Cooperativity Between Porosity and Phosphorus Content in Polyphosphamides for Improving Catalytic Appel Reactions

Although phosphamide-based organic polymers (POPs) are promising flame-retardant materials, they can also act as promising heterogeneous catalysts due to the presence of redox-acitve -NH-P(O) unit. Recently, POPs have been used as catalysts for photochemical, electrochemical CO₂ reduction or CO₂ utilization, and water-splitting reactions. Herein, a nitrogen-rich mesoporous POP is synthesized via covalently linking the -NH-P(O) moiety to a pyridine ring. In this study, POP with a BET surface area of 22 m² g^-1 with a phosphorus content of 15.1%, is explored for the catalytic Appel reaction with a highest TON of 696. Here, POP is compared with two analogous polyphosphamides, PPA (nonporous) and p-PPA (porous). PPA with a phosphorus content of 19.7% shows a lower TON of 462. p-PPA with a BET surface area between 1.773 m² g^-1 and 17.1% of phosphorus resulted in a TON of 561. The better catalytic performance of POP could be ascribed to an increase in the BET surface area. A wide range of substrate scope is achieved for both bromo and chloro Appel products. Post-characterization data after five consecutive cycles confirm the sustainability of POP. The cooperative action of redox-active phosphorus-center and high-porosity of POP lead superior catalytic activity.