In situ Activation of Racemic RuII Complexes: Separation of trans and cis Species and Their Application in Asymmetric Reduction

Ruthenium(II) dichlorides with racemic atropos-biaryl-based diphosphanes and optically active 1,2-diphenylethane-1,2-diamine (DPEN) as ligands have been synthesised. trans and cis isomers were formed due to the low basicity of the diphosphane ligands, in particular, with BITIANP and BIMIP. The trans and cis species were easily separated by filtration. In particular, when rac-BITIANP was used in combination with chiral DPEN, the asymmetric separation of optically pure complexes in cis and trans arrangements was realised and they were used as precatalysts in the asymmetric hydrogenation of ketones. Matching and mismatching combinations exhibited different performances.