The perhalogenated closo-dodecaborate dianions [B12 X12 ](2-) (X=H, F, Cl, Br, I) are three-dimensional counterparts to the two-dimensional aromatics C6 X6 (X=H, F, Cl, Br, I). Whereas oxidation of the parent compounds [B12 H12 ](2-) and benzene does not lead to isolable radicals, the perhalogenated analogues can be oxidized by chemical or electrochemical methods to give stable radicals. The chemical oxidation of the closo-dodecaborate dianions [B12 X12 ](2-) with the strong oxidizer AsF5 in liquid sulfur dioxide (lSO2 ) yielded the corresponding radical anions [B12 X12 ](⋅-) (X=F, Cl, Br). The presence of radical ions was proven by EPR and UV/Vis spectroscopy and supported by quantum chemical calculations. Use of an excess amount of the oxidizing agent allowed the synthesis of the neutral perhalogenated hypercloso-boranes B12 X12 (X=Cl, Br). These compounds were characterized by single-crystal X-ray diffraction of dark blue B12 Cl12 and [Na(SO2 )6 ][B12 Br12 ]⋅B12 Br12 . Sublimation of the crude reaction products that contained B12 X12 (X=Cl, Br) resulted in pure dark blue B12 Cl12 or decomposition to red B9 Br9 , respectively. The energetics of the oxidation processes in the gas phase were calculated by DFT methods at the PBE0/def2-TZVPP level of theory. They revealed the trend of increasing ionization potentials of the [B12 X12 ](2-) dianions by going from fluorine to bromine as halogen substituent. The oxidation of all [B12 X12 ](2-) dianions was also studied in the gas phase by mass spectrometry in an ion trap. The electrochemical oxidation of the closo-dodecaborate dianions [B12 X12 ](2-) (X=F, Cl, Br, I) by cyclic and Osteryoung square-wave voltammetry in liquid sulfur dioxide or acetonitrile showed very good agreement with quantum chemical calculations in the gas phase. For [B12 X12 ](2-) (X=F, Cl, Br) the first and second oxidation processes are detected. Whereas the first process is quasi-reversible (with oxidation potentials in the range between +1.68 and +2.29 V (lSO2 , versus ferrocene/ferrocenium (Fc(0/+) ))), the second process is irreversible (with oxidation potentials ranging from +2.63 to +2.71 V (lSO2 , versus Fc(0/+) )). [B12 I12 ](2-) showed a complex oxidation behavior in cyclic voltammetry experiments, presumably owing to decomposition of the cluster anion under release of iodide, which also explains the failure to isolate the respective radical by chemical oxidation.

Compounds containing boron atoms as spin carriers have recently received attention.[1] The icosahedral closo-dodecaborate ion [B 12 H 12 ] 2À is the archetypal boron cluster, and thus of special interest. Whereas the parent cluster [B 12 [3]Alkoxy-substituted ions [B 12 (OR) 12 ] 2À are oxidized at an even lower potential and even neutral B 12 (OR) 12 could be prepared.[4] Very recently, the perhydroxylated radical [B 12 (OH) 12 ]C À has been prepared and structurally characterized.[5] Smaller perhalogenated polyborane cluster radical anions [B n X n ]C À (X = H, Cl, Br, I; n = 6, 8-10), which are derived by one-electron oxidation from the corresponding closo clusters have been prepared and characterized by chemical and electrochemical methods. [6] Halogen substitution and an increasing cluster size significantly increase the resistance to oxidation and consequently the perhalogenated dodecaborates [B 12 X 12 ] 2À (X = halogen) are much more difficult to oxidize. Oxidation of dodecaborates [B 12 X 12 ] 2À (X = H, F, Cl, Br) to give the corresponding radical anions [B 12 X 12 ]C À has been investigated theoretically [7] and by electrochemical methods.[ [9] whilst in earlier electrochemical investigations, the derivatives containing heavier halogens (X = Cl, Br) did not have a well-defined oxidation wave in acetonitrile. [2a, 11] In a recent review, Kaim et al. stated that "Although the oxidation of [B 12 X 12 ] 2À

