Molybdenum complexes with O,N,S donor ligands as models for active sites in oxotransferases and hydroxylases

Synthesis and structure of a pyridine-stabilized silanone molybdenum complex and its reactions with PMe3 and acetone

The synthesis, structure and reactivity of a pyridine-stabilized silanone molybdenum complex are described.

Coordinating and supramolecular prospects of unsymmetrically substituted carbohydrazides

Unsymmetrically substituted carbohydrazides serve as multifunctional ligands, practicing their chelating and supramolecular roles with cis-dioxomolybdenum(vi) cationic core and the Lindqvist anion.

Light-Induced Activation of a Molybdenum Oxotransferase Model within a Ru(II)-Mo(VI) Dyad

Nature uses molybdenum-containing enzymes to catalyze oxygen atom transfer (OAT) from water to organic substrates. In these enzymes, the two electrons that are released during the reaction are rapidly removed, one at a time, by spatially separated electron transfer units. Inspired by this design, a Ru(II)-Mo(VI) dyad was synthesized and characterized, with the aim of accelerating the rate-determining step in the cis-dioxo molybdenum-catalyzed OAT cycle, the transfer of an oxo ligand to triphenyl phosphine, via a photo-oxidation process. The dyad consists of a photoactive bis(bipyridyl)-phenanthroline ruthenium moiety that is covalently linked to a bioinspired cis-dioxo molybdenum thiosemicarbazone complex. The quantum yield and luminescence lifetimes of the dyad [Ru(bpy)₂(L²)MoO₂(solv)]²⁺ were determined. The major component of the luminescence decay in MeCN solution (τ = 1149 ± 2 ns, 67%) corresponds closely to the lifetime of excited [Ru(bpy)₂(phen-NH₂)]²⁺, while the minor component (τ = 320 ± 1 ns, 31%) matches that of [Ru(bpy)₂(H₂-L²)]²⁺. In addition, the (spectro)electrochemical properties of the system were investigated. Catalytic tests showed that the dyad-catalyzed OAT from dimethyl sulfoxide to triphenyl phosphine proceeds significantly faster upon irradiation with visible light than in the dark. Methylviologen acts as a mediator in the photoredox cycle, but it is regenerated and hence only required in stoichiometric amounts with respect to the catalyst rather than sacrificial amounts. It is proposed that oxidative quenching of the photoexcited Ru unit, followed by intramolecular electron transfer, leads to the production of a reactive one-electron oxidized catalyst, which is not accessible by electrochemical methods. A significant, but less pronounced, rate enhancement was observed when an analogous bimolecular system was tested, indicating that intramolecular electron transfer between the photosensitizer and the catalytic center is more efficient than intermolecular electron transfer between the separate components.

Mononuclear dioxomolybdenum(VI) thiosemicarbazonato complexes: Synthesis, characterization, structural illustration, in vitro DNA binding, cleavage, and antitumor properties

Four dioxomolybdenum(VI) complexes were synthesized by reacting [MoO2(acac)2] with N-ethyl-2-(5-bromo-2-hydroxybenzylidene) hydrazinecarbothioamide (1), N-ethyl-2-(5-allyl-3-methoxy-2-hydroxybenzylidene) hydrazinecarbothioamide (2), N-methyl-2-(3-tert-butyl-2-hydroxybenzylidene) hydrazinecarbothioamide (3), and N-ethyl-2-(3-methyl-2-hydroxybenzylidene) hydrazinecarbothioamide (4). The molecular structures of 1, 2, and all the synthesized complexes were determined using single crystal X-ray crystallography. The binding properties of the ligand and complexes with calf thymus DNA (CT-DNA) were investigated via UV, fluorescence titrations, and viscosity measurement. Gel electrophoresis revealed that all the complexes cleave pBR 322 plasmid DNA. The cytotoxicity of the complexes were studied against the HCT 116 human colorectal cell line. All the complexes exhibited more pronounced activity than the standard reference drug 5-fluorouracil (IC50 7.3μM). These studies show that dioxomolybdenum(VI) complexes could be potentially useful in chemotherapy.

Complexes of cis-dioxomolybdenum(VI) and oxovanadium(IV) with a tridentate ONS donor ligand: synthesis, spectroscopic properties, X-ray crystal structure and catalytic activity

New cis-dioxomolybdenum(VI) and oxovanadium(IV) complexes of the Schiff base, derived from S-methyl dithiocarbazate and 2,3-dihydroxybenzaldehyde (H2dhsm), have been synthesized. The complexes of the type cis-[MoO2(dhsm)] (1a), cis-[MoO2(dhsm)(D)] (1b-1d) [D=neutral monodentate ligand; EtOH, pyridine (py) or imidazole (imz)], [VO(dhsm)(NN)] (2a, 2b) [NN=2,2'-bipyridine (bipy) or 1,10-phenanthroline (phen)] and [VO(dhsm)] (2c) have been isolated, characterized by (1)H NMR, IR, UV-Vis and EPR spectral studies and investigated by cyclic voltammetry. The X-ray crystal structure of cis-[MoO2(dhsm)(EtOH)] (1b) has been determined and shows that the complex has a distorted octahedral geometry in which the H2dhsm behaves as a dianionic ONS tridentate ligand coordinating via phenoxide oxygen, hydrazinic nitrogen and thiolate sulfur. The oxomolybdenum(IV) complex [MoO(dhsm)] (1e) has obtained from dioxomolybdenum(VI) complex (1b) by oxo abstraction with PPh3. The reactivity of the complexes toward catalytic oxidation of alcohols in the presence of H2O2 and t-BuOOH as co-oxidants under solvent free conditions is reported.

Synthesis and characterization of Mo(VI) complexes derived from ONO donor acylhydrazones

Four new dioxomolybdenum(VI) complexes were prepared using different acylhydrazones. Hydrazones used for complexation were derived from 2-hydroxy-4-methoxybenzaldehyde, 2-hydroxy-4-methoxyacetophenone, benzhydrazide and nicotinoyl hydrazide. The complexes were characterized by various spectroscopic techniques, thermal and elemental analyses. The (1)H NMR and IR spectral data indicate tridentate nature of the ligands through enolization. IR spectra provide information about the dimeric nature of the complexes. The thermal analyses of the complexes showed the presence of lattice water in some of the complexes.