Easy To Synthesize, Robust Organo-osmium Asymmetric Transfer Hydrogenation Catalysts.

Asymmetric transfer hydrogenation (ATH) is an important process in organic synthesis for which the Noyori-type RuII catalysts [(arene)Ru(Tsdiamine)] are now well established and widely used. We now demonstrate for the first time the catalytic activity of the osmium analogues. X-ray crystal structures of the 16-electron OsII catalysts are almost identical to those of RuII. Intriguingly the precursor complex was isolated as a dichlorido complex with a monodentate amine ligand. The OsII catalysts are readily synthesised (within 1 h) and exhibit excellent enantioselectivity in ATH reactions of ketones.