The synthesis, structural characterization, and acid-base chemistry of [C(SiMe2OCH2CH2OMe)3]Na (2), a sterically encumbered zwitterionic organosodium compound, is reported. 2 is a strong Brønsted base that forms frustrated Lewis pairs (FLPs) with a number of boron-containing Lewis acids ranging from weakly Lewis acidic aryl and alkyl boranes to various alkyl borates. These intermolecular FLPs readily cleave H2, which confirms that even poor Lewis acids can engage in FLP-mediated H2 cleavage provided that the present bulky base is of sufficiently high Brønsted basicity.

Flash vacuum pyrolysis studies of substituted 6-acetoxy-2,4-cyclohexadienones (3 and 10) from 300 to 500 °C provide strong experimental evidence that direct [3,5]-sigmatropic rearrangements in these molecules are favored over the more familiar [3,3]-sigmatropic rearrangements. The preference holds when the results are extrapolated to 0.0% conversion, indicating that this is a concerted process. Pyrolysis of 6,6-diacetoxy-2-methyl-2,4-cyclohexadienone (9) at 350 °C gives a modest yield of the initial [3,5]-sigmatropic rearrangement product, 2,6-diacetoxy-6-methyl-2,4-cyclohexadienone (11). Qualitative arguments and electronic structure theory calculations are in agreement that the lowest energy pathway for each [3,5]-sigmatropic rearrangement is via an allowed, concerted pseudopericyclic transition state. The crystal structures of compounds 3, 9, and 10 prefigure these transition states. The selectivity for the [3,5] products increases with an increasing temperature. This unexpected selectivity is explained by a concerted, intramolecular, and pseudopericyclic transition state (TS-5) that forms a tetrahedral interemediate (ortho-acid ester 4'), followed by similar ring openings to isomeric phenols, which shifts the equilibrium toward the phenols from the [3,5] (but not the [3,3]) products.

The ability to direct the morphology of cobalt sol-gel materials by using the simple synthetic parameters in epoxide-driven polycondensations has been dramatically demonstrated, and the influence of such morphological differences upon the supercapacity of the materials has been explored. Precursor salt, epoxide, and solvent all influence the speed of the sol-gel transition and the size and shape of the features observed in the as-prepared materials, thereby leading to highly varied microstructures including spheres, sponge-like networks, and plate assemblies of varied size. These morphological features of the as-prepared cobalt aerogels were observed for the first time by high resolution scanning electron microscopy (HRSEM). The as-prepared aerogel materials were identified by powder X-ray diffraction and thermogravimetry as weakly crystalline or amorphous cobalt basic salts with the general formula Co(OH)(2-n)X(n) where X = Cl or NO3 according to the precursor salt used in the synthesis. For all samples, the morphology was preserved through mild calcining to afford spinel phase Co3O4 in a variety of microstructures. Wide-ranging specific surface areas were determined for the as-prepared and calcined phases by physisorption analysis in agreement with the morphologies observed by HRSEM. The Co3O4 aerogels were evaluated for their supercapacitive performance by cyclic voltammetry. The various specimens exhibit capacitances ranging from 110 to 550 F g(-1) depending upon the attributes of the particular aerogel material, and the best specimen was found to have good cycle stability. These results highlight the epoxide-driven sol-gel condensation as a versatile preparative route that provides wide scope in materials' properties and enables the analysis of structure-performance relationships in metal oxide materials.

Alkali metal reduction of (η(5)-C9H5-1,3-(SiMe3)2)2Co (1) in tetrahydrofuran (THF) permits isolation of the unusual and reactive 20 electron Co(I) anion [Na(THF)6][(η(5)-C9H5-1,3-(SiMe3)2)2Co] (2). Crystallographic characterization of both 1 and 2 provide support for the one electron reduction from Co(II) to Co(I). Reactivity studies of 2 are further consistent with a Co(I) equivalent, based on both one electron chemical oxidation to reform 1 and reaction with a variety of σ and π donors. Upon addition of pyridines or vinyltrimethylsilane to 2, known dimer [(C9H5-1,3-(SiMe3)2)2Co2] (3) is formed, likely through 16 electron (η(5)-C9H5-1,3-(SiMe3)2)Co(L) intermediates. Ethylene addition to 2 establishes an equilibrium between (η(5)-C9H5-1,3-(SiMe3)2)Co(η(2)-H2C═CH2)2 (8) and 2, suggestive of reversible ligand ejection from 2. Crossover experiments between a related metal indenide salt and 2 confirm ligand extrusion from the anion, even in the absence of strong supporting donors. Reaction of 2 with PMe3 results in formation of 3, (η(5)-C9H5-1,3-(SiMe3)2)Co(PMe3)2 (13), and a paramagnetic species, with the product ratios being highly dependent on the conditions of synthesis. Collectively, 2 demonstrates an alternative entry point into the chemistry of 14 electron Co(I) equivalents when compared to typical ligand loss from neutral 18 electron cyclopentadienyl cobalt bis(ligand) complexes, perhaps permitting generation of low electron count species more effective for small molecule activation.

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