On Pentakis(pentafluoroethyl)stannate, [Sn(C2 F5 )5 ]- , and the Gas-Free Generation of Pentafluoroethyllithium, LiC2 F5.

Pentafluoroethyllithium, LiC2 F5 , 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 LiCF3 . The usual production of LiC2 F5 , however, from gaseous HC2 F5 or IC2 F5 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 LiC2 F5 from the already commercialized stannate salt [PPh4 ][Sn(C2 F5 )5 ]. The [Sn(C2 F5 )5 ]- 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(C2 F5 )4 . The reaction of the latter with n-butyllithium provides an insight into the mechanism of LiC2 F5 generation.

The Dynamic Equilibrium of Hexakis(pentafluoroethyl)distannane Adducts [XSn(C2 F5 )3 {Sn(C2 F5 )3 }]- (X=Cl, Br, I, Sn(C2 F5 )3 ).

The tin-tin bond cleavage of hexaorganodistannanes by nucleophiles is a long-known reaction and widely used for stannate formation or stannyl group transfer. Herein, we detail our experiments to provide analytical evidence for the existence of the reasonably stable anionic complexes [XSn(C2 F5 )3 {Sn(C2 F5 )3 }]- (X=Cl, Br, I, Sn(C2 F5 )3 ) derived from hexakis(pentafluoroethyl)distannane. NMR investigations at low temperature lend further mechanistic insights. Thus, by detection of the imposing ion [Sn(C2 F5 )3 {Sn(C2 F5 )3 }2 ]- , one can surmise that the chemistry of Sn2 (C2 F5 )6 has more in common with the isolobal iodine than with classical distannanes.

Tris(pentafluoroethyl)stannane: Tin Hydride Chemistry with an Electron-Deficient Stannane.

A versatile two-step synthesis of tris(pentafluoroethyl)stannane, HSn(C2 F5 )3 , is presented. Electron-withdrawing C2 F5 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(C2 F5 )3 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(C2 F5 )3 (X=I, Br), are formed that allow facile separation of the tin-containing byproducts from the reaction mixtures.

Synthesis and Reactivity of Donor-Stabilized Bis(pentafluoroethyl)stannylene [Sn(C2 F5 )2 (D)n ] (D=THF, DMAP, PMe3 , [Sn(C2 F5 )3 ]- ).

In this contribution we report on the synthesis of bis(pentafluoroethyl)stannane, H2 Sn(C2 F5 )2 . In the reaction with donor molecules a ready elimination of hydrogen and the formation of the corresponding donor-stabilized monomeric bis(pentafluoroethyl)stannylene, Sn(C2 F5 )2 , becomes apparent. With dependence on the Lewis basicity and steric demand of the donor, varying coordination numbers are realized. Whereas the reaction with nitrogen bases like 4-(dimethylamino)pyridine (DMAP) leads to the complexation of two donor molecules, [Sn(C2 F5 )2 (dmap)2 ], treatment with PMe3 or [Sn(C2 F5 )3 ]- furnished the corresponding neutral or anionic monoadducts, [Sn(C2 F5 )2 (D)] (D=PMe3 , [Sn(C2 F5 )3 ]- ). In contrast, the utilization of sterically demanding donors, such as iPr2 O, as well as the thermal treatment of ether complexes, [Sn(C2 F5 )2 (D)n ] (D=Et2 O, THF), leads to the formation of oligomeric and cyclic stannylene moieties [Sn(C2 F5 )2 ]n . The reactivity of H2 Sn(C2 F5 )2 and the donor-stabilized stannylenes was proven by hydrostannylation and complexation reactions with tetracarbonylnickel and bimetallic compounds. In the latter case, a donor-dependent stannylene or distannylene insertion into the metal-metal bond was observed.

The Tris(pentafluoroethyl)stannate(II) Anion, [Sn(C2 F5 )3 ]- -Synthesis and Reactivity.

