Oxide Ligands Research Articles

Inverse Trans Influence in Low-Valence Actinide-Group 10 Metal Complexes of Phosphinoaryl Oxides: A Theoretical Study via Tuning Metals and Donor Ligands.

The recognition and in-depth understanding of inverse trans influence (ITI) have successfully guided the synthesis of novel actinide complexes and enriched actinide chemistry. Those complexes, however, are mainly limited to the involvement of high-valence actinide and/or metal-ligand multiple bonds. Examples containing both low oxidation state actinide and metal-metal single bond remain rare. Herein, more than 20 actinide-transition metal (An-TM) complexes of phosphinoaryl oxide ligands have been designed in accordance with several experimentally known analogs, by changing the metal atoms (An = Th, Pa, U, Np, and Pu; and TM = Ni, Pd, and Pt), actinide oxidation states (IV and III) and metal-metal axial donor ligands (X = Me3SiO, F, Cl, Br, and I). The relativistic density functional theory study of structural (trans-An-X and cis-An-O toward An-TM), bonding (topological electron/energy density), and electronic properties reveals the order of the ITI stabilizing actinide-metal bond. Computed electron affinity (EA) values, related to the electrochemical reduction, linearly correlate with experimentally measured reduction potentials. Although the same ITI order for the ligand donors was shown as in a previous study, the correlation between electrochemical reduction and the ITI was found to be weak when the actinide atoms were changed. For most complexes, the reduction is primarily of an actinide-based mechanism with minor participation of transition metal and phosphinoaryl oxide, whereas that of thorium-nickel complexes is different.

Synthesis, crystal structures, photoluminescence, electrochemistry and DFT study of aluminium(III) and gallium(III) complexes containing a novel tetradentate Schiff base ligand.

Single crystals of the aluminium and gallium complexes of 6,6'-{(1E,1'E)-[1,2-phenylenebis(azanylylidene)]bis(methanylylidene)}bis(2-methoxyphenol), namely diaqua(6,6'-{(1E,1'E)-[1,2-phenylenebis(azanylylidene)]bis(methanylylidene)}bis(2-methoxyphenolato)-κ4O1,N,N',O1')aluminium(III) nitrate ethanol monosolvate, [Al(C22H18N2O4)(H2O)2]NO3·C2H5OH, 1, and diaqua(6,6'-{(1E,1'E)-[1,2-phenylenebis(azanylylidene)]bis(methanylylidene)}bis(2-methoxyphenolato)-κ4O1,N,N',O1')gallium(III) nitrate ethanol monosolvate, [Ga(C22H18N2O4)(H2O)2]NO3·C2H5OH, 2, were obtained after successful synthesis in ethanol. Both complexes crystallized in the triclinic space group P-1, with two molecules in the asymmetric unit. In both structures, in one of the independent molecules the tetradentate ligand is almost planar while in the other independent molecule the ligand shows significant distortions from planarity, as illustrated by the largest distance from the plane constructed through the central metal atom and the O,N,N',O'-coordinating atoms of the ligand in 1 of 1.155 (3) Å and a distance of 1.1707 (3) Å in 2. The possible reason for this is that there are various strong π-interactions in the structures. This was confirmed by density functional theory (DFT) calculations, as were the other crystallographic data. DFT was also used to predict the outcome of cyclic voltammetry experiments. Ligand oxidation is more stabilized in the gallium complex. Solid-state photoluminescence gave an 80 nm red-shifted spectrum for the gallium complex, whereas the aluminium complex maintains the ligand curve with a smaller red shift of 40 nm.

Catalytic asymmetric oxidation of sulfides to sulfoxides using (R)-6,6$$^{\prime }$$-Diphenyl-BINOL as a chiral ligand

The chiral metal complex produced in situ from (R)-6,6 $$^{\prime }$$ -Diphenyl-BINOL and $$\mathrm{Ti}(\mathrm{O}-{} { i}-\mathrm{Pr})_{4}$$ as a catalytic system for asymmetric sulfoxidation of aryl methyl and aryl benzyl sulfides in the presence of 70% aqueous TBHP as the oxidant has been investigated. The influence of variation of reagents mole ratios, temperature, solvent and oxidant was examined, and the optimized conditions were then used to oxidize a number of aryl methyl and aryl benzyl sulfides, producing sulfoxides in high enantiopurities (up to 90% ee) and good yields (up to 81%). (R)-6,6’-Diphenyl Binol in combination with $$\hbox {Ti(O-i-Pr)}_{4}$$ has been developed as an efficient chiral ligand for the asymmetric oxidation of aryl methyl and aryl benzyl sulfides by using 70% aqueous TBHP as an oxidant. High enantioselectivity and good chemical yield have been achieved for various aryl methyl and aryl benzyl sulfides.

