Search

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.

Irradiation of Ru( η 6 -mes) 2 2+ (mes is 1,3,5-trimethylbenzene, or mesitylene) in acetonitrile results in the substitution of one mesitylene ring by solvent to yield the half-sandwich complex, Ru( η 6 -mes)(CH 3 CN) 3 2+ . The quantum efficiency of this process exhibits little dependence upon the excitation wavelength or the presence of oxygen, but varies with solvent in the order acetonitrile > water > acetone. Photolysis of Ru( η 6 -mes)(CH 3 CN) 3 2+ in acetonitrile occurs via two competing pathways: substitution of mesitylene by solvent to produce Ru(CH 3 CN) 6 2+ , and exchange of coordinated CH 3 CN with bulk solvent. Quantum efficiencies for both pathways increase with decreasing excitation wavelength and, at each wavelength, CH 3 CN exchange is more efficient than mesitylene substitution. Photochemical mechanisms for these processes are discussed and comparisons with related complexes are presented.