A Novel Double-Separation Strategy for Aqueous Phase Catalysis

Development of efficient methods to complete recovery of supported catalysts is one of the important goals of Green Catalysis . In this context, magnetic nanoparticles (MNPs) have gained a great deal of attention because of their easy separation from the reaction mixture [1]. Despite the substantial success achieved in the field of magnetically separable nanocatalysts, the application of these systems in pure water as reaction solvent remained a major challenge. Although MNPs display good dispersion in many solvents, in the case of using pure water as the reaction medium, the organic substrates often cannot favorably react at the catalytically active sites. Therefore, it seems that there is still much room to make novel magnetically recyclable catalysts displaying improved catalytic performance in pure water. In this study, a novel imidazolium ionic liquid bearing triethylene glycol moiety was prepared and immobilized on the surface of silica-coated iron oxide nanoparticles. After introduction of Pd species through a subsequent ion-exchange process the material was found as a highly water dispersible, active and yet magnetically recoverable catalyst in some important organic transformations such as aerobic oxidation of alcohols, Ullmann homocoupling of chlorobenzene, transfer hydrogenation and direct reductive N-formylation of nitroarenes in water. Owing to the presence of hydrophilic ionic liquid on the surface, the catalyst showed highly stable dispersion in water and an extremely low affinity to the organic phase; thus providing the possibility of recovering the catalyst from the reaction mixture by using a simple and efficient double separation strategy (successive extraction/final magnetic separation) This novel double-separation strategy with negligible leaching makes the material an eco-friendly and economical catalyst to perform the organic transformation in pure water as a green solvent.