Imination enables efficient formation of a pillararene-inspired host with endo-cavity hydrogen-bonding capability

Abstract

The efficient design of novel macrocycles with enhanced properties over their parent scaffold represents a major challenge in supramolecular chemistry. Here, we exemplify imination as a purification-free method to develop novel pillar[n]arene-like macrocycles with partial-belt nitrogen functionalization. Compared to similarly sized pillar[n]arene-inspired arenes, the strategy provides an increased scalability and an up to 16-fold improvement in macrocyclization yield. X-ray crystallography and theoretical calculations reveal a similar electron density and cavity size as pillar[5]arene. The altered geometry and enhanced flexibility, however, permit complexing di-, tri- and tetrasubstituted cyanobenzenes, generating guest complementarity to all-carbon pillar[n]arenes. The suitable positioning of hydrogen bond acceptors facilitates binding based on endo-cavity hydrogen bonding, a feature largely unreported in peralkylated pillar[n]arenes. Reduction straightforwardly afforded a polyamine macrocycle of modified geometry.