- Towards a comprehensive hydride donor ability scale
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Rates of hydride transfer from several hydride donors to benzhydrylium ions have been measured at 20 °C and used for the determination of empirical nucleophilicity parameters N and sN according to the linear free energy relationship log k20 °C=sN(N+E). Comparison of the rate constants of hydride abstraction by tritylium ions with those calculated from the reactivity parameters sN, N, and E showed fair agreement. Therefore, it was possible to convert the large number of literature data on hydride abstraction by tritylium ions into N and sN parameters for the corresponding hydride donors, and construct a reactivity scale for hydride donors covering more than 20 orders of magnitude.
- Horn, Markus,Schappele, Ludwig H.,Lang-Wittkowski, Gabriele,Mayr, Herbert,Ofial, Armin R.
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supporting information
p. 249 - 263
(2013/02/25)
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- METHOD FOR PRODUCING SILACYCLO MATERIALS
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A method for producing silacycloalkanes by reacting an alkoxysilanc, R1ySi(OR2)4-y with a Grignard reagent, XMgR3MgX where each R1 is independently an alkyl group having 1 to 4 carbon atoms, an alkenyl group having 2 to 4 carbon atoms, a hydrogen atom, or CF3 each R2 is independently an alkyl group having 1 to 4 carbon atoms; y has a value of 1 or 2; R3 is selected from an alkylene group having 1 to 10 carbon atoms; and X is a halogen.
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Page/Page column 9-10
(2009/06/27)
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- SYNTHETIC PROCESS FOR CYCLIC ORGANOSILANES
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A process for preparing a cyclic organosilane using a solvent that promotes ring-closure reactions between an organosilane compound and a dihalo organic compound is disclosed. The ring-closure reactions may form a 4-, 5- or 6-member cyclic organosilane. The process involves a mixture including a dihalo organic compound, an organosilane having at least two functional groups, a solvent and magnesium (Mg). The two functional groups in the organosilane may include halogen, alkoxy or a combination thereof. In the presence of Mg, a Grignard intermediate is formed from the dihalo organic compound in the mixture. The solvent favors intra-molecular or self-coupling reactions of the Grignard intermediate. The intra-molecular or self-coupling reaction promotes ring-closure reaction of the Grignard intermediate to form the cyclic organosilane.
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Page/Page column 11-12
(2008/06/13)
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- Electrochemical synthesis of cyclic alkylsilanes
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The electrochemical reduction of aliphatic α,ω-dibromides in the presence of polychlorosilanes of the formula RnSiCl(4-n) (n=0, 2) was shown to afford heterocyclic silicon compounds in good yield (up to 91percent).In contrast to non-electrochemical methods of synthesis of silacycloalkanes, based on the ring closure of terminal unsaturated compounds, the electrochemical route does not produce α-methylated byproducts and the heterocycle formation occurs quite selectively.The yield of cyclic organosilicon compounds goes through a maximum for 1,1-dimethyl-1-silacyclopentane (91percent) and roughly decreases for 1,1-dimethyl-1-silacyclobutane (18percent) and 1,1-dimethyl-1-sialacycloheptane (57percent).The formation of 5-silaspiro nonane by the electrochemical process occurs with high selectivity despite the multitude of possible reaction pathways and the high probability of polymer formation due to the high functionality of the silicon.The relatively high selectivity of the electrochemical ring closure is suggested to be due to the orientating effect of an electrode in the course of an irreversible reduction of a C-Hal bond in the monosilylated intermediate.A possible mechanism for the process is discussed.Keywords: Silicon; Electrochemistry; Electrochemical synthesis
- Jouikov, V.,Krasnov, V.
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p. 213 - 220
(2007/10/02)
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- A Convenient Synthetic Route to Methylated Silacyclohexanes
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The von Braun degradation of substituted piperidines is a general and economical route to a variety of substituted primary and secondary α,ω-dibromopentanes.Grignard ring closure procedures have been carried out with seven different dibromopentanes in moderate to good yields.Ring closures with MeClSiCl2 lead to product mixtures which are appreciably enriched in one isomer, affording a convenient entry into a variety of derivatives which can be used for stereochemical studies.Assignment of structures based on 1H NMR and mass spectral fragmentation patterns is discussed
- Nguyen, Binh T.,Cartledge, Frank K.
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p. 2206 - 2210
(2007/10/02)
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- REACTIVITY AND SELECTIVITY IN THE CYCLIZATION OF SILA-5-HEXEN-1-YL CARBON-CENTERED RADICALS
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A trio of sila-5-hexen-1-yl radicals has been prepared from the corresponding halides by reaction with tri-n-butyltin hydride (deuteride).The radicals possessing a dimethylsilyl function α or β to the carbon radical center demonstrated marked reduction in total (but especially exo-trig) cyclization compared to the all-carbon system.The γ-silyl radical behaved, contrariwise, quite comparably to the all-carbon system.The difference in cyclization found in the α-silyl radical was demonstrated to result from both a pronounced decrease in cyclization rate via the expected exo-trig mode and from a significantly enhanced rate of hydrogen abstraction from TBTH.Both the α- and γ-silyl radicals cyclized via the endo-trig mode at rates close to that of the parent 5-hexen-1-yl radical itself.The cyclizations studied were demonstrated to be irreversible.The kinetic control thus shown by the preferred formation of endo cyclized product from the α- and β-silyl radicals is highly unusual and represents the first report of carbon-centered 5-hexen-1-yl type radicals violating the Baldwin-Beckwith rule (exo-trig cyclization preferred by 5-hexen 1-yl radicals).Rationalization of the cyclization behavior of the α- and γ-silyl radicals involves both steric and electronic factors.The behavior of the most unusual case, the β-silyl radical, which has the lowest cyclization propensity and no exo mode product, remains largely unexplained because its hydrogen abstraction rate from TBTH is unavailable as yet.Some speculative considerations involving the preferred radical conformation in this system and its relation to cyclization are given.
- Wilt, James W.
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p. 3979 - 4000
(2007/10/02)
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