Homogeneous Hydrogenated

Wilkinson s catalyst [Rh(Ph3P)3Cl]. An important catalyst for homogeneous hydrogenation which also catalyses oxidation by O2 and CO abstraction from organic derivatives. 

Chiral ligands for homogeneous hydrogenation of olefins and ketones... 

F. J. McOiiillin, Homogeneous Hydrogenation in Organic Chemisty, D. Reidel Publishing Co., Boston, Mass., 1976, pp. 46—48. 

B. R. James, Homogeneous Hydrogenation, John Wiley Sons, Inc., New York, 1973, p. 148. 

N O Y O R I Chiral homogeneous hydrogenation Homogeneous chiral hydrogenation ol unsaluraled alcohols, or cartMxyNc acids, enamides, ketones in the presence ol BINAP Ru or Rh complex 8 as catalyst. 

OH Polybutadiene Homogeneous hydrogenation [e.g., Ni or CoAriethyl aluminum (or Ru, Rh catalysis)] heterogeneous catalysis (Raney Ni) Hydrogenated mixed 1.4- and 1,2-polybutadienes as heat-resistant polyurethane prepolymers... 

The hydrogenation of 5a-cholestanone (58) in methanolic hydrobromic acid over platinum gives 3j5-methoxycholestane ° (61). This compound is also obtained from the palladium oxide reduction of (58) in methanol in the absence of acid. Hydrogenation of 5 -cholestanone also gives the 3j5-methoxy product under these conditions. Reduced palladium oxides are quite effective for the conversion of ketones to ethers. The use of aqueous ethanol as the solvent reduces the yield of ether. Ketals are formed on attempted homogeneous hydrogenation of a 3-keto group in methanol. ... 

An even more effective homogeneous hydrogenation catalyst is the complex [RhClfPPhsfs] which permits rapid reduction of alkenes, alkynes and other unsaturated compounds in benzene solution at 25°C and 1 atm pressure (p. 1134). The Haber process, which uses iron metal catalysts for the direct synthesis of ammonia from nitrogen and hydrogen at high temperatures and pressures, is a further example (p. 421). 

In benzene or similar solvents, tris(triphenylphosphine)halogenorhodium(I) complexes, RhX[P(C6H5)3]3, are extremely efficient catalysts for the homogeneous hydrogenation of nonconjugated olefins and acetylenes at ambient temperature and pressures of 1 atmosphere (6). Functional groups (keto-, nitro-, ester, and so on) are not reduced under these conditions. 

Good reviews of asymmetric homogeneous hydrogenation catalysts and their syntheses are those of Caplar et al. 28) and Vineyard et al. (106). 

F. J. McQuillin, Homogeneous Hydrogenations in Organic Chemistry. Reidel, Boston, Massachusetts, 1976. 

E. Joo, L. A. Oro, Homogeneous Hydrogenation, Kluwer Academic Publisher, Dordrecht, 1994. 

RhCl(PPh3)3 is a very active homogenous hydrogenation catalyst, because of its readiness to engage in oxidative addition reactions with molecules like H2, forming Rh—H bonds of moderate strength that can subsequently be broken to allow hydride transfer to the alkene substrate. A further factor is the lability of the bulky triphenylphosphines that creates coordinative unsaturation necessary to bind the substrate molecules [44]. 

RhCl(PPhi)i as a homogenous hydrogenation catalyst [44, 45, 52]. The mechanism of this reaction has been the source of controversy for many years. One interpretation of the catalytic cycle is shown in Figure 2.15 this concentrates on a route where hydride coordination occurs first, rather than alkene coordination, and in which dimeric species are unimportant. (Recent NMR study indicates the presence of binuclear dihydrides in low amount in the catalyst system [47].)... 

A. J. Bircii u. D. H. Williamson, Homogeneous Hydrogenation Catalysts in Organic Synthesis, Organic Reactions, Vol. XXIV, S. 4-186, 1976. 

J. D. Morrison u. W. F. Master, Asymmetric Homogenous Hydrogenation, Advances in Catalysis, Vol. XXV,... 

The mechanism of homogeneous hydrogenation catalyzed by RhCl(Ph3P)3 ° involves reaction of the catalyst with hydrogen to form a metal hydride (PPh3)2RhH2Cl (43), which rapidly transfers two hydrogen atoms to the alkene. 

For a review of homogeneous hydrogenation directed to only one face of a substrate molecule, see Brown, J.M. Angew. Chem. Int. Ed. Engl., 1987, 26, 190. 

A. Homogeneous Hydrogenation Catalyzed by Cobalt Cyanide Complexes. 433... 

Most organopentacyanides are stable towards [Co(CN)jH], with the exception of allyl complexes which react to liberate propylene derivatives (105). This is one of the steps in the homogeneous hydrogenation of butadienes catalyzed by cobalt cyanide complexes (see Section VII,A). 

The cobalt cyanide complexes are excellent catalysts for the homogeneous hydrogenation at room temperature of a variety of organic (and inorganic)... 

Only a few other cobalt complexes of the type covered in this review (and therefore excluding, for example, the cobalt carbonyls) have been reported to act as catalysts for homogeneous hydrogenation. The complex Co(DMG)2 will catalyze the hydrogenation of benzil (PhCOCOPh) to benzoin (PhCHOHCOPh). When this reaction is carried out in the presence of quinine, the product shows optical activity. The degree of optical purity varies with the nature of the solvent and reaches a maximum of 61.5% in benzene. It was concluded that asymmetric synthesis occurred via the formation of an organocobalt complex in which quinine was coordinated in the trans position (133). Both Co(DMG)2 and cobalamin-cobalt(II) in methanol will catalyze the following reductive methylations ... 

R. S. Coffey Recent advances in homogeneous hydrogenation of carbon-carbon multiple bonds, pp. 5-76. 

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