Synthesis, X-ray structure, spectroscopic electrochemistry, anti-nociceptive activity and DFT study of cis-[Ru(EPh3)(L)Cl2] complexes (E = P, as and Sb) (L = thioether-azoimine tridentate SNN donor ligands)

Abstract

The complexes cis-[Ru(EPh3)(L1)Cl2] (1–3) {L1 = (2-PhS)C6H4N = NC(COCH3)-NC6H5, E = P (1); As (2), Sb (3)} and cis-[Ru(PPh3)(L2)Cl2] (4) {L4 = (2-CH3S)C6H4N = N-(COCH3) = NC6H5} have been synthesized by reacting Ru(EPh3)3Cl2 and thioether-azoimine ligand (H2L1 and H2L4) in refluxing ethanol. The complexes have been characterized by IR, NMR, UV–Vis spectroscopy and cyclic voltammetry. The structures of 2 and 4 have been confirmed by single crystal X-ray diffraction. The electronic spectra of the complexes show MLCT and intense LLCT transitions. Cyclic voltammetric studies show one quasi reversible Ru(III)/Ru(II) oxidation couple and one L(0/−1) electron reduction, respectively. Antinociceptive activity study shows that the most active compound is complex 4 which has 70% inhibition at 45 µmol/Kg. The ligands were inactive, however, the complexes 1–4, significantly reduced the pain response in dose dependent manner (p < 0.05) in the acetic-acid-induced writhing test relative to control ligands. The compounds 2 and 4 possessed strong antinociceptive activity and thus are strong candidates for further detailed studies. The structure–activity relationships were also investigated by comparing the antinociceptive activity of complexes 1 and 4. The results show that changing the phenyl group as in complex 1 to a methyl group as in complex 4 increased the antinociceptive effects. The electronic structure, redox and absorption properties of the complexes have been explained based on DFT and TDDFT calculations.