Intramolecular electron transfer from Mn or ligand phenolate to photochemically generated RuIII in multinuclear Ru/Mn complexes.: Laser flash photolysis and EPR studies on photosystem II models

In a mononuclear Mn-IV and a trinuclear Mn-II complex, the ligands of which contain electron-rich phenols (coordinated to the Mn('s)) and covalently attached ruthenium(II) 2,2'-trisbipyridyl(=bpy)-type groups, intramolecular electron transfer (ET) from the phenolate ligand tin the mononuclear Mn-IV complex) or from a Mn-II tin the trinuclear Mn-II complex) to the photochemically (lambda(exc) = 455 nm) generated Ru-III takes place with k greater than or equal to 5 x 10(7) s(-1), giving rise to the corresponding phenoxyl radical (complexed to Mn-IV) or to Mn-III, respectively. Thus, in the trinuclear Mn-II complex, the source of the electron that reduces the photogenerated Ru-III(bpy(.-)) moiety is a Mn-II, in contrast to the situation with the mononuclear Mn-IV complex, where the electron stems from a phenolate. The half-life of the coordinated phenoxyl-type Ru(bpy)/Mn complex las produced in the presence of [Co-III(NH3)(5)Cl](2+)) is of the order 0.5--1 ms. The Ru(bpy) compound containing three (phenolate-ligated) Mn-II atoms is the first example of a photochemically induced intramolecular ET from a multinuclear Mn cluster to an attached "sensitizer", and the Ru complex containing one (phenolate-ligated) Mn-IV is the first case of an ET from a synthetic Mn-IV-coordinated phenolate to a photochemically produced oxidant (Ru-III).