Computational Mechanistic Study on the Nickel-Catalyzed C–H/N–H Oxidative Annulation of Aromatic Amides with Alkynes: The Role of the Nickel (0) Ate Complex

Density functional theory (DFT) was used to unveil intimate mechanistic insights on the monodentate-chelation system that is used in the Ni-catalyzed C–H/N–H oxidative annulation of aromatic amides with alkynes, a reaction that was originally reported by our group Chem Sci. 2017, 8, 6650−6655, DOI: 10.1039/C7SC01750B). The proposed reaction mechanism involves two reaction paths. The initial path is initiated by Ni­(II), and the other, the main catalytic cycle, is initiated by Ni(0). Both paths require the presence of a catalytic amount of KOBut. The results of the DFT studies presented here indicate that the rate-determining step in the initial Ni­(II) system involves a concerted metalation–deprotonation (CMD) mechanism and an anionic Ni(0) ate complex is the key intermediate in the main catalytic cycle. Furthermore, a previously proposed oxidative addition–alkyne insertion sequence is revised to a ligand-to-ligand hydrogen transfer (LLHT) mechanism, which is the rate-determining step in the main catalytic cycle. The computed regioselectivity of the asymmetrical alkynes and meta-substituted aromatic amides that are produced in such reactions is in good agreement with the experimental results.