Tetrasilane

Tetrasilane is a silane with the structure formula SiH3–(SiH2)2–SiH3. It is the silane analog of butane.

Preparation
Tetrasilane can be prepared by reacting magnesium silicide (Mg2Si) with acids like 20% phosphoric acid in 50–60 °C.
 * $$\mathrm{Mg_2Si + \ 4 H^+\ \longrightarrow \ Si_nH_{2n+2}}$$

The reaction can produce silanes up to n=15. The reaction of magnesium silicide with 25% hydrochloric acid produces 40% monosilane, 30% disilane, 15% trisilane, 10% tetrasilane and 5% higher silanes. The mixture can be separated by fractional distillation.

In addition, higher silanes can also be obtained by discharges monosilane:
 * $$\mathrm{SiH_4 \ \rightarrow \ SiH_2 \ + \ H_2}$$
 * $$\mathrm{SiH_2 \ + \ SiH_4 \rightarrow \ H_3Si{-}SiH_3}$$
 * $$\mathrm{SiH_2 \ + \ H_3Si{-}SiH_3 \rightarrow \ H_3Si{-}SiH_2{-}SiH_3}$$
 * $$\mathrm{SiH_2 \ + \ H_3Si{-}SiH_2{-}SiH_3 \rightarrow \ H_3Si{-}SiH_2{-}SiH_2{-}SiH_3}$$

Properties
Tetrasilane is a colourless, pyrophoric liquid that has a disgusting odour. Even below 54 °C, it will still spontaneous combust. It is even more unstable than trisilane, slowly decomposing at room temperature, releasing hydrogen and forming shorter chain silanes.

Reactions
Photochemical disproportionation of tetrasilane will produce 3-silylpentasilane and disilane.
 * $$\mathrm{2 \ Si_4H_{10} \rightarrow \ Si_2H_6 \ + H_3Si{-}SiH(Si_2H_6)_2 }$$

With the presence of aluminium chloride, heating tetrasilane in xylene will allow isomerization to isotetrasilane.
 * $$\mathrm{2 \ H_3Si{-}SiH_2{-}SiH_2{-}SiH_3 \longrightarrow \ H_3Si{-}SiH(SiH_3)_2 }$$