Borane–tetrahydrofuran

Borane–tetrahydrofuran is an adduct derived from borane and tetrahydrofuran (THF). These solutions, which are colorless, are used for reductions and hydroboration, reactions that are useful in synthesis of organic compounds. The use of borane–tetrahydrofuran has been displaced by borane–dimethylsulfide, which has a longer shelf life and effects similar transformations.

Preparation and uses
The complex is commercially available but can also be generated by the dissolution of diborane in THF. Alternatively, it can be prepared by the oxidation of sodium borohydride with iodine in THF.

The complex can reduce carboxylic acids to alcohols and is a common route for the reduction of amino acids to amino alcohols (e.g. valinol). It adds across alkenes to give organoboron compounds that are useful intermediates. The following organoboron reagents are prepared from borane-THF: 9-borabicyclo[3.3.1]nonane, Alpine borane, diisopinocampheylborane. It is also used as a source of borane (BH3) for the formation of adducts.

Safety
The solution is highly sensitive to air, requiring the use of air-free techniques.