Catecholborane


Catecholborane 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 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 with trisbisborane in an ethereal solvent such as diethyl ether. 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.
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 a less reactive in hydroborations than borane-THF or borane-dimethylsulfide.
When catecholborane is treated with a terminal alkyne, a trans vinylborane is formed:
The product is a precursor to the Suzuki reaction.
Catecholborane may be used as a stereoselective reducing agent when converting β-hydroxy ketones to syn 1,3-diols.