Formation, electrochemical and radical scavenging properties of novel ruthenium compounds with N, X-donor (X = O, N) heterocyclic chelators

• Ruthenium compounds with N, X-donor (X = O, N) heterocyclic chelators.
• Metallic compounds with distorted octahedral geometries.
• Lower IC50 values of metallic compounds than their corresponding free-ligands.
• Two redox couples of the dinuclear compound, (μ-Cl)2[RuIIICl(Hchpr)(PPh3)]2(4).

Herein, we communicate the formation of novel ruthenium compounds with N, X-donor (X = O, N) heterocyclic-derived ligands. A paramagnetic ruthenium(IV) complex, [RuCl(pho)(bzca)(PPh3)](1) (pho = 2-aminophenolate; bzca = 2-carboxylate-1H-benzimidazole) was isolated from the reaction of the ruthenium(II) precursor, trans-[RuCl2(PPh3)3] and 2-((1H-benzimidazole)methylamino)phenol (Hbzap). The 1:1 molar reaction between the same metal precursor and N-(benzoxazole)-2-hydroxybenzamide (H2bhb) led to the formation of cis-Cl, trans-P-[RuIII(Hbhb)Cl2(PPh3)2](2). The dinuclear ruthenium compounds, (μ-Htba,Cl)2[RuIICl(PPh3)]2(3) (Htba = N-(thiophene)methyl-benzoxazole-2-amine) and (μ-Cl)2[RuIIICl(Hchpr)(PPh3)]2(4) (H2chpr = 2-amino-3-((tetrahydro-2H-pyran-4-ylimino)methyl)-4H-chromen-4-one) were formed from the equimolar ratio coordination reactions between trans-[RuCl2(PPh3)3] and the respective free-ligands, Htba and H2chpr. These metal complexes were characterized via IR-, NMR- and UV–Vis spectroscopy, molar conductivity measurements and structural elucidations were confirmed by single crystal X-ray analysis. The X-ray studies revealed that all the metallic compounds exhibited octahedral geometries and that the Hbzap free ligand has undergone a unique molecular transformation to afford the pho and bzca bidentate chelators in 1. The electrochemical properties of the respective metal complexes were investigated by voltammetric analysis. The cyclic voltammograms (CVs) of 1–3 showed one redox couple while within the CV of the dinuclear compound 4, two redox couples were observed. The ligands and their metal complexes were also subjected to DPPH radical scavenging studies. The IC50 values showed that all the metallic compounds have higher radical scavenging activities than their corresponding free-ligands and the natural antioxidant, Vitamin C.

In the cyclic voltammogram (CV) of the dinuclear compound (μ-Cl)2[RuIIICl(Hchpr)(PPh3)]2(4) (H2chpr = 2-amino-3-((tetrahydro-2H-pyran-4-ylimino)methyl)-4H-chromen-4-one), two redox couples were observed while in the squarewave voltammogram (SWV) at lower potentials relative to each redox process (viz.A and B), two smaller peaks are observed. The peaks indicated by the arrows are due to the second metal centre undergoing analogous redox processes.Figure optionsDownload as PowerPoint slide