Recent Progress of Metal/Metal Oxide Nanoparticles for Asymmetric Hydrogenation and Transfer Hydrogenation

Metal/metal oxide nanoparticles for asymmetric hydrogenation and transfer hydrogenation have emerged as a frontier and evolved into a hot topic of asymmetric catalysis in recent years. Their catalytic modes resemble that of "nano-reactor", where substrates diffuse through organic shells into catalytic active sites. Thus, high local catalyst concentration usually dramatically improves TON and TOF. In the case of nanoparticles as active sites, Orito's platinum catalytic system received most extensive interests. Achievements have been made in chiral modifier structural modification, catalyst supports, reaction medium, nanoparticle morphology and catalytic mechanism. Moreover, other metal nanoparticles including palladium, rhodium, ruthenium, iridium and iron exhibited favorable catalytic efficiency in the asymmetric hydrogenation and transfer hydrogenation of alkenes, ketones and imines, especially for iridium and iron nanoparticles, ee values over 95% were obtained. In another case of metal/metal oxide nanoparticles as catalyst supports, comparable efficiency and enantioselectivity were observed to homogeneous catalysts, meanwhile, this protocol overcame the drawbacks of homogeneous catalysts with easier recovery and reuse. This review presents a brief overview on the recent progress in the asymmetric hydrogenation and transfer hydrogenation catalyzed by metal/metal oxide nanoparticles, as well as the related catalytic mechanism. However, there are still many challenges in this promising research field of metal/metal oxide nanoparticles for asymmetric catalysis. In addition to the continuous understanding of the catalytic mechanism, it is highly desirable to develop new types of metal/metal oxide nanoparticles with high efficiency, high enantioselectivity, and convenient recyclability.