Stille- and Ullmann-type coupling reactions catalysed by palladium supported biochar/g-C₃N₄-polyethyleneimine as a...

Biochar, a carbon-rich product from biomass pyrolysis, is gaining traction as a soil amendment, catalyst support, and pollutant adsorbent. This study synthesized a novel Pd@biochar/g-C₃N₄-PEI heterogeneous catalyst for C-C and C-N coupling reactions to produce biphenyls and aryl amines. Biochar/g-C₃N₄ was produced through the pyrolysis of walnut shells at 550 °C for 2 hours. Toluene diisocyanate was used to covalently bond PEI to the biochar/g-C₃N₄ surface, followed by the immobilization of palladium nanoparticles on this modified surface. The PEI modifier facilitates the dispersion and stabilization of the Pd nanoparticles, thereby promoting the coupling reactions. Pd@biochar/g-C₃N₄-PEI characterization using FT-IR, BET, SEM, TEM, TGA, ICP, EDS, and XRD confirmed the successful incorporation of PEI and Pd nanoparticles onto the biochar/g-C₃N₄ composite. The catalytic activity of Pd@biochar/g-C₃N₄-PEI was evaluated through the Stille coupling reaction and C-N coupling reactions, demonstrating high efficiency and recyclability. The catalyst exhibited excellent performance in the synthesis of various biphenyl derivatives using different aryl halides and triphenyltin chloride. Similarly, in the synthesis of aryl amines, the catalyst showed remarkable activity with various aryl halides and amines. Furthermore, the catalyst could be recycled and reused for at least five consecutive runs without significant loss of activity, highlighting its potential for sustainable applications in organic synthesis.