Zur Seitenansicht


 Das Dokument ist frei verfügbar


CF₃-substituierte SiSi- und SiOSi-Bindungssysteme konnten einerseits durch Bindungsknüpfung ausgehend von trifluormethylierten Monosilanen, andererseits durch CF₃-Übertragung auf bestehende SiSi- und SiOSi-Gerüste dargestellt werden. Als Vorstufen für den Aufbau zweidimensionaler oligomerer Systeme wurden Trifluormethylsilane des Typs CF₃R₂SiX, CF₃RSiX₂ (X = Halogen, H, OMe, NR₂; R = Me, Ph) und (CF₃)₂SiX₂ (X = Br, NMe₂) dargestellt und charakterisiert. Die Reaktion von HSiCl₃ mit CF₃Br in Gegenwart von tertiären Aminen führt zu CF₃SiCl3 in ca. 18% Ausbeute. [CF₃Me₂Si]₂ ist durch reduktive Enthalogenierung von CF₃Me₂SiCl oder durch Umsetzung von CF₃Me₂SiH mit HgR₂ ( R = Me, Et) erhältlich. Höhere Oligosilane (z.B. CF₃MeSi(SiMe₂CF₃)₂, (CF₃Me₂Si)₃SiMe, CF₃Si(SiMe₃)₃) werden durch Trifluormethylierung der entsprechenden SiSi-Gerüste dargestellt. Die Reaktion von Si₂Cl₆ mit P(NEt₂)₃/ CF₃Br führt zu donorstabilisierten CF₃SiCl, welches mit CF₃Br zu (CF₃)₂SiCl₂ abreagiert. In gleicher Weise wird die SiSi-Bindung der Disilane [CF₃Me(X)Si]₂ und CF₃Me(X)SiSiMeX₂ (X = Halogen) in Gegenwart von Basen unter Silylen-Bildung gespalten. Ausgehend von CF₃R₂SiX sind CF₃-substituierte Disiloxane durch Hydrolyse oder durch Umsetzung mit Metalloxiden erhältlich. Die Hydrolyse von CF₃MeSiX₂ (X = Cl, OMe) führt zu trifluormethylierten Oligo- und Polysiloxanen [CF₃RSiO]ₙ (R = Me, Ph), wobei Kristallstrukturanalysen von [CF₃MeSiO]₃[MeSiO1.5]₄ und [CF₃MeSiO]₄ vorliegen. Der Einfluß der CF₃-Substitution auf die Acidität des Siliciums wurde an den Komplexverbindungen (CF₃)₂SiX₂D, CF₃SiCl₃D (X = Cl, Br; D = Bipy, Phen, DMSO) sowie an [CF₃MeSi(bipy)₂]I₂ und 1-Trifluormethylsilatran untersucht. Alle Verbindungen wurden NMR- sowie z.T. IR/ Raman-spektroskopisch untersucht und charakterisiert. Durch Tieftemperatur-NMR-Experimente konnten Zwischenprodukte der basenkatalysierten SiSi-Spaltung von Me₂Cl₄Si₂ erfaßt bzw. das Austauschverhalten CF₃-substituierter Disilane beobachtet werden.


