Reversible C–H Bond Activation of Unactivated Arenes by a Nickel-Silylene Complex

A nickel-silylene complex is shown
to reversibly activate benzene
via C–H bond activation at ambient temperature. The benzene
C–H bond formally adds across the Ni–Si core to form
a nickel-silyl complex with an H–Si–Ni–Ph linkage
bearing a highly covalent Ni–Si bond (2.2363(6) Å). Dissolution
of this product in neat arene solvent, e.g., toluene, trifluorotoluene,
or anisole, resulted in the complete conversion to the aryl C–H
activated product of the solvent and, thereby, demonstrates the facile
reversibility of C–H bond activation across the Ni–Si
core. The various arene C–H bond activations by the reactive
Ni(0)-silylene species were investigated using density functional
theory calculations. In all cases, the arene initially forms an η2-adduct to Ni(0), and then C–H activation proceeds
via a concerted oxidative addition at only the Ni center. The Si center
assists C–H bond activation by sharing the redox burden with
Ni while stabilizing the resultant hydride.