SUBSTITUTIONAL PHOTOCHEMISTRY OF RU(ETA(6)-MES)(2-MES)(CH3CN)(2+)(3) (MES EQUALS 1,3,5-TRIMETHYLBENZENE)()(2) AND RU(ETA(6))

Irradiation of Ru(eta(6)-mes)(2)(2+) (mes is 1,3,5-tri methylbenzene, or mesitylene) in acetonitrile results in the substitution of one mesi tylene ring by solvent to yield the half-sandwich complex, Ru(eta(6)-m es)(CH3CN)(3)(2+). The quantum efficiency of this process exhibits lit tle dependence upon the excitation wavelength or the presence of oxyge n, but varies with solvent in the order acetonitrile > water > acetone . Photolysis of Ru(eta(6)-mes)(CH3CN)(3)(2+) in acetonitrile occurs vi a two competing pathways: substitution of mesitylene by solvent to pro duce Ru(CH3CN)(6)(2+), and exchange of coordinated CH3CN with bulk sol vent. Quantum efficiencies for both pathways increase with decreasing excitation wavelength and, at each wavelength, CH3CN exchange is more efficient than mesitylene substitution. Photochemical mechanisms for t hese processes are discussed and comparisons with related complexes ar e presented. (C) 1997 Elsevier Science S.A.