Tuning the hydrogen donor/acceptor behavior of ionic liquids in Pd-catalyzed multi-step reactions

• Synthesis of palladium nanoparticles in ionic liquids
• Thioether-phosphine stabilizers adapted to metal nanoparticles in ionic liquids
• Pd-catalyzed C–C couplings and H-transfer multi-step reactions
• The role of ionic liquids in multipath mechanisms for Pd-catalyzed reactions

Palladium nanoparticles stabilized by thioether-phosphine ligands (1–3) were used as catalytic precursors in Heck–Mizoroki cross-coupling and CC reduction reactions in ionic liquids. The ionic liquid [EMI][MeHPO3] (A) exhibited an important hydrogen donor/acceptor behavior depending on the reaction conditions. Tandem or parallel pathways for C–C coupling and H-transfer reactions were observed, leading to the coupled product trans-4-phenyl-3-buten-2-one (I) and the corresponding reduced partner 4-phenylbutan-2-one (II) pointing to a molecular-like catalytic reactivity of the process. When the reaction was carried out under hydrogen pressure and low temperature, the reduction to II was inhibited by the presence of thioether-phosphine ligands.

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