Wilkinson complexes

When using appropriate solvents for swelling of the interlayers, the intercalated metal ions are accessible to both substrates and catalysis. One of the first such demonstrations was also carried out with the Wilkinson complex for hydrogena-... 

The discovery of Wilkinson complex, RhCl[P(C6H5)3]3, acting as an effective catalyst for hydrogenation of olefins opened the door for developing asymmetric reaction catalyzed by rhodium complexes with a chiral phosphine ligand. 

Knowles et al.38 prepared the first chiral Wilkinson complexes with an outstanding inductive activity. The vigorous development in this area is covered by an excellent review article 39). 

It has recently been demonstrated that a stereoselective synthesis of dipeptides by hydrogenation of the corresponding monodehydropeptides (N-protected free acids or methyl esters) is possible. In this reaction, chiral catalysts, for example BPPM (13), in the form of a Wilkinson complex have been used. These are superior to the corresponding DIOP complexes (DIOP = P,P -[2,2-dimethyl-l,3-dioxolane-4,5-bis(methylene)]bis(diphenylphosphane). A d.s. value of 90—99% was generally obtained 49 ... 

According to more recent studies,599 the catalytic cycle shown here for the Wilkinson complex and a boronic ester includes the most probable 48 Rh(m) intermediate formed by the addition of the B—H bond (Scheme 6.9). 

When isotetralin or 1,4-dihydrotetralin is reduced in the presence of the Wilkinson complex, an identical mixture of 9(10)-octalin and l(9)-octalin is formed [Eq. (11.25)], requiring the involvement of double-bond migration 133... 

Curtin-Hammett principle, 23 industrial applications, 8, 26 mechanism, 21 phosphine ligands, 7, 18 reaction conditions, 18 scope and limitations, 27 Wilkinson complex, 17 Rhodium-catalyzed olefin isomerization ab initio calculations, 110... 

In 1968, the first homogeneous asymmetric hydrogenation was reported independently by Homer and Knowles (8). The Wilkinson complex and related complexes modified by the incorporation of a chiral tertiary phosphine, such as P(C6H5)(n-C3H7)(CH3), catalyzed the hydrogenation of certain hydrocarbon olefins in optical yields of 3-15%. 

SCHEME 2. Hydrogenation of alkenes catalyzed by the Wilkinson complex. 

Since the catalytic activity of the Wilkinson complex, RhCl(PPh3)3. for the hydrosilylation of ketones was discovered, the application of this reaction to asymmetric synthesis has been studied... 

Allylic double bonds can be isomerized by some transition metal complexes. Isomerization of alkyl allyl ethers 480 to vinyl ethers 481 is catalysed by Pd on carbon [205] and the Wilkinson complex [206], and the vinyl ethers are hydrolysed to aldehydes. Isomerization of the allylic amines to enamines is catalysed by Rh complexes [207]. The asymmetric isomerization of A jV-diethylgeranylamine (483), catalysed by Rh-(5)-BINAP (XXXI) complex to produce the (f )-enaminc 484 with high optical purity, has been achieved with a 300 000 turnover of the Rh catalyst, and citronellal (485) with nearly 100% ee is obtained by the hydrolysis of the enamine 484 [208]. Now optically pure /-menthol (486) is commerically produced in five steps from myrcene (482) via citronellal (485) by Takasago International Corporation. This is the largest industrial process of asymmetric synthesis in the world [209]. The following stereochemical corelation between the stereochemistries of the chiral Rh catalysts, diethylgeranylamine (483), diethylnerylamine (487) and the (R)- and (5)-enamines 484... 

Facile decarbonylation of aldehydes with the Rh complex (Wilkinson complex) is known [43,44], The reaction is explained by the oxidative addition of aldehyde to Rh, followed by decarbonylation and reductive elimination. However, the Rh-catalysed intramolecular reaction of some unsaturated aldehydes proceeds without the decarbonylation, and cyclic ketones are obtained. Treatment of unsaturated aldehyde... 

Pereira and Srebnik added tetrachloromethane to alkenes 430 catalyzed by the Wilkinson complex and Schwartz reagent 431 mediated by pinacolborane [473]. The mechanism of the reaction leading to 432 was proposed not to involve radicals, which was supported by failure of inhibition by galvinoxyl or BHT. 

Generally, Wilkinson complexes which are coordinated with polymeric legands show a relatively high stability in reactions. This is explained as a contribution of the hydrophobic environment of the polymer (113,114). Besides, the polymer plays a role of holding metal without its coagulation. Poly(naphtoquinone)-K-FeCl3 in the ammonia synthesis (115) and poly(acrylic acid)-Rh(III) in the hydrogenation are shown as examples (116,117). 

It is known that the Wilkinson complex PhCl(PPh3)3 is able to catalyse the migration of a double bond. A chiral rhodium complex should in principle bring about the asymmetric synthesis274-276 described in equation 20, or to its analogue in a... 

Disubstituted cyclopentanones. 3,4-Disubstituted-4-pentenals (1) cyclize to cis-3,4-disubstituted cyclopentanones (2) in 50-85% yield in the presence of the Wilkinson complex. In contrast, 2,3-disubstituted-4-pentenals (3) under the same conditions cyclize to /ranj-2,3-disubstituted cyclopentanones (4) in low yield because of concomitant formation of cyclopropanes (5). ... 

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