Synthesis and proton transfer-linked redox tuning of ruthenium(II) complexes with tridentate 2,6-bis(benzimidazol-2-yl)pyridine ligands

New ruthenium complexes of two tridentate ligands 2,6-bis(benzimidazol-2-yl)pyridine (L7) and 2,6-bis(1-methylbenzimidazol-2-yl)pyridine (L8) have been synthesised. Proton and 13C NMR spectroscopy served well for their characterization, and the observed change. Proton chemical shift yields information about the electron distribution accompanying deprotonation of the ligands. The [RuL72]n+ chelate acta as a tetrabasic acid, with pKa ranging from 2.5 to 10.7, depending on the ruthenium oxidation state. The absorption spectra and oxidation potentials are consequently sensitive to solution pH and to solvent. The proton-coupled oxidative electron-transfer reactions of the complexes afford stable higher oxidation states such as RuIV. The properties of the complexes are discussed in comparison to those of previously reported bis(tridentate ligand)ruthenium compounds.