Stereocontrolled Synthesis of Chiral Helicene‐Indenido ansa‐ and Half‐Sandwich Metal Complexes and Their Use in Catalysis

Abstract

Despite recent tremendous progress in the synthesis of nonplanar chiral aromatics, and helicenes in particular, their conversion to half‐sandwich or sandwich transition metal complexes still lags behind, although they represent an attractive family of modular and underexplored chiral architectures with a potential catalytic use. In this work, starting from various chiral helicene‐indene proligands, we prepared the enantio‐ and diastereopure oxa[6]‐ and oxa[7]helicene‐indenido half‐sandwich RhI and RhIII complexes and oxa[7]helicene‐bisindenido ansa‐metallocene FeII complex. To document their use, oxahelicene‐indenido half‐sandwich RhIII complexes were employed as chiral catalysts in enantioselective C‐H arylation of benzo[h]quinolines with 1‐diazonaphthoquinones to afford a series of axially chiral biaryls in mostly good to high yields and in up to 96 : 4 er. Thus, we developed stereocontrolled synthesis of chiral helicene‐indenido ansa‐ and half‐sandwich metal complexes, successfully demonstrated the first use of such helicene Cp‐related metal complexes in enantioselective catalysis, and described an unusual sequence of efficient central‐to‐helical‐to‐planar‐to‐axial chirality transfer.