Triphenylantimony(V) catecholato complexes with 4-(2,6-dimethylphenyliminomethyl)pyridine. Structure, redox properties: The influence of pyridine ligand

The complexation of triphenylantimony(V) catecholates (3,6-DBCat)SbPh3 (1), (4,5-pip-3,6-DBCat)SbPh3 (2) and (4,5-Cl2-3,6-DBCat)SbPh3 (3) with neutral 4-(2,6-dimethylphenyliminomethyl)pyridine (Py-CHN–Ar) leads to the formation of hexacoordinated complexes (3,6-DBCat)SbPh3·(Py-CHN–Ar) (4), (4,5-pip-3,6-DBCat)SbPh3·(Py-CHN–Ar) (5) and (4,5-Cl2-3,6-DBCat)SbPh3·(Py-CHN–Ar) (6) (where 3,6-DBCat is 3,6-di-tert-butyl-catecholate, 4,5-pip-3,6-DBCat is 4,5-(N,N′-piperazine-1,4-diyl)-3,6-di-tert-butyl-catecholate, 4,5-Cl2-3,6-DBCat is 4,5-dichloro-3,6-di-tert-butyl-catecholate) containing NPyridine-coordinated neutral donor ligand Py-CHN–Ar. In the absence of donor ligands chlorine-containing catecholate 3 undergoes rearrangement in acetonitrile to form ionic complex [Ph4Sb]+[(4,5-Cl2-3,6-DBCat)2SbPh2]- (7). Complexes have been isolated and characterized by spectroscopic methods and cyclic voltammetry. The pyridine-containing catecholate (3,6-DBCat)SbPh3·Py (8) was also synthesized in order to compare it's the electrochemical behaviour with those of iminopyridine complexes 4–6. The presence of NPyridine-coordinated iminopyridine ligand changes the mechanism of catecholate oxidation in 4 and 6: the first oxidation wave (at Eox1p = 0.94 V for 4 and 0.99 V for 6) is two-electron and corresponds to the oxidation of dianionic catecholate ligand to a coordinated o-benzoquinone. In contrast to catecholates 4 and 6, the electrochemical behaviour of piperazine-containing catecholate 5 does not practically differ from that one for initial catecholate 2. The molecular structures of complexes 3–7 in crystals have been determined by single-crystal X-ray analysis.

The Role of the OH Group in Citric Acid in the Coordination with Fe3O4 Nanoparticles.

The role of the C?OH group in citric acid (CA) in the molecular coordination with Fe3O4 nanoparticles (NPs) has been elusive for a long time. In this study, attenuated total reflection-Fourier transform infrared (ATR-FTIR) spectral deconvolution and thermogravimetric analysis (TGA) have been used to quantitatively clarify its significance in CA adsorption and its corresponding conformation. The experimental results show that the coordination and the corresponding conformation are exclusively determined by COOH not C?OH at pH 3, where its adsorption behavior conforms to the Brunauer?Emmett?Teller (BET) multilayer model with a maximal monolayer coordination number of 2.1/nm2. However, C?OH is involved in the coordination at pH 10, and CA conforms to the Langmuir monolayer model with 1.4/nm2 as its maximal monolayer coordination number, which is more stable than the COOH-only coordination. Especially, the conformational transformation is observed for the first time at pH 3, where the CA molecules adjust their conformation upon elution to maximize the utilization of the available binding sites on Fe3O4 NPs. This finding deepens the understanding on the fundamental mechanism for the interaction between the C?OH and COOH groups containing the organic ligand and metal oxide.

Regioselective synthesis and characterization of monovanadium-substituted β-octamolybdate [VMo7O26]5.

