Trishomoaromatic $\left(B_3{N}_{3}P{h}_6\right)$ dianion. Characterization and two-electron reduction

Benzene, a common aromatic compound, can be converted into an unstable antiaromatic /(8 /pi /)-electron intermediate through two-electron reduction. However, as an isoelectronic equivalent of benzene, borazine $\left(B_3{N}_{3}P{h}_6\right)$, having weak aromaticity, undergoes a totally different two-electron reduction to afford /((B_3 N_3 R_6)^{2-}/) homoaromatic compounds. Reported here is the synthesis of homoaromatic /((B_3 N_3Ph_6)^{2-}/) by the reduction of $B_3{N}_{3}P{h}_6$ 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 /((B_3 N_3Ph_6)^{2-}/), which is formed by the geometric and orbital reorganization and exhibits /((/pi,/sigma)/)-mixed homoaromaticity. Moreover, /((B_3 N_3Ph_6)^{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. (© 2020 Wiley‐VCH Verlag GmbH and Co. KGaA, Weinheim)