- Primary Processes in the Low-pressure Pyrolysis of Methylsilane
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The low-pressure pyrolysis of methylsilane in the unimolecular fall-off region proceeds mainly by formation of molecular hydrogen: MeSiH3 MeSiH+H2; however, unimolecular formation of methane also occurs: MeSiH3 SiH2+CH4.Arrhenius parameters for both processes are estimated and some thermochemical deductions made.
- Davidson, Iain M. T.,Ring, Morey A.
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- Experimental and Theoretical Study of the Spin-Spin Coupling Tensors in Methylsilane
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The experimental and theoretical 13C-29Si spin-spin coupling tensors, 1JCSi, are reported for methylsilane, 13CH329SiH3. The experiments are performed by applying the liquid crystal NMR (LC NMR) method. The data obtained by dissolving CH3SiH3 in nematic phases of two LC's is analyzed by taking into account harmonic and anharmonic vibrations, internal rotation, and solvent-induced anisotropic deformation of the molecule. The necessary parameters describing the relaxation of the molecular geometry during the internal rotation, as well as the harmonic force field, are produced theoretically with semiempirical (AM1 and PM3) and ab initio (MP2) calculations. A quantum mechanical approach has been taken to treat the effects arising from internal rotation. All the J tensors are determined theoretically by ab initio MCSCF linear response calculations. The theoretical and experimental J coupling anisotropies, Δ1JCSi = -59.3 Hz and -89 ± 10 Hz, respectively, are in fair mutual agreement. These results indicate that the indirect contribution has to be taken into account when experimental 1DCSiexp couplings are to be applied to the determination of molecular geometry and orientation. The theoretically determined J tensors are found to be qualitatively similar to what was found in our previous calculations for ethane, which suggests that the indirect contributions can be partially corrected for by transferring the corresponding J tensors from a model molecule to another.
- Kaski, Jaakko,Lantto, Perttu,Rantala, Tapio T.,Schroderus, Jyrki,Vaara, Juha,Jokisaari, Jukka
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- Communication: The insertion of silylene in C-H bonds; Rate constant limits and the energy barrier
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The technique of laser flash photolysis has been used to set limits on the rate constants for the bimolecular reactions of SiH2 with methane (CH4) and tetramethylsilane (SiMe4) at both ambient and elevated temperatures (ca 600 K). These limits show that the energy barriers to insertion reactions of SiH2 in the C-H bonds of CH4 are at least 45(±6) kJ mol-1 and in the C-H and/or Si-C bonds of SiMe4 are at least 23(±6) kJ mol-1. The best thermochemical estimate of the activation energy for SiH2+CH4 is 59(±12) kJ mol-1. Reasons for the greatly diminished reactivity of SiH2 with C-H as compared with Si-H bonds are discussed.
- Becerra, Rosa,Walsh, Robin
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- PROCESS FOR THE STEPWISE SYNTHESIS OF SILAHYDROCARBONS
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The invention relates to a process for the stepwise synthesis of silahydrocarbons bearing up to four different organyl substituents at the silicon atom, wherein the process includes at least one step a) of producing a bifunctional hydridochlorosilane by a redistribution reaction, selective chlorination of hydridosilanes with an ether/HCI reagent, or by selective chlorination of hydridosilanes with SiCI4, at least one step b) of submitting a bifunctional hydridochloromonosilane to a hydrosilylation reaction, at least one step c) of hydrogenation of a chloromonosilane, and a step d) in which a silahydrocarbon compound is obtained in a hydrosilylation reaction.
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Page/Page column 61; 62
(2021/12/08)
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- PROCESS FOR THE PRODUCTION OF ORGANOHYDRIDOCHLOROSILANES
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The invention relates to a process for the manufacture of organomonosilanes, in particular, bearing both hydrogen and chlorine substituents at the silicon atom by subjecting a silane substrate comprising one or more organomonosilanes, with the proviso that at least one of these silanes has at least one chlorine substituent at the silicon atom, to the reaction with one or more metal hydrides selected from the group of an alkali metal hydride and an alkaline earth metal hydride in the presence of one or more compounds (C) acting as a redistribution catalyst.
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Page/Page column 28; 29; 30; 32; 37
(2019/04/16)
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- PROCESS FOR THE PRODUCTION OF ORGANOHYDRIDOCHLOROSILANES
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The invention relates to a process for the manufacture of organomonosilanes bearing both hydrogen and chlorine substituents at the silicon atom by subjecting a silane substrate comprising one or more silanes selected from organomonosilanes, organodisilanes and organocarbodisilanes, with the proviso that at least one of these silanes has at least one chlorine substituent at the silicon atom, to a redistribution reaction in the presence of a phosphane or amine acting as a redistribution catalyst.
