Designing aromatic heterocyclic superacids in terms of Brønsted and Lewis perspectives†
The unexplored area of organic superacids was investigated in terms of both Brønsted and Lewis concepts of acids and bases. The primary requirement of a superacid-high affinity for electron/fluoride ions was fulfilled using two strategies: (i) using the superhalogen-type heterocyclic framework and (ii) selecting systems that have an electron count one short of attaining (4n + 2) Hückel aromaticity. With these in mind, eleven systems were considered throughout the study, expected to cross the target of 100% H2SO4 acidity and/or the fluoride affinity of SbF5. To enhance the pKa and F− affinity values of the considered systems, electron-withdrawing ligands F and CN were employed. The superhalogen and aromaticity properties were verified by vertical detachment energy (VDE) and nucleus independent chemical shift (NICS) calculations, respectively. Finally, the collective effect of the potential super Lewis acids was looked into using a BL3 skeleton with them acting as ligands.