A ruthenium(II) complex with a C-2-symmetric diphosphine/diamine tetradentate ligand for asymmetric transfer hydrogenation of aromatic ketones

The trans-(RuCl2)-Cl-II complexes with structurally similar N,N'-bis[o-(diphenylphosphino)benzylidene]cyclohexane-1,2-diamine and N,N'-bis[o-(diphenylphosphino)-benzyl]cyclohexane-1,2-diamine ligands have been synthesized, and their molecular structures have been determined. The C-2-symmetric diphosphine/diamine-based Ru complex acts as an excellent catalyst precursor in asymmetric transfer hydrogenation of acetophenone in a 0.1 M 2-propanol solution, leading to 2-phenylethanol in 97% ee and in 93% yield after 7 h at 45 degrees C. This transfer hydrogenation is characterized by low reversibility under these conditions.