Cobalt complexes with redox-active anthraquinone-type ligands

Abstract

Three anthraquinone-type multidentate ligands, HL1-3 (HL = 2-R-1H-anthra[1,2-d]imidazole-6,11-dione; HL1: R = (2-pyridyl), HL2; R = (4,6-dimethyl-2-pyridyl), HL3; R = (6-methoxy-2-pyridyl)), were prepared, and their complexation behaviour was investigated. Three bis-chelate cobalt complexes with the formula [CoII(L1-3)2]·n(solv.) (1, 2, and 3 for HL1, HL2, and HL3, respectively), in which the ligands adopted tridentate binding modes, were synthesized and structurally characterized by single-crystal X-ray analyses. Electrochemical studies of 1-3 in CH2Cl2 reveal three reversible redox waves, assigned to ligand and cobalt-centred processes. Additional complexes were obtained in which HL1 adopted a bidentate binding mode, stabilising the mono-chelate [CoII(HL1)(NO3)2(DMF)2] (4) species and tris-chelate [CoIII(L1)3] (5) complex in which the cobalt ion was in its 3+ state. The electrochemical properties of complex 5 were investigated in DMF, and the Co(ii)/Co(iii) redox couple was found to be negatively shifted compared to that of complex 1, while the ligand-based processes became irreversible. Tridentate chelation is found to stabilise the anthraquinone ligands and unlocks their redox multi-stability.

The strongin vitroandvivocytotoxicity of three new cobalt(ii) complexes with 8-methoxyquinoline

“…6 These activated Co( ii / iii ) complexes include hydroxamatocobalt( ii ) complexes, 7 salicylaldehyde-derivative copper( ii ) complexes, 8 phen-dicarboxylic acid based cobalt( ii ) antitumor drugs, 9 cobalt( ii ) oxoisoaporphine complexes, 10 2-benzimidazolyl-pyridine copper( ii ) complexes, 11 thiosemicarbazone cobalt( ii ) complexes, 1 a ,12 diamidonaphthalene cobalt( ii ) complexes, 13 cobalt dioxolene/isonicotinic compounds, 14 tris(2-pyridylmethyl)amine cobalt pro-drugs, 15 cobalt( ii ) pyridyl complexes, 16 and anthraquinone-type cobalt complexes. 17…”

“…6 These activated Co(II/III) complexes include hydroxamatocobalt(II) complexes, 7 salicylaldehyde-derivative copper(II) complexes, 8 phen-dicarboxylic acid based cobalt(II) antitumor drugs, 9 cobalt(II) oxoisoaporphine complexes, 10 2-benzimidazolyl-pyridine copper(II) complexes, 11 thiosemicarbazone cobalt(II) complexes, 1a,12 diamidonaphthalene cobalt (II) complexes, 13 cobalt dioxolene/isonicotinic compounds, 14 tris(2-pyridylmethyl)amine cobalt pro-drugs, 15 cobalt(II) pyridyl complexes, 16 and anthraquinone-type cobalt complexes. 17 Many different metal 8-hydroxyquinoline derived compounds can function as important DNA inhibitors, 18 protein synthesis inhibitors, 19 amyloid-β (Aβ) oligomer drugs, 20 photosensitizers, 21 mitochondrial apoptosis related antineoplastic agents, 22 bFGF-mediated angiogenesis specific inhibitors, 23 topoisomerase IIa inhibitors, 24 telomerase inhibitors, 25 cell autophagy inductors, 26 and so on. In particular, a series of cobalt(III) complexes of 8-hydroxyquinoline and its derivatives has been designed, showing remarkable antitumor activity.…”

The (Dioximate)NiII/I2 System: Ligand Oxidation and Binding Modes of Triiodide Species

“…A wealth of studies of redox-active metal complexes reported in the literature are aimed at developing metal–organic conductive materials, metal–organic frameworks (exhibiting charge-transfer, , semiconducting or conducting capabilities , ), and noninnocent ligand-supported transition metal molecular catalysts . In this area of research, iodine-containing systems play a significant role and varieties of (metal complex)/I 2 combinations have been reported to produce mixed-valence species along with a diversity of polyiodides.…”