- Variable pathways for oxygen atom insertion into metal-carbon bonds: The case of Cp*W(O)2(CH2SiMe3)
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CpW(O)2(CH2SiMe3) (1) (Cp* = η5-pentamethylcyclopentadienyl) reacts with oxygen atom donors (e.g., H2O2, PhIO, IO4-) in THF/water to produce TMSCH2OH (TMS = trimethylsilyl). For the reaction of 1 with IO4-, the proposed pathway for alcohol formation involves coordination of IO4- to 1 followed by concerted migration of the -CH2TMS ligand to the coordinated oxygen of IO4- with concomitant dissociation of IO 3- to produce Cp*W(O)2(OCH 2SiMe3) (3), which undergoes protonolysis to yield free alcohol. In contrast to the reaction with IO4-, the reaction of 1 with H2O2 results in the formation of the η2-peroxo complex Cp*W(O)(η2-O 2)(CH2SiMe3) (2). In the presence of acid (HCl) or base (NaOH), complex 2 produces TMSCH2OH. The conversion of 2 to TMSCH2OH catalyzed by Br?nsted acid is proposed to occur through protonation of the η2-peroxo ligand, which facilitates the transfer of the -CH2TMS ligand to a coordinated oxygen of the η2-hydroperoxo ligand. In contrast, the hydroxide promoted conversion of 2 to TMSCH2OH is proposed to involve hydroxide coordination, followed by proton transfer from the hydroxide ligand to the peroxide ligand to yield a κ1-hydroperoxide intermediate. The migration of the -CH2TMS ligand to the coordinated oxygen of the κ1-hydroperoxo produces an alkoxide complex, which undergoes protonolysis to yield free alcohol.
- Mei, Jiajun,Carsch, Kurtis M.,Freitag, Cody R.,Gunnoe, T. Brent,Cundari, Thomas R.
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Read Online
- Energetic Sila-Nitrocarbamates: Silicon Analogues of Neo-Pentane Derivatives
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Four silanes based on the neo-pentane skeleton Me4-xSi(CH2R)x containing carbamate groups (x = 1-4, R = OC(O)NH2) have been prepared via the corresponding alcohols Me4-xSi(CH2OH)x, starting from the chlorosilanes Me4-xSiClx. Subsequent nitration leads to the corresponding primary nitrocarbamates (R = OC(O)NHNO2), examined for the purpose as potential energetic materials, including the silicon analogue of pentaerythritol tetranitrocarbamate (sila-PETNC) and a siloxane based nitrocarbamate side-product. All compounds were thoroughly characterized by spectroscopic methods including X-ray diffraction. Thermal stabilities and sensitivities toward impact and friction were examined, as well as detonation values by calculating energies of formation using the EXPLO5 V6.02 software.
- Axthammer, Quirin J.,Klap?tke, Thomas M.,Krumm, Burkhard,Reith, Thomas
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p. 4683 - 4692
(2016/05/24)
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- Organosilicon Phosphorus-Based Electrolytes
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Disclosed are electrolytes that are organosilicon phosphorus-based, and supercapacitors which incorporate them. These electrolytes are cationic salts with a phosphorous containing organosilicon moiety. They appear particularly suitable for use in applications such as electric and hybrid electric vehicles.
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Page/Page column 2-3
(2010/03/02)
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- Synthesis and characterization of alkylsilane ethers with oligo(ethylene oxide) substituents for safe electrolytes in lithium-ion batteries
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Alkylsilane ethers, containing one or three carbon spacer groups between the silicon atom and oligo(ethylene oxide) moiety, were designed and synthesized. These compounds are non-hydrolyzable and less flammable than their alkoxysilane counterparts. A full cell test using them as electrolyte solvents showed good cycling performance in lithium-ion batteries.
- Zhang, Lingzhi,Lyons, Leslie,Newhouse, Jocelyn,Zhang, Zhengcheng,Straughan, Megan,Chen, Zonghai,Amine, Khalil,Hamers, Robert J.,West, Robert
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supporting information; experimental part
p. 8224 - 8226
(2011/06/21)
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- Correlation of the specific rates of solvolysis of trimethylsilylmethyl trifluoromethanesulfonate using a two-term Grunwald-Winstein equation
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The specific rates of solvolysis of trimethylsilylmethyl trifluoromethanesulfonate have been measured at 25.0 °C in ethanol, methanol, and 2,2,2-trifluoroethanol (TFE) and their mixtures with water. Determinations were also made in aqueous acetone and in TFE-ethanol mixtures. An extended (two-term) Grunwald-Winstein equation correlation gave sensitivities towards changes in solvent nucleophilicity and solvent ionising power as expected for an SN2 pathway, consistent with a previous proposal. For four solvents specific rates were determined at three or four additional temperatures and appreciably negative entropies of activation were observed, consistent with the proposed mechanism. At -20 °C, the specific rate of methanolysis is almost identical to that for methyl trifluoromethanesulfonate, suggesting a fortuitous balance between steric hindrance effects and a favourable electronic effect upon the introduction of the trimethylsilyl group.
