Synthesis of CuCorePtShell Nanoparticles as Model Structures for Core–Shell Electrocatalysts by Direct Platinum Electrodeposition on Copper

The synthesis of Cu(core)Pt(shell) model catalysts by the direct electrochemical deposition of Pt on Cu particles is presented. Cu particles with an average diameter of 200 nm have been deposited on glassy‐carbon electrodes by double pulse electrodeposition from a copper sulfate solution. Subsequent deposition from a platinum nitrate solution under potential control allows for a high selectivity of the Pt deposition towards Cu. Using a combination of cyclic voltammetry, XPS and sputtering, the structure of the generated particles has been analyzed and their core–shell configuration proven. It is shown that the electrocatalytic activity for the oxygen reduction is similar to that of other PtCu catalyst systems. The synthesized structures could allow for the analysis of structure–activity relations of core–shell catalysts on the way to the simple and controlled synthesis of supported Cu(core)Pt(shell) nanoparticles as oxygen reduction catalysts.     

Pyrrole β-amides: Synthesis and characterization of a dipyrrinone carboxylic acid and an N-Confused fluorescent dipyrrinone

Pyrrole β-amides are useful building blocks for the preparation of novel molecular architectures that can be used in supramolecular chemistry and sensor development. Under basic conditions, pyrrole β-amides with an α-aldehyde produce different condensation products when reacted with pyrrolinones depending on the amide substitution. Secondary amides form the expected dipyrrinones, but unexpectedly undergo a subsequent trans-amidation with the pyrrolinone nitrogen to produce an unsymmetrical imide (an N-confused fluorescent dipyrrinone). Under the same conditions, tertiary amides produce the expected dipyrrinone carboxylic acids, which have been shown to have strong self-association properties as determined by vapor pressure osmometry measurements, NMR studies, and X-ray crystal structure determination. Furthermore, an N-confused fluorescent dipyrrinone was produced from the same trans-amidation reaction during attempts to decarboxylate a dipyrrinone amide with a 9-carboxylic moiety.     

Reactions of Bromine Fluoride Dioxide,BrO2F,for the Generation of the Mixed‐Valent Bromine Oxygen Cations Br3O4+ and Br3O6+

A reliable synthesis of unstable and highly reactive BrO₂F is reported. This compound can be converted into BrO₂⁺SbF₆^?, BrO₂⁺AsF₆^?_, and BrO₂⁺AsF₆^??2 BrO₂F. The latter decomposes into mixed‐valent Br₃O₄?Br₂⁺AsF₆^? with five‐, three‐, one‐, and zero‐valent bromine. BrO₂⁺ H(SO₃CF₃)₂^? is formed with HSO₃CF₃. Excess BrO₂F yields mixed‐valent Br₃O₆⁺OSO₃CF₃^? with five‐ and three‐valent bromine. Reactions of BrO₂F and MoF₅ in SO₂ClF or CH₂ClF result in Cl₂BrO₆⁺Mo₃O₃F₁₃^?. The reaction of BrO₂F with (CF₃CO)₂O and NO₂ produces O₂Br‐O‐CO‐CF₃ and the known NO₂⁺Br(ONO₂)₂^?. All of these compounds are thermodynamically unstable.     

Protection‐Group‐Free Synthesis of Sequence‐Defined Macromolecules via Precision λ‐Orthogonal Photochemistry

An advanced light‐induced avenue to monodisperse sequence‐defined linear macromolecules via a unique photochemical protocol is presented that does not require any protection‐group chemistry. Starting from a symmetrical core unit, precision macromolecules with molecular weights up to 6257.10 g mol^?1 are obtained via a two‐monomer system: a monomer unit carrying a pyrene functionalized visible light responsive tetrazole and a photo‐caged UV responsive diene, enabling an iterative approach for chain growth; and a monomer unit equipped with a carboxylic acid and a fumarate. Both light‐induced chain growth reactions are carried out in a λ‐orthogonal fashion, exciting the respective photosensitive group selectively and thus avoiding protecting chemistry. Characterization of each sequence‐defined chain (size‐exclusion chromatography (SEC), high‐resolution electrospray ionization mass spectrometry (ESI‐MS), and NMR spectroscopy), confirms the precision nature of the macromolecules.     

