Asymmetric Catalysis with Substitutionally Labile yet Stereochemically Stable Chiral-at-Metal Iridium(III) Complex

A metal-coordination-based
high performance asymmetric catalyst
utilizing metal centrochirality as the sole element of chirality is
reported. The introduced substitutionally labile chiral-at-metal octahedral
iridium­(III) complex exclusively bears achiral ligands and effectively
catalyzes the enantioselective Friedel–Crafts addition of indoles
to α,β-unsaturated 2-acyl imidazoles (19 examples) with
high yields (75%–99%) and high enantioselectivities (90–98% ee) at low catalyst loadings (0.25–2 mol %). Counterintuitively,
despite its substitutional lability, which is mechanistically required
for coordination to the 2-acyl imidazole substrate, the metal-centered
chirality is maintained throughout the catalysis. This novel class
of reactive chiral-at-metal complexes will likely be of high value
for a large variety of asymmetric transformations.