Homogeneous and heterogeneous strategies of enantioselective hydrogenation: Critical evaluation and future prospects

Asymmetric hydrogenation of unsaturated prochiral substrates is one of the most powerful tools for the creation of enantiopure products. This remarkable reaction could be driven by homogeneous or heterogeneous catalysts. The homogeneous systems, although usually non-reusable, offer well-defined active sites, numerous options for structural optimization, and excellent performance. In contrast, heterogeneous systems are generally less structurally uniform and sometimes require more complex synthesis. At the same time, heterogeneous catalysts are reusable, are simpler to separate, and provide access to continuous processes. There are multiple practical limitations affecting both homogeneous and heterogeneous reactions, such as substrate scope, stability, and compatibility of substrates with solvents. Besides the material discovery, engineering aspects such as overall safety of the system and its lifecycle must be considered. This critical review aims to provide an introductory discussion on the advantages, issues, and future developments one needs to consider upon entry into the field of enantioselective hydrogenation.