Nucleophilicity of the Nitrile N Atom Whose Lone Pair Is Blocked by Metal Coordination. The π-Hole Interaction between an Arene Carbon and the Metal-Bound Nitrile Nitrogen

Abstract

Cocrystallization of CuI with NCNMe₂ in the presence of substituted perfluoroarenes─iodoperfluorobenzene (IFB), 4,4′-diiodoperfluorobiphenyl (4,4′-FIBP), and 4-bromoperfluorobenzonitrile (4-BrFBN)─led to the formation of three types of adducts 1·2(IFB), 1·4,4’FIBP, and 1·4-BrFBN (1 is Cu₄I₄(NCNMe₂)₄), all studied by X-ray crystallography. In these cocrystals, the coordinated nitrile N atom (whose electron pair is engaged in metal coordination) still acts as an electron donor, forming π-hole interactions, specifically, π-hole_arene···N_nitrile, with the perfluoroarenes. These interactions were examined in the context of their occurrence alongside other interactions involving C atoms of the electron-deficient aromatic rings and nucleophilic atoms of the copper cluster. Comprehensive theoretical calculations, including MEP, QTAIM/NCI plot analysis, EDA, ELF projections, and ETS-NOCV calculations, revealed that the nitrile ligand N atom maintains significant negative potential and that π-hole interactions are energetically more favorable than σ-hole interactions in the studied systems. This nucleophilicity is based on a noticeable contribution of the heterocumulene form, Cu–N^–═C═N⁺Me₂, in the resonance hybrid of Cu-bound NCNMe₂: a phenomenon influenced by both the coordination and the conjugation between the NR₂ and CN groups The discovery of π-hole_arene···N_nitrile contacts adds a new dimension to our understanding of coordinated push–pull nitriles, in particular dialkylcyanamides, revealing that the coordinated nitrile N atom can still function as a nucleophile in noncovalent binding.