Rhodium cyclopentadienyls

The rhodium cyclopentadienyl complex [T75-C5(CH3)5RhCl2]2, in the presence of base at 50 atm H2, also effects stereoselective catalytic hydrogenation of benzenes. Substrates with unprotected —OH or —C02H groups were not effectively hydrogenated, but aryl ethers, esters, and ketones and N,iV -dimethylaniline were all reduced, some-... 

O-Methylation of mandelic acid leads to the enantiomers of a-methoxy-M-phcnylacetic acid (10), which are also commercially available. This methylation without noticeable racemiza-tion was achieved with diazomethane, using aluminum tris(tert-butanoate) as catalyst8. Alternatively, dimethyl sulfate/ sodium hydroxide has been used15, as described in detail for the racemic compound10. The acids have been used for the construction of quite sophisticated chiral auxiliaries, e.g., a rhodium cyclopentadienyl complex (Section 7.2.2.), and for chiral dienes applied in both normal and inverse Diels-Alder reactions (Section D.1.6.1.1.1.). Chiral dienes, e.g., 1, for normal Diels -Alder reactions were prepared by pyrolysis (460 C) of a tricyclic precursor cstcrified with (S)-O-methylmandeloyl chloride or with the free acid and dicyclohexylcarbodiimide/4-dimethylaminopyridine11 -13. 

Reactions with aikynes may aiso result in the formation of cyclized products. Thus a ruthenium-catalysed reaction with aromatic amides has been used to give isoquinoline derivatives. On the basis of values of the kinetic isotope effect, A h/ d> proposed that the rate-determining step is a concerted acetate-assisted metalation-deprotonation process to yield the intermediate (30), followed by aikyne insertion and ring closure. The reaction of arylketones with alkynes may yield indenols when catalysed by rhodium cyclopentadienyl in the presence of silver and copper salts. The reaction proceeds regioselectively, so that reaction of acetophenone with 1-phenyl-1-propene... 

Similar complexes of the type ar -zirconocene/rhodium-cyclopentadienyl, such as 353, were also obtained and fully characterized. ... 

Reaction of the cyclopentadienyl rhodium and iridium tris(acetone) complexes with indole leads to the species 118 (M = Rh, Ir) [77JCS(D)1654 79JCS(D)1531]. None of these compounds deprotonates easily in acetone, but the iridium complex loses a proton in reaction with bases (Na2C03 in water, r-BuOK in acetone) to form the ri -indolyl complex 119. This reaction is easily reversed in the presence of small amounts of trifluoroacetic acid. 

Table 2 Formation of cyclopentadienyl derivatives 75 via transmetallated alkyne-inserted rhodium-carbene complexes (see Scheme 15)...

Scheme 43.3 Cofactor reduction using the pentamethyl cyclopentadienyl rhodium(bipyridine) complex (9/10).

Cyclopentadienyl rhodium silyl derivatives include Cp Rh(H)2(SiEt3)2, which has been used as a precursor to heterometallic clusters.257 The photolysis of CpRh(PPh3)(7]2-C2H4) with SiHR3 (R = Et, Pr1) results in oxidative... 

Oxybis[bis(cyclopentadienyl)titanium], 3803 Pentamethylcyclopentadienyl-bis(thiolatothiatriazyl)rhodium, 3534 Poly(cyclopentadienyltitanium dichloride), 1843... 

C7H704Rh, Rhodium(I), dicarbonyl(2,4-pentanedionato)-, 34 128 C7HgN4, Bis(l-pyrazolyl)methane, bpm, complex with nickel(ll), 34 139 CgH5FeKN20, Ferrate(ll), carbonyldicyano-(cyclopentadienyl)-, potassium, 34 172 CgH23Ns, Tetraethylenepentamine, tetren, complex with nickel(ll), 34 147, 148 CgH24B2N4, Diborane(4), tetrakis(dimethyl-amino)-, 34 1... 

The cyclopentadienyl group, or its substituted derivatives, might be expected to stabilize dioxygen complexes or to ultimately react with dioxygen under the influence of transition metal centers. In rare cases, other (uncharged) dienes can also be found to stabilize dioxygen complexes of rhodium. Also discussed here are some reports of metallaben-zene systems and their reactions with dioxygen. 

Rhodium (i 5-Cyclopentadienyl)-iodo-pyridin-trifluoromethyl-XIII/9b. 348 (F3C—RhR] + Py)... 

Although much effort has been devoted to decarbonylation of cyclopropylcarbonyl metal complexes (vide supra), only (cyclopentadienyl)dicarbonyliron (Fp) derivatives have been successfully decarbonylated either photochemically22,24 or using Wilkinson s rhodium catalyst [(PPh3)2RhCl]2 (equation 35). Further decarbonylation by irradiation led to metallacyclopentane formation, whereas thermal decomposition resulted in the formation of the corresponding Cp(CO)Fe(allyl) complexes. 

Bromopentacarbonylmanganese, 49 tom -Bromotetracarbonyl(methyl-methylidyne)chromium, 50 frmethylidyne)tungsten, 49 Carbonylhydridotris(triphenylphosphine)-rhodium(I), 329 Chromium carbonyl, 51 Decacarbonyldimanganese, 49 Dicarbonylcyclopentadienylcobalt, 96 Dicarbonyl(cyclopentadienyl)[(dimethyl-sulfonium)methyl]iron(II) tetrafluoroborate, 98... 

Fig, 15, Structure of the four-membered dimetallacycle [ i-bis(trifluoromethyl)acetyl-ene]bis[carbonyl(r)5-cyclopentadienyl)rhodium](/ /i—Rh) (126a) (244), a typical example of a strictly planar M2C2 framework. Bond lengths in picometers. 

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