SPOs as Non‐Innocent Ligands in Chiral‐at‐Iridium Catalyzed Asymmetric Hydrogenations

Abstract

AbstractA series of bis‐cyclometalated chiral‐at‐metal iridium(III) complexes containing a coordinated secondary phosphine oxide (SPO) have been synthesized and evaluated as catalysts in the asymmetric transfer hydrogenation (ATH) of acetophenone. The catalytic results show that SPO ligands have a non‐innocent role in activating the catalytic process. Additionally, it has been observed that for the same chiral descriptor (Δ‐at‐Ir or Λ‐at‐Ir), the major enantiomer formed depends on the nature of the cyclometalating ligand. These enantiodivergent results contravene the general assumption that the chiral‐at‐metal core‘s chirality dictates the sense of the chiral induction. A combined analysis of the main structural features of the catalysts deduced from XRD structures and in situ NMR spectroscopy allowed us to propose a simplified catalytic cycle and a working hypothesis to explain the observed enantioselectivities.