A Dicationic Diradicaloid through Intramolecular One‐Electron Transfer from a B‐B σ‐Bond to an Aromatic π‐System

Herein we report on a novel type of main group diradicaloid with the triplet state arising from unprecedented reversible intramolecular one‐electron transfer from a B‐B σ‐bond (HOMO) into a boron‐bound organic π‐acceptor orbital (LUMO of pyrazine). The deep‐red bis(diboranyl)pyrazine dication, with a bridging pyrazine between two diboranyl units and sp 3 ‐hybridised boron atoms, represents also the first example for a fully‐reversible thermal redox equilibrium between a diborane as electron donor and an organic π‐acceptor. The compound is stable in solution and in the solid state under ambient conditions. Two modified systems were synthesised, demonstrating that a decrease of the B‐B σ‐bond orbital energy as well as an increase of the π*‐acceptor orbital energy leads to an extinction of the diradicaloid character.