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

Abstract

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.