Rhodium-Catalyzed Amination of Aromatic Olefins [1]

Summary.  The oxidative amination of styrene with secondary amines in the presence of cationic rhodium catalysts yields regiospecifically the corresponding anti-Markovnikov enamines. Styrene as the hydrogen acceptor gave concomitantly ethylbenzene. In the presence of 1,5-cyclooctadiene (cod) preferential reduction to cyclooctene takes place. The addition of cod reduces the rate of the reaction, but also the amount of ethylbenzene produced. Here, for the first time the ratio of enamine: ethylbenzene is > 1, which is favourable in case of more expensive styrene derivatives. A screening of various ligands for oxidative amination reveals that hemilabile 2-(ω-phosphino-n-alkyl)-pyridines are superior ligands for this reaction compared to simple alkyl and aryl phosphines. Received May 30, 2000. Accepted July 11, 2000     

Electrothermal Description of Organic Semiconductor Devices by p(x)-Laplace Thermistor Models

We consider a p(x)-Laplace thermistor model for electrothermal effects in organic semiconductor devices and propose a hybrid finite-volume/finite-element scheme which is combined with path-following methods to find a numerical solution. (© 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Visibly transparent & radiopaque inorganic organic composites from flame-made mixed-oxide fillers

Radiopaque composites have been produced from flame-made ytterbium/silica mixed oxide within a crosslinked methacrylate resin matrix. The refractive index of the filler powder increased with ytterbium oxide loading. A high transparency was achieved for a matching refractive index of the filler powder and the polymer in comparison to commercial materials with 52 wt% ceramic filling. It was demonstrated that powder homogeneity with regard to particle morphology and distribution of the individual metal atoms is essential to obtain a highly transparent composite. In contrast, segregation of crystalline single-oxide phases drastically decreased the composite transparency despite similar specific surface areas, refractive indices and overall composition. The superior physical strength, transparency and radiopacity compared to composites made from conventional silica based-fillers makes the flame-made mixed-oxide fillers especially attractive for dental restoration materials.     

Photoelectron yield of small silver and gold particles suspended in gas up to a photon energy of 10 eV

The photoelectric yieldY of clean Ag and Au particles suspended in He-gas has been measured up to photon energieshv=10 eV.Y shows strong deviations from the bulk in the case of Ag but not in the case of Au. Surface adsorbates generate dramatic changes inY, pointing to the decisive role of the surface electron density profile on the optical properties.     

Monitoring adsorption on small particles

A review on the application of photoelectron emission from small particles suspended in a gas to monitor the adsorption properties and to detect adsorbates on the particles is given. The relation between surface coverage with an adsorbate and the shift in photothreshold and photoelectric yield is demonstrated by two examples: The adsorption of O₂ on silver particles and of perylene on carbon particles. A third example concerns the detection of polyaromatic hydrocarbons (PAH) on particles arising from combustions.