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Synthesis and applications of high-spin iron tetra-azamacrocyclic complexes
Ochoa, Samantha Brewer
Ochoa, Samantha Brewer
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2018
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Abstract
Herein we describe the synthesis, characterization, and role several iron complexes in the coupling of pyrrole and phenylboronic acid to form 2-phenylpyrrole. The oxidation state and spin state of the iron complexes were characterized using X-ray crystallography, UV-vis absorbance spectroscopy, cyclic voltammetry, and in some cases electron paramagnetic reasonance spectroscopy. Furthermore, the results indicate that the iron(III) complexes are essential for catalytic and regioselective production of the 2-phenylpyrrole product. The complexes were compared to evaluate the effect of five properties on catalyst reaction yields: the coordination requirements of the catalyst, half-potential, topological constraint/rigidity, N-atom modification(s), increasing oxidative stability of the complex, and geometric parameters.^The need for two labile cis-coordination sites was confirmed based on a 42% decrease in catalytic reaction yield observed when complexes containing penta-dentate ligands were used in place of complexes with tetra-dentate ligands. A strong correlation between iron(III/II) redox potential and catalytic reaction yields was also observed, with [Fe2+L6(Cl)2] providing the highest yield (81%, -405 mV). A Lorentzian fitting of redox potential versus yields predicts that these catalysts can undergo more fine tuning to further increase yields. Interestingly, the remaining properties explored did not show a direct, strong relationship to catalytic reaction yields. Furthermore, the role of the sacrificial oxidant, the lack of radical participation, and the formation of æ-oxodiiron species was established leading to a more detailed mechanistic cycle. Finally, a library of five pyclen-based ligands have been developed for use as iron and europium chelators.^A preliminary investigation into iron PCTA complexes indicate that the iron center can bind to all seven of the ligand donors, however, the iron complex does not afford a CEST signal. Establishing that heptadentate ligands containing carboxylic acid pendent arms are not ideal for the developments of iron PARACEST agents.
Contents
Subject
Subject(s)
Iron.
Carbon.
Iron compounds.
Macrocyclic compounds.
Carbon.
Iron compounds.
Macrocyclic compounds.
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Dissertation
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1 online resource (xviii, 152 pages) :
Department
Chemistry and Biochemistry