- Kevill, Dennis N.,Goken, Erin G.,Park, Byoung-Chun
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p. 173 - 175
(2007/10/03)
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- Direct chemical synthesis of chiral methanol of 98% ee and its conversion to [2H1,3H]methyl tosylate and [ 2H1,3H-methyl]methionine
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This paper describes the synthesis of chiral methanols [(R)- and (S)-CHDTOH] in a total of 12 steps starting from (chloromethyl) dimethylphenylsilane. The metalated carbamates derived from (dimethylphenylsilyl)methanol and secondary amines were borylated at low temperatures (-78 or -94°C) using borates derived from fert-butyl alcohol and (+)-pinane-2,3-diol or (R,R)-1,2-dicyclohexylethane-1,2-diol to give diastereomeric boronates (dr 1:1 to 5:1). The carbamoyloxy group could be replaced smoothly with inversion of configuration by an isotope of hydrogen using LiAIH(D)4 [or LiBEt3H(D,T)]. If the individual diastereomeric boronates were reduced with LiAID4 and oxidized with H2O2/NaHCO3, monodeuterated (dimethylphenylsilyl)methanols of ee > 98% resulted. The absolute configurations of the boronates were based on a single-crystal X-ray structure analysis. Brook rearrangement of the enantiomers of (dimethylphenylsilyl)-[ 2H1,3H]methanol prepared similarly furnished the chiral methanols which were isolated as 3,5-dinitrobenzoates in 81% and 90% yield, respectively. For determination of the enantiomeric excesses (98%), the methyl groups were transferred to the nitrogen of (S)-2-methylpiperidine and 3H{1H} NMR spectra were recorded. The Brook rearrangement is a stereospecific process following a retentive course. The chiral methanols were also transformed into methyl tosylates used to prepare [2H 1,3H-methyl]methionines in high overall yields (>80%).
- Simov, Biljana Peric,Wuggenig, Frank,Mereiter, Kurt,Andres, Hendrik,France, Julien,Schnelli, Peter,Hammerschmidt, Friedrich
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p. 13934 - 13940
(2007/10/03)
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- Thermolysis of alkoxyaluminum and siloxyaluminum acylates
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Thermolysis of alkoxyaluminum acylates (RO)nAl(OCORt)3-n (n = 1, 2; R = i-Pr, s-Bu, t-Bu, Rt = Ph, CH2I; R = PhCH2, Rt = Me, Et, Ph; R = Me3Si, Et3Si, Rt = Me) was studied. The main direction of thermolysis of derivatives of primary and secondary alcohols and of unsubstituted carboxylic acids is ester and alcohol formation. Trialkylsiloxyaluminum acylates termolyze to give in the first stage no other products than trialkylacyloxysilanes. Thermolysis of iodoacylates (RO)2AlOCOCH2I (R = Pr, s-Bu) involves oxidation of the alkoxy group to carbonyl compounds with simultaneous formation of a ketene and hydrogen iodide. tert-Butoxyaluminum acylates regardless of the structure of substituent in the acyloxy group undergo symmetrization to aluminum tert-butylate.
- Stepovik,Kazakina,Martynova
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p. 1371 - 1377
(2007/10/03)
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- N-(chloromethyloxycarbonyl)pyrrolidine as a source of the HOCH2- synthon
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The reaction of N-(chloromethyloxycarbonyl)pyrrolidine (1) with lithium powder and a catalytic amount of DTBB (2.5 mol %) in the presence of different electrophiles [Me3SiCl, Bu(i)CHO, Bu(t)CHO, PhCHO, Et2CO, (CH2)5CO, PhCOMe, Ph2CO] in THF at -78°C leads, after hydrolysis with water, to the expected functionalised carbamates 2. Deprotection of the acetophenone derivative 2g with DIBALH at THF reflux yields, after hydrolysis, the corresponding 1,2-diol 3g.
- Guijarro, Albert,Yus, Miguel
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p. 5593 - 5596
(2007/10/03)
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- Kinetics and Products of the Gas-phase Reactions of (CH3)4Si, (CH3)3SiCH2OH, (CH3)3SiOSi(CH3)3 and (CD3)3SiOSi(CD3)3 with Cl Atoms and OH Radicals
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Direct air-sampling atmospheric-pressure ionisation tandem mass spectrometry and FTIR spectroscopy were used to analyse the products of the OH radical- and Cl atom-imitiated reactions of hexamethyldisiloxane, hexamethyldisiloxane, tetramethylsilane and trimethylsilylmethanol at room temperature and atmospheric pressure.The data obtained indicate the initial formation of (CH3)3SiOSi(CH3)2OCHO and (CD3)3SiOSi(CD3)2OCDO from hexamethyldisiloxane and hexamethyldisiloxane, respectively, and (CH3)3SiOCHO from both tetramethylsilane and trimethylsilylmethanol.