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Page/Page column 35; 36
(2019/04/16)
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- INTEGRATED PROCESS FOR THE MANUFACTURE OF METHYLCHLOROHYDRIDOMONOSILANES
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The present invention relates to an integrated process for the manufacture of methylchlorohydridomonosilanes in particular, from products of the Müller-Rochow Direct Process.
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Page/Page column 35; 36; 37; 41
(2019/04/16)
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- Nucleophile induced ligand rearrangement reactions of alkoxy- and arylsilanes
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The ligand-redistribution reactions of aryl- and alkoxy-hydrosilanes can potentially cause the formation of gaseous hydrosilanes, which are flammable and pyrophoric. The ability of generic nucleophiles to initiate the ligand-redistribution reaction of commonly used hydrosilane reagents was investigated, alongside methods to hinder and halt the formation of hazardous hydrosilanes. Our results show that the ligand-redistribution reaction can be completely inhibited by common electrophiles and first-row transition metal pre-catalysts.
- Docherty, Jamie H.,Dominey, Andrew P.,Thomas, Stephen P.
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p. 3330 - 3335
(2019/05/10)
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- Disilane Cleavage with Selected Alkali and Alkaline Earth Metal Salts
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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.
- Santowski, Tobias,Sturm, Alexander G.,Lewis, Kenrick M.,Felder, Thorsten,Holthausen, Max C.,Auner, Norbert
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supporting information
p. 13202 - 13207
(2019/10/22)
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- Making Use of the Direct Process Residue: Synthesis of Bifunctional Monosilanes
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The industrial production of monosilanes MenSiCl4?n (n=1–3) through the Müller–Rochow Direct Process generates disilanes MenSi2Cl6?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.
- Sturm, Alexander G.,Santowski, Tobias,Schweizer, Julia I.,Meyer, Lioba,Lewis, Kenrick M.,Felder, Thorsten,Auner, Norbert,Holthausen, Max C.
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supporting information
p. 8499 - 8502
(2019/06/13)
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- CLEAVAGE OF METHYLDISILANES TO METHYLMONOSILANES
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The invention relates to a process for the manufacture of methylmonosilanes comprising the step of subjecting one or more methyldisilanes to the cleavage reaction of the silicon-silicon bond, and optionally a step of separating the resulting methylmonosilanes.
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Paragraph 25-27
(2019/04/16)
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- PROCESS FOR THE PRODUCTION OF ORGANOHYDRIDOCHLOROSILANES FROM HYDRIDOSILANES
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The invention relates to a process for the manufacture of organomonosilanes bearing both hydrogen and chlorine substituents at the silicon atom by subjecting one or more organomonosilanes to the reaction with one or more di- or carbodisilanes in the presence of one or more compounds (C) acting as a redistribution catalyst, wherein at least one of the silanes has only hydrogen and organic residues at the silicon atoms.
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Page/Page column 40; 41
(2019/04/16)
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- CLEAVAGE OF METHYLDISILANES, CARBODISILANES AND METHYLOLIGOSILANES WITH ALKALI-AND ALKALINE EARTH METAL SALTS
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The invention relates to a process for the manufacture of methylmonosilanes comprising the step of subjecting one or more methyldisilanes, one or more methyloligosilanes, one or more carbodisilanes, or mixtures thereof to cleavage conditions resulting in the cleavage of silicon- silicon bonds or silicon-carbon bonds in carbodisilanes, and optionally a step of separating the resulting methylmonosilanes.
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Page/Page column 53; 54
(2019/04/16)
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- Method for preparing hydrogen silane by using calcium hydride to conduct reduction on chlorosilane
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The invention discloses a method for preparing hydrogen silane by using calcium hydride to conduct reduction on chlorosilane and belongs to the technical field of chlorosilane reduction. The problemsof harsh reaction conditions, low reaction speed and the like of chlorosilane reduction through CaH2 in the prior art are solved. In an organic solvent, under catalysis of a catalyst, calcium hydrideis used as a reducing agent, and chlorosilane is reduced into hydrogen silane; the catalyst is borane or borohydride or lithium aluminum hydride, and the organic solvent is tetrahydrofuran or diethylene glycol dimethyl ether or other ether solvents. The method can be applied to hydrogen silane preparation through chlorosilane reduction.
