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 1 H and 13 C{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).