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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 SiCl4 to HSiCl3 using organohydridosilanes as recyclable hydrogen transfer reagents in combination with onium chlorides as efficient catalysts. We put the same protocol to further use demonstrating the quantitative conversion of higher oligosilane residues, which form as another unwanted and potentially hazardous byproduct of Siemens processes, to HSiCl3 in a low-temperature recycling step.

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 MenSi2Cl6‐n (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. The reaction with metal hydrides, in particular lithium hydride (LiH), leads to efficient reduction of chlorine containing disilanes but also induces disproportionation into mono‐ and oligosilanes. Alkali and alkaline earth chlorides, formed in the course of the reduction, specifically induce disproportionation of highly chlorinated disilanes, whereas highly methylated disilanes (n>3) remain unreacted. Nearly quantitative DPR conversion into monosilanes was achieved by using concentrated HCl/ether solutions in the presence of lithium chloride., Too valuable for disposal or incineration: Simple recycling of the Müller–Rochow Direct Process residue with LiH yields monosilanes suitable for the reintroduction into the silicone production chain.

An experimental and theoretical study of the base- stabilized disilene 1 is reported, whichforms at lowtemper- atures in the disproportionation reaction of Si 2 Cl 6 or neo- Si 5 Cl 12 with equimolar amounts of NMe 2 Et. Single-crystal X- ray diffraction and quantum-chemical bonding analysis dis- close an unprecedented structure in silicon chemistry featuring adative Si!Si single bond between two silylene moieties, Me 2 EtN!SiCl 2 !Si(SiCl 3 ) 2 .The central ambiphilic SiCl 2 group is linked by dative bonds to the amine donor and the bis(trichlorosilyl)silylene acceptor,which leads to push–pull stabilization. Based on experimental and theoretical examina- tions aformation mechanism is presented that involves an autocatalytic reaction of the intermediately formed anion Si(SiCl 3 ) 3 ¢ with neo-Si 5 Cl 12 to yield 1.

The Muller-Rochow direct process (DP) for the large-scale production of methylchlorosilanes Men SiCl4-n (n=1-3) generates a disilane residue (Men Si2 Cl6-n , n=1-6, DPR) in thousands of tons annually. This report is on methylchlorodisilane cleavage reactions with use of phosphonium chlorides as the cleavage catalysts and reaction partners to preferably obtain bifunctional monosilanes Mex SiHy Clz (x=2, y=z=1; x,y=1, z=2; x=z=1, y=2). Product formation is controlled by the reaction temperature, the amount of phosphonium chloride employed, the choice of substituents at the phosphorus atom, and optionally by the presence of hydrogen chloride, dissolved in ethers, in the reaction mixture. Replacement of chloro by hydrido substituents at the disilane backbone strongly increases the overall efficiency of disilane cleavage, which allows nearly quantitative silane monomer formation under comparably moderate conditions. This efficient workup of the DPR thus not only increases the economic value of the DP, but also minimizes environmental pollution.

A combined experimental and theoretical study of the high-temperature reaction of SiCl4 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 defined model compounds, i.e. cyclo-Si5Cl10, n-Si5Cl12 and n-Si4Cl10. A DFT assessment provides mechanistic insight into the oligosilane formation. Experimental 29Si NMR investigations, supported by quantum-chemical 29Si NMR calculations, consistently show that the reaction product is composed of discrete molecular perchlorinated oligosilanes. Low-temperature chlorination is an unexpectedly selective means for the transformation of cyclosilanes to acyclic species by endocyclic Si-Si bond cleavage, and we provide a mechanistic rationalization for this observation. In contrast to the raw material, the product obtained after low-temperature chlorination represents an efficient source of neo-Si5Cl12 or the amine-stabilized disilene EtMe2N*SiCl2Si(SiCl3)2 through reaction with aliphatic amines.

