Biomimetic carboxylate-bridged diiron complexes : from solution behavior to modeling the secondary coordination sphere
Author(s)Minier, Mikael A. (Mikael Antoine)
Massachusetts Institute of Technology. Department of Chemistry.
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Chapter 1: Understanding the Utility of Hydrogen Bonding Donors in the Secondary Coordination Sphere of Non-heme Metal Complexes Chapter 1 is a mini-review that covers systematic studies on the effect of hydrogen bonding donors on the properties of metal complexes. Generalizing across different metals studied in biomimetic chemistry, the review allows for the comparison between different systems and generalizations are drawn about the effects of secondary coordination sphere hydrogen bond donors. Chapter 2: ¹⁹F NMR Study of Ligand Dynamics in Carboxylate-Bridged Diiron(II) Complexes Supported by a Macrocyclic Ligand A series of asymmetrically carboxylate-bridged diiron(II) complexes featuring fluorine atoms as NMR spectroscopic probes, [chemical formula ...] (10), [chemical formula ...] (11), and [chemical formula ...] (12) were prepared and characterized by X-ray crystallography, M6ssbauer spectroscopy, and VT ¹⁹F NMR spectroscopy. These complexes are part of a rare family of syn-N diiron(II) complexes, [chemical formula ...], that are structurally very similar to the active site of MMOHred. Solution characterization of these complexes demonstrates that they undergo intramolecular carboxylate rearrangements, or carboxylate shifts, a dynamic feature relevant to the reactivity of the diiron centers in bacterial multicomponent monooxygenases. Chapter 3: Structural Characterization of Carboxylate-Bridged and Hydroxo-Bridged Dizinc(II) Complexes Supported by a Macrocyclic Ligand Using a syn-N dinucleating macrocyclic ligand, H2PIM, a doubly carboxylate-bridged dizinc(II) complex, [chemical formula ...] (6) was prepared. In crystallizations of 6, two pseudoisomorphs of [chemical formula ...] (7) were discovered. On route to the synthesis of 6, a zinc complex, [chemical formula ...] (4) was prepared and the product upon reaction with air, [chemical formula ...] (5), was crystallized. Chapter 4: Secondary Coordination Sphere Modulation of Redox Potentials in Azide-Bridged Diiron(II) Complexes Observation that the H₂PIM macrocyclic ligand provides an extra binding site for the binding of small molecules adjacent to corresponding diiron(II) complexes inspired the appendage of a secondary coordination sphere hydroxyl group to the ligand. The new ligand, H₂PIM2, models not only the primary coordination sphere of the diiron sites of methane monooxygenase and toluene/o-xylene monooxygenase, but also that of a local threonine in the secondary coordination sphere. This chapter explores the differences between the PIM system and PIM2 system through the electrochemistry of the azido diiron(II) derviatives. Chapter 5: Synthesis and Characterization of a Linear Dinitrosyl-Triiron Complex Nitric oxide is released during the immune response by the host during bacterial infection. To counteract this response, bacteria have evolved nitric oxide reductases to convert NO to N₂O. Some of these nitric oxide reductases contain a flavodiiron active site that have bridging carboxylates and hydroxides. Only a handful of synthetic complexes currently exist as models for the protein reactivity. Here we report the reaction of [chemical formula ...] (4) with NO(g) and Ph₃CSNO to prepare the dinitrosyl-triiron complex [chemical formula ...] (5). The reaction was monitored by U V-Vis and ReactIR spectroscopy and compound 5 was characterized by X-ray crystallography, 5 7Fe M6ssbauer spectroscopy, Evans' method, and FTIR spectroscopy. The IR spectrum of compound 5 compares favorably to experimental spectroscopic data obtained for the proposed mononitrosylated intermediate of the protein. Chapter 6: Doubly and Triply Carboxylate Bridged Bis(ethylzinc) Complexes and Formation of the ([mu]-Oxo)tetrazinc Carboxylate [chemical formula ...] Ethylzinc 2,6-bis(p-tolyl)benzoate converts between two forms in solution. Through NMR spectroscopic techniques and X-ray crystallography, the species in equilibrium were identified as [chemical formula ...] (1), [chemical formula ...] (2), and diethyl zinc [chemical formula ...]. The equilibrium provides a model for understanding the speciation between doubly and triply m-terphenylcarboxylate-bridged diiron(II) and mononuclear iron(II) complexes. Evidence is presented for the occurrence of coordinatively unsaturated trigonal zinc species in solution. Both 1 and 2 decompose in air to form the T-symmetric oxozinc carboxylate, [chemical formula ...] (3). Appendix A: Synthesis and Characterization of Mononuclear, Pseudotetrahedral Cobalt(III) Compounds The preparation and characterization of two mononuclear cobalt(III) tropocoronand complexes, [chemical formula ...] and [chemical formula ...], are reported. The cobalt(III) centers exist in rare pseudotetrahedral conformations, with twist angles of 65℗ʻ and 74℗ʻ for the [Co(TC-5,5]+ and [Co(TC-6,6)]+ species, respectively. Structural and electrochemical characteristics are compared with those of newly synthesized [chemical formula ...] and [chemical formula ...] analogs. The spin state of the pseudotetrahedral [chemical formula ...] was determined to be S = 2, a change in spin state from the value of S = 1 that occurs in the square-planar and distorted square-planar complexes, [chemical formula ...] and [chemical formula ...], respectively. Appendix B: Synthetic Strategies toward Sterically Demanding Macrocyclic Ligands In order to prevent the formation of iron complexes of nuclearity higher than 2, a picket-fence macrocyclic ligand, H2tipp4PIM was designed. This chapter discusses the progress towards the synthesis of this ligand as well as design strategies.
Thesis: Ph. D. in Inorganic Chemistry, Massachusetts Institute of Technology, Department of Chemistry, 2015.Cataloged from PDF version of thesis. Vita.Includes bibliographical references.
DepartmentMassachusetts Institute of Technology. Department of Chemistry
Massachusetts Institute of Technology