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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.

A preparatively facile, highly selective synthesis of bifunctional monosilanes R2 SiHCl, RSiHCl2 and RSiH2 Cl is reported. By chlorination of R2 SiH2 and RSiH3 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. Elucidation of the underlying reaction mechanisms shows that alcohol assistance through hydrogen-bond networks is equally efficient and selective. Remarkably, formation of alkoxysilanes or siloxanes is not observed under moderate reaction conditions.

The industrial production of monosilanes Men SiCl4-n (n=1-3) through the Muller-Rochow Direct Process generates disilanes Men Si2 Cl6-n (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.

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.

Here we report that “liquid bright gold” (LBG), a precursor for the thermal gilding of ceramics, can be structured using photolithography. No expensive and complicated equipment (such as high vacuum) is needed making the method favorable over electron beam evaporation and sputtering processes. Additionally, the method stands out by its simplicity needing only a few steps to create gold structures within a size range of 50 μm to 1 μm, which in turn consist of either an irregular network or isolated nanoparticles, depending on the treatment. Such hierarchically structured gold patterns could find a variety of applications, as exemplified for the patterned growth of silicon nanowires.

The crystal structure of hexaphenyldisilane, Si2(C6H5)6, was determined from synchrotron powder diffraction data. The compound crystallizes in orthorhombic space group P212121 with the following un...

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.

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. Along with the uncommon shape, also different crystallographic growth directions, namely, [100] and [110], were observed on the very same sample. The growth orientations were determined by analysis of the NWs' azimuths on the Si (111) substrates as well as by detailed transmission electron microscopy (TEM) and selected area electron diffraction (SAED) investigations.

The well-established Muller–Rochow Direct Process for the chloromethylsilane synthesis produces a disilane residue (DPR) consisting of compounds MenSi2Cl6−n (n=1–6) in thousands of tons annually. Technologically, much effort is made to retransfer the disilanes into monosilanes suitable for introduction into the siloxane production chain for increase in economic value. Here, we report on a single step reaction to directly form cyclic, linear, and cage-like siloxanes upon treatment of the DPR with a 5 m HCl in Et2O solution at about 120 °C for 60 h. For simplification of the Si−Si bond cleavage and aiming on product selectivity the grade of methylation at the silicon backbone is increased to n≥4. Moreover, the HCl/Et2O reagent is also suitable to produce siloxanes from the corresponding monosilanes under comparable conditions.

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.

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.

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. The absorption and photoluminescence of selected derivatives were studied in solution, as solid powder samples, and in doped-polymer thin films. In well-dissolved solution, the silacyclobutenes show only very weak fluorescence emission (quantum yield approximately 0.1%), due to competition with photochemical and non-radiative photophysical relaxation. When the solubility is degraded in a poor (aqueous) solvent, the formation of nanoscale aggregates leads to a significant enhancement factor in the emission intensity, due to the suppression of the photoreactivity in the more rigid molecular environment, although the quantum yield still remains below a few percent. In the solid-state, however, photoreactivity is completely suppressed leading to fluorescence quantum efficiencies of 8-23% depending on the 1,1-substituents, which demonstrates these compounds' potential as chromophores for condensed-phase luminescence applications. Two dominant competing photochemical reactions have been identified in solution (for excitation in the lowest-energy absorption band, >260 nm), which are analogous to related (sila-)cyclobutenes and stilbenoids. The first involves ring-opening due to cleavage of the 1,4-Si-C bond to form metastable silabutadienes, which was confirmed by isolating the stereospecifically formed allylsilane which results from a secondary reaction with trapping agents such as methanol or water. The second photochemical reaction involves ring closure of the 2,3-diphenyl substructure to form a dihydrophenanthrene analogue, which was confirmed by isolating the phenanthrene derivative that results following subsequent hydrogen abstraction in the presence of oxygen. Measurements of the silacyclobutenes in doped-polymer thin films reveal a spectroscopic behavior ranging from that in solution to the nano-aggregate case as the silacyclobutene dopant concentration is increased.

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.

