The closo-dodecahydrododecaborate [NEt3H]2[B12H12] has been prepared on a lab scale by an improved synthesis from cheap and readily available starting materials Na[BH4] and I2 in diglyme (diethylene glycol dimethyl ether). Subsequent chlorination with elemental chlorine in aqueous solution at normal pressure yielded the per-chlorinated weakly coordinating [B12Cl12]2- anion. By simple metathesis reaction a variety of useful salts [cation]2[B12Cl12] (cation=[NEt3H]+, [NBu4]+, Li+, Na+, K+, Cs+) is available. These salts are useful starting materials, which have the potential to open up the chemistry of [B12Cl12]2- as a weakly coordinating dianion. Exemplarily, they were used in further reactions to prepare [NO]2[B12Cl12], [PPN]2[B12Cl12], and [CPh3]2[B12Cl12]. The crystal structures of Cs2[B12Cl12].SO2, [CPh3]2[B12Cl12].2C2H4Cl2, and [CPh3]2[B12Cl12].2SO2 and preliminary crystal structures of [NO]2[B12Cl12].SO2 and [PPN]2[B12Cl12].CH2Cl2 were determined. The crystal structure of the SO2 solvate Cs2[B12Cl12].SO2 is related to the crystal structure of solvent free Cs2[B12Cl12]. [CPh3]2[B12Cl12].2C2H4Cl2 and [CPh3]2[B12Cl12].2SO2 have very similar structures in the solid state. In both cases the [CPh3]+ cations form only very weak contacts to the [B12Cl12]2- anion and SO2 or C2H4Cl2 solvent molecules respectively. The averaged experimental B-B (178.7 pm) and B-Cl (178.9 pm) bond lengths within [B12Cl12]2- are essentially unchanged in all determined structures and are reproduced well by PBE0/TZVPP quantum chemical calculations (B-B 178.6 pm, B-Cl 179.3 pm). All results indicate that [B12Cl12]2- is a readily accessible weakly-coordinating dianion.

The gas phase reactivity of perhalogenated closo-dodecaborate clusters [B(12)X(12)](2-) (X = F, Cl, Br, I) with N-tetraalkylated ammonium counter ions was investigated by electrospray ionization ion trap mass spectrometry (ESI-IT-MS). Collisions with the background gases introduced a broad variety of gas phase reactions. This study represents the first experimental approach to a new class of boron-rich boron clusters that are not accessible in the condensed phase. The anionic ion pair [B(12)X(12) + N(C(n)H(2n+1))(4)](-) is generally found as the ion of highest mass. Its reaction sequence starts with an alkyl transfer from the ammonium ion to the dodecaborate cluster. Subsequently, the alkylated intermediate [B(12)X(12) + C(n)H(2n+1)](-) decomposes to give very reactive ions of the general formula [B(12)X(11)](-). These ions possess a free boron vertex and immediately bind to the residual gases N(2) and H(2)O in the ion trap by formation of the corresponding adducts [B(12)X(11) + N(2)](-) and [B(12)X(11) + H(2)O](-). Subsequent fragmentations of the water adduct repetitively substitute halogen atoms by hydroxyl groups. The fragmentation process of the free anion [B(12)X(12)](2-) depends on the applied excitation energy and on the halogen substituent X. A radical dehalogenation of the B(12) unit is observed for X = I, whereas for X = Cl or F the loss of small molecules (mainly BX(3)) dominates. The different reaction behavior is explained by the different electron affinity of the halogens and the strength of the boron-halogen-bonds. Surprisingly, isolation of the fragment ion [B(12)I(9)](-) in the ion trap yields the highly stable [B(24)I(18)](2-) dianion. This observation suggests a reaction between two negative ions in the gas phase.