The monovanadium-substituted polyoxometalate anion [VMo7O26]5-, exhibiting a β-octamolybdate archetype structure, was selectively prepared as pentapotassium [hexaikosaoxido(heptamolybdenumvanadium)]ate hexahydrate, K5[VMo7O26]·6H2O (VMo7), by oxidation of a reduced vanadomolybdate solution with hydrogen peroxide in a fast one-pot approach. X-ray structure analysis revealed that the V atom occupies a single position in the cluster that differs from the other positions by the presence of one doubly-bonded O atom instead of two terminal oxide ligands in all other positions. The composition and structure of VMo7 was also confirmed by elemental analyses and IR spectroscopy. The selectivity of the synthesis was inspected by a 51V NMR investigation which showed that this species bound about 95% of VV in the crystallization solution. Upon dissolution of VMo7 in aqueous solution, the [VMo7O26]5- anion is substantially decomposed, mostly into [VMo5O19]3-, α-[VMo7O26]4- and [V2Mo4O19]4-, depending on the pH.

Identification of nitrite treated tuna fish meat via the determination of nitrous oxide by head space-gas chromatography/mass spectrometry.

Tuna fish meat is an expensive and highly perishable sea food. Fresh meat has a bright red colour which soon turns into an unsightly brown during storage. To prolong the aspect of freshness, the red colour is stabilised or even enhanced e.g. with carbon monoxide or nitric oxide, the product of a nitrite / ascorbic acid treatment, which bind as a ligand to myoglobin. These procedures are illegal. Here we present a method for identifying tuna meat samples, which have undergone fraudulent wet salting with nitrite. The method uses headspace-gas chromatography/mass spectrometry (GC/MS) for the determination of nitrous oxide, which is formed as the final product of the two-step reduction nitrite (added agent) to nitric oxide (ligand) to nitrous oxide (target compound). Complex bound nitric oxide is set free with sulfuric acid, which also promotes the reduction to nitrous oxide. The method was validated using 15N labelled nitrite as well as treated and untreated reference fish samples. A survey of 13 samples taken from the Swiss market in 2019 showed that 45% of all samples were illegally treated with nitrite.

2.2]Paracyclophane bis(pyridine)-based metallosupramolecular rhombs in the gas phase: Competitive cleavage of non-covalent and weak covalent bonds.

The gas-phase fragmentation behavior of self-assembled metallo-supramolecular rhombs based on an unusual chiral [2.2]paracyclophane bis(pyridine) ligand is studied by collision-induced dissociation mass spectrometry. The fragmentation patterns strongly depend on the charge state of the respective mass-selected aggregate. For the doubly charged ions, simple symmetric fragmentation is observed in full accordance with previous results reported for related metallo-supramolecular species. The triply charged species cleaves unsymmetrically which can be rationalized by a preferred formation of ions with low charge density. CID of the quadruply charged rhomb reveals a complex fragmentation. Besides ligand oxidation to the radical cation, facile cleavage of the central covalently bound part of the [2.2]paracyclophane ligand takes place which is even preferred over rupture of the weak dative pyridine-Pd bond.

Fas ligand and nitric oxide combination to control smooth muscle growth while sparing endothelium

Metallic stents cause vascular wall damage with subsequent smooth muscle cell (SMC) proliferation, neointimal hyperplasia, and treatment failure. To combat in-stent restenosis, drug-eluting stents (DES) delivering mTOR inhibitors such as sirolimus or everolimus have become standard for coronary stenting. However, the relatively non-specific action of mTOR inhibitors prevents efficient endothelium recovery and mandates dual antiplatelet therapy to prevent thrombosis. Unfortunately, long-term dual antiplatelet therapy leads to increased risk of bleeding/stroke and, paradoxically, myocardial infarction. Here, we took advantage of the fact that nitric oxide (NO) increases Fas receptors on the SMC surface. Fas forms a death-inducing complex upon binding to Fas ligand (FasL), while endothelial cells (ECs) are relatively resistant to this pathway. Selected doses of FasL and NO donor synergistically increased SMC apoptosis and inhibited SMC growth more potently than did everolimus or sirolimus, while having no significant effect on EC viability and proliferation. This differential effect was corroborated in ex vivo pig coronaries, where the neointimal formation was inhibited by the drug combination, but endothelial viability was retained. We also deployed FasL-NO donor-releasing ethylene-vinyl acetate copolymer (EVAc)-coated stents into pig coronary arteries, and cultured them in perfusion bioreactors for one week. FasL and NO donor, released from the stent coating, killed SMCs close to the stent struts, even in the presence of flow rates mimicking those of native arteries. Thus, the FasL-NO donor-combination has a potential to prevent intimal hyperplasia and in-stent restenosis, without harming endothelial restoration, and hence may be a superior drug delivery strategy for DES.

