Carborane Salts Research Articles

IR-Spectroscopic and X-ray-Structural Study of Vinyl-Type Carbocations in Their Carborane Salts.

The butylene carbocation in its salts with anions CHB11F11– and CHB11Cl11– forms isomers CH2=C+–CH2–CH3 (I) and CH3–C+=CH–CH3 (II), which were characterized here by infrared (IR) spectroscopy and X-ray diffraction analysis. The strongest influence on the structure of the cations is exerted by geometric ordering of their anionic environment. In the crystalline phase, the cations uniformly interact with neighboring anions, and the C=C bond is located in the middle part of the cations forming a −CH=C+– moiety with the highest positive charge on it and the lowest νC=C frequency, at 1490 cm–1. In the amorphous phase with a disordered anionic environment of the cations, contact ion pairs Anion–···CH2=C+–CH2–CH3 form predominantly, with terminal localization of the C=C bond through which the contact occurs. The positive charge is slightly extinguished by the anion, and the C=C stretch frequency is higher by ∼100 cm–1. The replacement of the hydrogen atom in cations I/II by a Cl atom giving rise to cations CH2=C+–CHCl–CH3 and CH3–C+=CCl–CH3 means that the donation of electron density from the Cl atom quenches the positive charge on the C+=C bond more strongly, and the C=C stretch frequency increases so much that it even exceeds that of neutral alkene analogues by 35–65 cm–1. An explanation is given for the finding that upon stabilization of the vinyl cations by polyatomic substituents such as silylium (SiMe3) and t-Bu groups, the stretching C=C frequency approaches the triple-bond frequency. Namely, the scattering of a positive charge on these substituents enhances their donor properties so much that the electron density on the C=C bond with a weakened charge becomes much higher than that of neutral alkenes.

Unsaturated Vinyl-Type Carbocation [(CH3)2C=CH]+ in Its Carborane Salts.

The isobutylene carbocation (CH3)2C=CH+ was obtained in amorphous and crystalline salts with the carborane anion CHB11Cl11–. The cation was characterized by X-ray crystallography and IR spectroscopy. Its crystal structure shows a relatively uniform ionic interaction of the cation with the surrounding anions, with a slightly shortened distance between the C atom of the =CH group and the Cl atom of the anion, pointing to a higher positive charge on this group. In the amorphous phase, the asymmetric interaction of the cation with the anion increases, approaching ion pairing. This gives rise to a strong hyperconjugation between the two CH3 groups and the 2pz orbital of the central carbon sp2 atom (the red shift of the CH stretch is 150 cm–1); this effect stabilizes the cation. Over time, as the structure of the amorphous phase becomes more ordered, the hyperconjugation weakens and disappears in the crystalline phase with the disappearance of ion pairing. The carbocation stabilization in the crystalline phase is achieved due to the transfer of a portion of the charge to the neighboring anions, whereas the charge on the C=C bond becomes the strongest: the C=C stretch frequency drops to ∼160 cm–1 relative to neutral isobutylene. The collected IR spectra for the optimized cation under vacuum (in the 6-311G ++ (d, p) basis for all HF, MP2, and DFT calculations) predict that a positive charge on the C=C bond increases its stretching frequency; this computational result contradicts the experimental data, perhaps because it does not take into account the significant impact of the environment.

Stability of Calcium Ion Battery Electrolytes: Predictions from Ab Initio Molecular Dynamics Simulations.

Multivalent batteries, such as magnesium-ion, calcium-ion, and zinc-ion batteries, have attracted significant attention as next-generation electrochemical energy storage devices to complement conventional lithium-ion batteries (LIBs). Among them, calcium-ion batteries (CIBs) are the least explored due to difficult reversible Ca deposition-dissolution. In this work, we examined the stability of four different Ca salts with weakly coordinating anions and three different solvents commonly employed in existing battery technologies to identify suitable candidates for CIBs. By employing Born-Oppenheimer molecular dynamics (BOMD) simulations on salt-Ca and solvent-Ca interfaces, we find that the tetraglyme solvent and carborane salt are promising candidates for CIBs. Due to the strong reducing nature of the calcium surface, the other salts and solvents readily decompose. We explain the microscopic mechanisms of salt/solvent decomposition on the Ca surface using time-dependent projected density of states, time-dependent charge-transfer plots, and climbing-image nudged elastic band calculations. Collectively, this work presents the first mechanistic assessment of the dynamical stability of candidate salts and solvents on a Ca surface using BOMD simulations, and provides a predictive path toward designing stable electrolytes for CIBs.

