Anodic Oxidation of 18 Halogenated and/or Methylated Derivatives of CB₁₁H₁₂^–

Anodic oxidation of [CB₁₁H₁₂]⁻ and 18 of its halogenated and/or methylated derivatives was examined. Reversible oxidation was found for four of the anions in liquid SO₂ and for four more in 1,1,1,3,3,3-hexafluoroisopropyl alcohol. The oxidation occurred at ∼1 V (for [CB₁₁Me₁₂]⁻) up to more than 4 V (for [1-H-(2–6)-F₅-(7–12)-(CF₃)₆-CB₁₁]⁻) relative to ferrocene/ferricinium. The anodic peak potentials are reproduced by a set of additive position-sensitive substituent increments

Chlorinated Cubane-1,4-dicarboxylic Acids

Herein, we report radical chlorination of cubane-1,4-dicarboxylic acid leading preferentially to one monochlorinated cubane dicarboxylate (ca. 70%) that is accompanied by four dichlorinated derivatives (ca. 20% in total). The exact positions of the chlorine atoms have been confirmed by X-ray diffraction of the corresponding single crystals. The acidity constants of all dicarboxylic acids in water were determined by capillary electrophoresis (3.17 ± 0.04 and 4.09 ± 0.05 for monochlorinated and ca. 2.71 ± 0.05 and 3.75 ± 0.05 for dichlorinated cubanes). All chlorinated derivatives as well as the parent diacid showed high thermal stability (decomposition above 250 °C) as documented by differential scanning calorimetry. The probable reaction pathways leading to individual isomers were proposed, and the energies of individual transition states and intermediates were obtained using density functional theory calculations (B3LYP-D3BJ/6-311+G(d,p)). The relative strain energies for all newly prepared derivatives as well as for hypothetical hexahalogenated (fluorinated, chlorinated, brominated, and iodinated) derivatives of cubane-1,4-dicarboxylic acids were predicted using wavefunction theory methods. The hexafluorinated derivative was identified as the most strained compound (57.5 kcal/mol), and the relative strain decreased as the size of halogen atoms increased (23.7 for hexachloro, 16.7 for hexabromo, and 4.0 kcal/mol for the hexaiodo derivative)

Chlorinated Cubane-1,4-dicarboxylic Acids

Herein, we report radical chlorination of cubane-1,4-dicarboxylic acid leading preferentially to one monochlorinated cubane dicarboxylate (ca. 70%) that is accompanied by four dichlorinated derivatives (ca. 20% in total). The exact positions of the chlorine atoms have been confirmed by X-ray diffraction of the corresponding single crystals. The acidity constants of all dicarboxylic acids in water were determined by capillary electrophoresis (3.17 ± 0.04 and 4.09 ± 0.05 for monochlorinated and ca. 2.71 ± 0.05 and 3.75 ± 0.05 for dichlorinated cubanes). All chlorinated derivatives as well as the parent diacid showed high thermal stability (decomposition above 250 °C) as documented by differential scanning calorimetry. The probable reaction pathways leading to individual isomers were proposed, and the energies of individual transition states and intermediates were obtained using density functional theory calculations (B3LYP-D3BJ/6-311+G(d,p)). The relative strain energies for all newly prepared derivatives as well as for hypothetical hexahalogenated (fluorinated, chlorinated, brominated, and iodinated) derivatives of cubane-1,4-dicarboxylic acids were predicted using wavefunction theory methods. The hexafluorinated derivative was identified as the most strained compound (57.5 kcal/mol), and the relative strain decreased as the size of halogen atoms increased (23.7 for hexachloro, 16.7 for hexabromo, and 4.0 kcal/mol for the hexaiodo derivative)

