Ligand-Metal Electron Transfer Processes in Complexes of Late Transition Metals with Redoxactive Guanidine Ligands: Fundamental Understanding and Applications in Redox Catalysis

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Coordination compounds with redox-active ligands are currently intensively studied, due to the additional possibilities that arise from ligand redox-activity. A redox-active ligand could act as electron reservoir to enhance substrate activation in catalytic applications. Moreover, redox-active ligands often are present as radical ligands, and the increased spin density on the ligand leads to a special, ligand-centered reactivity. Finally, the properties (e.g. Lewis acidity) of a metal directly bound to a redox-active ligand change with the redox state of the redox-active ligand. My research group studies coordination compounds with redox-active guanidine ligands. These ligands could be devided into two classes, the Guanidino-Functionalized Aromatics (GFAs), consisting of two or more guanidino groups directly attached to an aromatic core, and the urea azines and related compounds, consisting of two guanidinyl groups (or related groups) that are directly connected to each other via an N-N bond. Both compound classes are of relevance for the planned studies. The project is composed of two sub-projects, TP1 and TP2. The directed stimulation of intramolecular electron-transfer processes by a variety of different stimulants is the main topic in TP1. In difference to the first funding period that concentrated on preferably small bis- and tetrakisguanidine ligands, redox-active oligoguanidines, built of two or more electronically coupled redox-active units, are included into the studies. The fundamental studies in TP1 are the basis for some of the work in TP2 on bond activations and catalytic applications with coordination compounds with redox-active guanidine ligands. Moreover, proton-coupled electron transfer reactions with free redox-active guanidines are studied within TP2.