Triply Halide-Bridged Dinuclear Iridium(III) Complexes with Chiral Diphosphine Ligands as New Easy-to-Handle Iridium Catalysts for Asymmetric Hydrogenation of Imines and N-Heteroaromatics.

Iridium(III) complexes bearing chiral ligands have proved to be active species in asymmetric hydrogenation of C=N bonds, though there are only a few iridium(III) precursors. We prepared triply halide-bridged dinuclear iridium complexes bearing chiral diphosphine ligands by simple treatment of the iridium(I) precursor, chiral diphosphine, and aqueous hydrogen halide. The strong advantage of these dinuclear iridium complexes is that they are air and moisture stable, leading to easy handling in asymmetric synthesis. The dinuclear iridium complexes exhibited high catalytic activity toward asymmetric hydrogenation of imines and N-heteroaromatics. Moreover, we demonstrated the application of triply halide-bridged dinuclear ruthenium(II) and rhodium(III) catalyst precursors for the asymmetric hydrogenation of ketonic substrates and simple olefins, respectively.