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.
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 described the reaction of alkali-metal boron hydride (LiBH4, NaBH4, 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
[edit ]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
[edit ]- ^ Process for producing catecholborane – Patent 4739096
- ^ 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.
- ^ Janice Gorzynski Smith, Organic Chemistry: Second Ed. 2008. pp 1007
- ^ 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 .
- ^ 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 . hdl:1807/78811 . PMID 27434758.