Chlorinated Cubane-1,4-dicarboxylic Acids

Herein, we report radical chlorination of cubane-1,4-dicarboxylic acid leading preferentially to one monochlorinated cubane dicarboxylate (ca. 70%) that is accompanied by four dichlorinated derivatives (ca. 20% in total). The exact positions of the chlorine atoms have been confirmed by X-ray diffraction of the corresponding single crystals. The acidity constants of all dicarboxylic acids in water were determined by capillary electrophoresis (3.17 ± 0.04 and 4.09 ± 0.05 for monochlorinated and ca. 2.71 ± 0.05 and 3.75 ± 0.05 for dichlorinated cubanes). All chlorinated derivatives as well as the parent diacid showed high thermal stability (decomposition above 250 °C) as documented by differential scanning calorimetry. The probable reaction pathways leading to individual isomers were proposed, and the energies of individual transition states and intermediates were obtained using density functional theory calculations (B3LYP-D3BJ/6-311+G(d,p)). The relative strain energies for all newly prepared derivatives as well as for hypothetical hexahalogenated (fluorinated, chlorinated, brominated, and iodinated) derivatives of cubane-1,4-dicarboxylic acids were predicted using wavefunction theory methods. The hexafluorinated derivative was identified as the most strained compound (57.5 kcal/mol), and the relative strain decreased as the size of halogen atoms increased (23.7 for hexachloro, 16.7 for hexabromo, and 4.0 kcal/mol for the hexaiodo derivative)

Chlorinated Cubane-1,4-dicarboxylic Acids

Herein, we report radical chlorination of cubane-1,4-dicarboxylic acid leading preferentially to one monochlorinated cubane dicarboxylate (ca. 70%) that is accompanied by four dichlorinated derivatives (ca. 20% in total). The exact positions of the chlorine atoms have been confirmed by X-ray diffraction of the corresponding single crystals. The acidity constants of all dicarboxylic acids in water were determined by capillary electrophoresis (3.17 ± 0.04 and 4.09 ± 0.05 for monochlorinated and ca. 2.71 ± 0.05 and 3.75 ± 0.05 for dichlorinated cubanes). All chlorinated derivatives as well as the parent diacid showed high thermal stability (decomposition above 250 °C) as documented by differential scanning calorimetry. The probable reaction pathways leading to individual isomers were proposed, and the energies of individual transition states and intermediates were obtained using density functional theory calculations (B3LYP-D3BJ/6-311+G(d,p)). The relative strain energies for all newly prepared derivatives as well as for hypothetical hexahalogenated (fluorinated, chlorinated, brominated, and iodinated) derivatives of cubane-1,4-dicarboxylic acids were predicted using wavefunction theory methods. The hexafluorinated derivative was identified as the most strained compound (57.5 kcal/mol), and the relative strain decreased as the size of halogen atoms increased (23.7 for hexachloro, 16.7 for hexabromo, and 4.0 kcal/mol for the hexaiodo derivative)

Molecular Rods Combining <i>o</i>‑Carborane and Bicyclo[1.1.1]pentane Cages: An Insertion of the Triple Bond Located Next to a Highly Strained Cage

Octacarbonyl dicobalt and bis­(dimethyl sulfide)­decaborane B₁₀H₁₂(Me₂S)₂ were successfully added to 1,3-diethynylbicyclo[1.1.1]­pentane in good yields. This is an interesting example of a cycloaddition reaction achieved next to the bicyclopentane cage that tends to rearrange in many other cases. It proves that both reagents attack the triple bond in a more or less concerted manner that prevents the rearrangement. Products of the latter reaction are of a particular interest because the bicyclopentane and <i>o</i>-carborane cages are immediately linked in their rodlike structures. The new kind of molecular rotors was thus constructed. ¹H and ¹³C nuclear magnetic resonance spectra in solution reveal an averaged rotational symmetry of the molecules with a well-defined geometry that has been confirmed by X-ray structural analysis in several examples