From Ferrous HRP to Compound I and Back: The Role of Protein and the Mediators in Reversible Redox Transitions

Highly oxidized iron species play key role in the catalysis of many heme and non-heme enzymes due to their ability to activate substrates via electron or hydrogen atom transfer. In Nature, such highly reactivate and unstable states are typically generated by activation and reduction of molecular oxygen by ferrous porphyrin with the ensuing transfer of redox equivalents onto the cofactor and/or protein itself. Oxygen activation is also associated with a variety of side-reactions, including generation of ROS and self-inactivation. This study investigates alternative approaches to sustaining catalytic activity of highly-oxidized heme species via direct oxidation of cofactor-bound solvent ligand under externally applied electric potential. We developed experimental framework that allows to quickly and reversibly traverse a range of oxidation states of heme cofactor between ferrous iron and Compound I while monitoring redox changes spectroscopically in the UV-Vis or IR domains. We investigate the role of redox mediators, their structures and redox potentials on the ability to catalyze electron transfer to and from the active site of horseradish peroxidase. We show that self-catalyzed modification of the protein moiety enhances the rate the electron transfer, eventually enabling sustained redox transitions in the absence of a mediator. Our results also demonstrate the role on intra-protein solvent molecule as an intrinsic reductant, rationalizing spontaneous conversion of Compounds I and II to the ferric state.

Synthesis of cationic gold(III) complexes using iodine(III)

We report the synthesis and characterization of cationic Au(III) complexes supported by nitrogen-based ligands. The syntheses are achieved by reacting Au(I) complexes [Au(N-Me-imidazole)2]+ and [Au(pyridine)(NHC)]+ with iodine(III) reagents PhI(OTf)(OAc) and [PhI(pyridine)2]2+ yielding a series of cationic gold(III) complexes. In contrast, reactions of phosphine ligated gold(I) complexes with iodine(III) reagents results in the oxidation of the phosphine ligand.

Universal Method for Producing Reduced Graphene Oxide/Gold Nanoparticles Composites with Controlled Density of Grafting and Long-Term Stability.

In this study, we report a universal approach allowing the non-covalent deposition of gold nanoparticles on reduced graphene oxide surface in a controlled fashion. We used a modified Hummers method to obtain graphene oxide, which then underwent surficial functionalization with carboxyl moieties coupled with simultaneous reduction. Nanoparticles were synthesized ex-situ and capped with a thiolated poly-ethylene glycol (PEG) ligand. The interactions between the surface of modified graphene oxide and nanoparticle ligands enabled the formation of stable hybrid graphene-nanoparticles materials in the aqueous phase. Using this technique, we were able to cover the surface of graphene with gold nanoparticles of different shapes (spheres, rods, triangles, stars, and bipyramids), broad range of sizes (from 5 nm to 100 nm) and controlled grafting densities. Moreover, materials obtained with this strategy exhibited long-term stability, which coupled with the versatility and facility of preparation, makes our technique appealing in the light of increasing demand for new graphene-based hybrid nanostructures.

Synthesis, Spectroscopic Studies and Supramolecular Architecture in a Dinuclear Uranyl Complex, 2-Aminopyridinium [bis(µ2-hydroxo)-tetrakis(nitrato–κ2–O,O′)-tetraoxo-diuranium(VI)] Monohydrate

The titled dinuclear uranyl complex, U2O18N4H2·2(C5H7N2) 2(H2O) was crystallised in Monoclinic (C2/c) space group with the cell parameters a = 18.0728(3) b = 10.6896(3) c = 13.9068(3)A, α = γ = 90.00° β = 103.988(2)°. In the structure, the U(VI) atom is eight coordinated with slightly distorted hexagonal bipyramidal geometry around the U(VI) ion. Two oxide ligands in the axial positions and four oxygen atoms from two bidentate nitrate ligands and two oxygen atoms from two hydroxy groups in the equatorial plane form the coordination sphere around the uranium atom. The two hydroxy groups act as bridging ligands between the uranyl ions generating a dinuclear unit having an inversion centre. The coordinated and non coordinated nitrate O atoms, axial uranyl O atoms, bridged hydroxy O atom, the non coordinated 2-aminopyridinium ion and the lattice water molecule play a vital role in assembling the three-dimensional structure via an extensive network of intermolecular O–H···O, N–H···O and C–H···O hydrogen bonds and aromatic π–π stacking interaction. The U(VI) atom is eight coordinated with slightly distorted hexagonal bipyramidal geometry. The three-dimensional structure is built through extensive network of intermolecular O–H···O, N–H···O, C–H···O hydrogen bonds and aromatic π–π stacking interaction.

