Fe-amino acid complexes immobilized on silica gel as active and highly selective catalysts in cyclohexene epoxidation

Abstract

In this work, the syntheses, structure, superoxide dismutase (SOD) activity, and the catalytic use in the oxidative transformations of cyclohexene of covalently grafted Fe(III)-complexes formed with various or various combinations of C-protected amino acid (L-histidine, L-tyrosine, L-cysteine and L-cystine) ligands are presented. The structural features of the surface complexes were studied by XANES/EXAFS and mid/far-IR spectroscopies. The compositions of the complexes were determined by ICP-MS and the Kjeldahl method. The SOD activities of the materials were evaluated in a biochemical test reaction. The obtained materials were used as catalysts for the oxidation of cyclohexene with peracetic acid in acetone. Both covalent grafting and building the complex onto the surface of the chloropropylated silica gel were successful in most cases. In many instances, the obtained structures and the coordinating groups were found to substantially vary upon changing the conditions of the syntheses. All the covalently immobilized Fe(III)-complexes displayed SOD activities, and most of them were found to be capable of catalyzing the oxidation of cyclohexene with appreciably high activities and outstanding epoxide selectivities.

Silica‐Supported 1st Row Transition Metal (Nano)Catalysts: Synthetic and Catalytic Insight

“…The catalyst activity could be improved by adding small amounts of pyrazoles, which were supposed to be coordinated at the metal center. Iron‐amino acid complexes from histidine, tyrosine, cysteine, and cystine were immobilized on silica gel for cyclohexene oxidation showing moderate activity but high selectivity towards 1,2‐epocyclohexane when peracetic acid played the role of oxidant [158] . Moreover, reuse of the catalyst was possible without significant loss of selectivity.…”

“…Iron-amino acid complexes from histidine, tyrosine, cysteine, and cystine were immobilized on silica gel for cyclohexene oxidation showing moderate activity but high selectivity towards 1,2-epocyclohexane when peracetic acid played the role of oxidant. [158] Moreover, reuse of the catalyst was possible without significant loss of selectivity. XAS and EXAFS spectroscopy enable to determine the coordination numbers and geometries around the around the Fe(III) center.…”