ortho-Fluoro or orthoEffect? 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 o-F groups (−6.6 kcal/mol per o-F) compared to m-F groups (−1.8 kcal/mol per m-F). To answer the question of whether this is an o-F effect or an orthoeffect, in this study the effect of CF3and CH3groups 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 η2-CN complexes and the C–CN oxidative addition products shows stabilization of the C–CN oxidative addition product with the electron-withdrawing CF3group and destabilization with the electron-donating CH3group in both tetrahydrofuran and toluene. There is a slightly larger orthoeffect with CF3(−7.4 kcal/mol) than with F. However, due to steric crowding, two o-CF3groups did not show considerably more stabilization than one o-CF3group. There is a linear relationship between ΔG°and the number of metagroups (2.0 kcal/mol stabilization per m-CF3and 0.8 kcal/mol destabilization per m-CH3). 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 η2-CN complexes increases.