Ruthenium–Nitrosyl Complexes Derived from Ligands Containing Two Carboxylate Functional Groups and Studies on the Photolability of Coordinated NO

Abstract

AbstractRuthenium complexes [RuIII(L1)(PPh3)2(Cl)] (1) and [RuIII(L2)(PPh3)2(Cl)] (2) (in which L1H2 and L2H2 are iminodiacetic acid and pyridine‐2,6‐dicarboxylic acid, respectively, and H stands for a dissociable proton) derived from the ligands that contain two carboxylate groups were synthesized and characterized. These complexes were treated with in situ generated NO derived from acidified nitrite solution, which afforded the formation of two {Ru–NO}6 complexes [Ru(L1)(PPh3)2(NO)](ClO4) (1a) and [Ru(L2)(PPh3)2(NO)](ClO4) (2a). The molecular structure of the representative complex [Ru(L2)(PPh3)2(NO)](ClO4) (2a) was determined using X‐ray crystallography. Characterization of complexes 1a and 2a by IR and NMR spectroscopic studies revealed the presence of {Ru–NO}6 species with S = 0 ground state. ESI‐MS data also supported the formation of 1a and 2a. Exposure to UV light promoted rapid loss of NO from both ruthenium nitrosyls to generate RuIII photoproducts of the type [Ru(L)(PPh3)2(S)](ClO4) (in which S stands for solvent). The quantum yields of NO photorelease for complexes 1a and 2a were measured using a chemical actinometry study. The NO released in solution was estimated using the Griess reagent, and the results were compared with the data obtained from sodium nitroprusside (SNP). A 2,2‐diphenyl‐1‐picrylhydrazine (DPPH) radical quenching assay was performed to estimate the amount of generated reactive nitrogen species and/or reactive oxygen species under aerobic conditions during photolysis of NO.