Bis-Calix[4]pyrroles: Preparation, structure, complexation properties and beyond

Calix[4]pyrrole and its derivatives are key members of the supramolecular Parthenon along with other well-recognized receptor systems, such as crown ethers, cyclodextrins (CDs), cucurbiturils, calixarenes and pillararenes. Calix[4]pyrroles are relatively easy-to-make and widely recognized for their ability to bind anions and ion pairs. Many review papers relating to aspects of calix[4]pyrrole chemistry have been published within the past decades. These reviews have focused primarily on monomeric calix[4] pyrroles. The emergent area of bis-calix[4]pyrroles, species wherein two calix[4]pyrrole subunits are linked by one or more "walls", has not benefited from such treatment, even though the species in question often exhibit enhanced binding affinities and selectivities relative to their single calix[4[pyrrole congeners. This review is designed to summarize recent progress involving bis-calix[4]pyrroles. Advances in the design, synthesis, and coordination chemistry of bis-calix[4]pyrroles containing "one wall", "two walls", "three walls", and "four walls", as well as their possible application in ion recognition, sensing and logic gate construction, will be detailed. The hope is that this review will provide a guide for the design and preparation of new multi-component calix[4]pyrrole receptors possessing improved recognition properties, thereby advancing host-guest chemistry in new and useful directions. (C) 2020 Elsevier B.V. All rights reserved.