Experimental and theoretical examination of C-CN bond activation of benzonitrile using zerovalent nickel

The 2 nickel(O) fragment [Ni(dippe)] was reacted with benzonitrile and initially formed both 772-nitrile and 27 _arene complexes at -60 'C. When the sample was warmed to room temperature, the latter completely converted to the 772 -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 712 -arene intermediates, as well as six well-defined transition states located on the potential energy surface between the q 2_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 q2 -nitrile complex to the 77 2_ arene intermediate and the ?72 -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.