For (pentafluoroethyl)phenylstannanes, (C F ) SnPh (n=1-3), and dimethylbis(pentafluoroethyl)stannane, (C F ) SnMe , a high yield synthesis was developed by the use of LiC F as a C F transfer reagent. The treatment of these products with gaseous hydrogen chloride or hydrogen bromide afforded (C F ) SnX (X=Cl, Br; n=1-3) in good yields. The (pentafluoroethyl)stannanes were fully characterized by H, C, F and Sn NMR, IR spectroscopy and mass spectrometry. The treatment of the (pentafluoroethyl)tin halides (C F ) SnX with 1,10-phenanthroline (phen) led to the formation of the corresponding octahedrally coordinated complexes [(C F ) SnX (phen)], the structures of which were elucidated by X-ray diffraction analyses. The bromostannane (C F ) SnBr reacted with sodium cyclopentadienide to give the (η -cyclopentadienyl)tris(pentafluoroethyl)stannane, (C F ) SnCp, for which single-crystal X-ray diffraction analysis could be performed. The coupling constants J( Sn, C) and J( Sn, F) of all new stannanes are strongly correlated and sensitive to the substitution pattern at the tin atom. For both coupling constants a negative sign could be assigned.
It is our hypothesis that fluoro substitution provides a powerful tool to modulate the desired characteristics and to increase the specificity of studies of structure-activity relationships. 4-Bromodiphenyl ether (PBDE 3) and its five corresponding monofluorinated analogues (F-PBDEs 3) have been synthesized and fully characterized (using (1)H, (13)C and (19)F NMR spectroscopy, and mass spectrometry). The accurate structure from X-ray crystal analysis was compared with iterative calculations using semi-empirical self-consistent field molecular-orbital (SCF-MO) models. The compounds studied were 4-bromodiphenyl ether (PBDE 3), the (13)C(6)-isotopically labeled PBDE 3 ((13)C(6)-PBDE 3) and 2-fluoro-4-bromodiphenyl ether (3-2F), 2'-fluoro-4-bromodiphenyl ether (3-2'F), 3-fluoro-4-bromodiphenyl ether (3-3F), 3'-fluoro-4-bromodiphenyl ether (3-3'F), and 4'-fluoro-4-bromodiphenyl ether (3-4'F). Solid-state intermolecular interactions for PBDE 3 and the F-PBDEs 3 isomers are dominated by weak C-H(F,Br)...pi and C-H...F interactions. The C-F bond lengths varied between 1.347 (2) and 1.362 (2) A, and the C4-Br bond length between 1.880 (3) and 1.904 (2) A. These bond lengths are correlated with electron-density differences, as determined by (13)C shifts, but not with the strength of the C-F couplings. The interior ring angles of ipso-fluoro substitution increased (121.9-124.0 degrees ) as a result of hyperconjugation, a phenomenon also predicted by the calculation models. An attraction between the vicinal fluoro and halo substituents (observed in fluoro substituted chlorobiphenyls) was not observed for the bromo substituted F-PBDEs. The influence of a fluoro substituent on the conformation was only observable in PBDEs with di-ortho substitution. Calculated and observed torsion angles showed a positive correlation with increasing van der Waals radii and/or the degree of substitution for mono- to tetra-fluoro, chloro, bromo and methyl substitutions in the ortho positions of diphenyl ether. These findings utilizing F-tagged analogues presented here may prove fundamental to the interpretation of the biological effects and toxicities of these persistent environmental pollutants.
Syntheses of salts containing the tris(pentafluoroethyl)stannate(II) ion, [Sn(C F ) ] , were achieved through deprotonation of the corresponding stannane, HSn(C F ) , as well as by direct pentafluoroethylation of SnCl with LiC F . The electron-withdrawing substituents have substantial influence on the stability and reactivity of the anion as documented by its treatment with main group halides. Alkyl halides (R-X) underwent nucleophilic substitutions to afford RSn(C F ) , whereas Si, Ge, Sn, P halides gave rise to oxidation processes yielding hypervalent [SnX (C F ) ] salts (X=Cl, Br, I). Moreover the unsymmetrical distannane, nBu SnSn(C F ) , was disclosed as an alternative precursor for the Sn(C F ) moiety. Although neither the solid state structure nor its spectra in alkane solution reveal unexpected peculiarities, unusual dissociation of the compound in coordinating solvents into [nBu Sn(D) ] and [Sn(C F ) ] ions was observed.