Highly Efficient Carborane-Based Activators for Molecular Olefin Polymerization Catalysts

Several ammonium carborane salts ([HNR3][HCB11X11], X = H, Me, Cl) were prepared and evaluated as activators with bis-metallocene and constrained geometry precatalysts at 140 and 190 °C. Activators...

Novel bis[(1,2,3-triazolyl)methyl]carborane derivatives via regiospecific copper-catalyzed 1,3-dipolar cycloaddition

1,2-Bis(azidomethyl)-о-carborane and 1,7-bis(azidomethyl)-m-carborane, prepared from the corresponding carboranylmethyl triflates and sodium azide, were conveniently functionalized by azide–alkyne cycloaddition affording novel bis[(1,2,3-triazolyl)methyl]carborane derivatives. Regiospecificity of this process was achieved by employing copper(II) acetate hydrate. Reaction of bis[(1,2,3-triazolyl)methyl]carborane derivatives with MeI yielded 3-methyl-1,2,3-triazolium carborane salts.

Pairing Heterocyclic Cations with closo-Icosahedral Borane and Carborane Anions, II: Benchtop Alternative Synthetic Methodologies for Binary Triazolium and Tetrazolium Salts with Significant Water Solubility

Two efficient processes for the synthesis of 12 relatively water-soluble binary triazolium and the first tetrazolium borane [B12H12] and carborane [CB11H12] salts by a one-step, open-air metathesis reaction have been developed. First, a combination of exhaustive trituration of the two solid reactant salts with refluxing anhydrous acetonitrile followed by flash filtration through a plug of silica gel afforded excellent recovery for a broad series of otherwise water-soluble heterocyclium salts. Second, an alternative aqueous metathesis, driven to completion by precipitation of silver halides, followed by removal of water, redissolution in acetonitrile, and filtration through a silica-gel plug, also yielded such heterocyclium borane and carborane salts. Mixed 1:1 dication heterocyclium borane salts were first synthesized using this second procedure, and one example showed melting-point depression behavior.

Oligomeric Carbocation-like Species from Protonation of Chloroalkanes

The protonation of chloroethane by the strongest known solid superacid, the carborane acid H(CHB(11)Cl(11)), has been studied by quantitative IR spectroscopic methods to track mass balance and uncover previously unobserved chemistry. In the first step, an intermediate EtCl·H(CHB(11)Cl(11)) species without full proton transfer to EtCl can be observed when d(5)-deuterated chloroethane is used. It rapidly eliminates HCl (but not DCl) to form ethyl carborane, Et(CHB(11)Cl(11)), which binds a second molecule of chloroethane to form the Et(2)Cl(+) chloronium ion. This undergoes a slower, previously unrecognized HCl elimination reaction to form a butyl carborane, Bu(CHB(11)Cl(11)), beginning an oligomerization process whereby unsymmetrical dialkylchloronium ions decompose to alkyl carboranes of formula Bu(C(2)H(4))(n)(CHB(11)Cl(11)) up to n = 4. Over time, a parallel competing process of de-oligomerization take place in the presence of free carborane acid that finishes with the formation of hexyl or butyl carboranes. Upon heating to 150 C, the final products are all converted to the remarkably stable tert-butyl cation carborane salt.

Designing ionic liquids with boron cluster anions: alkylpyridinium and imidazolium [nido-C2B9H11] and [closo-CB11H12] carborane salts

A range of new alkylpyridinium and imidazolium carborane salts with [nido-C(2)B(9)H(12)](-), [closo-CB(11)H(12)](-), and [RC(2)B(11)H(11)](-) (R = methyl or butyl) anions have been prepared and characterized by physical and thermal methods, including the solid state structures of five of the salts determined by single crystal X-ray diffraction. The tendency of the salts to form low-melting ionic liquids has been assessed; all the salts studied with [nido-C(2)B(9)H(12)](-) anions melted below 100 degrees C and, significantly, have melting points that are 25-85 degrees C lower than those of the corresponding [closo-CB(11)H(12)](-) analogs, demonstrating that a wider range of boron-rich ionic liquid materials can be readily accessed.

