Palladium Nanoparticles Stabilized in Ionic Liquid-Based Periodic Mesoporous Organosilica: An Efficient Heterogeneous Catalyst for Oxidative Acylation of Ketones

Novel heterogeneous catalytic system comprised of palladium nanoparticles (NPs) immobilized into the ionic liquid based periodic mesoporous organosilica (Pd@PMO-IL) have been described for the model acylation reaction toward the facile construction of acylated ketones. A straightforward grafting method has been adopted for the functionalization of PMO containing 1-methyl-3-(trimethoxysilylpropyl)-imidazolium chloride (IL) by utilizing uncondensed alkoxy and hydroxy groups, thereby eliminating the need for an additional silicon source. The synthesized catalyst- Pd@PMO-IL was characterized by XRD, N2 adsorption/desorption, TGA, FT-IR, 29Si(CP-MAS), 13C(CP-MAS)-NMR, XPS, ICP-OES, FE-SEM, and HR-TEM techniques to confirm the anchoring of 1-methyl-3-(trimethoxysilylpropyl)-imidazolium chloride and Pd in the catalyst. The catalyst Pd@PMO-IL demonstrated high catalytic activity in the model acylation reaction, along with other aldehyde derivatives to produce corresponding acylated ketones from moderate to excellent yields. Results from XPS analysis revealed the in-situ reduction of PdII in the fresh catalyst to Pd0 at the reaction condition. HR-TEM analysis confirmed the presence of 5-9 nm size of Pd NPs formed inside the mesopores of PMO-IL support. Further, the catalyst was recycled for four consecutive cycles and showed insignificant loss in catalytic activity. The imidazolium in the PMO-IL support could be the reason for successful stabilization and uniform distribution of insitu generated Pd NPs in the catalyst, resulting in highly active and recyclable catalytic system.