Preorganization-enhanced halogen bonding via intramolecular hydrogen bonding: a theoretical study

Cationic and neutral halogen bonding (XB) donors use two types (I and II) of intramolecular hydrogen bonding (HB) to preorganize structures and increase the efficiency of halide anion recognition. Herein, several XB donors with and without preorganization function were studied. The amine group was introduced to form type I intramolecular HBs (inside of the binding site) for cationic XB donors, and the hydroxyl group was employed to provide type II intramolecular HBs (outside of the binding site) for neutral XB donors. From energetic prospective, the complexation between the receptors and halide anions was enhanced with the preorganization function, which is mainly contributed by the improved coplanarity of the donor geometries. The type II intramolecular HBs are predicted to be much stronger than the type I intramolecular HBs, and the coplanarity of the preorganization structures including type II intramolecular HBs would be further improved with the binding of halide anions. We hope that the results reported herein will assist in the application of preorganization in anion recognition process.