Zinc biomimetic catalysts for epoxidation of olefins with H2O2

Abstract

A Zn complex was stepwise intercalated in a Mg/Al layered double hydroxide material (HT) holding phenylalanine in its interlayer spacing. The material was characterized by powder X-ray diffraction, FTIR and solid state 13C NMR spectroscopy. By analogy, the [Zn(phe)(H2O)](NO3) complex bearing deprotonated phenylalanine (phe) amino acid as ligand and a labile water molecule, mimicking biological moieties, was also prepared as model and characterized by HR-MS, FTIR and 1H solution NMR spectroscopy. Both the Zn-containing HT material and model complex were tested in the catalytic epoxidation of cyclooctene, styrene and 1-octene. All tests were carried out with hydrogen peroxide (H2O2) or tert-butylhydroperoxide (TBHP), leading selectively to epoxides in most cases. Both temperature and oxygen source were found to be key factors in controlling epoxide selectivity, especially when using H2O2, where results were outstanding. Furthermore, the reported results show that the catalytic performance of this Zn system is at the same level of similar systems, holding heavier metals and less sustainable, found in the literature, while the Zn-containing HT catalyst had also the advantage of recyclability.