Water-soluble arene ruthenium complexes: From serendipity to catalysis and drug design

Shortly after the discovery of benzene ruthenium dichloride and some controversy about its polymeric or dimeric nature in the 1960s, the hydrolysis of this material in water to give a mixture of benzene ruthenium aqua complexes was discovered. However, it took a long time until this reaction and the hydrolysis of other arene analogs were used as an entry to the synthesis of water-soluble arene ruthenium complexes. These complexes are able to activate molecular hydrogen in aqueous solution and allow the design of arene ruthenium bioconjugates. They can serve as catalysts or catalyst precursors for hydrogenation and transfer hydrogenation reactions in water and they are at present one of the most promising classes of metal complexes to replace cisplatin in future cancer therapy, due to their inherent cytotoxicity and their good cellular uptake, conditioned by well balanced lipophilic and hydrophilic properties.