Synthesis of a Lewis superacidic borirane in a carborane environment shows new reactivity patterns, suggesting broader implications for boron chemistry.
The title compound, a carborane-fused borirane bearing an additional iPr-substituted carboranyl group (C₂B₁₀H₁₀)B(C₂B₁₀H₁₀iPr), was successfully synthesized via salt elimination between [Li₂C₂B₁₀H₁₀] and (C₂B₁₀H₁₀iPr)BBr₂, and fully characterized in both the solid state and in solution. Benefiting from the unique tris(carboranyl)borane environment, the Lewis acidity of the boron center in this borirane is significantly enhanced compared to conventional boriranes. Its fluoride ion affinity (FIA) is greater than that of SbF₅, allowing it to be classified as a Lewis superacid for the first time among boriranes. In addition, the compound stores a substantial amount of ring strain energy within its carborane-fused three-membered ring. The combination of Lewis superacidity and ring strain gives rise to unprecedented reactivity patterns, including (1) an NHC-triggered intramolecular transfer hydrogenation in which an alkane moiety serves as the hydrogen source; (2) a formal CB/CO σ-bond metathesis reaction with THF, representing a new mode of THF ring-opening; and (3) a dearomative N-C bond insertion reaction with DMAP.
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Xiang et al. (2025) studied this question.
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