Metal-promoted Fusion of B₆H₉-

The reaction of K+B6H9 - with FeCl2/FeCl3 in dimethyl ether at -78°C produces B12H16, the first neutral B12 hydride, in 43% isolated yield. Dodecaborane(16), a colorless sublimable air-stable solid, was characterized from its IR and mass spectra, 11B and 1H FT NMR spectra, two-dimensional 11B-11B NMR spectrum, and an X-ray crystal structure determination. The cage skeleton is of the conjuncto type, consisting of open B6 and B8 units joined along a common B-B edge with their respective open faces on opposite sides of the molecule, and contains discrete B6 pyramidal units, consistent with its formation via metal-mediated fusion of B6 anions. There are ten terminal and six bridging hydrogens, two of the borons having only bridging H atoms attached. Treatment of B12H16 with KH in THF solution generates the B12H15 - ion, which can be reprotonated with HCl to restore the original borane. The molecular structure and framework bonding are discussed in terms of both skeletal electron-counting and localized valence-bond descriptions. Crystal data are as follows: space group Pna21, a = 10.686 (3) Å, b = 8.686 (4) Å, c = 11.351 (4) Å, V = 1054 Å3, R = 0.045 for 1021 reflections having F0 \u3e 3σ(F0 2). © 1985 American Chemical Society