Synthesis, Characterization, and Biological Activity of Water-Soluble, Dual Anionic and Cationic Ruthenium-Arene Complexes Bearing Imidazol(in)ium-2-dithiocarboxylate Ligands

Diamidocarbene-derived palladium and nickel-sulfur clusters

Novel palladium and nickel-sulfur clusters were synthesized using a diamidocarbene-derived carbon disulfide ligand. Structural characterization revealed a tetranuclear metal-sulfur cluster geometry with each metal center exhibiting square-planar coordination. The ligand was redox-active, accommodating oxidation states ranging from 0 to -2.

Homoleptic ruthenium(II) complexes bearing imidazol(in)ium-2-dithiocarboxylate ligands: synthesis, characterization, and redox properties

Five cationic ruthenium(II) chelates with the generic formula [Ru(S2C·NHC)3](PF6)2 were readily obtained upon cleavage of the [RuCl2(p-cymene)]2 dimer with representative imidazol(in)ium-2-dithiocarboxylate zwitterions (NHC·CS2) in the presence of KPF6. The homoleptic complexes were fully characterized by various analytical techniques and the molecular structure of one of them was determined by single-crystal X-ray diffraction analysis. As expected, it featured an octahedral RuS6 core surrounded by three imidazol(in)ium rings and their nitrogen substituents. The robustness of the Ru-S bonds combined with the chelate effect of the κ2-S,S'-dithiocarboxylate units and the steric protection imparted by bulky 1,3-diarylimidazol(in)ium groups most likely accounted for the outstanding stability of these species in solution. Cyclic voltammetry showed that the five homoleptic complexes featured characteristic waves for a monoelectronic redox process corresponding to the RuIII/RuII couple with E1/2 values ranging between 0.97 and 1.27 V vs. Ag/AgCl. This half-wave potential was clearly dependent on the nature of their ancillary ligands as the evolution of the Ep,ox values roughly paralleled the basicity sequence of the NHCs used to prepare them, in line with the trends observed when monitoring the chemical shifts of the CS2- unit on 13C NMR spectroscopy and the CS2- asymmetric stretching vibration wavenumbers on IR spectroscopy.

Coordination of azol(in)ium dithiocarboxylate ligands to Au(III): unexpected formation of a novel family of cyclometallated Au(III) complexes, DFT calculations and catalytic studies

A series of cyclometallated gold(III) complexes 21-27 of general formula [Au(dppta)(azdtc)Cl] (dppta = N,N-diisopropyl-P,P-diphenylphosphinothioic amide-κ2C,S; azdtc = azol(in)ium-2-dithiocarboxylate-κ1S) were prepared and characterized by spectroscopic and diffractometric techniques. Treatment of [Au(dppta)(azdtc)Cl] complexes with methanol led to their quantitative transformation into a novel family of (C^S, S^S)-cyclometallated gold(III) complexes of general formula [Au(dppta)(azmtd)] (azmdt = azol(in)ium-2-(methoxy)methanedithiol-κ2S,S) 28-34. All the [Au(dppta)(azdtc)Cl] complexes 21-27 catalyzed the alkylation of indoles, whereas [Au(dppta)(azmtd)] complexes 28-34 were inactive. Among the synthesized derivatives, complex 22 displayed the highest catalytic activity, leading to a series of functionalized indoles in excellent yields.

Synthesis, characterization, and biological activity of cationic ruthenium-arene complexes with sulfur ligands

