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.