Reaction Chemistry of the syn-[Mo2O2(μ-S)2(S2)(DMF)3] Complex with Cyanide and Catalytic Thiocyanate Formation

Generation and Reactivity of Polychalcogenide Chains in Binuclear Cobalt(II) Complexes

A series of six binuclear Co(II)-thiolate complexes, [Co2(BPMP)(S-C6H4-o-X)2]1+ (X = OMe, 2; NH2, 3), [Co2(BPMP)(μ-S-C6H4-o-O)]1+ (4), and [Co2(BPMP)(μ-Y)]1+ (Y = bdt, 5; tdt, 6; mnt, 7), has been synthesized from [Co2(BPMP)(MeOH)2(Cl)2]1+ (1a) and [Co2(BPMP)(Cl)2]1+ (1b), where BPMP1- is the anion of 2,6-bis[[bis(2-pyridylmethyl)amino]methyl]-4-methylphenol. While 2 and 3 could allow the two-electron redox reaction of the two coordinated thiolates with elemental sulfur (S8) to generate [Co2(BPMP)(μ-S5)]1+ (8), the complexes, 4-7, could not undergo a similar reaction. An analogous redox reaction of 2 with elemental selenium ([Se]) produced [{Co2(BPMP)(μ-Se4)}{Co2(BPMP)(μ-Se3)}]2+ (9a) and [Co2(BPMP)(μ-Se4)]1+ (9b). Further reaction of these polychalcogenido complexes, 8 and 9a/9b, with PPh3 allowed the isolation of [Co2(BPMP)(μ-S)]1+ (10) and [Co2(BPMP)(μ-Se2)]1+ (11), which, in turn, could be converted back to 8 and 9a upon treatment with S8 and [Se], respectively. Interestingly, while the redox reaction of the polyselenide chains in 9a and 11 with S8 produced 8 and [Se], the treatment of 8 with [Se] gave back only the starting material (8), thus demonstrating the different redox behavior of sulfur and selenium. Furthermore, the reaction of 8 and 9a/9b with activated alkynes and cyanide (CN-) allowed the isolation of the complexes, [Co2(BPMP)(μ-E2C2(CO2R)2)]1+ (E = S: 12a, R = Me; 12b, R = Et; E = Se: 13a, R = Me; 13b, R = Et) and [Co2(BPMP)(μ-SH)(NCS)2] (14), respectively. The present work, thus, provides an interesting synthetic strategy, interconversions, and detailed comparative reactivity of binuclear Co(II)-polychalcogenido complexes.

A new series of bioactive Mo(V)2O2S2-based thiosemicarbazone complexes: Solution and DFT studies, and antifungal and antioxidant activities

This paper deals with the synthesis, characterization, and studies of biological properties of a series of 5 coordination compounds based on binuclear core [Mo(V)2O2S2]2+ with thiosemicarbazones ligands bearing different substituents on the R1 position of the ligand. The complexes are first studied using MALDI-TOF mass spectrometry and NMR spectroscopy to determine their structures in solution in relation to single-crystal X-Ray diffraction data. In a second part, the antifungal and antioxidative activities are explored and the high potential of these coordination compounds compared to the uncoordinated ligands is demonstrated for these properties. Finally, DFT calculation provides important support to the solution studies by identifying the most stable isomers in each [Mo2O2S2]2+/Ligand system, while the determination of HUMO and LUMO levels is performed to explain the antioxidative properties of these systems.

Tuning the nuclearity of [Mo2O2S2]2+-based assemblies by playing with the degree of flexibility of bis-thiosemicarbazone ligands

[MoV2O₂S₂]²⁺-based thiosemicarbazone complexes appear as very promising molecules for biological applications due to the intrinsic properties of their components. This paper deals with the synthesis and characterization of six coordination complexes obtained by the reaction of [MoV2O₂S₂]²⁺ clusters with bis-thiosemicarbazone ligands that contain flexible or rigid spacers between the two thiosemicarbazone units. Interestingly, structural characterization by single-crystal X-ray diffraction, MALDI-TOF MS technique and NMR spectroscopy revealed that the nuclearity of the complex is controlled by the nature of the spacer between the thiosemicarbazone units. Binuclear complexes, namely [MoV2O₂S₂(L^1-3)], are isolated with flexible spacers while tetranuclear complexes [(MoV2O₂S₂)₂(L^4-6)₂] are formed when the bis-thiosemicarbazone ligands are built on rigid spacers.

In Vitro Characterization of a Threonine-Ligated Molybdenyl-Sulfide Cluster as a Putative Cyanide Poisoning Antidote; Intracellular Distribution, Effects on Organic Osmolyte Homeostasis, and Induction of Cell Death

Binuclear molybdenum sulfur complexes are effective for the catalytic conversion of cyanide into thiocyanate. The complexes themselves exhibit low toxicity and high aqueous solubility, which render them suitable as antidotes for cyanide poisoning. The binuclear molybdenum sulfur complex [(thr)Mo2O2(μ-S)2(S2)]- (thr - threonine) was subjected to biological studies to evaluate its cellular accumulation and mechanism of action. The cellular uptake and intracellular distribution in human alveolar (A549) cells, quantified by inductively coupled plasma mass spectrometry (ICP-MS) and cell fractionation methods, revealed the presence of the compound in cytosol, nucleus, and mitochondria. The complex exhibited limited binding to DNA, and using the expression of specific protein markers for cell fate indicated no effect on the expression of stress-sensitive channel components involved in cell volume regulation, weak inhibition of cell proliferation, no increase in apoptosis, and even a reduction in autophagy. The complex is anionic, and the sodium complex had higher solubility compared to the potassium. As the molybdenum complex possibly enters the mitochondria, it is considered as a promising remedy to limit mitochondrial cyanide poisoning following, e.g., smoke inhalation injuries.

