Rhodium, chlorotris catalyst

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. 

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. 

Braun reaction, 0-73). In a similar reaction, treatment of N-alkyl-substituted amides with chlorotris(triphenylphosphine)rhodium RhCl(PPh3)3 or certain other catalysts give nitriles and the corresponding alcohols.419... 

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... 

Not all decarbonylations give the expected product, and the relative yields are influenced by the rhodium catalyst employed. Chlorotris(triphenylphosphme)rhodium(I) rapidly and selectively decarbonylated the en /o-norbomene isomer shown in equation (4) to form a tricycline product, but [Rh(dppp)2]Cl additionally forms an isomeric alkene. In the case of the corresponding exo-isomer (equation 5), [RhCl(PPh3)3] is the less selective catalyst. It was also found that [Rh(dppp)2]Cl was a superior catalyst... 

The most important catalyst in this class is Wilkinson s Catalyst, chlorotris(triphenylphosphine)rhodium(I). The catalytic cycle of this complex is shown in Scheme 7. The basic catalytic cycle is very simple, but parasitic side reactions make its study more difficult. 

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. 

The fu-st example of rhodium catalysis for this purpose utilized chlorotris(triphenylphosphine)rho-dium(I) to catalyze the allylic oxidation of a range of alkenes. - This catalyst has also been shown to successfully oxidize cyclic allylsilanes to afford p-silyl-2-cycloalkenones in very good yields and with exclusive rearrangement (equation 43). 

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. ... 

Recently Blum reported that chlorotris(triphenylphosphine) rhodium (XI) is an active catalyst for the decarbonylation of aroyl halides and showed several examples (2). But in this case too, the real catalyst seems to be chlorocarbonylbis(triphenylphosphine)rhodium (XII), which is formed in situ from XI by the stoichiometric reaction with acyl halides. Formation of alkyl halides by decarbonylation of acyl halides can be carried out by the Hunsdiecker reaction, but the reaction is unsatisfactory when applied to aroyl halides. Therefore, the decarbonylation reaction of aroyl halides by the rhodium complex is a new and useful means of introducing halogen onto the aromatic ring. 

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. 

Wilkinson s catalyst A homogeneous catalyst with the formula chlorotris(triphenylphosphine) rhodium. 

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