The structure and stability of [3]-radialenes and their dianions – A DFT study

Abstract

B3LYP/6-311+G ∗ calculations were carried out on neutral [3]-radialenes substituted by various groups and their mono- and dianions. It is found that cyano substitution enables efficient stabilization of dianions, which is higher the greater number of the CN groups is present. In hexacyano-[3]-radialene 3, dianion is by 126 kcal mol −1 more stable than the initial neutral compound, which is a remarkable finding. It is also more stable than its monoanion 3 − by 13.3 kcal mol −1. Other dianions dissociate to monoanions, which are substantionally more stable. The origin of the pronounced stabilization of dianion 3 2− is identified as the anionic resonance effect. The latter is corroborated by examination of the bond lengths and redistribution of the electron density upon double reduction and by calculation of the perpendicular NICS(1) zz component of the magnetic shielding tensor calculated 1 Å above the center of the three-membered ring. It is concluded that dianions of the [ n]-radialenes for n > 3, heavily substituted by the CN groups, should provide excellent candidates for polyanions, which could make strong complexes with the electron accepting system like, e.g., TTF in a polymeric fashion, thus eventually yielding strong organic conductors or perhaps the organic “metals”. It is shown that 3 is a strong oxidant in acetonitrile.