Studying the Structural and Electronic Configurations during Photocatalytic Activation of O2 at a Diiron(II) Complex

Abstract

Several mono and carboxylate-bridged diiron nuclear enzymes are critical in activating dioxygen in biological processes such as DNA synthesis, hydrocarbon metabolism and cell proliferation1. Iron-containing enzymes such as cytochrome P450, peroxidases, catalases and methane monooxygenase (MMO) have been shown to activate dioxygen by using two electrons and protons to produce iron (IV) oxo intermediates2. The remarkable efficiency of these enzymes is attributed to formation of iron(IV) cations which serve as active oxidants in enzymatic reactions and can attack C-H bonds of a wide range of hydrocarbon substrates. It is widely postulated that ferryl-oxo species are key intermediates in the mechanism of cytochrome P450 and MMO. However due to the complexity of protein environments in biological iron enzymatic systems, monitoring the structural changes occurring during dioxygen activation is a complex undertaking.This project serves to study the light driven activation of a well characterized artificial analogue of an diiron MMO enzyme, (µ-peroxo) (µ-carboxylato) diiron(III) complex, [Fe2(µ-O2)(N-EtHPTB)(µ-PhCO2)]2+ in a chromophore/diiron complex assembled unit. Such types of assemblies provide new avenues for study of catalytic reaction mechanisms. They are promising examples of artificial molecular systems leading to dioxygen activation as visible light is efficiently absorbed at the chromophore, and light energy is in turn converted into a chemical potential via an electron relay through charge accumulation processes at the iron metal center. Formation of high valent iron peroxo species have been shown by UV-Vis, EPR and Resonance Raman spectroscopy as well as X-ray spectroscopic analysis. XANES and EXAFS revealed formation of an iron peroxo and oxo species with shorter bond distances and different coordination numbers.(1) Do, L. H.; Hayashi, T.; Moenne-Loccoz, P.; Lippard, S. J. J.Am.Chem.Soc. 2010, 132, 1273.(2) Lawrence Que, J.; Y.N.Ho, R. Chem.Rev 1996, 96, 2607.