Chiral Cyclopentadienyl Ligands as Stereocontrolling Element in Asymmetric C–H Functionalization

Forced Asymmetry in Cp The cyclopentadienyl (Cp) ligand—a pentagon of carbons—is a common feature in transition metal catalysts, but chiral variants of the structure have rarely been applied to asymmetric reactions. Two studies now demonstrate distinct approaches to rendering a Cp-derived rhodium catalyst enantioselective in a tandem carbon-hydrogen activation-ring closure reaction that couples olefins with benzamides (see the Perspective by Wang and Glorius ). Hyster et al. (p. 500 ) tethered a biotin derivative to the Cp ligand to enable docking in a chiral streptavidin protein cavity, which in turn was engineered to further optimize catalytic performance. Ye and Cramer (p. 504 ) appended chiral substituents on the Cp framework to bias the rest of the coordination environment around the metal center.