Cycloruthenated complexes: pH-dependent reversible cyclometallation and reactions with nitrite at octahedral ruthenium centers

A cycloruthenated 2-phenylimidazole: chromogenic sensor for nitrite in acidic buffer and fluoride in CH3CN

A cycloruthenated 2-phenylimidazole as a colorimetric sensor can detect fluoride in CH3CN by a great red-shift in absorption. However, it demonstrated sensitivity and selectivity to nitrite rather than fluoride in acidic buffer.

Dissociation of Bipyridine and Coordination with Nitrosyl: Cyclometalated Ruthenium Nitrosyl Complex

A novel family of ruthenium nitrosyl complexes [Ru(bpy)(C^∧N)(MeCN)NO](PF₆)₂ (2a-2e, bpy = 2,2'-bipyridine, HC^∧N = 2-phenylpyridine and its derivatives) has been prepared by reacting cyclometalated ruthenium complexes [Ru(bpy)₂(C^∧N)][PF₆] (1a-1e) with NO⁺, which were comprehensively characterized by mass, IR, NMR, and UV-vis spectra as well as the single-crystal X-ray structure determinations. Herein, the coordination geometry of Ru atoms in 2a-2e is a distorted octahedron and {Ru^II-NO⁺}⁶ is present in these complexes. Theoretical calculations suggest that the reactions involving dissociation of one bipyridine and coordination with NO⁺ proceed spontaneously (ΔG < 0) and the transformation from 1a-1e to the intermediates is dominated by substituents (ΔG_RI varies from -1.19 to -1.53 eV), which influence the binding energy between Ru(II) and NO⁺ in complexes 2a-2e (-89.42 to -101.17 kcal/mol) and thus control the photorelease of NO on a certain scale. The weak absorption bands in the visible region could be attributed to the contribution of dπ(Ru^II) → π*(NO⁺), which were enhanced greatly under light, indicating the possible release of NO. The photoinduced NO, as well as singlet oxygen (¹O₂), was then confirmed by EPR spectra, and the amount of NO released from 2a-2e was estimated via Griess reagent assay. The cytotoxicity of these complexes with or without visible light irradiation was also investigated using an MTT assay.

First cycloruthenation of 2-alkenylpyridines: synthesis, characterization and properties

Several cyclometalated ruthenium complexes 1-5 with 2-alkenylpyridines as C,N-chelating ligands were synthesized and then characterized by NMR, MS, IR and UV-Vis spectra. According to the single crystal of complex 2, it is evident that carbon from vinyl group is successfully bonded to Ru(ii) center. Moreover, the Ru-N bond trans to the Ru-C bond is elongated (2.127(5) Å), which is consistent with the strong trans effect of the carbon atom compared to that of the nitrogen atom. With different electron-donating groups linked to vinyl, these complexes exhibited regular changes in MLCT absorption bands, which were identified by UV-Vis and CV spectra in combination with DFT and TD-DFT. Interestingly, protonated intermediate species of these complexes in acidic solutions were tracked by the absorption changes and MS spectra, which displayed a possible protonation process of these complexes with the cleavage of Ru-C σ bonds.

A highly sensitive and selective colorimetric probe based on a cycloruthenated complex: an Hg2+-promoted switch of thiophene coordination

A cyclometalated ruthenium complex [Ru(pthb)(bpy)2]+ (1, bpy = 2,2'-bipyridine, Hpthb = 3,3-dimethyl-2-(5-pyridylthiophen-2-yl)vinyl-benzo[e]indolium-1-propylsulfonate) could be converted from a C-coordinated structure to non-metallated species with N,S-bonded Hpthb upon treatment with mercury(ii) ions in water. Strikingly, the switch in the coordination mode resulted in a great absorption change along with a change in the solution color of 1 from dark red to light yellow. Therefore, 1 can be used as a colorimetric probe to detect mercury(ii) ions by the naked eye. Although the emission was not observed for 1 in water, it still demonstrated an appreciably low detection limit of 21 nM by using UV-Vis absorption spectroscopy, which was comparable with those of some probes determined by ratiometric fluorescence spectroscopy.