Rhodium cyclopentadienyl cations

The compound Rh( 5116)2 has not yet been obtained, but the action of cyclopentadienyl magnesium bromide on rhodium (III) acetylacetonate yields a derivative of the cation [Rh( 6H6)2], which forms a yellow solution in water (25). It gives precipitates with the usual reagents and is generally similar in properties to the [Co(CsHs) o] + ion. 

On treatment with proton sponge 1, cationic rhodium complexes of type 262 have been shown to undergo double intramolecular dehydrofluorinative/C—C coupling to produce quantitatively rhodium complexes of hybrid cyclopentadienyl-phosphine ligands 263 (equation 27)240. 

The preparation of two cyclo-octatetraene-gold complexes, (ct)AuCl and (cot)-AU2CI4, has been reported. The structures of biscyclo-octatetraenyl complexes of titanium, vanadium, thallium, and uranium, were deduced from their i.r. spectra. Protonation of (p-cyclo-octatetraene) (p-cyclopentadienyl) complexes has been studied. For the ruthenium and osmium complexes protonation occurs on the eight-membered ring to give CgH moiety co-ordinated to the metal atom via both an T -alkyl and an olefin-metal bond. For the cobalt and rhodium complexes a bicyclic cation (287) is produced which undergoes isomerization to the monocyclic (288). ... 

An -ray structure determination of a cationic intermediate (8) isolated during the acylation of [Fe(CO)8(rraAw, ra j-hexa-2,4-diene)] establishes that Friedel-Crafts acylation involves stereospecific endo attack. The stereochemistry of reaction parallels protonation of tricarbonyl(diene)iron, cyclopentadienyl(cyclohexa-l,3-diene)rhodium complexes, and ( j -cyclopentadienyl)rhodium complexes of limonene (9), a-phellandrene (10), and carvone (11). ... 

The role of the cyclopentadienyl ligand in the a-bond activation of methane by [Co(ri -C5H5)] has been studied and a reaction mechanism proposed which includes several intermediates containing Co-alkyl bonds.A series of Ir-Me species have been synthesised as part of an investigation into the effect of the hydridotris(pyrazolyl)borate ligand on C-H bond activation by cationic iridium complexes. The rhodium species 23 has been synthesised as part of a study into... 

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