Zeolite-Encapsulated Transition Metal Chelation Reactions

The encapsulation of transition metal complexes within zeolite frameworks has attracted significant attention due to the resulting materials’ enhanced catalytic, structural, and thermal properties. In this study, a series of triazole-based Schiff base ligands were synthesized and used to prepare metal complexes with Cu(II), Ni(II), and Fe(II), which were then encapsulated into Na–Y zeolite using the flexible ligand method. The encapsulation was carried out through ion exchange followed by coordination within the supercages of zeolite-Y. The resulting encapsulated complexes were characterized by various spectroscopic and analytical techniques including ¹H NMR, ¹³C NMR, HRMS, IR, and powder X-ray diffraction (XRD). Spectroscopic data confirmed the successful formation of metal–ligand complexes and their immobilization within the zeolite framework. IR spectroscopy indicated coordination through azomethine nitrogen and phenolic oxygen atoms. XRD analysis demonstrated that the zeolite’s crystallinity remained intact after metal loading and encapsulation, with additional diffraction lines indicating successful complex formation within the supercages. Catalytic studies on the hydroxylation of phenol using H₂O₂ as an oxidant revealed that the encapsulated metal complexes showed moderate activity with high selectivity toward catechol. Among the tested catalysts, Cu- and Fe-based systems exhibited superior performance. The encapsulated complexes were reusable with no significant loss of activity, as evidenced by similar IR and XRD profiles post-reaction.