A series of crystalline sodium and potassium organo substituted cyclotrisiloxanolates (I–IV) has been synthesized from the corresponding organotrialkoxysilanes and alkali bases in aqueous alcohol solvent media. Sodium ethyl- and n-propylcyclotrisiloxanolates (I, II) are obtained in high yields in a wide range of reaction conditions, while for the reaction of methyl- and vinyltrialkoxysilanes the use of potassium hydroxide under strictly controlled conditions for the formation of crystalline products (III, IV) is required. The four differently substituted alkali metal cation based cyclotrisiloxanolates were characterized by single crystal X-ray analyses that proved the six-membered siloxanolate cycles to adopt a distorted sofa or boat conformation, most probably resulting from intermolecular interactions. Regarding the crystal packing the corresponding cations and coordinated water molecules form layers that are coated with organotrisiloxanolate anions and ethanol molecules. This supramolecular organization is best described by hydrophilic layers with hydrophobic coatings regardless the nature of alkali metal cations. Relevant quantum chemical calculations show that the contribution of O–H⋯O bonding for the stabilization of the hydrophilic layers is predominant over that of the coordination K–O and Na–O bonds. The analysis of the bonding situation between the hydrophobic parts of the organotrisiloxanolate anions proves that the sum of energies of the H⋯H and C⋯H interactions might be characteristic for bonding within the interlayer space and this is much less for sodium cyclotrisiloxanolates compared to their potassium cation analogs (6.89/7.32 kcal mol−1 vs. 10.1/12.7 kcal mol−1). From these calculations important insight into the energies of non-covalent interactions, which play a crucial role for the stabilization of the molecular structures of sodium and potassium organocyclotrisiloxanolates, is obtained.

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 SinCl2n+2 (n = 2, 3) from which the octachlorotrisilane (n = 3, Cl8Si3, 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 BBr3 and PCl3, we achieved highly p- and n-type doped Si-NWs by means of atmospheric-pressure chemical vapor deposition (APCVD). These as grown NWs were investigated by means of scanning electron microscopy (SEM) and transmission electron microscopy (TEM), as well as electrical measurements of the NWs integrated in four-terminal and back-gated MOSFET modules. The intrinsic NWs appeared to be highly crystalline, with a preferred growth direction of [111] and a specific resistivity of ρ = 6 kΩ·cm. The doped NWs appeared to be [112] oriented with a specific resistivity of ρ = 198 mΩ·cm for p-type Si-NWs and ρ = 2.7 mΩ·cm for n-doped Si-NWs, revealing excellent dopant activation.

Seven silicon based model compounds that contain stilbene, butadiene or styrene subunits with different molecular structures were synthesized and characterized by NMR spectroscopy and single crystal X-ray crystallography. The UV–Vis absorption and photoluminescence spectra were measured in THF solution as well as in the solid state. The interpretation of the spectra reveals that the absorption and emission properties of the compounds originate from the stilbene or butadiene molecular subunits. This investigation provides basic information about the influence of silicon groups, molecular structures and substituents at silicon to absorption and emission properties in organic compounds. Furthermore, due to the functionality of the phenylethynyl substituents at silicon, these compounds may serve as optical active tools and precursors for the introduction of interesting physical properties into new materials for different applications.

We report on a comparative investigation of the structural and magnetic properties of three oxygen-bridged polynuclear (N = 6, 8, 10) Cu(II) cyclomethylsiloxanolate complexes, Cu6[(MeSiO2)6]2·6DMF (1), {Cu8[(MeSiO2)8]2·8DMF}·EtOH (2) and {Cu10[(MeSiO2)10]2·10DMF}·6DMF (3). All three molecular complexes have a planar ring-shaped configuration of the copper S = 1/2 spins. The analysis of the magnetic data, with particular emphasis placed on the high-temperature behaviour, together with the structural information enables us to correlate the evolution of the exchange coupling J between the magnetic S = 1/2 centers of the quantum ring as a function of the number N of magnetic sites to the structural changes of the molecular crystals.

Crystalline phenylsilanetriol, PhSi(OH)3 (1) was obtained by smooth hydrolysis of phenyltrimethoxysilane and characterised by different analytical methods (wide angle X-ray powder diffraction, NMR, IR, thermogravimetric analysis). The title-compound is surprisingly stable in the solid state but slowly condenses in acetone solution. Reaction of 1 with Me3SiCl and Me2(CH2Cl)SiCl gave the corresponding tris-triorganylsiloxy substituted derivatives in high yields.

A metal-free catalytic intramolecular hydrosilylation reaction is reported. The key intermediates in the catalytic cycle are silyl cationic species. The reaction is used to produce 2-silanorbornanes 2 from 3-cyclopentenemethylsilanes 1 under mild conditions and in high isolated yields.Key words: hydrosilylation, catalysis, silaheterocycles, silyl cations.

