Can Electron-Rich π Systems Bind Anions?

In general, anion-pi interactions exist between anions and aromatics with a positive quadrupole moment. The interaction between anions and aromatics with a negative quadrupole moment is expected to be unstable due to Coulombic repulsion. However, here we investigated the cases of aromatics with a negative quadrupole moment such as electron-rich alkyl/alkenyl/alkynyl-substituted benzenes and triphenylene, which interact with halides. Favorable binding was demonstrated with coupled cluster theory with singles, doubles, and perturbative triples excitations [CCSD (T)] at the complete basis set (CBS) limit. Stability increases with chain length, unsaturation, and halogenation. Energy decomposition analysis based on symmetry adapted perturbation theory (SAPT) shows that electrostatic repulsion is overcome by induction effects arising from the alkyl substituents.