- Sustainable Catalytic Synthesis of Diethyl Carbonate
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New sustainable approaches should be developed to overcome equilibrium limitation of dialkyl carbonate synthesis from CO2 and alcohols. Using tetraethyl orthosilicate (TEOS) and CO2 with Zr catalysts, we report the first example of sustainable catalytic synthesis of diethyl carbonate (DEC). The disiloxane byproduct can be reverted to TEOS. Under the same conditions, DEC can be synthesized using a wide range of alkoxysilane substrates by investigating the effects of the number of ethoxy substituent in alkoxysilane substrates, alkyl chain, and unsaturated moiety on the fundamental property of this reaction. Mechanistic insights obtained by kinetic studies, labeling experiments, and spectroscopic investigations reveal that DEC is generated via nucleophilic ethoxylation of a CO2-inserted Zr catalyst and catalyst regeneration by TEOS. The unprecedented transformation offers a new approach toward a cleaner route for DEC synthesis using recyclable alkoxysilane.
- Putro, Wahyu S.,Ikeda, Akira,Shigeyasu, Shinji,Hamura, Satoshi,Matsumoto, Seiji,Lee, Vladimir Ya.,Choi, Jun-Chul,Fukaya, Norihisa
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p. 842 - 846
(2020/12/07)
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- Hydrogenolysis of Polysilanes Catalyzed by Low-Valent Nickel Complexes
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The dehydrogenation of organosilanes (RxSiH4?x) under the formation of Si?Si bonds is an intensively investigated process leading to oligo- or polysilanes. The reverse reaction is little studied. To date, the hydrogenolysis of Si?Si bonds requires very harsh conditions and is very unselective, leading to multiple side products. Herein, we describe a new catalytic hydrogenation of oligo- and polysilanes that is highly selective and proceeds under mild conditions. New low-valent nickel hydride complexes are used as catalysts and secondary silanes, RR′SiH2, are obtained as products in high purity.
- Comas-Vives, Aleix,Eiler, Frederik,Grützmacher, Hansj?rg,Pribanic, Bruno,Trincado, Monica,Vogt, Matthias
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supporting information
p. 15603 - 15609
(2020/04/29)
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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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- Synthesis of Polycyclic and Cage Siloxanes by Hydrolysis and Intramolecular Condensation of Alkoxysilylated Cyclosiloxanes
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The controlled synthesis of oligosiloxanes with well-defined structures is important for the bottom-up design of siloxane-based nanomaterials. This work reports the synthesis of various polycyclic and cage siloxanes by the hydrolysis and intramolecular condensation of monocyclic tetra- and hexasiloxanes functionalized with various alkoxysilyl groups. An investigation of monoalkoxysilylated cyclosiloxanes revealed that intramolecular condensation occurred preferentially between adjacent alkoxysilyl groups to form new tetrasiloxane rings. The study of dialkoxy- and trialkoxysilylated cyclotetrasiloxanes revealed multistep intramolecular condensation reactions to form cubic octasiloxanes in relatively high yields. Unlike conventional methods starting from organosilane monomers, intramolecular condensation enables the introduction of different organic substituents in controlled arrangements. So-called Janus cubes have been successfully obtained, that is, Ph4R4Si8O12, in which R=Me, OSiMe3, and OSiMe2Vi (Vi=vinyl). These findings will enable the creation of siloxane-based materials with diverse functions.
- Sugiyama, Tomoaki,Shiba, Hiroya,Yoshikawa, Masashi,Wada, Hiroaki,Shimojima, Atsushi,Kuroda, Kazuyuki
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p. 2764 - 2772
(2019/02/01)
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- PREPARATION OF ORGANOMONOALKOXY (OR MONOHYDROXY) SILANES FROM ALKOXYSILANES/ORGANOMETALLIC COMPOUNDS
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Organomonoalkoxy/monohydroxy silanes, particularly halogenated or aklenylated organomonoalkoxy (or monohydroxy) silanes, which are useful intermediates in organic syntheses, are prepared by reacting an alkoxysilane with an organometallic compound suited for substituting at least certain of the alkoxy functions of the alkoxysilane with a monovalent hydrocarbon radical other than alkoxy and co-preparing a metallic alkoxylate by-product capable of denaturing the substituted silanes thus obtained, including contacting the metallic alkoxylate with at least one agent (A) reactive with the alkoxy functions of the alkoxylate to generate one or more species inert relative to the alkoxysilane, such agent (A) being selected from among the electrophile and/or mineral acid groups.
