Date of Award:

2013

Document Type:

Dissertation

Degree Name:

Doctor of Philosophy (PhD)

Department:

Chemistry and Biochemistry

Advisor/Chair:

Lisa M. Berreau

Abstract

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 [(6-Ph2TPA)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 [(6-Ph2TPA)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 [(6-Ph2TPA)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.

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Chemistry Commons

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