Pd-γ-Fe2O3-MEL-TEG-MME as a Novel Heterogeneous Catalyst for Carbon-Carbon Cross-Coupling Reactions in Water

Carbon-carbon coupling reactions catalyzed by transition metals are essential tools to further develop the synthesis of natural products and other structurally complex compounds [1]. A number of transition metals such as palladium, nickel and copper have been developed to catalyze coupling reactions. Since the pioneering study, homogeneous palladium catalysts have attracted most of the attention as a result of their better functional-group tolerance, and high catalytic activity. Generally, homogeneous catalysis can provide excellent yield, while heterogeneous catalysis offers the advantages of simplified product separation and recycling of the catalyst [2]. These properties make heterogeneous catalysts as suitable candidates for green chemistry catalysis due to their great stability, durability, cost effectiveness, and diminishing heavy metal environmental contamination [3]. In this regard, a variety of heterogeneous Pd catalysts have been prepared by immobilization of homogeneous Pd catalysts on the surface of different solid materials [4]. Nevertheless, these heterogeneous catalytic systems still demand time consuming and tedious chemical or physical procedures, such as filtration or centrifugation for their recovery. Hence, the development of alternative and easily separable heterogeneous Pd catalysts without much problems of metal pollution in the final products while maintaining high accessibility and catalytic activity is extremely desirable. Depositing of the catalysts on magnetic nanoparticles as supporting material provides an opportunity to recover the catalyst from the reaction mixture simply by a magnetic field [5].A novel Pd heterogeneous catalyst, denoted as Pd-γ-Fe2O3-MEL-TEG-MME, was synthesized and characterized by different methods such as FT-IR, TEM, TGA, XPS, VSM, ICP and elemental analysis. It was used as a magnetically recyclable Pd heterogeneous catalyst for carbon-carbon cross-coupling reactions including fluoride-free Hiyama and Heck reactions in water. By this method various biaryls and substituted olefines were synthesized in good to high yields.

Keywords:

Heterogeneous catalyst , coupling reactions , water , magnetic nanoparticle