Absorption of Water Vapor by Bambus[6]uril and a Density Functional Theory Study of Its Aqua Complexes.

The absorption/desorption of water vapor by bambus[6]uril (Bu[6]) has been studied. According to kinetic experiments, the absorption capacity of Bu[6] is 4 moles of water per 1 mole of Bu[6] with the absorption duration of 20 min and the complete desorption duration of 100 min. Experimental rate constants for water vapor absorption and desorption by Bu[6] have been determined to be 0.166 min-1 and 0.0221 min-1, respectively. The obtained results are in agreement with theoretical calculations using the DFT method. A hypothetical structure of bambus[6]uril tetrahydrate (Bu[6]·4H2O) has been proposed based on the experimental and DFT data.

Al3+ solvation in solutions of aluminum nitrate in a protic ionic liquid: Nuclear magnetic resonance verification of the solvation shell composition.

The closest environment of Al3+ cations was analyzed in detail in solutions of aluminum nitrate in the prototypical protic ionic liquid ethyl ammonium nitrate (EAN) using 1 H and 14 N nuclear magnetic resonance (NMR) spectra. For Al (NO3 )3 -EAN mixtures with different water content, a quantitative analysis of the integral intensities of the 1 H and 14 N signals was carried out and the composition of the first solvation shell of the aluminum cation was refined.

Hydrogen-Bonding-Assisted Cationic Aqua Palladium(II) Complex Enables Highly Efficient Asymmetric Reactions in Water.

Metal-bound water molecules have recently been recognized as a new facet of soft Lewis acid catalysis. Herein, a chiral palladium aqua complex was constructed that enables carbon-hydrogen bonds of indoles to be functionalized efficiently. We embraced a chiral 2,2'-bipyridine as both ligand and hydrogen-bond donor to configure a robust, yet highly Lewis acidic, chiral aqua complex in water. Whereas the enantioselectivity could not be controlled in organic solvents or under solvent-free conditions, the use of aqueous environments allowed the σ-indolylpalladium intermediates to react efficiently in a highly enantioselective manner. This work thus describes a potentially powerful new approach to the transformation of organometallic intermediates in a highly enantioselective manner under mild reaction conditions.

Mechanistic Study of Enhanced Protonation by Chromium(III) in Electrospray Ionization: A Superacid Bound to a Peptide.

Addition of trivalent chromium, Cr(III), to solutions undergoing electrospray ionization (ESI) enhances protonation and leads to formation of [M + 2H]2+ for peptides that normally produce [M + H]+. This effect is explored using electronic structure calculations at the density functional theory (DFT) level to predict the energetics of various species that are potentially important to the mechanism. Gas- and solution-phase reaction free energies for glycine and its anion reacting with [Cr(III)(H2O)6]3+ and for dehydration of these species have been predicted, where glycine is used as a simple model for a peptide. For comparison, calculations were also performed with Fe(III), Al(III), Sc(III), Y(III), and La(III). Removal of water from these complexes, as would occur during the ESI desolvation process, results in species that are highly acidic. The calculated pKa of Cr(III) with a single solvation shell is -10.8, making [Cr(III)(H2O)6]3+ a superacid that is more acidic than sulfuric acid (pKa = -8.8). Binding to glycine requires removal of two aqua ligands, which gives [Cr(III)(H2O)4]3+ that has an extremely acidic pKa of -28.8. Removal of additional water further enhances acidity, reaching a pKa of -84.7 for [Cr(III)(H2O)]3+. A mechanism for enhanced protonation is proposed that incorporates computational and experiment results, as well as information on the known chemistry of Cr(III), which is substitutionally inert. The initial step involves binding of [Cr(III)(H2O)4]3+ to the deprotonated C-terminus of a peptide. As the drying process during ESI strips water from the complex, the resulting superacid transfers protons to the bound peptide, eventually leading to formation of [M + 2H]2+.

Strong Influence of Humidity on Low-Temperature Thin-Film Fabrication via Metal Aqua Complex for High Performance Oxide Semiconductor Thin-Film Transistors.

Oxide semiconductors thin film transistors (OS TFTs) with good transparency and electrical performance have great potential for future display technology. In particular, solution-processed OS TFTs have been attracted much attention due to many advantages such as continuous, large scale, and low cost processability. Recently, OS TFTs fabricated with a metal aqua complex have been focused because they have low temperature processability for deposition on flexible substrate as well as high field-effect mobility for application of advanced display. However, despite some remarkable results, important factors to optimize their electrical performance with reproducibility and uniformity have not yet been achieved. Here, we newly introduce the strong effects of humidity to enhance the electrical performance of OS TFTs fabricated with the metal aqua complex. Through humidity control during the spin-coating process and annealing process, we successfully demonstrate solution-processed InOx/SiO2 TFTs with a good electrical uniformity of ∼5% standard deviation, showing high average field-effect mobility of 2.76 cm2V-1s-1 and 15.28 cm2V-1s-1 fabricated at 200 and 250 °C, respectively. Also, on the basis of the systematic analyses, we demonstrate the mechanism for the change in electrical properties of InOx TFTs depending on the humidity control. Finally, on the basis of the mechanism, we extended the humidity control to the fabrication of the AlOx insulator. Subsequently, we successfully achieved humidity-controlled InOx/AlOx TFTs fabricated at 200 °C showing high average field-effect mobility of 9.5 cm2V-1s-1.

Chemistry of a novel zerovalent ruthenium π-acidic alkene complex, Ru (η (6)-1,3,5-cyclooctatriene)(η (2)-dimethyl fumarate)2.

A novel zerovalent ruthenium complex with a π-acidic ligand, Ru(η (6)-cyclooctatriene)(η (2)-dimethyl fumarate)2 (1), was prepared from Ru(η (4)-cyclooctadiene)(η (6)-cyclooctatriene) [Ru(cod)(cot)]. Complex 1 or Ru(cod)(cot) catalyzes various new carbon-carbon bond-forming reactions that include the [2 + 2] cycloaddition of alkenes and alkynes via ruthenacycles, the creation of a new hydrocarbon, pentacyclo[6.6.0.0(2,6).0(3,13).0(10,14)]tetradeca-4,11-diene [PCTD], by dimerization of 2,5-norbornadiene via C-C bond cleavage, and the codimerization of alkynes and/or alkenes. Complex 1 was shown to be an excellent mother complex for various zerovalent ruthenium complexes. Complex 1 reacts with amines, phosphines or water to give new zerovalent ruthenium complexes with the ligands. The resulting aqua complexes have a water ligand with an oxygen atom that is a chiral center, i.e., ruthenium complexes with a 'chiral water' ligand were prepared and fully characterized.