B2H6

B2H6, commonly called diborane, is a boron–hydrogen compound with the molecular formula B2H6. It is the dimer of borane (BH3) and, at room temperature, exists as a colorless gas. In many contexts it is generated and used as a convenient source of BH3 in organic synthesis.

Structure and bonding: The molecule consists of two boron centers linked by two bridging hydrogen atoms that form three-center two-electron B–H–B bonds, in addition to four terminal B–H bonds. This electron-deficient framework accounts for boron hydride reactivity and the tendency of B2H6 to form adducts with Lewis bases.

Synthesis and handling: In situ generation is common, typically from borane (BH3) sources, which dimerize to B2H6. In donor solvents such as tetrahydrofuran (THF) or diglyme, BH3 forms stable adducts and B2H6 can be formed or stabilized. The gas is highly reactive toward water, oxygen, and many organic substrates, and must be handled under inert atmosphere.

Reactions and applications: B2H6 behaves as a Lewis acid and serves as a source of BH3 for hydroboration reactions, adding boron and hydrogen across unsaturated bonds. Hydroboration-oxidation of alkenes and alkynes using BH3 or B2H6 produces alcohols after oxidation. Diborane is also used to prepare various organoborane intermediates and related boron-containing reagents.

Safety and storage: Diborane is flammable and pyrophoric, forms explosive mixtures with air, and is acutely toxic. It reacts violently with water and oxygen, releasing hydrogen gas and boric species. It is normally stored and handled under strictly dry, inert conditions and away from bases and oxidizers.