Rh and Ir complexes containing multidentate, C2-symmetry ligands. Structural and catalytic properties in asymmetric hydrogenation

A comparative investigation of the interaction of Rh(I) and Ir(I) with a series of mixed-donor multidentate, C2-symmetry ligands has been carried out. The complexes have been prepared by the reaction of [MCl(cod)]2 (cod=1,5-cyclooctadiene) with AgPF6 and further treatment with the ligand. All ligands form 1:1 (metal:ligand) species with the above metal ions although, in a few instances, species of type [M2L2]2+ were also detected. The structures of these complexes were elucidated by analytical and spectroscopic data (elemental analysis, mass spectroscopy, IR, 1H- and 13C-NMR). Complexes were tested in the asymmetric hydrogenation of prochiral olefins, providing enantioselectivities up to 36%.