Can the hexamethylhydrazinium dication [Me3N–NMe3]2+ be prepared?

The long sought hexamethylhydrazinium(2+) dication, Me(3)N-NMe(3)(2+), calculationally unstable towards "coulombic explosion" because of formal positive charges on adjacent N atoms, can be synthesized and isolated as a CHB(11)Cl(11)(-) carborane salt.

Do Sitting-Atop Metalloporphyrin Complexes Exist? Observation of N−H- - -π Bonding in Arene Solvates of a Diprotonated Porphyrin Dication

The existence of sitting-atop metalloporphyrin complexes, the proposed intermediates in the metalation of free-base porphyrins, has been explored via the microscopic reverse reaction, i.e., protonation of metalloporphyrins with a strong acid. The reaction of M(Tp-TP) (M = Zn, Cu, Ni; Tp-TP = dianion of tetra-p-tolylporphyrin) with mesitylenium carborane salts produced only the demetalated porphyrin in its diprotonated form, [H4Tp-TP][carborane]2 (carborane = CHB11H5Cl6-, CHB11H5Br6-, CHB11Cl11-). In arene solvents, the H4Tp-TP2+ dication shows an unusually upfield shifted 1H NMR resonance at ca. -6 ppm, which X-ray crystallography reveals to arise from N-H- - -pi hydrogen bonding of the acidic protons to arene solvent molecules.

Synthesis, structure and properties of the Cp 2Zr{CH(SiMe 3) 2} + cation

The generation and properties of the Cp 2Zr{CH(SiMe 3) 2} + cation are described. An X-ray crystallographic analysis shows that the carborane salt [Cp 2Zr{CH(SiMe 3) 2}][HCB 11Me 5Br 6] contains an agostic Zr–μ-Me–Si interaction in the solid state. Low temperature NMR spectra of the borate salt [Cp 2Zr{CH(SiMe 3) 2}][B(C 6F 5) 4] show that this interaction is retained in solution. Variable temperature NMR spectra establish that the SiMe 2(μ-Me) and unbound SiMe 3 units of Cp 2Zr{CH(SiMe 3) 2} + exchange by a “pivot” process involving partial rotation around the Zr–CH(SiMe 3) 2 bond, with a barrier of Δ G ‡ = 9.2(1) kcal/mol at −89 °C. Cp 2Zr{CH(SiMe 3) 2} + does not coordinate alkenes or alkynes.

Carborane Acids. New “Strong Yet Gentle” Acids for Organic and Inorganic Chemistry

AbstractFor Abstract see ChemInform Abstract in Full Text.

Carborane acids. New “strong yet gentle” acids for organic and inorganic chemistry

Icosahedral carborane anions such as CHB11Cl11- are amongst the least coordinating, most chemically inert anions known. They are also amongst the least basic, so their conjugate acids, H(carborane), are superacids (i.e. stronger than 100% H2SO4). Acidity scale measurements indicate that H(CHB11Cl11) is the strongest pure Brønsted acid presently known, surpassing triflic and fluorosulfuric acid. Nevertheless, it is also an extremely gentle acid--because its conjugate base engages in so little chemistry. Carborane acids separate protic acidity from anion nucleophilicity and destructive oxidative capacity in the conjugate base, to a degree not previously achieved. As a result, many long-sought, highly acidic, reactive cations such as protonated benzene (C6H7+), protonated C60(HC60+), tertiary carbocations (R3C+), vinyl cations (R2C=C(+)-R), silylium ions (R3Si+) and discrete hydronium ions (H3O+, H5O2+ etc.) can be readily isolated as carborane salts and characterized at room temperature by X-ray crystallography.

Zirconium-Mediated Oxidative Coupling of Carbons-Adjacent nido-Carborane Dianions of the C2B10 System. Synthesis and Structural Characterization of Full-Sandwich High- and Sub-Valent Zirconacarboranes

A full-sandwich high-valent zirconacarborane containing the unusual B-B-linked bis(carboranyl) ligand [o-C6H4(CH2)(2)C2B10H9](2)(4-) was unprecedentedly isolated from the reaction of ZrCl4(THF)(2) with the carbons-adjacent carborane salt [{mu-1,2-[o-C6H4(CH2)(2)]-1,2-C2B10H10}(2)Na-4(THF)(6)](n). This reaction also generated a divalent zirconacarborane.

