Stereochemical Aspects of the Fluorination of the B12H122- Anion

The methods of (19)F and (11)B NMR spectroscopy and X-ray diffraction analysis are used to characterize the synthesized and isolated B(12)H(3)F(9)(2-), B(12)H(9)F(3)(2-), and B(12)H(11)F(2-) anions, which are missing from the fluorination scheme B(12)H(12)(2-) + xHF(-) -> B(12)H(12).(x)F(x) + xH(2). The B(12)H(11)F(2-) anion is synthesized by reacting B(12)H(12)(2-) with KHF(2) in melt. The (11)B and (19)F NMR spectral data are presented for all of the B(x)H(12-x)F(x)(2-) anions isolated. The structures of all fluorinated compounds are determined, and the results are used to construct a complete scheme of the stereoselective fluorination of B(12)H(12)(2-), illustrating the spatial-aromatic character of the latter. It is shown that, at all fluorination steps, the previously introduced fluorine atoms behave as strong meta orienting agents with respect to the newly introduced atoms.