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

The Ni⁰-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 (S_NAr) assisted by an sp²–sp³ diboron complex [B₂nep₂·(OPh)]^‑Na⁺, which forms a Ni⁰-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···O coordination, a Na⁺···F cationic dipole interaction, and a charge transfer arising from NaOPh. On the other hand, the Ph–F bond activation catalyzed by Ni⁰(dcpe) and Ni⁰(PCy₃)₂ complexes has also been studied to allow a comparison between the monophosphine and bisphosphine ligands. Results suggest that Ni⁰(PCy₃)₂ is less effective than Ni⁰(dcpe) for the concerted oxidative addition of the Ph–F bond because the Ni d_π orbital of Ni⁰(PCy₃)₂ is at a lower energy level than that of Ni⁰(dcpe) in the equilibrium geometry. The characteristic molecular orbital features of Ni⁰-catalyzed Ph–F bond activation via both the nucleophilic aromatic substitution reaction (heterolytic) and the concerted oxidative addition (homolytic) were theoretically disclosed.