Ruthenium(ii) complexes incorporating the bidentate ligand containing an imidazolium moiety: synthesis, characterization, and electrochemical properties and their application in a visible-light induced hydrogen-evolving system

Abstract

Two Ru(II) complexes, [(bpy)₂Ru(IL-2)]³⁺ (bpy = 2,2′-bipyridine) (1) and [(phen)₂Ru(IL-2)]³⁺ (phen = 1,10-phenanthroline) (2), have been prepared by using a newly designed bidentate ligand, 1,3-dimethyl-2,3-dihydro-1H-imidazo[4,5-f][1,10]phenanthroline-2-yl (IL-2). The complexes and the bidentate ligand synthesized have been fully characterized by ¹H NMR, ¹³C NMR, high resolution mass spectrometry (HRMS), elemental analysis, and X-ray crystallography in two cases. All the complexes exhibited typical ligand-based π–π* and metal-to-ligand charge transfer (MLCT) bands in the UV and visible regions, respectively. The absorption maxima occurred at 430 and 428 nm with the lower energy shoulder peaks at 463 and 461 nm for 1 and 2, respectively. ³MLCT emissions were observed at 617 and 610 nm, respectively. The electrochemistry exhibited one reversible oxidation (Ru^III/II), and two reversible and one irreversible reductions caused by ligands. A two-component photolysis system consisting of Ru(II) and Pd-precursor complexes has been confirmed to be active for the photo-induced hydrogen production in the presence of triethanolamine (TEOA) as a sacrificial electron donor without an electron mediator (MV²⁺).