Wilkinson’s catalyst tris

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]. 

This reaction competes with intramolecular hydroacylation of pent-4-enals to form cyclopen-tanones. In the case of exo- and ent/o-norborn-5-ene-2-carboxaldehyde (4) if treated with Wilkinson s catalyst [tris(triphenylphosphane)rhodium(I) chloride] only decarbonylation occurs. While the exo-aldehyde exo-4 leads to norbornadiene (5), the e fi o-aldehyde endo-4 reacts to form nortricyclene (6 tricyclo[2.2.1.0 ]heptane). These results support organometallic pathways and exclude radical intermediates, since here identical products should be formed. 

The isomerization of an allyl ether to a propenyl ether can be achieved either by treatment with potassium t-butoxide in dimethyl sulfoxide or by Wilkinson s catalyst, tris(triphenylphosphine)chlororhodium. ... 

In the presence of nickel(0), tethered diene-VCPs react to produce eight- and five-membered ring products (Scheme 2). Palladium(O) and cobalt(m) were also tried but produced only decomposition products. However, in the presence of Wilkinson s catalyst (RhCl(PPh3)3), tethered diene-VCP 1 was cleanly converted to triene 4 in 91% yield. Although the desired cycloaddition reaction was not obtained, the cleavage of the cyclopropane ring was encouraging.22... 

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. 

Reaction of cyclobutanecarbaldehydes with tris(triphenylphosphane)rhodium(I) chloride (Wilkinson s catalyst) gives the decarbonylated compounds in moderate yields.9,10,12 14 For example, (l/ ,25, 3R)-3-acetoxymethyl-2-tci7-butyfdiphenyfsiloxycyclobutanecarbaldehyde was refluxed with the catalyst to give (l/ ,2/ )-l-acetoxymethyl-2-/tr/-butyldiphenylsiloxycyclobu-tane (6).9... 

Aldehydes, both aliphatic and aromatic, can be decarbonylated454 by heating with chloro-tris(triphenylphosphine)rhodium455 or other catalysts such as palladium.456 RhCl(Ph3P)3 is often called Wilkinson s catalyst.457 In an older reaction aliphatic (but not aromatic) aldehydes are decarbonylated by heating with di-f-peroxide or other peroxides,458 usually in a solution... 

Cyciopentanones. I hc cyclization of 4-pentenals to cyclopentanones catalyzed by Wilkinson s catalyst (4, 560) has been improved considerably by modification of the phosphine ligands.1 Catalysts containing tri-p-tolylphosphine. tri-p-anisylphos-phine, and lris(p-dimethylaminopheny )phosphine are particularly useful. Simple cyclopentanones can he prepared in high yields. The reaction also provides a route to spirocyclic and bicyclic ketones (equations I and II). Unfortunately this method is not applicable to synthesis of larger rings. 

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. ... 

Scheme 9.9 depicts what most consider to be the mechanism for hydrogenation with Wilkinson s catalyst. The inner cycle of reactions (surrounded by the diamond-shaped dotted-line box) represents the key catalytic steps based on the work of Halpem69 and Tolman.70 They showed that compounds 52 to 55, while detectable and isolable, were not responsible for the actual catalytic process and, moreover, the buildup of these intermediates during hydrogenation may even slow down the overall reaction.71 This work provided a valuable lesson for chemists trying to determine a catalytic mechanism—compounds that are readily isolable are probably not true intermediates. Through careful kinetic and spectroscopic... 

Decarbonylation of a /9-aldehyde 3 has been achieved at elevated temperatures using a catalytic amount of tris(triphenylphosphane)rhodium(I) chloride (Wilkinson s catalyst) and of a 1 -cy-clopropylalkyl phenyl ketone using potassium tert-butoxide. ... 

Similarly, intramolecular [4 4- 2] cycloaddition of unactivated dienynes is also catalyzed and dramatically accelerated by low-valent rhodium complexes, e.g., Wilkinson s catalyst [chloro-tris(triphenylphosphane)rhodium] and phosphite analogs, under mild conditions46. Thus, ( , )-l-(2-propynyloxy)-2,4-hexadiene (3, Z = O) and similar dienynes, with 5 mol% of chlorotris(tri-phenylphosphane)rhodium in 2,2,2-trifluoroethanol for 30 minutes at 55 C. give up to quantitative yield of the cycloadducts with excellent to complete diastereoselection. According to control... 

For a few combinations of less reactive dienes and dienophiles, transition metal catalyzed variants of the Diels Alder reaction have been developed. An example is the cycloaddition of an unpolar diene and an unactivated alkyne however, except when the reaction is catalyzed with iron, nickel, cobalt, or rho-dium(I) complexes, the temperature required often causes competing decomposition, even for the intramolecular version. [2] Wilkinson s catalyst [3] - tris(triphenylphosphane)rho-dium(I) chloride - frequently used for hydrogenations and for decarbonylations, permits the cyclization of 4 to the annelated cyclo-hexadiene 5 in excellent yield in only 15 minutes at 55 °C in trifluoroethanol as solvent (Scheme 2). [2c]... 

A common way to generate a chiral catalyst involves a modification of Wilkinson s catalyst (340) in which an optically active tertiary phosphine, bis- or tris-phosphines are used as ligands in place of triphenyl-phosphine. If the phosphorous atom of the added phosphine is the stereogenic center, the optical yields are usually 4-22%, as in the conversion of atropic acid (447) to hydratropic acid (448) with 22% ee." " " An example of this type of phosphine is (-)-methylpropylphenylphosphine. bis(Phosphines) are commonly used, including 449 (called dipamp)" " and 450 (called R-camp)." " ... 

For allyl ethers, rearrangement of the double bond to the more thermodynamically stable enol ether can be accomplished using tris[triphenylphosphine]rho-dium(l) chloride (Wilkinson s catalyst). A possible mechanism for the rhodium(I)-... 

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). 

All of the olefins discussed so far contain a functional group, other than the C=C bond, that binds to the metal to create a defined structure. The asymmetric hydrogenation of olefins that lack this second functional group has been a major challenge. Few complexes of any type catalyze the hydrogenation of tri-substituted and tetra-substituted olefins, let alone catalyze asymmetric hydrogenation of these olefins. Recall from Section 15.3 on achiral catalysts for olefin hydrogenation that Wilkinson s catalyst and ruthenium-hydride complexes display little reactivity for the reduction of tri-substituted alkenes, and no reactivity for... 

Tris(triphenylphosphine)chlororhodium(l) (Wilkinson s Catalyst). This complex catalyzes the hydrogenation of alkenes. It is prepared by the reduction of rhodium trichloride in the presence of triphenylphosphine (1). 

Diisocyano-Rh dimers photocatalytically decompose water [13] and diisocyano complexes catalyze hydrogenation and isomerisation of alkenes and alkynes (although they are far less active than the Wilkinsons catalyst [14]). Alkene hydrogenation is a probe reaction for such reaction centres, especially since the hydrogenation of alk-l-enes over Wilkinson s catalyst [hydrido-carbonyl tris(triphenylphosphine).Rh ] in benzene is quite selective (i.e. was 45 times faster than the cis-aIk-2-ene [15]). Surprisingly, the active centres in such catalysts are still not entirely understood, despite extensive analysis [16]. Rh complexed with 4,4 -diisocyanobiphenyl and 1,4-diisocyanobenzene is active in hydrogenation and isomerization of 1-hexene [14], while Rh complexed with aliphatic amines is active in catalysis of hydrogenation of alkenes and cycloalkenes [16]. 

Tris(triphenylphosphine)rhodium chloride (Wilkinson s catalyst)... 

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). 

---