Abstract: | The closo‐dodecaborate B12H12]2? is degraded at room temperature by oxygen in an acidic aqueous solution in the course of several weeks to give B(OH)3. The degradation is induced by Ag2+ ions, generated from Ag+ by the action of H2S2O8. Oxa‐nido‐dodecaborate(1?) is an intermediate anion, that can be separated from the reaction mixture as NBzlEt3]OB11H12] after five days in a yield of 18 %. The action of FeCl3 on the closo‐undecaborate B11H11]2? in an aqueous solution gives either B22H22]2? (by fusion) or nido‐B11H13(OH)? (by protonation and hydration), depending on the concentration of FeCl3. In acetonitrile, however, B11H11]2? is transformed into OB11H12]? by Fe3+ and oxygen. The radical anions B12H12] ˙ ? and B11H11] ˙ ? are assumed to be the primary products of the oxidation with the one‐electron oxidants Ag2+ and Fe3+, respectively. These radical anions are subsequently transformed into OB11H12]? by oxygen. The crystal structure analysis shows that the structure of OB11H12]? is derived from the hypothetical closo‐oxaborane OB12H12 by removal of the B3 vertex, leaving a non‐planar pentagonal aperture with a three‐coordinate O vertex, as predicted by NMR spectra and theory. |