Diborane (B2H6)
The compounds of boron and hydrogen are usually called as boranes. Diborane is the simplest boron hydride (borane) with the formula B2H6.
Diborane is a colorless, sweet odor, highly flammable gas at room temperature. At high concentrations, it ignites spontaneously in moist air at room temperature.
Reactions of diborane
In air 
With water 
With ammonia
Preparation of diborane:
It is prepared by treating boron trifluoride with LiAlH4 in diethyl ether.
A convenient laboratory method for the preparation of diborane involves the oxidation of sodium borohydride with iodine.
Diborane is produced on an industrial scale by the reaction of BF3 with sodium hydride.
Diborane is stored in cylinders with internal pressure higher than atmospheric pressure to prevent explosive reactions with air.
Properties
- Diborane highly toxic gas with a boiling point of 180 K. Diborane catches fire spontaneously upon exposure to air. It burns in oxygen releasing an enormous amount of energy.
- Most of the higher boranes are also spontaneously flammable in air.
- Diborane readily hydrolyse in water to give boric acid and hydrogen gas.
- Diborane on reaction with ammonia gives initially B2H6.2NH3 complex which is formulated as [BH2(NH3)2]+ [BH4]–; on further heating gives borazine, B3N3H6 known as “inorganic benzene”.
Structure of diborane
Structure of Diborane:
Diborane consists of four terminal hydrogen atoms and two boron atoms which lie in one plane. Above and below this plane, there are two bridging hydrogen atoms.
Each boron atom in diborane, with sp3 hybridization has four hybrid orbitals. Out of four hybrid orbitals three orbitals have one electron each and one is an empty orbital. The two single electron hybrid orbitals in each boron atoms will form two bonds( a two–center two–electron bond) with 1s hydrogen atoms. The two boron atoms left with each an unpaired electron orbital and an empty orbital forms two bridging(B–H–B) bonds with two 1s hydrogen atoms, it is a 3–centered 2–electron bond it is also called as banana bond.
The bond lengths in B–H terminal is 1.19Å and in B–H bridging it is 1.33Å.
Diborane used as rocket propellant
Uses of diborane:
- Used as rocket propellants.
- Used in the production of borophosphosilicate glasses.
- Used as a reducing agent in chemical reaction.
- It is also used as a rubber vulcanizer, as a catalyst for olefin polymerization, as a flame–speed accelerator, and as a doping agent in the manufacture of semiconductor devices.