Coordination polymers with carborane anions: silver dinitrile complexes.

Crystalline materials have been isolated and characterized from mixing the silver carborane salts Ag(CB(11)H(12)) or Ag[Co(C(2)B(9)H(11))(2)] with nitrile ligands, either terminal acetonitrile or potentially bridging alkanedinitriles. Most of the complexes showed B-H...Ag interactions between the silver center and carborane anion. [Ag(acetonitrile)(2)(CB(11)H(12))] has a hexagonal network structure. [Ag(malonitrile)(2)(CB(11)H(12))] is a discrete dimeric complex, while [Ag(4)(succinonitrile)(5)(CB(11)H(12))(4)], [Ag(glutaronitrile)(2)][Co(C(2)B(9)H(12))(2)], and [Ag(glutaronitrile)[Co(C(2)B(9)H(11))(2)]] all show coordination chain structures. The carborane anions in [Ag(adiponitrile)[Co(C(2)B(9)H(11))(2)]] bridge between Ag centers to give a 3D CdSO(4)-related coordination polymer. The structure of [Ag(malonitrile)(2)](BF(4)) was also determined to have an unusual chiral diamondoid structure with a skewed 2-fold interpenetration.

Synthesis of the C59N+ Carbocation. A Monomeric Azafullerene Isoelectronic to C60.

A heterofullerene isoelectronic to C60 is reported. The azafullerenium cation C59N+ can be isolated in good yield as a carborane salt via the two-electron oxidation of the C−C bond of (C59N)2 dimer. [C59N][Ag(CB11H6Cl6)2] has been characterized by electronic, IR, Raman, and 13C NMR spectroscopies, MALDI spectrometry, DFT calculations, and X-ray crystallography.

Synthesis of the C59N+ carbocation. A monomeric azafullerene isoelectronic to C60.

A heterofullerene isoelectronic to C60 is reported. The azafullerenium cation C59N+ can be isolated in good yield as a carborane salt via the two-electron oxidation of the C-C bond of (C59N)2 dimer. [C59N][Ag(CB11H6Cl6)2] has been characterized by electronic, IR, Raman, and 13C NMR spectroscopies, MALDI spectrometry, DFT calculations, and X-ray crystallography.

Synthesis and characterization of water-soluble boron-substituted ortho-carborane derivatives

Abstract The synthesis of water-soluble, boron-substituted carborane derivatives was achieved by treatment of boron-substituted bromoalkyl carborane derivatives with trimethylphosphine to yield the corresponding phosphonium salts. These new carborane salts exhibit solubility in both aqueous and polar organic media. Herein we report the synthesis and characterization of the first water-soluble, boron-substituted carborane species, closo-9,12-(CH2CH2CH2P(CH3)3+Br–)2-1,2-C2B10H10, 4, and closo-3-[CH2CH2CH2P(CH3)3+Br–]-1,2-C2B10H11, 5. The crystal structure of 5 is reported. Additionally, another method of preparing mono- and difunctionalized water-soluble phosphonium salts of B3-substituted carborane derivatives was developed. This method produces both the monophosphonium salt, closo-3-[CH2CH(CH2I)CH2P(CH3)3+I–]-1,2-C2B10H11, 8, and the diphosphonium salt, closo-3-[CH2CH(CH2P(CH3)3+I–)2]-1,2-C2B10H11, 9. © 2000 Academie des sciences / Editions scientifiques et medicales Elsevier SAS synthesis / boron-substituted ortho-carboranes / phosphonium salts / water-soluble derivatives / X-ray crystallography

Observations on silver salt metathesis reactions with very weakly coordinating anions

Silver salt metathesis reactions using the very weakly nucleophilic anion B 11 CH 12 − reveal several unexpected features of this otherwise familiar reaction. In contrast to AgClO 4 , which undergoes rapid metathesis with IrCl(CO)(PPh 3 ) 2 , the silver carborane salt Ag(B 11 CH 12 ) forms a very stable adduct. This work shows that the role of the counterion to silver is much more important to the mechanism and outcome of silver halide abstraction reactions