The X-ray crystal structures of four 1-(halodimethylsilylmethyl)-2-quinolinones have been measured and used to model the reaction profile for nucleophilic substitution at silicon. Similar structural correlations have been performed in solution, the percentage SiO bond formation being obtained from the 13 C chemical shifts of the quinolinone carbons and the extent of pentacoordination from the 29 Si chemical shift of the silicon. Excellent agreement is obtained between the two methods confirming the validity of the NMR technique for structural correlation in solution.

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 purifiedviasublimation and, for the first time, single crystals of hexabromodisilane, Si2Br6, and a new polymorph of hexaiododisilane, Si2I6, could be isolated. Molecules of Si2Br6are located on a special position of site symmetry 2/mwith a quarter of a molecule in the asymmetric unit. Molecules of Si2I6are located on a special position of site symmetry \overline{3} with a sixth of a molecule in the asymmetric unit. The bond lengths of Si2Br6and Si2I6are in the usual ranges and both molecules adopt a staggered conformation. It is interesting to note that Si2Br6and Si2I6do not form isomorphous structures. Moreover, an orthorhombic polymorph of the present structure of Si2I6is already known [Jansen & Friede (1996).Acta Cryst.C52, 1333–1334]. Although the title compounds feature such small and simple molecules they show completely different crystal structures.

A series of differently substituted alkeneinylhalogensilanes R 2 Si(X)–CC–C(Me)CH 2 (X=Cl: R=Me ( 2 ), Cl ( 3 ), Ph ( 4 ); X=F: R=Me ( 5 ), Mes ( 6 ), Tip ( 7 )) is reacted with t -BuLi in solvents of different polarity to give mainly E / Z -isomeric 2,4-bispentenylidene-1,3-disilacyclobutanes ( 11 , 23 and 31 ) and E / Z -isomeric 2,4,6-trispentenylidene-1,3,5-trisilacyclohexanes ( 12 and 24 ) competitively. Obviously the four- and six-membered silacycles are formed stepwise by intermolecular coupling reactions of the lithiated precursors R 2 Si(X)C(Li)CC(Me)– t -Bu which preliminary result from the 1,4-addition of the lithium organyle to the alkeneinylhalogensilanes. Alternatively, silacumulene formation (R 2 SiCCC(Me)CH 2 – t -Bu) might be discussed, but the isolation of Cl 3 Si–C(CC(Me)CH 2 – t -Bu)–CC–C(Me)CH 2 ( 22 ) as coupling product starting from trichlorosilane 3 and t -BuLi and high molecular multistep coupling products starting from the fluorinated precursors 5 and 7 strongly favour the the coupling reactions over silacumulene formation. Consequently, all attempts to isolate a stable silacumulene from the silicon sterically overcrowded starting compounds 6 and 7 failed.

Equimolar amounts of trichlorovinylsilane (9), lithium-tert-butyl, and 1,3-enynes were reacted to yield the corresponding isomeric silacyclobutanes and silacyclobutenes competitively. As reaction pathway the mixture 9/tBuLi is discussed to give a silene equivalent, Cl2Si=CHCH2tBu (10), yielding the four-membered ring silacycles by formal [2 + 2] cycloaddition reactions of 10 with the C=C double or the C=C triple bond of the 1,3-enyne. The relative ratio of the products formed depends on the polarity of the multiple bonds in the enyne, which is mainly determined by the substituent pattern. Thus, from the organosubstituted 1,3-enynes R1 C=C-C(R2)=CR3R4 (R1 = Me, Et, SiMe3, Ph; R2 = H, Me, Ph; R3=Me, OMe, Ph; R4=H; and R1C=C-R' (R' = 1-cyclohexenyl, cyclohexanevinylidyne)) and 9/tBuLi the silacyclobutanes 12, 13, and 15 and the silacyclobutenes 14,16-24, and 27 (from 10 and 3-hexyne) are prepared in a one-step synthesis and isolated from the reaction mixtures. The silacyclobutanes and -butenes are thermally stable and can be distilled under vacuo up to temperatures of about 150°C without decomposition. The experimental results are confirmed qualitatively by semiempiric calculations at the AM-1 level and their analysis using FMO theory. The solid state structure of the silacyclobutene 19 (C17H30Cl2Si2) has been determined by single crystal X-ray diffractometry. 19 is orthorhombic, space group P212121, a = 1030.94(2) pm, b = 1244.6(2) pm, c = 1605.5(3) pm, Z = 4.Key words: neopentylsilene, dichloroneopentylsilene, silacyclobutenes, silacyclobutanes, 1,3-enynes.

