Organometallic ruthenium nitrosyl obtained by C-H bond activation: Photoinduced delivery of nitric oxide (NO) and NO-mediated anti-proliferation activity studies

An azo dye methyl red, having carboxylato and azo functional groups, was used as a ligand to synthesize cyclometalated Ru(III) complex [Ru(L1)(PPh3)2Cl] (1), [where L1H2=2-((4-(dimethylamino)phenyl)diazenyl)benzoic acid, H = dissociable protons], via C-H bond activation. Complex 1 was treated with nitric oxide (NO) to afford organometallic ruthenium nitrosyl complex [Ru(L2H)(PPh3)2(NO)Cl](ClO4) (1a), [where L2H=2-((4-(dimethylamino)-3-nitrophenyl)diazenyl)benzoic acid, H= dissociable proton]. The molecular structures of complexes 1.CH3OH and 1a.CH3OH were determined by X-ray crystallography. Diamagnetic complex 1a with S=0 ground state afforded 1H and31P NMR spectra. In the nitrosyl complex, coordinated NO was found to be photolabile under UV and visible light and liberated NO was trapped by reduced myoglobin. Photoreleased NO under visible light was utilized to investigate the anti-proliferation activity studies on human (A549 and HEK 293T), mouse (NIH3T3) and HeLa cancer cell-lines.