Decarbonylations, aldehydes, chlorotris rhodium

Kampmeier, J. A., Harris, S. H., Mergelsberg, I. Intramolecular trapping of alkyl- and aryirhodium hydride intermediates in the decarbonylation of aldehydes by chlorotris(triphenylphosphine)rhodium. J. Org. Chem. 1984,49, 621-625. 

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. 

Palladium chloride and metallic palladium are useful for carbonylating olefinic and acetylenic compounds. Further, palladium is active for decarbonylation of aldehydes and acyl halides. Homogeneous decarbonylation of aldehydes and acyl halides and carbonylation of alkyl halides were carried out smoothly using rhodium complexes. An acyl-rhodium complex, thought to be an intermediate in decarbonylation, was isolated by the oxidative addition of acyl halide to chlorotris(triphenylphosphine)rhodium. The mechanisms of these carbonylation and decarbonylation reactions are discussed. 

Chlorotris(triphenyIphosphine)rhodium, [(C Hs)3P]3RhCI. Mol. wt. 913.09 This organometallic complex is obtained as purple-red crystals by interaction of ethanolic solutions of RhCla-SHsO and a sixfold molar excess of triphenyl-phosphine. It catalyzes exceedingly rapid hydrogenation of double and triple bonds. Aliphatic aldehydes are decarbonylated to the corresponding paraffins according to the equation ... 

The best studied decarbonylation reagent is chlorotris(triphenylphos-phine)rhodium(I), RhCl(PPh3)3, which decarbonylates aldehydes and acyl and aroyl halides under mild conditions (i.e., thermally in solution at temperatures below 100°C). The reactions are stoichiometric and are summarized by Equations... 

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