Copper(II)-Purine Complexes Encapsulated in NaY Zeolite

Y-encapsulated CuII–purine complexes were synthesized, characterized and studied in the catalytic oxidation of cyclohexene. Encapsulation was achieved by ion-exchanging the complex from aqueous solutions containing both the purine ligand, 9-methyl-6-(methylamino)purine, and copper, in different pH, with a purine/CuII molar ratio of 5:1. The resulting materials were characterized by surface analysis (XPS, SEM and XRD), chemical analysis, spectroscopic methods (EPR, FTIR and UV/Vis) and thermal analysis (TGA), which indicated that the CuII–purine complexes were effectively encapsulated in NaY, most probably inside the supercages, without any modification of the morphology and structure of the zeolite. Different CuII–purine complexes were formed, depending on the pH during synthesis. The coordination geometry of Y-encapsulated CuII–purine complexes was obtained with preferentially 1:2 and 1:3 Cu/L stoichiometry: complexes A and B (1:2) and complex C (1:3). Complex A was formed at pH 7, and complexes B and C (Scheme 2) were formed at pH = 5.4. Oxidation of cyclohexene with tBuOOH (TBHP) as the oxygen source, gave 2-cyclohexene-1-one, 2- cyclohexene-1-ol, cyclohexene oxide and 3-tert-butylcyclohexenyl peroxide