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

Abstract

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.