Homogeneous/heterogeneous palladium based catalytic system for Heck reaction. The reversible transfer of palladium between solution and support |
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| Authors: | Iweta Pryjomska-Ray Andrzej Gniewek Anna M Trzeciak Józef J Zió?kowski W?odzimierz Tylus |
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| Affiliation: | (1) Faculty of Chemistry, University of Wrocław, 14 F. Joliot-Curie St., 50-383 Wrocław, Poland;(2) Institute of Inorganic Technology, Wrocław University of Technology, 27 Wybrzeże Wyspiańskiego, 50-370 Wrocław, Poland |
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| Abstract: | Pd(II)/Al2O3 and Pd(0)/Al2O3, containing 0.6% of palladium were characterized by EDX, SEM and XRD methods and used as catalysts of the Heck coupling of
bromobenzene with butyl acrylate at 140 °C in molten Bu4N]Br salt. Monoarylated (trans-PhCH = CHC(O)OBu) (1) and diarylated (Ph2C = CHC(O)OBu) (2) products were obtained in amounts dependent on kind of base present in the system (Scheme 1). During the reaction palladium
was partially leached from the support forming Bu4N]PdBr4] complex that catalyze Heck reaction or undergo readsorption on Al2O3. These soluble palladium complexes are partially reduced to Pd soluble nanoparticles which can also be anchored on Al2O3 giving active catalyst of Pd(0)/Al2O3 type. Reduction of Pd(II) to Pd(0) during catalytic process at the presence of bases (NaHCO2, NaHCO3, NaOAc, Cs2CO3) was studied by XPS method and the total reduction was observed in reactions of PdCl2(PhCN)2 with NaHCO2 or with NaHCO3 and Bu4N]Br. It was experimentally proved that heterogenized catalyst, Pd(0)/Al2O3, after oxidative addition of aryl halides, serve as a source of soluble palladium species and colloidal nanoparticles that
are active as homogeneous catalysts. |
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| Keywords: | Heck reaction XPS XRD SEM heterogenized catalyst Pd colloid Pd nanoparticles |
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