Unveiling the Role of Non-Structural Supramolecular Water Assisted Coupling of Pyrroles and Isocyanates to Amidopyrroles

Abstract

DFT calculations uncovered the crucial role of non-structural water molecules trapped inside the cavity of a self-assembled hexameric-resorcinarene capsule and facilitating the reaction of N-methylpyrrole and phenyl isocyanate to generate amidopyrrole through two crucial steps: C-C coupling and 1,3C→N proton wire mechanism. Incidentally, the reaction in the bulk solvent is energetically demanding and underscore the role of encapsulation. In fact, the H-bonding with the incorporated water molecules augments the Brønsted acidity of the capsule, resulting in a trade-off in the rate-determining step as compared to the solution, accelerating the overall rate of the reaction. Our work, thus, hints towards the advantage of ubiquitous presence of water-enriched local domains, that regulates reaction kinetics, selectivity and mass transfer in natural processes, attributed to remote bond polarization, proton shuttling and ability of water to act as co-catalysts.