Multiple one-electron oxidation and reduction of trinuclear bis(2,4-pentanedionato)ruthenium complexes with substituted diquinoxalino2,3-a:2',3'-cphenazine ligands

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Polyhedron, 26 (13): 3409--3418 (2007)
DOI: 10.1016/j.poly.2007.03.030


The complexes (m3-L1/L2)Ru(acac)23, acac- = 2,4-pentanedionato, L1 = 2,3,8,9,14,15-hexachlorodiquinoxalino2,3-a:2',3'-cphenazine and L2 = 2,3,8,9,14,15- hexamethyldiquinoxalino2,3-a:2',3'-cphenazine, undergo stepwise 1-electron oxidn. involving a total of three electrons and stepwise 1-electron redn. with three (L2) or four electrons (L1). All reversibly accessible states were characterized by UV-visible-NIR spectroelectrochem. Oxidn. leads to mixed-valent intermediates (μ3-L)Ru(acac)23+ and (μ3-L)Ru(acac)232+ of which the RuIIIRuIIRuII combinations exhibit higher comproportionation consts. Kc than the RuIIIRuIIIRuII states - in contrast to a previous report for the unsubstituted parent systems (μ3-L3)Ru(acac)23+/2+, L3 = diquinoxalino2,3-a:2',3'-cphenazine. No conspicuous intervalence charge transfer absorptions were obsd. for the mixed-valent intermediates in the visible to near-IR regions. The monocations and monoanions were characterized by EPR spectroscopy, revealing rhombic Ru(III) type signals for the former. Electron addn. produces Ru(II) complexes of the reduced forms of the ligands L; a high resoln. EPR spectrum with 14N and 35,37Cl hyperfine coupling and negligible g anisotropy was found for (μ3-L1)Ru(acac)23-. DFT calcns. of (m3-L1)Ru(acac)23 confirm several ligand-centered low-lying unoccupied MOs for redn. and several metal-based high-lying occupied MOs for electron withdrawal, resulting in low-energy metal-to-ligand charge transfer (MLCT) transitions. on SciFinder(R)



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