Ruthenium-catalyzed reduction of racemic tricarbonyl(η6-aryl ketone)chromium complexes using transfer hydrogenation: A simple alternative to the resolution of planar chiral organometallics

Reductions of rac-(η6-aryl ketone)Cr(CO)3 complexes (aryl ketone = 1-indanone, 1-tetralone, 4-chromanone and thiochroman-4-one) by transfer hydrogenation in 2-propanol, using the catalyst precursors [RuCl2(η6-benzene)]2 and (−)-ephedrine, resulted in optically active syn-(R,S)-(η6-aryl alcohol)Cr(CO)3 and resolved (R)-(η6-aryl ketone)Cr(CO)3 compounds in 31-97% ee. Reduction of rac-(η6-thiochroman-4-one)Cr(CO)3 using (+)-norephedrine, instead of (−)-ephedrine, inverted the configuration of the products obtained, resulting in syn-(S,R)-(η6-thiochroman-4-ol)- and (S)-(η6-thiochroman-4-one)-Cr(CO)3 with 49% and >95% ee, respectively.