A Chiral Cation Strategy for Ir(III)-Catalyzed Enantioselective C-H Activation Enabled by a Bifunctional Neutral...

The development of asymmetric variants of Group 9 Cp*M(III)-catalyzed C-H functionalization is fundamentally challenged by the coordinative saturation of the catalyst. While established strategies employ chiral Cp^X ligands or chiral anions, a general approach using external L-type chiral ligands has remained elusive. Herein, we introduce a chiral cation strategy that enables an achiral Cp^*tBuIr(III) catalyst to achieve high enantioselectivity, orchestrated by a designed bifunctional neutral nitrile-phosphine oxide ligand. This system provides direct and efficient access to pyrazole-containing diaza[6]helicenes─a class of N-doped heteroaromatics with low enantiomerization barriers that have been difficult to access. The synthesized helicenes exhibit promising chiroptical properties, including circularly polarized luminescence. Combined mechanistic and computational studies unveil that enantiocontrol is determined during the C-H activation step, facilitated by the formation of a chiral cationic Cp^*tBuIr(III) complex where the bifunctional neutral nitrile-phosphine oxide ligand is integral to the stereodefining transition state. This work establishes a distinct ligand platform for asymmetric C-H functionalization using simple, achiral Cp*M(III) complexes.