New avenues for redox-active ligands: Non-classical reactivity with late transition metals facilitated by o-aminophenol derived architectures

Many homogeneous and heterogeneous catalyst systems contain one or more transition metals. The widespread employment of these metals as catalysts is ascribed to their accessible d-orbitals to activate chemical bonds, and the ability to undergo metal-based oxidation state changes to facilitate desirable chemical transformations. The fine-tuning of homogeneous catalyst systems is commonly achieved by the coordination of (spectator) ligands, which can vary greatly in steric bulk or electron-donating ability. For such ligands the energy required for oxidation or reduction of the ligand is much bigger than that needed to change the oxidation state of the metal. Accordingly, the redox changes required for bond making and breaking processes typically occur at the metal center. Redox-active ligands have more energetically accessible levels for reduction and/or oxidation upon coordination to a metal. As a result, either solely ligand-centered redox processes can occur, with the metal center remaining in the same oxidation state, or more diffuse scenarios, wherein both the ligand and metal change oxidation states in a synergistic fashion. Although initially thought of as a spectroscopic curiosity, redox-active ligands are nowadays recognized for their ability to induce new reactivity at metal centers. Within this thesis we have shown that o-aminophenol derived architectures can give fascinating spectroscopic properties upon coordination to late transition metals. Moreover, these ligands can expand upon a metal’s "common" reactivity by actively taking part in intramolecular redox processes. We have demonstrated that intramolecular single-electron transfer processes can facilitate homolytic bond cleaving reactions and the generation of reactive nitrogen-centered radicals