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Paragraph 0066-0070; 0075-0076; 0098-0099
(2018/07/30)
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- Hydrodealkoxylation reactions of silyl ligands at platinum: Reactivity of SiH3 and SiH2Me complexes
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The platinum(ii) complex [Pt(H)2(dcpe)] (1; dcpe = 1,2-bis(dicyclohexylphosphino)ethane) reacts with an excess of the dialkoxymethylsilanes (HSiMe(OR)2; R = Me, Et) to give the bis(silyl) complex [Pt(SiH2Me)2(dcpe)] (3) and trialkoxymethylsilanes by hydrodealkoxylation reactions. These rearrangements of the silyl ligands involve Si-O bond activations. The exchange of the alkoxy moieties against silicon-bound hydrogen atoms occurs stepwise. The intermediate complexes [Pt(H){SiMe(OEt)2}(dcpe)] (5), [Pt{SiMe(OEt)2}2(dcpe)] (6), [Pt{SiHMe(OEt)}2(dcpe)] (7) and [Pt{SiHMe(OMe)}2(dcpe)] (8) were detected. Treatment of the complex 1 with an excess of dichloromethylsilane yields the bis(silyl) complex [Pt(SiMeCl2)2(dcpe)] (9). The hydrido silyl complex [Pt(H)(SiMeCl2)(dcpe)] (10) was identified as an intermediate. The reactions of the complexes [Pt(SiH3)2(dcpe)] (2) and [Pt(SiH2Me)2(dcpe)] (3) with iodomethane lead to a transfer of the SiH3 and SiH2Me ligands. Methylsilane and dimethylsilane, respectively, as well as the platinum diiodo complex [Pt(I)2(dcpe)] (11) were identified as main products.
- Mitzenheim, Cathérine,Braun, Thomas,Laubenstein, Reik,Braun, Beatrice,Herrmann, Roy
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p. 6394 - 6404
(2016/05/09)
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- Mechanism of the Iron(II)-Catalyzed Hydrosilylation of Ketones: Activation of Iron Carboxylate Precatalysts and Reaction Pathways of the Active Catalyst
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A detailed mechanistic study of the catalytic hydrosilylation of ketones with the highly active and enantioselective iron(II) boxmi complexes as catalysts (up to >99% ee) was carried out to elucidate the pathways for precatalyst activation and the mechanism for the iron-catalyzed hydrosilylation. Carboxylate precatalysts were found to be activated by reduction of the carboxylate ligand to the corresponding alkoxide followed by entering the catalytic cycle for the iron-catalyzed hydrosilylation. An Eyring-type analysis of the temperature dependence of the enantiomeric ratio established a linear relationship of ln(S/R) and T-1, indicating a single selectivity-determining step over the whole temperature range from -40 to +65°C (ΔΔG?sel,? 233? K = 9 ± 1 kJ/mol). The rate law as well as activation parameters for the rate-determining step were derived and complemented by a Hammett analysis, radical clock experiments, kinetic isotope effect (KIE) measurements (kH/kD = 3.0 ± 0.2), the isolation of the catalytically active alkoxide intermediate, and DFT-modeling of the whole reaction sequence. The proposed reaction mechanism is characterized by a rate-determining σ-bond metathesis of an alkoxide complex with the silane, subsequent coordination of the ketone to the iron hydride complex, and insertion of the ketone into the Fe-H bond to regenerate the alkoxide complex.
- Bleith, Tim,Gade, Lutz H.
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supporting information
p. 4972 - 4983
(2016/05/10)
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- Synthesis of the first persilylated ammonium ion, [(Me3Si) 3NSi(H)Me2]+, by silylium-catalyzed methyl/hydrogen exchange reactions
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This work describes the unexpected synthesis and characterization of the first persilylated ammonium ion, [(Me3Si)3NSi(H)Me 2]+, in the reaction of (Me3Si)3N with [Me3Si-H-SiMe3][B(C6F5) 4]. NMR and Raman studies revealed a transition-metal-free silylium ion catalyzed substituent redistribution process when [Me3Si-H- SiMe3]+ was used as the silylating reagent. These observations were affirmed in the reaction with [Et3Si-H-SiEt 3][B(C6F5)4]. A Lewis acid catalyzed scrambling process always occurs if an excess of silanes is present in the formation of silylium cations while employing the standard Bartlett-Schneider- Condon type reaction. Additionally, the thermodynamics of this process was accessed by DFT computations at the pbe1pbe/aug-cc-pVDZ level, indicating alkyl substituent exchange equilibria at the silane and preference of the formation of [(Me3Si)3NSi(H)Me2]+ over [(Me 3Si)4N]+.
