Synthesis of NNN Chiral Ruthenium Complexes and Their Cytotoxicity Studies.

The synthesis and characterization of chiral pincer-ruthenium complexes of the type (R2NNN)RuCl2 (PPh3) (R = 3-methylbutyl and 3,3-dimethylbutyl) is reported here. The cytotoxicity studies of these complexes were studied and compared with the corresponding activity of achiral complexes. The cytotoxic effect of pincer-ruthenium complexes on human dermal fibroblasts and human tongue carcinoma cells assessed using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay displayed an inhibition of normal and cancer cell growth in a dose-dependent manner. Intracellular reactive oxygen species (ROS) level measurement, lactate dehydrogenase assay, DNA fragmentation, and necrosis studies revealed that treatment with pincer-ruthenium complexes induced a redox imbalance in SAS cells by upregulating ROS generation and caused necrotic cell death by disrupting the cellular membrane integrity.

Selective and high yield transformation of glycerol to lactic acid using NNN pincer ruthenium catalysts.

The conversion of glycerol selectively to lactic acid has been accomplished in high yields (ca. 90%) by using a NNN pincer-Ru catalyst. DFT explains the role of the Ru-P bond and sterics in favoring the catalysis.

Geometry-Driven Iminosemiquinone Radical to Cu(II) Electron Transfer and Stabilization of an Elusive Five-Coordinate Cu(I) Complex: Synthesis, Characterization, and Reactivity with KO2.

The noninnocent ligand H2LAP(Ph) contained a bulky phenyl substituent at the ortho position to the aniline moiety. The ligand reacted with 0.5 equiv of CuCl2·2H2O in the presence of Et3N under air and provided the corresponding Cu(II)-bis(imonosemiquinone) complex (1). The complex upon oxidation by a stoichiometric amount of ferrocenium hexafluorophosphate (FcPF6) yielded the four-coordinate [Cu(II)-(imonosemiquinone)(iminoquinone)]PF6 complex (3), while the oxidation by an equivalent amount of CuCl2·2H2O produced the five-coordinate Cu(I)-bis(iminoquinone)Cl complex (2). Thus, a ligand-based oxidation followed by ligand-to-metal electron-transfer was realized for the latter oxidation process. Removal of the Cl- ion from complex 2 rendered the four-coordinate complex 4. The oxidation state of both Cu(I) and iminoquinone moieties remained unaltered upon the change in the coordination number. All the complexes were characterized by X-ray crystallography. Complexes 2, 3, and 4 were diamagnetic with an St = 0 ground state as evident by electron paramagnetic resonance (EPR) and 1H NMR measurements. The UV-vis-NIR spectra of all the complexes were dominated by charge-transfer transitions. Two oxidations and two reductions waves were noticed in the cyclic voltammogram (CV) of complex 1. Complex 2 and complex 3 underwent one oxidation and three reductions. Unlike complex 3, which experienced ligand-based oxidation, in complex 2 the oxidation was metal-centered [oxidation of Cu(I)-to-Cu(II)]. UV-vis-NIR spectral changes during the fixed-potential coulometric one-electron oxidation and thereafter EPR analysis consolidated the metal-based oxidation in complex 2. Complex 2 was air stable; however, it oxidized KO2 to oxygen molecule, and complex 1 was formed in due course as evident by UV-vis-NIR spectral changes and EPR measurements. Time dependent density functional theory calculations have been incorporated to assign the transitions that appeared in the UV-vis-NIR spectra of the complexes.