Synthesis of Pd/conjugated microporous polymer heterogeneous catalysts via imine groups and high catalytic efficiency on Suzuki–Miyaura coupling reaction

Four kinds of conjugated microporous polymers (CMPs) with imine structures were synthesized by a Sonogashira coupling reaction followed by a postreaction between aldehydes and amines. Palladium nanoparticles (Pd NPs) were successfully supported on the CMPs to prepare Pd/CMP heterogeneous catalysts and were used to catalyze the Suzuki–Miyaura coupling reaction. The number of aromatic nuclei and nitrogen atoms in the CMPs highly affects Pd loading. In the Suzuki–Miyaura coupling reaction, the Pd/CMP with good Pd NPs dispersibility and appropriate Pd content (Pd/CMP-NA) exhibited the highest catalytic efficiency with 100% conversion and 95.4% yield which can be used for many substrates. The Pd/CMP-NA heterogeneous catalyst was easy to recover and still exhibited good catalytic efficiency after 5 cycles. To further understand the catalytic mechanism of Pd/CMP-NA on the Suzuki–Miyaura coupling reaction, we proposed a rational catalytic cycle. This paper provides an idea for the structural design of CMPs used for Suzuki–Miyaura catalytic reaction.