Project Details
Projekt
High-Valent Metal-Oxo Coordination Complexes for Homogenous Water Oxidation
Subject Area
Inorganic Molecular Chemistry - Synthesis and Characterisation
Term
from 2017 to 2024
Project identifier
Deutsche Forschungsgemeinschaft (DFG) - Project number 390531541
The project seeks to study the potential of mononuclear first-row transition metal complexes, namely manganese, iron, and cobalt complexes, as catalysts for homogenous water oxidation and to elucidate the fundamental mechanism of O-O bond formation. We will aim at gaining molecular insight by applying a two-step approach: (a) the synthesis and electronic structure characterization of high-valent Mn-, Fe- and Co-oxo complexes in custom-tailored, trigonal ligand environments and (b) reactivity-, mechanistic-, and kinetic studies of their generation and oxidative substrate transformations, including water, and related O-O bond formation. Both steps of the research plan are part of an iterative approach: The electronic characterization, reactivity, and mechanistic studies will create insight into the structure-function relationships and allow for the re-design of new complex generations. The basis for all research will be the synthesis of custom-tailored chelating ligands and their corresponding trigonal precursor complexes, prerequisite for the formation of reactive species with lifetimes amendable to spectroscopic and reactivity studies. The highly modular synthesis of the proposed N-anchored tris-carbene and/or tris-phenolate ligand framework is sufficiently adaptable to swiftly vary the secondary coordination environment. The N-heterocyclic carbene and phenolate ligands of the tripodal chelators are carefully chosen due to their remarkable ability to stabilize unusual high (and low) metal oxidation states, and will be further optimized by introducing additional functional groups to the ligand framework. With all proposed chelators and the synthetic protocols for non-heme Fe-, Mn-, and particularly Co-oxo and -peroxo species at hand, we hope to reveal the effects of secondary interactions on oxidative reactivity with special emphasis on all aspects affecting H2O/substrate oxidation and O-O bond formation. Detailed spectroscopic investigations will aim at distinguishing reaction outcome, e.g., 2-e- oxidation to H2O2 or 4-e- oxidation to yield O2, and reaction mechanisms. To obtain evidence for water oxidation, the generation of H2O2 and/or O2 in the product mixture will be verified. We will complement the spectroscopic investigations by also studying compounds obtained via alternative synthetic routes; e.g., by employing various oxygen transfer reagents. Comparative spectroscopy is expected to give independent verification of the intermediates. In operando characterization of intermediates and kinetic studies will be pursued by time-resolved UV-Vis electronic absorption and IR vibrational spectroscopy as well as high-resolution cryo-spray mass spectrometry and EPR spectroscopy. The combined use of experiment, spectroscopy, and (time-dependent) density functional theory will assist to validate bonding models and mechanisms, investigate oxidizing properties, and create informational feedback looping back to ligand- and complex synthesis.
DFG Programme
Research Grants
