Substitutional photochemistry of sandwich and half-sandwich complexes of ruthenium(II)

Ruthenium(II) sandwich complexes of the type Ru( η 6 -arene) 2 2+ (arene is benzene or 1,3,5-trimethylbenzene) undergo photosubstitution of one arene ring by solvent (S) to yield Ru( η 6 -arene)(S) 3 2+ . Reaction occurs from the lowest ligand field triplet state of the complex with a quantum efficiency that decreases with increasing methylation of the arene. Half-sandwich complexes of general formula Ru( η 6 -arene)(L) 3 2+ (L is CH 3 CN or NH 3 ) undergo competitive photosubstitution of arene and L by solvent. The relative importance of these pathways depends upon a number of factors, including excitation wavelength, solvent, and the nature of L. Mechanisms for these photoreactions are discussed and comparisons to earlier studies are presented.