The present research project focuses on the synthesis and structural characterization of new mono- and multinuclear arene ruthenium complexes that are soluble in water and inert towards hydrolysis, with the aim of exploiting their inherent catalytic or biological potential. Background Although being the cheapest of all noble metals, ruthenium has almost no industrial application and was only scarcely used in catalytic reactions, until the discovery of highly enantioselective ruthenium-based hydrogenation catalysts by R. Noyori and of efficient ruthenium-based olefin metathesis catalysts by R. H. Grubbs. These two major discoveries led to the Nobel prizes of 2001 and 2005 and also stimulated the coordination chemistry of ruthenium. Aim Within this project, we propose to work on three main topics involving three Ph. D. students: Mononuclear arene ruthenium complexes containing N,O-chelating ligands as catalysts in aqueous solution, Trinuclear arene ruthenium clusters with biologically active substitutents for anti-cancer drug development, and Bimetallic arene ruthenium-tin complexes for various catalytic applications. Significance While water-soluble organometallics in general are still very rare, arene ruthenium complexes with this particular property, the chemistry of which we have pioneered, open new perspectives for use as catalysts in aqueous solution and as potential anti-cancer drugs.