Epoxidation of cyclohexene with K10-montmorillonite and Schiff-base macrocyclic copper complexes

Copper(II) complexes of 12- and 13-membered diaza dioxa Schiff-base macrocyclic ligand, 1,4-diaza-7,10-dioxacyclododeca-1,3-diene, H2[12]1,3-dieneN2O2; 2,3-dimethyl-1,4-diaza-7,10-dioxacyclododeca-1,3-diene, (CH3)2[12]1,3-dieneN2O2; 2,3-diphenyl-1,4-diaza-7,10-dioxacyclododeca-1,3-diene, (C6H5)2[12]1,3-dieneN2O2; 2,4-dimethyl-1,5-diaza-8,11-dioxacyclotrideca-1,4-diene, (CH3)2[13]1,4-dieneN2O2; 2,4-diphenyl-1,5-diaza-8,11-dioxacyclotrideca-1,4-diene, (C6H5)2[13]1,4-dieneN2O2 were entrapped into an montmorillonite-K10 (denoted as K10) by simultaneous/pillaring encapsulation method. In this method the simultaneous encapsulation also occurred but the complex, also dissolved in methanol, was added to the clay dispersion. All materials were characterized by FTIR, DRS, UV–Vis and atomic absorption spectroscopy (AAS). In all cases the copper(II) 12- and 13-membered diaza dioxa Schiff-base complex is mainly physically entrapped within the matrix, although some host–guest interactions with the matrix could be present. All new materials show catalytic activity in the epoxidation of cyclohexene using tert-butylhydroperoxide (TBHP) as oxygen source in solvent. The solids presented high cyclohexene epoxide selectivity and were reused for three times, but a small decrease in the catalytic activity was observed. FTIR spectra of catalysts after the catalytic reactions suggest that during the reaction no structural changes of the K10 took place, but some active phase leaching and deactivation have occurred which are responsible for the decrease in the catalytic activity on reutilisation.