ANIONIC INTERMEDIATES IN THE REDUCTIVE COUPLING OF 1-CHLORO-2-PHENYLTETRAMETHYLDISILANE WITH LITHIUM AND SUBSEQUENT REDISTRIBUTION PROCESSES

Oligosilyl anions have been found to participate in the reaction of 1-chloro-2-phenyltetramethyldisilane with excess lithium in THF at room temperature. The overall reaction was monitored by H-1 NMR, HPLC, and UV spectroscopy. The reaction proceeds in four steps. In the first slow stage, the disilyl chloride reacts with lithium to form a disilyllithium anion, which immediately reacts with the remaining disilyl chloride to yield 1,4-diphenyloctamethyltetrasilane. In a second faster stage, the tetrasilane accepts an electron from lithium to form a radical anion and subsequently mono-, di-, and trisilyl anions, which react with the disilyl chloride to form alpha,omega-diphenyltrisilanes, -tetrasilanes, and -pentasilanes. The third stage begins when all of the silyl chloride has been consumed and the cleavage of Si-Si bonds in alpha,omega-diphenyloligosilanes by silyl anions produces dodecamethylcyclohexasilane. A thermodynamic product distribution is formed in this scrambling process. During the final stage more electrons are being added to the system from lithium and an equilibrium mixture of (2-phenyltetramethyldisilyl)lithium, (phenyl-dimethylsilyl)lithium, and dodecamethylcyclohexasilane is established. The silyl anions formed in the process are characterized by various methods (H-1 NMR, C-13 NMR, Si-29 NMR, UV, and EPR spectroscopy).