RhI, IrIII ,and CoIII Complexes with Atropchiral Biaryl Cyclopentadienyl Ligands: Syntheses, Structures, and Catalytic Activities

Abstract

Chiral cyclopentadienyl (Cpx) group 9 metal complexes have become versatile catalysts for a variety of efficient enantioselective C–H functionalizations. Atropchiral binaphthyl-derived Cpx ligands having tuning options at the 3,3′-positions present a robust choice of catalyst, giving high enantioselectivities and good reactivities. Herein, we report streamlined syntheses of binaphthyl backbone Cpx ligands that feature new substituents at the 3,3′-positions: namely, trimethylsilyl, I, and Br. We introduce as well Cpx ligands with a new atropchiral MeO-biphenyl backbone. All ligands are smoothly complexed with rhodium(I) salts. The CpxRhI complexes obtained were systematically mapped by X-ray crystal analysis in order to collect steric parameters that might guide a rational selection of the chiral Cpx ligand for enantioselective reactions. The catalytic performances of the complexes were evaluated by two RhIII-catalyzed C–H functionalizations as benchmark transformations. In both cases, a simpler to access ligand provided superior reactivity and enantioselectivity. Additionally, related CpxCoIII and CpxIrIII complexes equipped with the developed ligands were prepared and characterized.