Evidences of release and catch mechanism in the Heck reaction catalyzed by palladium immobilized on highly cross-linked-supported imidazolium salts

• Synthesis of alkenes is efficiently promoted by a silica-supported highly cross-linked imidazolium-based palladium catalyst.
• Important differences between Heck and Suzuki reactions have been evidenced when the reactions were carried out in the presence of the scavenging support.
• The imidazolium-based support is able to recapture the leached Pd species.
• Suzuki reaction between aryl bromides and phenylboronic acid is catalyzed by leached Pd species.
• Pd species could be recaptured giving a product with a minimal metal contamination.

Palladium (10 wt%) on a highly cross-linked imidazolium-based material was used as catalyst in 0.1 mol% in the Heck reaction between several alkenes and aryl iodides. Products were obtained from good to high yields. Deeper investigations showed a release of Pd species in solution and their capture by the imidazolium-based support. When a sixfold amount of support was employed the re-captured Pd species (0.5–0.6 wt%) were not anymore catalytically active. This result represents a new interesting aspect of this work since the highly cross-linked imidazolium-based material can act also as Pd scavenger avoiding the release of the metal in solution. Important differences between Heck and Suzuki reactions have been evidenced when the reactions were carried out in the presence of the scavenging support.

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