Hydrofluoroarylation of Alkynes with Ni Catalysts. C–H Activation via Ligand-to-Ligand Hydrogen Transfer, an Alternative to Oxidative Addition

Abstract

The mechanism of the hydrofluoroarylation of alkynes, RC≡CR, by nickel phosphine complexes, described by Nakao et al. (Dalton Trans. 2010, 39, 10483), was studied by density functional theory (DFT) calculations. The oxidative addition of a C–H bond of partially fluorinated benzenes, C6FnH6–n (n = 0–5) to a Ni(0) phosphine complex is reversible, but the oxidative addition of a C–F bond yields a stable product via a high-energy barrier. A pathway via the Ni(II) hydride complex is eliminated on the basis of a calculated H/D kinetic isotope effect (KIE) that does not agree with the measured value. An alternate pathway was determined, using as reactant a Ni(phosphine)(alkyne) complex that is shown to be the major species in the reactive media under the catalytic conditions. This pathway is initiated by arene coordination to the Ni alkyne complex followed by proton transfer from the σ-C–H bond of the coordinated arene to the alkyne as the C–H activation step. Analysis of the charge distribution shows that the a...