Mastering artificial water oxidation is a key step on moving away from fossil fuels toward a carbon emission-free society. Unfortunately, the crucial chemical transformation of this reaction, the O-O bond formation, is still not well understood, even though there are various known active water oxidation catalysts, such as Ru-based catalysts bearing a Py5 ligand. Those were recently investigated both experimentally and using a static density functional theory (DFT) approach based on geometry

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... mizations. In this work, we shed light on the O-O formation catalyzed by those Ru-based complexes, utilizing enhanced sampling techniques such as the Bluemoon ensemble and metadynamics together with high-performance DFT-based molecular dynamics simulations. This allowed unprecedented detailed insights into the process of the oxygen-oxygen bond formation and also extended the view on the reaction network and the flexibility of the product state because of the consideration of the dynamics at ambient conditions. Our model system contained both the catalyst and a large number of explicit water molecules which can participate in the reaction and stabilize intermediates. Moreover, it is demonstrated how crucial the choice of the collective variable is in order to capture relevant features of the studied reaction.