Controlled Flexible Coordination in Tripodal Iron(II) Phosphane Complexes: Effects on Reactivity

The possibility to alter properties of metal complexes without significant steric changes is a useful tool to tailor the reactivity of the complexes. Herein we present the synthesis of iron complexes with the tripodal phosphane ligands Triphos and Triphos^Si and report on their different coordination properties. Whereas reaction of Triphos^Si and FeX₂ (X = Cl, Br) exclusively afforded (Triphos^Si)­FeX₂ with a κ²-coordinated ligand, the homologous C-derived Fe complexes show rapid conversion in solution to afford [(Triphos)­Fe­(CH₃CN)₃]­[Fe₂Cl₆] or [(Triphos)­Fe­(CH₃CN)₃]­[FeBr₄], respectively. The structural conversion was found to be temperature- and solvent-dependent and was accompanied by a linear change of the overall magnetization. The different ligand influence was shown to have a significant effect on the ability of (Triphos^Si)­FeCl₂ and (Triphos)­FeCl₂ to perform the Sonogashira cross-coupling reaction of 4-iodotoluene and phenyl acetylene as well as the hydrosilylation of acetophenone. The results presented herein show the different coordination properties of two structurally homologous tripodal ligands and demonstrate the importance of geometrically controlled ligand field splitting on the stability and reactivity of metal complexes. The C/Si exchange therefore provides a simple and straightforward tool to manipulate properties and reactivity of metal complexes

Synthesis and Characterization of Phosphorus-Containing Isocyclam Macrocycles and Their Nickel Complexes

The tetradentate azamacrocycle cyclam (=1,4,8,11-tetraazacyclotetradecane) was studied profoundly for the coordination of transition metal ions, and the resulting complexes were investigated extensively for their catalytic performance in, e.g., O2 activation and electrocatalytic CO2 reduction. Although the successful synthesis of analogous P4 macrocycles was described earlier, no tetradentate N,P mixed 14-membered macrocycles have been prepared to date and their chemistry remains elusive. Thus, in this work, we showcase the synthesis of phospha-aza mixed cyclam-based macrocycles by selectively “exchanging” one or two secondary amines in the macrocycle isocyclam (=1,4,7,11-tetraazacyclotetradecane) with tertiary phosphines. In addition, we herein present the preparation of the corresponding nickel complexes along with their complex chemical and structural characterization to provide first coordination studies

Controlled Flexible Coordination in Tripodal Iron(II) Phosphane Complexes: Effects on Reactivity

The possibility to alter properties of metal complexes without significant steric changes is a useful tool to tailor the reactivity of the complexes. Herein we present the synthesis of iron complexes with the tripodal phosphane ligands Triphos and Triphos^Si and report on their different coordination properties. Whereas reaction of Triphos^Si and FeX₂ (X = Cl, Br) exclusively afforded (Triphos^Si)­FeX₂ with a κ²-coordinated ligand, the homologous C-derived Fe complexes show rapid conversion in solution to afford [(Triphos)­Fe­(CH₃CN)₃]­[Fe₂Cl₆] or [(Triphos)­Fe­(CH₃CN)₃]­[FeBr₄], respectively. The structural conversion was found to be temperature- and solvent-dependent and was accompanied by a linear change of the overall magnetization. The different ligand influence was shown to have a significant effect on the ability of (Triphos^Si)­FeCl₂ and (Triphos)­FeCl₂ to perform the Sonogashira cross-coupling reaction of 4-iodotoluene and phenyl acetylene as well as the hydrosilylation of acetophenone. The results presented herein show the different coordination properties of two structurally homologous tripodal ligands and demonstrate the importance of geometrically controlled ligand field splitting on the stability and reactivity of metal complexes. The C/Si exchange therefore provides a simple and straightforward tool to manipulate properties and reactivity of metal complexes

Controlled Flexible Coordination in Tripodal Iron(II) Phosphane Complexes: Effects on Reactivity

The possibility to alter properties of metal complexes without significant steric changes is a useful tool to tailor the reactivity of the complexes. Herein we present the synthesis of iron complexes with the tripodal phosphane ligands Triphos and Triphos^Si and report on their different coordination properties. Whereas reaction of Triphos^Si and FeX₂ (X = Cl, Br) exclusively afforded (Triphos^Si)­FeX₂ with a κ²-coordinated ligand, the homologous C-derived Fe complexes show rapid conversion in solution to afford [(Triphos)­Fe­(CH₃CN)₃]­[Fe₂Cl₆] or [(Triphos)­Fe­(CH₃CN)₃]­[FeBr₄], respectively. The structural conversion was found to be temperature- and solvent-dependent and was accompanied by a linear change of the overall magnetization. The different ligand influence was shown to have a significant effect on the ability of (Triphos^Si)­FeCl₂ and (Triphos)­FeCl₂ to perform the Sonogashira cross-coupling reaction of 4-iodotoluene and phenyl acetylene as well as the hydrosilylation of acetophenone. The results presented herein show the different coordination properties of two structurally homologous tripodal ligands and demonstrate the importance of geometrically controlled ligand field splitting on the stability and reactivity of metal complexes. The C/Si exchange therefore provides a simple and straightforward tool to manipulate properties and reactivity of metal complexes

Detection of Nitric Oxide and Nitroxyl with Benzoresorufin-Based Fluorescent Sensors

A new family of benzoresorufin-based copper complexes for fluorescence detection of NO and HNO is reported. The copper complexes, CuBRNO1–3, elicit 1.5–4.8-fold emission enhancement in response to NO and HNO. The three sensors differ in the nature of the metal-binding site. The photophysical properties of these sensors are investigated with assistance from density functional theory calculations. The fluorescence turn-on observed upon reaction with HNO is an unexpected result that is discussed in detail. The utility of the new sensors for detecting HNO and NO in HeLa cells and RAW 264.7 macrophages is demonstrated

