What are non-valent metals

High-valent metal-oxo coordination complexes for homogeneous water oxidation

Project
Subject area Inorganic Molecular Chemistry - Synthesis, Characterization
Funding Funding since 2017
German Research Foundation (DFG) - project number 390531541
The aim of the project is to examine new transition metal complexes, namely high-valent manganese, iron and cobalt complexes, for their catalytic abilities for homogeneous water oxidation and to contribute to the elucidation of the fundamental mechanisms of the underlying O-O binding mechanisms. These goals are to be pursued at the molecular level in a two-step process: 1.) Synthesis with tailor-made trigonal ligands and characterization of the electronic structure of the Mn, Fe and Co-oxo complexes as well as 2.) Reactivity, mechanistic and kinetic studies during complex preparation and oxidative Substrate transformation. Both stages of the process are part of the iterative research plan: characterization of the electronic structure as well as the reactivity and mechanistic studies show structural and functional relationships that enable a well thought-out redesign and improved complex representation. Complex and ligand synthesis is a prerequisite, however, in order to generate the formation of reactive but sufficiently stable species for spectroscopy and reactivity studies. The modular synthesis planning of the envisaged ligands is designed to be adaptable in order to quickly and easily change the ligand framework structure and thus the complex reactivity by synthesis. Tripodal chelate ligands with N-heterocyclic carbene and phenolate arms are specifically synthesized, as they are extremely good at stabilizing unusually high (and low) oxidation states and can be optimized by introducing further functional groups. On the basis of the large number of proposed ligands and developed syntheses for non-heme Fe- and Mn-oxo and especially Co-oxo and per-oxo species, we hope to understand the effects of the primary and secondary ligand interactions on the investigated reactions - especially the effects the ligand frameworks on H2O oxidation and OO bond formation. Detailed spectroscopic investigations are used to differentiate between possible reaction processes - e.g. 2-e oxidation to H2O2 or 4-e oxidation to O2. In order to provide evidence of H2O formation, we will detect H2O2 and / or O2 spectroscopically and compare the identified reaction products with isostructural compounds that have been prepared using alternative synthetic routes, e.g. with classic oxygen transfer reagents. This comparative spectroscopy enables the intermediates observed to be identified. The in operando characterization of the intermediates and the kinetic investigations are carried out with time-resolved UV-Vis electron absorption and IR oscillation spectroscopy and high-resolution cryo-spray mass spectroscopy and EPR spectroscopy. The combination of experiment, spectroscopy and calculation should verify the binding models and at the same time provide feedback for improved ligand and complex synthesis.
DFG procedureSach grants