New Supramolecular Structural Motif Coupling a Ruthenium(II) Polyazine Light Absorber to a Rhodium(I) Center

Two new complexes, [(bpy)2Ru(dpp)RhI(COD)](PF6)3 and [(Me2bpy)2Ru(dpp)RhI(COD)](PF6)2(BF4) (bpy = 2,2′-bipyridine, Me2bpy = 4,4′-dimethyl-2,2′-bipyridine, dpp = 2,3-bis(2-pyridyl)pyrazine, and COD = 1,5-cyclooctadiene), representing a new Ru(II),Rh(I) structural motif, have been prepared and characterized by mass spectrometry, 1H NMR spectroscopy, electrochemistry, electronic absorption spectroscopy, and emission spectroscopy. These two complexes represent a new type of supramolecular complex with a [(TL)2Ru(dpp)]2+ (TL = terminal ligand) light absorber (LA) coupled to a Rh(I) center and are models for Ru(II),Rh(I) intermediates in the photochemical reduction of water using dpp-bridged Ru(II),Rh(III) photocatalysts. Electrochemical study reveals overlapping reversible RuII/III and irreversible RhI/II/III oxidations and a quasi-reversible dpp0/– reduction, demonstrating that the lowest unoccupied molecular orbital (LUMO) is dpp(π*) based. The COD ligand is sterically bulky, displaying steric repulsions bet...