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Phosphinoamide-scaffolded heterobimetallic palladium–titanium complexes are highly effective catalysts for allylic aminations of allylic chlorides with hindered secondary amine nucleophiles. Three titanium-containing ligands are shown to assemble active catalysts in situ and enable catalysis at room temperature. A variety of sterically bulky secondary amines are efficiently allylated in high yields with as little as 1 mol % palladium catalyst. Piperidine and pyrrolidine products are also efficiently generated via intramolecular aminations with hindered amine nucleophiles.

An access to the dioxabicyclo[3.2.1]octane core of sorangicin A was developed, using a keto lactone formation, a Mukaiyama–Michael reaction and an epoxide opening as the key steps.

Oxaziridines constitute a subset of a class of versatile oxidants whose characteristic feature is the presence of two electronegative heteroatoms within a strained three-membered ring (Figure ​(Figure1).1). Other small organic heterocycles in this class include diaziridines1 and dioxiranes,2 which have been developed as reagents for a variety of oxidative transformations. η2-Peroxo and η2-hydroperoxy complexes of various transition metals are also members of this class,3 and these structures are the active oxidizing species in a broad range of synthetically useful oxidative transformations, including the Sharpless asymmetric epoxidation,4 VO(acac)2-catalyzed epoxidations,5 and MeReO3-catalyzed hydroxylation of unactivated alkanes.6 Peroxometal complexes are relevant in biological systems as well; dinuclear μ-η2:η2-peroxodicopper(II) complexes found within the active sites of metalloenzymes such as hemocyanin and tyrosinase have been extensively studied for their role in oxygen metabolism.7 Figure 1 Representative oxidizing heterocycles with two electrophilic heteroatoms within a three-membered ring.

This review summarizes the resent research on fiber based structured materials for catalytic application. This material class comprises a wide range of differently structured supports made from ceramic, metal or glass. Within the last decades due to their flexibility fiber based catalysts were applied to several reactions ranging from pollutant control to fuel processing and showed significant advantages in mass and heat transfer, pressure drop and productivity. The review focusses on mass transfer and pressure drop characteristics and the published correlations for them. A classification in comparison to established support structures is done not only showing superior properties but also the demand for further studies in hydrodynamics and transfer processes.

Nucleic acid-templated reactions enable the design of conditional reaction systems, in which bond formation occurs only when a particular DNA or RNA molecule is present. Such reaction systems are currently being explored for applications in DNA/RNA diagnosis, drug screening and as a means to design gene expression specific therapy. However, biological nucleic acid templates usually have low abundance. Therefore, either the targeted nucleic acid template has to be multiplied by means of an amplification step or the template itself has to act as a catalyst which amplifies product formation. This critical review highlights the recent advancements in nucleic acid-templated reactions that proceed with turnover in template and thereby provide a means of amplification. Improvements in reaction engineering and the development of new chemistries have pushed the limits from 101 to 102–103 turnovers. This includes reaction systems that lead to the ligation of oligonucleotides or to the interconversion of appended functional groups beyond ligation as well as templated chemistries that enable the activation of catalysts for subsequent triggering of reactions between non-nucleotidic substrates. The present limitations and future opportunities are discussed.

A dinuclear phenol zinc complex for the asymmetric aldol condensation of α-hydroxyacetamide (I) is developed.

Cubic gallium oxynitride is synthesized by solvothermal processing of a gallium ethylene diamine complex and H2O (autoclave, 200 °C, 1 d).

Solid oxide fuel cells are the most promising power conversion units for fossil and biomass fuels combining ceramic and metallic components. Because of long-term high temperature operation and thermal cycling the standard materials cannot be applied for integration of active ceramic components. Different approaches are used nowadays for the integration of ceramic cells into stacks and of system components in the power plant. In this paper an overview on the application of glass and glass ceramic sealants, active and reactive air brazes as well as compressive mica sealants for solid oxide fuel cells is made. The crystallizing glasses are more favorable for cell integration in the stack for operation in a broad temperature range. Metallic brazes are mainly limited to integration of anode or metal supported cells in ferritic alloy gaskets for operation at T

A general asymmetric allylic alkylation of ester enolate equivalents at the carboxylic acid oxidation state is reported. N-Acylbenzoxazolinone-derived enol carbonates are synthesized in good yield and employed in the palladium-catalyzed alkylation reaction. Good yields (up to 99%) and enantioselectivities (up to 99% ee) are obtained and the imide products are readily converted to a series of carboxylic acid derivatives without loss of enantiopurity. High enantioselectivity in the reaction is achieved by a new strategy for ligand design involving variation of the steric properties of the diarylphosphine moiety.

In contrast to previously reported methods, the catalytic asymmetric alkylation methodology presented herein is quite general in scope for both the allylic electrophile and enolate nucleophile.

