High Valent Metal-Oxo Corrolazines: Synthesis, Characterization, and Reactivity

High-valent metal-oxo species are important intermediates in biological and synthetic systems and perform difficult oxidation reactions such as hydroxylation of unactivated C–H bonds. Due to the inherent instability of these intermediates, it remains challenging to study factors that control their reactivity. The corrolazine ligand, which is a modified porphyrinoid framework, is able to stabilize metal ions in high oxidation states. This has allowed for spectroscopic characterization and mechanistic study of high-valent metal-oxo complexes. This thesis is focused on the preparation and characterization of high-valent metal-oxo corrolazine complexes with an emphasis on reactivity in O–H or C–H bond cleavage reactions. Chapter 1 provides an introduction to the importance of metal-oxo species in biology, valence tautomerism as a way to stabilize formally high oxidation states in oxo-metalloporphyrinoid complexes, Lewis acids as a way to control reactivity in biomimetic complexes, and a summary of previous work on the synthesis, characterization, and reactivity of high-valent metal-oxo corrolazines. Chapter 2 describes the synthesis and characterization of two high-valent metal-oxo corrolazine complexes, MnV(O)(TBP8Cz) and CrV(O)(TBP8Cz). The H-atom abstraction reactivity of the two complexes were compared and the MnV(O) was found to be more reactive than the CrV(O) complex. The difference in H-atom abstraction reactivity was rationalized using thermodynamic arguments. The formation of a valence tautomer of MnV(O)(TBP8Cz) with the nonmetallic Lewis acid B(C6F5)3 to give MnIV(O–B(C6F5)3)(TBP8Cz•+) is described in Chapter 3. The reactivity of MnIV(O–B(C6F5)3)(TBP8Cz•+) with H-atom donor substrates was tested and compared to the ZnII adduct and the starting MnV(O) complex. In Chapter 4, the characterization of MnIV(O–LA)(TBP8Cz•+) complexes (LA = Zn(OTf)2 and B(C6F5)3) by X-ray absorption spectroscopy (XAS) is described. An expanded reactivity study of MnIV(O–LA)(TBP8Cz•+) complexes (LA = TFA, Zn(OTf)2, B(C6F5)3, and HBArF) with C–H bonds was undertaken, and the reaction rates were found to be entirely dependent on the strength of the Lewis acids. In Chapter 5, a novel, electron-deficient high-valent manganese-arylimido corrolazine complex, MnV(NC6Cl3H2)(TBP8Cz), is synthesized and characterized. The electronic structure and corresponding reactivity of this compound could be controlled by the addition of either a weak acid (TFA) or strong acid (HBArF). In Chapter 6, the synthetic methodology of a new corrolazine ligand with para-isopropylphenyl substituents is described