Mechanistic Studies of Aliphatic Ligand Hydroxylation of a Copper Complex by Dioxygen: A Model Reaction for Copper Monooxygenases

Abstract

Mechanistic studies on the aliphatic ligand hydroxylation in a copper complex of tridentate ligand 1a {N,N-bis[2-(2-pyridyl)ethyl]-2-phenylethylamine} by O2 have been performed in order to shed light on the structure and reactivity of the active oxygen species of our functional model for copper monooxygenases (Itoh, S.; et al. J. Am. Chem. Soc. 1995, 117, 4714). When the copper complex [CuII(1a)(ClO4)2] was treated with an equimolar amount of benzoin and triethylamine in CH2Cl2 under O2 atmosphere, efficient hydroxylation occurred selectively at the benzylic position of the ligand to provide oxygenated product 2a {N,N-bis[2-(2-pyridyl)ethyl]-2-phenyl-2-hydroxyethylamine} quantitatively. An isotope labeling experiment using 18O2 confirms that the oxygen atom of the OH group in 2a originates from molecular oxygen. Spectroscopic analyses using UV−vis, resonance Raman, and ESR on the reaction of [CuI(1a)]+ and O2 at low temperature show that a μ-η2:η2-peroxodicopper(II) complex is an initially formed intermed...