Orbital Effect-Induced Anomalous Anion–π Interactions between Electron-Rich Aromatic Hydrocarbons and Fluoride

摘要

Anion–π interactions generally exist between an anion and an electron-deficient p-ring because of the electron-accepting character of the ring. In this paper, we report orbital effect-induced anomalous binding between electron-rich π systems and F~- through anion–π interactions calculated at the MP2/6-31+G(d,p) and ωB97X-D/6-31+G(d,p) levels of theory. We find that anion–π interactions between F~- and electron-rich π rings increase markedly with increasing number of π electrons and size of the π rings. This is contrary to intuition because anion–π interactions would be expected to gradually decrease because of gradually increasing Coulombic repulsion between the negative charge of the anions and gradually increasing number of π electrons of the aromatic surfaces. Energy decomposition analysis showed that the key to this anomalous effect is the more effective delocalization of negative charge to the unoccupied π~* orbitals of larger π rings, which is termed an “orbital effect”.