Dual role of carboxylic acid additive: mechanistic studies and implication for the asymmetric C–H amidation

Acid additive effects in the Ir-catalyzed C–H amidation of arylphosphoryl compounds were examined. Structure of catalytically active metal species was elucidated: mono-cationic iridium catalyst [Cp∗Ir(III)(OAc)](NTf2) being mainly responsible for the C–H bond activation. Mechanistic studies revealed a dual role of carboxylic acid additive operating both in the generation of an iridacyclic intermediate and in the protodemetalation process to release amidated products. The fact that asymmetric C–H amidation was achieved albeit in moderate enantioselectivity by using chiral carboxylic acid supports our proposal especially with regard to the role of acid additive.