Browsing by Subject "Ligand design"

Now showing 1 - 3 of 3
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    Design and synthesis of new ligand saffolds and transition metal complexes for small molecule activation
    (2013-08) Miller, Deanna Lynn
    The objective of this thesis is to explore the synthesis of new ligand scaffolds designed to support late first row transition metals and to study their potential for small molecule activation. Many researchers have utilized sterically encumbered ligands to protect reactive metal centers. In the second chapter, the design and synthesis of novel cage ligands featuring a hydrophobic cavity to provide protection to reactive metal centers will be explored. Ideally, the cavity will effectively prevent bimolecular decomposition reactions that often plague small molecule activation. The synthesis and characterization of two cage ligands, a trianionic tri(amido)amine and a neutral tri(amino)amine variant, will be presented. Additionally, the preparation and characterization of the zinc(II) complex of the tri(amido)amine cage ligand will be discussed and its uptake of small molecules explored. In addition to employing protection of reactive metal centers in ligand design, a bio-inspired ligand design will be explored. The biological cofactor dihydronicotinamide adenine dinucleotide (NADH) can efficiently reduce and oxidize substrates through the transfer of a hydride (or a proton and two electrons). The third chapter explores the design and synthesis of a NADH-type ligand scaffold. The systems presented herein have three NADH-like moieties built into the ligand, designed to reduce substrates via either hydride transfer or proton coupled electron transfer. Having three NADH moieties allows for the possibility of multi-electron redox chemistry. The synthesis and characterization of zinc(II) and cobalt(II) complexes will be discussed. Additionally, the reaction of both the NADH ligand and the zinc(II) complex with known hydride acceptors will be explored. Finally, in chapter four, the synthesis and characterization of a family of diiron and iron cobalt bimetallic complexes with a third type of ligand design will be presented. Previous work in the Connie Lu group has shown reactivity toward small molecules using heterobimetallic complexes supported by a tripodal phosphine amide ligand scaffold. Herein, the same ligand scaffold is applied to late transition metals to explore their synthesis, reactivity toward small molecules, and electronic and magnetic properties to allow for a better understanding of metal-metal bonding interactions.
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    Synthesis and reactivity of high-valent copper complexes and the design of copper monooxygenase model complexes
    (2022-02) Bouchey, Caitlin
    Copper plays a vital role in various enzymatic and catalytic transformations. Specifically, copper-oxygen and high-valent copper species are implicated as intermediates in oxidations by metalloenzymes and catalysts. In order to study the nature and the role of copper in these transformations, copper model complexes have been sought after and investigated for their properties and reactivities. This thesis describes several such copper model complexes. Chapter 1 outlines the biological precedence of copper-oxygen complexes in a monooxygenase enzyme and a class of copper complexes that mimic the monooxygenase active site. Additionally, the literature relevant to high-valent copper complexes discussed herein is reviewed. In chapter 2, the development of two biomimetic, monoanionic ligands and their copper complexes is discussed. The characterization of the ligands and complexes and efforts to access copper-oxygen complexes bearing the monoanionic ligands are shown. Chapter 3 details the generation of a new high-valent copper-nitrite complex and its oxidative proton-coupled electron transfer (PCET) and anaerobic phenol nitration reactivity. Mechanistic considerations for the unusual anaerobic phenol nitration are made. Lastly, chapter 4 describes the synthesis and characterization of two copper-amidate complexes and the generation of their high-valent counterparts. The PCET reactivity of the high-valent copper-amidate complexes are contrasted with each other and previous high-valent copper-oxygen complexes. The results from the projects described herein provide insights into copper coordination chemistry, electronic structure, and reactivity, which helps augment the knowledge of copper enzymes and catalysts.
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    Synthesis, characterization, and reactivity of metal-metal bonded complexes with cobalt, iron, and manganese
    (2014-11) Tereniak, Stephen J.
    Metal-metal bonding is important in dirhodium catalysts that mediate carbene insertions into C-H bonds, cyclopropanations, aziridinations, and ylide formations. Additionally, it has been suggested that certain intermediates in NiFe hydrogenases contain a nickel-iron bond. In light of the successful applications of dirhodium complexes in organic chemistry, as well as the role metal-metal bonds play in biology, the design of synthetic bimetallic complexes with mid-to-late first-row transition metals is of great interest. Yet, few examples of mid-to-late first-row transition metal complexes exhibiting metal-metal bonding have been reported, and even more strikingly, very few mid-to-late heterobimetallic complexes have been prepared. In the second chapter of this thesis, the synthesis and characterization of an isostructural series of dicobalt, cobalt-iron, cobalt-manganese, diiron, and iron-manganese complexes supported by a new binucleating ligand is disclosed. The diiron compound has a much shorter crystallographic metal-metal distance than the other four complexes. Experimental and theoretical work suggests that the short iron-iron distance is due to the full delocalization of the d orbitals, which leads to an S = 3 ground state. This is in contrast to the other four bimetallics, in which the magnetic interactions are modeled as high-spin metal centers that antiferromagnetically couple. In the third chapter, the synthesis and characterization of a dicobalt organometallic complex and a series of organometallic aluminum-cobalt complexes is described. Isostructural dicobalt benzyl and aluminum-cobalt benzyl compounds are compared using experiment and theory. A series of C-C bond forming experiments from the reaction of R-X compounds with the metal-cobalt benzyl complexes suggests that both the dicobalt compound and the aluminum-cobalt compound are capable of one-electron chemistry, whereas only the aluminum-cobalt complex undergoes two-electron reactions. These results are explained by the electronic structure of the two compounds: the aluminum-cobalt complex has the aluminum(III)cobalt(I) oxidation state, whereas calculations suggest that the dicobalt complex is cobalt(II)cobalt(II). In the fourth chapter, the synthesis and characterization of a series of hexairon and tetrairon clusters related by one-, two-, or three-electron redox steps is reported. In the fifth chapter, the role of some of these clusters in the dioxygen reactivity of a diiron(II) complex is revealed.