Zeolite-encapsulation copper(II) complexes with 14-membered hexaaza macrocycles: synthesis, characterization and catalytic activity

Abstract

Copper(II) complexes with 14-membered hexaaza macrocyclic ligand “1,3,6,8,10,13-hexaaza cyclotetradecane, 1,8-dimethyl-“[Cu((Me)2[14]aneN6)](ClO4)2” 2; 1,8-diethyl-“[Cu((Et)2[14]aneN6)](ClO4)2” 3; 1,8-dibuthyl-“[Cu((Bu)2[14]aneN6)](ClO4)2” 4; and 1,8-dibenzyl-1,3,6,8,10,13-hexaazacyclotetradecane“[Cu((benzyl)2[14]aneN6)](ClO4)2” 5”, have been prepared by the one-pot template reactions of formaldehyde and ethylenediamine with alkyl and benzyl amine within the cavities of zeolite Y. These complexes were entrapped in the supercage of zeolite Y by a two-step process in the liquid phase: (i) inclusion of a Cu(II) precursor complex, [Cu(en)2]2+-NaY 8, and (ii) in situ one-pot template reaction of the copper(II) precursor complex with the formaldehyde and amine. The new materials “[Cu((Me)2[14]aneN6)]-NaY 9, [Cu((Et)2[14]aneN6)]-NaY 10, [Cu((Bu)2[14]aneN6)]-NaY 11, [Cu((Benzyl)2[14]aneN6)]-NaY 12” were characterized by several techniques: chemical analysis and spectroscopic methods (FT-IR, UV-Vis, XRD, BET, DRS). Analysis of the data indicates that the Cu(II) complexes are encapsulated in the NaY zeolite supercages and exhibit different from those of the free complexes, which can arise from distortions caused by steric effects due to the presence of sodium cations, or from interactions with the zeolite matrix. By comparing the performance of the heterogeneous system with the neat complex in the oxidation of tetrahydrofurane (THF) using hydrogen peroxide as oxygen donor, a protection effect of the matrix over the active center was evidenced by a higher conversion and product selectivity. Encaged complexes yield mainly tetrahydrofurane-2-ol (THF-2-ol) and insignificant amount of tetrahydrofurane-2-one (THF-2-one), while with their homogeneous counterparts, selectivity’s to THF-2-one are higher.