Chiral nitrogen-metal complexes for the asymmetric reduction of ketones

Chiral cobalt-diamine complexes have been prepared and tested in catalytic reduction of β-ketoesters and ketones with molecular hydrogen or hydride transfer reduction (HTR). Modest to high conversions, but low e.e.s were obtained in the first case, whereas encouraging e.e.s (up to 58%) but low conversions were observed in the reduction of acetophenone by HTR. Synthesis of chiral nitrogen tetradentate ligands for Co, Ir and Rh are described. Furthermore, (1R,2R)-(−)-N-tosyl-1,2-ethanediamine proved to be a particularly efficient ligand for iridium in the hydride transfer reduction of acetophenone (87% conversion, 92% e.e.). Graphic