Transmission of Electronic Effects through the {<i>closo</i>-1-CB₉} and {<i>closo</i>-1-CB₁₁} Cages: Apparent Dissociation Constants for Series of [<i>closo</i>-1-CB₉H₈-1-COOH-10-X] and [<i>closo</i>-1-CB₁₁H₁₀-1-COOH-12-X] Acids

The apparent ionization constants p<i>K</i>_a′ for series of carboxylic acids [<i>closo</i>-1-CB₉H₈-1-COOH-10-X]⁻ (<b>1</b>) and [<i>closo</i>-1-CB₁₁H₁₀-1-COOH-12-X]⁻ (<b>2</b>), where X = H, I, <i>n</i>-C₆H₁₃, ⁺NMe₃, ⁺N₂, ⁺SMe₂, OC₅H₁₁, were measured in EtOH/H₂O (1/1, v/v) at 24 °C. Correlation analysis of the p<i>K</i>_a′ values using Hammett substituent constants σ_p(X) gave the reaction constant ρ = 0.87 ± 0.04 for series <b>1</b> and ρ = 1.00 ± 0.09 for series <b>2</b>. These values are higher than for derivatives of PhCHCHCOOH (ρ = 0.70 ± 0.09 in 55% EtOH) and correspond to 56% and 65% efficiencies in transmission of electronic effects by [<i>closo</i>-1-CB₉H₁₀]⁻ (<b>E</b>) and [<i>closo</i>-1-CB₁₁H₁₂]⁻ (<b>F</b>), respectively, as compared to benzene (<b>A</b>). Experimental results were supported with DFT calculations of relative acidity for series of acids derived from <b>A</b>, <b>E</b>, and <b>F</b> in aqueous medium

The preparation of 3-substituted-1,5-dibromopentanes as precursors to heteracyclohexanes

The methodology to prepare 3-substituted 1,5-dibromopentanes I and their immediate precursors, which include 3-substituted 1,5-pentanediols VII or 4-substituted tetrahydropyrans VIII, is surveyed. Such dibromides I are important intermediates in the preparation of liquid crystalline derivatives containing 6-membered heterocyclic rings. Four dibromides 1a–1d containing simple alkyl and more complex fragments at the 3-position were prepared. 3-Propyl- and 3-pentyl-pentane-1,5-diol (2a,b) were prepared starting from either glutaconate or malonate diesters, while tetrahydropyrans 3c and 3d were obtained from tetrahydro-4H-pyran-4-one. The advantages and disadvantages of each route are discussed. Dibromides 1c and 1d were used to prepare sulfonium zwitterions 11c and 11d

Synthesis and Characterization of 12-Pyridinium Derivatives of the [<i>closo</i>-1-CB₁₁H₁₂]⁻ Anion

Diazotization of [<i>closo</i>-1-CB₁₁H₁₀-1-R-12-NH₂]⁻[NMe₄]⁺ (<b>4­[NMe</b>_<b>4</b><b>]</b>) in neat 4-methoxypyridine leads to 12-(4-methoxypyridinium) zwitterions [<i>closo</i>-1-CB₁₁H₁₀-1-R-12-(4-MeOC₅H₄N)] (<b>2</b>) in ∼50% yield. Demethylation of <b>2</b> with LiCl in dimethylformamide provides access to 12-pyridones <b>5­[NMe</b>_<b>4</b><b>]</b>, which can be O-alkylated with alkyl triflates giving 12-(4-alkoxypyridinium) zwitterions, such as <b>1</b>. This three-step process is more efficient than direct diazotization of amine <b>4­[NMe</b>_<b>4</b><b>]</b> in neat higher 4-alkoxypyridine. The new method was demonstrated for the synthesis of [<i>closo</i>-1-CB₁₁H₁₀-1-C₅H₁₁-12-(4-C₇H₁₅OC₅H₄N)] (<b>1c</b>), which exhibits a smectic A phase. Molecular and electronic structures of 4-methoxypyridinium zwitterion <b>2b</b> and its C(1) isomer [<i>closo</i>-1-CB₁₁H₁₁-1-(4-MeOC₅H₄N)] (<b>3b</b>) were investigated by single-crystal X-ray diffraction and spectroscopic methods, respectively, and the experimental results were compared to those obtained with density functional theory methods. Lastly, the mechanism for formation of zwitterions <b>2</b> was investigated computationally revealing low energy for dediazoniation of the [<i>closo</i>-1-CB₁₁H₁₀-1-R-12-N₂] (<b>14</b>) intermediate (Δ<i>G</i>₂₉₈ ≈ 25 kcal/mol) to form boronium ylide <b>15</b>, with weak dependence on substituent R. Dinitrogen derivative <b>14c</b> was observed by ¹¹B NMR spectroscopy

Electrochemical Activity of Glucose Oxidase on a Poly(ionic liquid)–Au Nanoparticle Composite

Glucose oxidase (GOx) adsorbed on an ionic liquid-derived polymer containing internally organized columns of Au nanoparticles exhibits direct electron transfer and bioelectrocatalytic properties towards the oxidation of glucose. The cationic poly­(ionic liquid) provides an ideal substrate for the electrostatic immobilization of GOx. The encapsulated Au nanoparticles serve to both promote the direct electron transfer with the recessed enzyme redox centers and impart electronic conduction to the composite, allowing it to function as an electrode for electrochemical detection

Synthesis and Characterization of Quinuclidinium Derivatives of the [<i>closo</i>-1-CB₁₁H₁₂]⁻ Anion as Potential Polar Components of Liquid Crystal Materials

Antipodal substitution of the [<i>closo</i>-1-CB₁₁H₁₂]⁻ anion with a 4-pentylquinuclidinium fragment and alkyl groups in positions C(1) and B(12) gave polar zwitterions <b>1­[n]</b> and <b>2­[n]</b>. The molecular structure of <b>1­[5]</b> was established using X-ray diffraction (XRD) methods: <i>P</i>1̅, <i>a</i> = 15.162(2) Å, <i>b</i> = 16.546(3) Å, <i>c</i> = 19.794(3) Å; α = 84.871(2)°, β = 84.057(2)°, γ = 84.058(3)°; <i>Z</i> = 8. All compounds exhibit high temperature in-plane ordered smectic phases that are stabilized by dipolar interactions. The ordered phases were investigated by powder XRD methods. Thermal and dielectric parameters for two derivatives, <b>1­[0]</b> and <b>1­[6]</b>, were evaluated in nematic hosts, <b>ClEster</b> and <b>BPhF</b>. The dielectric data were analyzed with the Maier-Meier formalism augmented with density functional theory methods, and the results were compared to those for similar zwitterions previously reported