Dinuclear ruthenium and osmium arene trihydrido complexes:: Versatile water-soluble synthons in organometallic chemistry

Recent developments in the chemistry of dinuclear ruthenium arene complexes are reviewed. Although cationic ruthenium and osmium arene trihydrido complexes have been known for more than 20 years, little synthetic use has been made of these unsaturated molecules prior to the discovery of their hydrophilicity. Most salts of the dinuclear cations [(eta(6)-arene)(2)M-2(mu(2)-H)(3)](+) (M = Ru, Os) are soluble not only in polar organic solvents but also in water. The aqueous solutions can be handled without hydrolytic degradation. This property conditions these unsaturated complexes (with an electron count of only 30) to be versatile synthons in organometallic chemistry, especially in reactions carried out in water.