Diazo-coupled porous organic polymers as efficient catalysts for metal-free Henry and Knoevenagel reactions

Owing to linkage and building block diversity, Porous Organic Polymers (POPs) are versatile materials with high potential in organic catalysis. Herein, nitrogen-rich POPs bearing -OH phenolic groups were synthesized via the diazo-coupling reactions between phloroglucinol and benzidine (PgBd-POP), and between 1,3,5-tris(4-amino-phenyl)triazine and 4,4'-[1,1 '-biphenyl]-4,4 '-diylbis(diazene-2,1-diyl))diphenol (TAPT-Bd(PhOH)2-POP), under mild reaction conditions. The mesoporous polymers exhibited a BET surface area of 276 +/- 4 m(2) g(-1) and 1.94 +/- 0.06 m(2) g(-1), and chemical stability up to 315 degrees C and 330 degrees C, respectively. Both POPs were used as catalysts in metal-free Henry and Knoevenagel condensation reactions between aromatic aldehydes and nitromethane and ethyl cyanoacetate, respectively, under mild conditions. PgBd-POP showed a remarkable efficiency of up to 99% conversion and >99% selectivity, for the Henry nitroaldol reaction between 4-nitrobenzaldehyde and nitro-methane, after only 1 h at room temperature, whereas TAPT-Bd(PhOH)(2)-POP generally exhibited the highest catalytic activity towards the Knoevenagel reaction, with up to 99% conversion for the condensation of 4-nitro-benzaldehyde with ethyl cyanoacetate, after 1 h at room temperature. These results confirm the potential of this class of porous materials as green catalysts for organic reactions.

Automated summary

Porous Organic Polymers (POPs) are versatile materials with high potential in organic catalysis. Nitrogen-rich POPs with -OH phenolic groups were synthesized under mild reaction conditions and showed excellent catalytic activity in metal-free Henry and Knoevenagel condensation reactions.