On the Nature of the ‘Heterogeneous' Catalyst:  Nickel-on-Charcoal

Lipshutz, Bruce H.; Tasler, Stefan; Chrisman, Will; Spliethoff, Bernd; Tesche, B.

doi:10.1021/jo020296m

Cited by 162 publications

(86 citation statements)

References 97 publications

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“…[21,22] For many of the subsequent cross-coupling transformations, in particular for reactions involving Ni/C, a reduction step to a zero-valent metal prior to coupling is required. [13,21,22,26,27] To accurately compare the results obtained by direct microwave heating with the outcome of a conventionally heated reaction at the same temperature we have used a reactor system that allows us to perform both types of transformations in an identical reaction vessel and to monitor the internal reaction temperature in both experiments directly with a fiber-optic probe device. [28] This system has the advantage that the same reaction vessel and the same method of temperature measurement is used.…”

Section: Resultsmentioning

confidence: 99%

Microwave‐Assisted Cross‐Coupling and Hydrogenation Chemistry by Using Heterogeneous Transition‐Metal Catalysts: An Evaluation of the Role of Selective Catalyst Heating

Irfan

Fuchs

Glasnov

et al. 2009

Chemistry A European J

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The concept of specific microwave effects in solid/liquid catalytic processes resulting from the selective heating of a microwave-absorbing heterogeneous transition-metal catalyst by using 2.45 GHz microwave irradiation was evaluated. As model transformations Ni/C-, Cu/C-, Pd/C-, and Pd/Al2O3-catalyzed carbon-carbon/carbon-heteroatom cross-couplings and hydrogenation reactions were investigated. To probe the existence of specific microwave effects by means of selective catalyst heating in these transformations, control experiments comparing microwave dielectric heating and conventional thermal heating at the same reaction temperature were performed. Although the supported metal catalysts were experimentally found to be strongly microwave absorbing, for all chemistry examples investigated herein no differences in reaction rate or selectivity between microwave and conventional heating experiments under carefully controlled conditions were observed. This was true also for reactions that use low-absorbing or microwave transparent solvents, and was independent of the microwave absorbtivity of the catalyst support material. In the case of hydrogenation reactions, the stirring speed was found to be a critical factor on the mass transfer between gas and liquid phase, influencing the rate of the hydrogenation in both microwave and conventionally heated experiments.

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Section: Resultsmentioning

confidence: 99%

Microwave‐Assisted Cross‐Coupling and Hydrogenation Chemistry by Using Heterogeneous Transition‐Metal Catalysts: An Evaluation of the Role of Selective Catalyst Heating

Irfan

Fuchs

Glasnov

et al. 2009

Chemistry A European J

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“…When studying the occurrence of leaching, either hot filtration of the solid catalyst or the three-phase test [164,165] designed by Davies and Lipshutz, showed the occurrence of palladium leaching. The threephase test involves performing the Suzuki reaction as usual in the presence of the solid catalyst, but adding also a silica containing a covalently bound organic compound able to undergo the C À C coupling with the reagents present in the liquid phase.…”

Section: The Anchored [Sncl 5 ]mentioning

confidence: 99%

Silica‐Bound Homogenous Catalysts as Recoverable and Reusable Catalysts in Organic Synthesis

2006

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Very frequently the most costly components in a chemical reaction are not the starting materials or the reaction products, but the catalyst. In addition to the advantages from the economic point of view, recovery and reuse of the catalyst is equally important in order to avoid wastes, so improving the greenness of the process. There is a current tendency to transform homogeneous into heterogeneous catalysis, that will even be accelerated in the near future. Starting from a successful homogeneous catalyst, one general methodology allowing its recovery and reuse is to immobilize a suitable derivative of the active catalyst on an insoluble solid support. When the catalyst does not deactivate and is sufficiently stable under the reaction conditions, the ultimate immobilization methodology is to attach covalently the catalytically active species to the support. In this contribution, after introducing some general principles describing the fundamentals of the covalent anchoring, the emphasis is placed more on giving an overview of the most important types of covalently anchored catalysts, including Brçnsted and Lewis acids, covalently anchored bases and hydrogenation complexes. Hot topics such as silica-bound organocatalysts and the application of periodic mesoporous organosilicas as heterogeneous catalysts is also covered.

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“…[203] Ni NPs on carbon were used as catalysts for hydrogenating unsaturated compounds, [204] hydrodehalogenation of aryl halides, [205] Kumada, [206] Suzuki [207] and Negishi-type C-C coupling [208] and aromatic amination. [209] However, the C-C and C-N coupling reactions showed that Ni leached from the support during the reaction, re-adsorbing at the end of the reaction.…”

Section: Nps Supported On Metal Oxides or Carbon Supportsmentioning

confidence: 99%

Transition‐metal nanoparticles: synthesis, stability and the leaching issue

Pachón

Rothenberg

2008

Applied Organom Chemis

416

202

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This perspective examines the state-of-the-art of catalysis by metal nanoparticles. We outline various methods for preparing metal nanoparticle suspensions, and highlight the role of the stabilizers and the stabilizing principles. Subsequently, we examine some catalytic applications of homometallic and bimetallic nanoparticle suspensions in a variety of reactions. The cases are divided according to the stabilizing agent: polymers, dendrimers, ionic liquids, surfactants, micelles and micoremulsions, ligands and solid supports. We explain the importance of atom/ion leaching (all too frequent in nanoparticle catalysis, especially for the catalytically active group VIII metals) and consider ways of minimizing it. The future perspectives of nanoparticles as catalysts are discussed.

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On the Nature of the ‘Heterogeneous' Catalyst: Nickel-on-Charcoal

Cited by 162 publications

References 97 publications

Microwave‐Assisted Cross‐Coupling and Hydrogenation Chemistry by Using Heterogeneous Transition‐Metal Catalysts: An Evaluation of the Role of Selective Catalyst Heating

Microwave‐Assisted Cross‐Coupling and Hydrogenation Chemistry by Using Heterogeneous Transition‐Metal Catalysts: An Evaluation of the Role of Selective Catalyst Heating

Silica‐Bound Homogenous Catalysts as Recoverable and Reusable Catalysts in Organic Synthesis

Transition‐metal nanoparticles: synthesis, stability and the leaching issue

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