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Nicholas E Leadbeater

Publications and source records attributed to Nicholas E Leadbeater.

At least 19 recordsLinked to original sources
PubMed2006

Alkoxycarbonylation of aryl iodides using gaseous carbon monoxide and pre-pressurized reaction vessels in conjunction with microwave heating.

The microwave-promoted alkoxycarbonylation of aryl iodides using reaction vessels pre-pressurized with carbon monoxide is reported. Reactions are performed using 0.1 mol% palladium acetate as catalyst, DBU as base and are complete within 20-30 min. A range of aryl iodide substrates can be converted to the corresponding esters using this methodology. Primary and secondary alcohols work well whereas a tertiary alcohol substrate proves less reactive. The potential for scale-up of the reaction has also been explored.

Journal Article↗
PubMed2006

Real-time monitoring of microwave-promoted Suzuki coupling reactions using in situ Raman spectroscopy.

The progress of microwave-promoted Suzuki reactions has been monitored using an in situ Raman spectroscopy apparatus assembled from commercially available components. It was possible to see if any reaction occurred and, if so, when it reached completion. In addition, the monitoring technique has given us an insight into the reaction, confirming that, when run in aqueous media, the coupling is in competition with the rapid deboronation of the boronic acid.

Journal Article↗
PubMed2005

Suzuki coupling of aryl chlorides with phenylboronic acid in water, using microwave heating with simultaneous cooling.

[reaction: see text]. We present here a methodology for the Suzuki coupling of aryl chlorides with phenylboronic acid using Pd/C as a catalyst, water as a solvent, and microwave heating. We show that simultaneous cooling in conjunction with microwave heating prolongs the lifetime of the aryl chloride substrates during the course of the reaction and, as a result, yields of the desired biaryl as well as overall recovery of material can be increased.

Journal Article↗
PubMed2005

A reassessment of the transition-metal free suzuki-type coupling methodology.

We present here a reassessment of our transition-metal free Suzuki-type coupling protocol. We believe that, although the reaction can be run without the need for addition of a metal catalyst, palladium contaminants down to a level of 50 ppb found in commercially available sodium carbonate are responsible for the generation of the biaryl rather than, as previously suggested, an alternative non-palladium-mediated pathway. We present a revised methodology for Suzuki couplings using ultralow palladium concentrations for use with aryl and vinyl boronic acids and discuss the effects of the purity of the boronic acid on the reaction.

Journal Article↗
PubMed2003

Rapid, easy cyanation of aryl bromides and chlorides using nickel salts in conjunction with microwave promotion.

We report here a fast, easy, and efficient method for the preparation of aryl nitriles from aryl bromides and chlorides. The methodology for aryl bromides involves the use of either Ni(CN)(2) or NaCN and NiBr(2). With aryl chlorides, a mix of NaCN and NiBr(2) is used and the reaction proceeds via the in situ formation of the corresponding aryl bromide. The reaction can be performed in air and is complete within 10 min.

Journal Article↗
PubMed2003

First examples of transition-metal free Sonogashira-type couplings.

[reaction: see text] We report here our observation that, using appropriate reaction conditions, the Sonogashira reaction can be performed without the need for transition-metal catalysts. Our approach involves the use of water as a solvent, poly(ethylene glycol) as a phase-transfer agent, and sodium hydroxide as a base. The methodology works, to differing extents, for aryl iodides and bromides.

Journal Article↗
PubMed2003

Transition-metal-free Suzuki-type coupling reactions: scope and limitations of the methodology.

The scope and limitations of the transition-metal-free Suzuki-type coupling of aryl halides and arylboronic acids to form biaryls are presented. Confirmation that the reaction is indeed metal-free is presented. The effects of changing base, solvent, reaction temperature, phase-transfer catalyst, and substrate are shown and the implications of these results discussed in terms of their impact on the synthetic versatility of the methodology. The main findings are that the reaction works well for aryl bromides, water is necessary as a solvent for the reaction, the optimum temperature for the reaction is 150 degrees C, the reaction is best performed by using microwave promotion with the exception of an electron-poor aryl bromide example where conventional heating may be used, only limited boronic acids can be used as coupling partners, sodium carbonate is the best base for the reaction, tetrabutylammonium bromide proves to be the best phase-transfer catalyst for the reaction, the reaction is limited to couplings between aryl halides and aryl boronic acids with sp(2)-sp(3) couplings proving ineffective, and NaBPh(4) can be used in the place of phenylboronic acid as a phenylating agent.

Journal Article↗
PubMed2003

Rapid and amenable suzuki coupling reaction in water using microwave and conventional heating.

It is possible to prepare biaryls in good yield very rapidy (5-10 min) on small (1 mmol) and larger (10-20 mmol) scales from aryl halides and phenylboronic acid using water as a solvent and palladium acetate as catalyst. The reaction can be performed equally well using microwave and conventional heating, showing that using these conditions probably no nonthermal microwave effects are associated with the impressive speed of the reaction.

Journal Article↗
PubMed2003

Microwave-assisted Mannich-type three-component reactions.

Mannich-type three-component reactions have been performed successfully using microwave heating in conjunction with the use of ionic liquids as heating agents. Good product yields and short reaction times have been achieved.

Chemistry, Organic↗
PubMed2002

Polymer-bound 1-aryl-3-alkyltriazenes as modular ligands for catalysis. Part 2: screening immobilized metal complexes for catalytic activity.

A range of polymer-supported triazenes and their metal-bound analogues were screened for use in catalysis. Fe, Cu and Zr complexes were, together with the polymer-supported triazene ligand alone, screened in the addition of Et(2)Zn to benzaldehyde. A supported Pd triazene complex was screened for activity in Suzuki and Sonogashira reactions and a supported Ru triazene complex screened for transfer hydrogenation.

Amines↗
PubMed2002

A study of the ionic liquid mediated microwave heating of organic solvents.

The use of ionic liquids as aids for microwave heating of nonpolar solvents has been investigated. We show that hexane and toluene together with solvents such as THF and dioxane can be heated way above their boiling point in sealed vessels using a small quantity of an ionic liquid, thereby allowing them to be used as media for microwave-assisted chemistry. Using the appropriate ionic liquid, the heating can be performed with no contamination of the solvent. To show the applicability of the system, two test reactions have been successfully performed.

Journal Article↗