- Divergent reactivity of divinylsilanes toward sulfonamides in different oxidative systems
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Oxidative sulfonamidation of divinylsilanes with various sulfonamides in different solvents is reported. With t-BuOI as an oxidant, halogenation is the main process, whereas aziridines are the minor products. With NBS in CH2Cl2 the products of bromination or bromosulfonamidation were obtained, whereas in MeCN or THF the Ritter-type solvent interception products are formed. The obtained bromosulfonamidation products undergo base-induced cyclization to various heterocycles, including imidazolines, 1,4-oxazocanes, or Si,N-containing heterocycles of a new type, 1,3,5-diazasilinanes, in up to quantitative yield.
- Astakhova, Vera V.,Moskalik, Mikhail Yu.,Shainyan, Bagrat A.
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- NHC-catalyzed dehydrogenative self-coupling of diphenylsilane: A facile synthesis of octaphenylcyclotetra(siloxane)
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A unique application of the CuIPr N-heterocyclic carbene (NHC) to the dehydrogenative self-coupling of diphenylsilane has been discovered. This transformation is carried out open to air at room temperature, yielding octaphenylcyclotetra(siloxane) quantitatively in 1 h. This preparation constitutes a significant improvement over existing methods for the preparation of this compound and demonstrates a novel mode of reactivity for CuIPr. The diphenylsilanone tetramer is the precursor to a number of industrially significant polymers.
- Albright, Abigail,Gawley, Robert E.
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- Reactivity of an Octanuclear Copper(I) Siloxide Compound - Isolation of a Copper(II) Oxo Compound with a Supertetrahedral Core
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The reactivity of the octanuclear copper(I) siloxide compound [L4Cu8], (1) (L2- = -OPh2SiOSiPh2O-), towards external substrates was tested. In the presence of N-donor molecules like acetonitrile and propionitrile 1 decomposes with formation of cyclic siloxane rings. Contact with 2,2′-bipyridine (bipy) leads to the formation of a mixed valent tricopper complex [L2Cu3(bipy)2], (3), which likely represents an intermediate of the disproportion of 1 to elemental copper and a mononuclear copper(II) complex [LCu1(bipy)], (2), which was isolated and characterized as the final product. The addition of O2 to 1 leads to an unprecedented supertetrahedral copper(II) complex [L6Cu10(μ4-O)4(MeCN)4], (4), that incorporates four μ4-oxido ligands. The structural parameters for compounds 2-4 were elucidated by single-crystal X-ray crystallography.
- Schax, Fabian,Limberg, Christian
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- A simple synthesis of octaphenylcyclotetra(siloxane)
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An essential industrial monomer octaphenylcyclotetra(siloxane) or (Ph2SiO)4 was obtained by very simple procedures, The product was confirmed by NMR, IR, MS, elemental analysis, and X-ray crystallography.
- Luo, Mei,Yan, Bing
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- Two cyclotetrasiloxanes at 143 K
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The crystal structures of octaphenylcyclotetrasiloxane [C48H40O4Si4, (I)] and 2,4,6,8-tetrakis(tetramethylene)cyclotetrasiloxane [a tetraspiro compound: cyclotetrasiloxane-2,4,6,8-tetraspiro-tetrakis (cyclopentane), C16H32O4Si4, (II)] were determined at 143 K. Compound (I) is compared with the room-temperature structure and the structure of the monoclinic polymorph, both reported previously. Whereas the siloxane ring of (I) is nearly planar, the siloxane ring of (II) exhibits a chair conformation. The angles between the siloxane ring and the various phenyl substituents of (I) vary considerably and are on average smaller in the triclinic form than in the monoclinic form. Greatly differing Si-O-Si angles, as found in the monoclinic form (153 and 167°), appear only in one of the molecules in the asymmetric unit of (I) [153.4(1) and 163.7(1)°]; the Si-O-Si angles of the second molecule differ by only 3.0°. The Si-O-Si angles of (II) display a difference of 5.2°. The silacyclopentane rings of (II) exhibit different conformations.
- Hensen, Karl,Gebhardt, Frank,Kettner, Markus,Pickel, Peter,Bolte, Michael
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- Synthesis and crystal structure of [K{O(Ph2SiO)2SiPh2OH}] 2·C6H6; the first structurally characterised example of a monometallated derivative of an α,ω-siloxane diol. Solution chemistry in relation to KOH-promoted ring-opening polymerisation of (Ph2SiO)3
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The first structurally characterised example of a ; monometallated derivative of an α,ω-siloxane diol compound [K{O(Ph2SiO)2SiPh2OH}]2-C 6H6 has been isolated {from [(Ph2SiOH)2O] and KOBut, 1:1 molar ratio} and structurally characterised by X-ray crystallography, proton NMR, IR and variable-temperature 29Si NMR and its chemistry in relation to KOH-promoted ring-opening polymerisation of (Ph2SiO)3 is discussed.
