Siemens Reloaded: Chloride-Assisted Selective Hydrodechlorination of SiCl to HSiCl.

Trichlorosilane is the key intermediate for the large-scale production of polycrystalline silicon in the Siemens and Union Carbide processes. Both processes, however, are highly inefficient, and over two thirds of the trichlorosilane employed is converted to unwanted silicon tetrachloride accumulating in millions of tons per year on a global scale. In this combined experimental and theoretical study we report an energetically and environmentally benign synthetic protocol for the highly selective conversion of SiCl to HSiCl using organohydridosilanes as recyclable hydrogen transfer reagents in combination with onium chlorides as efficient catalysts.

Disilane Cleavage with Selected Alkali and Alkaline Earth Metal Salts.

The industry-scale production of methylchloromonosilanes in the Müller-Rochow Direct Process is accompanied by the formation of a residue, the direct process residue (DPR), comprised of disilanes Me Si Cl (n=1-6). Great research efforts have been devoted to the recycling of these disilanes into monosilanes to allow reintroduction into the siloxane production chain. In this work, disilane cleavage by using alkali and alkaline earth metal salts is reported.

Making Use of the Direct Process Residue: Synthesis of Bifunctional Monosilanes.

The industrial production of monosilanes Me SiCl (n=1-3) through the Müller-Rochow Direct Process generates disilanes Me Si Cl (n=2-6) as unwanted byproducts ("Direct Process Residue", DPR) by the thousands of tons annually, large quantities of which are usually disposed of by incineration. Herein we report a surprisingly facile and highly effective protocol for conversion of the DPR: hydrogenation with complex metal hydrides followed by Si-Si bond cleavage with HCl/ether solutions gives (mostly bifunctional) monosilanes in excellent yields. Competing side reactions are efficiently suppressed by the appropriate choice of reaction conditions.

Lewis Base Catalyzed Selective Chlorination of Monosilanes.

A preparatively facile, highly selective synthesis of bifunctional monosilanes R SiHCl, RSiHCl and RSiH Cl is reported. By chlorination of R SiH and RSiH with concentrated HCl/ether solutions, the stepwise introduction of Si-Cl bonds is readily controlled by temperature and reaction time for a broad range of substrates. In a combined experimental and computational study, we establish a new mode of Si-H bond activation assisted by Lewis bases such as ethers, amines, phosphines, and chloride ions.

Thermal Synthesis of Perchlorinated Oligosilanes: A Fresh Look at an Old Reaction.

A combined experimental and theoretical study of the high-temperature reaction of SiCl and elemental silicon is presented. The nature and reactivity of the product formed upon rapid cooling of the gaseous reaction mixture is investigated by comparison with the defined model compounds cyclo-Si Cl , n-Si Cl and n-Si Cl . A DFT assessment provides mechanistic insight into the oligosilane formation.

A Disilene Base Adduct with a Dative Si-Si Single Bond.

An experimental and theoretical study of the base-stabilized disilene 1 is reported, which forms at low temperatures in the disproportionation reaction of Si2 Cl6 or neo-Si5 Cl12 with equimolar amounts of NMe2 Et. Single-crystal X-ray diffraction and quantum-chemical bonding analysis disclose an unprecedented structure in silicon chemistry featuring a dative Si→Si single bond between two silylene moieties, Me2 EtN→SiCl2 →Si(SiCl3 )2 . The central ambiphilic SiCl2 group is linked by dative bonds to the amine donor and the bis(trichlorosilyl)silylene acceptor, which leads to push-pull stabilization.

Amorphous silicon: new insights into an old material.

Amorphous silicon is synthesized by treating the tetrahalosilanes SiX4 (X=Cl, F) with molten sodium in high boiling polar and non-polar solvents such as diglyme or nonane to give a brown or a black solid showing different reactivities towards suitable reagents. With regards to their technical relevance, their stability towards oxygen, air, moisture, chlorine-containing reaction partners RCl (R=H, Cl, Me) and alcohols is investigated. In particular, reactions with methanol are a versatile tool to deliver important products.

Crystal structure of 1,3-bis-(2,6-diiso-propyl-phen-yl)-4,5-dimethyl-1H-imid-azol-3-ium bromide di-chloro-methane disolvate.

