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Spectroscopy silenes

Subsequently, other members of the family of siienes (Me3Si)2Si= C(OSiMe3)R have been prepared, where R = Me, Et, i-Pr, CH2Ph, bicyclooctyl, CEt3, 1-methylcyclohexyl, and Mes. The first four siienes listed were not stable in inert solvents, and hence were not observable by NMR spectroscopy, since they rapidly reacted intermolecularly to give linear and/or cyclic head-to-head dimers.87 This is illustrated in Eq. (14) for the benzyl compound where the initially formed silene 5 yielded the cyclic head-to-head dimer 6 as well as the linear head-to-head dimer 7. The latter four siienes were all relatively stable and were characterized by NMR spectroscopy.105... [Pg.81]

The bulky, stable silenes of Brook et al. (104,122-124,168) and Wiberg et al. (166,167) have been the only systems capable of being studied by nuclear magnetic resonance (NMR) spectroscopy to date. Table III lists the 13C and 29Si chemical shifts and the relevant coupling constants of these compounds. [Pg.16]

Photolysis of acyldisilanes at A > 360 nm (103,104) was shown, based on trapping experiments, to yield both silenes 22 and the isomeric siloxy-carbenes 23, but with polysilylacylsilanes only silenes 24 are formed, as shown by trapping experiments and NMR spectroscopy (104,122-124) (see Scheme 4). These silenes react conventionally with alcohols, 2,3-dimethylbutadiene (with one or two giving some evidence of minor amounts of ene-like products), and in a [2 + 2] manner with phenyl-propyne. Ketones, however, do not react cleanly. Perhaps the most unusual behavior of this family of silenes is their exclusive head-to-head dimerization as described in Section V. More recently it has been found that these silenes undergo thermal [2 + 2] reactions with butadiene itself (with minor amounts of the [2 + 4] adduct) and with styrene and vinyl-naphthalene. Also, it has been found that a dimethylsilylene precursor will... [Pg.33]

Grobe, Auner and coworkers studied the thermal decomposition of 22,1 and methylsilacyclobutane 14 under low pressure flow pyrolysis conditions26. They characterized the transient silenes 2, 25 and 26 by mass spectrometric methods and by low temperature NMR spectroscopy of the adducts 27-29 of the silenes with hexadeuteriomethyl ether (equation 6)27. [Pg.863]

A stable neopentylsilene, 1,1-dimesity 1-2-neopentyl-1-silene 134, was synthesized by the Couret group from fluorodimesitylvinylsilane and t-BuLi82. It was characterized by NMR spectroscopy. [Pg.879]

Silenes of the family Me3SiR1Si=C(OSiMe3)Ad-l 137 undergo a complex silene-to-silene photoisomerization reaction90,94,96. When silenes 137 are generated by photolysis of acylsilanes 138, the isomeric silenes 139 and 140 are formed in a subsequent reaction. The reaction was followed by UV and NMR spectroscopy. The disappearance of 138 cleanly follows first-order kinetics and the overall kinetics were consistent with the transformation 138 -> 137 -> 139. 137 as well as 139 were characterized by NMR spectroscopy and, in addition, the structure of 137 was established by trapping with methanol. The identity of 139 and 140 was confirmed by the isolation of their head-to-tail dimers from which crystals, suitable for X-ray analyses, were isolated (equation 34)90. [Pg.881]

Reaction of simple aromatic aldehydes with Brook - type silenes (Me3Si)2Si=C(0 SiMe3)R1 gives exclusively a cis/trans mixture of the 2-siloxetanes 469, the nominal [2 + 2] cycloadducts, which can be identified by NMR spectroscopy (equation 154)235. [Pg.959]

From that value a force constant of k = 5.6 mdynA 1 for the Si=C double bond is deduced255. This frequency is clearly higher than the usual range for Si—C stretch vibrations but substantially less than for C=C stretches, both because Si is heavier than C and because the Si=C bond is weaker than the C=C bond. More suitable for the experimental characterization is the vinylic Si—H stretch vibration which gives rise to a medium band at 2239 cm-1 (25) or 2187 cm-1 (2)29, hypsochromically shifted by around 100 cm-1 relative to the Si—H stretch in simple silanes. A detailed analysis of the vibrational spectra of matrix-isolated MeHSi=CH2 26 using polarized IR spectroscopy established IR transition moment directions relative to the tot -transition moment (Si-C axis) in 26156. These data provide detailed information about the vibrational modes and about the structure of 26156. The bathochromic shift of the Si=C stretch in the isomeric 1,3-silabuta-l,3-dienes 289 and 290 by around 70 cm 1 compared with the Si=C stretch in simple silenes (Table 15), was interpreted as an indication of Si=C—C=C and C=Si—C=C 7r-conjugation159. [Pg.995]

Silene 2, 1-fluorosilene 602 and 1,1-difluorosilene 603 have been examined by FT ion cyclotron resonance spectroscopy in order to estimate the jr-bond strength. Bracketing studies with various bases (B) and fluoride acceptors (A) gave values for the proton and fluoride affinity of the silenes284. The TT-bond energy was calculated by thermochemical cycles and found to increase with fluorine substitution. The data are given in Table 16. [Pg.996]

J.K. Wright, B. High-Performance Liqnid Chromatography Coupled to Nuclear Magnetic Resonance Spectroscopy and Mass Spectrometry Applied to Plant Products. Identification of Ecdysteroids from Silene Ofites, Chromatographia, 374-378 (1999). [Pg.187]


See other pages where Spectroscopy silenes is mentioned: [Pg.76]    [Pg.82]    [Pg.94]    [Pg.95]    [Pg.97]    [Pg.19]    [Pg.21]    [Pg.34]    [Pg.422]    [Pg.601]    [Pg.881]    [Pg.888]    [Pg.978]    [Pg.985]    [Pg.991]    [Pg.995]    [Pg.1526]    [Pg.1526]    [Pg.5889]    [Pg.5889]    [Pg.601]    [Pg.6]    [Pg.86]    [Pg.137]    [Pg.990]   
See also in sourсe #XX -- [ Pg.95 , Pg.96 , Pg.97 , Pg.98 , Pg.99 ]




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Silenes

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