Group XI Complexes Supported by Chiral N-Heterocyclic Ligands Built on the Imidazo[1,5-a]pyridin-3-ylidene Skeleton: Synthesis, Characterization, and Evaluation in Selective Catalysis

A series of copper(I), silver(I), and gold(I) complexes supported by C₁-symmetric chiral N-heterocyclic ligands elaborated on the imidazo[1,5-a]pyridin-3-ylidene core structure is reported. The flexibility of the synthesis of the imidazolium salts (X = Br, Cl) enabled to combine bulky α-tertbutyl benzylamines at N(2) with an array of aryl substituents at C(5) that are electronically and sterically diversified. Comparative structural analysis of the copper complexes and calculation of their buried volume revealed a marked shielding of the coordination sphere of the metal center together with the possibility of varying substantially the steric environment by adequate combination of substituents at N(2) and C(5). The ability of the chiral ligands to effectively induce asymmetry in homogeneous transition metal catalysis was established by subjecting a selection of precatalysts to the Cu-catalyzed enantioselective borylative carboxamidation of vinyl arenes and the Cu-catalyzed enantioselective borylacylation of vinyl arenes.