Chlorinated Cubane-1,4-dicarboxylic Acids

Herein, we report radical chlorination of cubane-1,4-dicarboxylic acid leading preferentially to one monochlorinated cubane dicarboxylate (ca. 70%) that is accompanied by four dichlorinated derivatives (ca. 20% in total). The exact positions of the chlorine atoms have been confirmed by X-ray diffraction of the corresponding single crystals. The acidity constants of all dicarboxylic acids in water were determined by capillary electrophoresis (3.17 ± 0.04 and 4.09 ± 0.05 for monochlorinated and ca. 2.71 ± 0.05 and 3.75 ± 0.05 for dichlorinated cubanes). All chlorinated derivatives as well as the parent diacid showed high thermal stability (decomposition above 250 °C) as documented by differential scanning calorimetry. The probable reaction pathways leading to individual isomers were proposed, and the energies of individual transition states and intermediates were obtained using density functional theory calculations (B3LYP-D3BJ/6-311+G(d,p)). The relative strain energies for all newly prepared derivatives as well as for hypothetical hexahalogenated (fluorinated, chlorinated, brominated, and iodinated) derivatives of cubane-1,4-dicarboxylic acids were predicted using wavefunction theory methods. The hexafluorinated derivative was identified as the most strained compound (57.5 kcal/mol), and the relative strain decreased as the size of halogen atoms increased (23.7 for hexachloro, 16.7 for hexabromo, and 4.0 kcal/mol for the hexaiodo derivative)

Molecular Rods Combining <i>o</i>‑Carborane and Bicyclo[1.1.1]pentane Cages: An Insertion of the Triple Bond Located Next to a Highly Strained Cage

Octacarbonyl dicobalt and bis­(dimethyl sulfide)­decaborane B₁₀H₁₂(Me₂S)₂ were successfully added to 1,3-diethynylbicyclo[1.1.1]­pentane in good yields. This is an interesting example of a cycloaddition reaction achieved next to the bicyclopentane cage that tends to rearrange in many other cases. It proves that both reagents attack the triple bond in a more or less concerted manner that prevents the rearrangement. Products of the latter reaction are of a particular interest because the bicyclopentane and <i>o</i>-carborane cages are immediately linked in their rodlike structures. The new kind of molecular rotors was thus constructed. ¹H and ¹³C nuclear magnetic resonance spectra in solution reveal an averaged rotational symmetry of the molecules with a well-defined geometry that has been confirmed by X-ray structural analysis in several examples

Electrochemical Oxidation of [1-X-12-I-CB₁₁Me₁₀^–] Anions: Formation of Borenium Ylides [12-Dehydro-1-X-CB₁₁Me₁₀] and Iodonium Ylide Anions [{12-(1-X-CB₁₁Me₁₀^–)}₂I⁺]

Cyclic voltammograms of 12-iodinated icosahedral carborane anions [1-X-12-I-CB₁₁Me₁₀^–] (X = H, CH₃, C₂H₅, C₃H₇, C₄H₉, C₆H₁₃, and COOCH₃) show two one-electron anodic oxidation peaks at the Pt electrode in liquid SO₂. Oddly, the first is irreversible and the second partially reversible. Mass spectrometry of the principal anionic product of preparative anodic oxidation of [1-H-12-I-CB₁₁Me₁₁^–], identical with the anionic product of its reaction with [Et₃Si–H–SiEt₃]⁺ and/or Et₃Si⁺, allows it to be identified as the iodonium ylide anion [{12-(1-H-CB₁₁Me₁₀^–)}₂I⁺]. Its reversible oxidation to a neutral ylide radical [{12-(1-H-CB₁₁Me₁₀^•)}­{12-(1-H-CB₁₁Me₁₀^–)}­I⁺] is responsible for the second peak. A DFT geometry optimization suggests that both the ylide anion and the ylide radical are very crowded and have an unusually large C–I–C valence angle of ∼132°; they are the first compounds with two bulky highly methylated CB₁₁ cages attached to the same atom. Molecular iodine is another product of the electrolysis. We propose an electrode mechanism in which initial one-electron oxidation of [1-X-12-I-CB₁₁Me₁₀^–] is followed by a transfer of an iodine atom from the B–I bond to SO₂ to yield a weakly bound radical ISO₂^• which disproportionates into SO₂ and I₂. The other product is the borenium ylide [12-dehydro-1-X-CB₁₁Me₁₀], which has a strongly Lewis acidic naked vertex in position 12 that rapidly adds to another [1-X-12-I-CB₁₁Me₁₀^–] anion to form the observed stable ylide anion [{12-(1-X-CB₁₁Me₁₀^–)}₂I⁺]. In acetonitrile, where it presumably exists as a solvent adduct, [12-dehydro-1-X-CB₁₁Me₁₀] has been trapped with H₂O and, to a small extent, with MeOH, but not with several other potential trapping agents