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.

Silylenes and silanides, prominent Si(ii) species, are not only interesting in their own right, but also constitute important building blocks in oligosilane and organosilane chemistry. The past decade has witnessed tremendous advances in the understanding of the ambiphilic behavior of silylenes and the nucleophilic properties of silanides, as well as the mutual relationships between both species. Especially the readily available SiCl/[SiCl] system is intriguing, because it features highly functionalized silicon centers, amenable to late-stage modifications. Moreover, SiCl and [SiCl] are interconvertible by mere chloride association/dissociation. This Feature Article first provides a brief introduction to isolable (functionalized) silylenes and silanides and then focusses on the SiCl/[SiCl] couple. Classical high-temperature protocols for the generation of SiCl are juxtaposed with convenient recent solution phase methods that provide access to RN-SiCl and [SiCl]via deprotonation of HSiCl or the amine-/chloride-induced disproportionation of SiCl. We give a comprehensive overview of key mechanistic issues and highlight the utility of RN-SiCl and [SiCl] for the synthesis of open-chain and cyclic oligosilanes as well as nanoscale, fullerene-type silicon clusters.

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.

Treatment of SiCl with [EtN][BCl] in CHCl furnished the known products of a chloride-induced disproportionation reaction of the disilane, such as SiCl, [Si(SiCl)], and [SiCl·2Cl]. No Si-B-bonded products were detectable. In contrast, the addition of SiCl to [EtN][BICl] afforded the Si-B adduct [EtN][ISiBI]. Thus, a quantitative Cl/I exchange at the silicon atom accompanies the trihalogenosilanide formation. [EtN][ISiBI] was also accessible from a mixture of SiI, [EtN]I, and BI. According to X-ray crystallography, the anion [ISiBI] adopts a staggered conformation with an Si-B bond length of 1.977(6) Å. Quantum-chemical calculations revealed a polar covalent Si-B bond with significant contributions from intramolecular I···I dispersion interactions.

The halosilicates(II) [nBu 4 N] 2 [Si 6 Br 12 ·2Br] and [nBu 4 P] 2 [Si 6 I 12 ·2I] were prepared by mere addition of the appropriate halide salt to the corresponding disilane Si 2 X 6 (X = Br, I). In the first case, the Br 3 Si-substituted derivative [nBu 4 N] 2 [Si 7 Br 14 ·2Br] formed as a second product. We have been able to obtain single crystals of [Ph 4 P] 2 [Si 7 Br 14 ·2Br] by switching the Brsalt from [nBu 4 N]Br to [Ph 4 P]Br. All three compounds, [nBu 4 N] 2 [Si 6 Br 12 ·2Br] (monoclinic, P2 1 /c), [nBu 4 P] 2 [Si 6 I 12 ·2I] (triclinic, P1), and [Ph 4 P] 2 [Si 7 Br 14 ·2Br] (triclinic, P1) were structurally characterized by X-ray crystallography and found to form "inverse sandwich complexes", in which two Xions are located above and below a planarized Si 6 ring. The free periodated cyclohexasilane Si 6 I 12 is accessible from [nBu 4 N] 2 [Si 6 Cl 12 ·2Cl] and BI 3 (1:5 molar ratio; CH 2 Cl 2 ) via a decomplexation/halide-exchange cascade. Si 6 I 12 (monoclinic, C2/c) adopts a