Diboron tetrachloride
Diboron tetrachloride is a tetrahalodiborane chemical compound with the formula B2Cl4. It is a colorless liquid.
Synthesis
The modern synthesis involves the chlorination of diboron tetrabromide by gallium(III) chloride.It can also be formed by the electrical discharge procedure of boron trichloride at low temperatures:
The most efficient synthesis technique uses no dechlorinating metal, instead passing radio-frequency alternating current through gaseous boron trichloride.
Structure
The molecular structure of diboron tetrachloride, B2Cl4, was determined by gas electron diffraction. The molecules have D2d symmetry, i.e. the two planar BBCl2 units are perpendicular to each other. The B-B distance is 1.70 Å, the B-Cl distance is 1.750 Å, the Cl-B-Cl angle is 118.7°. B2Cl4 thus differs significantly from B2F4, which is a planar molecule overall.Reactions
The compound is used as a reagent for the synthesis of organoboron compounds. For instance, diboron tetrachloride adds to ethylene:Diboron tetrachloride absorbs hydrogen quickly at room temperature:
With boranes, it replaces a hydrogen to form dichloroborane and a polyhedral dichloroborane. Heat induces disproportionation back to boron trichloride and a polyhedral boron chloride.