Date of Award:
Doctor of Philosophy (PhD)
Chemistry and Biochemistry
Lisa M. Berreau
The work presented in this dissertation has focused on synthesizing complexes of relevance to dioxygenase enzymes that oxidatively cleave aliphatic carbon-carbon bonds. The goal of this research was to elucidate mechanistic aspects of the activation of aliphatic carbon-carbon bonds towards cleavage by reaction with oxygen, and also investigate the regioselectivity of these reactions. The oxidative cleavage of a variety of enolizable substrates has been explored by utilizing several transition metal complexes supported by an aryl-appended tris(pyridylmethyl)amine ligand.
In order to probe the widely-accepted “chelate hypothesis” for how changes in regiospecificity are achieved as a function of metal ion, we synthesized the compound [(6Ph2TPA)Fe(PhC(O)COHC(O)Ph)]OTf. Based on UV-vis and IR spectroscopy, the acireductone enolate was found to bind via a six-membered chelate ring. By comparison with the reactivity of [(6Ph2TPA)Ni(PhC(O)COHC(O)Ph)]ClO4, we determined that the chelate hypothesis was an insufficient explanation of the observed regioselectivity. Rather, ferrous ion-mediated hydration of a vicinal triketone intermediate was the key factor in determining the regioselectivity of the C-C cleavage reaction.
We have developed a high-yielding synthetic route to protected precursors of C(1)H acireductones. Preparation of the complexes [(6Ph2TPA)M(PhC(O)COCHOC(O)CH3)]ClO4 (M = Fe, Ni) followed by judicious choice of deprotecting conditions allowed us to investigate the oxygen reactivity of a mono-nuclear complex with a dianionic acireductone substrate for the first time. This provides a promising strategy to continue investigations of complexes of relevance to the enzyme- substrate adduct of the acireductone dioxygenases.
Divalent late first-row transition metal complexes have been used to investigate some new strategies for the activation of dioxygen and subsequent cleavage of C-C bonds. We have utilized photoreduction of a Ni(II) center to generate a highly O2-reactive Ni(I) fragment that leads to cleavage of a chloro-diketonate substrate. Additionally, we have found a Cu(II)-mediated thermal cleavage of chloro-diketonate substrates at room temperature. This reaction is interestingly accelerated by the addition of a catalytic amount of chloride ion.
Allpress, Caleb J., "Oxidative Aliphatic Carbon-Carbon Bond Cleavage Reactions" (2013). All Graduate Theses and Dissertations. 2003.
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