Oxygen-activating diiron-enzymes are found in all aerobic organisms and utilize a diiron site to perform demanding chemical transformations. The major aim of this research project is to gain insight into the mechanism of oxygen-activation at diiron-enzyme active sites through the synthesis and characterization of high-valent, high-spin diiron-oxo complexes that mimic the structure and reactivity of key reaction intermediates. Specifically, novel diiron complexes will be utilized to model the reactive species of soluble methane monooxygenase (sMMO), an enzyme that utilizes methane as its sole source of carbon. The sequestration of methane by methanotropic bacteria is responsible for the elimination of nearly a billion tons of this potent greenhouse gas per year. In addition, there is considerable industrial interest in replicating the sMMO reaction to provide an environmentally-friendly process to generating methanol as a means of safely transporting natural gas reserves and as a chemical feedstock. The enzyme ribonucleotide reductase (RNR) also contains a similar diiron site that initiates long-range electron-transfer to the enzyme active site and is essential in DMA biosynthesis. Thus, understanding how the diiron site of sMMO and RNR activates oxygen to carry out their respective functions will have broad environmental and social implications. The crucial reactive intermediate in oxidizing methane to methanol is performed at a poorly understood diiron(IV)-oxo species known as intermediate Q, which is produced via the diiron(lll)-peroxo intermediate, P. Building upon the recent successes of generating high-valent diiron-complexes, this proposal describes the synthetic route to designing novel ligand motifs and small-molecule diiron model complexes that reproduce the geometric and electronic structures of P and Q. These diiron-complexes will be characterized by a variety of spectroscopic and structural methods, including electronic absorption, resonance Raman, Mossbauer and X-ray absorption spectroscopies, and their reactivity towards organic substrates will be evaluated.
This proposal outlines the synthesis of small-molecule diiron-complexes that replicate the structure and reactivities of important biological species and aims to further our understanding of how processes that require oxygen-activation are carried out at diiron centers by these enzymes. Additionally, this project may lead to better catalysts that will allow chemists to utilize oxygen to carry out environmentally friendly transformations of hydrocarbons, thereby reducing greenhouse emissions.
