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Abstract

In nature, redox enzymes such as copper amine oxidase are used for selective oxidation of organic compounds.[1,2] These enzymes regulate their reactivity through electron transfer between the central copper atom and a redox redox-active cofactor.cofactor.[3] In the reduced form, a temperature temperature-dependent electron transfer equilibrium is established. established.[4] Inspired by such equilibria, this work develops redox-active ligands that have easily controllable reactivity in copper and cobalt complexes. Guanidino-functionalized aromatics (GFA) are particularly suitable for this. It can be shown that optimal conditions for electromerism can be created through careful selection of guanidino groups and additional substituents. If cobalt is used as the center of the metal complex, control of the electronic structure of the corresponding bisguanidine complex can be achieved for the first time by using the coligand, acetylacetonate. With the help of a specifically selected bisguanidine, the first stable mononuclear copper complex can be prepared with quantitative electromerism between 200 and 300 K. In addition to the temperature, the equilibrium depends on the choice of solvent. The transition is facilitated by the presence of an entatic state. It can be shown that external effects, such as the solvent contribution to the entropy change, exceed internal effects such as the redox potential. The ability to switch between the copper(I) and copper(II) electromers via intramolecular electron transfer offers the opportunity for biomimetic regulation of the reactivity of these complexes. In a systematic analysis, this is used for the first time for GFA with regard to electron self-exchange rates between homoleptic, diamagnetic, monocationic copper(I) complexes and their corresponding paramagnetic dicationic copper(II) complexes. This shows a drastic influence of the electronic structure of the paramagnetic complexes on the speed of self-exchange. The speeds differ by several orders of magnitude depending on the bisguanidine chosen. In addition to the direct use of the homoleptic copper complexes, it is also possible to convert them into active dinuclear biomimetic copper-oxygen complexes. Here, too, the difference in reactivity between the complexes of the various bisguanidines can be seen in the reaction with phenolates. These can convert the phenolates into the corresponding catechol at different rates.