Supramolecular Shish Kebabs: Higher Order Dimeric Structures from Ring-in-Rings Complexes with Conformational Adaptivity

Abstract

Use of abiotic chemical systems for understanding higher order superstructures is challenging. Here we report a ring-in-ring(s) system comprising a hydrogen-bonded macrocycle and cyclobis(paraquat-o-phenylene) tetracation (o-Box) or cyclobis(paraquat-p-phenylene) tetracation (CBPQT⁴⁺ , p-Box) that assembles to construct discrete higher order structures with adaptive conformation. As indicated by mass spectrometry, computational modeling, NMR spectroscopy, and single-crystal X-ray diffraction analysis, this ring-in-ring(s) system features the box-directed aggregation of multiple macrocycles, leading to generation of several stable species such as H4G (1 a/o-Box) and H5G (1 a/o-Box). Remarkably, a dimeric shish-kebab-like ring-in-rings superstructure H7G2 (1 a/o-Box) or H8G2 (1 a/p-Box) is formed from the coaxial stacking of two ring-in-rings units. The formation of such unique dimeric superstructures is attributed to the large π-surface of this 2D planar macrocycle and the conformational variation of both host and guest.

Keywords: Host-Guest Systems; Pseudo-Rotaxanes; Ring-in-Rings; Self-Assembly; Supramolecular Chemistry.