Substitution reactions of gaseous ions in a three‐dimensional quadrupole ion trap

Substitution reactions between gaseous ions and neutral substrate molecules are of ongoing high interest. To investigate these processes in a qualitative and quantitative manner, we have constructed a device, with which a defined amount of a volatile substrate can be mixed with a defined amount of helium gas and added into a three‐dimensional quadrupole ion trap. From the known inner volume of the device, the known ratio n_substrate:n_He of the mixture, and the determined absolute partial pressure of helium in the ion trap, we can derive the partial pressure of the substrate in the ion trap and, thus, convert the directly observable pseudo–first‐order rate constants of the substitution reactions into absolute bimolecular rate constants. We have tested the device by investigating a series of S_N2 reactions of Br ^? and CF₃CH₂O ^? anions as well as ligand exchange reactions of ligated Na⁺ cations. As the obtained results suggest, the described device makes it possible to determine the bimolecular rate constants of substitution reactions as well as other ion‐molecule reactions with satisfactory accuracy and reliability.     

Modification of the Cp′ ring in the ferrocifen precursor and its influence on the recognition by the estrogen receptor

A synthetic pathway giving access to diphenyl ethylene organometallic derivatives possessing the ferrocifen precursor skeleton modified in the Cp′ ring is described. It relies on reaction of the (η⁵-propionylcyclopentadienyl) (η⁶-benzene)iron(II) salt 7 with substituted cyclopentadienyl anions or their heteroanalogs followed by the McMurry coupling reaction with 4,4′-dihydroxybenzophenone. Using this approach pentamethylcyclopentadienyl and 3,4-dimethylphospholyl analogs of ferrocifen precursor (10 and 11) have been synthesized. Even with the presence of the bulky and containing phosphorus η⁵-ligands these compounds are still recognized by the two subtypes of estrogen receptor(ERα and ERβ).     

Syntheses and Crystal Structures of 4,5-Dihydro-2-(2′-hydroxyphenyl)oxazole-Containing Metal Complexes

The synthesis of the complexes 3 of various metals ligated to chiral 4,5-dihydro-2-(2′-oxidophenyl-?O)oxazoles-?N is described (Scheme). Three of them, i.e. 3a , 3e , and 3f containing Cu^II, Zn^II and Ni^II, respectively, were analyzed by X-ray diffraction studies. A series of Cu^II complexes ( 6a – d ) with differently substituted dihydrooxazoles have been synthesized.     

Fluorine-Stabilized Sulfur–Carbon Multiple Bonds

Alkylidene and alkylidyne sulfur fluorides contain sulfur–carbon multiple bonds. In contrast to the sulfur ylides, alkylidene sulfur fluorides fulfill all the criteria for double bonds, i.e. they have short bond lengths, strong anisotropic distribution of electron density, and rotation about the C? S bond is restricted. Alkylidyne sulfur fluorides have especially short bond distances and, due to a high amplitude bending motion, appear to be more or less linear, depending on the physical state. The advantage of the C? S multiple bond systems in contrast with numerous others, e.g. those of phosphorus and silicon, is that they exist without steric stabilization. Moreover, the limits of the triple-bond principle are outlined: the prognosis for triple bonds between two elements of higher periods is poor, because carbene-like or fully bridged structures win in terms of stability.     

The effect of terminal chain modifications on the mesomorphic properties of 4,4′-disubstituted diphenyldiacetylenes

The typical sidewalls produced in the fabrication of protrusion electrodes are proposed to create a low voltage (4.5 V_rms) and high transmittance (93%) blue-phase liquid crystal display (BP-LCD). The tilted electrodes produce a strong horizontal electrical field that reduces the operating voltage considerably. The common problem of the ‘dead zones’ is solved by reflecting the light onto the electrodes. In order to estimate the phase retardation of the reflected light, a ray tracing simulation program for anisotropic mediums has been developed. The proposed device is more competitive than vertical field switching based BP-LCD and also, has the advantages of protruded in-plane-switching structures. These facts make this technology a potential candidate for the next generation of BP-LCDs.