Heterolytic versus Homolytic: Theoretical Insight into the Ni0‑Catalyzed Ph–F Bond Activation

The Ni-0-catalyzed borylation of fluorobenzene (PhF) was theoretically investigated. Density functional theory (DFT) calculations disclosed that the Ph-F bond activation occurred heterolytically via an unprecedented nucleophilic aromatic substitution reaction (SNAr) assisted by an sp(2)-sp(3) diboron complex [B(2)nep(2)center dot(OPh)]-Na+, which forms a Ni-0-ate complex as an active species. The diboron-ate complex stabilizes the transition state of the Ph-F bond activation through three interactions, a Ni center dot center dot center dot O coordination, a Na+center dot center dot center dot F cationic dipole interaction, and a charge transfer arising from NaOPh. On the other hand, the Ph-F bond activation catalyzed by Ni-0(dcpe) and Ni-0(PCy3)(2) complexes has also been studied to allow a comparison between the monophosphine and bisphosphine ligands. Results suggest that Ni-0(PCy3)(2) is less effective than Ni-0(dcpe) for the concerted oxidative addition of the Ph-F bond because the Ni dp orbital of Ni-0(PCy3)(2) is at a lower energy level than that of Ni-0(dcpe) in the equilibrium geometry. The characteristic molecular orbital features of Ni-0-catalyzed Ph-F bond activation via both the nucleophilic aromatic substitution reaction (heterolytic) and the concerted oxidative addition (homolytic) were theoretically disclosed.