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Pyrolysis 1,3-disilacyclobutanes

The rate of pyrolysis of 1,3-disilacyclobutanes 44 (see Table III) was shown by the same authors to be dependent upon the substituents on... [Pg.90]

Another procedure for the synthesis of 1,3-disilacyclobutanes is the pyrolysis of monosilacyclobutanes (eq. 5), [9, 14, 16], but this method has difficulties and disadvantages [14]. One of these is that polysilmethylene formation is a side-reaction when it is carried out in the gas-phase. [Pg.26]

In another study several simple silenes RR Si=CH2 (R, R = Me, Vinyl etc.) were formed by laser-powered pyrolysis and were found to form linear polymers, in contrast to the usual behavior of silenes which yield cyclodimers when formed by conventional thermolysis techniques16. Reactions of the silenes in the presence of several monomers such as vinyl acetate, allyl methyl ether and methyl acrylate were also studied. Laser-induced decomposition of silacyclobutane and 1,3-disilacyclobutane gave rise to silenes and other oxygen-sensitive deposits17,18. [Pg.1237]

Interrante and coworkers developed two polysilaethylene precursor systems, which upon pyrolysis gave nearly phase-pure SiC (95-99% SiC) in high ceramic yield (75-90%) (Scheme ll)116. The first procedure begins with a multistep synthesis of 1,1,3,3-tetrachloro-l,3-disilacyclobutane (monomer), 5. Alternately, gas phase pyrolysis will convert 6 to 5. [Pg.2283]

Pyrolysis of l,l,3,3-trimethyl-2,4-dimethylene-l,3-disilacyclobutane in a vertical nitrogen-flow system at 600 °C produced a mixture of starting material and methylenedisilacyclopentane (Equation 6) <1995JA11695>. [Pg.917]

This report by Conlin raised a lot of questions in my mind, but these questions remained dormant until in a futile attempt to prepare a,a-silylenevinylene polymers we accidentally synthesized 1,3-di-methylene-l,3-disilacyclobutane 5. This serindipitious synthesis allowed us to establish a two-case generality for the isomerization of methylenesilacyclobutanes since gas-phase pyrolysis of 5 cleanly and solely produced methylenedisilacyclopentene 7 (Eq. 9). This isomerization was kinetically followed in a stirred-flow reactor to afford Arrhenius parameters that clearly revealed this to be a concerted reaction. (Well, maybe not that clearly since you wouldn t bet your life on a log A of 12.5, but there certainly aren t any 54 kcal/mol sigma bonds in 5.)... [Pg.19]

Despite the calculated, rather low first ionization potential, suggesting an isolated, easy-to-detect band in the silaethene PE spectrum, numerous pyrolysis experiments with promising precursors, such as 1,3-disilacyclobutane, yielded no reproducible PE band in the expected region. Eventually, in the thermal retrodiene cleavage of a 5,6-bis(trifluoromethyl) derivative of 2-silabicyclo[2.2.2]octa-5,7-diene, a novel band exhibiting vibrational fine structure appeared within the precalculated region (Figure 4). [Pg.563]

The pyrolysis of 1,1-disubstituted silacyclobutanes has been used as a method for the preparation of 1,1,3,3-tetrasubstituted 1,3-disilacyclobutanes183. Copyrolysis of two different 1,1-disubstituted silacyclobutanes yielded mixtures containing 1,3-disilacyclobutanes arising from all possible combinations of the two silenes present (equation 51). The preparative method failed in the case of cyclopentadienyl-substituted silacyclobutanes183, 184, presumably due to competing intramolecular reactions of the silene. The thermolysis of trimethylsilylcyclopentadiene may also proceed via a silene184. [Pg.1054]

Thermal silylcarbene-to-silene rearrangements have been known for a long time1. The pyrolytic product from trimethylsilyldiazomethane, 1,1,2-trimethylsilene, was trapped in an argon matrix230, and the pyrolysis of bis(trimethylsilyl)diazomethane126 was reported to produce fair amounts of 2,4-bis(trimethylsilyl)hexamethyl-l,3-disilacyclobutane, the expected dimerization product of 2-(trimethylsilyl)-1,1,2-trimethylsilene. A second product was the disilane expected from an ene addition of one... [Pg.1060]

A silene-to-silylene isomerization by a 1,2-shift of a trimethylsilyl group from silicon to carbon was originally proposed in order to account for the formation of 1,1,3-trimethyl-1,3-disilacyclobutane during the pyrolysis of allylpentamethyldisilane (equation 93)214. Since silenes are planar and since the rc-component of the C=Si double bond is quite strong ( 40 kcal mol ) 19, m, it is not easy for the molecule to align the migrating SiH or SiSi bond with the carbon p-orbital that forms the new bond. [Pg.1072]

The retro-ene mechanism was considered unlikely225 since the dimer of 1-methoxy-1-methylsilene, l,3-dimethoxy-l,3-dimethyl-l,3-disilacyclobutane, was not observed. However, since little is known about the effect of the methoxy substituent on the dimerization and cross-dimerization rates of silenes, we consider this argument somewhat inconclusive. It is supported, however, by the observation225 that 1-methyl-1-propylsilene, formed by the pyrolysis of 1 -propyl-1 -methyl- 1-silacyclobutane under similar conditions, fails to undergo a retro-ene-type fragmentation, although such a process should be more exothermic, as it would produce a silene and an olefin instead of two silenes. [Pg.1081]

The head-to-tail dimerization of simple silenes is an essentially irreversible process. Pyrolysis of the 1,3-disilacyclobutane products requires high temperatures and does not represent a useful source of silenes. [Pg.1100]

While several highly substituted 1,2-disilacyclobutanes are known to revert under very mild conditions to silenes , it is generally believed that 1,3-disilacyclobutanes need more drastic conditions to undergo the cycloreversion yielding silenes . Kinetic data for the pyrolyses of several 1,3-disilacyclobutanes (24, 47, 48) have been reported by Davidson and CO workers and are summarized in Table 2 . Silene formation was inferred from detection of trapping products with TMSOMe and HCl. It was found that methyl substitution at silicon slows down the pyrolysis rate. The initial process for the decomposition of... [Pg.866]


See other pages where Pyrolysis 1,3-disilacyclobutanes is mentioned: [Pg.120]    [Pg.6]    [Pg.864]    [Pg.866]    [Pg.867]    [Pg.982]    [Pg.521]    [Pg.522]    [Pg.932]    [Pg.74]    [Pg.42]    [Pg.596]    [Pg.149]    [Pg.1033]    [Pg.1051]    [Pg.1053]    [Pg.1054]    [Pg.1055]    [Pg.1056]    [Pg.1062]    [Pg.1088]    [Pg.365]    [Pg.69]    [Pg.72]    [Pg.987]    [Pg.98]    [Pg.718]    [Pg.864]    [Pg.867]    [Pg.982]    [Pg.28]    [Pg.198]    [Pg.126]    [Pg.95]   
See also in sourсe #XX -- [ Pg.90 , Pg.91 ]




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1.2- Disilacyclobutanes

Disilacyclobutane

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