A new hexanuclear copper(II) sandwich complex based on two 12-membered macrocyclic methylsiloxanolate ligands, [Cu6{(MeSiO2)6}2]·6DMF, was synthesized and characterized by single-crystal X-ray diffraction analysis and magnetic measurements. The cluster compound crystallizes in the monoclinic system, space group P21/n (No. 14), with a = 13.3728(5) A, b = 15.4281(7) A, c = 17.4335(7) A, β = 98.932(3)° and Z = 2. The unit cell contains two identical molecular clusters, each consisting of six interacting Cu2+ (S = ) ions. Within the cluster the six oxygen-bridged Cu2+ ions are arranged in an almost regular hexagon. An analysis of the high-temperature part of the magnetic susceptibility reveals that the complex has a strong average ferromagnetic Cu–Cu exchange interaction of |Jav/kB| = (50.4 ± 1) K with a high-spin S = 3 ground state. A satisfactory fit for the magnetic susceptibility and the magnetization in the whole accessible temperature range is obtained from a Heisenberg model with nonuniform exchange couplings within a ring, corresponding to a system of two weakly coupled trimers with a ferromagnetic intratrimer exchange coupling of |J/kB| = 72.5 K and a ferromagnetic intertrimer exchange coupling of |J′/kB| = 7 K. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)

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. Interpretation of the spectra revealed that photoluminescence in this series of compounds originated from the stilbene or its vinylogue subunits. Different linkages of these groups to the silicon atoms (cyclic or open structures, four- or five-membered cycles) strongly affected both the excitation and the emission spectra, which show different emission maxima depending on the state of the sample (solid state or in solution) and the wavelength of light used for excitation. Thus, owing to their optoelectronic properties these compounds might be useful tools for the design of sensitive sensor materials and of optical switches.

Als Bindeglied zwischen Solarenergie und dezentraler Wasserstofferzeugung konnen bald perhalogenierte Polysilane fungieren – zuganglich aus Siliciumtetrahalogenid und Wasserstoff im Plasmareaktor. Das aus perhalogeniertem Polysilan erzeugte Silicium kann zu Modulen fur die Photovoltaik verarbeitet werden und festes hydriertes Polysilan als permanenter Wasserstofftrager zum Einsatz kommen.

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.

Due to the diminishing reserves of carbon based primary energy carriers and the need to reduce carbon dioxide (CO2) emissions worldwide, an alternative energy concept was developed using elemental silicon as secondary energy carrier. Starting from sand, silicon can be accessible on a carbon/carbon dioxide free route in a process cycle using cost-effective—at best renewable—energy anywhere in the world. The reduction process sand→silicon, just as the generation of every synthetic secondary energy carrier, requires a significant amount of energy, which then is partially stored in the metal. Using existing technology, silicon can be transported and stored without any risk. Reactions of silicon with oxygen or nitrogen are exothermic and result in the release of thermal energy as well as formation of economically valuable products—instead of CO2. From silicon nitride, ammonia is obtained as a feed stock for the fertilizer industry as well as for hydrogen production. Alternatively, hydrogen is produced from silicon directly by simple reactions with water or alcohols, giving sand or silicon-based compounds as byproducts. These are available for a variety of different technical applications and, if required, can be recycled easily.

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. Mol­ecules of Si2I6 are located on a special position of site symmetry \overline{3} with a sixth of a mol­ecule in the asymmetric unit. The bond lengths of Si2Br6 and Si2I6 are in the usual ranges and both mol­ecules adopt a staggered conformation. It is inter­esting to note that Si2Br6 and Si2I6 do not form isomorphous structures. Moreover, an ortho­rhom­bic polymorph of the present structure of Si2I6 is 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 new hexanuclear copper(II) sandwich complex based on two 10-membered macrocyclic phenylsiloxanolate ligands, {Cu6[(C6H5SiO2)5]2(OH)2(C10H8N2)2}·4(DMF)·3(H2O) (1), was synthesized and characterized by single-crystal X-ray diffraction and measurements of the magnetic susceptibility and isothermal magnetization. The cluster compound crystallizes in the triclinic system, space group P (No. 2), with a = 14.925(3) A, b = 16.745(2) A, c = 23.053(3) A, α = 83.079(9)°, β = 84.836(13)°, γ = 65.019(17)°, and Z = 2. The unit cell contains two identical molecules, each consisting of six interacting Cu2+ (S = 1/2) ions. Within the molecule, the six Cu2+ ions are arranged in two almost linear, parallel trimers. While pairs of oxygen atoms link the Cu2+ ions within the trimers, single oxygen atoms residing at the ends of the trimers provide the strongest intertrimer bonds. Magnetic measurements reveal an antiferromagnetic intratrimer exchange interaction, J/kB = 85 K, as the dominant magnetic coupling of the complex. By introducing a weak antiferromagnetic intertrimer coupling, J′/kB = 3.5 K, a satisfactory description of the magnetic behavior over a wide range of temperature and magnetic field is obtained. The departure of the model curves from the data at the lowest available temperature indicates the presence of additional, weak intra- and/or intermolecular interactions. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)

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.

