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

Abstract

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 pK_a 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 Ru^IV. The properties of the complexes are discussed in comparison to those of previously reported bis(tridentate ligand)ruthenium compounds.