Rhodium trichloride hydrogenation

Acetyl chlotide is reduced by vatious organometaUic compounds, eg, LiAlH (18). / fZ-Butyl alcohol lessens the activity of LiAlH to form lithium tti-/-butoxyalumium hydtide [17476-04-9] C22H2gA102Li, which can convert acetyl chlotide to acetaldehyde [75-07-0] (19). Triphenyl tin hydtide also reduces acetyl chlotide (20). Acetyl chlotide in the presence of Pt(II) or Rh(I) complexes, can cleave tetrahydrofuran [109-99-9] C HgO, to form chlorobutyl acetate [13398-04-4] in about 72% yield (21). Although catalytic hydrogenation of acetyl chlotide in the Rosenmund reaction is not very satisfactory, it is catalyticaHy possible to reduce acetic anhydride to ethylidene diacetate [542-10-9] in the presence of acetyl chlotide over palladium complexes (22). Rhodium trichloride, methyl iodide, and ttiphenylphosphine combine into a complex that is active in reducing acetyl chlotide (23). 

In the example of Fig. 7.15 [43j rhodium particles have been deposited by spin coat impregnation of a Si02/Si substrate with an aqueous solution of rhodium trichloride. After drying, the particles were reduced in hydrogen. The images show samples prepared at three different rotation speeds in the spin coating process, but with concentrations adjusted such that each sample contains about the same amount of rhodium atoms. The particles prepared at high rotation speeds are smaller, which... 

Surprisingly, there are only a few catalysts known capable of hydrogenating ketones in fully or largely aqueous systems. For example, most of the water-soluble rhodium, mthenium and indium phosphine complexes preferentially hydrogenate the C=C bonds in unsaturated ketones, as does the solvated ion pair formed from aqueous rhodium trichloride and Aliquat-336 [206]. 

Also, the chloride salt may be obtained by treating the yellow hydrous oxide, Rh203 5H20, with hydrochloric acid. The solution is carefully evaporated to form a dark red and water-soluble salt, rhodium trichloride tetrahy-drate, RhCl3 4H20. Heating the tetrahydrate in a stream of hydrogen chloride gas at 180°C forms the anhydrous salt, RhCR. 

The product is hydrated rhodium trichloride, which, according to Claus 6 contains eight molecules of water. Leidie,1 on the other hand, concluded that the amount of water varies and does not correspond to any definite hydrate. It is an amorphous, briek-red, deliquescent substance which, on heating to 90-95° C., still retains four to five molecules of water and two of hydrogen chloride. At 100° C. it loses water and hydrogen chloride simultaneously, and at 175-180° C. it is completely dehydrated. At 360° C. it becomes insoluble in water, hut it is most... 

When heated in dry hydrogen chloride gas, the water of crystallisation is liberated without the formation of rhodium sesquioxide, and the salt is transformed, slowly at 360° C., but rapidly at 440° C., into insoluble rhodium trichloride and potassium chloride. The latter may be dissolved away with hot water. 

The action of PF3 and hydrogen at high temperatures and pressures upon mixtures of anhydrous rhodium trichloride and copper forms (equation 57) the colorless liquid [RhH(PF3)4] (b.p. 89°C/ 725 torr).32-35-208 The liquid decomposes slowly at 20°C to form [Rh(PF2)(PF3)3]2, but on heating to 140nC it decomposes to rhodium metal.32 The hydrido complex can also be formed by the action of strong acids on the potassium salt K[Rh(PF3)4] (equation 58).34... 

The dihydrido complexes (Table 62) can be obtained by the oxidative addition of molecular hydrogen to rhodium(I) complexes (equation 186).10,119,922""926 The tri(f-butyl)phosphine complexes can be prepared either from the chlororhodium(I) complex,923 or rhodium trichloride.927 The former method seems more reliable since the latter reports the complex as a matt green substance, a color uncharacteristic of tertiary phosphine rhodium(III) complexes. Indeed, Masters and Shaw report that the related tertiary phosphines PBu2R (R = Et, Pr) give green rhodium(II) complexes in this reaction (see Section 48.5.2.1 above).268,269... 

The dihydrido complex [RhH2Cl(PPh3)2] is a very important intermediate in the homogeneous catalytic hydrogenation of alkenes.20 The monohydrido complexes (Table 63) can be made by the oxidative addition of HY species to rhodium(I) complexes (equation 187). Similar complexes can be obtained when bulky tertiary phosphines are allowed to react with alcoholic solutions of hydrated rhodium trichloride.268 269... 

One of the most carefully studied hydrogenations is the one catalyzed by the Rh(I) complex RhCl(PPh3)3, usually known as the Wilkinson catalyst. It was discovered in 1965 and is easily prepared by the reduction of rhodium trichloride hydrate in the presence of triphenylphosphine. 

The solvated ion pair [(C8Hi7)3NMe] [RhCl4]", formed from aqueous rhodium trichloride and Aliquat-336 in a two-phase liquid system, hydrogenates a,p-unsaturated ketones and esters selectively at the C==C double bond. The reduction of benzylideneacetone follows first-order kinetics in substrate below 0.2 M, and approaches second-order in hydrogen at partial pressures below 0.12 atm (1 atm = 101.3 kPa). The catalysis also depends on the nature of the solvent, the phase transfer catalyst and stirring rates. 

Olefin additions Bromine azide. Bromine chloride. Bromine (chlorine) dipyridine nitrate. N-Bromoacetamine. N-Bromoacetamide-DMSO-Water. N-Bromoacetamide-Hydrogen fluoride. n-Butyllithium. Dichloroketene. Dichloromethyl 2-chloromethyl ether. N,N-Dichlorourethane. Dichlorovinylene carbonate. Difluoramine. Ethyl azidoformate. Ethyl bromoacetate. Iodine azide. Iodine isocyanate. Iodine nitrate, lodobenzene dichloride. 1-lodoheptafluoropropane. Mercuric acetate. Nitrosyl chloride. Nitrosyl fluoride. Nitryl iodide. Rhodium trichloride. Silver fluoride. 

Azran, J., 0. Buchman, I. Amer, and J. Blum, Selective Hydrogenation of a, 8-Unsaturated Carbonyl Compounds by Rhodium Trichloride and Aliquat 336 in a Two-Phase Liquid System,7. MoL CataL, 34, 229 (1986). 

Proton magnetic resonance studies have also shown the presence of metal-hydrogen species in cyanide solutions of rhodium, platinum, and iridium (Table IX). In particular, the addition of CN- to a boiled aqueous solution of rhodium trichloride, followed by reduction with sodium boro-hydride, yields a solution that contains an Rh—H complex in moderately high concentrations and is stable in the absence of oxygen for several years (108). The observed coupling of the proton with the Rh10 nucleus (spin ) confirms the presence of an Rh—H bond (108). 

Hydrogenation. Rhodium in nanosize (from reduction of rhodium trichloride with NaBH4 and stabilized with water-soluble alkylammonium salts) is effective for hydrogenation of arenes at atmospheric pressure and room temperature under biphasic conditions. 

Similarly rhodium trichloride reduced by ethanol in the presence of tris-o-tolylphosphine gives an active rhodium(i) catalyst RhClKo-tolyOaPJa, via the characterised rhodium(ii) intermediate RhCl2[(o-tolyl)3P]2. The rhodium(i) in the above three-co-ordinate species can readily abstract a hydrogen atom, even from a second rhodium(i) molecule. Reduction of RhQ3(py)3 by NaBH in DMF yields a catalyst for Irans-deuteriation of olefins. ... 

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