Synthesis, Structures, and Solution Studies of a New Class of [Mo2O2S2]-Based Thiosemicarbazone Coordination Complexes

This paper deals with the synthesis, structural studies, and behavior in solution of unprecedented coordination complexes built by the association of a panel of 14 representative thiosemicarbazone ligands with the cluster [Mo₂O₂S₂]²⁺. These complexes have been thoroughly characterized both in the solid state and in solution by XRD and by NMR, respectively. In particular, HMBC ¹H{¹⁵N} and ¹H DOSY NMR experiments bring important elements for understanding the complexes' behavior in solution. These studies demonstrate that playing on the nature and the position of various substituents on the ligands strongly influences the coordination modes of the ligands as well as the numbers of isomers in solution, mainly 2 products for the majority of complexes and up to 5 for some of them.

Screening of biological properties of MoV2O2S2- and MoV2O4-based coordination complexes: Investigation of antibacterial, antifungal, antioxidative and antitumoral activities versus growing of Spirulina platensis biomass

This paper deals with the biological potential of coordination compounds based on binuclear core [Mo^V₂O₂E₂]²⁺ (E = O or S) coordinated with commercially available ligands such as oxalates (Ox^2-), L-cysteine (L-cys^2-), L-histidine (L-his^-), Iminodiacetate (IDA^2-), Nitrilotriacetate (HNTA^2- or NTA^3-) or ethylenediamine tetraacetate (EDTA^4-) by means of various in vitro assays in a screening approach. Results suggest that the obtained complexes show weak antibacterial and antifungal properties while not being cytotoxic on cancerous and mammalian cells. In contrast, [Mo₂O₂E₂(L-cys)₂]^2- complexes stand out as powerful antioxidant, whereas [Mo₂O₂E₂(EDTA)]^2- associating tetraphenylphosphonium counter-cations display strong antibiotic activity. Finally, some complexes have evidenced a positive activity towards the growing of spirulina platensis together with a modification of the proportions of biological components inside the cells. These findings reveal promising bioactivity of the bridged binuclear Mo^(+V) cores inside complexes and encourage further research for new highly active yet non-toxic molecules for biological and biomedical applications.

Coordination Properties of Non-Rigid Phosphinoyldithioformate Complexes of the [Mo2O2(µ-S)2]2+ Cation in Catalytic Sulfur Transfer Reactions with Thiiranes

Two “Mo2O2S2”-based complexes with phosphinoyldithioformate ligands were synthesized from the metathesis reaction of [R2P(O)CS2]− with (Me4N)2[Mo2O2(µ-S)2(Cl)4] to give [Mo2O2(µ-S)2{R2P(O)CS2}2] (1; R = Ph, 2; R = Bn). The complexes were fully characterized, including the X-ray crystal structure for 1. Variable temperatures 31P NMR of 1 and 2 exhibit non-rigid behavior in solution where three and two coordination isomers were present, respectively. The organic substituent on the P atom greatly impacts the complex non-rigid properties and behavior. The catalytic activity of 1 and 2 towards sulfur atom transfer (SAT) using propylene sulfide and cyclohexene sulfide was explored, employing homogeneous reaction conditions at an ambient temperature on the NMR scale. The complexes showed distinctly different properties along with high conversions in short reaction times. A catalytic cycle consistent with the results is proposed.

Water-Soluble α-Amino Acid Complexes of Molybdenum as Potential Antidotes for Cyanide Poisoning: Synthesis and Catalytic Studies of Threonine, Methionine, Serine, and Leucine Complexes

Water-soluble complexes are desirable for the aqueous detoxification of cyanide. Molybdenum complexes with α-amino acid and disulfide ligands with the formula K[(L)Mo₂O₂(μ-S)₂(S₂)] (L = leu (1), met (2), thr (3), and ser (4)) were synthesized in a reaction of [(DMF)₃MoO(μ-S)₂(S₂)] with deprotonated α-amino acids; leu, met, thr, and ser are the carboxylate anions of l-leucine, l-methionine, l-threonine, and l-serine, respectively. Potassium salts of α-amino acids (leu (1a), met (2a), thr (3a), and ser (4a)) were prepared as precursors for complexes 1-4, respectively, by employing a nonaqueous synthesis route. The ligand exchange reaction of [Mo₂O₂(μ-S)₂(DMF)₆](I)₂ with deprotonated α-amino acids afforded bis-α-amino acid complexes, [(L)₂Mo₂O₂(μ-S)₂] (6-8). A tris-α-amino acid complex, [(leu)₂Mo₂O₂(μ-S)₂(μ-leu + H)] (5; leu + H is the carboxylate anion of l-leucine with the amine protonated), formed in the reaction with leucine. 5 crystallized from methanol with a third weakly bonded leucine as a bridging bidentate carboxylate. An adduct of 8 with SCN^- coordinated, 9, crystallized and was structurally characterized. Complexes 1-4 are air stable and highly water-soluble chiral molecules. Cytotoxicity studies in the A549 cell line gave IC₅₀ values that range from 80 to 400 μM. Cyclic voltammetry traces of 1-8 show solvent-dependent irreversible electrochemical behavior. Complexes 1-4 demonstrated the ability to catalyze the reaction of thiosulfate and cyanide in vitro to exhaustively transform cyanide to thiocyanate in less than 1 h.