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Page/Page column 9
(2010/08/07)
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- CYCLIC AMINO COMPOUNDS FOR LOW-K SILYLATION
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Disclosed herein are mono-functional silylating compounds that may exhibit enhanced silylating capabilities. Also disclosed are method of synthesizing and using these compounds. Finally methods to determine effective silylation are also disclosed.
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- Monosodiumoxyorganoalkoxysilanes: Synthesis and properties
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The reaction of organoalkoxysilanes with sodium hydroxide was studied in detail. Studies indicate that this reaction involves more than one stage and involves rather complex multistep process, which leads to the formation of both monosodiumoxyorganoalkoxysilanes (MSOAS) and several secondary products. Analysis of experimental evidence makes it possible to advance the mechanism behind this phenomenon and to define the optimum conditions for the preparation of pure MSOAS with high yields. Different MSOAS were synthesized and their basic physicochemical properties were studied. MSOAS are shown to constitute multifunctional reagents with chemically independent functional groups, and their reaction with trimethylchlorosilane selectively proceeds via - ONa groups, whereas their interaction with triethylesilanol and higher alcohols proceeds exclusively via - OAlk groups. Exchange interaction between MSOAS and organoalkoxysilanes via - ONa and - OAlk groups was found and studied in detail. Temperature corresponding to the onset of thermal degradation of MSOAS was estimated to be equal to ~ 180-190°C.
- Rebrov,Muzafarov
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p. 514 - 541
(2007/10/03)
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- Process for making haloalkylalkoxysilanes
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A haloalkylalkoxysilane is prepared by reacting an olefinic halide with an alkoxysilane in which the alkoxy group(s) contain at least two carbon atoms in the presence of a catalytically effective amount of ruthenium-containing catalyst. The process can be used to prepare, inter alia, chloropropyltriethoxysilane which is a key intermediate in the manufacture of silane coupling agents.
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- Process for preparing low-chloride or chloride-free alkoxysilanes
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A process for preparing an alkoxysilane with an acidic chloride content of less than 10 ppm by weight, comprising: reacting a chlorosilane with an alcohol in a water-free and solvent-free phase to form a product mixture containing alkoxysilane and residual acidic chloride, with removal of resultant hydrogen chloride from the product mixture, then adding liquid or gaseous ammonia, in an amount corresponding to a stoichiometric excess, based on the content of acidic chloride, to form an ammonia-containing product mixture, treating the ammonia-containing product mixture at a temperature between 10 and 50 DEG C., wherein the ammonia and acidic chloride undergo neutralization, to form a crude product, and optionally, then separating off a salt formed in the course of neutralization, from the crude product, and recovering the alkoxysilane by distilling the crude product.
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- Synthesis of dialkoxydimethylsilanes and 2,2-dimethyl-1,3-dioxa-1- silacyclo compounds
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In the presence of iodine, magnesium reacts with alcohols to give magnesium alkoxides, which are treated with octamethylcyclotetrasiloxane to produce dialkoxydimethylsilanes. Similarly, magnesium reacts with 1,3, 1,4 and 1,5 diols and then with octamethylcyclotetrasiloxane, producing 2, 2- dimethyl-1 3-dioxa-2-silacyclo compounds.
- Lin, Ji-Mao,Zhou, Ai-Min,Zhang, Hui,Hao, Ai-You
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p. 2527 - 2532
(2007/10/03)
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- Catalytic Activity of Titanium Alkoxy Derivatives in Alcoholysis of Ethoxysilanes
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Titanium tetraalkooxides, regardless of their structure, are effective catalysts for alcoholysis of ethoxysilanes. Titanium alkoxychlorides demonstrate the highest catalytic activity, whereas the catalytic activity of coordination-saturated titanium compounds is the lowest. The influence of the catalyst nature on its activity is analyzed.
- Khonina,Kochneva,Suvorov
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- Reaction of Tetraalkoxysilanes with Alkyl(aryl)chlorosilanes
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Alkyl(aryl)trichloro- or dialkyl(diaryl)dichlorosilanes react with tetraalkoxysilanes Si(OMe)4, Si(OEt)4, and Si(OBu)4 to give partially etherfied alkyl(aryl)chlorosilanes RSiCl2(OAlk), RSiCl(OAlk)2, and R2SiCl(OAlk).
- Chernyshev, E. A.,Komalenkova, N. G.,Tagachenkov, A. A.,Bykovchenko, V. G.
