lewis, J., Raithby, P.R., (1989) J. Chem. Soc., Dalton Trans., p. 2023Sabo, S., Chaudret, B., Gervais, D., (1983) J. Organomet. Chem., 258, pp. C19Dubois, R.A., Garrou, P.E., (1986) Organometallics, 5, p. 466Blickensderfer, J.R., Kaesz, H.D., (1975) J. Am. Chem. Soc., 97, p. 2681Bonnet, J.J., Lavigne, G., Lugan, N., (1987) Inorg. Chem., 26, p. 585Deeming, A.J., Smith, M.B., (1993) J. Chem. Soc., Dalton Trans., p. 2041Benvenutti, M.H.A., Braga, D., Grepioni, F., Mann, B.E., Vargas, M.D., (1993) Organometallics, 12, p. 2955Vargas, M.D., Pereira, R.M.S., Braga, D., Grepioni, F., (1993) J. Chem. Soc., Chem. Commun., p. 1008Careni, M., Mori, G., Predieri, G., Rezende, N.S., Sappa, E., (1993) J. Chromatogr., 634, p. 143Farrugia, L.J., Rae, S.E., (1992) Organometallics, 11, p. 196Predieri, G., Tiripicchio, A., Vignali, C., Sappa, E., (1988) J. Organomet. Chem., 342, pp. C33Harding, M.M., Nicholls, B.S., Smith, A.K., (1983) J. Chem. Soc. Dalton Trans., p. 1479Carty, A.J., MacLaughlin, S.A., Nucciaroni, D., (1987) Phosphorus-31 NMR Spectroscopy in Stereochemical Analysis, , Verkade, J. G., Quin, L. D., Eds.VCH: Deerfield Beach, FL, Chapter 16Regragui, R., Dixneuf, P.H., Taylor, N.J., Carty, A.J., (1986) Organometallics, 5, p. 1MacLaughlin, S.A., Carty, A.J., Taylor, N.J., (1982) Can. J. Chem., 60, p. 87Collman, J.P., Hegedus, L.S., Norton, J.R., Finke, R.G., (1987) Principles and Applications of Organotransition Metal Chemistry, , University Science Books: Mill Valley, CABassetti, M., Sunley, G.J., Fanizzi, F.P., Maitlis, P.M., (1990) J. Chem. Soc., Dalton Trans., p. 1799Monti, D., Frachey, G., Bassetti, M., Haynes, A., Sunley, G.J., Maitlis, P.M., Cantoni, A., Bocelli, G., (1995) Inorg. Chim. Acta, 240, p. 495Sheldrick, G.M., (1993) SHELX93, Program for Crystal Structure Determination, , University of Gottingen: Göttingen, GermanyWalker, N., Stuart, D., (1983) Acta Crystallogr., Sect. B, 39, p. 158Keller, E., SCHAKAL93, Graphical Representation of Molecular Models, , University of Freiburg, Freiburg, FRG