ORGANOMETALLIC AQUA IONS OF THE TRANSITION-METALS

A state-of-the-art report on organometallic water complexes of the general composition [L(pi)M(H2O)(n)](n+), where L(pi) is a carbon pi ligand, arene, cyclopentadienyl (pentamethylcyclopentadienyl, Cp*) or olefin. Systems studied to date are [Cp(2)(*)Ti(H2O)(2)](2+), [Cp(*)Cr(H2O)(3)](2+) [Cp*Co(Rh,Ir)(H2O)(3)](2+), [(arene)Ru(Os)(H2O)(3)](2+), [(TMT)Ru(H2O)(3)](2+) (TMT = tetramethylthiophene), [(COD, NBD)Ru(H2O)(4)](2+) (COD = 1,5-cyclooctadiene; NBD = norbornadiene), [(CO)Ru(H2O)(5)](2+), [(C(4)R(4))M(H2O)(3)](2+) (M = Ni, Pd, Pt) as well as some olefin aqua complexes of Rh(I). In many of these systems, the tripodal oxygen ligand [CpCo{PO(OR)(2)}(3)](-) can serve as a model for three coordinated water molecules, where tripod complexes are stabilized in comparison with analogous water complexes. Structural, electrochemical and kinetic parameters of water exchange are discussed.