Frustrated Lewis Pair Catalyzed Asymmetric Hydrogenation

Catalytic asymmetric hydrogenation of unsaturated substrates is one of the most important transformations in organic chemistry, which provides a significant approach to produce optically active compounds both in academia and chemical industry due to its atom-economy and high efficiency. Since the original work of Knowles and Sabacky in 1960s, transition-metal-catalyzed asymmetric hydrogenation has been well developed with great achievements. However, metal-free asymmetric hydrogenation utilizing molecular hydrogen is extremely challenging, and has long been an unsolved problem. Frustrated Lewis pairs (FLPs) with a combination of sterically encumbered Lewis acids and Lewis bases preclude the formation of classical Lewis acid-base adducts via dative bonds due to the steric effects, and they therefore possess novel and interesting properties and reactivities. Since frustrated Lewis pairs was first disclosed to enable heterolytic cleavage of H-2 reversibly by Stephan and co-workers in 2006, its applications on activating various of small molecules such as H-2, CO2, NO and catalytic hydrogenation of unsaturated compounds were reported. Asymmetric hydrogenation under H-2 by metal-free catalysts has been realized and has witnessed important progress. In this perspective, the achievements on frustrated Lewis pair catalyzed asymmetric hydrogenation are discussed from two aspects: (1) asymmetric hydrogenation induced by chiral substrates; (2) asymmetric hydrogenation catalyzed by chiral frustrated Lewis pairs.