- Labbow, Rene,Reiss, Fabian,Schulz, Axel,Villinger, Alexander
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supporting information
p. 3223 - 3226
(2014/08/05)
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- A photo Lewis acid generator (PhLAG): Controlled photorelease of B(C 6F5)3
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A molecule that releases the strong organometallic Lewis acid B(C 6F5)3 upon irradiation with 254 nm light has been developed. This photo Lewis acid generator (PhLAG) now enables the photocontrolled initiation of several reactions catalyzed by this important Lewis acid. Herein is described the synthesis of the triphenylsulfonium salt of a carbamato borate based on a carbazole function, its establishment as a PhLAG, and the application of the photorelease of B(C6F5) 3 to the fabrication of thin films of a polysiloxane material.
- Khalimon, Andrey Y.,Piers, Warren E.,Blackwell, James M.,Michalak, David J.,Parvez, Masood
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supporting information; experimental part
p. 9601 - 9604
(2012/07/14)
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- METHOD FOR PRODUCING -HETERO-SUBSTITUTED ALKYLHALOHYDROSILANE AND USE THEREOF
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Method for efficiently producing α-hetero-substituted alkylhalohydrosilane,and use thereof. A method for producing (A) a halohydrosilane compound represented by the general formula (1): H-SiR2c(CR13-bYb)aX3-a-c (1) (wherein, R1 represents a hydrogen atom or a substituted or unsubstituted hydrocarbon group; R2 represents a substituted or unsubstituted hydrocarbon group; X represents a halogen atom; Y represents a hetero substituent; a is 1 or 2; b is any one of 1, 2 and 3; c is 1 or 0), by allowing (B) a halosilane compound represented by the general formula (2) : SiR2c(CR13-bYb)aX4-a-c (2) (wherein, R1, R2, X, Y, a, b and c are as defined above) to react with (C) a hydrosilane compound. A method for producing a reactive silicon group-containing polymer using the halohydrosilane compound (A).
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Page/Page column 23-24
(2011/04/25)
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- Process For Preparing Si-H-Containing Silanes
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Silanes of the general formula (1) [in-line-formulae]RaSiHbX4-b-a ??(1)[/in-line-formulae] are prepared by disproportionating at least one more highly chlorinated silane in the presence of a homogeneous catalyst in an apparatus with at least one reactive distillation column and at least one additional reactor selected from among prereactors and side reactors, where R is an alkyl, aryl, alkaryl or haloalkyl radical, X is a halogen atom, a is 0 or 1, and b is 2, 3 or 4.
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Page/Page column 4-5
(2009/01/24)
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- METHOD FOR PRODUCING ORGANOSILANE
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By reducing an organosilane represented by the formula (1), €?€?€?€?€?€?€?€?SiX n R 4-n €?€?€?€?€?(1) (wherein X represents a halogen or alkoxide, n represents an integer of 1-3, and R represents an alkyl group or aryl group), there is produced a corresponding organosilane represented by the formula (2), €?€?€?€?€?€?€?€?SiH n R 4-n €?€?€?€?€?(2) (wherein n represents an integer of 1-3, and R represents an alkyl group or aryl group). In this production method, an aromatic hydrocarbon series organic solvent is used as a reaction solvent, and aluminum lithium hydride is used as a hydrogenating agent.
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Page/Page column 4
(2008/06/13)
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- IR laser-induced thermolysis and UV laser-induced photolysis of 1,3-diethyldisiloxane: Chemical vapour deposition of nanotextured hydridoalkylsilicones
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IR laser thermolysis and UV laser photolysis of gaseous 1,3-diethyldisiloxane proceed via different mechanisms: the former involves 1,1-H2 and ethene elimination, whereas the latter is dominated by 1,1,H2 and ethane elimination. The
- Urbanova,Bastl,Subrt,Pola
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p. 1557 - 1562
(2007/10/03)
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- Reaction of Hydrogen Peroxide with Organosilanes under Chemical Vapour Deposition Conditions
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When a stream of vapour at low pressure which contained a mixture of H2O2 with an organosilane, RSiH3 (R = alkyl or alkenyl), impinged on a silicon wafer, deposition of oxide films of nominal composition RxSiO(2-0.5x), where x 3 or higher alkenyl groups. or higher alkenylgroups. Possible mechanism for the Si-C bond cleavage reaction are discussed, with energetic rearrangement of radical intermediates of type Si(H)(R)(OOH)' being favoured.
- Moore, Darren L.,Taylor, Mark P.,Timms, Peter L.