The title solvated salt, C29H41N2 (+)·Br(-)·2CH2Cl2 was obtained from the reaction of the Arduengo-type carbene 1,3-bis-(2,6-diiso-propyl-phen-yl)-1,3-dihydro-4,5-dimethyl-2H-imidazol-2-ylidene with Si2Br6 in di-chloro-methane. The complete cation is generated by a crystallographic mirror plane and the dihedral angle between the five-membered ring and the benzene ring is 89.8 (6)°; the dihedral angle between the benzene rings is 40.

Hexabromo- and hexaiododisilane: small and simple molecules showing completely different crystal structures.

The title compounds were prepared through dephenylation of hexaphenyldisilane with acetyl bromide or acetyl iodide in the presence of the corresponding aluminium halide. Both substances were purified via sublimation and, for the first time, single crystals of hexabromodisilane, Si2Br6, and a new polymorph of hexaiododisilane, Si2I6, could be isolated. Molecules of Si2Br6 are located on a special position of site symmetry 2/m with a quarter of a molecule in the asymmetric unit.

Microwave-assisted carbohydrohalogenation of first-row transition-metal oxides (M = V, Cr, Mn, Fe, Co, Ni, Cu) with the formation of element halides.

The anhydrous forms of first-row transition-metal chlorides and bromides ranging from vanadium to copper were synthesized in a one-step reaction using the relatively inexpensive element oxides, carbon sources, and halogen halides as starting materials. The reactions were carried out in a microwave oven to give quantitative yields within short reaction times.

A general approach toward shape-controlled synthesis of silicon nanowires.

Controlling the morphology, electronic properties, and growth direction of nanowires (NWs) is an important aspect regarding their integration into devices on technologically relevant scales. Using the vapor-solid-solid (VSS) approach, with Ni as a catalyst and octachlorotrisilane (Si(3)Cl(8), OCTS) as a precursor, we achieved epitaxial growth of rectangular-shaped Si-NWs, which may have important implications for electronic mobility and light scattering in NW devices. The process parameters were adjusted to form cubic α-NiSi(2) particles which further act as the shaping element leading to prismatic Si-NWs.

Synthesis and electrical characterization of intrinsic and in situ doped Si nanowires using a novel precursor.

Perchlorinated polysilanes were synthesized by polymerization of tetrachlorosilane under cold plasma conditions with hydrogen as a reducing agent. Subsequent selective cleavage of the resulting polymer yielded oligochlorosilanes Si(n)Cl(2) (n) (+2) (n = 2, 3) from which the octachlorotrisilane (n = 3, Cl(8)Si(3), OCTS) was used as a novel precursor for the synthesis of single-crystalline Si nanowires (NW) by the well-established vapor-liquid-solid (VLS) mechanism. By adding doping agents, specifically BBr(3) and PCl(3), we achieved highly p- and n-type doped Si-NWs by means of atmospheric-pressure chemical vapor deposition (APCVD).

Directed deposition of silicon nanowires using neopentasilane as precursor and gold as catalyst.

In this work the applicability of neopentasilane (Si(SiH(3))(4)) as a precursor for the formation of silicon nanowires by using gold nanoparticles as a catalyst has been explored. The growth proceeds via the formation of liquid gold/silicon alloy droplets, which excrete the silicon nanowires upon continued decomposition of the precursor. This mechanism determines the diameter of the Si nanowires.

1,3-Bis(2,6-diisopropyl-phen-yl)-1H-imidazol-3-ium bromide dichloro-methane disolvate.

In the title compound, C(27)H(37)N(2) (+)·Br(-)·2CH(2)Cl(2), both the cation and the anion are located on a crystallographic mirror plane. Both of the dichloro-methane solvent mol-ecules show a disorder across a mirror plane over two equally occupied positions. In the crystal, the cations are connnected to the bromide ions via C-H⋯Br hydrogen bonds.

1,3-Bis(2,6-diisopropyl-phen-yl)-1H-imidazol-3-ium chloride dichloro-methane disolvate.