Syntheses of salts containing the tris(pentafluoroethyl)stannate(II) ion, [Sn(C2 F5 )3 ]- , were achieved through deprotonation of the corresponding stannane, HSn(C2 F5 )3 , as well as by direct pentafluoroethylation of SnCl2 with LiC2 F5 . 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(C2 F5 )3 , whereas Si, Ge, Sn, P halides gave rise to oxidation processes yielding hypervalent [SnX2 (C2 F5 )3 ]- salts (X=Cl, Br, I). Moreover the unsymmetrical distannane, nBu3 SnSn(C2 F5 )3 , was disclosed as an alternative precursor for the Sn(C2 F5 )3 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 [nBu3 Sn(D)n ]+ and [Sn(C2 F5 )3 ]- ions was observed.

Synthesis of Mono-, Bis- and Tris(pentafluoroethyl)tin Derivatives, (C2 F5 )4-n SnXn (X=Ph, Me, Cl, Br, Cp; n=1-3).

For (pentafluoroethyl)phenylstannanes, (C2 F5 )4-n SnPhn (n=1-3), and dimethylbis(pentafluoroethyl)stannane, (C2 F5 )2 SnMe2 , a high yield synthesis was developed by the use of LiC2 F5 as a C2 F5 transfer reagent. The treatment of these products with gaseous hydrogen chloride or hydrogen bromide afforded (C2 F5 )4-n SnXn (X=Cl, Br; n=1-3) in good yields. The (pentafluoroethyl)stannanes were fully characterized by 1 H, 13 C, 19 F and 119 Sn NMR, IR spectroscopy and mass spectrometry. The treatment of the (pentafluoroethyl)tin halides (C2 F5 )4-n SnXn with 1,10-phenanthroline (phen) led to the formation of the corresponding octahedrally coordinated complexes [(C2 F5 )4-n SnXn (phen)], the structures of which were elucidated by X-ray diffraction analyses. The bromostannane (C2 F5 )3 SnBr reacted with sodium cyclopentadienide to give the (η1 -cyclopentadienyl)tris(pentafluoroethyl)stannane, (C2 F5 )3 SnCp, for which single-crystal X-ray diffraction analysis could be performed. The coupling constants 1 J(119 Sn,13 C) and 2 J(119 Sn,19 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.

Innovative application of fluoro tagging to trace airborne particulate and gas-phase polybrominated diphenyl ether exposures.

Polybrominated diphenyl ethers (PBDEs) are flame retardants applied as coatings to many consumer products, including household items. PBDEs are released and produce airborne vapors and dusts. Inhalation of particle-phase and/or gas-phase PBDEs is therefore a major route of exposure. In an attempt to mimic realistic airborne exposures, actual uptake, and deposition of particles and vapors, we prepared and characterized particles for future animal exposure studies. To trace the particles in environmental and biological systems, we employed fluoro tagging. We synthesized, characterized, and employed three PBDE congeners, 35, 47, and 99, and five fluoro-substituted PBDEs (F-PBDEs), 17-F5' 25-F5', 28-F3', 35-F5', 47-F3, and 99-F3', for this study. The PBDE congeners were selected because they are commonly found in house dust. For that reason, we coated spherical silica particles of 3 microm and C18 endcapped silica as representative and inert support materials, with 20, 30, and 40% PBDEs. We determined the particle size distributions by aerodynamic particle size spectrometry and the morphology by scanning electron microscopy. The suitability of the fluoro-tagged tracers to mimic their corresponding parent PBDEs was investigated by extraction studies from spiked blood serum. Our study is of fundamental importance to the development of xenobiotic tracers for monitoring routes of human exposure to PBDEs and understanding uptake of PBDEs from particles and vapors.

Toxicity assessment of air-delivered particle-bound polybrominated diphenyl ethers.

Human exposure to polybrominated diphenyl ethers (PBDEs) 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 and 99) and delivering them directly onto lung cells grown at an air-liquid interface (ALI). The silica particles and particles-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.