Trishomoaromatic (B3 N3 Ph6 ) Dianion: Characterization and Two-Electron Reduction.

Benzene, a common aromatic compound, can be converted into an unstable antiaromatic 8π-electron intermediate through two-electron reduction. However, as an isoelectronic equivalent of benzene, borazine (B3 N3 Ph6 ), having weak aromaticity, undergoes a totally different two-electron reduction to afford (B3 N3 R6 )2- homoaromatic compounds. Reported here is the synthesis of homoaromatic (B3 N3 Ph6 )2- by the reduction of B3 N3 Ph6 with either potassium or rubidium in the presence of 18-crown-6 ether. Theoretical investigations illustrate that two electrons delocalize over the three boron atoms in (B3 N3 Ph6 )2- , which is formed by the geometric and orbital reorganization and exhibits (π,σ)-mixed homoaromaticity. Moreover, (B3 N3 Ph6 )2- can act as a robust 2e reductant for unsaturated compounds, such as anthracene, chalcone, and tanshinones. This 2e reduction is of high efficiency and selectivity, proceeds under mild reaction conditions, and can regenerate neutral borazine.