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p. 2673 - 2678
(2007/10/03)
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- Laser-induced decomposition of silacyclobutane: Extensive H(Si)/H(C) scrambling via 1,2-H shift in silene and radical reactions
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The mechanism of the silacyclobutane decomposition has been further refined through a study of the laser induced decomposition of 1,1-dideuterio-1-silacyclobutane. It is concluded that the identified volatile and solid products and the hydrogen and deuterium content in them are in accord with 1,2-H(D)-shift in intermediate silene and with radical reactions.
- Khachatryan, Lavrenti,Volnina, Elvira A.,Fajgar, Radek,Pola, Josef
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p. 263 - 270
(2007/10/03)
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- Formation of organosilicon compounds 115: The applicability as precursors for β-SiC of carbosilanes resulting from the gas phase pyrolysis of methylsilanes
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The thermal properties of polycarbosilanes from the gas phase pyrolysis of SiMe4, Me3SiCl, Me2SiCl2 and the polymeric (Me2Si-CH2)n has been investigated. They decompose above 400 °C to form volatile methylsilanes, H2, CH4, viscous carbosilanes and insoluble glassy products via condensation reactions. The ceramic yield is between 10 and 20 wt.% at about 900 °C and falls to only a few weight per cent when heating is continued to 1000 °C. The gas phase pyrolysis of Me2SiH2 at 650 °C produces plastic, meltable polycarbosilanes (PCS). Tempering the compounds to 900 °C gives a ceramic residue in 85% yield with Si:C:H 1:1.2:0.4. Heating this residue under thermal gravimetry (TG) conditions to 1500 °C (argon atmosphere) results in a further weight loss of 0.7% and formation of β-SiC. Silicon carbide is also formed when the PCS from Me2SiH2 (Si:C:H 1:1.5:2.5) are heated to 1400 °C, with a weight loss of 16.3% under nitrogen and one of 42% in vacuum.
- Toegel,Antony,Bill,Scheer, Petra,Eichhoefer,Fritz
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p. 125 - 131
(2007/10/03)
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Bu3SnH is an effective reagent for partial conversion of Si-Cl into Si-H groups. The presented hydrogenation mechanism postulates the coordination of the catalyst (Lewis bases) or the solvent to silicon, giving an intermediate with higher coordinated silicon atom in the first step, followed by the attack of tributyltin hydride by a single electron transfer. This mechanism implies that the intermediate having a hypervalent silicon atom reacts more rapidly than the starting tetracoordinated silane.
- Paetzold,Roewer,Herzog
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p. 147 - 152
(2007/10/03)
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- Hydrogenation of Silicium-Halogen-Compounds with Trialkylstannyl Chloride/Sodium Hydride
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Organotinchlorides of the general formula R3SnCl and R2SnCl2 (R = Me, n-Bu, Ph) can easily be converted into the corresponding hydrides R3SiH and R2SiH2 employing NaH in diethylene glycol dialkyl ethers.Using trialkyltinhydrides like Bu3SnH in combination with a catalyst (tertiary amines, N-heterocycles, phosphonium or ammonium salts), Si-Cl bonds in mono- and disilanes are hydrogenated.In the case of disilanes, Si-Si bond cleavage and concurrent hydrogenation can be afforded with strongly nucleophilic catalysts.Partial hydrogenation is also possible.The whole process can be run cyclically. - Keywords: Alkylstannylhydride; Hydrogenation; Organochlorsilane.
- Hengge, E.,Grogger, C.,Uhlig, F.,Roewer, G.,Herzog, U.,Paetzold, U.
