1‐Oxa‐ nido ‐dodecaborate [OB 11 H 12 ] − from the Controlled Oxidation of the closo ‐Borates [B 11 H 11 ] 2− and [B 12 H 12 ] 2−

The closo ‐dodecaborate [B 12 H 12 ] 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 Ag 2+ ions, generated from Ag + by the action of H 2 S 2 O 8 . Oxa‐ nido ‐dodecaborate(1−) is an intermediate anion, that can be separated from the reaction mixture as [NBzlEt 3 ][OB 11 H 12 ] after five days in a yield of 18 %. The action of FeCl 3 on the closo ‐undecaborate [B 11 H 11 ] 2− in an aqueous solution gives either [B 22 H 22 ] 2− (by fusion) or nido ‐B 11 H 13 (OH) − (by protonation and hydration), depending on the concentration of FeCl 3 . In acetonitrile, however, [B 11 H 11 ] 2− is transformed into [OB 11 H 12 ] − by Fe 3+ and oxygen. The radical anions [B 12 H 12 ] ˙ − and [B 11 H 11 ] ˙ − are assumed to be the primary products of the oxidation with the one‐electron oxidants Ag 2+ and Fe 3+ , respectively. These radical anions are subsequently transformed into [OB 11 H 12 ] − by oxygen. The crystal structure analysis shows that the structure of [OB 11 H 12 ] − is derived from the hypothetical closo ‐oxaborane OB 12 H 12 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.