Spectroscopic and Structural Characterization of Synthetic Models of Dioxygen-Activating Nonheme Diiron and Monoiron Systems

Abstract

Using monoiron and diiron active sites, Nature has found a way to activate O2 toperform powerful oxidations. Upon the binding of O2 into the active site, the iron centers are oxidized to high-valent intermediates, and these highly oxidized species are able to break strong C-H bonds, such as those found in methane (104.5 kcal/mol). There has been a great interest in understanding the mechanistic cycle of these reactive oxidants as well as how nature can craft active sites that can perform difficult transformations. Understanding how enzymes activate O2 requires the employment of a variety of techniques, including structural characterization through X-ray absorption spectroscopy (XAS), single crystal X-ray diffraction (XRD), and nuclear magnetic resonance (NMR). Other spectroscopic techniques, like electronic absorbance, resonance Raman, and electron paramagnetic resonance (EPR) help further our understanding of the wide variety of these oxygen-activating enzyme active sites. Due to the complexity of handling these enzymes, biomimetic synthetic complexes have been synthesized and investigated, with well over 100 characterized high-valent iron complexes. These small molecules allow for a greater understanding of why Nature employs iron centers to perform biologically vital transformations. In Chapter 2, ultraviolet-visible spectrophotometry (UV-Vis) and resonance Raman spectroscopy have been employed to better understand the role of a proton in helping to regulate the O—O bond cleavage step to unleash a powerful high-valent oxoiron oxidant(V) in a synthetic complex. Chapter 3 is an investigation of synthetic diiron systems whereby the structures of complexes have been structurally characterized using XAS and other techniques. This work is an effort in helping to better understand the mechanism by which diiron enzymes can form high-valent iron centers through the activation of O2. In Chapter 4, a combination of reactivity and spectroscopy has been employed to better understand how electronic parameters and the steric environments can perturb the oxidizing potential of FeIV(O) species. Overall, this thesis demonstrates the power of combining a variety of spectroscopic techniques to help generate and support hypotheses for enzyme mechanisms.