- Chlorine Abstraction from Chloromethanes by Dimethylsilanediyls
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Photolysis of dodecamethylcyclohexasilane in carbon tetrachloride gives hexachloroethane; its formation is a result of chlorine abstraction from carbon tetrachloride by dimethylsilanediyl.
- Nakao, Ren,Oka, Kunio,Dohmaru, Takaaki,Nagata, Yoshio,Fukumoto, Tsugio
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- SYNTHESIS AND PROPERTIES OF SUBSTITUTED METHYLCYCLOPOLYSILANES
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Co-condensation of five equivalents Me2SiCl2 and one equivalent RR'SiCl2 with lithium provides the five- and six-membered rings RR'Si(Me2Si)4 and RR'Si(Me2Si)5.This method provides a direct route to the phenyl substituted methylcyclopolysilanes (R,R'=Me, Ph) which can be used for further functionalization of the silicon rings.It also provides several new sterically hindered methylcyclopolysilanes (R,R'=Ph, Ph; Me, t-Bu) which could not be synthesized by the conventional demethylation routes.These products have all been isolated and characterized by their ultraviolet, 1H-, 13C- and 29Si-NMR spectra.
- Helmer, Bradley J.,West, Robert
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- REACTIONS OF 1,2-DIMETHOXYTETRAMETHYLDISILANE WITH STYRENES: FORMATION OF A NEW TYPE OF SILACYCLOPENTANES HAVING PHENYL SUBSTITUENTS ON RING CARBONS
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The reaction of 1,2-dimethoxytetramethyldisilane with styrene and α-methylstyrene in the presence of NaOMe catalyst in tetrahydrofuran (THF) gave the new silacyclopentanes 1,1-dimethyl-2,4-diphenyl-1-silacyclopentane (IIIa) and 1,1,2,4-tetramethyl-2,4-diphenyl-1-silacyclopentane (IIIb), respectively.These silacyclopentanes were found to exist as cis-trans mixtures.The use of sodium metal in place of NaOMe afforded similar results.Reactions of a polysilane mixture, MeO(SiMe2)nOMe (n 3), with the styrenes also gave similar results.In some cases, polysilacycloalkanes such as 1,2,3-trisilacyclopentanes (IV) and 1,2,3,4-tetrasilacyclohexanes (V) were obtained as by-products.A mechanism for the formation of the silacyclopentanes and polysilacycloalkanes is presented.It was found that electron impact decomposition of silacyclopentanes IIIa and IIIb, trisilacycloalkane IV and tetrasilacycloalkane V gave molecular ions corresponding to the silacyclopropane, cyclotrisilane and cyclotetrasilane systems.
- Watanabe, Hamao,Inose, Jun,Muraoka, Tsutomu,Saito, Masayuki,Nagai, Yoichiro
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- Synthesis, properties and characterization of octadecamethylbicyclodecasilane
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The title compound 1 was obtained by Wurtz-type dehalogenative coupling of sym-dichlorotetramethyldisilane and trichloromethylsilane under appropriate conditions.Spectroscopic data for 1 are compared with those for bi(undecamethylcyclopentasilanyl) (2), a possible structural isomer.An X-ray structural study and 29Si-INEPT-INADEQUATE-NMR spectroscopy confirmed that only the trans-isomer of 1 is formed.Several attempts were made to obtain functional derivatives, but monocyclic and catenated oligosilanes were always obtained owing to breakdown of the bicyclic compound.Chemical and electrolytic reduction towards an anion radical was carried out at various temperatures.The ESR signal at 150 K shows an overlap of two distinct species: along with the spectrum of the well known Si5Me10(radical anion) that of a hitherto unknown species was observed.
- Jenkner, Peter K.,Hengge, Edwin,Czaputa, Rainer,Kratky, Christoph
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- Silanones and silanethiones from the reactions of transient silylenes with oxiranes and thiiranes in solution. The direct detection of diphenylsilanethione
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The transient silylenes SiMe2 and SiPh2 react with cyclohexene oxide (CHO), propylene oxide (PrO), and propylene sulfide (PrS) in hydrocarbon solvents to form products consistent with the formation of the corresponding transient silanones and silanethiones, respectively. Laser flash photolysis studies show that these reactions proceed via multistep sequences involving the intermediacy of the corresponding silylene-oxirane or -thiirane complexes, which are formed with rate constants close to the diffusion limit in all cases and exhibit UV absorption spectra similar to those of the corresponding complexes with the nonreactive O- and S-donors, tetrahydrofuran and tetrahydrothiophene. The SiMe2-PrO and SiPh2-PrO complexes both exhibit lifetimes of ca. 300 ns, and are longer-lived than the corresponding complexes with CHO, which are both in the range of 230-240 ns. On the other hand, the silylene-PrS complexes are considerably shorter-lived and vary with silyl substituent; the SiMe2-PrS complex decays with the excitation laser pulse (i.e., τ ≥ 25 ns), while the SiPh2-PrS complex exhibits τ = 48 ± 3 ns. The decay of the SiPh2-PrS complex affords a long-lived transient product exhibiting λ max ≈ 275 nm, which has been assigned to diphenylsilanethione (Ph2Si=S) on the basis of its second order decay kinetics and absolute rate constants for reaction with methanol, tert-butanol, acetic acid, and n-butyl amine, for which values in the range of 1.4 × 108 to 3.2 × 109 M-1 s-1 are reported. The experimental rate constants for decay of the SiMe2-epoxide and -PrS complexes indicate free energy barriers (ΔG?) of ca. 8.5 and ≥7.1 kcal mol-1 for the rate-determining steps leading to dimethylsilanone and -silanethione, respectively, which are compared to the results of DFT (B3LYP/6-311+G(d,p)) calculations of the reactions of SiH 2 and SiMe2 with oxirane and thiirane. The calculations predict a stepwise C-O cleavage mechanism involving singlet biradical intermediates for the silylene-oxirane complexes, and a concerted mechanism for silanethione formation from the silylene-thiirane complexes, in agreement with earlier ab initio studies of the SiH2-oxirane and -thiirane systems.
