Insertion of Carbenes into Deprotonated nido-Undecaborane, B11H13(2-)

Electrolyte Engineering with Carboranes for Next-Generation Mg Batteries

To realize an energy storage transition beyond Li-ion competitive technologies, earth-abundant elements, such as Mg, are needed. Carborane anions are particularly well-suited to realizing magnesium-ion batteries (MIBs), as their inert and weakly coordinating properties beget excellent electrolyte performance. However, utilizing these materials in actual electrochemical cells has been hampered by the reliance on the Mg2+ salts of the commercially available [HCB11H11]- anion, which is not soluble in more weakly binding solvents apart from the higher glymes. Herein, we demonstrate it is possible to iteratively engineer the [HCB11H11]- anion surface synthetically to address previous solubility issues and yield a highly conductive (up to 7.33 mS cm-1) and electrochemically stable (up to +4.2 V vs Mg2+/0) magnesium electrolyte that surpasses the state of the art. This novel non-nucleophilic electrolyte exhibits highly dissociative behavior regardless of concentration and is tolerant of prolonged periods of cycling in symmetric cells at high current densities (up to 2.0 mA cm-2, 400 h). The hydrocarbon functionalized carborane electrolyte presented here demonstrates >96% Coulombic efficiency when paired with a Mo6S8 cathode. This approach realizes a needed candidate to discover next-generation cathode materials that can enable the design of practical and commercially viable Mg batteries.

Divalent closo-monocarborane solvates for solid-state ionic conductors

Li-ion batteries have held the dominant position in battery research for the last 30+ years. However, due to inadequate resources and the cost of necessary elements (e.g., lithium ore) in addition to safety issues concerning the components and construction, it has become more important to look at alternative technologies. Multivalent metal batteries with solid-state electrolytes are a potential option for future battery applications. The synthesis and characterisation of divalent hydrated closo-monocarborane salts - Mg[CB₁₁H₁₂]₂·xH₂O, Ca[CB₁₁H₁₂]₂·xH₂O, and Zn[CB₁₁H₁₂]₂·xH₂O - have shown potential as solid-state electrolytes. The coordination of a solvent (e.g. H₂O) to the cation in these complexes shows a significant improvement in ionic conductivity, i.e. for Zn[CB₁₁H₁₂]₂·xH₂O dried at 100 °C (10^-3 S cm^-1 at 170 °C) and dried at 150 °C (10^-5 S cm^-1 at 170 °C). Solvent choice also proved important with the ionic conductivity of Mg[CB₁₁H₁₂]₂·3en (en = ethylenediamine) being higher than that of Mg[CB₁₁H₁₂]₂·3.1H₂O (2.6 × 10^-5 S cm^-1 and 1.7 × 10^-8 S cm^-1 at 100 °C, respectively), however, the oxidative stability was lower (<1 V (Mg²⁺/Mg) and 1.9 V (Mg²⁺/Mg), respectively). Thermal characterisation of the divalent closo-monocarborane salts showed melting and desolvation, prior to high temperature decomposition.

Na2B11H13 and Na11(B11H14)3(B11H13)4 as potential solid-state electrolytes for Na-ion batteries

Solid-state sodium batteries have attracted great attention owing to their improved safety, high energy density, large abundance and low cost of sodium compared to the current Li-ion batteries. Sodium-boranes have been studied as potential solid-state electrolytes and the search for new materials is necessary for future battery applications. Here, a facile and cost-effective solution-based synthesis of Na₂B₁₁H₁₃ and Na₁₁(B₁₁H₁₄)₃(B₁₁H₁₃)₄ is demonstrated. Na₂B₁₁H₁₃ presents an ionic conductivity in the order of 10^-7 S cm^-1 at 30 °C, but undergoes an order-disorder phase transition and reaches 10^-3 S cm^-1 at 100 °C, close to that of liquids and the solid-state electrolyte Na-β-Al₂O₃. The formation of a mixed-anion solid-solution, Na₁₁(B₁₁H₁₄)₃(B₁₁H₁₃)₄, partially stabilises the high temperature structural polymorph observed for Na₂B₁₁H₁₃ at room temperature and it exhibits Na⁺ conductivity higher than its constituents (4.7 × 10^-5 S cm^-1 at 30 °C). Na₂B₁₁H₁₃ and Na₁₁(B₁₁H₁₄)₃(B₁₁H₁₃)₄ exhibit an oxidative stability limit of 2.1 V vs. Na⁺/Na.

Zinc Ammonio-dodecaborates: Synthesis, Lewis Acid Strength, and Reactivity

Two series of zinc salts, [EtZn][A] and Zn[A]₂, with weakly coordinating anions [A]^- as counterions have been prepared, and their activities as catalysts for hydrosilylation reactions of 1-hexene, benzophenone, and acetophenone have been investigated. The counterions and per- and partially chlorinated 1-ammonio-closo-dodecaborate anions [Me₃NB₁₂Cl₁₁]^- [1]^-, [Pr₃NB₁₂H₅Cl₆]^- [2]^-, [Bu₃NB₁₂H₄Cl₇]^- [3]^-, and [Hex₃NB₁₂H₅Cl₆]^- [4]^- were chosen as potential and more readily available alternatives to carborate anions such as [CHB₁₁Cl₁₁]^- and [HexCB₁₁Cl₁₁]^-. The basicity of anion [4]^- was determined as being close to that of the triflimide anion [N(SO₂CF₃)₂]^-, and the fluoride ion affinities (FIAs) of compounds [EtZn][2] and Zn[2]₂ are lower than those of the Lewis acids B(C₆F₅)₃ and Zn[HexCB₁₁Cl₁₁]₂. The higher anion basicity and the resulting lower Lewis acidity of the zinc centers result in low activity in 1-hexene hydrosilylation catalysis and only moderate activity in the hydrosilylation catalysis of benzophenone and acetophenone.

Synthesis of closo-CB11H12- Salts Using Common Laboratory Reagents

Lithium and sodium salts of the closo-carbadodecaborate anion [CB₁₁H₁₂]^- have been shown to form stable solid-state electrolytes with excellent ionic conductivity for all-solid-state batteries (ASSB). However, potential commercial application is currently hindered by the difficult, low-yielding, and expensive synthetic pathways. We report a novel and cost-effective method to synthesize the [CB₁₁H₁₂]^- anion in a 40% yield from [B₁₁H₁₄]^-, which can be synthesized using common laboratory reagents. The method avoids the use of expensive and dangerous reagents such as NaH, decaborane, and CF₃SiMe₃ and shows excellent reproducibility in product yield and purity.

Polyhalogenated Bicyclo[1.1.1]pentane-1,3-dicarboxylic Acids

Herein we report the highly selective radical chlorination of 2,2-difluorobicyclo[1.1.1]pentane-1,3-dicarboxylic acid. Together with radical hydrodechlorination by TMS₃SiH, four new bicyclo[1.1.1]pentane cages carrying two fluorine and one to three chlorine atoms in bridge positions have been obtained. The exact positions of all halogen atoms have been confirmed by X-ray diffraction. The acidity constants (pK_a) for all new derivatives have been determined by capillary electrophoresis, and these experimental values show excellent agreement with pK_as predicted by DFT methods. Extensive DFT calculations have been used to rationalize the selective formation of four out of nine possible F₂Cl_1-4 isomers of bridge-halogenated bicyclo[1.1.1]pentanes and to obtain relative strain energies for all possible isomers.