Transition metal ions catalysis

BenzoMoxazoles (130) undergo a base-promoted formal arylation using an aromatic acyl chloride, giving product (131) in up to 91% yield. " The reaction proceeds via N-acylation of oxazole to form an iminium intermediate, which hydrates to give a Lewis acetal, ring-opens, extrudes CO, ring-closes and then dehydrates. The reaction avoids the previous use of transition metal ion catalysis, and one example of an alkyl acid chloride is also reported. 

Kinetics of the oxidation of ascorbic acid by S20g in the pH range 3.4-4.6, in the absence of metal ion catalysis, gave the empirical rate law -d[S20g ]/df = k([H2A] -I- [HA ])[S20g ] which is unaffected by the addition of a radical trap suggesting parallel two-electron transfer processes from H2A and HA to dehydroascorbic acid. The role of transition-metal-ion catalysis on these and other reactions of S20 has been studied. 

First, the use of water limits the choice of Lewis-acid catalysts. The most active Lewis acids such as BFj, TiQ4 and AlClj react violently with water and cannot be used However, bivalent transition metal ions and trivalent lanthanide ions have proven to be active catalysts in aqueous solution for other organic reactions and are anticipated to be good candidates for the catalysis of aqueous Diels-Alder reactions. 

Inspired by the many hydrolytically-active metallo enzymes encountered in nature, extensive studies have been performed on so-called metallo micelles. These investigations usually focus on mixed micelles of a common surfactant together with a special chelating surfactant that exhibits a high affinity for transition-metal ions. These aggregates can have remarkable catalytic effects on the hydrolysis of activated carboxylic acid esters, phosphate esters and amides. In these reactions the exact role of the metal ion is not clear and may vary from one system to another. However, there are strong indications that the major function of the metal ion is the coordination of hydroxide anion in the Stem region of the micelle where it is in the proximity of the micelle-bound substrate. The first report of catalysis of a hydrolysis reaction by me tall omi cell es stems from 1978. In the years that... 

Late transition metal or 3d-transition metal irons, such as cobalt, nickel, and copper, are important for catalysis, magnetism, and optics. Reduction of 3d-transition metal ions to zero-valent metals is quite difficult because of their lower redox potentials than those of noble metal ions. A production of bimetallic nanoparticles between 3d-transi-tion metal and noble metal, however, is not so difficult. In 1993, we successfully established a new preparation method of PVP-protected CuPd bimetallic nanoparticles [71-73]. In this method, bimetallic hydroxide colloid forms in the first step by adjusting the pH value with a sodium hydroxide solution before the reduction process, which is designed to overcome the problems caused by the difference in redox potentials. Then, the bimetallic species... 

These reactions are subject to catalysis by certain transition metal ions and with small amounts of MnBr2 or CuCl the reaction proceeds satisfactorily with alkyl bromides.134... 

Throughout this book a major stress is on catalysis in organisms. Catalysis is confined to non-metals and metal ions of attacking power, either as Lewis acids or in oxidation/reduction and this excludes the simplest ions such as Na+, K+ and Ca2+ (and Cl- among anions). The transition metal ions and zinc are the most available powerful catalysts. The metals in a transition series are known to have selective binding properties, exchange rates and oxidation/reduction states, which can be put to use in catalysis in quite different ways (Table 2.13). It is noticeable that especially the complexes of metal elements... 

The chapter Electron Spin Resonance in Catalysis by Lunsford was prompted by the extensive activity in this field since the publication of an article on a similar subject in Volume 12 of this serial publication. This chapter is limited to paramagnetic species that are reasonably well defined by means of their spectra. It contains applications of ESR technique to the study of adsorbed atoms and molecules, and also to the evaluation of surface effects. The application of ESR to the determination of the state of transition metal ions in catalytic reactions is also discussed. 

Catalysis by Transition Metal Ions and Complexes in Hydrocarbon Oxidation by Dioxygen... 

CATALYSIS BY TRANSITION METAL IONS AND COMPLEXES IN HYDROCARBON OXIDATION BY DIOXYGEN... 

Transition metal ion and La3 +-catalysis of the alcoholysis of phosphate diesters 308... 

One more example of metal ion catalysis will be considered briefly. In a now classic paper, Cox (1974) showed that the enolization of 2-acetylpyri-dine (but not 4-acetylpyridine) is catalysed by divalent transition metal ions. Proton abstraction by acetate ions is strongly accelerated by Zn2+, Ni2+ and Cu2+ ions and the transition state stabilization by these ions roughly parallels their abilities to bind to the substrate (Table A6.5). The three metal ions are significantly superior to the proton as electrophilic catalysts, no doubt because they can chelate to both the pyridine nitrogen and the... 

Open-shell transition metal ions play central roles in many modem research fields such as catalysis, molecular magnetism, or bioinorganic chemistry, to name only a few. Central to this... 

Catalytic Decomposition of Hydrogen Peroxide by Ferrous Ions Catalysis by Transition Metal Ions and Complexes in Liquid-Phase Oxidation of Hydrocarbons and Aldehydes by Dioxygen... 

Competition between Homolytic and Heterolytic Catalytic Decompositions of Hydroperoxides Reactions of Transition Metals with Free Radicals Reactions of Transition Metal Ions with Dioxygen Catalytic Oxidation of Ketones Cobalt Bromide Catalysis Oscillating Oxidation Reactions... 

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