Magnetically recoverable catalysts based on mono- or bis-(NHC) complexes of palladium for the Suzuki-Miyaura reaction in aqueous media: two NHC-Pd linkages are better than one

Pre-synthesized mono-and bis(NHC) palladium complexes have been grafted onto magnetic core/shell gamma-Fe2O3/silica particles and tested as catalysts in model Suzuki-Miyaura coupling reactions. The bis(NHC) immobilized complex was found to be a robust catalyst that can operate under mild conditions in aqueous media, even for the activation of chloroarene, whereas the mono(NHC) counterpart rapidly deactivates. Moreover, it can be readily recovered by magnetic separation and reused many times, providing very high productivities, and with so low leaching of palladium that the crude products obtained contain <= 10 ppm Pd.