Bowl-Shaped Phosphate-Based Polymer Nanocontainers Loaded with Pd Nanoparticles for Catalytic C–C Coupling Reactions

Interesting nanoscopic morphologies which can support nanoparticles in order to generate heterogeneous catalysts are highly useful in various catalytic organic transformations. Herein, we report the design and synthesis of phosphate-based nanocontainers promoting the catalytic activity of Pd nanoparticles generated in situ from Pd(II) salts. The polymers were synthesized via a time- and cost-efficient, less rigorous synthetic route (i.e., 30 min stirring at room temperature). Based on the linker length in these phosphate-based polymers, the morphological changes were observed from a sphere-rich morphology to more a bowl-like morphology. Interestingly, the precursor/POCl 3 ratio contributed to the drastic change in the morphology. The bowl-shaped morphology could load Pd nanoparticles as high as 36.46%, while only 12.46% loading was observed for the spheres. The as-synthesized Pd nanoparticle-loaded organic polymer networks were channelized as a robust catalytic platform for C–C cross-coupling reactions with isolated yields up to 99% and recyclability for five runs without a rigorous protocol. The bowl-shaped morphologies performed better in catalytic C–C coupling reactions as compared to the spherical ones due to the higher Pd nanoparticle loading in the former. Apart from that, a theoretical study elucidated the pivotal role of phosphate moieties in stabilizing the in situ generated Pd nanoparticles. The prepared catalysts were robust and air stable, which make them an alternative to expensive, air-sensitive, commercial Pd catalysts.