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.