Molecules of the title compound, [Cu4Na4(C6H5O2Si)12(C4H10O)8], are located on special positions of site symmetry \overline{4}. The Cu atoms are coordinated in a square planar fashion. The Na atoms, on the other hand, show an irregular sixfold coordination mode. The molecular conformation is stabilized by O—H...O hydrogen bonds.

3-(Cyclohexylamino)propylmethoxydimethylsilane 1 is readily hydrolized to give the silanol 3-(cyclohexyl-amino)propyldimethylsilanol 2, which forms hydrogen bonded chains in the solid state.

The reaction between in situ formed 1.1-dichloro-2-neopentyl-1-silene, Cl2Si=CHCH2tBu (2), and 1,1-dimethylpentafulvene (5) leads to the formation of exo/endo-isomeric [4+2] cycloadducts 9 and [2+2] stereoisomers 10 in good yields. NMR spectroscopic investigations of the product mixture prove the different modes of the silene cycloaddition reactions ([4+2] vs [2+2] addition). Treatment of 9 and 10 with LiAlH4 and LiMe yield the stereo- and regioisomeric derivatives (LiAlH4: 16, 17: MeLi: 18. 19). whereas PhMgBr reacts with 10 to give only the mono substitution, the [4+2] compound 20. and the diphenylated silacyclobutane 21. The reactions of silene 2 with pentafulvenes 6-8 lead to similar results.

Reactions of 1.1-dichloro-2-neopentyl-3-vinyl-l-silacyclobutane ( 1a, b ) with carbonyl metallates [{M(CO) n } m ] 2- (M = Fe, m = 1, n = 4; M = Cr, m = 1, n = 5; M = W, m = 2, n = 5) in THF/HMPA lead to novel compounds [(CO) n MSiC 10 H 18 ] · HMPA (M = Fe, n = 4; M = Cr, W, n = 5). 1 H, 13 C and 29 Si NMR spectroscopic studies in solution support the formation of four diastereomeric pairs of enantiomers. The X-ray structure analyses of the crystals show folded 1-metallated 1-silacyclobutane units in which the HMPA ligand increases the coordination number of Si to 3 + 1. Crystals of [(CO) 5 CrSiC 10 H 18 ] · HMPA ( 2 ) and of [(CO) 5 WSiC 10 H 18 ] · HMPA ( 3 ) (corresponding values in brackets) are isotypic: P 2 1 / n (No. 14); a = 1084(1)/[1099(1)], b = 1927(1)/[1937(1)], c = 1342.1(8)/[1342(1)] pm, β = 97.11(7)/[97.18(7)]°, Z = 4. In both crystals enantiomeric [1 S ,2 S ,3 S ]/[1 R ,2 R ,3 R ] pairs are present. In orthorhombic crystals of [(CO) 4 FeSiC 10 H 18 ]. · HMPA ( 4 ) ( P 2 1 2 1 2 1 (No. 19), a = 896.4(5), b = 1693(1), c = 1753(1) pm, Z = 4) only the [1 S ,2 S ,3 S ]-isomer is detected.

In the title compound, C27H37N2 +·Br−·2CH2Cl2, both the cation and the anion are located on a crystallographic mirror plane. Both of the dichloromethane solvent molecules 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.

In this work the applicability of neopentasilane (Si(SiH3)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. Different sources for the gold nanoparticles have been tested: the spontaneous dewetting of gold films, thermally annealed gold films, deposition of preformed gold nanoparticles, and the use of “liquid bright gold”, a material historically used for the gilding of porcelain and glass. The latter does not only form gold nanoparticles when deposited as a thin film and thermally annealed, but can also be patterned by using UV irradiation, providing access to laterally structured layers of silicon nanowires.

Structural characterization of a polymethylsilsesquioxane (PMSQ) and a DT-type methyl silicone resin (MeDT) has been carried out by various instrumental analyses including GPC, NMR, gas chromatography, and gas chromatography-mass spectrometry. Although the PMSQ had aMwaround 5000, the resin contained a significant amount of low molecular weight species consisting of T2[MeSi(OH)O2/2] and T3[MeSiO3/2] units, ranging from to including many isomers. One isomer of was isolated of which structure was determined as a cage structure. The species are supposed to consist mainly of cyclotetra- and cyclopentasiloxanes, but presence of strained rings such as cyclotrisiloxane rings also was suggested. In MeDT, species in which the T2units in the molecules from PMSQ is replaced with D2[Me2SiO2/2] were found, for example, , suggesting that general silicone resins consist of similar structures as silsesquioxanes. The Mark-Houwink exponent for these methyl resins was~0.3, indicating the molecular shape to be compact. Investigation on the formation chemistry of the cubic octamers indicates that siloxane bond rearrangement is an important mechanism in the molecule build-up process.