Five cationic ruthenium-arene complexes with the generic formula [Ru(SAc)(S2C·NHC)(p-cymene)](PF6) (5a-e) were prepared in almost quantitative yields using a straightforward one-pot, two-step experimental procedure starting from [RuCl2(p-cymene)]2, an imidazol(in)ium-2-dithiocarboxylate (NHC·CS2) zwitterion, KSAc, and KPF6. These half-sandwich compounds were fully characterized by various analytical techniques and the molecular structures of two of them were solved by X-ray diffraction analysis, which revealed the existence of an intramolecular chalcogen bond between the oxygen atom of the thioacetate ligand and a proximal sulfur atom of the dithiocarboxylate unit. DFT calculations showed that the C=S…O charge transfer amounted to 2.4 kcal mol-1. The dissolution of [Ru(SAc)(S2C·IMes)(p-cymene)](PF6) (5a) in moist DMSO-d6 at room temperature did not cause the dissociation of its sulfur ligands. Instead, p-cymene was slowly released to afford the 12-electron [Ru(SAc)(S2C·IMes)]+ cation that could be detected by mass spectrometry. Monitoring the solvolysis process by 1H NMR spectroscopy showed that more than 22 days were needed to fully decompose the starting ruthenium-arene complex. Compounds 5a-e exhibited a high antiproliferative activity against human glioma Hs683 and human lung carcinoma A549 cancer cells. In particular, the IMes derivative (5a) was the most potent compound of the series, achieving toxicities similar to those displayed by marketed platinum drugs.

Aldiminium and 1,2,3-triazolium dithiocarboxylate zwitterions derived from cyclic (alkyl)(amino) and mesoionic carbenes

The synthesis of zwitterionic dithiocarboxylate adducts was achieved by deprotonating various aldiminium or 1,2,3-triazolium salts with a strong base, followed by the nucleophilic addition of the in situ-generated cyclic (alkyl)(amino) or mesoionic carbenes (CAACs or MICs) onto carbon disulfide. Nine novel compounds were isolated and fully characterized by 1H and 13C NMR, FTIR, and HRMS techniques. Moreover, the molecular structures of two CAAC·CS2 and two MIC·CS2 betaines were determined by X-ray diffraction analysis. The analytical data recorded for all these adducts were compared with those reported previously for related NHC·CS2 betaines derived from imidazolinium or (benz)imidazolium salts. Due to the absence of electronic communication between the CS2 unit and the orthogonal heterocycle, all the CAAC·CS2, MIC·CS2, and NHC·CS2 zwitterions displayed similar electronic properties and featured the same bite angle. Yet, their steric properties are liable to ample modifications by varying the exact nature of their cationic heterocycle and its substituents.

Formation of Iridium(III) and Rhodium(III) Amine, Imine, and Amido Complexes Based on Pyridine-Amine Ligands: Structural Diversity Arising from Reaction Conditions, Substituent Variation, and Metal Centers

Herein, we present the different coordination modes of half-sandwich iridium(III) and rhodium(III) complexes based on pyridine-amine ligands. The pyridyl-amine iridium(III) and rhodium(III) complexes, the corresponding oxidation pyridyl-imine products, and 16-electron pyridyl-amido complexes can be obtained through the change in reaction conditions (nitrogen/adventitious oxygen atmosphere, reaction time, and solvents) and structural variations in the metal and ligand. Overall, the reaction of pyridine-amine ligands with [(η⁵-C₅(CH₃)₅)MCl₂]₂ (M = Ir or Rh) in the presence of adventitious oxygen afforded the oxidized pyridyl-imine complexes. The possible mechanism for the oxidation of iridium(III) and rhodium(III) amine complexes was confirmed by the detection of the byproduct hydrogen peroxide. Moreover, the formation of pyridyl-amine complexes was favored when nonpolar solvent CH₂Cl₂ was used instead of CH₃OH. The rarely reported complex with [(η⁵-Cp*)IrCl₃] anions can also be obtained without the addition of NH₄PF₆. The introduction of the sterically bulky i-Bu group on the bridge carbon of the ligand led to the formation of stable 16-electron pyridyl-amido complexes. The pyridyl-amine iridium(III) and rhodium(III) complexes were also synthesized under a N₂ atmosphere, and no H₂O₂ was detected in the whole process. In particular, the aqueous solution stability and in vitro cytotoxicity toward A549 and HeLa human cancer cells of these complexes were also evaluated. No obvious selectivity was observed for cancer cells versus normal cells with these complexes. Notably, the represented complex 5a can promote an increase in the reactive oxygen species level and induce cell death via apoptosis.