Why is the borane–THF complex used for hydroboration?
1 Answer
The borane-THF complex (BTHF) is used for hydroboration for reasons of safety and convenience.
Explanation:
The active ingredient is borane,
Borane exists naturally as the dimer
Also, it ignites spontaneously in moist air at room temperature.
In a solution in THF, borane exists as a loose Lewis acid-base complex. This allows boron to have an octet and makes the reagent more stable.
The solution is commercially available in a 1 mol/L concentration in volumes from 25 to 800 mL.
It is much more convenient to work with the solution than with a gas. Even so, the solution must be stored at 2 to 8 °C, and it must have a stabilizer added.
Borane forms a more stable and more soluble Lewis acid-base complex with dimethyl sulfide:
It is available in concentrations of 2, 5, and 10 mol/L and in volumes from 25 mL to 18 L.
That should make it a more convenient reagent than the BTHF complex.
There is only one problem: It has the highly disagreeable smell of rotten cabbage!