In the title compound, C(27)H(37)N(2) (+)·Cl(-)·2CH(2)Cl(2), the cation and the anion are each located on a crystallographic mirror plane. Both of the dichloro-methane solvent mol-ecules show a disorder across a mirror plane over two equally occupied positions. Additionally, one isopropyl group is also disordered.

N-(2,6-Diisopropyl-phen-yl)formamide toluene 0.33-solvate.

The crystal packing of the title compound, C(13)H(19)NO·0.33C(7)H(8), shows a channel at [001], which contains grossly disordered toluene solvent mol-ecules. The angle between the benzene ring and the mean plane of the formamide group is 71.

Binary Pt-Si nanostructures prepared by focused electron-beam-induced deposition.

Binary systems of Pt-Si are prepared by electron-beam-induced deposition using the two precursors, trimethyl(methylcyclopentadienyl)platinum(IV) (MeCpPt(Me)(3)) and neopentasilane (Si(SiH(3))(4)), simultaneously. By varying the relative flux of the two precursors during deposition, we are able to study composites containing platinum and silicon in different ratios by means of energy-dispersive X-ray spectroscopy, atomic force microscopy, electrical transport measurements, and transmission electron microscopy. The results show strong evidence for the formation of a binary, metastable Pt(2)Si(3) phase, leading to a maximum in the conductivity for a Si/Pt ratio of 3:2.

Subeutectic synthesis of epitaxial Si-NWs with diverse catalysts using a novel Si precursor.

The applicability of a novel silicon precursor with respect to reasonable nanowire (NW) growth rates, feasibility of epitaxial NW growth and versatility with respect to diverse catalysts was investigated. Epitaxial growth of Si-NWs was achieved using octochlorotrisilane (OCTS) as Si precursor and Au as catalyst. In contrast to the synthesis approach with SiCl(4) as precursor, OCTS provides Si without the addition of H(2).

Synthesis, structure, photoluminescence and photoreactivity of 2,3-diphenyl-4-neopentyl-1-silacyclobut-2-enes.

A series of six 2,3-diphenyl-4-neopentyl-1-silacyclobut-2-enes with different 1,1-substituents has been prepared and characterized by single-crystal X-ray crystallography. These compounds possess a cis-stilbene-like chromophore involving also the four-membered ring, and exhibit a photophysical behavior similar to that of previously reported 1,2-diphenyl-cycloalkenes. This chromophore system is confirmed by a theoretical investigation of the electronic structure and excitation spectra.

Direct formation of element chlorides from the corresponding element oxides through microwave-assisted carbohydrochlorination reactions.

A series of technically and economically important element chlorides-such as SiCl4, BCl3, AlCl3, FeCl2, PCl3 and TiCl4-was synthesized through reactions between hydrogen chloride and the corresponding element oxides in the presence of different carbon sources with microwave assistance. This process route was optimized for demonstration purposes for tetrachlorosilane formation and successfully demonstrates the broad applicability of various silicon oxide-containing minerals and materials for carbohydrochlorination. The chlorination reaction occurs at lower temperatures than with conventional heating in a tubular oven, with substantially shorter reaction times and in better yields: quantitatively in the case of tetrachlorosilane, based on the silicon content of the starting material.

Molecular optical switches: synthesis, structure, and photoluminescence of spirosila compounds.

Starting from a silicon dichloro substituted silole and a silacyclobutene, a series of new organosilicon-based spiro compounds was synthesized by using standard organometallic reaction procedures. The spiro compounds that combine two organic photoactive subunits at one silicon center were fully characterized by the usual analytical and spectroscopic methods, which include molecular structure determination by single-crystal X-ray analysis. Photoluminescence spectra of the compounds were recorded in the solid state and also as dilute solutions in THF.

Bis(mu6-cis-2,4,6,8,10,12,14,16-octamethylcyclooctasiloxane-2,4,6,8,10,12,14,16-octolato)octakis[(dimethylformamide)copper(II)] dimethylformamide solvate enclosing a pyrazine molecule.

The title compound, [Cu8(C8H24O2Si)2(C3H7NO)8].C4H4N2.C3H7NO, features a sandwich-like cage enclosing a pyrazine molecule, both situated on a centre of inversion.