-Fluoro or Effect? Oxidative Addition of Zerovalent Nickel into the C-CN Bond of Substituted Benzonitriles.

A recent study of the oxidative addition of zerovalent Ni to the C-CN bond of F-substituted benzonitriles showed significantly increased stabilization of the C-CN oxidative addition products with -F groups (-6.6 kcal/mol per -F) compared to -F groups (-1.8 kcal/mol per -F). To answer the question of whether this is an -F effect or an effect, in this study the effect of CF and CH groups on the oxidative addition of the [Ni(dmpe)] fragment [dmpe = 1,2-bis(dimethylphosphino)ethane] to the C-CN bond of benzonitriles has been studied. A density functional theory study of the reaction pathway between η-CN complexes and the C-CN oxidative addition products shows stabilization of the C-CN oxidative addition product with the electron-withdrawing CF group and destabilization with the electron-donating CH group in both tetrahydrofuran and toluene. There is a slightly larger effect with CF (-7.4 kcal/mol) than with F. However, due to steric crowding, two CF groups did not show considerably more stabilization than one -CF group. There is a linear relationship between Δ and the number of groups (2.0 kcal/mol stabilization per -CF and 0.8 kcal/mol destabilization per -CH). On the basis of natural population analysis, as the C-CN bond becomes more polarized, the stability of the C-CN oxidative addition products with respect to the η-CN complexes increases.