The reaction of [Ph(3)C](2)[B(12)Cl(12)] with R(3)SiH (R = Me, Et, iPr) in 1,2-difluorobenzene yielded the corresponding silylium compounds (R(3)Si)(2)B(12)Cl(12) containing the weakly coordinating dianion [B(12)Cl(12)](2-). The products were fully characterized by IR and Raman spectroscopy and by multinuclear ((1)H, (11)B, (13)C, (29)Si) NMR spectroscopy in solution and the solid state (magic angle spinning). (Et(3)Si)(2)B(12)Cl(12) and (iPr(3)Si)(2)B(12)Cl(12) were characterized by X-ray diffraction. In the solid state, the silylium cations are coordinated to the [B(12)Cl(12)](2-) anion via silicon-chlorine contacts, which are significantly shorter than the sum of the van der Waals radii. Two different coordination patterns were found. The [Et(3)Si](+) cations are coordinated to chlorine atoms of [B(12)Cl(12)](2-) in the 1 and 12 positions, while the [iPr(3)Si](+) cations coordinate to chlorine atoms in the 1 and 7 positions. The 1,12 regioisomer is calculated [for (Me(3)Si)(2)B(12)Cl(12)] to be favored over the 1,7 isomer by only 8 kJ mol(-1), indicating that packing effects may cause the difference. The silylium cations are very reactive and bind to every Lewis base, being stronger than the aromatic solvent (e.g., benzene, 1,2-difluorobenzene, etc.) used. Consequently, three different crystal structures containing cationic Lewis acid-base complexes [iPr(3)Si-donor](+) were obtained from preparations of (iPr(3)Si)(2)[B(12)Cl(12)]. The presence of traces of water leads to crystals of [iPr(3)Si(OH(2))](2)[B(12)Cl(12)] containing the protonated silanol [iPr(3)Si(OH(2))](+), which is only the second example of its kind. Structures containing the [iPr(3)SiOS(H)OSiiPr(3)](+) cation were obtained from the reaction of [Ph(3)C](2)[B(12)Cl(12)].2SO(2) with an excess of iPr(3)SiH in 1,2-difluorobenzene. [iPr(3)SiOS(H)OSiiPr(3)](2)[B(12)Cl(12)] and [iPr(3)SiOS(H)OSiiPr(3)][(iPr(3)Si)B(12)Cl(12)] were structurally characterized by X-ray diffraction. On the basis of the structural data and quantum chemical calculations, the crystallographically invisible hydrogen atom bound to the sulfur atom was identified. A comparison of the weakly coordinating dianion [B(12)Cl(12)](2-) with the widely applied corresponding chlorinated carboranes based on several criteria including the nu(N-H) scale established the dianion [B(12)Cl(12)](2-) to be as weakly coordinating as the single negatively charged carboranes.

The efficiency of methylating reagents strongly depends on the weakly coordinating properties of the anion. The introduction of carborane anions [CHB 11 R 5 X 6 ] À (R = Me, Cl; X = Cl, Br) and the synthesis of the methylating agents Me(CHB 11 Me 5 X 6 ) (X = Cl, Br) by Reed was a recent breakthrough.[1] The replacement of triflate anions by the more weakly coordinating carborane anions [CHB 11 R 5 X 6 ] À (R = Me, Cl; X = Cl, Br) significantly increased the methylating power.[2] Me(CHB 11 Me 5 X 6 ) (X = Cl, Br) methylates benzene and converts alkanes into the corresponding alkyl cations with concomitant formation of methane.[ [4c] These anions are thus of great interest as weakly coordinating dianions for methylating agents and stabilization of the resulting cations.We therefore attempted to methylate the perchlorinated dodecaborate cluster [B 12 Cl 12 ] 2À and explore its properties. In a well-known reaction, methyl fluoride was treated with the Lewis acid AsF 5 in liquid sulfur dioxide at temperatures below À30 8C to give [MeOSO][AsF 6 ] [Eq. (1)], which can be subsequently used to methylate very weak donor molecules. [5]

