Theoretical Mechanistic Study of Nickel(0)/Lewis Acid Catalyzed Polyfluoroarylcyanation of Alkynes: Origin of Selectivity for C–CN Bond Activation

The cooperative mechanism of Ni(0)/Lewis acid catalyzed carbocyanation of alkyne with 2,3,5,6-tetrafluorobenzonitrile was investigated using the DFT method. Our calculations indicate that the most feasible catalytic cycle consists of the oxidative addition of a C–CN bond to the Ni(0) center, alkyne insertion into the C­(aryl)–Ni­(II) bond, and reductive elimination. Notably, the Lewis acid (LA) interacting with the cyano nitrogen atom of the substrate can have a significant effect on activating the C–CN bond while suppressing C–H and C–F bond activations. The origin of lower C–CN activation barrier in the presence of LA can be attributed to the remarkably enhanced charge transfer (CT) amount from the Nicat 3d orbital to C-CN σ* + π* antibonding molecular orbital and the little decrease of interaction energy between Ni-catalyst and substrate. In the C–F and C–H bond activations in the presence of LA, on the contrary, the significant decrease of interaction energy between Ni-catalyst and substrate and almost no change of charge transfer amounts are the origin of the larger bond activation barrier. Thus, LA is essential to make the C–CN bond weaker than other bonds, which agrees well with the experimental observation. Electronic processes as well as interaction energy analyses are discussed in detail.