Silicon thermolysis

Difluorocarbene generated by the thermolysis of trimethyltnfluoromethylsilane reacts with disilanes by insertion into the silicon-silicon bond [S] (equation 9) Thermolysis of pentafluoroethyltnfluorosilane at 200 °C gives tetrafluoro ethylidene carbene, which reacts with phosphorus trifluonde to give trifluoro vinyltetrafluorophosphorane [9] (equation 10) and with perfluorotnmethylphos-phine to give perfluorodimethyhsopropylphosphine and perfluoro-2-butene [9] (equation 10)... 

The preference for formation of dihalocarbenes (but not the trihalomethyl radicals) upon thermolysis of trihalomethyl mercury, silicon and germanium derivatives seems to be a result of intermolecular coordination, of type [1], and of a thermodynamic preference for the carbene-forming pathway. The... 

Generally, only simple silenes having small groups (H, Me, CH2=CH) are obtained as transient species from the thermolysis of silacyclobutanes. In part this is due to the high temperatures (usually above 450°C) required for the ring cleavage. Substitution on the carbon atom adjacent to silicon in the ring can lead to carbon-substituted silenes. 1,3-Disilacyclobutanes do not readily revert to silenes under thermal conditions, but examples... 

The former silene is not stable at room temperature, owing to its tendency to dimerize in the absence of other reactants, but it can be stored as its [2+2] cycloadduct with A/-trimethylsilylbenzophenonimine, from which it is cleanly and easily liberated on mild thermolysis.99 The latter silene arose from the loss of LiX from the compound (r-Bu)2SiX-CLi (SiMe3)2, which subsequently underwent a spontaneous 1,3-silicon-to-silicon methyl shift. 

Complex 12 was found to be a good reactant in the double-silylation reaction. Thus, thermolysis of a toluene solution of 12 and diphenylacetylene at 120°C for 12 h afforded 5,6-carboranylene-1,1,4,4-tetramethyl-2,3-diphenyl-1,4-disilacyclohex-2-ene 13. When 1-hexyne was employed in the reaction with 12 under the same reaction conditions, the five-membered disila ring compound 18 was isolated. A key feature in the h NMR spectrum of 18 includes a singlet at 6.24 ppm assigned to the vinyl proton. A characteristic high-frequency 13C NMR resonance at 138.50ppm provides evidence for a tethered sp2 carbon atom between the two silicon atoms. 

The earliest work on silicon carbide fibers was done by Yajima and co-workers [3]. Yajima applied the Kumada [4] rearrangement to Burkhard s [5] dimethylpolysilane - an insoluble and infusible compound - (Eq. 1) and obtained by thermolysis at 400 - 450°C or by catalysis with polyborodiphenyl-siloxane at 350°C a melt spinnable and soluble polycarbosilane (Eq. 2). 

A related scrambling of groups in a silene has also been reported by Eaborn (143) to explain the structure of compounds isolated from the thermolysis of tris(trimethylsilyl)fluorodiphenylsilylmethane at 450°C, where Me and Ph groups freely interchange between silicon atoms [Eq. (19)]. A related rearrangement is probably also involved in the photochemical silene-to-silene isomerizations derived from acylpolysilanes described earlier. 

Orlov (8a) has compared the dissociative ionization and thermal decomposition of a series of Group IV compounds and discusses the use of the mass spectrometer to study the unstable or nonexistent compounds that are presumably thermolysis intermediates. These include bivalent compounds of Group IV such as silicon(II) derivatives and compounds with multiple bonds. Not only are ions observed important in such correlations, but the mass of the neutral fragment, as confirmed by the decomposition of metastable ions, is of equal importance. 

Silylated 1,2,3-trisilacyclopentanes (73) under photolysis split off their central Si atom as a silylene (trapped by a scavenger) <85JOM(292)l67>. l,2,3-Trisilacyclopent-4-enes (74) split off only their central silicon atom as silylene by flash vacuum thermolysis (650-720 °C), whereas by photolysis both central and terminal Si atoms may be extruded depending on the nature of the substituents (Ar better than Alk-stabilized silylene) <84CL393>. Pyrolysis of hexamethyl-1,2,4-trisilacyclopentane (75) is unique for Si-compounds since different products arise at normal <76ZAAC(419)249> and low <820M1453> pressure (Scheme 2). 

However, other siliranes are much more thermally stable than hexamethylsih-rane, and do not serve as sources of SiMe2 at such low temperatures. Boudjouk et al. made an important step when they found that bulky substituents such as the tert-butyl group on the silicon atom increased the stability of the silirane without preventing its thermolysis. 

Silicon tetrafluoride, for laboratory use, can be obtained from fluorosilicic acid1 or by thermolysis at 450-600°C of barium or disodium hexafluorosilicate.2 3 However, the most conventional synthesis of pure silicon tetrafluoride is by fluorination of silicon tetrachloride with sodium fluoride in acetonitrile.4... 

Difluorocarbene generated by the thermolysis of trimethyltnfluoromethylsilane reacts with disilanes by insertion into the silicon-silicon bond [S] (equation 9)... 

Silicon-carbon and silicon-nitrogen multiply bonded compounds 929 A ring-opened isomer 387 is obtained through thermolysis of 386b (equation 110). 

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