Write the preparation of diborane and describe its physical and chemical properties.

(N/A) Preparation:
- The simplest boron hydride known is diborane. It is prepared by treating boron trifluoride with $LiAlH_{4}$ in diethyl ether.
$4 BF_{3} + 3 LiAlH_{4} \rightarrow 2 B_{2}H_{6} + 3 LiF + 3 AlF_{3}$
- $A$ convenient laboratory method for the preparation of diborane involves the oxidation of sodium borohydride with iodine.
$I_{2} + 2 NaBH_{4} \rightarrow B_{2}H_{6} + 2 NaI + H_{2}$
- Diborane is produced on an industrial scale by the reaction of $BF_{3}$ with sodium hydride.
$2 BF_{3} + 6 NaH \stackrel{450 \ K}{\longrightarrow} B_{2}H_{6} + 6 NaF$
Physical properties:
- Diborane is a colourless,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.
Chemical properties:
- Boranes are readily hydrolyzed by water to give boric acid.
$B_{2}H_{6(g)} + 6 H_{2}O_{(l)} \rightarrow 2 B(OH)_{3(aq)} + 6 H_{2(g)}$
- Diborane undergoes cleavage reactions with Lewis bases $(L)$ to give borane adducts,$BH_{3} \cdot L$.
$B_{2}H_{6} + 2 NMe_{3} \rightarrow 2 BH_{3} \cdot NMe_{3}$
$B_{2}H_{6} + 2 CO \rightarrow 2 BH_{3} \cdot CO$
- Reaction of ammonia with diborane initially gives $B_{2}H_{6} \cdot 2 NH_{3}$,which is formulated as $[BH_{2}(NH_{3})_{2}]^{+}[BH_{4}]^{-}$; further heating gives borazine,$B_{3}N_{3}H_{6}$,known as "inorganic benzene" due to its ring structure with alternate $BH$ and $NH$ groups.
$3 B_{2}H_{6} + 6 NH_{3}$ $\rightarrow 2[BH_{2}(NH_{3})_{2}]^{+}[BH_{4}]^{-} \stackrel{\Delta}{}$ ${\longrightarrow} 2 B_{3}N_{3}H_{6} + 12 H_{2}$