Catecholborane

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Catecholborane
Catecholborane structure.png
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
EC Number 205-991-5
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
GHS pictograms The flame pictogram in the Globally Harmonized System of Classification and Labelling of Chemicals (GHS)The corrosion pictogram in the Globally Harmonized System of Classification and Labelling of Chemicals (GHS)
GHS signal word Danger
H225, H314
P210, P233, P240, P241, P242, P243, P260, P264, P280, P301+330+331, P303+361+353, P304+340, P305+351+338, P310, P321, P363, P370+378, P403+235, P405, P501
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
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[edit]

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[edit]

Catechol borane is less reactive than borane itself.

Preparation of an organoborane[edit]

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]

Vinylborane formation.png

Reduction of β-hydroxy ketones[edit]

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

References[edit]

  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". Organic Syntheses. ; Collective Volume, 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.