Palladium-Catalyzed C−H Activation/C−N Bond Formation Reactions: DFT Study of Reaction Mechanisms and Reactive Intermediates

Abstract

The mechanism and intermediates of palladium-catalyzed cascade C−H activation and C−N bond formation are investigated with density functional theory (DFT), modeling an experimental system, (benzo[h]quinoline)PdII(Cl)Py, and nitrogen source, PhINTs. For [PdCl4]2−-catalyzed C−H activation, the reaction is predicted to proceed via a deprotonation mechanism induced by internal or external base; external base-induced deprotonation is suggested by calculations to be more favored in a water-assisted manner. The reaction barriers for the deprotonation pathways are ca. 12−16 kcal/mol. Electrophilic activation via an arenium intermediate and oxidative addition are less feasible. For the C−N bond formation process, a singlet Pd(IV) imido complex is revealed to be the key reactive intermediate. A concerted or dissociative imido transfer initiated from the Pd(IV) imido complex is the preferred mechanism (ΔH⧧ = 10−13 kcal/mol). In contrast, another proposed intermediate, a triplet Pd(III) nitrene complex, is ∼15 kcal/m...