Iron(II) Aminopyridine Macrocycles in Catalytic Oxidations: Structures, Reactivity, and Mechanistic Studies of Reactive Intermediates.
Ye, Wanhua.
2017-04-18T14:05:22.014Z
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Abstract: This document comprises the results of research in the area of olefin epoxidation with new aminopyridine iron(II) macrocycles: identifying structural features and mechanistic studies of reactive intermediates. Advances in our understanding of the mechanistic role of Fe(IV)-oxo intermediates of non-heme iron enzymes, and the accessibility of similar iron(IV) intermediates in synthetic mod... read moreel complexes have prompted investigators to view high-valent iron(IV)-oxo species as key intermediates responsible for oxygen atom transfer to organic substrates in catalytic oxidations. Our lab is interested in using pyridine-macrocycle ligands (PyMACs) to explore the reactivity of the iron complexes in catalytic oxidations. These ligands combine the advantages of macrocyclic polyamines, which prevent iron loss under catalytic conditions by forming thermodynamically and kinetically stable iron complexes, and those of aminopyridine ligands that are capable of stabilizing a variety of iron-based intermediates. The macrocyclic nature of PyMACs may also stabilize the complexes with respect to irreversible oxidative ligand destruction during catalytic processes. In Chapter 2, the study is focused on the role of iron(IV) intermediates in oxidations catalyzed by an iron(II) complex with a pyridine-containing 14-membered macrocyclic ligand L (L = 2,7,12-trimethyl-3,7,11,17-tetra-azabicyclo[11.3.1]heptadeca-1(17),13,15-triene). This complex generates an iron(IV)-oxo intermediate using isopropyl 2-iodoxybenzoate as an oxidant. Spectroscopic characterization of iron(IV)-oxo intermediate and its reactivity with substrates (olefins or triarylphosphines) under stoichiometric or catalytic conditions are reported. In Chapter 3, iron(II) complexes with ligand L (L = 3,7,11-trimethyl-3,7,11,17-tetra-azabicyclo[11.3.1]heptadeca-1(17),13,15-triene) is synthesized and characterized. tert-Butyl hydroperoxide (TBHP) and hydrogen peroxide (H2O2), are used as terminal oxidants in the stoichiometric oxidation of substrates (triaryl phosphines or olefins) and in catalytic epoxidation studies. TBHP and isopropyl 2-iodoxybenzoate were used to generate alkylperoxoiron(III) and oxoiron(IV) species, respectively. The formation and reactivity of these intermediate species was investigated by the stopped-flow methodology. The mechanism of oxygen transfer to organic substrates involving reaction of oxoiron(IV) intermediate was elucidated on the basis of spectroscopic and kinetic data. In Chapter 4, a comparative study examining iron(II) complexes with a series of pyridine-containing macrocycles is reported, including a newly synthesized mononuclear non-heme iron(II) complex bearing a pyridine-containing 17-membered macrocyclic ligand, (L = 7-(3-propylacetamide)-2,12-dimethyl-3,7,11,17-tetra-azabicyclo[11.3.1]heptadeca-1(17),13,15-triene), in order to explore the relevance between the ligand environment and the reactivity of the corresponding oxoiron(IV) species in oxygen atom transfer reactions. The oxidative reactivity studies of oxoiron(IV) intermediate with organic substrates are carried out by monitoring spectral changes of the intermediates under stoichiometric conditions.
Thesis (Ph.D.)--Tufts University, 2011.
Submitted to the Dept. of Chemistry.
Advisor: Elena Rybak-Akimova.
Committee: Terry Haas, Bennett Clay, and William Armstrong.
Keywords: Chemistry, and Inorganic Chemistry.read less - ID:
- mg74qz432
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