Cu(II) Schiff base complexes on montmorillonite as nano-reactor heterogeneous catalysts for the epoxidation of cyclooctene: synthesis, characterization and immobilization

Abstract

Cu(II) tetradentate Schiff base complexes of N,N′-(bis(pyridin-2-yl)formylidene)ethane-1,2-diamine (pfed), N,N′-(bis(pyridin-2-yl)formylidene)propane-1,3-diamine (pfpd), N,N′-(bis(pyridin-2-yl)formylidene)benzene-1,2-diamine (pfbd), N,N′-(bis(pyridin-2-yl)formylidene)cycohexane-1,2-diamine (pfcd) and N,N′-(bis(pyridin-2yl)formylidene)meso-stilben-1,2-diamine (pfmd) were synthesized, characterized and immobilized on sodium montmorillonite. These catalysts were characterized by X-ray diffraction, IR spectroscopy, diffuse reflectance spectra (DRS) and atomic absorption spectroscopy. The IR and DRS data of the heterogeneous catalysts show that copper(II) complexes were physically entrapped within sodium montmorillonite. The basal spacing (d001) of heterogeneous catalysts indicates that Cu(II) Schiff base complexes were fixed in the axial direction into the interlayer of montmorillonite. All new heterogeneous catalysts show excellent catalytic activity in the epoxidation of cyclooctene using tert-butylhydroperoxide in acetonitrile. The supported [Cu(pfed)] exhibited a moderate 74 % selectivity for epoxidation with 76 % conversion. The catalytic activity and selectivity of heterogeneous catalysts have not changed after three times of reusing.