Photoinduced Electron Trnsfer Reactions of Transition-Metal Complexes with Amines. Mechanistic Studies of Alternate Pathways to Back Electron Transfer

Article abstract of DOI:10.1021/ja00537a037

A study of the photoreduction of polypyridyl complexes of ruthenium(II) and iron(II) by amines is reported.While two of the ruthenium(II) complexes studies are found to give "permanent" reduction on irradiation in the presence of triethylamine in anhydrous media, the two irom complexes studied and (bpy)₃Ru^{II 2+} are found not to give a permanent reduction.Nonetheless, all complexes studied are found to give acetaldehyde when irradiation is carried out in the presence of water, suggesting that an irreversible oxidation of triethylamine is taking place.Studies with spin traps such as nitrosodurene also result in interception of alkyl radicals derived from triethylamine and N,N-dimethylaniline.The combination of spin trapping and product studies points to a mechanism in which the amine radical cation formed in the initial electron transfer quenching step rapidly reacts with a second molecule of amine to give an alkyl radical whose fate is subsequently determined by the properties and redox behavior of the specific metal complex involved.