The exo/endo[4+2]-cycloadducts of Cl2Si=CHCH2 tBu and cyclopentadiene 1 are transformed into the Si-dimethoxy- and chloro-methyl-substituted derivatives 2 and 4. In the case of the 2-silabicyclo[2.2.1] compounds 2 (R1 = R2 = OCH3), 3 (R1 = R2 = CH3) and 4 (R1 = Cl; R2 = CH3) the allyl cleavage with HCl/ether gives the ring opened products 8, 9, and 10 in good yields. The reaction can also be carried out with HBr/ether. In 1 the cleavage of the allyl-silicon bond is disfavoured due to the two chlorine atoms at silicon. Instead HCl adds to the C=C double bond and stereospecifically gives the exo-6-chloro-2,2-dichloro-3-exo/endo-neopentyl-2-silabicyclo[2.2.1]heptanes 5. When the stronger acid CF3SO3H is used no addition to the double bond is observed but only the allyl cleavage takes place to give the triflate 7. The ring opened cyclopentene compounds can be reduced by LiAlH4 to give the corresponding Si-H-compounds 19 and 20. Intramolecular hydrosilylation of 19 leads to the exo/endo-2,2-dimethyl-3-neopentyl-2-silabicyclo[2.2.1]heptanes 21 and so the former bicyclic structure is regenerated.

Generation by two different methods of silylenes stabilized by o -amino(aryl) groups is reported. The halodemetallation of difluoro or dichloro-silanes with Li metal or lithium-naphthalene gave the same product, a stabilized sila-ylide (hypercoordinated silylene). Intramolecular Lewis base stabilization is not sufficient to isolate a monomeric species. The silylenes, however, have been trapped with 2,3-dimethylbutadiene. An unexpected intramolecular rearrangement to silaacenaphthene has been observed in the case of a six-membered ring amino(aryl) coordinated silylene. Photolysis of o -1-[( N , N -dimethylamino)inethyl]-2-[tris(trimethylsilyl)silyl]benzene produced, among other products, Me 3 SiSiMe 3 and the sila-ylide, which has been trapped with Et 3 SiH and dimethylbutadiene. Our mechanistic interpretation is supported by spectral observation of the photochemically generated reaction intermediates in a 3-methylpentane glass at low temperature.

The reaction of [C6H4CH2N(CH3)2]2SiCl2 (1) with hydrogen chloride gives the singly protonated adduct 2. Its solid state structure has been determined by single crystal X-ray diffraction. Centrosymmetric 2 is orthorhombic, space group Pbca, a = 1694.9(2), b = 1161.7(2), c = 2501.7(3) pm; Z = 8. Controlled hydrolysis of 1 leads to the 1,3-siloxanediol 4, probably via the precursors 3a-3c which could not be isolated. The hydrogen chloride formed during the hydrolysis protonates two of the dimethylamino groups, while the other two dimethylamino functions form hydrogen bonds to the silanol groups. Centrosymmetric 4: monoclinic, space group P21/c, a = 980.3(1), b = 933.9(1), c = 2177.5(2) pm, β = 99.94(1)°; Ζ = 4. If the hydrolysis is carried out in the presence of lithium naphthalenide, the metalated compound {[C6H4CH2N(CH3)2]2Si(OLi)OH}4•2 LiCl•2CHCl3 (5) is obtained. The solid state structure of 5 exhibits two cube-like subunits which are held together by nitrogen and oxygen lithium contacts, hydrogen bonds between silanol groups and nitrogen atoms, and which are linked by the four silicon centres. Tetrameric 5: monoclinic, space group C2/C or Cc; a = 1523.6(2), b = 2440.2(1), c = 2534.8(2) pm, β = 93.83(3)°; Ζ = 8. These results show that the intramolecular donor capabilities of the dimethylaminobenzyl ligand at silicon can stabilize 1,3-siloxanediol and SiOLi substructures. Compounds like 1 serve as model compounds for the controlled formation of precursors for silicone synthesis.