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p. 549 - 556
(2007/10/02)
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- Dehydrogenative Build-up Reactions to Silyl-Substituted Alkali Metal Germanides, Stannides, and Phosphides; Molecular Structure of Neopentasilane
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The build-up reaction between monosilane and dispersed sodium or potassium in diethyleneglycol dimethyl ether leads to alkali metal silylsilanides of the composition (Na/K)SiH3-n(SiH3)n (n = 0-3) (1, 1a-c; 2, 2a-c).By subsequent reactions with silyl nonafluorobutanesulfonate, C4F9SO3SiH3, benzenesulfonic acid, PhSO3H, and methyl p-toluenesulfonate the corresponding silanes SiH4-n(SiH3)n (n = 0-4) (3, 3a-d) and methylsilanes CH3SiH3-n(SiH3)n (n = 0-3) (4a-d) were obtained in good yield.The molecular structure of neopentasilane (3d) has been determined by electron diffraction analysis.Treatment of group IV and V hydrides GeH4, PH3, and SnH4 with mixtures of sodium or potassium silylsilanides (1, 1a-c; 2, 2a-c) leads to silyl-substituted sodium or potassium germanides (Na/K)GeH3-n(SiH3)n (n = 1-3) (5a-c, 6a-c), phosphides KPH2-n(SiH3)n (n = 1-2) (7a-b), and stannides NaSnH3-n(SiH3)n (n = 1-3) (8, 8a-c). - Key Words: Alkali metal silylsilanides / Alkali metal silylgermanides / Sodium silylstannides / Potassium silylphosphides / Neopentasilane / Electron diffraction
- Lobreyer, Thomas,Sundermeyer, Wolfgang,Oberhammer, Heinz
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p. 2111 - 2116
(2007/10/02)
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- Synthesis of the square-bipyramidal cluster 4-SiMe)2(CO)11> by two routes and its reaction with GeMe2H2. The crystal structures of 4-SiMe)2(CO)11> and 4-SiMe)2(CO)10>
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4-SiMe)2(CO)11> (1a) is the major product from the reaction of with (synthesised from SiMeH2Cl and Na2).An alternative, quantitative synthesis of 1a is from SiMeH3 and , 1a reacts with an
- Anema, Skelte G.,Lee, Siew Kim,Mackay, Kenneth M.,Nicholson, Brian K.
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p. 211 - 218
(2007/10/02)
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- Silicon-Carbon Bond Formation Kinetics: Study of the Reactions of CH3 with SiH3, Si(CH3)3, and SiCl3
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The kinetics of three Si-C bond-forming association reactions were investigated at the high-pressure limit: SiH3 + CH3 (1), Si(CH3)3 + CH3 (2), and SiCl3 + CH3 (3).Rate constants were measured using a heatable tubular reactor coupled to a photoionization mass spectrometer.The two radical reactants were produced simultaneously (CH3 always in great excess) using pulsed 193-nm photolysis of suitable precursors diluted in helium, and the radical decays were monitored in time-resolved experiments.The radical decay profiles were fitted to appropriate expressions to obtain the desired rate constants.Reaction 1 was studied between 301 and 526 K yielding the following Arrhenius expression for the association reaction: k1 = (5.6 +/- 2.4) * 10-11 exp((3.0 +/- 1.6) kJ mol-1 / RT). (All rate constants are in the units cm3 molecule-1 s-1.) Reaction 2 was investigated between 306 and 526 K yielding the expression k2 = (5.2 +/- 2.2) * 10-11 exp((2.4 +/- 1.4) kJ mol-1 / RT).Reaction 3 was studied at one temperature, 303 K, where k3 = (1.1 +/- 0.4) * 10-10.Treating these association reactions as cross-combination reactions, the measured rate constants were found to be predicted with reasonable accuracy using the geometric mean rule and the rate constants of the related self-association reactions of the reactant radicals.The mechanisms of these reactions are discussed.
- Niiranen, Jukka T.,Gutman, David
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p. 9392 - 9396
(2007/10/02)
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- Generation, characterization, and properties of iron-silylene and iron-silene cationic complexes in the gas phase
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Generation, characterization, and properties of iron-silylene (Fe=SiRR′) and iron-silene (Fe(CH2=SiRR′)) cations (R, R′ = H, CH3) are describe in the gas phase by using Fourier transform mass spectrometry (FTMS). Iron-(silylene/silene) cations were formed by reaction of Fe+ with appropriate silanes. Structures of these ions were probed by using both collision-activated dissociation (CAD) and ion/molecule reactions. CAD failed to yield structural information; however, reaction with isotopically labeled ethene provides compelling evidence for formation of iron-silene and iron-silylene species. There is no evidence for the interconversion of iron-silylene and iron-silene species, even upon slow collisional activation or by formation of ethene collision complexes (ca. 40 kcal/mol of excess energy). This indicates that there is a prohibitive barrier for iron mediated interconversion of silene and silylenes. Reactions of iron-silylene and iron-silene species with water and benzene are described. The nature of the bonding is presented and bond dissociation limits are obtained.
- Jacobson,Bakbtiar
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p. 10830 - 10844
(2007/10/02)
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- The synthesis and properties of (CH2F)SiH3 and related monofluoromethylsilanes
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The reduction of (CFCl2)SiCl3 by LiAlH4, Me3SnH, and (nBu)3SnH has been studied.The compound (CH2F)SiH3 (I) and all the compounds of the series (CFCl2-mHm)SiCl3-nHn, m = 0, 1 and n = 0-3 were detected and characterized by NMR spectroscopy.Conditions for the synthesis of I, (CHFCl)SiH3 (IX) and (CFCl2)SiH3 (V) with acceptable yields have been optimized.These novel compounds were studied by 1H, 19F, 13C and 29Si NMR spectroscopy; their infrared and Raman spectra were recorded and assigned with the assistance of a normal coordinate analysis of 1 and its isotopomer (CD2F)SiD3.The thermolyses of I, IX and (CHF2)SiH3 (X) which start at about 120, 200 and 180 deg C, respectively, have been studied.Whereas I decomposes by a migration of F from C to Si, compound X undergoes elimination of the carbene CHF, insertion of which into SiH bonds ultimately gives CH3Si derivatives.
