Collect. Czech. Chem. Commun. 2002, 67, 783-790

Some Halogenation Reactions of nido-7,8,9,11-P2C2B7H9

Josef Holub, Mario Bakardjiev and Bohumil Štíbr*

Institute of Inorganic Chemistry, Academy of Sciences of the Czech Republic (Research Centre for New Inorganic Compounds and Advanced Materials, University of Pardubice), 250 68 Řež, Czech Republic


Halogenations of the diphosphadicarbaborane nido-7,8,9,11-P2C2B7H9 using the AlCl3/CCl4, and I2/AlCl3/C6H6 halogenation systems resulted in the formation of a mixture of mono- and disubstituted derivatives 10-X-nido-7,8,9,11-P2C2B7H8 (for X = Cl and I, yields 6 and 21%, respectively) and 5,10-X2-nido-7,8,9,11-P2C2B7H7 (for X = Cl and I, yields 57 and 46%, respectively). These results show that the halogenation under electrophilic conditions takes place at positions most distant from the P atoms, but at sites adjacent to the CH units. In contrast, the bromination with N-bromosuccinimide in CH2Cl2 is probably of radical character, proceeding in positions adjacent to the P centres to give 3-Br-nido-7,8,9,11-P2C2B7H8 (yield 41%) and 2,3-Br2-nido-7,8,9,11-P2C2B7H7 (yield 5%). The mixtures of the halo derivatives were separated by column chromatography on silica gel. Individual compounds were characterized by mass spectrometry and multinuclear (11B, 1H, and 31P) spectroscopy combined with two-dimensional [11B-11B]-COSY NMR techniques. Various NMR effects of halogen substitutions are discussed.

Keywords: Boron; Boranes; Diphosphadicarbaboranes; NMR spectroscopy; Phosphaboranes; Phosphacarboranes; Halogenations; Carboranes.

References: 25 live references.