Borane

Borane (also systematically named trihydridoboron), also called borine, is an inorganic compound with the chemical formula BH
3. It is a colourless gas that only persists at elevated temperatures or in dilution. Borane is the simplest member of the boranes.

History

In 1937, the discovery of carbonyltrihydridoboron, the adduct of borane with carbon monoxide, among other borane adducts, played an important role in exploring the chemistry of "normal" boranes at a time when three-centre two-electron bonding was not yet known. This discovery also implied the existence of borane, however, it was not until some years later that direct evidence was observed.

Chemical properties

Preparation of molecular BH₃

The matrix isolated products of laser ablated boron atoms with hydrogen forms BH₃ as a minor constituent along with B₂H₆, diborane and BH(H₂) complex. Studies of gas phase diborane have detected monomeric BH₃.

Structure

The structure of BH₃ is trigonal planar (D_3hmolecular symmetry) with an experimentally determined B–H bond length of 119 pm. This the same as the terminal B–H bond length in diborane(6). The dominant behaviour of borane is its dimerisation to form diborane, as shown by the enthalpy of the reaction, which is predicted to be near -40 kcal/mol. For such an exothermic process, the concentration of BH₃ is negligible in solution.