An Efficient and Recyclable Mesostructured Polymer-Supported N-Heterocyclic Carbene-Palladium Catalyst for Sonogashira Reactions

Palladium catalyst systems are the most widely used for the formation of C-C and C-N bonds. Environmentally friendly heterogeneous palladium catalysts have strongly stimulated growth in this research area. Herein, a FDU (Fudan University)-15 mesopolymer with p6mm mesostructures that combine the advantages of organic polymers and mesoporous materials was investigated as a new solid support for Pd complexes. The FDU-15 mesopolymer-supported N-heterocyclic carbine (NHC) precursor was developed by a simple chemical functionalization approach. It has been used as a phosphine-free ligand to prepare the novel heterogeneous palladium catalyst FDU-NHC/Pd(II), which efficiently catalyzes Sonogashira reactions between aryl halides and terminal alkynes to afford the corresponding products in good yields. Various techniques such as X-ray diffraction, N(2) adsorption-desorption isotherms, high resolution transmission electron microscopy, and X-ray photoelectron spectroscopy have been used to characterize the catalyst. The results indicate that the mesoporous structure of FDU-15 was not affected by immobilization, however, the pore diameter, pore volume, and BET surface area decrease. The stability of the heterogeneous catalyst was also studied. The FDU-NHC/Pd(II) complex catalyst was easily separated from the reaction system by a simple filtration of the reaction mixture and it has been shown to be robust without a significant loss of catalytic activity after recycling and reuse in 10 times.