Computational design of Brønsted neutral organic superbases—[3]iminoradialenes and quinonimines are important synthetic targets†
Abstract
The gas-phase P(NR2)3 and
C(NR2)2 fragments as well as the 1,3-diamino-2-methylenecyclopentene ring enable very efficient cationic resonance across the extended linear π-system, thus considerably contributing to the amplified basicity. Conclusive evidence is provided that protonation triggers aromatization of the quinoid six-membered ring (as well as that of the 1,3-diamino-2-methylenecyclopentene) particularly if they are linearly aligned. Triadic analysis has shown: (1) that the extremely large basicities are obtained, if a synergistic effect is obtained between the three contributions corresponding to the initial state, intermediate stage and final state triadic terms, and (2) that the methyl groups enhance basicity predominantly via destabilization of the principal molecular orbitals of the initial bases. It is argued that powerful organic superbases should lead to a spontaneous proton transfer, when interacting with (organic and inorganic) superacids. Formation of their ion pair might provide new interesting molecular materials.