Search results for "Halogen"

An Experimental and Computational Study on the Effect of Al(OiPr)3 on Atom-Transfer Radical Polymerization and on the Catalyst-Dormant Chain Halogen …

2005

International audience; Compound Al(OiPr)3 is shown to catalyze the halide-exchange process leading from [Mo(Cp)Cl2(iPrN=CH-CH=NiPr)] and CH3CH(X)COOEt (X=Br, I) to the mixed-halide complexes [Mo(Cp)ClX(iPrN=CH-CH=NiPr)]. On the other hand, no significant acceleration is observed for the related exchange between [MoX3(PMe3)3] (X=Cl, I) and PhCH(Br)CH3, by analogy to a previous report dealing with the RuII complex [RuCl2(PPh3)3]. A DFT computation study, carried out on the model complexes [Mo(Cp)Cl2(PH3)2], [MoCl3(PH3)3], and [RuCl2(PH3)3], and on the model initiators CH3CH(Cl)COOCH3, CH3Cl, and CH3Br, reveals that the 16-electron RuII complex is able to coordinate the organic halide RX in a…

Synthese und eigenschaften von einem nitrosubstituierten p-polyphenylen und von nitrosubstituierten p-oligophenylenen. 15. Mitteilung1

1964

Bei aromatischen Nitrojodverbindungen nimmt die ULLMANN-Reaktion unter verhaltnismasig milden Bedingungen einen praktisch quantitativen Verlauf, wenn sich das Jod in der o-Stellung zu einer Nitrogruppe befindet. Mit einer entsprechenden bifunktionellen Verbindung, dem 4,4′-Dijod-3,3′-dinitrobiphenyl, konnte unter den gleichen Bedingungen ein nitrosubstituiertes p-Polyphenylen erhalten werden, ein hellgelbes, unlosliches und unschmelzbares Pulver, das sich bei hoherer Temperatur (> 250°C) zersetzt. Auf Grund des Jodgehaltes (Endgruppen) wurde ein mittlerer Kondensationsgrad von 52 berechnet; das entspricht einer p-Phenylenkette aus 104 Benzolringen. Das Polymere ist kristallin und besitzt ei…

Palladium‐Catalyzed Electrophilic C–H‐Bond Fluorination: Mechanistic Overview and Supporting Evidence

2018

International audience; Palladium-catalyzed electrophilic fluorination is a particularly attractive and challenging synthetic issue. Because of the rapid evolution of this topic, a critical point on the mechanistic and experimental advances is provided herein. In the present review, we focused on current mechanistic understanding in electrophilic fluorination (and related halogenations) catalyzed by palladium, mainly with N-directing group. Our discussion is based on the well-characterized or calculated pertinent metal species and intermediates used for analyzing the plausible catalytic cycles. A particular effort has been devoted to gathering supporting data for the putative species involv…

Enantioselective Palladium-Catalyzed Oxidative β,β-Fluoroarylation of α,β-Unsaturated Carbonyl Derivatives

2016

© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim The site-selective palladium-catalyzed three-component coupling of deactivated alkenes, arylboronic acids, and N-fluorobenzenesulfonimide is disclosed herein. The developed methodology establishes a general, modular, and step-economical approach to the stereoselective β-fluorination of α,β-unsaturated systems.

cis-bromination of alkynes without cationic intermediates

2005

Electroreduction of aliphatic chlorides at silver cathodes in water

2010

The effect of water on the reduction of aliphatic chlorides at silver cathodes was investigated by cyclovoltammetric experiments in acetonitrile, water and their mixture and focused electrolyses in water solutions. The addition of water to acetonitrile gives rise to the formation of new peaks and/or the displacement of pre-existent peaks at dramatically less negative potentials. In a water medium, silver shows a very large electrocatalytic effect towards the reduction of chlorinated aliphatic compounds belonging to the classes of chloromethanes, chloroethanes and chloroethenes, dramatically higher than that observed in aprotic solvents such as dimethylformamide (DMF) or acetonitrile (ACN). …

Kinetik der Bromierung von Phenolen und phenolischen Mehrkernverbindungen, 5. Mitt.

1984

The kinetics of the bromination of six differently substituted 2,6-bis(hydroxybenzyl)phenols having only one reactivepara position at the phenolic unit in the middle of the molecule were studied in acetic acid at 22°C. The reaction rate decreases if intramolecular hydrogen bonds between one or two hydroxy groups of the adjacent phenolic units and the hydroxy group of the reacting unit become possible, and it is especially low, if these hydrogen bonds are directed to the middle by bulky substituents inortho position. This must be explained by a smaller +M-effect of the hydroxy group of the reacting unit. A kinetic isotope effect is observed in deutero acetic acid, where the reaction rate is …

Kinetik der Bromierung von Phenolen und phenolischen Mehrkernverbindungen, 1. Mechanismus und meßmethode

1975

Die Bromierung von 2-(2-Hydroxy-5-methylbenzyl)-4,6-dimethylphenol (1) und 2-[2-Hydroxy-3-(2-hydroxy-5-methylbenzyl)-5-methylbenzyl]-4,6-dimethylphenol (2a) wurde in Eisessig bei 22°C untersucht. Die Reaktion last sich fur [Br2]0 = 1,4·10−3 bis 6,0·10−3 mol dm + und Konzentrationen der phenolischen Verbindungen [P]0 zwischen 1,1·10−3 und 5,5·10−3mol dm−3 durch das folgende Geschwindigkeitsgesetz beschreiben: Wahrend die gebildete Bromverbindung keinen Einflus auf die Reaktionsgeschwindigkeit hat, verlangsamt der entstehende Bromwasserstoff die Reaktion. Die Bromierung ist trotzdem zur Bestimmung der Reaktionsfahigkeit von Phenolen und phenolischen Mehrkernverbindungen gut geeignet, da die R…

Iodofluorination of alkenes and alkynes promoted by iodine and 4-iodotoluene difluoride

2006

It was found that a mixt. of mol. iodine and 4-iodotoluene difluoride are useful to generate in situ the electrophilic iodine/nucleophilic fluorine (IF) couple that was able to add in a Markovnikov fashion and with prevalent anti-stereoselectivity to various alkenes and alkynes.

Halogen exchange and expulsion: ligand stabilized dihalogen silicon dications

2000

The first ligand stabilized SiCl22+ dications were synthesized using N-methylimidazole as co-ordinating ligand. The compounds SiCl4, SiBr2Cl2, and SiH2Cl2 form six-co-ordinated dicationic compounds of almost octahedral symmetry with similar structures which were investigated by single crystal X-ray analysis and density functional calculations. The structures exhibit particularly short dative Si–N bonds of about 1.90 A. Complexes crystallized from the same solvent are isostructural. A different solvent, though, leads to geometrical variations. It was also discovered that the halogen exchange process among mixed silicon tetrahalides occurs under much milder conditions than previously thought …