Focussed laser light can be used to induce chemical or electrochemical reactions in the μm scale. The attainable high power densities allow to achieve fast reaction rates. At metals and insulators thermal heating dominates. On semiconductors short pulses or low energy densities cause mainly electronic processes under isothermal conditions. These will be emphasized in this paper for thin semiconductor films in electrolyte solutions. The induced reactions measured under potentiostatic or potentiodynamic conditions include electron (ETR) and ion transfer (ITR) as well.—Examples are discussed for n-type semiconducting passive films on some base metals with thicknesses in the range from nm to μm. The ETR depend mainly on the potential showing the tendency to saturation while the ITR depend on the field strength. Doping by ion implantation reduces ETR and ITR as well. Amorphous films show a smaller tendency to inner reactions like breakdown. Bubble formation can be detected in a microscopic scale. Substrate effects are due to epitaxy on various grains, changes of the structure and crystallinity (suboxide and TiN) and electronic processes at the substrate surface (Al/Al2O3).

published in Advance ACS Abstracts, May 15, 1994. 0022-3654/94/2098-62 12%04.50/0 palladium concentration was 1.2 X 10-4 M as determined by atomic emission spectroscopy. In the silver deposition experiments, the palladium solution was diluted by roughly a factor of 4. Experiments were also carried out to reduce Pd(I1) in the absence of the stabilizing PVS. Under these circumstances, the loss of reduced palladium was much greater than in the presence of PVS. This polymer is not removed by the treatment of the solution with Amberlite (in fact, when a pure PVS solution was treated with Amberlite, the conductivity actually increased, because the K+ ions of PVS were exchanged for free H+ ions). In order to coat the Pd colloids, two methods were used to reduce Ag+ ions. First, the radiolytic method was tried, which in many other cases has been quite useful for preparing concentric bimetallic particles. NaAg(CN)2 was added to the palladium colloid as well as 0.5 M propanol-2 and 0.1 M acetone. As described previously,4b exposure to y-rays leads to the formation of organic radicals that transfer electrons to the Pd particles. The Pd particles are polarized cathodically, and the stored electrons reduce the silver-cyano complexon thesurface of the Pd particles, which leads to a silver mantle. However, it was found that part of the radicals reduced the complexed silver ions directly in solution, the result being that individual silver particles were also formed. Second, formaldehyde was used as the reducing agent. When Ag+ ions are reduced by formaldehyde in the absence of colloidal palladium, an induction period of several minutes is observed. However, when Pd particles are present, the reduction occurs practically instantaneously and individual silver particles are not produced. This method was then applied in all experiments. In detail, the procedure was as follows: 2 X 10-4 M formaldehyde was added to 75 mL of Pd solution (at pH = 11). The solution was in a round flaskunder nitrogen, which had a side arm carrying a 1-cm optical cuvette and a septum. Several milliliters of deaerated AgC104 solution ( 5 X 10-5 to 2 X 10-3 M) was slowly injected (less than 1 mL per minute) under strong stirring. The total injection time was about 8 min. During the injection, the spectral changes took place immediately. This means that the stationary concentration of Ag+ ions was low during the injection, which is the reason why practically no spontaneous nucleation of individual Ag, particles occurred. The palladium concentration in the final solution was 2.9 X le5 M, and the total concentration of added silver varied between 2.2 X 10-6 and 2.0 X 10-4 M.

Typical reaction pathways for the synthesis of self-assembling polysaccharides (dextran, cellulose, and xylan) are discussed. Dextran- and cellulose derivatives with different sulfur-containing functional groups (thiol-, thioester- and thioether moieties) possess a remarkable ability to self-assemble on gold surfaces. Aminocellulose derivatives, obtained by nucleophilic substitution of cellulose-p-toluenesulfonic acid ester with di- and oligoamines, are able to form monolayers on various substrates. The NH 2 moieties of these biocompatible aminocellulose surfaces can be used to immobilize enzymes while maintaining enzyme activity. A novel approach to aminocellulose through introduction of polyamidoamine-based dendrons by the copper-catalyzed Huisgen reaction of azido cellulose with dendrons possessing ethynyl moieties is described. Furthermore, the preparation of cationic xylan derivatives and their adsorption behavior on cellulose and two types of self-assembled monolayers is reviewed. Xylan layers on various pulp fibers were found to enhance paper strength.

We report an oxaziridine-mediated enantioselective aminohydroxylation of olefins catalyzed by a chiral copper(II) bis(oxazoline) complex. A variety of styrenic olefins undergo efficient aminohydroxylation with excellent regioselectivity and synthetically useful levels of enantioselectivty (up to 84% ee). The reaction can be conducted on multi-gram scale with as little as 2 mol% of the copper(II) catalyst. Hydrolysis of the resulting 1,3-oxazolines under acidic conditions produces N-sulfonyl amino alcohols that can be purified by recrystallization to afford very high levels of enantioselectivity.

Stabilized ortho-bromo phenyllithium reagents, generated via lithium-halogen exchange of aryl iodides, undergo regioselective ring opening of mono-substituted N-Boc, N-Cbz, and N-tosyl-protected aziridines in good to excellent yields. The resulting ortho-bromo phenethylamines can be cyclized under transition-metal-catalyzed conditions to give 2-substituted chiral, non-racemic indolines in good yields.

N-Sulfonyl oxaziridines are susceptible to electrophilic activation using copper(II) catalysts and react with styrenes under these conditions to provide 1,3-oxazolidines in a formal aminohydroxylation of the alkene. We propose a two-step mechanism involving a cationic intermediate to account for the rate differences and regioselectivities observed using a variety of styrenes. In accord with our hypothesis, aminohydroxylations of a range of substrates bearing electron-stabilizing groups are successful, and 1,3-dienes are particularly good substrates for copper(II)-catalyzed aminohydroxylation. Reactions of unsymmetrical dienes provide good to excellent olefin selectivity, the sense and magnitude of which can be rationalized upon consideration of the stability of the cationic intermediates suggested by our mechanism. Diastereoselective synthesis of a diverse range of densely functionalized structures can be achieved by polyfunctionalization of dienes using aminohydroxylation as a key complexity-increasing step.

Isotetronic acids were regioselectively prepared by cyclization of 1,3-bis(trimethylsilyloxy)alk-1-enes with oxalyl chloride.