(Trifluoromethyl)organopolysilanes and -siloxanes were prepared either by coupling of (trifluoromethyl)monosilanes or by trifluoromethylation of SiSi and SiOSi backbones. The monosilanes CF₃R₂SiX, CF₃RSiX₂ (X = halogen, H, NR₂, OR; R = alkyl, aryl) have been obtained by trifluoromethylation of chlorosilanes with P(NEt₂)₃/ CF₃Br in high yields. A new approach to CF₃SiCl₃ by the reaction of HSiCl₃ with NR₃ in presence of CF₃Br was investigated. Reaction in diglyme at 25°C affords CF₃SiCl₃ in 20 % yield. The base-catalysed disproportionation of Si₂Cl₆ with P(NEt₂)₃/ CF₃Br leads to donor-stabilised (CF₃)₂SiCl2← P(NEt₂)₃, whereas the disproportionation of Me₂Cl₄Si₂ gives CF₃MeSiCl₂. By conversion of the donor-stabilised (CF₃)₂SiCl₂ to (CF₃)₂Si(NMe₂)₂ bis(trifluoromethyl)silanes are readily accessible in good yields. (CF₃)₂SiCl2← P(NEt₂)₃ has been converted also into the chemically and thermally stable complex (CF₃)₂SiCl2← Bipy. The NMR parameters and the chemical behaviour of these compounds are compared with the properties of (CF₃)₂SiX2← Bipy (X = Cl, Br) and CF₃SiX3← D (X = Cl, D = Bipy, Phen, DMSO), which have been synthesised by the reaction of the free silanes and the donor-ligand. The first trifluoromethylated oligosilanes ([CF₃Me₂Si]₂SiMeCF₃, (CF₃Me₂Si)₃SiMe, [CF₃Me₂Si]₂(SiMe)2 [SiMe₂CF₃]₂, CF₃Si(SiMe₃)₃) and some new CF₃-disilanes ([CF₃R₁R₂Si]₂, R₁,R₂ = Me, R₂ = NR₂) were prepared by trifluoromethylation of the corresponding chloro-silanes and characterised by NMR and vibrational spectroscopy. The yield of CF3 substituted silanes depends on the steric hindrance of the silanes and the number of CF₃ groups, which have to be transferred. Formation of CF₃SiSi backbones by coupling of (trifluoromethyl)monosilanes has been achieved by reaction of CF₃Me₂SiCl with Li/ HMPA or in the photo-induced coupling of CF₃Me₂SiH with HgR₂ (R = Me, Et) both leading to CF₃Me₂SiSiMe₂CF₃. The lewis-acidic disilanes CF₃Me(X)SiSi(X)MeCF₃ (X = Cl, Br) show a dynamic intramolecular halogen exchange in presence of ammonium salts. Heating the mixture to 100°C leads to a crude product, which contains CF₃SiSi fragments. Trifluoromethylated disiloxanes were prepared either by trifluoromethylation of the corresponding halo-disiloxanes or by hydrolyses of CF₃R₂SiCl leading to [CF₃R₁R₂Si]₂O (R₁, R₂ = Me; R₁ = Me, R₂ = Ph; R₁, R₂ = Ph). Coupling of CF₃MeSi(H)Br with ZnO gives [CF₃Me(H)Si]₂O in low yield. CF₃-oligosiloxanes have been obtained by hydrolyses of CF₃MeSiX₂ (X = Cl, OMe) or CF₃PhSiCl₂. Reaction in polar solvents like Et₂O leads to the partiall loss of the CF₃ moiety resulting in silsesquioxane structures. The incompletely condensed silsesquioxane [CF₃MeSiO]₃[MeSiO1.5]₄ has been isolated and structurally characterised. The hydrolyses in CHCl₃ leads to the formation of the first cyclic (trifluoromethyl)siloxane [CF₃MeSiO]₄ and linear polysiloxanes. [CF₃MeSiO]₄ has been isolated by sublimation in vacuum and its structure was determined by X-ray analysis. The (trifluoromethyl)siloxanes were characterised by IR and NMR spectroscopy, showing a typical "CF₃"-shift of the resonances compared to organopolysiloxanes. The electron withdrawing effect of the trifluoromethylgroup has also been studied by structure analysis of the atranes CF₃E(OCH₂CH₂)₃N (E = Si, Ge). The atranes were prepared by the reaction of CF₃E(OMe)₃ with N(CH₂CH₂OH)₃. They are stable complexes, which are insoluble in non-polar solvents but soluble in solvents like DMF, DMSO or NMP. The transannular E-N contact of both atranes is considerably shorter than in other organylatranes.