Phosphazene-Covalent Organic Framework-Encapsulated Palladium Nanocubes as a Robust Catalyst for Suzuki, Heck, and Sonogashira Cross-Coupling Reactions

In this work, we exploited the notable advantages of using phosphazene-based covalent organic frameworks (P-COF) as supports for highly distributed and utilization of active palladium metal sites, exhibiting excellent catalytic performance. Here, we present a sustainable heterogeneous nanocatalyst consisting of a P-COF encapsulated with palladium salt (Pd(OAc)2) for cross-coupling reactions, such as Suzuki–Miyaura, Mizoroki–Heck, and Sonogashira reactions. The electron-rich heteroatoms (P, N) within the P-COF framework effectively anchor the active sites (Pd), and this demonstrates an excellent catalytic performance and cyclic stability in cross-coupling reactions. Various characterization techniques, such as TEM, SEM-EDX, TGA, XPS, PXRD, BET, and FTIR analysis, were used to characterize the synthesized Pd-incorporated P-COF (Pd@P-COF) as a nanocatalyst. As a result, this sustainable catalyst exhibits a good to excellent yield for all the cross-coupling reactions under mild conditions, and it has excellent tolerance to the functional groups and wide substrates bearing electronic diversity at low catalyst loading. Furthermore, the recovered nanocatalyst of Pd@P-COF was subjected to recyclability, which shows there is no remarkable loss in its catalytic activity. This work highlights the importance of rational P-COF skeleton design in developing efficient catalytic systems and highlights the promising potential of Pd@P-COF in sustainable catalysis, with minimal loss of metal centers from the P-COF.