Tripodal Phosphoryl Amide Frameworks: Investigating The Relationship Between High Valent Metal–Oxido And Metal–Hydroxido Complexes.
- Author(s): Oswald, Victoria Frances
- Advisor(s): Borovik, Andrew S
- et al.
Metal ion cofactors within active sites are essential components for many proteins and have been directly linked to function. Active sites contain either a single or multiple metal ion(s) participating in a mixture of covalent and non-covalent interactions that function cooperatively to perform efficient and selective chemical transformations. Non-covalent interactions are often found within the volume of space that surrounds the metallocofactors, denoted as the microenvironment, which influence key properties such as the transfer of protons and electrons. Non-covalent interactions are the major forces that influence the microenvironments within protein active sites with hydrogen bonds (H-bonds) being the most dominant. Using these architectural features as inspiration, the works of this dissertation describes the design, preparation, and characterization of Mn/Fe– oxido and hydroxido complexes supported by frameworks that incorporate phosphoryl amide moieties.
Chapter 2 introduces the development of new ligand frameworks containing phosphorus. The design premise behind the usage of phosphoryl amides was that the deprotonated phosphoryl amide nitrogen atom would produce a ligand field that stabilizes high valent complexes, and that the P=O units would serve as an H-bond acceptor, an auxiliary metal binding site, and produce a negative polarized cavity to help stabilize high valent metal–hydroxido/oxido complexes.
Chapters 3 and 4 describe the development of Mn/Fe–OH complexes of the hybrid ligand [H2pout]3- that installs a combination of two H-bond donors and one H-bond acceptor within the secondary coordination sphere. The [H2pout]3- ligand was used to prepare the MII–OH complexes, which had sufficiently low redox potentials to synthetically prepare its corresponding Mn–O(H) (n = III, IV) analogs.
In Chapter 5 of this dissertation a new high spin, FeIV¬–oxido complex supported by a symmetrical phosphinic amide tripod is discussed along with its reactivity with Lewis acids. A series of LA (LA = Mg2+, Ca2+, Sr2+, Ba2+, and H+) were added to the FeIV–oxido complex and generated distinct FeIV species. The vibrational data shows a clear change in the Fe–O vibrations when Mg2+ or Ca2+ ions are added, corroborating that these ions affect the FeIV–oxido unit. Preliminary data with H+ suggests that protons interact with the FeIV–oxido complex, but not at the FeIV–oxido unit, suggesting that an FeIV–OH species is not produced.
Chapter 6 takes a different approach to generating an FeIV–OH species. The beginning of this chapter discussed the preparation and characterization of low valent Fe–aqua/hydroxide complexes within [poat]3- scaffold. The FeII/III–OH complexes have similar properties as previously developed frameworks; however, once oxidized beyond FeIII–OH, the reactivity is different. The one-electron oxidized complex exhibits magnetic properties that are unprecedented to anything we have seen before and has been assigned as an S = 2 system containing a high spin FeIII center antiferromagnetically coupled to a ligand radical.