pinacolboron

Pinacolborane, commonly abbreviated HBPin and also called pinacol borane, is an organoboron compound in which boron is bonded to a hydrogen atom and to the bulky pinacolato group derived from pinacol (2,3-dimethyl-2,3-butanediol). The pinacolato boron center forms a stable boron–oxygen chelate (BPin), making HBPin a convenient source of boron and hydrogen in one reagent. It is widely used in organic synthesis, especially for hydroboration reactions and as a practical boron source for making alkyl boronates.

HBPin is a colorless liquid or solid at room temperature under inert atmosphere and is sensitive to moisture and air to some extent; the pinacolato ligand stabilizes boron and enables handling. The B–H bond is relatively reactive toward olefins in hydroboration, typically proceeding under mild catalytic conditions with a range of catalysts. The resulting organoboron products are versatile intermediates for subsequent transformations.

Applications of HBPin include the hydroboration of alkenes and alkynes to give alkyl boronates (R-BPin). Oxidation of the C–B bond with hydrogen peroxide in base affords anti-Markovnikov alcohols, preserving the carbon framework. The RBPin intermediates can undergo further transformations, including Suzuki–Miyaura-type cross-couplings after conversion to the corresponding boronic esters, or functional-group interconversions to alcohols, amines, or additional carbon–carbon bonds.

HBPin is commercially available and can be prepared by several routes, typically involving the reaction of pinacol with boron hydride sources or via reduction of higher boron esters. Its use as a stable boron–hydrogen reagent has made it a standard in laboratories performing hydroboration and boron functionalization.

As with other boron reagents, HBPin is moisture sensitive and should be handled under inert atmosphere. Avoid contact with oxidizers and strong bases; use appropriate protective equipment and work in a well-ventilated area.