Salen-porphyrin-based conjugated microporous polymer supported Pd nanoparticles: highly efficient heterogeneous catalysts for aqueous C-C coupling reactions

The salen-porphyrin based conjugated microporous polymer (SP-CMP) was first constructed by polycondensation reaction of a salen-dialdehyde derivative and pyrrole. Due to the outstanding chemical and thermal stability, abundant micropores with a reasonable pore size, and ordered salen-porphyrin arrays in the A(4)B(4)-type polymer framework, the functional CMP was further applied as a Pd nanoparticle support by the coordinate interactions between the polydentate chelating sites with Pd(OAc)(2) and subsequent reduction with NaBH4. The as-synthesized composite material (Pd@SP-CMP) was fully characterized by powder X-ray diffraction (PXRD), thermogravimetric analysis (TGA), Fourier transform infrared (FT-IR) spectroscopy, X-ray photoelectron spectroscopy (XPS), and solid-state C-13 nuclear magnetic resonance (NMR). The porous property of Pd@SP-CMP was also characterized by N-2 adsorption/desorption isotherms and the obtained material exhibited a Brunauer-Emmett-Teller (BET) surface area of 266 m(2) g(-1), together with a pore volume of 0.192 cm(3) g(-1). The microscopic morphology of Pd@SP-CMP was further evaluated by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The Pd@SP-CMP material with highly dispersed Pd nanoparticles exhibited excellent catalytic activity towards Suzuki-Miyaura and Heck-Mizoroki coupling reactions in water or in the dioxane/water mixture. In addition, Pd@SP-CMP also displayed outstanding stability and recyclability, and it can be reused without loss of activity in ten successive reactions. More importantly, the salen-porphyrin based CMPs could be the promising candidates for developing high-performance heterogeneous catalysts.