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.

A systematic structure-selectivity study was carried out for the enantioselective hydrogenation of activated ketones with chirally modified Pt/Al 2 O 3 catalysts. For this, 18 modifiers containing an extended aromatic system able to form a strong adsorption complex with the Pt surface, and a suitable chiral group with an amino function capable to interact with the keto group of the substrate (HCd, Qd, HCn, Qn, and semi-synthetic derivatives, as well as synthetic analogues) were prepared and tested on 8 different activated ketones in AcOH and toluene under standard conditions. It was found that relatively small structural changes of the substrate and/or modifier structures strongly affected the enantioselectivity, and that no ™best∫ modifier exists for all substrates. The highest ees for all substrates were obtained with quinuclidine-derived modifiers in combination with naphthalene or quinoline rings, either in AcOH (substrates 1 ± 5 and 8, all carrying an sp 3 carbon next to the keto group) or toluene (6 and 7, with an sp 2 carbon next to the ketone). The presence and nature of the substituent R× at the quinuclidine significantly affected the ee (positive and negative effects). Certain combinations of an aromatic system and an amino function were preferred: For the quinuclidine moiety, quinoline and to a somewhat lesser extent naphthalene were a better match, while for the pyrrolidinylmethyl group anthracene was better suited. Methylation of the OH group often had a positive effect for hydrogenations in AcOH but not in toluene. With the exception of 8, higher ees were obtained for the Cd/ Qn series [leading to (R)-products] than for the Cn/ Qd series [leading to (S)-products]. In several cases, opposite structure-selectivity trends were detected when comparing reactions in toluene and AcOH, indicating a significant influence of the solvent.

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 b-functionalized ketones with ees up to 98.6%, platinum catalysts modified with cinchona alkaloids and related modifiers, successful for a-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.