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p. 241 - 243
(2007/10/03)
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- Kinetics of Acid-Catalysed Hydrolysis of Dimethyldiethoxysilane in Dioxane
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Kinetics of reactions occurring during hydrolysis of dimethyldiethoxysilane in dioxane in the presence of HCl have been studied by the silylation-gas liquid chromatography technique combined with the computer simulation.The rate constants for hydrolysis and ethanolysis of compounds of the Me2Si(OEt)2-n(OH)n series (n = 0,1 and n = 1,2, for hydrolysis and ethanolysis, respectively) were determined.The data provided an experimental evidence for the significance of the anomeric effect related to the silanol group.
- Kazmierski, Krzysztof,Cypryk, Marek,Chojnowski, Julian
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- Iodine- or Iodine Monobromide-Catalyzed Alkoxy-Alkoxy Exchange Reactions of Alkylalkoxysilanes: Formation of the Catalyst-Alkoxysilane Complexes and the Reaction Mechanism
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The formation of charge-transfer complexes of iodine and of iodine monobromide with alcohols and alkoxysilanes has been established spectroscopically, and the formation constants of iodine-ethoxytriethylsilane and iodine-diethoxydimethylsilane complexes has been determined as 0.55+/-0.01 and 0.61+/-0.02, respectively.On the basis of these observations and the kinetic information recently reported, the previously proposed mechanism for the iodine or iodine monobromide catalyzed alkoxy-alkoxy exchange reactions of alkoxysilanes is dicussed afresh.It has been confirmed that a mechanism involving a four-centered transition state containing a CT-complex is most favorable.
- Ito, Katsuko,Ibaraki, Takeshi
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p. 2853 - 2858
(2007/10/02)
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- Alcoholysis Equilibria of Dialkoxydimethylsilanes Catalyzed by Iodine or Iodine Monobromide
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Iodine or iodine monobromide was found to be an especially favorable catalyst for the study of the alcoholysis equilibria of dialkoxydimethylsilanes by gas chromatography.Iodine monobromide was employed to promote the reactions associated with tertiary alcohols, and iodine was used for the other reactions.Eight alcohols were allowed to react with diethoxydimethylsilane, and successive equilibrium constants, K1 and K2, were determined at 20 deg C.K1=2.36-2.75 and K2=0.66-0.69 (by the use of primary alcohols), K1=1.34-1.38 and K2=0.28-0.30 (secondary alcohols), and K1=0.15-0.16 (tertiary alcohols) were observed.These values express precisely the difference of reactivities of the three groups of alcohols with diethoxydimethylsilane.Out of the dialkoxydimethylsilanes used in this study, eight unreported compounds were isolated and characterized.
- Ito, Katsuko,Ibaraki, Takeshi
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p. 295 - 297
(2007/10/02)
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- Direct Thermal and Photochemical Generation of Silanones
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2-Silapyrans (1,2-oxasilins) are synthesized by the pyrolysis of 1-disilanyl-4-methoxy-1,3-butadienes via initial 1,5-silyl migration to afford an intermediate 1-sila-1,3-butadiene.Diels-Alder reaction of the silapyrans and perfluoro-2-butyne does not lead to isolable adducts but rather leads to apparent extrusion of silanone (R2Si=O), which is trapped by a variety of reagents.Reaction of the silapyrans and maleic anhydride provides stable adducts that extrude silanones upon either thermolysis or photolysis.No evidence could not be found for rearrangement of a silylsilanone to a siloxysilylene.
- Hussmann, Gregory,Wulff, William D.,Barton, Thomas J.
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p. 1263 - 1269
(2007/10/02)
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- The Disproportionation of Dimethyldialkoxysilanes Catalyzed by Iodine Monobromide
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Iodine monobromide is an extremely effective catalyst for the redistribution of alkoxyl groups on silicon atoms in dimethyldialkoxysilanes.The equilibrium constants of these reactions were determined at 40 deg C by means of gas chromatography.Assuming that the reaction intermediate is the dative form of a dimethyldialkoxysilaneiodine monobromide complex, a mechanism of the reaction was proposed.
- Ibaraki, Takeshi,Ito, Katsuko
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p. 3235 - 3236
(2007/10/02)
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- 6,6-DIMETHYL-6-SILAFULVENE. GENERATION AND TRAPPING REACTIONS
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6,6-Dimethyl-6-silafulvene generated from (allyl)(cyclopentadienyl)-dimethylsilane reacts with a trapping reagent such as methanol, benzaldehyde, and benzophenone to give (cyclopentadienyl)(methoxy)dimethylsilane, 6-phenylfulvene, and 6,6-diphenylfulvene, respectively.Without a trapping reagent, the silafulvene undergoes dimerization.
- Nakadaira, Yasuhiro,Sakaba, Hiroyuki,Sakurai, Hideki
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p. 1071 - 1074
(2007/10/02)
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