The alkali metal salts (M = Li, Na, K, Rb, Cs) of the perchlorinated closo-dodecaborate [B(12)Cl(12)](2-) were prepared by reaction of [NEt(3)H](2)[B(12)Cl(12)] with the corresponding alkali metal hydroxide. Crystallization of M(2)[B(12)Cl(12)] from liquid sulfur dioxide gave the sulfur dioxide complexes [Li(2)(SO(2))(8)][B(12)Cl(12)], Na(2)[B(12)Cl(12)].4SO(2), K(2)[B(12)Cl(12)].8SO(2), Rb(2)[B(12)Cl(12)].4SO(2), and Cs(2)[B(12)Cl(12)].SO(2), which were characterized by single crystal X-ray diffraction. In this work structurally characterized SO(2) complexes of the alkali metal cations K(+) and Rb(+) are reported for the first time. The structure of [Li(2)(SO(2))(8)][B(12)Cl(12)] contains discrete [Li(2)(SO(2))(8)](2+) dications and [B(12)Cl(12)](2-) dianions. Born-Haber cycles based on quantum chemical calculations and estimations of lattice enthalpies for the solid state explain the stability of the discrete dication [Li(2)(SO(2))(8)](2+) in the solid state. Heavier alkali metals form three-dimensional networks containing metal-anion and metal-sulfur dioxide contacts. The crystal structures of Na(2)[B(12)Br(12)].8SO(2) and Na(2)[B(12)I(12)].8SO(2) were determined to investigate the influence of the halogen substituent on the anion. They contain similar three-dimensional network structures. Na(2)[B(12)Br(12)].8SO(2) is isostructural to K(2)[B(12)Cl(12)].8SO(2). In addition the crystal structures of the complexes Na(2)[B(12)I(12)].8SO(2).H(2)O and Na(2)[B(12)H(12)].6SO(2).2H(2)O, which contain water ligands, are reported as well. A comparison of halogenated dodecaborates [B(12)X(12)](2-) (X = F, Cl, Br, I) based on [small nu, Greek, tilde](N-H) stretching frequencies of the corresponding [Oct(3)NH](2)[B(12)X(12)] (X = F - I) salts shows that the fluorinated anion [B(12)F(12)](2-) is the least basic and the iodinated anion [B(12)I(12)](2-) is the most basic anion in this series. These findings are in agreement with those for the corresponding series of perhalogenated carboranes and are explained by the polarizability of the halogen substituent.

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The acidity of protic cations and neutral molecules has been studied extensively in the gas phase, and the gas-phase acidity has been established previously as a very useful measure of the intrinsic acidity of neutral and cationic compounds. However, no data for any anionic acids were available prior to this study. The protic anions [H(B12X12)](-) (X = F, Cl, Br, I) are expected to be the most acidic anions known to date. Therefore, they were investigated in this study with respect to their ability to protonate neutral molecules in the gas phase by using a combination of mass spectrometry and quantum-chemical calculations. For the first time it was shown that in the gas phase protic anions are also able to protonate neutral molecules and thus act as Brønsted acids. According to theoretical calculations, [H(B12I12)](-) is the most acidic gas-phase anion, whereas in actual protonation experiments [H(B12Cl12)](-) is the most potent gas-phase acidic anion for the protonation of neutral molecules. This discrepancy is explained by ion pairing and kinetic effects.

A new synthesis of bis(triphenyl-λ(5)-phosphanylidene)ammonium fluoride ((Ph3PNPPh3)F, abbreviated as (PNP)F), is described. The title compound has been fully characterized by multinuclear NMR spectroscopy, vibrational spectroscopy, elemental analysis and single crystal and powder X-ray diffraction for the first time. In the solid state (PNP)F exists as a covalent molecular compound, in which the fluoride ion is asymmetrically bonded to the two phosphorus atoms of the [PNP](+) cation. The phosphorus-fluorine bond with 181.98(13) pm is surprisingly long and the longest P-F bond in any phosphorane. (PNP)F can be assumed to be a very good source of reactive fluoride. To investigate the fluoride ion donating properties, (PNP)F was reacted with a range of different fluoromethylsilanes Me(n)SiF(4-n) (n = 0-4). Reactions of (PNP)F with the fluoromethylsilanes were performed in aceto- or propionitrile and in 1,2-dimethoxyethane under inert conditions. The resulting hypervalent fluoromethylsilicates [Me(n)SiF(5-n)](-) (n = 0-3) were fully characterized by multinuclear NMR and vibrational spectroscopy and single crystal X-ray diffraction. From the reaction of (PNP)F with Me4Si in acetonitrile, the starting materials were recovered unchanged. To aid the understanding of the experimental results the fluoride ion affinities (FIA) for these silanes have been calculated by DFT calculations on the PBE0/def2-TZVPP level of theory. The fluoride ion affinity in the series of Me(n)SiF(4-n) (n = 0-4) decreases with the number of methyl groups and is too low for Me4Si to bind a fluoride ion under these reaction conditions.