- Buerger, H.,Moritz, P.
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p. 293 - 308
(2007/10/02)
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- Neue Wege zu Polysilanen
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Disilane dervatives undergo disproportionation reactions to polysilanes.Investigated were 1,2-dimethyldisilane and 1,2-dimethyltetrachlorodisilane with catalysts like NH4Cl, AgCN, and Na-cyanamide.In case of 1,2-dimethylsilane, with more than catalytic amounts of NH4Cl, a nitrogen containing polysilane is formed.Two new compounds MeSiH(NCO)2 and Me2Si2(NCO)4 were synthesized and characterized.The last one leads to a polymer at heating.Additionally an electrochemical formation of polydimethylsilane is described.
- Hengge, Edwin,Kalchauer, Wilfried
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p. 793 - 802
(2007/10/02)
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- Redistribution reactions of alkoxy- and siloxysilanes, catalyzed by dimethyltitanocene
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Dimethyltitanocene is an excellent catalyst for the redistribution of alkoxy- and siloxyhydrosilanes.The redistribution reactions of triethoxysilane, diethoxymethylsilane, 1,3,5,7-tetramethylcyclotetrasiloxane, pentamethyldisiloxane, and H-(SiMe2O)n-SiMe2H (n = 1 to 3) are described.The mechanism of these reactions is discussed in terms of TiH mediated displacements.The possibility of both Ti(III) and (IV) mediated displacements are considered and a mechanism involving the former, which fits all of the experimental data, is proposed.
- Xin, Shixuan,Aitken, Clare,Harrod, John. F.,Ying Mu,Samuel, E.
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p. 471 - 476
(2007/10/02)
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- Improved synthetic route to potassium silyl using crown ethers, potassium, and silane and its use to prepare methylsilane and disilylmethane
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The time for the reaction between K and SiH4 in glyme is reduced from months to hours by addition of 18-crown-6 to form SiH3.The usefulness of the reaction to prepare the SiH3- anion as a synthetic intermediate is demonstrated by the reaction of SiH3 with CH3I and CH2Cl2 to prepare H3SiCH3 and (H3Si)2CH2, respectively.The rate of the reactions between K and GeH4 is also increased but not as dramatically with the addition of 18-crown-6 to form GeH3.
- Fieselmann, Benjamin F.,Dickson, C. Robert
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- Precise Determination of Stabilities of Primary, Secondary, and Tertiary Silicenium Ions from Kinetics and Equilibria of Hydride-Transfer Reactions in the Gas Phase. A Quantitative Comparison of the Stabilities of Silicenium and Carbonium Ions in the Gas Phase
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Fourier transform ion cyclotron resonance spectroscopy has been used to examine kinetics and equilibria of hydride-transfer reactions of methyl-substituted silanes with various hydrocarbons having well-established gas-phase hydride affinities.The derived hydride affinities, D(R3Si(1+)-H(1-)), for the silicenium ions SiMeH2(1+), SiMe2H(1+), and SiMe3(1+) are 245.9, 230.1, and 220.5 kcal/mol, respectively, to be compared with the values of 270.5, 251.5, and 233.6 kcal/mol for the corresponding carbonium ions.This indicates that the silicenium ions are significantly more stable than the corresponding carbonium ions in the gas phase with H(1-) as a reference base.
- Shin, Seung Koo,Beauchamp, J. L.
