Efficient Access to Chiral Benzhydrols via Asymmetric Transfer Hydrogenation of Unsymmetrical Benzophenones with Bifunctional Oxo-Tethered Ruthenium Catalysts

A concise asymnietric transfer hydrogenation of diaryl ketones, promoted by bifunctional Ru complexes with an: therial linkage between 1,2-diphenylethyleriediamine (DPEN) and eta(6)-arene ligands, was successfully developed. Because of the effective discrimination of substituents at. the ortho position on the aryl group, unsymmetrical benzophenones were smoothly reduced in a 5:2 mixture of formic acid and triethylamine with an unprecedented, level of excellent enantioselectivity. For the non-ortho-substituted benzophenones, the oxotethered catalyst electronically discerned biased substrates, resulting in attractive performance yielding chiral diaryIniethanols with >99% ee.