Immobilization of copper Schiff base complexes in zeolite matrix: Preparation, characterization and catalytic study

New zeolite-immobilized hybrid catalysts Cu(NO2-salen)–NaY have been prepared by encapsulating copper(II) Schiff base complexes [where NO2-salenH2 is N,N′-(ethylene)-bis-(5-nitro-salicylaldiimine)] in NaY zeolite matrix. The hybrid materials have been characterized by UV–vis, IR and EPR spectrometry and by X-ray powder diffraction analysis. The neat copper(II) Schiff base complex [Cu(NO2-salen)(EtOH)] (1) has also been synthesized and characterized. A brilliant color change (green–gray) has been observed when the complexes are immobilized in zeolitic matrix. X-ray powder diffraction analysis of Cu(NO2-salen)–NaY catalysts reveals that the structural integrity of the mother zeolite in the hybrid material remained intact upon immobilization of the complex. Spectroscopic studies indicate that coordination geometry of the complex undergoes a significant distortion when it is entrapped in the zeolite cavity. While Cu(NO2-salen)–NaY catalysts showed moderate to excellent catalytic activity and product selectivity in the oxidation reactions, the pure complexes Cu(NO2-salen) remained virtually catalytically inactive in these reactions. The efficiency of the catalysts depends on the stereo-electronic properties of the copper Schiff base moiety.

On immobilization in zeolite matrix the [Cu(NO2-salen)(EtOH)] complex moiety showed a remarkable color change from green to gray. Spectroscopic analysis shows the complex moiety undergoes a severe distortion after immobilization. An excellent catalytic performance of the newly prepared hybrid catalysts was observed in oxidation of phenol and 1-naphthol. Figure optionsDownload as PowerPoint slide