CHEMISTRY OF TETRABORON TETRACHLORIDE - SYNTHESIS AND CHARACTERIZATION OF TETRABORON TETRABROMIDE (B4BR4) AND OBSERVATION OF B4BRCL3, B4BR2CL2, AND B4BR3CL

In the absence of added solvent, B4Cl4 and BBr3, present in a 1:5 mole ratio, generated B4BrCl3 in approximately 13% yield after 800 h at 95-degrees-C. Repeated exposure of B4Cl4 to fresh aliquots of BBr3 and pentane at 95-degrees-C did ultimately (2200 h) form B4Br4 and the mixed ligand species B4Br3Cl, B4Br2Cl2, and B4BrCl3, but the quantities provided were small. The boron-11 NMR data for the bromochlorotetraboranes are consistent with a tetrahedral configuration of the boron atoms rather than a square-planar-based array. In thc presence of AlBr3, B4Br4 was generated from the interaction of B4Cl4 with BBr3 at 95-degrees-C and isolated in 80% yield. After 144 h at 110-degrees-C, the reaction of B4Br4 with excess BCl3 regenerated B4Cl4 in ca. 90% yield.