1992 Volume 65 Issue 4 Pages 949-953
Kinetic studies concerning the addition reactions of lithium diethylamide (Et2NLi) to several vinylsilane derivatives, such as H2C=CH–Si(CH3)2X [X: methyl, phenyl, ethoxy, 2-(diethylamino)ethyl and vinyl], and H2C=CH–Si(CH3)2OSi(CH3)2X [X: 2-(diethylamino)ethyl and vinyl], were carried out. The reactivity of vinylsilane derivatives toward nucleophile was strongly influenced by the nature of the substituents on the Si atom. The reactivity of trimethylvinylsilane [rate constant k (trimethylvinylsilane; cHx; 50 °C) = 2.9 ± 0.2 · 10−4 dm3 mol−1 s−1] was found to be of the same order of magnitude as that of para-alkyl-substituted styrenes, such as 4-methylstyrene [k (4-methylstyrene; cHx; 50 °C) = 3.2 · 10−4 dm3 mol−1 s−1]. The reactivities of vinylsilane compounds having an aryl substituent, e.g. dimethylphenylvinylsilane [k (dimethylphenylvinylsilane; cHx; 50 °C) = 14.8 ± 0.3 · 10−4 dm3 mol−1 s−1] and dimethyldivinylsilane [k (dimethyldivinylsilane; cHx; 50 °C) = 14.8 ± 0.6 · 10−4 dm3 mol−1 s−1], were higher than that of trialkyl-substituted vinylsilane. This fact may be explained by a π-conjugation between the phenyl (or vinyl) and vinyl groups through an empty d-orbital of the Si atom. A vinylsilane compound having a 2-(dialkylamino)ethyl substituent, [2-(diethylamino)ethyl]dimethylvinylsilane, showed unique reactivity toward lithium diethylamide, indicating that the β-nitrogen atom plays an important role regarding the reactivity of the vinyl group. In the reaction between lithium diethylamide and vinylsilane having an ethoxyl group, an addition reaction to the vinyl group and a cleavage reaction of the Si–O linkage proceeded concurrently. No cleavage reaction, however, proceeded in the reaction of lithium diethylamide with vinylsilane compounds having a disiloxane linkage. 1,1,3,3-Tetramethyl-1,3-divinyldisiloxane exhibited a much higher reactivity than did the other vinylsilane compounds.
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