Journal of Organometallic Chemistry p. 47 - 59 (1997)
Update date:2022-07-31
Topics:
Wiberg, Nils
Passler, Thomas
Polborn, Kurt
Sterically overloaded trisilylmethanes R*(Me3Si)(Me2XSi)CY = Me2SiX-CYR*(SiMe3) (X = H, Br, F, OH, OMe, OC6F5, OTf, Me, nBu, Ph; Y = H, Br, Me) with R* = supersilyl SitBu3 are accessible via Me2SiH-CHR*(SiMe3) (from Me2SiHCl and LiCHR*(SiMe3)). The latter compound reacts (i) with Br2 to Me2SiBr-CHR*(SiMe3) which is transformed with AgF, H2O, MeOH, C6F5OLi, MeLi, nBuLi, PhLi into Me2SiX-CHR*(SiMe3) (X = F, OH, OMe, OC6F5, Me, nBu, Ph), (ii) with MeLi and then Br2 to Me2SiBr-CBrR*(SiMe3) which is transformed with KHF2, H2O, TfOH into Me2SiX-CBrR*(SiMe3) (X = F, OH, OTf). Compounds Me2SiX-CHR*(SiMe3) (X = F, OC6F5) react at room temperature with MeLi in THF mainly under H/Li and X/Me exchange. At -78°C, Me2SiX-CHR*(SiMe3) (X = OC6F5) is transformed by MeLi under exchange of a meta-or a para-fluorine of C6F5 by a Me group (X-ray structure analysis of the product with X = p-OC6F4Me). In contrast, reaction of Me2SiX-CBrR*(SiMe3) (X = F, OTf) with PhLi or with nBuLi leads to Me2SiR-CLiR*(SiMe3) (R = Ph, nBu), while Me2SiF-CBrR*(SiMe3) reacts with tBu3SiNa to Me2SiF-CNaR*(SiMe3). The latter compound transforms in THF in the presence of Me3SiCl into the silaethene Me2Si=CR*(SiMe3), which after evaporation of THF isomerizes into a 1,3-disilacyclobutane [-SiMe2-CH2-SiMe2-CHR*-], while it may be trapped in THF solution by reactants like MeOH, Me2CO, or CH2 =CMe-CMe=CH2. It follows from our studies that the metastability of compounds Me2Si=C(SiMe3)(SiMe3-n tBun) with an increasing number of tBu groups pass through a maximum for n = 2.
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