Linear Organo Di- and Polysilanes

The main method of preparing both linear and cyclic di- and polysilanes is a coupling of a chloroorganosilane by means of an alkali metal (Eq. 3.262)  

Sodium reacts very slowly with haloorganosilanes at 100 °C (boiling toluene) [481]. The reaction can be considerably speeded and carried out in diethyl ether, hexane or benzene if a liquid Na/K alloy is used, as in Eq. 3.263  

Haloorganosilanes are converted to organopolysilanes by metallic lithium, even at room temperature, in a polar solvent (THE or HMPT), e.g. in the preparation of tetrakis(trimethylsilyl)silane [482] (70% m.p. 319-321 °C) (Eq. 3.2M)  

Chloroisopropylsilanes [483] are obtained from hexachlorodisilane and isopropyllith-ium in petroleum ether (b.p. 40-60°C). Hexachlorodisilane and a Grignard reagent yield, after 2 h reflux in diethyl ether, pentachloroethyldisilane [484] (b. p. 184-185°C). 

The series I[Si(CH3)2] I( = 4-6)andX[Si(CH3)2]4X(X = Cl, Br) were prepared by the action of halogen on the corresponding permethylcyclosilanes [486]. Polymeth-ylpolysilanes react as follows with haloorganosilanes (X = Cl, Br, I) in the presence of aluminium chloride (Eq. 3.265)  

---