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Surprisingly, the anticancer activity of half-sandwich Ru arene complexes [(?6-arene)Ru(en)Cl]+ appears to be promoted and not inhibited by binding to the intracellular thiol glutathione. Labilization of the Ru--S bond allowing DNA binding appeared to be initiated by oxygenation of the thiolate ligand, although oxidation by itself did not seem to weaken the Ru--S bond. In this study, we have investigated the solvation and acidic perturbations of mono (sulfenato) and bis (sulfinato) oxidized species of [(η6-arene)Ru(en) (SR)]+ complex in the presence of Brønsted and Lewis acids. Sulfur K-edge X-ray absorption spectroscopy together with density functional theory calculations show that solvation and acidic perturbation of sulfenato species produce a significant decrease in the S3p character of the Ru--S bond (Ru4dσ* ← S1s charge donation). Also there is a drastic fall in the overall ligand charge donation to the metal center in both sulfenato and sulfinato species. Our investigation clearly shows that mono oxidized sulfenato species are most susceptible to ligand exchange, hence providing a possible pathway for in vivo activation and biological activity. [ABSTRACT FROM AUTHOR]

Herein, we report experimental, spectroscopic, and computational data that indicate that a rhodium ethylene complex, formally described as rhodium(I) and which forms a 2-rhoda(III) oxetane following reaction with H2O2, is more accurately described as a rhodium(III) metallacyclopropane. X-ray absorption spectroscopy clearly demonstrates a change in the oxidation state at rhodium following ligand coordination with tris(2-pyridylmethyl)amine. Both NMR and density functional theory studies suggest a high energy barrier to rotation of the coordinated ethylene, which is attributed to large geometric and electronic reorganization resulting from the loss of p-back-bonding. These results imply that the role of H2O2 in the formation of 2-rhoda(III) oxetanes is to oxidize the C2H4 fragment rather than the metal center, as has been previously suggested. [ABSTRACT FROM AUTHOR]