| Abstract
| - The nickel(0) fragment [Ni(dippe)] was reacted with benzonitrile and initially formed both η2-nitrile and η2-arene complexes at −60 °C. When the sample was warmed to room temperature, the latter completely converted to the η2-nitrile product, which is known to give an equilibrium mixture with the Ni(II) oxidative addition product [(dippe)Ni(Ph)(CN)]. Thermodynamic parameters for this equilibrium have been obtained in both polar and nonpolar solvents (THF vs toluene). Use of density functional theory showed three relatively stable η2-arene intermediates, as well as six well-defined transition states located on the potential energy surface between the η2-nitrile complex and the C−CN bond activation product. Among these transition states, those for the migration of the nickel metal between the carbon−carbon bonds of the phenyl ring are at lower energies than those connecting the η2-nitrile complex to the η2-arene intermediate and the η2-arene intermediate to the C−CN bond activation product. Calculations were carried out both in the gas phase and in solution using the PCM model, which was critical for simulation of the different polar solvent environments in these experiments.
- Investigation of the carbon−carbon bond cleavage in benzonitrile by [Ni(dippe)] shows that (1) the C−C bond being cleaved is not in the NiP2 plane in the cleavage transition state, (2) the two Ni−C bonds are formed before the C−CN bond is broken, and (3) there is a higher energy η2-arene intermediate involved prior to C−C cleavage.
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