Continuous-flow synthesis of Pd( <scp>ii</scp> )-anchored amino-functionalised magnetic silica nanoparticles as a robust recyclable catalyst for aqueous Sonogashira cross-coupling

A robust and magnetically recoverable palladium nanocatalyst, Fe₃O₄@SiO₂-NH₂-Pd(ii), was prepared through a scalable continuous-flow coprecipitation/silanisation strategy and evaluated in Sonogashira cross-coupling reactions in water. Although amino-functionalised magnetic silica supports have been reported, their use as heterogeneous catalysts for aqueous Sonogashira coupling has received comparatively limited attention. Under the optimised conditions, using water as the sole reaction medium, CuI/PPh₃ as the cocatalytic system, and triethylamine as the base, a broad range of iodoanilines and terminal alkynes underwent efficient coupling to afford the desired products in up to 99% isolated yield within short reaction times. The catalyst showed excellent durability and was readily recovered by magnetic separation and reused for at least 15 consecutive cycles with minimal palladium loss, as confirmed by ICP-OES analysis. Hot-filtration and recyclability studies indicate that the reaction proceeds predominantly through a heterogeneous pathway, with at most a minor contribution from soluble palladium species. Hammett analysis revealed clear substituent effects on the reaction rate, providing useful mechanistic insight into the catalytic cycle. The combination of continuous-flow synthesis, aqueous-phase catalysis, and magnetic recyclability highlights the practical potential of this nanocatalyst for more sustainable carbon-carbon bond formation.