Diboron tetrachloride

Diboron tetrachloride is a chemical compound with the formula B2Cl4. It is a colorless liquid.

Synthesis
The modern synthesis involves dechlorination of boron trichloride using copper.

It can also be formed by the electrical discharge procedure of boron trichloride at low temperatures:
 * BCl3 → BCl2 + Cl
 * Cl + Hg (electrode) → HgCl or HgCl2
 * 2 BCl2 → B2Cl4

The most efficient synthesis technique uses no dechlorinating metal, instead passing radio-frequency AC current through gaseous boron trichloride.

Reactions
The compound is used as a reagent for the synthesis of organoboron compounds. For instance, diboron tetrachloride adds to ethylene:
 * CH2=CH2 + B2Cl4 → Cl2B–CH2–CH2–BCl2

Diboron tetrachloride absorbs hydrogen quickly at room temperature:


 * 3 B2Cl4 + 3 H2 → B2H6 + 4 BCl3

With boranes, it replaces a hydrogen to form dichloroborane(3) and a polyhedral dichloroborane. Heat induces disproportionation back to boron trichloride and a polyhedral boron(I) chloride.