Catecholborane

Catecholborane
Catecholborane molecule
Names
IUPAC name
Catecholborane
Other names
1,3,2-benzodioxaborole
7,9-dioxa-8λ2-borabicyclo[4.3.0]nona-1,3,5-triene
Identifiers
3D model (JSmol)
ChemSpider
ECHA InfoCard 100.005.447
Properties
C6H5BO2
Molar mass 119.92 g/mol
Appearance Colorless liquid
Density 1.125 g/cm3, liquid
Melting point 12 °C (54 °F; 285 K)
Boiling point 50 °C (122 °F; 323 K) at 50 mmHg
Hazards
R-phrases (outdated) R11, R14, R34
S-phrases (outdated) S16, S26, S36/37/39, S43, S45
NFPA 704
Flammability code 4: Will rapidly or completely vaporize at normal atmospheric pressure and temperature, or is readily dispersed in air and will burn readily. Flash point below 23 °C (73 °F). E.g., propane Health code 1: Exposure would cause irritation but only minor residual injury. E.g., turpentine Reactivity code 2: Undergoes violent chemical change at elevated temperatures and pressures, reacts violently with water, or may form explosive mixtures with water. E.g., phosphorus Special hazard W: Reacts with water in an unusual or dangerous manner. E.g., cesium, sodiumNFPA 704 four-colored diamond
4
1
2
Flash point 2 °C (36 °F; 275 K)
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

Catecholborane (abbreviated HBcat) is an organoboron compound that is useful in organic synthesis. This colourless liquid is a derivative of catechol and a borane, having the formula C6H4O2BH.

Synthesis and structure

Traditionally catecholborane is produced by treating catechol with borane (BH3) in a cooled solution of THF. However, this method results in a loss of 2 mole equivalents of the hydride. Nöth and Männig devised a more economical method involves the reaction of alkali-metal boron hydride (LiBH4, NaBH4, of KBH4) with tris(catecholato)bisborane in an ethereal solvent such as diethyl ether.[1] In 2001 Herbert Brown released an additional procedure for catecholborane synthesis. His method involves treating tri-O-phenylene bis-borate with diborane in a solution of either triglyme or tetraglyme. Brown claimed his method produces 85% yield of 97% pure product, catecholborane.[2]

Unlike borane itself or alkylboranes, catechol borane exists as a monomer. This behavior is a consequence of the electronic influence of the alkoxy groups that diminish the Lewis acidity of the boron centre. Pinacolborane adopts a similar structure.

Reactions

Catechol borane is less reactive than borane itself.

Preparation of an organoborane

When catecholborane is treated with an alkyne, usually a terminal alkyne, through hydroboration a trans vinylborane is formed. The product is a precursor to the Suzuki reaction.[3]

[4]

Reduction of β-hydroxy ketones

Catecholborane may be used as a stereoselective reducing agent when converting β-hydroxy ketones to syn 1,3-diols. [5]

References

  1. ↑ Process for producing catecholborane - Patent 4739096
  2. ↑ New Economical, Convenient Procedures for the Synthesis of Catecholborane
  3. ↑ Janice Gorzynski Smith. Organic Chemistry: Second Ed. 2008. pp 1007
  4. ↑ Norio Miyaura (1990). "Discussion Addendum for:PALLADIUM-CATALYZED REACTION OF 1-ALKENYLBORONATES WITH VINYLIC HALIDES: (1Z,3E)-1-PHENYL-1,3-OCTADIENE". Org. Synth.; Coll. Vol., 68, p. 130
  5. ↑ "Reduction of Hydroxy Ketones with Catecholborane. A Stereoselective Approach to the Synthesis of Syn 1,3-Diols" (PDF). Retrieved 25 April 2017.
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