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Title:Bio-inspired first-row transition metal complexes for small molecule activation
Author(s):Park, Yun Ji
Director of Research:Weitzel, Alison R
Doctoral Committee Chair(s):Weitzel, Alison R
Doctoral Committee Member(s):Girolami, Gregory S.; Lu, Yi; Guironnet, Damien
Department / Program:Chemistry
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):Secondary coordination sphere
Nitrite reduction
Nitrate reduction
catalytic nitrite reduction
catalytic nitrate reduction
Abstract:Secondary coordination spheres play many important roles in the activity and function of metalloenzymes: they can help stabilize reactive intermediates and shuttle protons or electrons over the course of enzymatic transformations. Accordingly, there have been numerous efforts to mimic these advantageous structural and functional features; indeed, secondary coordination spheres are now employed in a number of synthetic inorganic systems. Our lab has recently designed first-row transition metal complexes bearing secondary coordination spheres. Such complexes have been designed to: 1) be tautomerizable to traverse between hydrogen bond donating and accepting within the secondary coordination 2) facilitate activation of molecules such as O2, NO2- and NO3- 3) catalytically reduce nitrogen-containing oxyanions. In the case of the latter, mechanistic studies have been performed to understand the role of the secondary coordination sphere, revealing its ability to stabilize intermediate as well as shuttle protons/electrons. Early work focused on the synthesis of a tautomerizable ligand platform and its metalation with various first-row transition metal centers. This ligand platform can tautomerize from a pyrrole-2-imine to an azafulvene-amine form, resulting in either hydrogen bond acceptors or hydrogen bond donors in the secondary coordination sphere depending on the binding mode. The synthesis and characterization of a series of Mn(II) complexes with this platform have been described. Of especial importance, intramolecular hydrogen bond interactions between bound substrates and the secondary coordination sphere, as well as independent tautomerization of each arm of the ligand platform, have confirmed that our metal complexes are useful to mimic metalloenzyme. Interested in probing the reactivity of these metal complexes towards biologically relevant molecules, O2, NO2- and NO3- were reacted with metal derivatives of the ligand platform. Upon addition, high-valent Mn(III) and Fe(III) complexes were generated, with noticeable stabilization of the generated species by the secondary coordination sphere. Furthermore, in order to assess the possibility of rendering these reactions catalytic, reduction of the Fe(III) complexes back to the starting Fe(II) complexes was undertaken and accomplished. This result intrigued me and led me to study the catalytic reduction of the nitrogen-containing anions in particular given their significant interest in biological and environmental studies. Mechanistic studies revealed the importance of the secondary coordination sphere in stabilizing intermediates, as well as shuttling protons and electrons throughout the catalytic reaction. Thus, this research demonstrates that metal complexes bearing flexible secondary coordination sphere can model functional and structural features of metalloenzymes, thereby providing important insights into the design of new catalysts to address unmet needs.
Issue Date:2016-11-30
Rights Information:Copyright 2016 Yun Ji Park
Date Available in IDEALS:2017-03-01
Date Deposited:2016-12

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