Some Reactions of Free Radicals and Grignard Reagents with Organosilicon Compounds

Abstract

Considerable confusion exists in the literature concerning the reactivity of allylsilanes in radical addition reactions. The reactions of allylsilanes with radical addition reagents have been reexamined and contrary to a previous report it has been found that both carbon tetrachloride and n-butyraldehyde add readily to allyitriethylsilane. Similar reactions of both trimethyl- and triphenylallylsilane with carbon tetrachloride and bromo= trichloromethane also gave good yields of adducts. The relative reactivities of the double bond in three series of ω-alkenylsilanes, R3Si(CH2)nCH=CH2 (R=Me, Ph or Cl) toward addition by the trichloromethyl radical have been determined and the relative reactivities of vinyl- and allyltrimethylsilane toward free radical addition by n-dodecanethiol have been investigated. The factors affecting the reactivities of the various ω-alkenylsilanes toward radical addition reagents are discussed. Unsuccessful attempts have been made to prepare compounds containing silacyclopropane rings via Grignard cyclisation reactions. The reactions of hydrosilyl Grignard reagents with chlorosilanes have been investigated and silyl chloride reduction has been observed to predominate in many cases. A mechanism for the reduction process is suggested. Silyl alkoxides were isolated in good yield from reaction of hydrosilylmethyl Grignard reagents with benzophenone together with smaller quantities of benzhydrol and 1,1-diphenylethylene. Possible mechanisms are discussed for the formation of the observed products. The products of reaction of benzoyl chloride and dimethyl-silylmethylmagnesium bromide are those derived primarily from reduction processes. A mechanism is proposed involving the intermediacy of 2-sileisobutene. The photolysis of hydrosilylmethyl Grignard reagents and their reaction with cuprous chloride have been examined with a view to the detection of silicon carbon Π-bonded intermediates.