- Generation and characterization of 1,2-Diaryl-1,1,2,2-tetramethyldisilane cation radicals
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Nanosecond laser flash photolysis methods were used to generate and spectrally characterize the cation radicals of 1,2-diaryl-1,1,2,2,- tetramethyldisilanes (Ar = p-X-Ph, X = H, CH3, OCH3) in hexafluoroisopropanol (HFIP) at room temperature. The disilane cation radicals rapidly reacted with methanol, with bimolecular rate constants ranging from 0.63 to 2.1 ×108 M-1 s-1. The cation radicals were found to react with tert-butanol 4-5 times more slowly than methanol, consistent with a small steric effect for nucleophile-assisted fragmentation of the Si-Si bond. The standard potentials for oxidation of the disilanes in HFIP were determined by two different methods: first, by measuring equilibrium constants for electron exchange between the disilanes and the cation radical of hexaethylbenzene and, second, by combining electrochemical data from cyclic voltammetry with the lifetimes of the disilane cation radicals measured by laser flash photolysis in the same media. Agreement between the two methods was excellent (≤3 mV). The oxidation of 1,2-di-p-methoxyphenyl-1,1,2,2,- tetramethyldisilane by slow scan cyclic voltammetry in acetonitrile was not found to be reversible, in contrast to prior literature reports. Possible explanations for the prior results are proposed.
- Guirado, Gonzalo,Haze, Olesya,Dinnocenzo, Joseph P.
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scheme or table
p. 3326 - 3331
(2010/08/20)
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- Conformation dependence of photophysical properties of σ-π conjugation as demonstrated by cis- and trans-1,2-diaryl-1,2-disilacyclohexane cyclic systems
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Several configurationally constrained cis- and trans-1,2-diaryl-1,2- dimethyl-1,2-disilacyclohexanes (3a-e) have been synthesized in order to measure their photophysical properties, such as UV absorption, magnetic circular dichroism (MCD), and photolumine
- Tsuji, Hayato,Shibano, Yuki,Takahashi, Tohru,Kumada, Makoto,Tamao, Kohei
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p. 1334 - 1344
(2007/10/03)
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- Photochemical carbon-silicon bond forming reaction on electron-deficient alkenes by disilanes and polysilanes via photoinduced electron transfer
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The phenanthrene-sensitized photoreaction of electron-deficient alkenes with disilanes in acetonitrile gave silylated alkanes in high yields.The photosilylation occurred in a highly regioselective manner at the position β to the electron-withdrawing group
- Mizuno, Kazuhiko,Nakanishi, Kazuhisa,Chosa, Jun-ichi,Otsuji, Yoshio
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- Failure in Several Attempts to Prepare Arylsilyl-lithium Reagents by the Gilman Cleavage of Disilanes with Lithium
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Several diarylsilanes 5,9 and 11 do not cleave with lithium in THF to give silyl-lithium reagents, in contrast to diphenyltetramethyldisilane 2, which is well known to give phenyldimethylsilyl-lithium.Trityldiphenylsilyl bromide 13 reacts with lithium to
- Rahman, Noorsaadah Abd.,Fleming, Ian,Zwicky, Anna B.
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p. 2401 - 2408
(2007/10/02)
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- Dearylation of α,ω-diphenylpermethylated oligosilanes with triflic acid
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The relative rates of displacement of phenyl groups for a series of α,ω-diphenylpermethylated oligosilanes with the formula Ph(SiMe2)nPh (n = 2-5) were studied.Triflic acid was utilized in the displacement reactions which occur as a two-step process with protonation at the ipso-carbon atom as the rate limiting step.The results showed the displacement of the first phenyl group is more facile than the second group.The largest difference in reactivities is found for the disilane.Competitive displacement reactions between various oligomers were analyzed to establish the influence of the chain length of oligosilanes on the relative reactivities of the terminal phenyl groups.Both the first and second phenyl group displacement reactions are faster for the longer chain oligomers than the shorter analogs.The 13C NMR spectra of the oligosilanes indicate the highest electron density on the ipso-carbon atoms in the disilane, in contrast to its lowest reactivity.This is interpreted by the increased stabilization of the positive charge in the transition state with an increase in the chain length.Thus, the reactivities of oligosilanes are governed by the structures of the transition states rather than the ground states.
- Ruehl, Karen E.,Matyjaszewski, Krzysztof
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