Compounds including the free or coordinated gas-phase cations [Ag(eta(2)-C(2)H(4))(n)](+) (n = 1-3) were stabilized with very weakly coordinating anions [A](-) (A = Al{OC(CH(3))(CF(3))(2)}(4), n = 1 (1); Al{OC(H)(CF(3))(2)}(4), n = 2 (3); Al{OC(CF(3))(3)}(4), n = 3 (5); {(F(3)C)(3)CO}(3)Al-F-Al{OC(CF(3))(3)}(3), n = 3 (6)). They were prepared by reaction of the respective silver(I) salts with stoichiometric amounts of ethene in CH(2)Cl(2) solution. As a reference we also prepared the isobutene complex [(Me(2)C=CH(2))Ag(Al{OC(CH(3))(CF(3))(2)}(4))] (2). The compounds were characterized by multinuclear solution-NMR, solid-state MAS-NMR, IR and Raman spectroscopy as well as by their single crystal X-ray structures. MAS-NMR spectroscopy shows that the [Ag(eta(2)-C(2)H(4))(3)](+) cation in its [Al{OC(CF(3))(3)}(4)](-) salt exhibits time-averaged D(3h)-symmetry and freely rotates around its principal z-axis in the solid state. All routine X-ray structures (2theta(max.) < 55 degrees) converged within the 3sigma limit at C=C double bond lengths that were shorter or similar to that of free ethene. In contrast, the respective Raman active C=C stretching modes indicated red-shifts of 38 to 45 cm(-1), suggesting a slight C=C bond elongation. This mismatch is owed to residual librational motion at 100 K, the temperature of the data collection, as well as the lack of high angular data owing to the anisotropic electron distribution in the ethene molecule. Therefore, a method for the extraction of the C=C distance in [M(C(2)H(4))] complexes from experimental Raman data was developed and meaningful C=C distances were obtained. These spectroscopic C=C distances compare well to newly collected X-ray data obtained at high resolution (2theta(max.) = 100 degrees) and low temperature (100 K). To complement the experimental data as well as to obtain further insight into bond formation, the complexes with up to three ligands were studied theoretically. The calculations were performed with DFT (BP86/TZVPP, PBE0/TZVPP), MP2/TZVPP and partly CCSD(T)/AUG-cc-pVTZ methods. In most cases several isomers were considered. Additionally, [M(C(2)H(4))(3)] (M = Cu(+), Ag(+), Au(+), Ni(0), Pd(0), Pt(0), Na(+)) were investigated with AIM theory to substantiate the preference for a planar conformation and to estimate the importance of sigma donation and pi back donation. Comparing the group 10 and 11 analogues, we find that the lack of pi back bonding in the group 11 cations is almost compensated by increased sigma donation.

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

Pushing the limits of coordination chemistry: The most weakly coordinated silver complexes of the very weakly coordinating solvents dichloromethane and liquid sulfur dioxide were prepared. Special techniques at low temperatures and the use of weakly coordinating anions allowed structural characterization of [Ag(OSO)][Al{OC(CF(3))(3)}(4)], [Ag(OSO)(2/2)][SbF(6)], and [Ag(Cl(2)CH(2))(2)][SbF(6)] (see figure). An investigation of the bonding shows that these complexes are mainly stabilized by electrostatic monopole-dipole interactions.The synthetically useful solvent-free silver(I) salt Ag[Al(pftb)(4)] (pftb=--OC(CF(3))(3)) was prepared by metathesis reaction of Li[Al(pftb)(4)] with Ag[SbF(6)] in liquid SO(2). The solvated complexes [Ag(OSO)][Al(pftb)(4)], [Ag(OSO)(2/2)][SbF(6)], and [Ag(CH(2)Cl(2))(2)][SbF(6)] were prepared and isolated by special techniques at low temperatures and structurally characterized by single-crystal X-ray diffraction. The SO(2) complexes provide the first examples of coordination of the very weak Lewis base SO(2) to silver(I). The SO(2) molecule in [Ag(OSO)][Al(pftb)(4)] is eta(1)-O coordinated to Ag(+), while the SO(2) ligands in [Ag(OSO)(2/2)][SbF(6)] bridge two Ag(+) ions in an eta(2)-O,O' (trans,trans) manner. [Ag(CH(2)Cl(2))(2)][SbF(6)] contains [Ag(CH(2)Cl(2))(2)](+) ions linked through [SbF(6)](-) ions to give a polymeric structure. The solid-state silver(I) ion affinities (SIA) of SO(2) and CH(2)Cl(2), based on bond lengths and corresponding valence units in the corresponding complexes and tensimetric titrations of Ag[Al(pftb)(4)] and Ag[SbF(6)] with SO(2) vapor, show that SO(2) is a weaker ligand to Ag(+) than the commonly used weakly coordinating solvent CH(2)Cl(2) and indicated that binding strength of SO(2) to silver(I) in the silver(I) salts increases with increasing size of the corresponding counteranion ([Al(pftb)(4)](-)>[SbF(6)](-)). The experimental findings are in good agreement with theoretical gas-phase ligand-binding energies of [Ag(L)(n)](+) (L=SO(2), CH(2)Cl(2); n=1, 2) and solid-state enthalpies obtained from Born-Fajans-Haber cycles by using the volume-based thermodynamics (VBT) approach. Bonding analysis (VB, NBO, MO) of [Ag(L)(n)](+) suggests that these complexes are almost completely stabilized by electrostatic interaction, that is, monopole-dipole interaction, with almost no covalent contribution by electron donation from the ligand orbitals into the vacant 5s orbital of Ag(+). All experimental findings and theoretical considerations demonstrate that SO(2) is less covalently bound to Ag(+) than CH(2)Cl(2) and support the thesis that SO(2) is a polar but non-coordinating solvent towards Ag(+).