Cyclopropenimine as a hydrogen bond acceptor—towards the strongest non-phosphorus superbases

Utilizing dialkylamino cyclopropenimines as hydrogen bond acceptors in tri-substituted guanidines and cyclopropenimines, we computationally designed the most basic superbases possessing intramolecular hydrogen bonds (IHB-superbases) so far. The values of proton affinity in the gas phase range between 296.6 and 306 kcal mol⁻¹, with estimated pK_a values in acetonitrile between 35.5 and 39.7. The obtained PAs of five new IHB-superbases surpass the basicity of the paradigmatic P4-tBu Schwesinger phosphazene, whereas pK_a values come close to that of P4-tBu. None of the designed superbases contain phosphorus, which puts them among few most basic non-phosphorus superbases desiged so far.