Lithium, reactions with dodecamethylcyclohexasilane

A similar result was observed in the sonochemical reaction of di-/butyldihalosilane in the presence of lithium wire [2]. On the other hand, the ultrasoimd promoted reaction of dimethyldichlorosilane with lithium is known to generate dodecamethylcyclohexasilane 1 [3]. Ultraviolet irradiation of this compound in the presence of 2,3-dimethyl-1,3-butadiene (DMB) indicates the formation of 1,1,3,4-tetramethyl-l-silacyclopent-3-ene 2 according to Eq. 1. 

Dodecamethylcyclohexasilane was first prepared by the reaction of sodium with dichlorodimethylsilane in benzene in an unspecified yield along with a considerable amount of hydrocarbon-insoluble dimethylsilylene polymer. This cyclosilane has also been prepared from lithium or sodium" and dichlorodimethylsilane in tetrahydrofuran. A recent modification of this reaction, employing a catalytic amount of triphenylsilyllithium, has increased the yield of the cyclosilane to 70% with essentially no formation of the insoluble polymer. ... 

Under an argon atmosphere, lithium (1.63 g, 235 mmol) and THF (110 mL) were placed in a 500 mL three-necked roimd-bottomed flask equipped with a stir bar, a dropping funnel, and a Dimroth condenser. The mixture was cooled to 0°C. A solution of dichlorodimethylsilane (13.2 g, 102 mmol) in THF (40 mL) was added dropwise for 1 h. The mixture was stirred at 0°C for additional 2 h and at room temperature overnight. A large amount of hexane was added to the reaction mixture, and insoluble materials were filtered off. The filtrate was washed with water, and the water was extracted with hexane. The combined hexane layer was washed with saturated aqueous sodium chloride, dried over anhydrous magnesium sulfate, and evaporated. The residue was recrystallized from ethanol to give dodecamethylcyclohexasilane (3.68 g, 62%) as colorless crystals. 

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