Functionalized Conjugated Microporous Polymers for Growing Sub-3 nm Pd Nanoparticles

Metal nanoparticles have high surface area as well as good catalytic activity and have shown broad applications in organic synthesis, electronic devices, and optical devices. However, the controlled synthesis of ultrafine nanoparticles still represents a challenging task. Herein, we reported the synthesis of three phenylene–ethynylene-based conjugated microporous polymers (CMPs) via the sila-Sonogashira–Hagihara reaction. Upon postfunctionalization of these CMPs with N-acetylcysteine (NAC), 3-mercaptopropionic acid (MPA), and 1-propanethiol (PT) through thiol–yne addition, the resulting NAC–CMP, MPA–CMP, and PT–CMP were used as the templates to direct the growth of ultrafine Pd nanoparticles, respectively. The nanoparticles grown inside the pores of CMPs exhibit relatively narrow size distribution (1.7 ± 0.2 nm in NAC–CMP, 1.6 ± 0.3 nm in MPA–CMP, and 1.7 ± 0.3 nm in PT–CMP). PdNPs–NAC–CMP exhibits the highest catalytic activity and stability in Suzuki–Miyaura coupling compared with the other two PdNPs–CMPs and commercial Pd/C catalyst. The strong binding interactions between NAC–CMP’s functional groups and Pd nanoparticles as well as good solvent–polymer affinity are playing critical roles in stabilizing Pd nanoparticles and enhancing the reaction rate. This study shed light on the effect of different directing groups on controlled growth of ultrafine metal nanoparticles and their catalytic activity and recyclability.