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Keywords:

  • Continuous-flow processes;
  • Heterogeneous catalysis;
  • Hydrogenation;
  • Palladium;
  • Supported catalysts

Abstract

Heterogeneous catalysis for organic synthesis under continuous-flow conditions becomes possible by a new reactor-based approach. Continuous-flow reactors with a monolithic glass/polymer composite interior are loaded with palladium particles by ion exchange followed by reduction. When incorporated into a continuous-flow setup (PASSflow) this reactor allows the transfer-hydrogenation of alkenes, alkynes, nitro-substituted aromatic compounds and benzyl ethers in the flow-through mode. In addition, the activity of the catalysts is well suited to achieve Suzuki, Sonogashira and Heck cross-coupling reactions in the absence of phosphanes or any other ligands, resulting in a greatly simplified purification. As an extension to this concept a bifunctional support was prepared inside the reactor consisting of Pd particles and an ion-exchange group (hydroxide form). In the Suzuki− Miyaura reaction the reactor serves as a base for immobilisation and activation of the boronic acid as boronate and as a catalyst for promoting the C−C coupling reaction under continuous-flow conditions. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)