Pd(ii) unsymmetrical salophen complex immobilized on modified γ-Fe2O3 magnetic nanoparticles: a novel and magnetically recyclable nanocatalyst for selective oxidation of thiols and sulfides.

In this study, an unsymmetrical salophen-type palladium(ii) complex, Pd(salophen-OH), where salophen-OH = 4-[((E)-{(2-[(E)-2-hydroxybenzylidene)amino]phenyl}imino)methyl]benzene-1,3-diol, was synthesized and immobilized on chloro-functionalized γ-Fe2O3 magnetic nanoparticles. Characterization of the γ-Fe2O3@Pd(salophen-OH) nanocomposite via ICP, FT-IR, XRD, FE-SEM/EDX, TEM, and VSM analyses verified the successful attachment of the palladium complex, the formation of a core-shell architecture, and the material's magnetic behavior. The γ-Fe2O3@Pd(salophen-OH) nanoparticles were employed as an efficient heterogeneous catalyst for the selective oxidation of sulfides to sulfoxides using 30% H2O2 as a green oxidant, and for the oxidative coupling of thiols to disulfides with tert-butyl hydroperoxide (TBHP) under ambient conditions. Both transformations proceeded smoothly, affording the desired sulfoxides and disulfides in good to excellent yields with high selectivity. The γ-Fe2O3@Pd(salophen-OH) nanocatalyst was easily recovered using an external magnet and reused for six consecutive cycles without significant loss of catalytic activity. Moreover, FT-IR and XRD tests on the recycled γ-Fe2O3@Pd(salophen-OH) showed that the catalyst kept its structural stability even after multiple cycles. This highlights its durability and potential for reuse in oxidation reactions.