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 C<sub>6</sub>H<sub>4</sub>O<sub>2</sub>BH.
Traditionally catecholborane is produced by treating catechol with borane (BH<sub>3</sub>) 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 (LiBH<sub>4</sub>, NaBH<sub>4</sub>, KBH<sub>4</sub>) 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.
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:
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 ò-hydroxy ketones to syn 1,3-diols.
Catecholborane oxidatively adds to low valent metal complexes, affording boryl complexes.