[2] It can be observed directly as a continuously produced, transitory, product in a flow system or from the reaction of laser ablated atomic boron with hydrogen.

Thus, it is an intermediate in the preparation of diborane according to the reaction:[5] The standard enthalpy of dimerization of BH3 is estimated to be −170 kJ mol−1.

Consequently, it is a strong Lewis acid and reacts with any Lewis base ('L' in equation below) to form an adduct:[7] in which the base donates its lone pair, forming a dative covalent bond.

[8] A stability sequence for several common adducts of borane, estimated from spectroscopic and thermochemical data, is as follows: BH3 has some soft acid characteristics as sulfur donors form more stable complexes than do oxygen donors.

[11] Molecular BH3 is believed to be a reaction intermediate in the pyrolysis of diborane to produce higher boranes:[5] Further steps give rise to successively higher boranes, with B10H14 as the most stable end product contaminated with polymeric materials, and a little B20H26.

[12] Borane adducts are widely used in organic synthesis for hydroboration, where BH3 adds across the C=C bond in alkenes to give trialkylboranes:[13] This reaction is regioselective.

More sterically hindered tertiary and silyl amines can deliver borane to alkenes at room temperature.