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Bei Betrachtung der geometrischen und elektronischen Struktur des Tris(pentafluorethyl)silanids erscheint das Anion auf den ersten Blick als Lewis-Base. Quantenmechanischen Rechnungen zufolge liegen die HOMO- und LUMO-Energien von Perfluoralkylsilaniden deutlich niedriger als die nicht fluorierter Derivate. Dies hat eine geringere Lewis-Basizität und zugleich eine erhöhte Lewis-Acidität des [Si(C2F5)3]−-Ions zur Folge. Mit diesen Erkenntnissen und einer der N-heterocyclischen Silylenen (NHSis) ähnlichen HOMO-LUMO-Lücke von 4.80 eV sind Perfluoralkylsilanide dazu prädestiniert, Lewis-amphoteres Verhalten ähnlich dem der Silylene aufzuweisen. Die Deprotonierung von Si(C2F5)3H mit sterisch anspruchsvollen Phosphazenbasen liefert thermisch stabile Phosphazenium-Salze des [Si(C2F5)3]−-Anions, welche in unterschiedlicher Weise an Benzaldehyd, Benzophenon, CS2 und CO2 addieren. Dieses Verhalten spiegelt die Reaktivität von Silylenen gegenüber Ketonen sowie Heterocumulenen wider und wird durch die Lewis-Amphoterie des Silanids begründet.

Electron-withdrawing substituents R in complexes [L-n M(PR2)] influence the P-M bond length due to a decreased sigma-donation and enhanced pi-back-bonding, leading to an increased Lewis acidity of the metal ion and therefore strengthening the M-L bond to electron-rich ligands L. This influences the Lewis acidity and the redox behavior of corresponding transition-metal complexes, which is important for the design of optimized catalytic systems. To investigate this effect, the electron-poor phosphanes R2PH with R = C2F5, C6F5, 2,4-(CF3)(2)C6H3 were treated with Pd(F(6)acac)(2) (F(6)acac = hexafluoroacetylacetonato) and Pd(acac)(2) (acac = acetylacetonato). While the reaction of the phosphanes with Pd(F(6)acac)(2) in all cases yielded the corresponding phosphido-bridged dinuclear palladium complexes [{(F(6)acac)Pd[mu-(PR2)]}(2)], the compounds obtained in the reaction with Pd(acac)(2) were structurally more diverse. For R = C2F5, the dinuclear palladium complex [{(acac)Pd{mu-[P(C2F5)(2)]}}(2)] was obtained, while the reaction with (C6F5)(2)PH yielded a trinuclear palladium complex bridged by four phosphido units. All complexes were fully characterized, including X-ray crystallography.

In this contribution we report on the synthesis of bis(pentafluoroethyl)stannane, H2Sn(C2F5)(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(C2F5)(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(C2F5)(2)(dmap)(2)], treatment with PMe3 or [Sn(C2F5)(3)](-) furnished the corresponding neutral or anionic monoadducts, [Sn(C2F5)(2)(D)] (D=PMe3, [Sn(C2F5)(3)](-)). In contrast, the utilization of sterically demanding donors, such as iPr(2)O, as well as the thermal treatment of ether complexes, [Sn(C2F5)(2)(D)(n)] (D=Et2O, THF), leads to the formation of oligomeric and cyclic stannylene moieties [Sn(C2F5)(2)](n). The reactivity of H2Sn(C2F5)(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.

For (pentafluoroethyl) phenylstannanes, (C2F5)(4-n)SnPhn (n=1-3), and dimethylbis(pentafluoroethyl)stannane, (C2F5)(2)SnMe2, a high yield synthesis was developed by the use of LiC2F5 as a C2F5 transfer reagent. The treatment of these products with gaseous hydrogen chloride or hydrogen bromide afforded (C2F5)(4-n)SnXn (X=Cl, Br; n=1-3) in good yields. The (pentafluoroethyl) stannanes were fully characterized by H-1, C-13, F-19 and Sn-119 NMR, IR spectroscopy and mass spectrometry. The treatment of the (pentafluoroethyl)tin halides (C2F5)(4-n)SnXn with 1,10-phenanthroline (phen) led to the formation of the corresponding octahedrally coordinated complexes [(C2F5)(4-n)SnXn(phen)], the structures of which were elucidated by X-ray diffraction analyses. The bromostannane (C2F5)(3)SnBr reacted with sodium cyclopentadienide to give the (eta(1)-cyclopentadienyl) tris(pentafluoroethyl) stannane, (C2F5)(3)SnCp, for which single-crystal X-ray diffraction analysis could be performed. The coupling constants (1)J(Sn-119, C-13) and (2)J(Sn-119, F-19) 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.

