Rhodium compounds synthesis

Synthesis. The most important starting material for rhodium compounds is rhodium(III) chloride hydrate [20765-98-4], RhCl3 nH2 O. Other commercially available starting materials useful for laboratory-scale synthesis include [Rh2(0000113)4] [5503-41 -3], [Rh(NH3)201]0l2 [13820-95-6], [Rh20l2(0O)4] [32408-34-7], and [Rh20l2(cod)2] [12092-47-6]. 

The hydrogenation of ketones with O or N functions in the a- or / -position is accomplished by several rhodium compounds [46 a, b, e, g, i, j, m, 56], Many of these examples have been applied in the synthesis of biologically active chiral products [59]. One of the first examples was the asymmetric synthesis of pantothenic acid, a member of the B complex vitamins and an important constituent of coenzyme A. Ojima et al. first described this synthesis in 1978, the most significant step being the enantioselective reduction of a cyclic a-keto ester, dihydro-4,4-dimethyl-2,3-furandione, to D-(-)-pantoyl lactone. A rhodium complex derived from [RhCl(COD)]2 and the chiral pyrrolidino diphosphine, (2S,4S)-N-tert-butoxy-carbonyl-4-diphenylphosphino-2-diphenylphosphinomethyl-pyrrolidine ((S, S) -... 

Rhodium compounds, 19 644-648 synthesis of, 19 646 uses for, 19 646-648 Rhodium oxide, 10 42 Rhodium plating, 9 822 19 648 Rhodium-platinum alloys, 19 602 Rhodochrosite, 15 540 Rhodochrosite ore, 15 589 Rhodococcus, as a host system for gene expression, 12 478 Rhodonite, 15 540 color, 7 331 Rhodopsin, 9 512 Rhoeadine, 2 90 Rhoedales... 

Catalyst Description. The LPO catalyst is a triphenylphosphine modified carbonyl complex of rhodium. Triphenylphosphine, carbon monoxide, and hydrogen form labile bonds with rhodium. Exotic catalyst synthesis and complicated catalyst handling steps are avoided since the desired rhodium complex forms under reaction conditions. Early work showed that a variety of rhodium compounds might be charged initially to produce the catalyst. Final selection was made on the basis of high yield of the catalyst precursor from a commodity rhodium salt, low toxicity, and good stability to air, heat, light, and shock. 

Rhodium compounds and complexes are also commercially important catalysts. The hydroformylation of propene to butanal (a precursor of hfr(2-ethyUiexyl) phthalate, the PVC plasticizer) is catalyzed by hydridocarbonylrhodium(I) complexes. Iodo(carbonyl)rhodium(I) species catalyze the production of acetic acid from methanol. In the flne chemical industry, rhodium complexes with chiral ligands catalyze the production of L-DOPA, used in the treatment of Parkinson s disease. Rhodium(II) carboxylates are increasingly important as catalysts in the synthesis of cyclopropyl compounds from diazo compounds. Many of the products are used as synthetic, pyrethroid insecticides. Hexacyanorhodate(III) salts are used to dope silver halides in photographic emulsions to reduce grain size and improve gradation. 

A variety of organic syntheses which involve reactions of olefins are catalyzed by rhodium compounds. As a consequence, considerable attention has been given to the study of the properties of olefin complexes of rhodium. The two ethylene complexes,1,2 the preparations of which are described here, are very useful in this respect. Moreover, since ethylene is very labile and volatile, a variety of compounds (including complexes of other olefins) are easily accessible from them by nucleophilic displacement of ethylene. Displacement of ethylene by carbon monoxide is illustrated by the synthesis of di-/z-chlorotetracarbonyldirhodium(I). 

As previously mentioned in paragraph 3.2.1., many patents on the use of palladium-based catalytic systems containing a metallic cocatalyst also mention the use of rhodium compounds (usually RhCL) in place of PdCL, but lower yields are always reported. We will not mention again here the same patents and will discuss only the systems for which a rhodium compound is explicitly mentioned as the, or the best, catalyst. Compared to the number of patents dealing with palladium compounds and metal-containing cocatalysts, the number of reports on similar rhodium-based systems is much more limited, confirming that, at least for the synthesis of carbamates and ureas, the combination of... 

R. C. Larock, New Applications of Organomercury, -Palladium, and -Rhodium Compounds in Organic Synthesis , in Aspects of Mechanistic and Organometallic Chemistry , ed. J. H. Brewster, Plenum Press, New York, 1978, p. 251. 

Vinyl acetate has been used as an acetylene equivalent in the synthesis of isoquinolones (Scheme 3.86) [90]. The reaction was catalyzed by a common rhodium compound and proceeded under very mild conditions to generate a diverse group of isoquinolones bearing a range of electron-donating and electron-withdrawing groups. 

Carbery et al. reported the novel design and rhodium-catalyzed synthesis of a heli-cenoidal DMAP analog bearing a 4-dialkylaminopyridine unit and a helical scaffold (Scheme 10.9) [11]. This compound could be employed successfully as a chiral Lewis base organocatalyst in the kinetic resolution of secondary alcohols with carboxylic acid anhydrides (Scheme 10.10) [11]. 

There are several examples of intramolecular reactions of monocyclic /3-lactams with carbenes or carbenoids most of these involve formation of olivanic acid or clavulanic acid derivatives. Thus treatment of the diazo compound (106) with rhodium(II) acetate in benzene under reflux gives (107), an intermediate in the synthesis of thienamycin (80H(14)1305, 80TL2783). 

Tertiary phosphine complexes [42] are the most important rhodium(I) compounds. RhCl(PPh3)3 ( Wilkinson s compound ), a hydrogenation catalyst, is the most important, but they exist in a range of stoichiometries. Synthesis follows several routes ... 

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