Pd(II) conjugated chitosan nanofibre mats for application in Heck cross-coupling reactions

Pd(II)-chitosan composite nanofibres of 62 ± 9 nm diameter are efficient catalysts for Heck cross-coupling reactions. Using a model reaction of iodo-benzene and n-butyl acrylate, we demonstrate that this material can be used as a recyclable catalytic support with a very low loading of palladium (0.17 mol% Pd).     

Magnetic nanoparticle-supported tetrazole-functionalized palladium catalyst: synthesis,DFT study and application for Sonogashira and Heck cross-coupling reactions

Research on Chemical Intermediates - A novel magnetic catalyst-immobilized nano-palladium was efficiently prepared via a (2 + 3) cycloaddition pathway and characterized with...     

Efficient and ligand free palladium catalyst for Suzuki and Heck cross-coupling reactions

A simple and efficient system for Suzuki cross-coupling reactions was developed using a ligandless catalyst of Pd nanoclusters generated in situ from Pd(acac)₂. The cross-coupling reactions proceeded under mild reaction conditions with a high reaction rate (5 min) to give various biaryls in high yields. The system also exhibited catalytic potential for Heck reaction between aryl bromides and styrene.     

Polymer hydrogel confined palladium nanoparticles as recyclable catalysts for Suzuki and Heck cross-coupling reactions

Reusable palladium nanoparticles highly dispersed in porous and hydrophilic interpenetrating polymer networks(IPN),i.e.,Pd@IPN hybrid gels,are employed for catalysis of Suzuki and Heck coupling reactions.Good yields are obtained with high turnover frequencies when the reactions are run with very low Pdloadings.The use of IPN gives better recyclability than that of crosslinked polyvinyl alcohol alone.The polymer networks allow the reactants to have easy access to the Pd metals.The catalysts combine high activity with the reusability offered by the heterogeneous system,without the need for strong coordination or chelating ligands.     

Ionically tagged benzimidazole palladium(II) complex: preparation and catalytic application in cross-coupling reactions

An imidazolium chloride tagged palladium(II) complex has been conveniently prepared and structurally analyzed. It is active toward cross-coupling of arylboronic acid with aryl halide and benzoyl chloride, giving moderate to high yield of the desired biaryls and aryl ketones, respectively. The present phosphine-free (N-N)Pd(II) complex could be efficiently recycled at least four times with minor decrease of activity in the aqueous Suzuki-Miyaura coupling reaction.     

Synthesis and characterization of 1-phenyl-3-alkylbenzimidazol-2-ylidene salts and their catalytic activities in the Heck and Suzuki cross-coupling reactions

The synthesis and characterization of 1-phenyl-3-alkyl-substituted carbene precursors that were prepared from 1-phenyl substituted benzimidazole and various alkyl halides are reported. The new benzimidazolium salts (1a–e) were characterized by ¹H NMR, ¹³C NMR, FT-IR spectroscopic methods and elemental analyses. New in situ generated palladium-benzimidazolium complexes were tested for catalytic activity in the Mizoroki-Heck and Suzuki-Miyaura cross-coupling reactions.     

Direct preparation of arylethynylzinc bromides and their application to cross-coupling reactions

A novel synthetic protocol for the preparation of arylethynylzinc bromides has been developed. Thus-obtained organozinc reagents were successfully employed in the subsequent cross-coupling reactions with a broad range of aryl halides providing the corresponding alkynylated compounds in good to excellent yields.     

Surfactant-free synthesis of palladium nanoclusters for their use in catalytic cross-coupling reactions

Surfactant-free Pd nanoclusters (Pd NCs) (size: 1-1.5 nm) showed high catalytic activity in the Suzuki-Miyaura cross-coupling and Mizoroki-Heck reactions. The Pd NCs had a high turnover number, up to 6.0 × 10(8), which can be recycled at least five times without loss of catalytic activity.     

Cobalt-catalyzed cross-coupling reactions of alkyl halides with aryl Grignard reagents and their application to sequential radical cyclization/cross-coupling reactions

Reactions of alkyl halides with arylmagnesium bromides in the presence of cobalt(II)(diphosphine) complexes are discussed. Treatment of 1-bromooctane with phenylmagnesium bromide with the aid of a catalytic amount of CoCl₂(dppp) [DPPP=1,3-bis(diphenylphosphino)propane] yielded octylbenzene in good yield. The reaction mechanism would include single electron transfer from an electron-rich cobalt complex to alkyl halide to generate the corresponding alkyl radical. The mechanism was justified by CoCl₂(dppe)-catalyzed [DPPE=1,2-bis(diphenylphosphino)ethane] sequential radical cyclization/cross-coupling reactions of 6-halo-1-hexene derivatives that yielded benzyl-substituted cyclopentane skeletons.     

