Zwitterionic Inorganic Benzene Valence Isomer with σ-Bonding between Two π-Orbitals

Despite the large number of plausible isomers of benzene (C₆H₆), only four valence isomers [(CH)₆] have been experimentally detected, all of which are nonionic and possess skeletal frameworks built from localized C-C bonds. Herein, we present the isolation of a diazatetraborabenzene analogue of a hypothetical zwitterionic valence isomer of benzene. Therein, two electrons are delocalized over the four boron atoms in the six-membered B₄N₂ ring, which is a result of the σ-bonding interaction between two odd-electron B-B π-orbitals. Simple treatment with a crown ether leads to the formation of a paramagnetic potassium-doped radical ion pair that exhibits a thermally populated triplet character.