Wilkinson complex decarbonylation with

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... 

One of the first reports concerned with the decarbonylation of a,P-unsaturated aldehydes by means of the Wilkinson complex was published by Tsuji and Ohno in 1965 (Scheme 8.2) [6]. Already these investigations illustrated the high temperatures mostly applied. It should be remembered that enals are typical products emerging in the hydroformylation of 1,3-butadienes. Moreover, the reaction proceeded also with saturated aldehydes to give alkanes. 

Decarbonylation of aldehydes is frequently used in synthetic organic chemistry [19]. Aromatic aldehydes and enals, but also saturated aldehydes, have been shortened by one C atom with this transformation. In most cases, rhodium complexes were used in a stoichiometric reaction, but also catalytic transformations have been described [20]. It was found that RhCl3-3H20 modified with dppp was less air-sensitive than [Rh(COD)Cl]2 (COD = 1,5-cyclooctadiene) modified with dppp or the Wilkinson complex and therefore better suited for lab-scale experiments [21]. While using the Wilkinson complex, strictly oxygen-free conditions were essential for the success. Besides homogeneous rhodium catalysts, also supported complexes were suggested recently [22]. The reaction in ionic liquids is a possibility to recycle the precious rhodium complex [23]. 

Decarbonylation of 3-methyl-3-phenylbutanal with the Wilkinson complex gave exclusively tert-butylbenzene (Scheme 8.8) [24]. No rearrangement product was observed. 

Aldehydes undergo a decarbonylation reaction by action of a transition metal complex [17]. For example, benzaldehyde was decarbonylated with Wilkinson complex to furnish benzene along with a rhodium carbonyl complex 47 (Scheme 7.14) [17e,f]. Oxidative addition of the aldehydic C-H bond to rhodium, migratory deinsertion of CO, and reductive elimination operate in sequence for the decarbonylation reaction. Decanal was also decarbonylated to furnish a mixture of nonane and nonene, which were produced via the alkylpalladium intermediate 48 (Scheme 7.15) [17d]. 

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]... 

Hydrogenation of ketones generally proceeds with more difficulty than reduction of olefins. This is due in part to lesser stability of complexes with ketones (which activate hydrogen) compared to olefin complexes and to the ability to coordinate of the resulting alcohols in contrast to the alkanes. Moreover, the resulting secondary alcohols show a tendency to oxidize themselves back to ketones. Some rhodium complexes oxidize secondary alcohols to ketones. Wilkinson s complexes RhX(PR3)3 do not represent suitable catalysts for reduction of aldehydes, because decarbonylation of the substrate and the formation of compounds of the type RhCl(CO)(PR3)2 takes place these compounds are not catalytically active. However, hydrogenation of ketones is effectively accelerated by complexes such as [Rh(NBD)(PR3) ] CIO (w = 2, 3). The... 

In contrast to a number of studies on the homogeneous hydrogenation of carbon-carbon multiple bonds [25], there had been few papers about hydrogenation of simple ketones before Schrock and Osborn [26] reported in 1970 a catalytic activity of cationic rhodium complexes with relatively basic phosphines as ligands. In fact, the Wilkinson s rhodium(I) complex usually lacks activity towards hydrogenation of carbonyl groups, and rather catalyzes decarbonylation of aldehydes. The catalytic cycle of the hydrogenation of ketones proposed by Schrock and Osborn is depicted in Scheme 3. 

Aldehydes can be decarbonylated by treatment with one equivalent Wilkinson s catalyst , (Ph3P)3RhCl (Scheme 4.95). The reaction is not catalytic, except at very high temperatures, because the rhodium is converted to a stable monocarbonyl complex 4.278. This can be converted back to the catalyst in a separate... 

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