Pincer Ru with a single stereogenic identity for highly efficient asymmetric transfer hydrogenation of ketones

The asymmetric reduction of carbonyl compounds by means of the Ru-chiral diphosphine-chiral diamine catalysts is widely useful in organic synthesis where high levels of enantioselectivities have been attributed to multiple ligand chiral elements as well as essential stereochemical matching synergies within them. Described here is the design and discovery of new pincer-type Ru-catalysts that feature only single stereogenic element within ligands, yet the such significantly simplified structure is demonstrated to be well competent for effecting asymmetric reductions as well as kinetic resolutions over a broad range of highly functionalized ketones/alcohols, including heteroaryl substituted substrates that were challenging by known catalyst systems. Alcohols were furnished not only in excellent enantioselectivities, but with turnover numbers (up to 100,000 TONs) that reach the highest levels known to date in asymmetric transfer hydrogenation of ketones. This work should help shed light on the intricate origin of enantioselection in these important processes, and further stimulate rational understanding as well as optimization of chiral catalysts towards efficiency and simplicity.