Abstract of the DissertationPreparation and Properties of Mono- and Bimetallic Paramagnetic
Co Complexes Supported by Tripodal Ligand Frameworks
by
Meghen E. Goulet
Doctor of Philosophy in Chemistry
University of California, Irvine, 2022
Distinguished Professor Andrew S. Borovik, Chair
Many important and synthetically challenging chemical reactions are carried out by
metalloenzymes, including water oxidation, nitrogen fixation, O2 reduction, and oxidation of C–H
bonds in substrates such as methane, fatty acids, and pharmaceutical products. Metalloenzymes are
able to catalyze these reactions in part due to their ability to access reactive intermediates which is
facilitated by the protein host. To replicate these effects synthetically, the Borovik lab designs organic
ligands that incorporate both primary and secondary coordination sphere interactions to control the
local environment within metal complexes. This dissertation presents research that employs these
ligand frameworks in both mono- and bimetallic small molecule Co complexes.
Chapter 1 provides a brief introduction to key features of metalloenzyme active sites that
support their reactivity. A concise overview of relevant synthetic ligand designs is given, in addition
to summaries of the following chapters.
Chapter 2 describes the preparation of mononuclear CoII– and CoIII–OH complexes within
an unsymmetric, hybrid tripodal ligand framework: [H2pout]3–. The characterization of these
complexes is discussed, including the molecular structure of K[CoIIIH2pout(OH)].
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K[CoIIIH2pout(OH)] is paramagnetic, an unusual trait for a CoIII center. The reactivity of
K[CoIIIH2pout(OH)] towards substrates with an O–H bonds is also examined. This work is the first
reactivity study of a CoIII–OH complex.
Chapter 3 describes the preparation of a trigonal monopyramidal, four-coordinate Co complex
supported by the C3 symmetric [poat]3– ligand framework. This complex, K[CoIIpoat] is used in
Chapter 3 – 5 to prepare unsymmetric bimetallic species. Chapter 3 focuses specifically on the
formation of a [poatCoIII–μ-OH–ZnIIMe3tacn]+ complex via a proposed CoII–oxidant adduct that
reacts in the presence of [ZnIIMe3tacn(OTf)2], where Me3tacn is a heterocyclic N-based ligand.
In Chapter 4, the preparation of a [poatCoII–μ-OH–FeIIIMe3tacn]+ complex from K[CoIIpoat]
and O2 in the presence of [FeIIMe3tacn(OTf)2] is discussed. The [poatCoII–μ-OH–FeIIIMe3tacn]+
complex is subsequently oxidized to [poatCoIII–μ-OH–FeIIIMe3tacn]2+ and the changes in the magnetic
coupling between the Co and Fe centers are examined. Mössbauer and EPR spectroscopies support
antiferromagnetic coupling in [poatCoII–μ-OH–FeIIIMe3tacn]+, but ferromagnetic coupling in
[poatCoIII–μ-OH–FeIIIMe3tacn]2+.
Finally, Chapter 5 describes the development of a new series of bimetallic species,
[Mx
IIpoat⋅⋅⋅My
IIMe3tacn]+, (Mx = Mn, Co, Zn; My = Mn, Fe, Co, Cu, Zn). The metal ion coordinated
in the [poat]3– ligand backbone is in a trigonal monopyramidal geometry, which is shielded by the
binding of a [My
IIMe3tacn]2+ solely through the P=O groups. The two metal ions interact through
three, triple-atom N–P=O bridging units and are highly symmetric, crystallizing in the R3 space group.
The metal ions were found to couple ferromagnetically to one another through the N–P=O bridges
and the magnetism of these complexes was studied to determine if the complexes exhibit single
molecule magnetic behavior. While the [CoIIpoat⋅⋅⋅My
IIMe3tacn]+ complexes were most thoroughly
investigated, the [Mx
IIpoat⋅⋅⋅My
IIMe3tacn]+ have also been prepared where Mx = Mn, Zn and My = Mn,
Zn, suggesting that these complexes could be expanded to a wide array of metal ion.