Synthesis, characterization and catalytic activity of <i>μ</i>-phenoxodicopper complexes with bi-Schiff bases derived from α-amino acids

Abstract

Several dicopper complexes and relevant dimetal complexes have been synthesized with the bi-Schiff base ligands formed by 2,6-diformyl-4-methylphenol (HDFA) with glycine, L-phenylalanine, L-histidine or histamine, and characterized by elemental analysis, IR, UV-vis, CD, EPR, and XPS. Using the Cu₂ complexes as models of dopamine <i>β</i>-hydroxylase

(D<i>β</i>H) and peptidylglycine <i>α</i>-hydroxylation monooxygenase (PHM), we have investigated the epoxidation of styrene with PhIO as the monooxygen donor. The results show that styrene oxide is the main product of epoxidation of styrene, and that no benzaldehyde is formed as the by-product. Turnover numbers (TNs) of each model complex in epoxidation of styrene are 4.7, 3.1, 2.8, and 2.5 mol^-1 Cu₂, for the complex derived from glycine, phenylalanine, L-hi stidine, and histamine, respectively. EPR study reveals that a hypervalent iodine oxo intermediate CuCu←O-IPh might be formed as the active species, ruling out the possibility of formation of the hypervalent metal-oxo species Cu(III)=O in the oxidation course.