Catecholborane

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.

Catecholborane
Catecholborane molecule
Names
Preferred IUPAC name
2H-1,3,2-Benzodioxaborole
Other names
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
UNII
  • InChI=1S/C6H5BO2/c1-2-4-6-5(3-1)8-7-9-6/h1-4,7H checkY
    Key: CENMEJUYOOMFFZ-UHFFFAOYSA-N checkY
  • InChI=1/C6H5BO2/c1-2-4-6-5(3-1)8-7-9-6/h1-4,7H
    Key: CENMEJUYOOMFFZ-UHFFFAOYAI
  • [B]1OC2=CC=CC=C2O1
  • c1cccc2OBOc12
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 labelling:
GHS02: FlammableGHS05: Corrosive
Danger
H225, H314
P210, P233, P240, P241, P242, P243, P260, P264, P280, P301+P330+P331, P303+P361+P353, P304+P340, P305+P351+P338, P310, P321, P363, P370+P378, P403+P235, P405, P501
NFPA 704 (fire diamond)
NFPA 704 four-colored diamond
1
4
2
W
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).
checkY verify (what is checkY☒N ?)
Infobox references

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 described 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 and coworkers prepared catecholborane by treatment of tri-o-phenylene bis-borate with diborane.[2]

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

Reactions

Catecholborane is less reactive in hydroborations than borane-THF or borane-dimethylsulfide.

When catecholborane is treated with a terminal alkyne, a trans vinylborane is formed:

C6H4O2BH + HC2R → C6H4O2B-CHCHR

The product is a precursor to the Suzuki reaction and is the only borane which stops at the alkene instead of reacting further to the alkane. [3][4]

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

Catecholborane oxidatively adds to low valent metal complexes, affording boryl complexes.[5]

C6H4O2BH + Pt(PR3)2 → (C6H4O2B)Pt(PR3)2H

References
  1. Process for producing catecholborane – Patent 4739096
  2. Kanth, Josyula V. B.; Periasamy, Mariappan; Brown, Herbert C. (2000). "New Economical, Convenient Procedures for the Synthesis of Catecholborane". Organic Process Research & Development. 4 (6): 550–553. doi:10.1021/op000291w.
  3. Janice Gorzynski Smith, Organic Chemistry: Second Ed. 2008. pp 1007
  4. Miyaura, Norio; Suzuki, Akira (1990). "Palladium-Catalyzed Reaction of 1-Alkenylboronates with Vinylic Halides: (1Z,3E)-1-Phenyl-1,3-octadiene". Organic Syntheses. 68: 130. doi:10.15227/orgsyn.068.0130.
  5. Neeve, Emily C.; Geier, Stephen J.; Mkhalid, Ibraheem A. I.; Westcott, Stephen A.; Marder, Todd B. (2016). "Diboron(4) Compounds: From Structural Curiosity to Synthetic Workhorse". Chemical Reviews. 116 (16): 9091–9161. doi:10.1021/acs.chemrev.6b00193. PMID 27434758.
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