Lithium, reactions disilane cleavage with

A disadvantage is that solutions of silyl anions prepared from the halosilanes by one of these methods inevitably contain metal halides as by-product. Salt-free perarylated silyl anions can be prepared by the reaction of a disilane with lithium, sodium or potassium in polar solvents such as THF or DME (Table i)28b,29 Alternative procedures for the preparation of halide-free Ph3SiK utilize the reductive cleavage of the Si—C bond of Ph3Si—CMe2Ph by a sodium-potassium alloy in Et20 (equation 17), as well as via the reaction of PhsSiH with KH in DME . 

Early work on the chemistry of organosilyl anions/anionoids has been thoroughly reviewed (/). The most frequently employed preparative routes involve either cleavage of a disilane, when HMPA (CAUTION—CANCER SUSPECT AGENT) is normally required as solvent, or reaction of bulky silyl chlorides with lithium metal. 

Halogen-free solutions may be obtained by cleavage of a disilane with elemental lithium or methyllithium, or by reaction of disilylmercury compounds with lithium. Other methods of preparation have been reviewed1, and this same source discusses the Grignard-like reactions of silyllithium and other silylmetal reagents. 

In the experiments described the enantiomerically pure disilane (/ )-l was cleaved with lithium metal in THF at -70 °C (Scheme 1). The completeness of the cleavage reaction was proven by GC-MS and H NMR spectroscopy after a trapping reaction with MesSiCl. The resulting disilane 3 could be isolated with ee > 98 %. In solution lithiomethylphenyl(l-piperidinylmethyl)silane (2) racemizes within a few hours at temperatures between 0 and 20 °C, but a very slow decomposition of 2 was also observed. Due to this decomposition no exact determination of the reaction rate law was possible. 

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