Four-Electron Oxidative Dehydrogenation Induced by Proton-Coupled Electron Transfer in Ruthenium(III) Complex with 2‑(1,4,5,6-Tetrahydropyrimidin-2-yl)phenolate

New ruthenium­(II or III) complexes with general formula [Ru­(O-N)­(bpy)2]n+ (O-N = unsymmetrical bidentate phenolate ligand; bpy = 2,2′-bipyridine) were synthesized, and their crystal structures and electrochemical properties were characterized. RuII complexes with 2-(2-imidazolinyl)­phenolate (Himn–) or 2-(1,4,5,6-tetrahydropyrimidin-2-yl)­phenolate (Hthp–) could be deprotonated by addition of excess KOtBu, although the deprotonated species were easily reprotonated by exposure to air. Unlike these RuII complexes, their RuIII analogs showed interesting ligand oxidation reactions upon addition of bases. With [RuIII(Himn)­(bpy)2]2+, two-electron oxidation of Himn– and reduction of the RuIII center resulted in conversion of the 2-imidazolinyl group to a 2-imidazolyl group. On the other hand, the corresponding Hthp– complex exhibited four-electron oxidation of the ligand to form 2-(2-pyrimidyl)­phenolate (pym–). These aromatization reactions of imidazolinyl and 1,4,5,6-tetrahydropyrimidyl groups were also achieved by the electrochemically generated RuIII complexes.