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p. 900 - 906
(2007/10/02)
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- Gas-Phase Reactions of H3Si- and Me3Si-. The formation of Si-O and Si-S Bonds. A Flowing Afterglow and ab Initio Study
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The ions H3Si- and Me3Si- undergo Si-O and/or Si-S bond forming reactions with CO2, COS, CS2, SO2, N2O, MeNCO, and MeNCS forming H3SiO3-, Me3SiO-, H3SiS-, or Me3SiS- ions as appropriate.The rates of these reactions vary markedly, e.g., the reaction of H3Si- with CS2 (to form H3SiS- + CS) occurs at every encounter, whereas that of H3Si- with N2O (to form H3SiO- plus N2) occurs for only one in every thousand collisions.Ab initio calculations (at 6-31G level) for the reactions of H3Si- with CO2, CS2, SO2, and N2O suggest different and complex reaction pathways.The reaction of H3Si- with CO2 is characterized by initial approach to carbon, and subsequent rearrangements are required to form H3SiO-.H3SiS- is formed by a simple path from CS2 following initial attack at sulfur.H3Si- reacts with SO2 in alternative ways to form five-coordinate intermediate which subsequently decomposes to H3SiO- plus SO.H3Si- is likely to attack N2O at the terminal nitrogen, and subsequent rearrangement forms H3SiO-.The length, or complexity of the reaction pathway appears inversely related to the measured efficiency in the majority of reactions.
- Sheldon, John C.,Bowie, John H.,DePuy, Charles H.,Damrauer, Robert
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p. 6794 - 6800
(2007/10/02)
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- Kinetic and Product Studies of the Thermal Decomposition of Dimethylsilane in a Single-Pulse Shock Tube and in a Stirred Flow Reactor
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Kinetic and product studies of the pyrolyses of dimethylsilane in a single-pulse shock tube (1135-1290 K) and in a stirred flow reactor (890-1000 K ) are reported.The shock-induced reaction is accelerated by free-radical and silylene chains which cannot be quenched by trapping agents.The mechanisms of the pyrolyses in various temperature ranges are discussed and modeling results for the stirred flow and shock tube reactions are shown to be in reasonable agreement with experimental observations.Mechanisms for the decomposition of dimethylsilylene to ethylene and acetylene via silacyclopropane and silacyclopropene intermediates, respectively, are proposed.Arrhenius parameters for molecular elimination of methane from dimethylsilane are deduced (log kCH4=14.8-73.000/2.3RT), establishing an activation energy for CH3SiH insertion into the (C-H) bond of methane of E24.5 kcal (pressure standard state).
- Rickborn, S. F.,Rogers, D. S.,Ring, M. A.,O'Neal, H. E.
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p. 408 - 414
(2007/10/02)
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- MAGNITUDE AND ORIGIN OF THE beta -SILICON EFFECT ON CARBENIUM IONS.
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Ab initio molecular orbital calculations have been carried out on alpha - and beta -substituted methyl and vinyl cations to obtain a quantitative measure of the substituent effect of a silyl group relative to a methyl group and hydrogen. Geometries optimized with the 3-21G **(***) basis set were used in calculations at the MP3/6-31G* level. The stabilization energies due to various substituents were determined by means of isodesmic reactions involving the parent methyl and classical vinyl cations. alpha -Methyl substitution of the methyl cation leads to a stabilization energy of 34. 0 kcal/mol compared to 17. 8 kcal/mol obtained through alpha -silyl substitution. The stabilization due to alpha -methyl and alpha -silyl groups is comparable for the vinyl cation (27. 2 and 24. 1 kcal/mol), suggesting that the inductive effect of silicon is more effective in this case.
- Wierschke,Chandrasekhar,Jorgensen
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p. 1496 - 1500
(2007/10/02)
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- Hetero-?-Systems, 9. About the Relationships between Silaethenes and Methylsilylenes
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Silaethenes 1 and the isomeric methylsilylenes 2 are separately existing species, but can readily be interconverted in an argon matrix via a photochemically induced 1,2-H shift.In case of the thermal excitation in the gas phase examples for both directions have been dedected spectroscopically: the isomerisation of a silaolefin into the corresponding silylene (1d -> 2d) and the formation of a silene from a silylene (2f -> 1f).
- Maier, Guenther,Mihm, Gerhard,Reisenauer, Hans Peter,Littmann, Dieter
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p. 2369 - 2381
(2007/10/02)
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- THERMOCHEMISTRY OF SILICON-CONTAINING COMPOUNDS PART 1.-SILICON-HALOGEN COMPOUNDS, AN EVALUATION
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Literature data on the heats of formation of silicon-halogen compounds have been collected and reviewed.The coverage includes all tetravalent monosilicon compounds containing Si-H-X, where X is a single halogen, as well as the subhalides SiXn, where n = 1,2 or 3.The data are critically evaluated from the standpoints of bond addivity and general chemical reactivity of the species involved as well as by detailed consideration of individual studies.Earlier compilations or reviews are discussed.A set of recommended values (with uncertainties) is proposed.For the divalent species, SiX2, a self-consistent set of lone-pair stabilisation energies is obtained.
- Walsh, Robin
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p. 2233 - 2248
(2007/10/02)
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