Pyrrole‐Based Cryptand‐Like Cages: A Critical Overview of Synthetic Strategies and Applications

Abstract

Pyrrole-based cryptand-like cages are important owing to their three-dimensional cavities together with three open crevices or clefts. The polar pyrrole subunits in the cages preorganize themselves to construct rigid and shape persistent molecular frameworks. Both the inner voids (cavity and cleft) are accessible to various guests such as metal ions, anions and, neutral molecules. The pyrrole ring offers hydrogen bond donor NH groups and its π-electrons to bind anions or neutral molecules, whereas sigma donation of pyrrolides stabilizes metal ions. In addition, the orientation of bridgehead positions of the cryptand molecules along with specific conformations of the pyrrole rings and/or connecting arms dictate the size of available void space which is directly related to the selectivity for specific guest molecules to be recognized. Thus, the cages have attracted attention in recent times for the development of supramolecular chemistry. In this review, we summarize different synthetic procedures of laterally symmetrical cryptand-like molecules, their structures, and applications in diverse aspects.

Influence of the solvent in the self-assembly and binding properties of [1 + 1] tetra-imine bis-calix[4]pyrrole cages

“…1). 24,25 Beer and co-workers described the synthesis of bis(tripyrrolyl) cryptand-like hexa-imine cages via a [2 + 3] Schiff base condensation of triformyl-alkyl-tripyrrolyls and a,u-alkyl diamines (Fig. 1a).…”