- Kostina, Svetlana S.,Leigh, William J.
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supporting information; experimental part
p. 4377 - 4388
(2011/06/11)
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- Phototransformation of perchlorate to chloride in the presence of polysilanes
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Perchlorate is a uniquely stable chemical described as an emerging thyroid disrupting agent that is presently detected in several terrestrial and aquatic matrices. The present study was undertaken to deoxygenate perchlorate to the chloride anion photolytically in the presence of dodecamethylcyclohexasilane (Me2Si)6 1. It is found that photolysis of 1 in the presence of dry NaClO4 in tetrahydrofuran (THF) at 254 nm leads to the disappearance of the salt. The removal of ClO4? occurred with the concurrent formation of ClO3? and ClO2?, which disappear to eventually produce the chloride anion quantitatively. The two cyclic silanes (Me2Si)5 3 and (Me2Si)4 4 in addition to several other siloxanes that include (Me2SiO)3, (Me2SiO)4, and (Me2Si)xO2 (x ≤ 4 and 5) were also detected. When the reaction was repeated using uniformly labelled 18O- [ClO4?] it was found that oxygen incorporated in the siloxane products was derived from perchlorate. Mixing 1 with perchlorate in THF in the dark or adding the salt to 1 after the latter being photolyzed in THF did not deoxygenate ClO4?. Based on experimental evidence gathered thus far it is concluded that dimethylsilylene, Me2Si: 2, a reactive intermediate produced by the photolysis of 1, is in part responsible for the deoxygenation of perchlorate. Direct oxygen transfer from ClO 4? to the silanes during photolysis is also suggested as a potential route of deoxygenating ClO4?. CSIRO 2007.
- Lazar, Carmen,Halasz, Annamaria,Beaulieu, Chantale,Thiboutot, Sonia,Ampleman, Guy,Hawari, Jalal
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p. 857 - 861
(2008/09/19)
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- Synthesis of α,ω-dihalopermethyloligosilanes and silane-siloxane copolymers
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α,ω-Dibromopermethyloligosilanes, Br(SiMe2)nBr (n = 2-4, 6), were prepared by the reaction of dodecamethylcyclohexasilane with bromine. The reaction of (Me2Si)6 with MCl4 (M = Sn, Ti) proceeds with the cleavage of Si-Si-and Si-C-bonds with the formation of α,ω-dichloropermethyloligosilanes, Cl(SiMe2)nCI (n = 2-4, 6), and chloro derivatives of cyclohexasilane, ClmSi6Me12-m (m = 1, 2). Silane-siloxane copolymers of regular structure were obtained by heterofunctional copolycondensation of α,ω-dihalopermethyloligosilanes with 1,5-dihydroxyhexamethyltrisiloxane.
- Chernyavskii,Zavin
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p. 1449 - 1453
(2007/10/03)
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- γ-Induced Generation of Dimethylsilylene from Dodecamethylcyclohexasilane
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γ-Irradiation of dodecamethylcyclohexasilane (I) generates dimethylsilylene in 65percent yield when benzene is used as a solvent.Kinetic studies using anthracene as quencher are consistent with a mechanism proposed for the generation of dimethylsilylene, Benzene is first excited by γ-rays and energy is transferred to (I).Excited (I) decomposes to give dimethylsilylene presumably in a way similar to (I) excited by u.v. light.The ratio of the rate constant for self-deactivation of benzene to that for energy transfer from benzene to (I), k2/k3, is 5.1 x 1E-2 mol l-1 at room temperature.Energy transfer to (I) is hindered by added anthracene.The ratio of the rate constant for energy transfer to anthracene to that for energy transfer to (I), k6/k3, is ca. 6 at room temperature.A similar energy transfer is possible in the case of u.v. irradiation.
- Oka, Kunio,Nakao, Ren,Nagata, Yoshio,Dohmaru, Takaaki
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p. 337 - 340
(2007/10/02)
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- The Permethylcyclosilanes (Me2Si)5 through (Me2Si)35
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The cyclic permethylpolysilanes (Me2Si)n, where n = 5-35, are all formed when dimethyldichlorosilane (Me2SiCl2) is added slowly to sodium-potassium (Na/K) alloy in tetrahydrofuran (THF).NMR, UV, and vibrational spectra are reported for compounds n = 5-19.The 13C NMR and 1H NMR spectra are explained in terms of methyl-methyl group interactions.Raman and IR spectra are assigned and partially explained on the basis of a standing wave model.
- Brough, Lawrence F.,West, Robert
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p. 3049 - 3056
(2007/10/02)
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