Iridium metal-carbon bond

Alaimo, P.J.. Arndtsen, B.A. and Bergman. R.G. (2000) Alkylation of iridium via tandem carbon-hydrogen bond activation/decarbonylation of aldehydes. Access to complexes with tertiary and highly hindered metal-carbon bonds. OrganometaUics, 19 (11), 2130-2143. 

The other carbon dioxide complex characterized by x-ray crystallography contains two linked C02 molecules in the coordination sphere (116). This complex, [IrCl(C204)(PMe3)3], was prepared by the interaction of C02 with chloro(cyclooctene)[tris(trimethylphosphine)]iridium(I), [IrCl(C8 H j 4)-(PMe3)3], in benzene solution. The structure, (25), shows essentially octahedral coordination about the iridium center, with one metal-carbon bond and a five-membered chelate ring formed with the second C02 molecule. 

The reduction behaviour of the alkylidene adduct of a cobalt-dithiolene complex (423) has been examined548 and the study has shown that, when the alkylidene-bridged structure (423) is reduced by one electron, it isomerizes rapidly and quantitatively to the ylide form (424). This represents the first example of reversible isomerization of the metal-carbon bond in a cobaltadithiolene complex. A surprising cis- to tra .s-dihydride isomerization which is unprecedented for 18-electron six-coordinate complexes has been observed549 in an octahedral iridium-c7.y-di hydride complex. 

Similar, albeit slower, reactions prevail in the later transition metals. The carbonyl oxygen of 3-metallacyclobuta-none complexes is the typical site for protonation rather than the less polarized metal-carbon bond (Section 2.12.7). The reaction of iridacyclobutanone complex 86 with />-toluenethiol, however, returns the carbon-bound iridium enolate complex 87 by eventual protonation of one Ir-C bond (Equation 28) <1995JOM143>. 

M. J. Wax, J. M. Stryker, J. M. Buchanan, C. A. Kovac, and R. G. Bergman, Reversible C—H Insertion/Reductive Elimination in ( 5-Pentamethylcyclopentadienyl)(trimethyl-phosphine)iridium Complexes. Use in Determining Relative Metal-Carbon Bond Energies and Thermally Activating Methane, J. Am. Chem. Soc. 106, 1121-1122 (1984). 

Lefort L, Lachicotte RJ, Jones WD. Insertion of SO2 into the metal-carbon bonds of rhodium and iridium compounds, and reactivity of the S02-inserted species. Organometallics 1998 17(7) 1420-1425. 

Iridium(I) complexes with metal-carbon o-bonds are markedly more stable than those of Rh(I). In contrast to Rh(I), both EtCOIr(CO)2(PPh3)2... 

Among the catalysts used are Lewis acids991 and phosphine-nickel complexes.992 Certain of the reverse cyclobutane ring openings can also be catalytically induced (8-40). The role of the catalyst is not certain and may be different in each case. One possibility is that the presence of the catalyst causes a forbidden reaction to become allowed, through coordination of the catalyst to the -it or a bonds of the substrate.993 In such a case the reaction would of course be a concerted 2S + 2S process. However, the available evidence is more consistent with nonconcerted mechanisms involving metal-carbon a-bonded intermediates, at least in most cases.994 For example, such an intermediate was isolated in the dimerization of nor-bornadiene, catalyzed by iridium complexes.995... 

It appears that the stronger metal-carbon interaction on iridium surfaces imposes the periodicity on the carbon atoms in the overlayer, while the structure of the graphite overlayer on the Pt( III) face is independent of the substrate periodicity and rotational symmetry. Ordering of the dehydrogenated carbonaceous residue on the stepped iridium surface is absent when the surface is heated to above 1100 K. Atomic steps of (100) orientation appear to prevent the formation of ordered domains that are predominant on the Ir(lll) crystal face. The reasons for this are not clear. Perhaps the rate of C-C bond breaking on account of the steps is too rapid to allow nucleation and growth of the ordered overlayer. On the (111) face, the slower dehydro-... 

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