Bismuth Undecahydro‐closo‐dodecaborane: A Retainable Intermediate of B−H Bond Activation by Bismuth(III) Cations

The [B₁₂H₁₂]^2? anion shows an extensive substitutional chemistry based on its three‐dimensional aromaticity. The replacement of functional groups can be attained by electrophilically induced substitution caused by Brønsted or Lewis acidic electrophiles (e.g. Pt²⁺). Until now, it was impossible to structurally characterize a metal‐substituted [B₁₂H₁₂]^2? cage. When an aqueous solution containing both Bi³⁺ cations and [B₁₂H₁₂]^2? anions was heated, the charge‐neutral bismuth undecahydro‐closo‐dodecaborane BiB₁₂H₁₁ was obtained, representing a new class of metalated [B₁₂H₁₂]^2? clusters. The title compound was characterized by single‐crystal X‐ray diffraction and NMR spectroscopic methods. Compared to the typical B?H bond, the short B?Bi single bond (230 pm) exhibits inverted polarity.