Enantioselective Hydrogenation Using Heterogeneous Modified Catalysts: An Update

Abstract

The state of the art for the enantioselective hydrogenation applying chirally modified heterogeneous catalysts is reviewed with emphasis on new developments between 1997 and 2002. Discussed are various combinations of metal–modifier–substrate which give enantioselectivities useful for synthetic applications. The three most important asymmetric catalysts types are nickel catalysts modified with tartaric acid, useful for β‐functionalized ketones with ees up to 98.6%, platinum catalysts modified with cinchona alkaloids and related modifiers, successful for α‐functionalized ketones with ees up to 98% and palladium catalysts modified with cinchona alkaloids which achieve ees up to 94% for selected activated CC bonds. Mechanistic investigations comprising surface science and spectroscopic studies often combined with computational modeling as well as kinetic studies are summarized and the various mechanistic models are discussed.

Heterogeneously Catalyzed Asymmetric Hydrogenation of C═C Bonds Directed by Surface-Tethered Chiral Modifiers

“…Moreover, the effect was specific to this particular class of substrates and a recent review by Studer et al indicates that no significant progress has been made in extending this approach. 8 Another system, the proline-directed asymmetric hydrogenation of isophorone ( Figure 1) and similar molecules, typically carried out with a Pd catalyst, has been investigated by Tungler and co-workers 9,10 who proposed that these reactions proceed by the same general mechanism as that which operates for asymmetric C=O hydrogenation -a reactive encounter between the adsorbed organic substrate and the adsorbed chiral agent (proline) in the presence of hydrogen adatoms. However, we have shown, 11 and others have confirmed, 12 that this interpretation is not correct.…”

Silica Supported Rhodium Metal Nanoparticles Stabilized With (-)-Diop. Effect of Ligand Concentration and Metal Loading on the Enantioselective Hydrogenation of Ketones

“…In recent years, the interest in the catalytic properties of metal colloids has increased, due to the high metallic surface of NPs includes a large number of metal atoms available to the substrate 7 . NPs of different metals have been assayed as catalysts in hydrogenation reactions of aromatic hydrocarbons [8][9][10] and recently it has been extended to enantioselective hydrogenation reactions [11][12][13][14][15][16] , hydroformylation and allylic alkylation [17][18][19][20][21] .…”

MCM-41-supported platinum carbonyl cluster-derived catalysts for asymmetric and nonasymmetric hydrogenation reactions

“…Here a conventional heterogeneous catalyst, such as platinum or raney nickel, is modified by treatment with readily available chiral substances . Although the overall success of this approach has been limited, platinum on alumina modified by cinchona alkaloids has been found to be a particularly effective catalyst for the enantioselective hydrogenation of α-ketoesters in general and pyruvate esters in particular [21][22][23][24][25][26][27][28][29][30][31][32][33]. This reaction is commonly referred to as the Orito reaction, in honor of its discoverer.…”