Palladium supported on triazolyl-functionalized polysiloxane as recyclable catalyst for Suzuki–Miyaura cross-coupling

• Very good catalytic activity of palladium supported on polysiloxane in Suzuki–Miyaura reaction.
• Strong ability of functionalized polysiloxane to bond palladium.
• Effect of polysiloxane substituents on the yield of catalytic reaction.
• TEM identification of Pd(0) nanoparticles in the reaction mixture.

Two palladium catalysts obtained in reaction of Pd(OAc)2 with differently substituted triazolyl polysiloxanes were used in the Suzuki–Miyaura cross-coupling of aryl bromides with phenylboronic acid. Catalytic reactions, performed at 60 °C in a 2-propanol-water mixture, led to high yields of cross-coupling products when 2- and 4-bromotoluene, bromobenzene, and 2-bromoanisole were used as substrates. In recycling experiments, very good results were obtained in eight subsequent runs. High yield of 2-methylbiphenyl was also obtained with catalysts formed in situ, from Pd(OAc)2 and polysiloxane. In these experiments, an inhibiting effect of free polymers containing butyl substituents on triazole rings was discovered. Under the same conditions, in the presence of polysiloxane functionalized with phenyl-substituted triazole, the yield of 2-methylbiphenyl remained on the level of 98–100%. The application of the TEM method to the catalysts recovered from the reaction mixture evidenced the presence of Pd(0) nanoparticles bonded to triazolyl polysiloxane. The participation of unstabilized Pd(0) forms in the reaction course was concluded from the results of the Hg(0) test.

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