Probing Noncovalent Interactions in [3,3]Metaparacyclophanes

Abstract

Arene–arene interactions are fundamentally important in molecular recognition. To precisely probe arene–arene interactions in cyclophanes, we designed and synthesized (2,6-phenol)­paracyclophanes and (2,6-aniline)­paracyclophanes that possess two aromatic rings in close proximity. Fine-tuning the aromatic character of one aromatic ring by fluorine substituents enables investigations on the intramolecular interactions between the electron-rich phenol and aniline with tetra-H- and tetra-F-substituted benzene. pK a measurements revealed that the tetra-F-template increases the acidity of the phenol (ΔpK a = 0.55). X-ray crystallography and computational analyses demonstrated that all [3,3]­metaparacyclophanes adopt cofacial parallel conformations, implying the presence of π–π stacking interactions. Advanced quantum chemical analyses furthermore revealed that both electrostatic interactions and orbital interactions provide the key contribution to the structure and stability of [3,3]­metaparacyclophanes.