Fluorine exchange between four-, five-, and six-coordinate silicon compounds

Abstract

. Can. J. Chem. 55,3845 (1977). Intermolecular fluorine exchange in the systems SiF4-SiF,-, MeSiF3-MeSiF4-, PhSiF3-PhSiF4-, SiF,--SiFs2-, SiF4-SiFs2-, and MeSiF,-SiFs2-has been studied by fluorine and proton nmr spectroscopy. Exchange is postulated to involve fluorine-bridged intermediates; alternative pathways of exchange, such as fluoride dissociation or impurity (HF and H20) catalyzed exchange, have been eliminated. Addition of NH3 to SF,--SiFs2-slows down exchange whereas addition of Et2NH to MeSiF, promotes exchange.RONALD KIRK MARAT et ALEXANDER F. JANZEN. Can. J. Chem. 55,3845 (1977). On Btudie par rmn du proton et du fluor 1'Cchange intermolCculaire du fluor dans les systtmes SF4-SiF5-, MeSiF3-MeSiF4-, PhSiF,-PhSiF4-, SiF,--SiFs2-, SiF4-SiF,2-et MeSiF3-SiFs2-. On fait I'hypothese que 1'Cxchange implique des intermediaires a fluor pontC; on Climine la possibilite d'un autre mode d'echange comme la dissociation du fluor ou de 1'6change catalysee par une impurete (HF et H20). L'addition de NH, au systeme SiF5--SiFs2-a pour effet de ralentir I'khange; par contre l'addition de Et2NH a MeSiF, la favorise.[Traduit par le journal]

Fluorination of sulfur-containing amino acids: Reaction of xenon difluoride with cysteine derivatives

“…-HF, -Xe scopy (Table 1) and the nmr data are in agreement with earlier assignments of fluoromethionine (7) and fluoroalkylsulfides (2)(3)(4)(5). Both 4 and 5 contain two chiral centers and the presence of diastereomers (A and B) is confirmed by 'H and "F nrnr (Table 1).…”

Bis(pyridine)difluoroboron, tris(pyridine)fluoroboron, and other (pyridine)haloboron cations. A systematic NMR study

“…Preliminary attempts to form pyr2BF2+.BF,-by disproportionation of pyr.BF3 in the absence of a heavier boron trihalide, by analogy with these cases, were unsuccessful. The "F NMR spectra of pyr.BF3 and 2-MepyrBF, did not change following (i) refluxing in toluene or (ii) refluxing in toluene with the addition of 1,1,1,3,3,3-hexamethyldisilazane, which has a high affinity for fluoride ion (19) and which we hoped would act as an irreversible extractant for F from pyr.BF3, giving three-coordinate pyr.BF2+ that further pyridine could attack. With 1,1,1,3,3,3-hexamethyldisilazane present, 15 min of reflux in toluene did remove some fluorine from the adducts as shown by the presence of a small "F NMR peak assigned to Me3SiF (larger in the 2-Mepyr case than with pyr itself), and the pyr.BF, resonances were broadened, suggesting some chemical exchange, but no I' F signals arising from boron cations or BF,-could be observed.…”

Nuclear magnetic resonance study of fluorine exchange in the system

“…(n-C3H7),NSiFS was prepared as described previously (6, 7). C6HSPF4 (4.8 g) was syringed onto (n-C3H7),NF (5.4 g) (7,8) in 50 mL acetonitrile in a nitrogen-filled dry box. Evaporation of the solvent gave crystalline (n-C,H,),NPhPF, (1.7 g), which was filtered, dried over P20s and under vacuum and identified by "P and "F nmr (2, 9).…”

“…Line-shape calculations were performed on an Amdahl 470-V7 computer with the IBM Fortran H (extended) compiler using a modified version of the program EXCHSYS (10,11). The exchange probability matrix is identical to that required for the 'H nmr study of fluorine exchange in CH,SiF, (7,11).…”

“…If the rate of fluorine exchange is indeed independent of PhPF, concentration ( a = 1 in eq. [3]), and if the order is one with respect to PhPF; concentration, as shown in Fig. 1, then the most reasonable mechanism of exchange is a bimolecular process involving five-and six-coordinate phosphorus species and a fluorine-bridged intermediate.…”