Search results for "catalyzed"

Ultra-Low Catalyst Loading as a Concept in Economical and Sustainable Modern Chemistry: The Contribution of Ferrocenylpolyphosphane Ligands

2007

The challenge of sustainability in modern chemistry will be met with new technologies and processes provided significant progress is made in several key research areas, such as the expansion of chemistry from renewable feedstock, the design of environmentally benign chemicals and solvents, the minimization of depletive resources, and the development of high-performance catalysis. In this prospect, ligand chemistry is a pivotal science that links modern-organic,-inorganic, -organometallic, and -coordination chemistry through a vast number of valuable applications, precisely associated to catalysis. We review in this article our recent work on catalysis promoted by original ferrocenyl tetra-,…

Über den angriff des carboniumions am monomeren styrol bei der kationischen copolymerisation von trioxane und styrol. 19. Mitt. über polyoxymethylene

1962

Bei der Saure-katalysierten Hydrolyse von kationisch dargestellten Copolymeren aus Trioxan und Styrol entsteht 4-Phenyl-1,3-Dioxan. Das last sich nur so erklaren, das in Analogie zur radikalischen und zur anionischen Polymerisation der Angriff des Carboniumions ebenfalls am β-Kohlenstoffatom des Styrols erfolgt. Formation of 4-phenyl-1,3-dioxan occurs during the acid catalyzed hydrolysis of cationically produced copolymers of trioxane and styrene. The only possible explanation involves an attack of the carboniumion at the β-carbonatom of styrene analogous to the radical and anionic polymerization.

Ligand Effect on Iron-Catalyzed Cross-Coupling Reactions: Evaluation of Amides as O-Coordinating Ligands

2019

The development of new highly efficient O‐coordinating ligands for iron‐catalyzed C(sp2)−C(sp3) cross‐coupling reactions is reported. A structure‐reactivity study on the effect of amides as ligands in the industrially‐important iron‐catalyzed cross‐coupling of aryl chlorides with challenging organometallics possessing β‐hydrogens was performed. Investigation of a series of new 21 ligands that rationally vary in O‐coordination aptitude as well as sterics around the amide bond pinpointed the features that are important for catalysis. The study led to the discovery of several highly efficient ligands for cross‐coupling, including TMU (TMU=tetramethylurea), N‐cyclic and coordinating benzamides.…

Copper-catalyzed click reactions: quantification of retained copper using 64Cu-spiked Cu(I), exemplified for CuAAC reactions on liposomes

2018

Abstract The Cu(I)-catalyzed azide-alkyne cycloaddition (CuAAC) is a powerful, highly reliable and selective reaction which allows for a rapid synthesis in high yields and under mild conditions (pH, temperature). However, the cytotoxicity of copper requires its complete removal prior to an application in vivo. This is an issue especially when it comes to CuAAC reactions on macromolecular structures or drug delivery systems, as copper might be retained by these systems. Thus, a quantification of the final copper content of these systems is inevitable, which we exemplified for a CuAAC reaction on liposomes using 64Cu-spiked Cu(I). In this respect, a Cu(II) nitrate solution was irradiated at t…

Iron‐Catalyzed Cross‐Couplings in the Synthesis of Pharmaceuticals: In Pursuit of Sustainability

2018

The scarcity of precious metals has led to the development of sustainable strategies for metal-catalyzed cross-coupling reactions. The establishment of new catalytic methods using iron is attractive owing to the low cost, abundance, ready availability, and very low toxicity of iron. In the last few years, sustainable methods for iron-catalyzed cross-couplings have entered the critical area of pharmaceutical research. Most notably, iron is one of the very few metals that have been successfully field-tested as highly effective base-metal catalysts in practical, kilogram-scale industrial cross-couplings. In this Minireview, we critically discuss the strategic benefits of using iron catalysts a…

N-Methylcaprolactam as a Dipolar Aprotic Solvent for Iron-Catalyzed Cross-Coupling Reactions: Matching Efficiency with Safer Reaction Media

2019

Although iron‐catalysis provides a powerful alternative to the more conventional palladium and nickel in the cross‐coupling arena, the major limitation is the necessity for carcinogenic N‐methylpyrrolidone as a co‐solvent in the vast majority of catalytic reactions. Herein, we introduce N‐methylcaprolactam as an efficient, non‐toxic and practical dipolar aprotic solvent for iron‐catalyzed C(sp2)−C(sp3) alkylative cross‐coupling of aryl chlorides and tosylates. The utility of this method is reflected by its wide substrate scope, high yields and capacity to cross‐couple challenging alkyl organometallics prone to b‐hydride elimination and homocoupling. Considering the broad utility of iron‐cat…

Nuclear transition rates in μ-catalyzedp-dfusion

1991

Nuclear transition rates in \ensuremath{\mu}-catalyzed p-d fusion have been calculated using numerically converged $^{3}\mathrm{He}$ bound-state and p-d scattering wave functions for the first time. The transition rates for M1 radiative capture in both quartet and doublet initial states have been computed using a model of meson-exchange currents which reproduces the thermal n-d capture cross section, and are in excellent agreement with experiment. The muon internal-conversion rate is in very good agreement with a recent reanalysis of old bubble-chamber measurements. Furthermore, our nonvanishing quartet capture rate resolves the anomaly in the Wolfenstein-Gerstein effect.

Detection of a plant enzyme exhibiting chlorogenate-dependant caffeoyltransferase activity in methanolic extracts of arbuscular mycorrhizal tomato ro…

2012

When Glomus intraradices-colonised tomato roots were extracted in methanol at 6 degrees C, chlorogenic acid (5-caffeoylquinic acid), naturally present in the extract, was slowly converted by transesterification into methyl caffeate. The progress of the reaction could be monitored by HPLC. The reaction only occurred when the ground roots were left in contact with the hydro-alcoholic extract and required the presence of 15-35% water in the mixture. When the roots were extracted in ethanol, chlorogenic acid was transformed to ethyl caffeate in the same conditions. The reaction was also detected in Glomus mosseae-colonised tomato root extracts. It was also detectable in non-mycorrhizal root ext…

A Copper‐Catalyzed Synthesis of Pyrroles through Photochemically Generated Acylazirines

2019

Exploring the catalytic performance of a series of bimetallic MIL-100(Fe, Ni) MOFs

2019

[EN] A series of mixed-metal Fe-III/Ni-II metal-organic frameworks (MOFs) of the MIL-100 type containing different metal ratios have been synthesized de novo, following an approach that requires tuning of the Fe-III/Ni-II reactivity. The resulting heterometallic MIL-100(Fe, Ni) materials maintain thermal, chemical and structural stability with respect to the parent MIL-100(Fe) MOF as can be deduced from various techniques. The nature and the oxidation state of the accessible metal cations have been evaluated by in situ infrared spectroscopy and extended X-ray absorption fine structure measurements. The obtained mixed-metal MOFs and the parent material have been evaluated as heterogeneous ca…