Enantioselective hydrogenation using heterogeneous modified catalysts: An update

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 beta-functionalized ketones with ees up to 98.6%, platinum catalysts modified with cinchona alkaloids and related modifiers, successful for alpha-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. 1 Introduction 2 Nickel Catalysts Modified with Tartaric Acid and Related Catalysts 2.1 Modifiers 2.2 Substrates 2.3 Catalysts 2.4 Summary: Ni-Based Catalysts 3 Platinum Catalysts Modified with Alkaloids and Related Catalysts 3.1 Modifiers and Solvents 3.2 Substrates 3.3 Catalysts 3.4. Practical Problems, Synthetic Applications and Technical Developments 3.5 Summary: Pt-Based Catalysts 4 Palladium Catalysts Modified with Alkaloids and Related Catalysts 4.1 Modifiers and Substrates 4.2 Catalysts 4.3 Summary: Pd-Based Catalysts 5 Miscellaneous Catalytic Systems 6 Mechanistic Investigations of Heterogeneous Catalytic Reactions 6.1 Structural Models of Activated Complexes 6.2 Surface Science and Spectroscopic Studies 6.3 Computational Modeling 6.4 Kinetic Studies 6.5 Kinetic Schemes 6.6 Assessment of the Mechanistic Proposals 7 Conclusions.