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.