Pentafluoroethyllithium, LiC F , has been established as an efficient and versatile reagent for the transfer of the pentafluoroethyl unit to a number of electrophiles. Here, the stability of this species up to -40 °C is of advantage, particularly in comparison to its smaller congener LiCF . The usual production of LiC F , however, from gaseous HC F or IC F and strong bases requires specially designed apparatuses, which severely impeded its value as a laboratory reagent. In this contribution we communicate an alternative gas-free and highly efficient protocol for the synthesis of LiC F from the already commercialized stannate salt [PPh ][Sn(C F ) ]. The [Sn(C F ) ] anion represents not only the first example of a structurally characterized hypervalent pentaalkylstannate but also serves as a precursor for the synthesis of the homoleptic tetrakis(pentafluoroethyl)stannane, Sn(C F ) . The reaction of the latter with n-butyllithium provides an insight into the mechanism of LiC F generation.
A versatile two-step synthesis of tris(pentafluoroethyl)stannane, HSn(C F ) , is presented. Electron-withdrawing C F groups significantly influence the polarity of the tin-hydrogen bond, which allows facile deprotonation of the compound, even in water. The utility of this electron-deficient stannane was illustrated in hydrostannylations of alkenes and alkynes, as well as in dehalogenation reactions. The remarkably high reactivity of HSn(C F ) is demonstrated in fast hydrostannylations, even in the absence of activators, whereby the regioselectivity of this process turns out to be solvent dependent. It is of great advantage that in dehalogenation reactions volatile halogenotris(pentafluoroethyl)stannanes, XSn(C F ) (X=I, Br), are formed that allow facile separation of the tin-containing byproducts from the reaction mixtures.
Organometallic reactions involving highly reactive organolithium reagents are widely used in organic synthesis. However, the use of such organometallics in batch mode on a pilot and industrial scale is challenging for safety reasons and frequently requires expensive cryogenic process conditions. A change to continuous processing in flow mode can provide major advantages for process safety and economics. In this study, we compare static and dynamic flow reactor technologies for two important organolithium (butyllithium and hexyllithium)-enabled transformations: deprotonations and bromine/lithium exchange reactions. Using higher concentrated (≥3 M) butyllithium (BuLi) solutions, that is, reaction mixtures with reduced hydrocarbon content, decreases the risk of reactor fouling and allows for increased space/time yields. In the flow mode, the observed reactions could be carried out under more convenient conditions, that is, at higher temperatures compared to the batch mode, and the deprotonation reaction even at ambient temperature instead of −78 °C. The formation of precipitates with the risk of clogging can be further reduced by changing from static flow to dynamic spinning disc reactor technology. The SpinPro reactor system from Flowid has been identified to ensure robust performance, as it tolerates salt precipitations and can provide excellent mass transfer conditions. Flow process technology using concentrated organolithium products can provide unique benefits for the manufacturing of pharmaceutical intermediates, agrochemical products, and specialty chemicals.
The treatment of phenyl-protected pentafluoroethylstannanes, Sn(C 2 F 5 ) 4-n Ph n (n = 1-3), with anhydrous HF results in the formation of the corresponding fluorostannanes which are associated in the solid state but form monomeric and dimeric fluoride complexes in solution. Due to the pronounced Lewis acidity caused by the electron-withdrawing pentafluoroethyl groups, these stannanes represent suitable precursors for the synthesis of neutral, monoanionic and dianionic hexacoor- [a] Centrum für Molekulare Materialien,
Human exposure to polybrominated diphenyl ether (PBDE) can occur via ingestion of indoor dust, inhalation of PBDE-contaminated air and dust-bound PBDEs. However, few studies have examined the pulmonary toxicity of particle-bound PBDEs, mainly due to the lack of an appropriate particle-cell exposure system. In this study we developed an in vitro exposure system capable of generating particle-bound PBDEs mimicking dusts containing PBDE congeners (BDEs 35, 47, 99) and delivering them directly onto lung cells grown at an air-liquid interface (ALI). The silica particles and particle-coated with PBDEs ranged in diameter from 4.3 to 4.5 μm and were delivered to cells with no apparent aggregation. This experimental set up demonstrated high reproducibility and sensitivity for dosing control and distribution of particles. ALI exposure of cells to PBDE-bound particles significantly decreased cell viability and induced reactive oxygen species generation in A549 and NCI-H358 cells. In male Sprague-Dawley rats exposed via intratracheal insufflation (0.6 mg/rat), particle-bound PBDE exposures induced inflammatory responses with increased recruitment of neutrophils to the lungs compared to sham-exposed rats. The present study clearly indicates the potential of our exposure system for studying the toxicity of particle-bound compounds.
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