Protective Effect of Dinitrosyl Iron Complexes with Glutathione in Red Blood Cell Lysis Induced by Hypochlorous Acid.

Hypochlorous acid (HOCl), one of the major precursors of free radicals in body cells and tissues, is endowed with strong prooxidant activity. In living systems, dinitrosyl iron complexes (DNIC) with glutathione ligands play the role of nitric oxide donors and possess a broad range of biological activities. At micromolar concentrations, DNIC effectively inhibit HOCl-induced lysis of red blood cells (RBCs) and manifest an ability to scavenge alkoxyl and alkylperoxyl radicals generated in the reaction of HOCl with tert-butyl hydroperoxide. DNIC proved to be more effective cytoprotective agents and organic free radical scavengers in comparison with reduced glutathione (GSH). At the same time, the kinetics of HOCl-induced oxidation of glutathione ligands in DNIC is slower than in the case of GSH. HOCl-induced oxidative conversions of thiolate ligands cause modification of DNIC, which manifests itself in inclusion of other ligands. It is suggested that the strong inhibiting effect of DNIC with glutathione on HOCl-induced lysis of RBCs is determined by their antioxidant and regulatory properties.

Phosphine Oxide Ligand Based Tetrahedral CoII Complexes with Field-induced Slow Magnetic Relaxation Behavior Modified by Terminal Ligands.

Two isostructural mononuclear CoII complexes, [Co(xantpo)(NCE)2 ] (E=S (1) and O (2); xantpo=9,9-dimethyl-4,5-bis(diphenylphosphoryl) xanthene), supported by a bidentate phosphine oxide ligand are reported. The cobalt complexes exhibit characteristic tetrahedral structures coordinated with two oxygen and two nitrogen atoms. Magnetic property measurements show their similar static magnetic behaviours but very different dynamic magnetic behaviours. Both complexes show field-induced slow magnetic relaxation behaviours, but the relaxation of 2 is much slower than that of 1. Fittings to the magnetic data and ab initio CASSCF calculations reveal significant changes in the zero field splitting (ZFS) parameters (D and E), which can be attributed to the small geometrical changes of the Co ions and the different ligand field strength of the two terminal ligands.

Thermodynamic features of bovine and human serum albumins under ozone and hydrogen peroxide induced oxidation studied by differential scanning calorimetry

Serum albumin is the prevailing protein of blood bearing not less than 70% of the free radical-trapping activity of serum. The effect of ozone and hydrogen peroxide on the thermal stability of human (HSA) and bovine (BSA) serum albumins is studied by the aid of the differential scanning calorimetry (DSC) method. A decrease and increase of denaturation enthalpy and temperature for both investigated proteins upon ozone-induced and peroxide induced oxidation are analyzed and the role of endogenous ligands (specifically fatty acids) in the protein oxidation is clarified. Both the thermal stability of long-chain fatty acids LCFA-poor HSA molecules and relative resistance of LCFA-rich HSA molecules to oxidation are shown not to depend on the oxidant type with the key role of LCFA-rich HSA species in thermal stability of the HSA under oxidation.

Reactivity of bio-inspired Cu(II) (N2/Py2) complexes with peroxide at room temperature

Developing coordination complexes of earth abundant metals that can perform substrate oxidations under benign conditions is an ongoing challenge. Herein, the reactivity of two mononuclear Cu-complexes toward the oxidant H2O2 is reported. Both complexes displayed ligand oxidation upon reaction with the oxidant. Analysis of spectroscopic data established that the respective product complexes contained mononuclear Cu(II) centers. Moreover, treatment of these Cu-complexes with oxidant in the presence of substrate resulted in the interception of ligand oxidation with preferential oxidation of the substrate. Computational studies identified plausible mechanistic pathways, suggesting a copper-oxyl intermediate as the likely reactive intermediate responsible for substrate and ligand oxidation. To our knowledge, this is the first Cu-mediated system that showed ligand oxidation, oxo-transfer capability, and external hydrocarbon oxidation under stoichiometric conditions.

