Hydrogenation catalysts Chlorotris rhodium

Aldehydes, both aliphatic and aromatic, can be decarbonylated by heating with chlorotris(triphenylphosphine)rhodium or other catalysts such as palladium. The compound RhCl(Ph3P)3 is often called Wilkinson s catalyst.In an older reaction, aliphatic (but not aromatic) aldehydes are decarbonylated by heating with di-tert-peroxide or other peroxides, usually in a solution containing a hydrogen donor, such as a thiol. The reaction has also been initiated with light, and thermally (without an initiator) by heating at 500°C. 

Chlorotris(triphenylphosphine)rhodium (Wilkinson s catalyst) is among the most efficient catalysts and permits hydrogenation in homogeneous solution. The Rh complex is readily prepared by heating rhodium chloride with excess triphenylphosphine in ethanol. 

Reduction of the heterocyclic ring of the benzo[h]quinoline occurs selectively using chlorotris(triphenylphosphine)rhodium(I) as the hydrogenation catalyst (R.H. Fish. J.L. Tan and A. D. Thormodsen, J. org. Chem., 1984, 4500). 

Similarly, reduction of the unsaturated lactone 4 by hydrogenation over palladium on carbon yielded only the tetrasubstituted monohydrogenated product. In this case Wilkinson s catalyst [chlorotris(triphenylphosphane)rhodium] is the catalyst of choice for the regio- and diastereose-lective reduction of the exocyclic double bond7. 

Acyl chlorides containing an a hydrogen are smoothly converted to alkenes, with loss of HCI and CO, on heating with chlorotris(triphenylphosphine)rhodium, with metallic platinum, or with certain other catalysts. The mechanism probably involves conversion of RCH2CH2COCI to RCH2CH2—RhCO(Ph3P)2Cl2 followed by a concerted syn elimination of Rh and H. See also 14-39 and 19-12. 

The water-soluble Wilkinson-type catalyst chlorotris(diphenylphosphinoben-zene-m-sulfonate)rhodium(I), RhQfdpm) (19), acts as catalyst for H2-evolution [158], hydrogenation and hydroformylation [159]. In a photosystem composed of Ru(bpy)i+ as photosensitizer, ascorbic acid, HA, as electron donor and RhCl(dpm)3, hydrogen evolution proceeds with a quantum efficiency corresponding to (p = 0.033. In the presence of ethylene or acetylene, hydrogen evolution is blocked and hydrogenation of the unsaturated organic substrates predominates. Table 6 summarizes the quantum yields for H2-evolution and... 

Some catalysts suffer a different type of alkyne poisoning. Chlorotris(triphenylphosphine)rhodium(I) is an effective terminal alkyne polymerization catalyst. When this complex is used in the reduction of these alkynes, it gradually loses its activity because of the competing polymerization reaction. Even initially the rate of alkyne hydrogenation is much slower than that of the corresponding alkene because of the greater binding constant of the former substrate. 

Enantiomerically pure carboxylic acids are routinely obtained from N-acylsultams by Hydrogen Peroxide assisted saponification with Lithium Hydroxide in aqueous THF. 4 Alternatively, transesterification can be effected under neutral conditions in allyl alcohol containing Titanium Tetraisopropoxide, giving the corresponding allyl esters which can be isomerized/hydrolyzed with Wilkinson s catalyst (Chlorotris(triphenylphosphine)rhodium(I)) in Et0H-H20. This provides a convenient route to carboxylic acids containing base-sensitive functionality. Primary alcohols are obtained by treatment with L-Selectride (Lithium Tri-s-butylborohydride) in THF at ambient temperature. ... 

Chlorotris(triphenylphosphine)rhodium(I), [RhCl(PPh3)3], was reported independently by three groups in 1965, " and its application to catalytic homogeneous hydrogenation has been studied intensively by Wilkinson s group. The Wilkinson catalyst is now the most widely used for hydrogenation of a variety of unsaturated substrates, and several extensive reviews of this catalyst have been published. ... 

Selective reduction of both double bonds in a,jS-unsaturated carbonyl compounds that also contain an isolated olefin is possible with appropriate catalyst and reaction conditions . Chlorotris(biphenylphosphine)rhodium hydrogenates the isolated double bond. Thus, carvone, 13, is reduced to dihydrocarvone, 14, with careful measure of the uptake of Hj ... 

The discovery of chlorotris(triphenylphosphine)rhodium and its utility as the first practical homogeneous catalyst for the hydrogenation of C=C and C=C bonds opened up an enormous and still developing field of chemistry, not only in catalysis but in stoichiometric reactions. ... 

Chlorotris(triphenylphosphine)rhodium(i) can also catalyse hydrogen transfer from dioxan to an alkene. The rate-determining step in this reaction is considered to be oxidative addition of C—bonds of dioxan to the catalyst ... 

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