The alkali-metal-directed hydrolysis of phenyltrialkoxysilanes, PhSi(OR)3 (R = Me, Et, nBu), was performed under various reaction conditions. The alkali metal ions were used both as templating entities and as structural elements. The crystalline sodium and potassium phenylsiloxanolates (Na-PhS and K-PhS) were obtained in two different molecular compositions based on a cis-tetraphenylcyclotetrasiloxanolate, cis-[PhSi(O)O−]4, or on a cis-triphenylcyclotrisiloxanolate, cis-[PhSi(O)O−]3, anions assembled into a chain or double-layer supramolecular structure through coordination with alkali cations and hydrogen-bonding contacts. Conditions for selective preparation of crystalline Na-PhS or K-PhS of both structural types were identified. The molecular and crystal structures of [(Na+)3{PhSi(O)O−}3]·8H2O (2), [(Na+)3{PhSi(O)O−}3]·4H2O·1EtOH (3) and [(K+)3{PhSi(O)O−}3]2·7H2O·3MeOH (4) were determined by single-crystal X-ray analysis. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)

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.

Reaction of bis(cyclopentenemethyl)diethylplumbane (2) with trityl cation leads to the formation of the plumbyl cation bis(cyclopentenemethyl)plumbylium (1), in which the positively charged lead atom interacts with the two C=C double bonds of the cyclopentene ligands. The plumbyl cation 1 is characterized by NMR spectroscopy (delta((207)Pb)=807 ppm, delta((13)C(C=C))= 136.1 ppm, (1)J(Pb,C=C)=14.4 Hz) and X-ray crystallography. The structure of 1 reveals a distorted trigonal-bipyramidal coordination sphere for the lead atom with a unique coordination of two C=C double bonds in apical positions. According to quantum-mechanical calculations (MP2/6-311G(d,p) (C, H), SDD (Pb)//MP2/6-31G(d), SDD (Pb)) this interaction stabilizes 1 by 28.3 kcal mol(-1) relative to the tricoordinated plumbylium ion 10. An "atoms in molecules" (AIM) analysis indicates a pi-type interaction between the lead atom and the C=C double bonds, reminiscent of that in the 2-norbornyl cation.

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.

