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Exhaustively Trichlorosilylated C1 and C2 Building Blocks: Beyond the Müller–Rochow Direct Process

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posted on 09.07.2018, 00:00 by Isabelle Georg, Julian Teichmann, Markus Bursch, Jan Tillmann, Burkhard Endeward, Michael Bolte, Hans-Wolfram Lerner, Stefan Grimme, Matthias Wagner
The Cl-induced heterolysis of the Si–Si bond in Si2Cl6 generates an [SiCl3] ion as reactive intermediate. When carried out in the presence of CCl4 or Cl2CCCl2 (CH2Cl2 solutions, room temperature or below), the reaction furnishes the monocarbanion [C­(SiCl3)3] ([A]; 92%) or the vicinal dianion [(Cl3Si)2C–C­(SiCl3)2]2– ([B]2–; 85%) in excellent yields. Starting from [B]2–, the tetrasilylethane (Cl3Si)2(H)­C–C­(H)­(SiCl3)2 (H2B) and the tetrasilylethene (Cl3Si)2CC­(SiCl3)2 (B; 96%) are readily available through protonation (CF3SO3H) or oxidation (CuCl2), respectively. Equimolar mixtures of H2B/[B]2– or B/[B]2– quantitatively produce 2 equiv of the monoanion [HB] or the blue radical anion [B], respectively. Treatment of B with Cl ions in the presence of CuCl2 furnishes the disilylethyne Cl3SiCCSiCl3 (C; 80%); in the presence of [HMe3N]­Cl, the trisilylethene (Cl3Si)2CC­(H)­SiCl3 (D; 72%) is obtained. Alkyne C undergoes a [4+2]-cycloaddition reaction with 2,3-dimethyl-1,3-butadiene (CH2Cl2, 50 °C, 3d) and thus provides access to 1,2-bis­(trichlorosilyl)-4,5-dimethylbenzene (E1; 80%) after oxidation with DDQ. The corresponding 1,2-bis­(trichlorosilyl)-3,4,5,6-tetraphenylbenzene (E2; 83%) was prepared from C and 2,3,4,5-tetraphenyl-2,4-cyclopentadien-1-one under CO extrusion at elevated temperatures (CH2Cl2, 180 °C, 4 d). All closed-shell products were characterized by 1H, 13C­{1H}, and 29Si NMR spectroscopy; an EPR spectrum of [nBu4N]­[B] was recorded. The molecular structures of [nBu4N]­[A], [nBu4N]2[B], B, E1, and E2 were further confirmed by single-crystal X-ray diffraction. On the basis of detailed experimental investigations, augmented by quantum-chemical calculations, plausible reaction mechanisms for the formation of [A], [B]2–, C, and D are postulated.

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