Silylene R*XSi (R* = (SiBu3)-Bu-t; X = H, Me, Ph, Hal, R*): Bildung und reaktionen

Thermolyses of disupersilylsilanes (R2SiX2)-Si-* (R* = supersilyl = (SiBu3) -Bu-t; X = H, Hal or H together with Me, Ph, Pr) at about 160 degreesC lead - besides R*X (R*H preferred to R*Br) - to silylenes R*XSi (X = H, Me, Ph, Pr), the intermediate existence of which is proven by trapping them with E t3SiH (formation of Et3Si-(R*XSi)-H), with I-2 (formation of I-(R*XSi)-I) o r with CH2=CH-CH=CH2 (formation of [1+4] cycloadducts). The rate of R*X eli mination increases in direction R-2*SiH2 < R-2*SiMeH < R-2*SiBrH and R-2*Si F2 < R-2*SiBr2 < R-2*SiI2. In addition, silylenes R*XSi are produced from m onosupersilylsilanides R*XSiHalM (X = H, Ph, Hal; M = Na, MgHal) by MHal el imination at low temperatures and trapped by inserting them into SiH- or Si M-bonds of Et3SiH, R*PhClSiH, R*Na and R*XSiHalM. Thermolyses of R*SiX2Na ( X = Cl, Pr, I) yield - via R*XSi - disilanides R*X2Si-(R*XSi)-Na which at a bout -20 degreesC eliminate NaX with formation of trans-configurated disile nes R*XSi=SiXR* as intermediates. In addition, R*SiCl2Na transforms into R* Cl2Si-(R*ClSi)(n)-Na (n = 2, 3) which eliminates NaCl with formation of cyc losilanes (R*ClSi)(n+1). Finally, disupersilylsilanides R-2*SiHalLi elimina te LiF at room temperature or LiCl at - 78 degreesC or LiBr at - 120 degree sC with formation of the silylene R-2*Si which stabilizes by formation of t he silane R-2*SiH2 and the disilacyclobutane -R*HSi-(SiBu2)-Bu-t-CMe2-CH2- in the molar ratio 1:6. Possibly, in the latter case R-2*Si is not formed i n the singulet state, as is usual with silylenes, but in the triplet state for the first time. (C) 2001 Elsevier Science B.V. All rights reserved.