"In situ" activation of racemic Ru(II) complexes : separation of trans and cis species and their application in asymmetric reduction

Over the last two decades new catalytically active Ru(II)-complexes characterised by the combination of a chiral diphosphine containing a chiral chelating diamine were developed1,2. These complexes are very suitable as pre-catalysts for asymmetric hydrogenation of acetophenone-like ketones, whose corresponding alcohols are important building-blocks for industrial and pharmaceutical applications. A drawback to this ground breaking discovery is frequently related to the expense of isolating the two pure chiral ligands. This research has been conducted to resolve Ru(II)-complexes where the ligand is a racemic atropisomeric diphosphine in combination with a chiral diamine (1,2-diphenyl-ethylenediamine, DPEN). Despite the expected presence of trans species, results unexpectantly unveiled a cis-species with low basic atropoisomeric ligands like BITIANP and BIMIP. The complete isolation of cis- and trans-themodinamically favoured isomers was achieved and their use in asymmetric reductions of standard substrate was evaluated.