Silicon compounds substituted by 2-(dimethylaminomethyl)phenyl groups [C6H4CH2N(CH3)2]nSiX4-n (X  Cl, H, organo group, n = 1–4) are available by the reaction of the appropriate chlorosilanes with 2-(dimethylaminomethyl)phenyllithium. A comparison of the 29Si NMR spectroscopic shifts δ with the values obtained for corresponding phenyl silanes shows that there is higher coordination of the silicon atom by N → Si contacts, except for the silanes 11 (X  Cl; n = 3) and 12 (n = 4). X-ray crystal structure analysis confirms pentacoordination of the silicon atom in the dichlorosilanes 4 (X  Cl; n = 2) and 5. For [C6H4CH2N(CH3)2]3SiH (10) heptacoordination of the silicon atom is found in the crystalline state [d(N → Si) ≈ 301 pm]. The tetrasubstituted derivative [C6H 4CH2N(CH3)2]4Si (12) has no N → Si contacts in solution and in the solid state: st eric congestion does not allow higher coordination. 10: colourless prisms, monoclinic, space group P 21/n; lattice constants: a = 889.0(3), b = 1677.5(8), c = 3471(1) pm; β = 90.35(3)°. 12: colourless prisms, pseudo tetragonal, space group I41/a; lattice constants: a = b = 1699.7(4), c = 3398.9(17) pm.

The 1-amino-2-neopentylsilenes 5-8 are formed in the reaction of LitBu with the aminovinylsilanes 1-4 in n-pentane (addition of LitBu to the vinylic double bond with subsequent 1,2-elimination of LiCl). The α-Li adducts initially formed are trapped by Me3SiOSO2CF3 to yield α-SiMe3-silanes. The silenes undergo insertion reactions into the Si—O bond of Me3SiOMe. In the absence of any trapping reagent dimerization occurs. One of the 1,3-disilacyclobutanes thus formed (15) could be examined by X-ray diffraction. Reacting with 1,3-butadienes the chlorosubstituted silenes 5 and 8 yield [2 + 2]-cycloaddition products. With 1,3-cyclohexadiene Diels-Alder adducts are also obtained, but with cyclopentadiene the [4+2] adducts are formed exclusively. Products of an ene-reaction are observed upon treatment of 2,5-norbornadiene with the silenes 5 and 8. The methylsubstituted silene 6 does not undergo any cycloaddition reaction at all, while from silene 7 only traces of the cycloadducts are produced. Both species mainly yield the dimers. The preference for the [2+2] reaction type, exhibited by the silenes 5 and 8, is due to their polarity. The almost complete absence or low yield of any cycloaddition products from 6 or 7 can be correlated with the energy levels of their frontier molecular orbitals. The distribution of the disilacyclobutanes and cycloaddition product isomers is explained by the characteristics of the stereospecifically Ε-configurated silenes. The product distribution can also be rationalized considering the ambiphilic nature of the system ViRR′SiCl/Li1Bu.

The title solvated salt, C29H41N2+·Br−·2CH2Cl2was obtained from the reaction of the Arduengo-type carbene 1,3-bis(2,6-diisopropylphenyl)-1,3-dihydro-4,5-dimethyl-2H-imidazol-2-ylidene with Si2Br6in dichloromethane. 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 40.7 (2)°. The anion also lies on the mirror plane and both dichloromethane molecules are disordered across the mirror plane over two equally occupied orientations. In the crystal, the cations are linked to the anionsviaC—H...Br hydrogen bonds.

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). By optimizing the growth conditions, effective NW synthesis is shown for alternative catalysts, in particular, Cu, Ag, Ni, and Pt with the latter two being compatible to complementary metal-oxide-semiconductor technology. As for these catalysts, the growth temperatures are lower than the lowest liquid eutectic; we suggest that the catalyst particle is in the solid state during NW growth and that a solid-phase diffusion process, either in the bulk, on the surface, or both, must be responsible for NW nucleation.