- Atkinson, Roger,Tuazon, Ernesto C.,Kwok, Eric S. C.,Arey, Janet,Aschmann, Sara M.,Bridier, Isabelle
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p. 3033 - 3040
(2007/10/03)
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- Process for preparing polyisocyanato/polyisocyanurates by catalytic cyclotrimerization of polyisocyanates
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Polyisocyanurate/polyisocyanates of enhanced stability are prepared by partial catalytic cyclotrimerization of a polyisocyanate in the presence of a catalytically effective amount of an aminosilyl catalyst and wherein the cyclotrimerization reaction is terminated when a predetermined desired amount of isocyanurate groups has been attained, by adding to the reaction mixture, after the cooling thereof to a temperature of below 50° C., a reaction terminating amount of an organic catalyst deactivating compound comprising at least one free hydroxyl moiety, or the reaction product of such hydroxylated organic catalyst deactivating compound with an isocyanate.
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- Synthesis and Antineoplastic Activity of Bisoxy>methyl>-Substituted 3-Pyrrolines as Prodrugs of Tumor Inhibitory Pyrrole Bis(carbamates)
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A series of bispyrrolines 2-4 were synthesized from either the appropriate α-silylated iminium salt, or an aziridine, or a 2H-azirine in a sequence involving 1,3-dipolar cycloaddition reactions.The antineoplastic activities of the pyrrolines were compared to the corresponding pyrroles.The C-2 gem-dimethyl-substituted pyrroline, 4, which cannot be converted to the pyrrole in vivo, was inactive.The activity of the 2-phenyl-substituted pyrrolines 3 was markedly dependent on the nature of the phenyl substituent, although the correspondingphenylpyrroles all showed comparable activity.The differences in the activities of the pyrrolines 3 may be due to the rate of metabolic conversion of the pyrroline to the pyrrole.Electron-withdrawing substituents on the phenyl ring appear to retard this process.
- Anderson, Wayne K.,Milowsky, Arnold S.
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p. 2241 - 2249
(2007/10/02)
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- Doubly Metalated Methanol. - Alcohol d1- and d3-Reagents
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The nucleophilic counterpart of the electrophilic hydroxymethylating protonated formaldehyde B is the hypothetical tautomer A, R = H, of methoxide.Experiments are described in which the generation of doubly metalated methanol C (= formaldehyde ketyl dianion) and its use as methanol d1-reagent are attempted.Treatment of stannylated methanol 1 with two equivalents of butyllithium furnishes a pentane-soluble reagent which hydroxymethylates electrophilic centers in moderate yields (umpolung of the formaldehyde a1-reactivity), see eq. (1) and table 3.Attempted isolation, 1H- and 13C-NMR measurements, and careful product analysis of the reaction with benzaldhyde (scheme 1 and table 2) support the view that the new reagent is actually not free lithium lithiomethoxide (2) but a tin derivative, see for instance 9 in eq. (2). - The O-silylated derivative 18 (= A, R = SiMe3) is likewise generated by Sn-Li-transmetallation, but cannot be trapped externally by electrophiles due to rapid Wittig rearrangement (-> 19 -> 20).The readily accessible dilithio derivatives 21a and 23a can be employed as direct propanol and allyl alcohol d3-reagents, respectively.
- Meyer, Norbert,Seebach, Dieter
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p. 1290 - 1303
(2007/10/02)
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- Sila-Drugs, 16th Communication. Sila-Analogues of Nifedipine-Like Dialkyl 4-Aryl-2,6-dimethyl-1,4-dihydropyridine-3,5-dicarboxylates, I
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The nifedipine-like 1,4-dihydropyridines 10a and 11a as well as their sila-analogues 10b, 10c, and 11b were synthesized for the first time. 10a, 10b, 10c, 11a, 11b, and their precursors 8a, 8b, 9a, and 9b were characterized by their physical and chemical properties, and their structures confirmed by analyses, 1H NMR and mass spectroscopy.The antispasmodic, vasodilating, and antihypertensive properties of 10a, 10b, 10c, 11a, and 11b were compared. - Keywords: Sila-analogues of Nifedipine Derivatives, Syntheses, Pharmacological Activity
- Tacke, R.,Bentlage, A.,Towart, R.,Meyer, H.,Bossert, F.,et al.
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p. 494 - 501
(2007/10/02)
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