Azine Steric Hindrances Switch Halogen Bonding to N ‐Arylation upon Interplay with σ‐Hole Donating Haloarenenitriles

An interplay between 4‐bromo‐ and 4‐iodo‐5‐nitrophthalonitriles (XNPN, X=Br or I) and any one of the azines (pyridine 1, 4‐dimethylaminopyridine 2, isoquinoline 3, 4‐cyanopyridine 4, 2‐methylpyridine 5, 2‐aminopyridine 6, quinoline 7, 1‐methylisoquinoline 8, and 2,2’‐bipyridine 9) proceeds differently depending on steric and electronic effects of the heterocycles. Sterically unhindered azines 1–3 underwent N‐arylation to give the corresponding azinium salts (characterized by ¹H and ¹³C{H} NMR and high‐resolution ESI‐MS). In contrast, azines 4–9 with sterically hindered N atoms or bearing an electron‐withdrawing substituent, form stable co‐crystals with XNPN, where two interacting molecules are bound by halogen bonding. In all obtained co‐crystals, X⋅⋅⋅N structure‐directed halogen bonds were recognized and theoretically evaluated including DFT calculations (PBE0‐D3/def2‐TZVP level of theory), QTAIM analysis, molecular electrostatic potential surfaces, and noncovalent interaction plot index. Estimated energies of halogen bonding vary from −7.6 kcal/mol (for 6 ⋅ INPN) to −11.4 kcal/mol (5 ⋅ INPN).