- Laermann, Barbara,Lazell, Michael,Motevalli, Majid,Sullivan, Alice C.
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- Reactions of silicon hydrides catalyzed by rhodium(III) sulfoxide complexes
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Dehydrocondensation reactions of silicon hydrides catalyzed by the rhodium(III) complex [RhCl3(Me2SO)3] in the absence of the second substrate were studied. It was found that the complex [RhCl3(Me2SO)3] catalyzed the dehydrocondensation reaction with the formation of compounds containing siloxane bonds. Analysis of NMR spectra has shown that the reaction of [RhCl3(Me2SO)3] with silicon hydride includes sequential desoxygenation of sulfoxide ligands to sulfide ligands with the complex [RhCl3(Me2S)3] formation.
- Eliseeva,Prudnikova,Panikorovskii,Skvortsov
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- Cobalt-Catalyzed Selective Synthesis of Disiloxanes and Hydrodisiloxanes
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Selective syntheses of symmetrical siloxanes and cyclotetrasiloxanes are attained from reactions of silanes and dihydrosilanes, respectively, with water, and the reactions are catalyzed by a NNNHtBu cobalt(II) pincer complex. Interestingly, when phenylsilane was subjected to catalysis with water, a siloxane cage consisting 12 silicon and 18 oxygen centers was obtained and remarkably the reaction proceeded with liberation of 3 equiv of molecular hydrogen (36 H2) under mild experimental conditions. Upon reaction of silane with different silanols, highly selective and controlled syntheses of higher order monohydrosiloxanes and disiloxymonohydrosilanes were achieved by cobalt catalysis. The liberated molecular hydrogen is the only byproduct observed in all of these transformations. Mechanistic studies indicated that the reactions occur via a homogeneous pathway. Kinetic and independent experiments confirmed the catalytic oxidation of silane to silanol, and further dehydrocoupling processes are involved in syntheses of symmetrical siloxanes, cyclotetrasiloxanes, and siloxane cage compounds, whereas the unsymmetrical monohydrosiloxane syntheses from silanes and silanols proceeded via dehydrogenative coupling reactions. Overall these cobalt-catalyzed oxidative coupling reactions are based on the Si-H, Si-OH, and O-H bond activation of silane, silanol, and water, respectively. Catalytic cycles consisting of Co(II) intermediates are suggested to be operative.
- Pattanaik, Sandip,Gunanathan, Chidambaram
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p. 5552 - 5561
(2019/06/05)
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- Renewable Isohexide-Based, Hydrolytically Degradable Poly(silyl ether)s with High Thermal Stability
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Several degradable poly(silyl ether)s (PSEs) have been synthesized by dehydrogenative cross-coupling between bio-based 1,4:3,6-dianhydrohexitols (isosorbide and isomannide) and commercially available hydrosilanes. An air-stable manganese salen nitrido complex [MnVN(salen-3,5-tBu2)] was employed as the catalyst. High-molecular-weight polymer was obtained from isosorbide and diphenylsilane (Mn up to 17000 g mol?1). Thermal analysis showed that these PSEs possessed high thermal stability with thermal decomposition temperatures (T?5 %) of 347–446 °C and glass transition temperatures of 42–120 °C. Structure–property analysis suggested that steric bulk and molecular weight have a significant influence to determine the thermal properties of synthesized polymers. Importantly, these polymers were degraded effectively to small molecules under acidic and basic hydrolysis conditions.
- Vijjamarri, Srikanth,Hull, Marianne,Kolodka, Edward,Du, Guodong
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p. 2881 - 2888
(2018/09/18)
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- Controlled synthesis of cyclosiloxanes by NHC-catalyzed hydrolytic oxidation of dihydrosilanes
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Hydrolytic oxidation of various hydrosilanes in acetonitrile and in the absence of organic solvents catalyzed by an N-heterocyclic carbene organocatalysis is described. The NHC organocatalyst exhibited a very high activity with only 0.1 mol% loading of the catalyst in acetonitrile for aryl-substituted dihydrosilanes to produce hydrogen gas and cyclosiloxanes almost quantitatively in several minutes. The calculated TOF (15 000 h-1) of this organocatalyst is comparable to those of precious metal-based heterogeneous catalysts and much superior to those of the existing homogeneous metal catalysts. The catalytic reaction selectively yielded cyclosiloxanes in high yield without the contamination of silanols. Furthermore, the catalytic reaction can also be furnished under solvent-free conditions at elevated temperatures with 2.5 mol% loading of the NHC in 5-12 hours.
