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

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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 center dot 2(IFB), 1 center dot 4,4'FIBP, and 1 center dot 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 pi-hole interactions, specifically, pi-holearene center dot center dot center dot Nnitrile, 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 pi-hole interactions are energetically more favorable than sigma-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 pi-holearene center dot center dot center dot Nnitrile 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.
Funding Information
  • Russian Science Foundation (22-13-00078)

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