This paper describes the synthesis of unsymmetrically substituted phosphinous acids and phosphane oxides featuring at least one electron-withdrawing pentafluoroethyl group. The presence of a diethylamino function as a protecting group allows a selective reaction of RClPNEt2 (R=CF3, C6F5, C6H5) with LiC2F5. On treatment with para-toluenesulfonic acid the isolated aminophosphanes R(C2F5)PNEt2 are readily converted into the corresponding phosphinous acids or phosphane oxides, respectively. Investigation of the tautomeric equilibrium between oxide and acid tautomer revealed (CF3)(C2F5)POH as a stable phosphinous acid, whereas the pentafluorophenyl and phenyl derivatives constitute a solvent dependent equilibrium between the acid and the oxide tautomer.

The bis(trifluoromethyl)phosphanide ion, P(CF(3))(2)(-), decomposes slowly above -30 degrees C in CH(2)Cl(2) and THF solution. An increase of the thermal stability of the P(CF(3))(2)(-) moiety is observed if excess CS(2) is added. The P(CF(3))(2)(-) moiety is stabilized because of the formation of the bis(trifluoromethyl)phosphanodithioformate anion. Solutions of a [P(CF(3))(2)CS(2)](-) salt still act as a source of P(CF(3))(2)(-), even in the presence of excess of CS(2). The stable compound [18-crown-6-K][P(CF(3))(2)CS(2)] was characterized by multinuclear NMR spectroscopy, elemental analysis, and vibrational spectroscopy in combination with quantum chemical calculations. The thermally unstable P(C(6)F(5))(2)(-) ion decomposes even at -78 degrees C in solution giving polymeric material. The intermediate formation of the bis(pentafluorophenyl)phosphanide anion in the presence of excess of CS(2) allows the isolation of [18-crown-6-K][P(C(6)F(5))(2)CS(2)]. The novel compound crystallizes with one solvent molecule CH(2)Cl(2) in the monoclinic space group P2(1)/n with a = 1151.8(1) pm, b = 1498.1(2) pm, c = 2018.2(2) pm, beta = 102.58(1) degrees, and Z = 4. Optimized geometric parameters of the [P(C(6)F(5))(2)CS(2)](-) ion at the B3PW91/6-311G(d) level of theory are in excellent agreement with the experimental values.

In the superacidic HF/SbF(5) system, methyl trifluoromethyl ether forms at -78 degrees C the new tertiary oxonium salt [(CH(3))(2)OCF(3)](+)[Sb(2)F(11)](-), which was characterized by Raman and multinuclear NMR spectroscopy and its crystal structure. The same oxonium salt was also obtained by methylation of CH(3)OCF(3) with CH(3)F and SbF(5) in HF solution at -30 to -10 degrees C. Replacement of one methyl group in the trimethyloxonium cation by the bulkier and more electronegative trifluoromethyl group increases the remaining O-CH(3) bond lengths by 0.037(1) A and the sum of the C-O-C bond angles by about 4.5 degrees. Methylation of CH(3)OCF(CF(3))(2) with CH(3)F in HF/SbF(5) solution at -30 degrees C produces [(CH(3))(2)OCF(CF(3))(2)](+)[Sb(2)F(11)](-). The observed structure and vibrational and NMR spectra were confirmed by theoretical studies at the B3LYP/6-311++G(2d,2p) and the MP2/6-311++G(2d,p) levels.