A CF3-substituted diphosphine dioxide ligand that enhances both photoluminescence intensity and solubility of Eu(III) complexes

The author developed the di(3-trifluoromethylphenyl)[3-(dioctylphosphinyl)propyl]phosphine oxide (DPDO-mCF3) ligand in order to prepare Eu(III) complexes with high photoluminescence intensity and solubility. By coordinating the DPDO-mCF3 ligand to Eu(III), photoluminescence intensities were increased to 6.4 and 4.3 times those of tris(4,4,5,5,6,6,6-heptafluoro-1-(2-naphthyl)-1,3-hexanedionato)europium(III) (Eu(III)(hfnh)3; 4) and tris(6,6,7,7,8,8,8-heptafluoro-2,2-dimethyl-3,5-octanedionato)europium(III) (Eu(III)(fod)3; 5), respectively. Coordination of the DPDO-mCF3 ligand also increased the asymmetry ratio, total photoluminescence quantum yield (ΦTOT), and absorbance of Eu(III) complexes. ΦTOT of Eu(III)(hfnh)3(DPDO-mCF3) (1) was 0.60 in ethyl acetate at a concentration of 1 × 10−3 mol/L and 0.82 in the solid state. In addition, ΦTOT of Eu(III)(fod)3(DPDO-mCF3) (2) is 0.39 in ethyl acetate at a concentration of 1 × 10−3 mol/L and 0.56 in the solid state. Solid-state quantum yields were larger than solution-state quantum yields across a wide wavelength region. Furthermore, the solubility of 2 in 2,3-dihydrodecafluoropentane (54 μmol/g) was far higher than that of 5 (7.2 μmol/g). DPDO-mCF3 is thus an innovative ligand for Eu(III) complexes, and Eu(III) complexes bearing a DPDO-mCF3 ligand are promising candidates for many applications, including LED devices, secure media, and sensing devices.

Visible-Light-Induced Nanoparticle Assembly for Effective Hydrogen Photogeneration

Visible-light-induced nanoparticle assembly consisting of quantum dots (QDs) and Pt nanoparticles (NPs) has been achieved. The assembled nanoparticle joined a single Pt nanoparticle and multiple QDs together through controllable oxidation of thiol ligands on QDs under aerobic visible light irradiation and sonication. With an optimal ratio of QDs to Pt NPs (ca. 475:1), the assembly could achieve consecutive electron transfer from photoexcited QDs to Pt NP and evolve H2 gas with a constant rate of ∼13.9 μmol h–1 from triethylamine (TEA) during 70 h, corresponding to a turnover number (TON) of 1.4 × 107 mol H2 per mol Pt NPs. Our work shows that the assembled architecture of semiconducting QDs is a promising strategy for effective and durable H2 photogeneration.

Di- and Tetrairon(III) μ-Oxido Complexes of an N3S-Donor Ligand: Catalyst Precursors for Alkene Oxidations.

The new di- and tetranuclear Fe(III) μ-oxido complexes [Fe4(μ-O)4(PTEBIA)4](CF3SO3)4(CH3CN)2] (1a), [Fe2(μ-O)Cl2(PTEBIA)2](CF3SO3)2 (1b), and [Fe2(μ-O)(HCOO)2(PTEBIA)2](ClO4)2 (MeOH) (2) were prepared from the sulfur-containing ligand (2-((2,4-dimethylphenyl)thio)-N,N-bis ((1-methyl-benzimidazol-2-yl)methyl)ethanamine (PTEBIA). The tetrairon complex 1a features four μ-oxido bridges, while in dinuclear 1b, the sulfur moiety of the ligand occupies one of the six coordination sites of each Fe(III) ion with a long Fe-S distance of 2.814(6) Å. In 2, two Fe(III) centers are bridged by one oxido and two formate units, the latter likely formed by methanol oxidation. Complexes 1a and 1b show broad sulfur-to-iron charge transfer bands around 400–430 nm at room temperature, consistent with mononuclear structures featuring Fe-S interactions. In contrast, acetonitrile solutions of 2 display a sulfur-to-iron charge transfer band only at low temperature (228 K) upon addition of H2O2/CH3COOH, with an absorption maximum at 410 nm. Homogeneous oxidative catalytic activity was observed for 1a and 1b using H2O2 as oxidant, but with low product selectivity. High valent iron-oxo intermediates could not be detected by UV-vis spectroscopy or ESI mass spectrometry. Rather, evidence suggest preferential ligand oxidation, in line with the relatively low selectivity and catalytic activity observed in the reactions.