Norbornyl cations of the group 14 elements Si --> Pb have been synthesized from substituted 3-cyclopentenemethyl precursors by intramolecular addition of transient cations to the C=C double bond of the 3-cyclopentenemethyl substituent (pi-route to norbornyl cations). The norbornyl cations 4a (E = Si, R = Me), 4e (E = Si, R = Et), 4f (E = Si, R = Bu), 4g (E = Ge, R = Bu), 4h (E = Sn, R = Bu), and 4i (E = Pb, R = Et) have been identified by their characteristic NMR chemical shifts (4a,e,f, delta((29)Si) = 80-87, delta((13)C)(CH=) = 149.6-150.6; 4g, delta((13)C)(CH=) = 144.8; 4h, delta((119)Sn) = 334, delta((13)C)(CH=) = 141.5; 4i, delta((207)Pb) = 1049, delta((13)C)(CH=) = 138). The significant deshielding of the vinylic carbon atoms (Deltadelta((13)C)) relative to those of the precursor (Deltadelta((13)C) = 19.3-20.3 (4a,e,f), Deltadelta((13)C) = 14.6 (4g), Deltadelta((13)C) = 11.1 (4h), Deltadelta((13)C) approximately 8 (4i)) and the small J coupling constants between the element and the remote vinyl carbons in the case of 4h and 4i (J(CSn) = 26 Hz, J(CPb) = 16 Hz) give experimental evidence for the intramolecular interaction and the charge transfer between the positively charged element and the remote C=C double bond. The experimental results are supported by quantum mechanical calculations of structures, energies, and magnetic properties for the norbornyl cations 4a,b (E = Ge, R = Me), 4c (E = Sn, R = Me), 4d (E = Pb, R = Me), and 4e,f at the GIAO/B3LYP/6-311G(3d,p)//MP2/6-311G(d,p) (Si, Ge, C, H), SDD (Sn, Pb) level of theory. The calculated (29)Si NMR chemical shifts for the silanorbornyl cations 4a,e,f (delta((29)Si) = 77-93) agree well with experiment, and the calculated structures of the cations 4a-f reveal their bridged norbornyl cation nature and suggest also for the experimentally observed species 4a,e-i a formally 3 + 1 coordination for the element atom with the extra coordination provided by the C=C double bond. This places five carbon atoms in the close vicinity of the positively charged element atom. The group 14 element norbornyl cations 4a,e-i exhibit only negligible interactions with the aromatic solvent, and they are, depending on the nature of the element group, stable at room temperature in aromatic solvents for periods ranging from a few hours to days. In acetonitrile solution, the intramolecular interaction in the norbornyl cations 4a,e-h breaks down and nitrilium ions with the element in a tetrahedral environment are formed. In contrast, reaction of acetonitrile with the plumbyl cation 4i forms an acetonitrile complex, 10i, in which the norbornyl cation structure is preserved. The X-ray structure of 10i reveals a trigonal bipyramidal environment for the lead atom with the C=C double bond of the cyclopentenemethyl ligand and the nitrogen atom of the acetonitrile molecule in apical positions. Density functional calculations at the B3LYP/6-311G(2d,p)//(B3LYP/6-31G(d) (C, H), SDD (Si, Ge, Sn, Pb)) + DeltaZPVE level indicate that the thermodynamic stability of the group 14 norbornyl cations increases from Si to Pb. This results in a relative stabilization for the plumbanorbornyl cation 4d compared to tert-butyl cation of 52.7 kcal mol(-)(1). In contrast, the intramolecular stabilization energy E(A) of the norbornyl cations 4a-d decreases, suggesting reduced interaction between the C=C double bond and the electron-deficient element center in the plumbacation compared to the silacations. This points to a reduced electrophilicity of the plumbacation compared to its predecessors.

We have measured the photoelectron (PE) spectra of two new silenes: the kinetically stable long-lived silene t-BuMe2Si(Me3Si)SiAd (3) and a transient silene which was generated in the gas phase by...

Low-pressure pyrolysis of 2,5-bis(1,1-dimethyl-1-silacyclobut-1-yl)-p-xylene (1) results in the formation of 1,2,4,5-tetrahydro-1,1,4,4-tetramethyl-1,4-disiladicyclobuta[a,d]benzene (2), here named as the butterfly compound and representing the first silacyclobutene diannelated [a,d]benzene. Both compounds, 1 and 2, were characterized by NMR, IR, and MS methods; furthermore, the molecular structures were determined by single-crystal X-ray diffraction analysis. Density functional and ab initio calculations prove that the difference in the benzene carbon−carbon bond lengths in 2 results primarily from substituent effects and is not caused by ring strain effects. Forming strongly bent silicon−carbon bonds, silicon decreases the amount of strain in the model compounds, in the 1-silacyclobut-2-ene 10 by 8.3 kcal/mol and in the 1,4-disiladicyclobuta[a,d]benzene 15 by 19.0 kcal mol-1, compared to the analogous hydrocarbons. The total strain energy is additive, depending on the number of annelated rings. The phot...

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. Besides tetramethoxysilane formation, methanolysis of silicon releases hydrogen gas under ambient conditions and is thus suitable for a decentralized hydrogen production; competitive insertion into the MeO-H versus the Me-OH bond either yields H- and/or methyl-substituted methoxy functional silanes. Moreover, compounds, such as Men Si(OMe)4-n (n=0-3) are simply accessible in more than 75 % yield from thermolysis of, for example, tetramethoxysilane over molten sodium. Based on our systematic investigations we identified reaction conditions to produce the methoxysilanes Men Si(OMe)4-n in excellent (n=0:100 %) to acceptable yields (n=1:51 %; n=2:27 %); the yield of HSi(OMe)3 is about 85 %. Thus, the methoxysilanes formed might possibly open the door for future routes to silicon-based products.

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.

Anhydrous transition metal chlorides and bromides MyXz (M: V, Cr, Mn, Fe, Co, Ni, Cu; X: Cl, Br) are synthesized in quantitative yields in a one-step reaction of the metal oxides, graphite, and flowing HX under microwave irradiation (quartz-tubes, 1000—1400 °C, 15 min).

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.