Silicon−Fluorine and Silicon−Carbon Bond Cleavage in Organofluorosilicates:  A Molecular Orbital Study

Abstract

The mechanism of silicon−fluorine and silicon−carbon bond cleavage in organofluorosilanes and -silicates is analyzed with the aid of molecular orbital calculations. The optimized geometries of reactants and intermediates are calculated, and these calculations support the view that cleavage of Si−F bonds occurs by way of fluorine-bridged Si--F--Si intermediates. Cleavage of a Si−C bond in PhSiF3 takes place in the presence of fluoride ion and oxidizing agents, and the calculations are in agreement with the formation of PhSiF4 - and PhSiF5 2-, followed by oxidation to a radical anion PhSiF5 •-. The latter species, however, is predicted to decompose rapidly to give anionic SiF5 -, and phenyl radicals. These calculations and the proposed mechanisms of bond cleavage are in agreement with experimental data, where available.

Interaction of Fluosilicic Acid with N-tert-Butyl-Substituted Urea. Crystal Structure of N,N-Di-tert-butylurea

“…This disproportionation of the Si-F bond lengths was HF 2 -F 6 2-found in the structure of the urea complex [(H 2 N) 2 COH] 2 SiF 6 [5] and confirmed by the results of simulation of the geometry of compound I: in this compound, a strong hydrogen bond éç···F (é···F 2.03 Å) is formed between one of the [(t-BuNH) 2 COH] + cations and the Si anion, which elongates one Si-F bond (1.76 Å) as compared with the other five Si-F bonds (1.64-1.66 Å). A dependence between the relative weakening of the Si-F bonds in organopentafluosilicates due to H-bonding and the affinity of the RSi anions to hydrolysis in aqueous solutions was discussed in [14].…”

“…The crystals are orthorhombic (FW = 172.27): a = 9.4579 (14), b = 13.823(2), c = 17.9603(18) Å , V = 2348.1(5) Å 3 , F (000) = 768, ρ calcd = 0.975 g/cm 3 , µ = 0.064 mm -1 , Z = 8, and space group ê2 1 2 1 2 1 .…”

(3‐Aminopropyl)trifluorosilanes and their N‐substituted derivatives

“…Their physical data are consistent with the literature data. 19 1 I NMR, 13 C, 19 F and 29 Si spectra in CDCl 3 were recorded on a Bruker 400 DPX spectrometer at 400.13, 100.61, 376.50 and 79.49 MHz, respectively. The chemical shifts (δ) were reported with reference at 0.00 ppm (Me 4 Si) or 7.26 ppm (CHCl 3 ) for the proton and at 77.00 ppm (centered on the signal of CDCl 3 ) for the carbon.…”

“…They were completely characterized by elemental analysis and spectroscopic studies (IR, 1 H, 13 19 F resonances appeared at lower field (by 2-10 ppm) as compared with that for model tetravalent silane VI. 11 Furthermore, the J Si−F coupling constants were considerably decreased (by 37-39 Hz) in comparison to that of the model silane (VI; Table 1).…”

Chemistry of xenon derivatives. Synthesis and chemical properties

“…A scheme with the nomenclature N-X-L (where X is the central atom, N is the number of valent electrons and L is the number of ligands) 390 illustrates the mechanism of this reaction which includes the formation of the anion 233, its oxidation to the radical 234 391 and subsequent recombination. 389 With a decrease in the content of the radical Cl .…”