The amino-substituted vinylchlorosilanes 4-7 are synthesized from N,N,N′-trimethylethylenediamine (8a) or tris(trimethylsilyl)ethylenediamine (8b), Li Bun and organodichlorovinylsilanes. 5 eliminates trimethylchlorosilane when distilled and yields 1,3-diaza-2-silacyclopentane 9, whereas the compounds 6 and 7 show a great tendency to oligomerize. The reaction of 4 with LiBut gives a neopentylsilene intermediate 10 a which can be trapped by isoprene or 1,3-butadiene yielding small amounts of the Diels-Alder products 11 and 12, respectively. The main reaction pathway for 10 a is rearrangement with migration of a Me3Sigroup from nitrogen to the silene’s carbon atom and a new N—Si bond formation to give the diazasilacyclopentane 10 which has been characterized by X-ray diffraction analysis. This intramolecular rearrangement appears to involve a pentacoordinated silene Si-atom. No dimerisation of 10a to a disilacyclobutane is observed. The introduction of a second Si-tris(trimethylsilyl)ethylenediamine substituent at the SiC frame work does not result in silene stabilisation: there is no evidence for Si-hexacoordination in silene 15 nor in the [4+2] cyclo-addition product with isoprene (14).

The silene 2 is formed by reacting 2-chloro-1,3-bis(trimethylsilyl)-2-vinyl-1,3-diaza-2-silacyclopentane (5) with LiBut in n-pentane in the temperature range from -10 to +10°C. The reaction primarily leads to the corresponding a-lithio adduct 6 by addition of the Li-organyl to the vinyl group of 5; subsequent 1,2-LiCl elimination yields 2 as an intermediate. 2 can be trapped by polar reagents Me3SiX (X = OMe, OSO2CF3) as well as by organic dienes which add across the Si=C bond; in the absence of trapping agents, trisilacyclohexane 7 is isolated. The cycloaddition behaviour of 2 is best described by the two mesomeric formulae (a) and (β), with competitive [4+2] and [2+2] addition routes: While with butadienes and norborna-2,5-diene the [2+2] products are formed mainly in a multiple step reaction via zwitterionic intermediates (1,4 dipoles), the ratio of the [4+2]/[2+2] derivatives from 2 and cyclohexa-1,3-diene becomes nearly equivalent. 2 is thus quite comparable in its reactivity to dichloroneopentylsilene, Cl2Si = CHCH2But.

The reaction of 2-chloro-1,3-bis(trimethylsilyl)-2-(1′-trimethylsilyl-ethenyl)-1,3-diaza-2-silacyclopentane (5) and LiBu leads to the α-lithio adduct 8 which can be trapped by Me3Sitriflate to give 13b, and is a useful silene precursor. Subsequent 1,2-LiCl elimination yields 2 as an intermediate, which does not cyclodimerise giving a 1,3-disilacyclobutane, but can be trapped by Me3SiOMe and suitable dienes which add across the Si=C bond. In contrast to silene 1, which favours the [2+2] addition, 2 exclusively forms the Diels-Alder isomers with 2-methyl-1,3-butadiene and 2,3-dimethyl-1,3-butadiene (6 and 7), and the ene products 11 and 12 with norborna-2,5-diene and cyclohexa-1,3-diene, respectively. This quite different cycloaddition behaviour results from the substitution pattern at the Si=C framework, with a changing polarity. 2 thus appears to be a rather electron deficient silene having a polarity more comparable to that of diorganosilenes rather than to 1, which may be compared in its reactivity with Cl2Si = CHCH2Bu.

The silenes A and B are formed by reacting 1,3-ditbutyl-2,4-dichloro-2,4-divinyl-1,3-diaza- 2.4-disilacyclobutane (2) and 1,3-dichloro-2,4-dineopentyl-1,3-divinyl-1,3-disilacyclobutane (15) with LiBut in n-pentane in the temperature range from −10 to 0 °C. The reaction primarily leads to the corresponding α-lithioadducts (addition of LiBut to the vinyl group of 2 and 15), and with subsequent 1,2-LiCl elimination yields A and B as intermediates. A can be trapped by polar reagents Me3SiX (X = OMe, OSO2CF3) as well as by organic dienes which add across the Si = C bond; in the absence of a trapping agent the spiro compound 6 is isolated. The silenes A and B differ in their cycloaddition behaviour to butadienes, norbornadiene and cyclohexa-1,3-diene: Whereas for A the regioselective [2 + 2]-cycloaddition to yield monosilacyclobutane derivatives is preferred due to electronic reasons, the reaction of B leads mainly to Diels-Alder products. Thus, A is quite comparable in its reactivity to dichloroneopentylsilene, while B reacts like its diorgano substituted analogues R2Si = CHCH2But (R = Me, But or Ph).