An iterative strategy for the synthesis of oligothiophenes by catalytic cross-coupling reactions

An iterative strategy for the synthesis of new sulfur-functionalized oligothiophenes by Suzuki or Stille cross-coupling reactions was applied to the reaction of 4-bromo-tert-butylphenylthioether with thiophene derivatives. The planarity of the oligothiophenes obtained was confirmed by the single-crystal X-ray structure analysis of 2-(4′-tert-butylthiophenyl)thiophene, which shows a potentially large electronic conjugation length. © 2004 Wiley Periodicals, Inc. Heteroatom Chem 15:121–126, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/hc.10224     

Suzuki cross-coupling reactions of gamma-alkylidenebutenolides: application to the synthesis of vulpinic acid

alpha-Hydroxy-gamma-alkylidenebutenolides were efficiently functionalized by Suzuki cross-coupling reactions via the corresponding enol triflates. The natural product vulpinic acid was prepared by this methodology.     

Synthesis of fluorene-based oligomeric organoboron reagents via Kumada, Heck, and Stille cross-coupling reactions

Boronic pinacol ester group is not reactive in Kumada, Heck and Stille coupling reaction conditions. Fluorene-based sophisticated organoboron compounds were synthesized by means of Palladium catalyzed Kumada, Heck and Stille cross-coupling reactions from halofluorenyl boronic esters.     

Cobalt-catalyzed cross-coupling reactions of alkyl halides with allylic and benzylic Grignard reagents and their application to tandem radical cyclization/cross-coupling reactions

Details of cobalt-catalyzed cross-coupling reactions of alkyl halides with allylic Grignard reagents are disclosed. A combination of cobalt(II) chloride and 1,2-bis(diphenylphosphino)ethane (DPPE) or 1,3-bis(diphenylphosphino)propane (DPPP) is suitable as a precatalyst and allows secondary and tertiary alkyl halides--as well as primary ones--to be employed as coupling partners for allyl Grignard reagents. The reaction offers a facile synthesis of quaternary carbon centers, which has practically never been possible with palladium, nickel, and copper catalysts. Benzyl, methallyl, and crotyl Grignard reagents can all couple with alkyl halides. The benzylation definitely requires DPPE or DPPP as a ligand. The reaction mechanism should include the generation of an alkyl radical from the parent alkyl halide. The mechanism can be interpreted in terms of a tandem radical cyclization/cross-coupling reaction. In addition, serendipitous tandem radical cyclization/cyclopropanation/carbonyl allylation of 5-alkoxy-6-halo-4-oxa-1-hexene derivatives is also described. The intermediacy of a carbon-centered radical results in the loss of the original stereochemistry of the parent alkyl halides, creating the potential for asymmetric cross-coupling of racemic alkyl halides.     

Infinite-period bifurcation for chemical reactions on catalytic surfaces: A simple model

A simple model is presented, exhibiting the phenomena of finite-amplitude-infinite-period bifurcation for catalytic systems.     

A cycloalkane-based thermomorphic system for palladium-catalyzed cross-coupling reactions

In this paper, we describe a practical and efficient protocol for Sonogashira, Suzuki-Miyaura, and Mizoroki-Heck cross-coupling using a CBT system. The use of substrates with cycloalkane-soluble tags facilitates separation of the desired products and the homogeneous Pd catalyst via simple liquid-liquid extraction, thereby eliminating the need for a catalyst removal process.     

Palladium-catalyzed cross-coupling reactions of silanolates: a paradigm shift in silicon-based cross-coupling reactions

This paper chronicles the conceptual development, proof of principle experiments, and recent advances in the palladium-catalyzed cross-coupling reactions of the conjugate bases of organosilanols. The discovery that led to the design and refinement of this process represents a classical illustration of how mechanistic studies can provide a fertile ground for the invention of new reactions. On the basis of a working hypothesis (which ultimately proved to be incorrect) and the desire to effect silicon-based cross-coupling without the agency of fluoride activation, a mild and practical palladium-catalyzed cross-coupling of alkenyl-, aryl-, and heteroaryl silanolates has been developed. The mechanistic underpinnings, methodological extensions, and the successful applications of this technology to the synthesis of complex molecules are described.     

Reinvestigation of aminomethyltrifluoroborates and their application in Suzuki-Miyaura cross-coupling reactions

A reinvestigation into the chemical composition of potassium aminomethyltrifluoroborates is reported. These trifluoroborato salts have been reassigned as zwitterionic ammoniomethyltrifluoroborates. Minor adjustments to the previously disclosed reaction conditions are reported that permit a similar level of activity as nucleophiles in Suzuki-Miyaura cross-coupling reactions.