Rhodium-Catalyzed Aldol-Type Chemistry Under Syngas: Selective Reductive Dimerizations of Aldehydes to Monoaldehydes and Further Oxidation to nor-Ketones

• Published in: Journal of catalysis 1994-05, Vol.147 (1), p.107-114
• Main Authors: Noels, A.F., Messere, R., Fontaine, M., Demonceau, A.
• Format: Article
• Language: English
• Subjects: 10 SYNTHETIC FUELS; 100200 - Synthetic Fuels- Production- (1990-); 400201 - Chemical & Physicochemical Properties; ALDEHYDES; CATALYSIS; CATALYTIC EFFECTS; Catalytic reactions; CHEMICAL REACTIONS; Chemistry; COMPLEXES; DIMERIZATION; Exact sciences and technology; General and physical chemistry; HOMOGENEOUS CATALYSIS; INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; ORGANIC COMPOUNDS; POLYMERIZATION; RHODIUM COMPLEXES; Theory of reactions, general kinetics. Catalysis. Nomenclature, chemical documentation, computer chemistry; TRANSITION ELEMENT COMPLEXES
• ISSN: 0021-9517; 1090-2694
• DOI: 10.1006/jcat.1994.1120

Under a pressure of syngas in pyridine, RhCl(PPh3)3 selectively catalyzes the dimerization of enolizable Cn aldehydes, possessing one methylene group in the α-position to the aldehyde function, into saturated dimers, C2n monoaldehydes. The yields are good to moderate. The pressure and relative composition of syngas, together with the use of a triphenylphosphine-ligated metal complex are crucial for obtaining good selectivities. Monosubstitution of the α-carbon severely limits the dimerization. Alcohols and aromatic aldehydes do not react. A tentative reaction mechanism is proposed in which water is involved. The dimer aldehydes can subsequently be oxidized in situ by air or various oxidants such as m-chloroperbenzoic acid or t-butylhydroperoxide into the corresponding nor-ketones. This process constitutes a novel access to such ketones.