Geometric and Electronic Structure Contributions to Reactivity of Mn- and Fe-hydroxo Complexes

With the support of the Chemical Mechanism, Function, and Properties Program of the Division of Chemistry, Professor Tim Jackson of the Department of Chemistry at the University of Kansas is developing new types of manganese and iron complexes that mimic intermediates in biological metal-dependent enzymes. The goal of this research is to use these new complexes to improve proton-coupled electron-transfer reactions, which are ubiquitous in biological and synthetic catalyst processes. This project will thus lead to a better understanding of biological processes and contribute to the design of new synthetic catalysts. Both manganese and iron are abundant metals; their increased use in industrial catalysis could improve manufacturing by reducing costs and reliance on rare and precious metals. The project lies at the interface of inorganic chemistry, physical chemistry, and biochemistry and is therefore well suited to provide an outstanding educational and training experience for scientists at all levels. Graduate students working on this project will travel to National Labs to receive training and perform research on specialized instrumentation. This project focuses on structure-reactivity relationships for concerted proton-electron transfer (CPET) reactions of manganese(III)- and iron(III)- hydroxo complexes. Transition metal-hydroxo complexes are used in several biological enzymes to perform proton-coupled electron transfer reactions. The proposed studies involve strategies to tune the primary and secondary coordination sphere of manganese-hydroxo and iron-hydroxo complexes to control their physical properties and chemical reactivity, probing the relationship between structure and function. Comparisons of reactivity of manganese-hydroxo and iron-hydroxo complexes are hindered by the paucity of complexes with the same coordination sphere. This project will generate new manganese-hydroxo and iron-hydroxo complexes to understand how geometric, electronic, and thermodynamic factors combine to effect reactivity. In this project, a combination of synthetic, kinetic, spectroscopic, and computational methods will be used to address the following questions: 1) Can second-sphere hydrogen bonding acceptors be used systematically to tune the thermodynamic and kinetic properties of manganese-hydroxo complexes? 2) How does the geometric and electronic structure of iron-hydroxo complexes control their reactivity? 3) Can the reactivity of metal-hydroxo complexes be enhanced by incorporating weak oxygen-donors in the primary coordination sphere? This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.