A dithiacyclam-coordinated silver(i) polymer with anti-cancer stem cell activity

A cancer stem cell (CSC) active, solution stable, silver(i) polymeric complex bearing a dithiacyclam ligand is reported. The complex displays similar potency towards CSCs to salinomycin in monolayer and three-dimensional cultures. Mechanistic studies suggest CSC death results from cytosol entry, an increase in intracellular reactive oxygen species, and caspase-dependent apoptosis

Tuning the Electrocatalytic Properties of Trimetallic Pentlandites: Stability and Catalytic Activity as a Function of Material Form and Selenium Concentration

Pentlandites are one possible cost-effective alternative to platinum group metals for green hydrogen production. This study delves into the catalytic performance of trimetallic pentlandite systems, exploring the influence of selenium concentration and material form on their efficiency by combining the investigation of materials in various forms (powder catalysts, ingots, and highly densified pellets) with a computational investigation. The experimentally observed solubility limit of selenium was clarified based on the formation energies approach. The best and most stable defect combination, namely, Se:S substitution and S vacancy, was identified and correlated with improved catalytic properties of the systems with small Se addition. Further findings highlight the evolving importance of intrinsic material properties, such as bond properties, intermetallic interactions, or electronic structure, over surface effects, including the activation process, as the material density increases. The research contributes valuable insight into the intricate mechanisms governing pentlandite catalysis. Understanding these dynamics allows for intentional modifications, advancing the application of pentlandites in hydrogen production

Loss of Specific Active-Site Iron Atoms in Oxygen-Exposed [FeFe]-Hydrogenase Determined by Detailed X‑ray Structure Analyses

The [FeFe]-hydrogenases catalyze the uptake and evolution of hydrogen with unmatched speed at low overpotential. However, oxygen induces the degradation of the unique [6Fe-6S] cofactor within the active site, termed the H-cluster. We used X-ray structural analyses to determine possible modes of irreversible oxygen-driven inactivation. To this end, we exposed crystals of the [FeFe]-hydrogenase CpI from Clostridium pasteurianum to oxygen and quantitatively investigated the effects on the H-cluster structure over several time points using multiple data sets, while correlating it to decreases in enzyme activity. Our results reveal the loss of specific Fe atoms from both the diiron (2FeH) and the [4Fe-4S] subcluster (4FeH) of the H-cluster. Within the 2FeH, the Fe atom more distal to the 4FeH is strikingly more affected than the more proximal Fe atom. The 4FeH interconverts to a [2Fe-2S] cluster in parts of the population of active CpIADT, but not in crystals of the inactive apoCpI initially lacking the 2FeH. We thus propose two parallel processes: dissociation of the distal Fe atom and 4FeH interconversion. Both pathways appear to play major roles in the oxidative damage of [FeFe]-hydrogenases under electron-donor deprived conditions probed by our experimental setup

Versatile Reactivity of a Solvent-Coordinated Diiron(II) Compound: Synthesis and Dioxygen Reactivity of a Mixed-Valent Fe^IIFe^III Species

A new, DMF-coordinated, preorganized diiron compound [Fe2(N-Et-HPTB)­(DMF)4]­(BF4)3 (1) was synthesized, avoiding the formation of [Fe­(N-Et-HPTB)]­(BF4)2 (10) and [Fe2(N-Et-HPTB)­(μ-MeCONH)]­(BF4)2 (11), where N-Et-HPTB is the anion of N,N,N′,N′-tetrakis­[2-(1-ethylbenzimidazolyl)]-2-hydroxy-1,3-diaminopropane. Compound 1 is a versatile reactant from which nine new compounds have been generated. Transformations include solvent exchange to yield [Fe2(N-Et-HPTB)­(MeCN)4]­(BF4)3 (2), substitution to afford [Fe2(N-Et-HPTB)­(μ-RCOO)]­(BF4)2 (3, R = Ph; 4, RCOO = 4-methyl-2,6-diphenyl benzoate]), one-electron oxidation by (Cp2Fe)­(BF4) to yield a Robin–Day class II mixed-valent diiron­(II,III) compound, [Fe2(N-Et-HPTB)­(μ-PhCOO)­(DMF)2]­(BF4)3 (5), two-electron oxidation with tris­(4-bromophenyl)­aminium hexachloroantimonate to generate [Fe2(N-Et-HPTB)­Cl3(DMF)]­(BF4)2 (6), reaction with (2,2,6,6-tetramethylpiperidin-1-yl)­oxyl to form [Fe5(N-Et-HPTB)2(μ-OH)4(μ-O)­(DMF)2]­(BF4)4 (7), and reaction with dioxygen to yield an unstable peroxo compound that decomposes at room temperature to generate [Fe4(N-Et-HPTB)2(μ-O)3(H2O)2]­(BF4)·8DMF (8) and [Fe4(N-Et-HPTB)2(μ-O)4]­(BF4)2 (9). Compound 5 loses its bridging benzoate ligand upon further oxidation to form [Fe2(N-Et-HPTB)­(OH)2(DMF)2]­(BF4)3 (12). Reaction of the diiron­(II,III) compound 5 with dioxygen was studied in detail by spectroscopic methods. All compounds (1–12) were characterized by single-crystal X-ray structure determinations. Selected compounds and reaction intermediates were further examined by a combination of elemental analysis, electronic absorption spectroscopy, Mössbauer spectroscopy, EPR spectroscopy, resonance Raman spectroscopy, and cyclic voltammetry