Pseudopeptidic macrocycles as cooperative minimalistic synzyme systems for the remarkable activation and conversion of CO2 in the presence of the chloride anion†
A series of pseudopeptidic compounds have been assayed as organocatalyts for the conversion of CO2 into organic carbonates through a cooperative multifunctional mechanism. Conformationally constrained pseudopeptidic macrocycles 3a and 3b have been revealed to be excellent synzymes for this purpose, being able to provide a suitable preorganization of the different functional elements and reaction components to activate the CO2 molecule and stabilize the different anionic intermediates involved, through a series of cooperative supramolecular interactions. As a result, remarkable catalytic efficiencies are found at low CO2 pressures and moderate temperatures, with TON and TOF values surpassing those reported for other organocatalytic supramolecular systems under similar conditions. The process works well for monosubstituted epoxides. The involvement of the different structural elements has been analyzed in detail and preliminary studies show the potential for recovery and reuse of these catalytic systems.