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The reactions of Vi 2 (Me)SiCl or Vi 3 SiCl with  t BuLi in pentane solution at low temperatures (-78 to 20 °C) are governed by the addition of  t BuLi to one of the vinyl groups, followed by LiCl elimination to yield the silaethenes Vi(Me)Si=CHNp (1) and Vi 2 Si=CHNp (2), re­spectively. The following reactions of 1 and 2 without or with trapping reagents have been studied in some detail. Both silaethenes undergo dimerization with formation of 1,3-disilacyclobutane derivatives, in case of 2 accompanied by trimers. A surprise is the generation of the disilanes Vi(Me)Si(CH=CH t Bu)Si(Me)Vi(CH 2 CH 2  t Bu) (3) and Vi 2 Si(CH=CH t Bu)SiVi 2 (CH 2 CH 2  t Bu) (17) very probably by intermolecular ene-type reac­tions. With DMB or isoprene as trapping agents [4 + 2]-cycloadducts 11, 14, 15, 21, ene-pro- ducts 10, 13 and substitution products 12, 22 are obtained. A very efficient indirect detection of 1 and 2 has been achieved with Me 3 SiOMe as quenching reagent, which gives excellent yields of the adducts Vi(Me)Si(OMe)CH(SiMe 3 )Np (16, 91%) and Vi 2 Si(OMe)CH(SiMe 3 )Np (23, 76%). respectively. Problems in the characterization of iso­mer mixtures arise from difficulties in the GC separation procedure and from the limited thermal stabilities of some of the products. 1 and 2 are very similar with respect to the reactivity of the Si=C double bond, but differ considerably in their tendency to undergo polymerization which is connected to the number of vinyl groups. Therefore, the yields of the typical Si=C products is drastically reduced in the case of 2. In spite of separation pro­blems most of the products have been characterized by a combination of GC/MS. GC/FT-IR and NMR measurements.

zeitschrift für naturforschung b

Silaethene XVI [1]. Bildung und Reaktivität der Silaethene Me(Vi)Si=CHCH 2  t Bu und Vi 2 Si=CHCH 2  t Bu / Silaethenes XVI [1]. Formation and Reactivity of the Silaethenes Me(Vi)Si=CHCH 2  t Bu and Vi 2 Si=CHCH 2  t Bu