Catalytic behavior of 1-(2-pyridylazo)-2-naphthol transition metal complexes encapsulated in Y zeolite

The goal of this study is the preparation of new heterogeneous catalysts to be used in the oxidation of organic molecules under mild conditions. The metals in zeolite (M–Y) were prepared by the ion exchange method. The in situ encapsulation of selected transition metal complexes as a guest, namely cobalt(II), nickel(II), copper(II), and zinc(II), with 1-(2-pyridylazo)-2-naphthol (PAN) ligand in supercages of Y zeolite (host) was accomplished by the flexible ligand method. The coordination geometry of neat and Y-encapsulated metal complexes has been determined by molecular simulations. The resulting catalysts were fully characterized by different techniques (FTIR, SEM, and chemical analysis), and the results indicated that complexes were encapsulated in supercages of Y zeolite. Catalytic studies were performed in liquid phase for cyclohexene and cyclohexanol oxidations, by using tert-butylhydroperoxide as the oxidizing agent at 40 and 60 °C, respectively. All prepared catalysts exhibited catalytic activity for the oxidation reactions.

Graphical abstractZeolite-supported transition metal complexes with PAN ligand have been prepared by flexible ligand method; these guest–host catalysts are more active in cyclohexanol oxidation than cyclohexene. Heterogenized zinc(II) complex is the best catalyst among the complexes analyzed; in addition, it was shown that it possesses distinct geometrical features.Figure optionsDownload full-size imageDownload high-quality image (97 K)Download as PowerPoint slideResearch highlights► Transition metal PAN complexes were encapsulated in NaY by flexible ligand method. ► Encapsulation of complexes has marked effects on catalytic activity in oxidation. ► The heterogenized Zn(II) complex shows the highest substrate conversion among complexes analyzed. ► The low activity of Ni(II) can be due to low concentration of four-coordinating species.