Symmetrical Tetraorganosilanes

Tetravinylsilane [59] and tetraallylsilane [60,61], in contrast to the organosilanes with no reactive groups, have the typical properties of unsaturated compounds they are reactive and can be polymerised. Tetrakis(pentafluorophenyl)silane [62] (m.p. 

245 °C) is sensitive to hydrolysis. Organolithium compounds are common starting materials for the preparation of symmetrical tetraorganosilanes. They react equally well with monosilane (tetrahydrosilane) and tetrahalosilanes (Eq. 3.3). 

A Lithium aluminium hydride in a reaction retort. B Tetrachlorosilane in the dropping funnel. C Stirrer. D Delivery tube for monosilane. E Condenser. F Freezing trap. G Pressure gauge. I Intensively cooled freezing trap. M Freezing trap. N, O, P Reaction vessels with solutions of organolithium compound. Q Mercury seal. S, T, H, K, L, R Stopcocks. U Air stop. X Nitrogen supply. Y Vacuum source. 

Lithium must always be in excess in the reaction vessels N,0 and P. This excess can be removed from the reaction product by pouring in onto a mixture of ice and dilute sulphuric acid. After hydrolysis, the organic phase is worked up as usual (washing, drying, distillation). This preparation yields [63], among other things, tetra-phenylsilane (40.5 %, m. p. 234-235 °C), tetraethylsilane (63 %, b. p. 149-150 °C at 98 kPa = 737 mm Hg) and tetranaphthylsilane (50%, m.p. 216-217°C). 

The Wurtz synthesis according to Eq. 3.4 is used only for some specific compounds, e.g. for tetrakis[biphenylyl-(4)]silane [65] (90% m.p. 281-283°C). 

---

Symmetrical tetraorganosilanes are synthesized by the reaction of silicon(IV) chloride with excess Grignard reagents or alkyllithiums (eq (45)) [41]. Similarly the combinations of suitable haloorganosilanes and organometallic compounds afford various unsymmetricai tetraorganosilanes (eq (46)) [42]. 

Figure 3.1 shows an apparatus for the preparation of symmetrical tetraorganosilanes from organolithium and monosilane. 

A reaction between two symmetrical tetraorganosilanes can also be used for the preparation of some unsymmetrical tetraorganosilanes. Heating a mixture of tetraethyl and tetrapropylsilane to ISC C for 5h in the presence of aluminimn chloride as catalyst gives three mixed species in statistical proportions [73] (Eq. 3.6) ... 

---