Tris rhodium chloride hydrogenation

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. 

Divalent sulfur is a poison for most noble metal catalysts so that catalytic hydrogenation of sulfur-containing compounds poses serious problems (p. 10). However, allyl phenyl sulfide was hydrogenated over tris trisphenyl-phosphine)rhodium chloride in benzene to give 93% yield of phenyl propyl sulfide [674. ... 

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... 

Hydrogenation of phthalic anhydride over copper chromite afforded 82.5% yield of the lactone, phthalide, and 9.8% of o-toluic acid resulting from hydrogenolysis of a carbon-oxygen bond [1015]. Homogeneous hydrogenation of a,a-dimethylsuccinic anhydride over tris(triphenylphos-phine)rhodium chloride gave 65% of a,a-dimethyl- and 7% of )S,)S-dimethyl-butyrolactone [1016]. 

Methyl cinnamate was reduced quantitatively to methyl 3-phenylpropa-noate by hydrogen over colloidal palladium at room temperature and atmospheric pressure [7057] ethyl cinnamate was reduced to ethyl 3-phenyIpropa-noate over tris(triphenylphosphine)rhodium chloride in ethanol at 40-60° and 4-7 atm in 93% yield [55], and over copper chromite at 150° and 175 atm in 97% yield [420]. On the other hand, hydrogenation of ethyl cinnamate over... 

Previous work has shown that the electronic characteristics of the benzene substituent in triarylphosphine chlororhodium complexes have a marked influence on the rate of olefin hydrogenation catalyzed by these compounds. Thus, in the hydrogenation of cyclohexene using L3RhCl the rate decreased as L = tri-p-methoxyphenylphosphine > triphenylphosphine > tri-p-fluorophenylphosphine (14). In the hydrogenation of 1-hexene with catalysts prepared by treating dicyclooctene rhodium chloride with 2.2-2.5 equivalents of substituted triarylphosphines, the substituent effect on the rate was p-methoxy > p-methyl >> p-chloro (15). No mention could be found of any product stereochemistry studies using this type of catalyst. 

P-31 NMR was a powerful tool in studies correlating the structure of tertiary-phosphine-rhodium chloride complexes with their behavior as olefin hydrogenation catalysts. Triphenylphosphine-rhodium complex hydrogenation catalyst species (1) were studied by Tolman et al. at du Pont and Company (2). They found that tris(triphenylphosphine)rhodium(I) chloride (A) dissociates to tri-phenylphosphine and a highly reactive intermediate (B). The latter is dimerized to tetrakis(triphenylphosphine)dirhodium(I) dichloride (C). 

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... 

Enones are reduced to saturated ketones by catalytic hydrogenation provided the reaction is stopped following the absorption of 1 mol of hydrogen. " A number of catalysts were found useful for this, including platinum, platinum oxide,Pt/C, " Pd/C, - Rh/C, " tris(triphenylphosphine)rhodium chloride, - nickel-aluminum alloy in 10% aqueous NaOH, and zinc-reduced nickel in an aqueous medium. Mesityl oxide is formed from acetone and reduced in a single pot to methyl isobutyl ketone using a bifunctional catalyst which comprised palladium and zirconium phosphate (Scheme 20). 

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... 

Rhodium is a good catalyst for alkene hydrogenation (Section 6.1), as are many of its complexes such as tris(triphenylphosphine)rhodium chloride (Wilkinson s catalyst). 

Development by Geoffrey Wilkinson of a soluble catalyst for hydrogenation [tris(triphenylphosphine)rhodium chloride, Section 7.13 and Special Topic G] led to Wilkinson s earning a share of the 1973 Nobel Prize in Chemistry. His initial discovery, while at Imperial College, University of London, inspired many other researchers to create novel catalysts based on the Wilkinson catalyst. Some of these researchers were themselves recognized by the 2001 Nobel Prize in Chemistry, 50% of which was awarded to William S. Knowles (Monsanto Corporation, retired) and Ryoji Noyori (Nagoya... 

Materials. The ultraviolet initiator Darocur 1173 (2-hydroxy-2-methyl-l-phenyl-propan-1-one) was purchased from EM Science and was used as received. Dimethylacrylamide (DMA), methacryloyl chloride (MC), allyloxytrimethylsilane and (tris(triphenylphosphine)rhodium)chloride were purchased from Aldrich Chemical Co. DMA and MC were distilled under nitrogen prior to use. 1,3-Tetramethyldisiloxane, methacryloylpropyltrichlorosilane, and 1,3-tetramethyldisiloxane platinum complex (2 % platinum in xylenes) were purchased from Gelest, The fluorinated allylic ether, allyloxy octafluoropentane, was prepared by the phase transfer catalyzed reaction of allyl bromide with octafluoropentanol using tetrabutylammonium hydrogen sulfate, tetrahydrofuran and 50% (w/w) NaOH (11). The fluorinated side-chain methacrylate end-capped siloxane (FSi) was prepared according to a literature procedure. All other solvents and reagents were used as received. 

Olivetol-dy. The synthetic procedure of Pitt l. (6) was used with some modifications to increase the incorporation of deuterium. Methyl 5-(3,5-dimethoxyphenyl)penta-2,4-dienoate was reacted with LiAlDi+ followed by hydrogenation with D using the catalyst tris(triphenylphosphine)rhodium chloride. The 5-(3,5--dimethoxyphenyl)pentan-l-ol-l,1,2,3,4,5was then reacted with PBr3, LiAlDii, and BBr3 according to Pitt. (6) to yield... 

Wilkinson and co-workers (3) showed that the maximum activity of the tertiary phosphine rhodium(I) chloride catalysts occurred at a ligand. -rhodium ratio of about 2. This ratio was used in the systems studied for the effects of hydrogen pressure (Table I). In the triphenyl-phosphine system (abbreviated as L°), the rate of hydrogenation increased with pressure in the accessible pressure range, in accord with previous observations (2) by Wilkinson and co-workers. However, with the p-dimethylamino substituted tertiary phosphines L1 and L2 the rates of hydrogenation were essentially independent of the hydrogen pressure within the experimental errors. For tris (p-dimethylaminophenyl) phos-... 

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... 

---