- Qing, Guoping,Cui, Chunming
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p. 8746 - 8750
(2017/07/22)
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- Tandem-reduction of DMF with silanes via necklace-type transition over Pt(0) nanoparticles: Deciphering the dual Si-H effect as an extension of steric effects
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Dimethylformamide (DMF) undergoes double-reduction to yield trimethylamine as a result of the concerted activation of DMF by two Si-H bonds (from different Si atoms) over Pt(0) nanoparticles as catalytic centers. Sterics on the Si atom govern the reaction and are also decisive for the structure of siloxane products due to potential limitations on the concerted activation. This journal is
- Taori, Vijay P.,Buchmeiser, Michael R.
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supporting information
p. 14820 - 14823
(2015/02/19)
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- Electrochemical activation of diorganyl dialkoxysilanes for siloxane backbone extension
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The reaction of diorganyl dialkoxysilanes PhRSi(OAlk)2 (R = Ph, vinyl, OMe; Alk = Me, Et) with electrochemically reduced forms of oxygen provides reactive intermediates that insert into hexamethyldisiloxane or permethyl cyclosiloxanes, D3
- Keyrouz, Robert,Jouikov, Viatcheslav
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p. 902 - 904
(2007/10/03)
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- A facile and efficient synthesis of organocyclosiloxanes
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A new facile preparative method for the synthesis of organocyclosiloxanes is reported. Ring closure of the dichlorosilanes with NaHCO3 and pyridine gave mixture of organocyclosiloxanes with cyclotrisiloxane as a main product.
- Zuev, Vjacheslav V.,Kalinin, Alexei V.
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p. 1289 - 1294
(2007/10/03)
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- Product-Specific Methods of Syntheses of Hexaphenylcyclotrisiloxane and Octaphenylcyclotetrasiloxane - Monomers of Phenylsilicones
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Pure hexaphenylcyclotrisiloxane (P3) and octaphenylcyclotetrasiloxane (P4) were synthesized with high yields via proper choice of preparation conditions, such as catalysts, solvents and reaction temperatures, from diphenylsilanediol.Up to 98percent yield of this pure starting material can be obtained from diphenyldichlorosilane through modifying a known procedure on carefully adjusting the temperature of hydrolysis and washing procedure.This method produced pure P3 exclusively with high yield (approximately 90percent) in ethanol in the presence of concentrated sulfuric acid as the catalyst at various reaction temperatures.P4 was produced exclusively in high yield (approximately 90percent) in alcohols in the presence of sodium hydroxide.A method applying HPLC was used to analyze the reaction products quantitatively. - Key words: Hexaphenylcyclotrisiloxane; Octaphenylcyclotetrasiloxane; Diphenylsilanediol.
- Yang, Mei-Hui,Chou, Chyuan,Lin, Chih-Hwa
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p. 923 - 928
(2007/10/03)
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- THE SILICON-OXYGEN DOUBLE-BONDED INTERMEDIATES. A NEW METHOD FOR THE FORMATION OF ORGANOSILANONES
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The kinetics and mechanism of thermal decomposition of R1R2(H)SiOOR3 silylperoxides have been studied.It has been shown that peroxides generated diorganosilanones, R1R2Si=O, with a high yield in the temperature range 130-180 deg C.A mechanism is suggested for the silanone formation.The interaction of silanones with cyclosiloxanes, triethylsilane, α-methylstyrene has been investigated as well as the cyclisation of silanones.
- Tomadze, A. V.,Yablokova, N. V.,Yablokov, V. A.,Razuvaev, G. A.
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- Preparation of cyclic diphenylsiloxanes
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In the preparation of a cyclic diphenylsiloxane of the formula STR1 WHEREIN N IS 3 OR 4, BY HYDROLYSIS OF A DIPHENYLDIHALOGENOSILANE, THE IMPROVEMENT WHICH COMPRISES ADDING THE DIPHENYLDIHALOGENOSILANE, IN THE PRESENCE OF AN ORGANIC, APROTIC SOLVENT TO AN AQUEOUS BASIC SOLUTION, THE BASE BEING EMPLOYED IN AN AMOUNT WHICH IS AT LEAST STOICHIOMETRICALLY EQUIVALENT TO THE HALOGEN CONTENT, WHEREBY THE CYCLIC DIPHENYLSILOXANE IS OBTAINED IN HIGH YIELD AND PURITY. The base is preferably lithium hydroxide, potassium hydroxide or sodium hydroxide and is used in the form of an at least 5 molar solution, about 2.1 to 2.5 equivalents being used per mole of diphenyldihalogenosilane.
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