The reaction of (tBuO)2Si(Cl)Vi (3) with LitBu has been investigated in pentane or toluene (non-polar) and mixtures of pentane or toluene with THF (polar), respectively, in order to gain information about the influence of substituents and the polarity of the solvent on the reaction mechanism. In accord with earlier results, using Me2Si(Cl)Vi (1) [8] ortBu2Si(Cl)Vi (2) [5] as precursors, the course of reaction in non-polar solvents is dominated by 1,2-elimination of LiCl from the α-lithio intermediate R2Si(Cl)CH(Li)CH2HtBu yielding 1,1,3,3-tetra(tertbutoxy)-1,3-disilacyclobutane (4) via the corresponding silaethene derivative. On the other hand, the presence of small amounts (5% by volume) of THF in the solvent system leads to a considerable decrease in the yield of 4 and favours secondary reactions of the α-lithio derivative by solvate formation giving chain compounds like (tBuO)2Si(X)CH2CH2 tBu (X = Cl, tBu) and (tBuO)2Si(CH=CHtBu)Si(OtBu)2CH2CH2 tBu (5b). MNDO calculations on the model compounds Me2Si=CH2, Me2Si=CH2 · OH2 and (HO)2Si=CH2, (HO)2Si=CH2 · OH2, respectively, show that for the gas phase molecules the formation of the dimethyl derivatives from the corresponding α-lithio intermediate is less endothermic than that of the dihydroxy analogues. Therefore, the differences observed in the product pattern of the reactions of 1 and 3, respectively, especially in polar systems, can only be explained by a combination of substituent and solvent effects on the kinetics.

Dichloroneopentylsilene, Cl2Si=CHCH2Bu' (1), is produced from vinyltrichlorosilane (2) and LiBu' in n-pentane at —78 °C. The reactions of 1 with aromatic aldehydes like benzaldehyde and the 4-methoxy- or 4-fluoro-substituted derivatives, naphthalene-1- and -2- and 9-anthracenecarbaldehyde, furfurale and its S-analogous thiophene carbaldehyde yield 1,2-silaoxetanes by [2+2] cycloaddition with the carbonyl group. The same is true for the reactions of 1 with pivaline-, butyr- and acetaldehyde. The silaoxetanes cannot be isolated; the formation of dichlorovinylsiloxanes and the olefinic compounds R—CH=CH —CH2Bu′suggests that the cycloreversion of the Si—O four-membered ring competes with an intramolecular isomerization, evidently via formation of a zwitterionic intermediate . The product formation by coupling reactions of lithiated aldehydes and 2 is excluded by performing analogous reactions with the chlorosilanes Me2SiCl(R) (R = Cl, Me, Vi).

In triclinic crystals of 2,2,4,4,6,6-hexaphenylcyclotrisiloxane, C36H30O3Si3, the endocyclic C—C—C bond angles in the phenyl groups at the C atoms bound to silicon are reduced to about 117°. The other geometric parameters do not show any significant differences from expected values.

1,4-Diaza-8,8,8-trimethoxy-8-silaoctane (1) loses methanol upon heating and gives an eight-membered silatrane-like silaheterocyle, 1,6-diaza-2,2-dimethoxy-2-silacyclooctane (2).

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. In addition, the crystal structure contains one dimethyl­formamide mol­ecule which is disordered over a centre of inversion. The copper layer, containing eight atoms, is located between two siloxanolate fragments. The whole structure of Cu atoms and siloxanolate rings is distorted by the pyrazine mol­ecule, leading to an oval form. As a result, the angles between the Cu atoms differ at the copper layer. The difference in the angles could lead to some deviations in the Cu–Cu exchange inter­actions within the copper ring, which is of inter­est for mol­ecular magnetism.

A new polymorph of diphenylbis(triphenylsilyl)silane, C48H40Si3, has been discovered. Until now, only an orthorhombic polymorph of the title compound was known. The newly found trigonal polymorph crystallizes in R\overline{3} with one molecule in the asymmetric unit.

The title compound, [Sn(CH3)2(C5H10NS2)2], previously reported by Morris & Schlemper [J. Cryst. Mol. Struct. (1979), 9, 13–31], has been rerefined against new intensity data. Geometric parameters agree quite well. However, the positions of the hydroxyl H atoms could be determined employing the new data. Furthermore, the results of the present structure determination are of significantly higher precision. There are one and a half mol­ecules in the asymmetric unit. The Sn atom of one mol­ecule is located on a twofold rotation axis, whereas all other atoms are located in general positions.