Hydrogenation is a core technology in chemical synthesis. High rates and selectivities are attainable only by the coordination of structurally well-designed catalysts and suitable reaction conditions. The newly devised [RuCl(2)(phosphane)(2)(1,2-diamine)] complexes are excellent precatalysts for homogeneous hydrogenation of simple ketones which lack any functionality capable of interacting with the metal center. This catalyst system allows for the preferential reduction of a C=O function over a coexisting C=C linkage in a 2-propanol solution containing an alkaline base. The hydrogenation tolerates many substituents including F, Cl, Br, I, CF(3), OCH(3), OCH(2)C(6)H(5), COOCH(CH(3))(2), NO(2), NH(2), and NRCOR as well as various electron-rich and -deficient heterocycles. Furthermore, stereoselectivity is easily controlled by the electronic and steric properties (bulkiness and chirality) of the ligands as well as the reaction conditions. Diastereoselectivities observed in the catalytic hydrogenation of cyclic and acyclic ketones with the standard triphenylphosphane/ethylenediamine combination compare well with the best conventional hydride reductions. The use of appropriate chiral diphosphanes, particularly BINAP compounds, and chiral diamines results in rapid and productive asymmetric hydrogenation of a range of aromatic and heteroaromatic ketones and gives a consistently high enantioselectivity. Certain amino and alkoxy ketones can be used as substrates. Cyclic and acyclic alpha,beta-unsaturated ketones can be converted into chiral allyl alcohols of high enantiomeric purity. Hydrogenation of configurationally labile ketones allows for the dynamic kinetic discrimination of diastereomers, epimers, and enantiomers. This new method shows promise in the practical synthesis of a wide variety of chiral alcohols from achiral and chiral ketone substrates. Its versatility is manifested by the asymmetric synthesis of some biologically significant chiral compounds. The high rate and carbonyl selectivity are based on nonclassical metal-ligand bifunctional catalysis involving an 18-electron amino ruthenium hydride complex and a 16-electron amido ruthenium species.

https://onlinelibrary.wiley.com/doi/pdf/10.1002/1521-3773%2820010105%2940%3A1%3C40%3A%3AAID-ANIE40%3E3.0.CO%3B2-5

Asymmetric Catalysis by Architectural and Functional Molecular Engineering: Practical Chemo‐ and Stereoselective Hydrogenation of Ketones

The synthesis of a large number of fine chemicals, particularly in the field of flavor and fragrance chemistry [1,2] and pharmaceuticals [3], involves the selective hydrogenation of unsaturated carbonyl intermediates as a critical step. The hydrogenation of α,β-unsaturated carbonyls into saturated carbonyls is comparatively easy to achieve because thermodynamics favor the hydro-genation of the C═C bonds; therefore, research efforts were more directed at improving the selectivity to unsaturated alcohols. When a substituent is present on the carbon atom of the carbonyl group (i.e. with ketones), there is no chance to hydrogenate selectively the C═O bond, and saturated ketones are obtained with a high yield. This review is thus mostly restricted to the hydrogenation of α, β-unsaturated aldehydes into the corresponding unsaturated alcohols.

Selective Hydrogenation of α,β-Unsaturated Aldehydes

Advances in developing new heterogeneous catalysts which hydrogenate preferentially the C=O group of ά,β-unsaturated aldehydes to obtain the desired products, namely unsaturated alcohols, will be reviewed by considering the parameters which control the intramolecular selectivity: support material, nature and particle size of the individual metals, selective poisoning, presence of a second metal, preparation method or catalyst precursor, temperature of reduction, host-guest interactions in zeolites, substituents on the C=C bond and pressure effects. Recent attempts with bimetallic and silver catalysts to hydrogenate only the C=O group of other polyfunctional organic compounds in the gas phase without simultaneous hydrogenation of aromatic or furan rings will be shown.

Selective hydrogenation of ά,β-unsaturated aldehydes and other C=O and C=C bonds containing compounds

Promoters of metal catalysts play an essential role in the hydrogenation of unsaturated bonds, such as in carbonylic compounds. This promotion is a key to a high selectivity to unsaturated alcohols in hydrogenation of α,β-unsaturated aldehydes. Analysis of the information available in the literature on the adsorptions through the C—C and C—O groups, respectively, together with the information on the catalytic behaviour of the promoter-free and promoted catalysts, allows us to suggest a model of surfaces active in selective hydrogenation of unsaturated aldehydes.

On the role of promoters in hydrogenations on metals; α,β-unsaturated aldehydes and ketones

Metal-support effects on the intramolecular selectivity of crotonaldehyde hydrogenation over platinum

Hydrogenation of α,β-unsaturated aldehydes over PtSn/Nylon

Liquid phase hydrogenations over platinum-tin catalysts

Nitrobenzene hydrogenation on Pt-Sn catalysts

On Pt–Ge catalysts cinnamaldehyde is hydrogenated to cinnamyl alcohol with a selectivity of 90–95% at conversions higher than 90%.

Z. Poltarzewski

Papers

Hydrogenation of α,β-unsaturated aldehydes over PtSn/Nylon

Liquid phase hydrogenations over platinum-tin catalysts

Nitrobenzene hydrogenation on Pt-Sn catalysts

Selective hydrogenation of α,β-unsaturated aldehydes to give unsaturated alcohols over platinum–germanium catalysts

Hydrogenation of αβ-Unsaturated Aldehydes over Pt-Sn/Nylon.