Experimental and Theoretical Examination of C--CN and C--H Bond Activations of Acetonitrile Using Zerovalent Nickel.

Experimental and density functional theory show that the reaction of acetonitrile with a zerovalent nickel bis(dialkylphosphino)ethane fragment (alkyl = methyl, isopropyl) proceeds via initial exothermic formation of an η2-nitrile complex. Three well-defined transition states have been found on the potential energy surface between the η2-nitrile complex and the activation products. The lowest energy transition state is an η3-acetonitrile complex, which connects the η2-nitrile to a higher energy η3-acetonitrile intermediate with an agostic C--H bond, while the other two lead to cleavage of either the C--H or the C--CN bonds. Gas-phase calculations show C--CN bond activation to be endothermic, which contradicts the observation of thermal C--CN activation in THF. Therefore, the effect of solvent was taken into consideration by using the polarizable continuum model (PCM), whereupon the activation of the C--CN bond was found to be exothermic. Furthermore the C--CN bond activation was found to be favored exclusively over C--H bond activation due to the strong thermodynamic driving force and slightly lower kinetic barrier. [ABSTRACT FROM AUTHOR]