Rh-I, Ir-III ,and Co-III Complexes with Atropchiral Biaryl Cyclopentadienyl Ligands: Syntheses, Structures, and Catalytic Activities

Chiral cyclopentadienyl (Cp-x) group 9 metal complexes have become versatile catalysts for a variety of efficient enantioselective C-H functionalizations. Atropchiral binaphthyl-derived Cp-x 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 Cp-x ligands that feature new substituents at the 3,3'-positions: namely, trimethylsilyl, I, and Br. We introduce as well Cp-x ligands with a new atropchiral MeO-biphenyl backbone. All ligands are smoothly complexed with rhodium(I) salts. The (CpRhI)-Rh-x 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 Cp-x ligand for enantioselective reactions. The catalytic performances of the complexes were evaluated by two Rh-III-catalyzed C-H functionalizations as benchmark transformations. In both cases, a simpler to access ligand provided superior reactivity and enantioselectivity. Additionally, related (CpCoIII)-Co-x and (CpIrIII)-Ir-x complexes equipped with the developed ligands were prepared and characterized.