Homogeneous tris-triphenylphosphine

A very significant recent development in the field of catalytic hydrogenation has been the discovery that certain transition metal coordination complexes catalyze the hydrogenation of olefinic and acetylenic bonds in homogeneous solution.Of these catalysts tris-(triphenylphosphine)-chloror-hodium (131) has been studied most extensively.The mechanism of the deuteration of olefins with this catalyst is indicated by the following scheme (131 -> 135) ... 

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. 

The tritium labelled V.fischeri AHL 31 was prepared with a specific activity of 45-55 Ci/mmol by the tritiation of the corresponding unsaturated precursor, AT-(3-oxo-4-hexenoyl)-L-HSL 30 in the presence of a homogeneous Wilkinson s catalyst, tris(triphenylphosphine)rhodium[I] chloride (Scheme 13) [71]. 

Many catalysts, certainly those most widely used such as platinum, palladium, rhodium, ruthenium, nickel, Raney nickel, and catalysts for homogeneous hydrogenation such as tris(triphenylphosphine)rhodium chloride are now commercially available. Procedures for the preparation of catalysts are therefore described in detail only in the cases of the less common ones (p. 205). Guidelines for use and dosage of catalysts are given in Table 1. 

Reduction of the double bond only was achieved by catalytic hydrogenation over palladium prepared by reduction with sodium borohydride. This catalyst does not catalyze hydrogenation of the aldehyde group [31]. Also sodium borohydride-reduced nickel was used for conversion of cinnamaldehyde to hydrocinnamaldehyde [31]. Homogeneous hydrogenation over tris(triphenylphosphine)rhodium chloride gave 60% of hydrocinnamaldehyde and 40% of ethylbenzene [5(5]. Raney nickel, by contrast, catalyzes total reduction to hydrocinnamyl alcohol [4S. Total reduction of both the double... 

Besides solid transition metals, certain soluble transition-metal complexes are active hydrogenation catalysts.4. The most commonly used example is tris(triphenylphosphine)-chlororhodium, which is known as Wilkinson s catalyst.5 This and related homogeneous catalysts usually minimize exchange and isomerization processes. Hydrogenation by homogeneous catalysts is believed to take place by initial formation of a rc-complex, followed by transfer of hydrogen from rhodium to carbon. 

The activity of homogeneous catalysts also has been demonstrated Wilkm son s catalyst tris(triphenylphosphine) rhodium chloride induces petfluoroalkyl iodides to add to olefins at 80 °C [10] (equation 10) Tetrakis(tnphenylphosphme)-palladtum promotes the addition to both alkenes and alkynes in hexane [11] Amines and amine salts induce addition at 120-140 °C [12] (equation 11)... 

In the early papers (26, 17) on homogeneous hydrogenation by tris(triphenylphosphine)rhodium(I) chloride, Wilkinson and coworkers found the kinetic isotope effect for deuterium addition to be... 

In 1965 Wilkinson invented the rhodium-tris(triphenylphosphine) catalyst as a hydrogenation catalyst [60]. It still forms the basis for many of the chiral hydrogenations performed today. The most effective homogeneous hydrogenation catalysts are complexes consisting of a central metal ion, one or more (chiral) ligands and anions which are able to activate molecular hydrogen and to add the two H atoms to an acceptor substrate. Experience has shown that low-valent Ru,... 

Hydrogenation of olefins on a soluble catalyst has been reported recently [61,62]. Tris(triphenylphosphine)rhodium chloride [(Ph3P)3RhCl] will promote homogeneous hydrogenation of reactive double bonds, including the A -bond in Ai -dien"3-ones, where the product of deuteration was the ia,2a-dideutero-compound (17) [62]. The mechanism is not... 

In view of its industrial importance, a number of homogeneous catalysts have been examined for use in selective hydrogenations of nitroalkanes to amines.Tris(triphenylphosphine)ruthenium(II) chloride is particularly effective. The mechanism of this hydrogenation is known to involve nitronate anion formation. ... 

Tris(triphenylphosphine)chlororhodium(I). The homogenous catalysis of the hydrogenation of ethylene and other olefins by RhCl( PPha) a, recently discovered by Wilkinson and co-workers (6J), probably involves a dihydride intermediate. A plausible mechanism for this reaction, involving steps of the type already described, is shown in Reaction 36. 

Selective hydrogenation of polyenes to monoenes is possible with homogeneous catalysts. Dichlorodicarbonylbis(triphenylphosphine)ruthenium(II) catalyzed the selective reduction of 1,5,9-cyclododecatriene to cyclododecene, as well as dichloro-tris(triphenylphosphine)ruthenium(II) ... 

Heterogeneous catalysis (Pd) in tritiation of l,4-dien-3-ones leads mainly to l) -tritiation (ca. 76%). Tritium distribution studies indicate that the reaction is probably a 1,4-addition of tritium onto the more exposed p-face of the dienone, which is tilted downwards with respect to ring b (211). Homogeneous catalysis with tris(triphenylphosphine)rhodium chloride, however, is known to favour la-tritiation. Similarly, homogeneous hydrogenation of the less reactive... 

Tris(triphenylphosphine)ruthenium(ll) chloride is a good catalyst for the homogeneous hydrogenation of aliphatic aldehydes to alcohols. Ketones and nitro-groups are not reduced under these conditions. ... 

A method for the electrochemical reduction of D-xylose to 2-deoxy-D-r/rr o-pentitol has been described. The homogeneous hydrogenation of sugars using tris-triphenylphosphine ruthenium chloride is improved in the presence of hydrogen chloride, which inhibits competitive decarbonylation of the sugar. L-(2,3)-Threitol is easily prepared from ( + )tartaric acid by lithium aluminium hydride reduction of the 2,3-0-isopropylidene derivative of diethyl tartrate, followed by acid hydrolysis of the resultant ketal. ... 

Osborn, J. A. Jardine, R H. Young, J. R Wilkinson, G. The preparation and properties of tris(triphenylphosphine)halogeno-rhodium(I) and some reactions thereof including catalytic homogeneous hydrogenation of olefins and acetylenes and their derivatives. /. Chem. Soc. A 1966,1711-1732. 

Tris(triphenylphosphine)chlororhodium (I) (Wilkinson s catalyst) has been the most widely studied homogeneous hydrogenation catalyst. Analogous polymeric catalysts have been prepared for use in hydrogenation. A variety of alkenes, cycloalkenes, dienes, and alkynes have been reduced by polymer-bound catalysts, indicating the wide scope of their use (Grubbs et al., 1977). 

The homogenous catalyst tris(triphenylphosphine)chlororhodium was chosen for hydrogenation to avoid the possibility of hydrogenolysis of the allylic acetate. 

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