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

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.