The Cl-induced heterolysis of the Si-Si bond in SiCl generates an [SiCl] ion as reactive intermediate. When carried out in the presence of CCl or ClC═CCl (CHCl solutions, room temperature or below), the reaction furnishes the monocarbanion [C(SiCl)] ([A]; 92%) or the vicinal dianion [(ClSi)C-C(SiCl)] ([B]; 85%) in excellent yields. Starting from [B], the tetrasilylethane (ClSi)(H)C-C(H)(SiCl) (HB) and the tetrasilylethene (ClSi)C═C(SiCl) (B; 96%) are readily available through protonation (CFSOH) or oxidation (CuCl), respectively. Equimolar mixtures of HB/[B] or B/[B] 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 CuCl furnishes the disilylethyne ClSiC≡CSiCl (C; 80%); in the presence of [HMeN]Cl, the trisilylethene (ClSi)C═C(H)SiCl (D; 72%) is obtained. Alkyne C undergoes a [4+2]-cycloaddition reaction with 2,3-dimethyl-1,3-butadiene (CHCl, 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 (CHCl, 180 °C, 4 d). All closed-shell products were characterized by H,C{H}, and Si NMR spectroscopy; an EPR spectrum of [ nBuN][B] was recorded. The molecular structures of [ nBuN][A], [ nBuN][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], C, and D are postulated.

The geminal frustrated Lewis pair tBu2PCH2B(Fxyl)2 (1; Fxyl=3,5‐(CF3)2C6H3) is accessible in 65 % yield from tBu2PCH2Li and (Fxyl)2BF. According to NMR spectroscopy and X‐ray crystallography, 1 is monomeric both in solution and in the solid state. The intramolecular P⋅⋅⋅B distance of 2.900(5) Å and the full planarity of the borane site exclude any significant P/B interaction. Compound 1 readily activates a broad variety of substrates including H2, EtMe2SiH, CO2/CS2, Ph2CO, and H3CCN. Terminal alkynes react with heterolysis of the C−H bond. Haloboranes give cyclic adducts with strong P−BX3 and weak R3B−X bonds. Unprecedented transformations leading to zwitterionic XP/BCX3 adducts occur on treatment of 1 with CCl4 or CBr4 in Et2O. In less polar solvents (C6H6, n‐pentane), XP/BCX3 adduct formation is accompanied by the generation of significant amounts of XP/BX adducts. FLP 1 catalyzes the hydrogenation of PhCH=NtBu and the hydrosilylation of Ph2CO with EtMe2SiH.

Trichlorosilylated tetrelides [(Cl3Si)3E]− have been prepared by adding 1 equiv of a soluble Cl− salt to (Cl3Si)4Si (E=Si) or 4 Si2Cl6/GeCl4 (E=Ge). To assess their donor qualities, the anions [(Cl3Si)3E]− (E=C, Si, Ge) have been treated with BCl3, AlCl3, and GaCl3. Both BCl3 and GaCl3 give 1:1 adducts with the anionic centers. AlCl3 leads to Cl− abstraction from [(Cl3Si)3E]− with formation of (Cl3Si)4E (E=Si or Ge). (Cl3Si)4Ge is cleanly converted to the perhydrogenated (H3Si)4Ge by use of Li[AlH4]. Another case of Cl− abstraction was observed for [(Cl3Si)3Ge⋅GaCl3]−, which reacts with GaCl3 to afford the neutral dimer [(Cl3Si)3Ge−GaCl2]2.

The exhaustive trichlorosilylation of hexachloro‐1,3‐butadiene was achieved in one step by using a mixture of Si2Cl6 and [nBu4N]Cl (7:2 equiv) as the silylation reagent. The corresponding butadiene dianion salt [nBu4N]2[1] was isolated in 36 % yield after recrystallization. The negative charges of [1]2− are mainly delocalized across its two carbanionic (Cl3Si)2C termini (α‐effect of silicon) such that the central bond possesses largely C=C double‐bond character. Upon treatment with 4 equiv of HCl, [1]2− is converted into neutral 1,2,3,4‐tetrakis(trichlorosilyl)but‐2‐ene, 3. The Cl− acceptor AlCl3, induces a twofold ring‐closure reaction of [1]2− to form a six‐membered bicycle 4 in which two silacyclobutene rings are fused along a shared C=C double bond (84 %). Compound 4, which was structurally characterized by X‐ray crystallography, undergoes partial ring opening to a monocyclic silacyclobutene 2 in the presence of HCl, but is thermally stable up to at least 180 °C.

The exhaustive trichlorosilylation of hexachloro‐1,3‐butadiene was achieved in one step by using a mixture of Si2Cl6 and [nBu4N]Cl (7:2 equiv) as the silylation reagent. The corresponding butadiene dianion salt [nBu4N]2[1] was isolated in 36 % yield after recrystallization. The negative charges of [1]2− are mainly delocalized across its two carbanionic (Cl3Si)2C termini (α‐effect of silicon) such that the central bond possesses largely C=C double‐bond character. Upon treatment with 4 equiv of HCl, [1]2− is converted into neutral 1,2,3,4‐tetrakis(trichlorosilyl)but‐2‐ene, 3. The Cl− acceptor AlCl3, induces a twofold ring‐closure reaction of [1]2− to form a six‐membered bicycle 4 in which two silacyclobutene rings are fused along a shared C=C double bond (84 %). Compound 4, which was structurally characterized by X‐ray crystallography, undergoes partial ring opening to a monocyclic silacyclobutene 2 in the presence of HCl, but is thermally stable up to at least 180 °C.