Pinacolborane is the borane with the formula (CH<sub>3</sub>)<sub>4</sub>C<sub>2</sub>O<sub>2</sub>BH. Often pinacolborane is abbreviated HBpin. It features a boron hydride functional group incorporated in a five-membered C<sub>2</sub>O<sub>2</sub>B ring. Like related boron alkoxides, pinacolborane is monomeric. It is a colorless liquid. It features a reactive B-H functional group.
In the presence of catalysts, pinacolborane hydroborates alkenes and, less rapidly, alkynes.
Pinacolborane also affects catalyst-free hydroboration of aldehydes, ketones, and carboxylic acids.
Pinacolborane is used in borylation, a form of C-H activation.
Dehydrogenation of pinacolborane affords dipinacolatodiborane (B<sub>2</sub>pin<sub>2</sub>):