Catecholborane

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, KBH4) with tris(catecholato)bisborane in an ethereal solvent such as diethyl ether. In 2001, Herbert Brown and coworkers prepared catecholborane by treatment of tri-o-phenylene bis-borate with diborane.

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.

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

References

References

1. [http://www.freepatentsonline.com/4739096.html Process for producing catecholborane – Patent 4739096]
2. (2000). "New Economical, Convenient Procedures for the Synthesis of Catecholborane". Organic Process Research & Development.
3. Janice Gorzynski Smith, ''Organic Chemistry: Second Ed''. 2008. pp 1007
4. (1990). "Palladium-Catalyzed Reaction of 1-Alkenylboronates with Vinylic Halides: (1Z,3E)-1-Phenyl-1,3-octadiene".
5. (2016). "Diboron(4) Compounds: From Structural Curiosity to Synthetic Workhorse". Chemical Reviews.