Syntheses, crystal structures and electrochemical properties of a series of ruthenium(II) bipyridine complexes with ferrocene carboxylate ligands

The reaction of Ru(bpy)(2)(PPh3)(CF3SO3), Ru(bpy)(PPh3)(2)(CF3SO3)(2) or Ru(bpy)(2)(CF3SO3)(2) with mono- or di-carboxylate ligands in the presence of triethylamine afforded the heterometallic Ru(II) and Fe(II) complexes [Ru(bpy)(PPh3)(2)(eta(2)-O(2)CFc)](CF3SO3) (1), [Ru(bpy)(2)(PPh3)(O(2)CFc)](CF3SO3) (2), [Ru(bpy)(2) (eta(2)-O(2)CFc)](CF3SO3) (3) and [{Ru(bpy)(2)(PPh3)}(2){O(2)CFcCO(2)}](CF3SO3)(2) (4). The molecular structures of complexes 1 and 2 have been determined by single-crystal X-ray diffraction analysis and show that the ruthenium units are coordinated by the ferrocene carboxylate ligand in a monodentate mode or a bidentate-chelating mode. Electrochemical studies reveal that complexes 1, 2, 3 and 4 contain reversible or quasi-reversible Ru and Fe oxidation waves. The redox potentials have been well ascribed. By comparing the coordination environment of the central ruthenium atoms, we found that the Ru-II/Ru-III redox potential shifted to the negative direction along with the increase of electron-deficient bpy ligands. The redox potentials for the ferrocenecarboxylate ligand ranged from +0.5 to +0.6 V. (C) 2020 Elsevier Ltd. All rights reserved.