Question

What happens when diborane reacts with Lewis bases?
A.It forms boron trihydride $\left( {{\text{B}}{{\text{H}}_3}} \right)$ due to cleavage.
B.It undergoes cleavage to give borane adduct ${\text{B}}{{\text{H}}_{\text{3}}}{\text{L}}$ (where L = Lewis base).
C.It oxidised to give ${{\text{B}}_{\text{2}}}{{\text{O}}_{\text{3}}}$
D.It does not react with Lewis bases.

Answer 1

The Lewis base is a species having filled an orbital and an electron lone pair. The lone pair is not involved in bonding but it forms a dative bond with a Lewis acid.
The structure of diborane consists of boron and hydrogen. It has two borane atoms and four hydrogen atoms. The formula for diborane is ${{\text{B}}_{\text{2}}}{{\text{H}}_{\text{4}}}$.

Complete step by step answer:
The reaction of diborane with Lewis base is as follows:

Diborane on reaction with Lewis base (L) undergoes cleavage to give borane adduct ${\text{B}}{{\text{H}}_{\text{3}}}{\text{L}}$.
Consider the reaction of diborane with ammonia,
${\text{3}}{{\text{B}}_{\text{2}}}{{\text{H}}_{\text{4}}} + 6{\text{N}}{{\text{H}}_3} \to 2{{\text{B}}_{\text{3}}}{{\text{N}}_3}{{\text{H}}_{\text{6}}}{\text{ + 12}}{{\text{H}}_2}$
Thus, ${{\text{B}}_{\text{3}}}{{\text{N}}_3}{{\text{H}}_{\text{6}}}$ is a borane adduct. ${{\text{B}}_{\text{3}}}{{\text{N}}_3}{{\text{H}}_{\text{6}}}$ is known as borazine. This reaction takes place at an elevated temperature ${180^ \circ } - {190^ \circ }{\text{C}}$.

So, the correct answer is Option B.

Additional Information:
The cleavage of diborane does not form boron trihydride.
Diborane on burning in air gives ${{\text{B}}_{\text{2}}}{{\text{O}}_{\text{3}}}$. The reaction is as follows:${{\text{B}}_{\text{2}}}{{\text{O}}_{\text{6}}} + 3{{\text{O}}_2} \to {{\text{B}}_{\text{2}}}{{\text{O}}_{\text{3}}} + 3{{\text{H}}_2}{\text{O}}$.
Common properties of diborane are:
Diborane is colorless.
At room temperature, diborane is highly flammable. It is generally flammable in air.
It is a sweet smelling gas.
It hydrolyses in water and produces boric acid and hydrogen gas.

Note:
Examples of Lewis bases are:
1.Lone pair donors: ${\text{N}}{{\text{H}}_{\text{3}}}{\text{,}}\,{{\text{H}}_{\text{2}}}{\text{O, O}}{{\text{H}}^ - },{\text{ CH}}_3^ -$.
2.Simple anions: ${{\text{H}}^ - },{\text{ }}{{\text{F}}^ - }$.
3.Complex anions: ${\text{SO}}_4^{2 - },{\text{ PO}}_4^{3 - }$.
$\pi$-systems rich in electron: ethyne, benzene.