Diboron tetrachloride

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Diboron tetrachloride
Diboron-tetrachloride-2D.svg
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Names
Preferred IUPAC name
Diboron tetrachloride
Systematic IUPAC name
Tetrachlorodiborane(4)
Identifiers
3D model (JSmol)
ChemSpider
PubChem CID
UNII
  • InChI=1S/B2Cl4/c3-1(4)2(5)6
    Key: LCWVIHDXYOFGEG-UHFFFAOYSA-N
  • InChI=1S/B2Cl4/c3-1(4)2(5)6
    Key: LCWVIHDXYOFGEG-UHFFFAOYAN
  • ClB(Cl)B(Cl)Cl
Properties
B2Cl4
Molar mass 163.42 g·mol−1
Appearancecolorless liquid
Density 1.5 g/cm3 (0 °C)
Melting point −92.6 °C (−134.7 °F; 180.6 K)
Boiling point 65.5 °C (149.9 °F; 338.6 K)
Thermochemistry
137.7 J/mol K
Std molar
entropy (S⦵298)
232.3 J/mol K
−523 kJ/mol
−468.8 kJ/mol
Related compounds
Related compounds
 Diboron tetrafluoride
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).

Diboron tetrachloride is a tetrahalodiborane chemical compound with the formula B2Cl4. It is a colorless liquid. [1]

Contents

Synthesis

The modern synthesis involves the chlorination of diboron tetrabromide by gallium(III) chloride. [2]

It can also be formed by the electrical discharge procedure of boron trichloride at low temperatures: [1] [3]

BCl3 → BCl2 + Cl
Cl + Hg (electrode) → Hg2Cl2 or HgCl2
2 BCl2 → B2Cl4

The most efficient synthesis technique uses no dechlorinating metal, instead passing radio-frequency AC current through gaseous boron trichloride. [4]

Structure

The molecular structure of diboron tetrachloride, B2Cl4, was determined by gas electron diffraction. [5] The molecules have D2d symmetry, i.e. the two planar BBCl2 units are perpendicular to each other (torsion angle Cl-B-B-Cl 90°). The B-B distance is 1.70(4) Å, the B-Cl distance is 1.750(5) Å, the Cl-B-Cl angle is 118.7(3)°. B2Cl4 thus differs significantly from B2F4, which is a planar molecule overall.

Structure of B2Cl4 in the gas phase as determined by gas electron diffraction B2Cl4 gas phase structure.png
Structure of B2Cl4 in the gas phase as determined by gas electron diffraction

Reactions

The compound is used as a reagent for the synthesis of organoboron compounds. For instance, diboron tetrachloride adds to ethylene: [6]

CH2=CH2 + B2Cl4 → Cl2B–CH2–CH2–BCl2

Diboron tetrachloride absorbs hydrogen quickly at room temperature: [3]

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. [4]

References

  1. 1 2 P. L. Timms (1972). "Low Temperature Condensation". Advances in Inorganic Chemistry and Radiochemistry. Academic Press. p. 143. ISBN   0-12-023614-1.
  2. ↑ Merle Arrowsmith; Julian Böhnke; Holger Braunschweig; Andrea Deißenberger; Rian D. Dewhurst; William C. Ewing; Christian Hörl; Jan Miesa; Jonas H. Muessig (2017). "Simple solution-phase syntheses of tetrahalodiboranes(4) and their labile dimethylsulfide adducts". Chemical Communications (59). doi:10.1039/C7CC03148C.
  3. 1 2 Urry, Grant; Wartik, Thomas; Moore, R. E.; Schlesinger, H. I. (1954). "The Preparation and Some of the Properties of Diboron Tetrachloride, B2Cl4". Journal of the American Chemical Society. 76 (21): 5293–5298. doi:10.1021/ja01650a010. ISSN   0002-7863.
  4. 1 2 Morrison, John A. (1991-01-01). "Chemistry of the polyhedral boron halides and the diboron tetrahalides". Chemical Reviews. 91 (1): 35–48. doi:10.1021/cr00001a003. ISSN   0009-2665.
  5. ↑ Ryan, Robert R.; Hedberg, Kenneth (1969-06-01). "Effect of Temperature on the Structure of Gaseous Molecules. II. An Electron‐Diffraction Investigation of the Molecular Structures of B2Cl4 and SiCl4. The Potential Function for Internal Rotation in B2Cl4". The Journal of Chemical Physics. 50 (11): 4986–4995. doi:10.1063/1.1670995. ISSN   0021-9606.
  6. ↑ Urry, Grant; Kerrigan, James; Parsons, Theran D.; Schlesinger, H. I. (1954). "Diboron Tetrachloride, B2Cl4, as a Reagent for the Synthesis of Organo-boron Compounds. I. The Reaction of Diboron Tetrachloride with Ethylene". Journal of the American Chemical Society. 76 (21): 5299–5301. doi:10.1021/ja01650a011. ISSN   0002-7863.


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