373-74-0Relevant articles and documents
(p-d) ? Bonding in Fluorosilanes? Gas-Phase Structures of (CH3)4-nSiFn with n = 1-3 and of t-Bu2SiF2
Rempfer, Beate,Oberhammer, Heinz,Auner, Norbert
, p. 3893 - 3897 (1986)
The gas-phase structures (rg values) of the methylfluorosilanes (CH3)4-nSiFn with n = 1-3 and of di-tert-butyl-difluorosilane, t-Bu2SiF2, have been determined by electron diffraction.In the case of CH3SiF3 the microwave rotational constant was included in the structure analysis.In the methylfluorosilane series a steady decrease of Si-F and Si-C bond lengths is observed with increasing fluorination: Si-F = 1.600(2), 1.586(2), and 1.570(2) Angstroem and Si-C = 1.848(2), 1.836(2), and 1.828(4) Angstroem for (CH3)3SiF, (CH3)2SiF2, and CH3SiF3, respectively.These trends are rationalized by increasing polar contributions and contraction of the silicon valence shell.Ab initio calculations for SiF4 indicate that (p-d) ? bonding is negligible.Substitution of the methyl groups in (CH3)2SiF2 by tert-butyl groups leads to lengthening of Si-F and Si-C bonds and strong variations in the silicon bond angles: Si-F = 1.586(2), 1.606(4) Angstroem; Si-C = 1.836(2), 1.869(3) Angstroem; CSiC = 116.7(6) deg, 125.5(11) deg; and FSiF = 104.6(4) deg, 97.7(8) deg in (CH3)2SiF2 and t-Bu2SiF2, respectively.
Conversion of Poly(methylhydrosiloxane) Waste to Useful Commodities
D?hlert, Peter,Enthaler, Stephan
, p. 345 - 352 (2016/02/23)
Poly(methylhydrosiloxane) [PMHS, R(OSiMeH)nOR] is applied in chemistry as cheap, low-toxic, air and moisture stable reducing reagent. However, along with the desired products significant amounts of silicone waste is produced, since only ~1.7 % of the PMHS is employed for the reduction process. The formation of PMHS-waste reduces the sustainability of such reduction protocols. For instance PMHS can be applied as reagent (a) in the methanolysis to produce molecular hydrogen; (b) in the reduction of sulfoxides to form the corresponding sulfides; (c) in the hydrodeoxygenation of fatty esters to produce hydrocarbons. An option for the treatment of the PMHS-waste can be the application of depolymerization methods to convert it to useful commodities. In more detail, the silicone waste is reacted in a depolymerization reaction with boron trifluoride diethyl etherate (BF3OEt2) to produce methyltrifluorosilane (MeSiF3) and difluoromethylsilane (MeSiF2H), which can be interesting building blocks for the silicone industry, overall demonstrating a resource conserving process.
The synthesis and properties of (CH2F)SiH3 and related monofluoromethylsilanes
Buerger, H.,Moritz, P.
, p. 293 - 308 (2007/10/02)
The reduction of (CFCl2)SiCl3 by LiAlH4, Me3SnH, and (nBu)3SnH has been studied.The compound (CH2F)SiH3 (I) and all the compounds of the series (CFCl2-mHm)SiCl3-nHn, m = 0, 1 and n = 0-3 were detected and characterized by NMR spectroscopy.Conditions for the synthesis of I, (CHFCl)SiH3 (IX) and (CFCl2)SiH3 (V) with acceptable yields have been optimized.These novel compounds were studied by 1H, 19F, 13C and 29Si NMR spectroscopy; their infrared and Raman spectra were recorded and assigned with the assistance of a normal coordinate analysis of 1 and its isotopomer (CD2F)SiD3.The thermolyses of I, IX and (CHF2)SiH3 (X) which start at about 120, 200 and 180 deg C, respectively, have been studied.Whereas I decomposes by a migration of F from C to Si, compound X undergoes elimination of the carbene CHF, insertion of which into SiH bonds ultimately gives CH3Si derivatives.
Thermolysis of trifluoromethylsilanes. Novel fluoromethylsilanes by insertion of CF2 and CHF into Si-H bonds
Beckers, H.,Buerger, H.
, p. 207 - 219 (2007/10/02)
The thermal decomposition in the gas phase of CF3SiH3 and (CF3)2SiH2 begins at ca. 200 and ca. 100 deg C, respectively.It is catalyzed by KF, and involves as initial step a clean CF2 elimination with an α-fluorine shift.Reactive species such as HBr trap CF2 quantitatively (to give in this case CHF2Br), while addition to the less reactive cyclohexene (to give 7,7-difluorobicycloheptane) is accompanied by secondary reactions.These dominate in the absence of an efficient CF2 trapping agent, and spectroscopic product analyses reveal that they mainly arise from insertion of the carbenes CHnF(2-n) into Si-H bonds followed by CH(n+1)F(1-n) elimination (n = 0, 1).This sequence corresponds to H/F exchange at the Si atom.Insertion of CF2 (generated by thermolysis of CF3SiF3 below 100 deg C) into an Si-H bond of H3SiF to give CHF2SiH2F in good yield is the first example of such a reaction and demonstrates its usefulness for the selective synthesis of CHF2Si compounds.In addition, some dismutation of SiHnF(3-n) moieties accompanies the carbene elimination/insertion reactions and the resulting novel fluoromethylsilanes were characterized by 1H and 19F NMR and (in part) IR spectroscopy.The synthesis of (CF3)2SiHBr by cleavage of (CF3)2Si(H)N(i-Pr)2 with BBr3 and its conversion with LiAlH4 to (CF3)2SiH2 are reported.The mechanism of the CF2/SiH insertion reaction is discussed.
