N-doping and structural regularity of covalent organic frameworks (COFs) tune the catalytic activity for knoevenagel condensation reaction

Pursuing the effects of catalytic efficiency with heteroatom doping and structural regularity in COFs-based heterogeneous catalyst is useful for future structure design. Herein, 2,4,6-trialdehyde resorcinol (TP) was reacted with the structural units 4,4',4''-(1,3,5-triazine-2,4,6-triyl)trianiline (TTA) and 5,5',5''-(1,3,5-triazine-2,4,6-triyl)tris (pyridin-2-amine) (TPA) to synthesise two covalent organic frameworks (TP-TPA-COF and TP-TTA-COF) with different doping levels of nitrogen atoms. At the same time, a porous organic polymer (TP-TPA-POP) with the same framework as TP-TPA-COF but with different structural regularity was also prepared. Based on the characterisation of the three materials, the catalytic properties of the nitrogen content and the regularity of the backbone on the effects of the Knoevenagel condensation reaction were investigated. Studies showed that the yield of Knoevenagel condensation reaction with N-doped TP-TPA-COF reached 98%, which is much higher than that of TP-TTA-COF (without N-doping, 57%) and TP-TPA-POP (amorphous, 62%), respectively. It proves that the doping of nitrogen atoms and the regular structure are more favourable for the catalysis of Knoevenagel condensation reaction by COFs.