Control of thermal and photochemical reaction pathways by NO2 pendants in macrocyclic complexes: The redox photochemistry of Cu(10-methyl-1,4,8,12-tetraazacyclopentadecan-10-Y)2+, Y = NO2, NH2, in charge transfer and ligand field excited states

The irradiation of Cu(10-methyl-1,4,8,12-tetraazacyclopentadecan-10-NO2)X+, X = halide, HCO2−, CH3CO2− and C6H5CH2CO2−, in deaerated CH3CN or CH3OH at 350 nm resulted in the reduction of the pendent NO2 to NO. Flash photolysis revealed the formation of the nitroso products via the photo-induced oxidation of the axial ligand X−. Intermediates in a 10 ns–1 s time scale have been tentatively assigned as species formed by the addition of the X radicals to the NO2. Similar redox processes were observed when the irradiation of the complexes was carried out in the ligand field band, λexc = 560 nm. Conversion of the ligand field excited states to X− to Cu(II) charge transfer excited state account for the photoreactivity of the former excited states.