Synthesis, Properties, and Application of Tetrakis(pentafluoroethyl)gallate, [Ga(C2 F5 )4 ].

Weakly coordinating anions (WCAs) are important for academic reasons as well as for technical applications. Tetrakis(pentafluoroethyl)gallate, [Ga(C2 F5 )4 ]- , a new WCA, is accessible by treatment of [GaCl3 (dmap)] (dmap=4-dimethylaminopyridine) with LiC2 F5 . The anion [Ga(C2 F5 )4 ]- proved to be reluctant towards deterioration by aqueous hydrochloric acid or lithium hydroxide. Various salts of [Ga(C2 F5 )4 ]- were synthesized with cations such as [PPh4 ]+ , [CPh3 ]+ , [(O2 H5 )2 (OH2 )2 ]2+ , and [Li(dec)2 ]+ (dec=diethyl carbonate). Thermolysis of [(O2 H5 )2 (OH2 )2 ][Ga(C2 F5 )4 ]2 gives rise to a dihydrate of tris(pentafluoroethyl)gallane, [Ga(C2 F5 )3 (OH2 )2 ]. All products were characterized by NMR and IR spectroscopy, mass spectrometry, X-ray diffraction, and elemental analysis. Furthermore, an outlook for the application of [Li(dec)2 ][Ga(C2 F5 )4 ] as a conducting salt in lithium-ion batteries is presented.

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.

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.

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.

Fluoride complexation by bidentate silicon Lewis acids.

Diethynyldiphenylsilane (1) and divinyldiphenylsilane (2) were functionalized by hydrosilylation reactions with HSiMe2Cl, HSiMeCl2 and HSiCl3. Fluorination of the resulting compounds generates bidentate open-chain Lewis acids of increasing acidity. All semi-flexible [Ph2Si(CH[double bond, length as m-dash]CHSiFnMe3-n)2 (n = 1, 2, 3)] and flexible [Ph2Si(CH2-CH2SiFnMe3-n)2 (n = 1, 2, 3)] bidentate Lewis acids were obtained in good to excellent yields. The different fluoride ion complexation behavior was explored in detail by multinuclear (low temperature) NMR spectroscopy. The Lewis acidic bidentate molecules as well as the resulting mono- and bissilicates were completely characterized by NMR spectroscopy, mass spectrometry and in part by elemental analysis and X-ray diffraction experiments.