'The Fe(III) complexes with a doubly-deprotonated polydentate acylhydrazone. Crystal structure of the first diamagnetic m-oxo-diiron(III) complex

The synthesis of two Fe(III) complexes with a doubly deprotonated polydentate of the acylhydrazone class is described. The first complex was obtained by hydrolyzing the previously synthesized high-spin pentagonal-bipyramidal (PBP) [Fe(Hdapsox)Cl-2] (H(2)dapsox = 2',2"'-(2,6-pyridindiyldiethylidene)dioxamohydrazide); the second was obtained by a template synthesis in a base medium starting from iron(III) chloride, 2,6-diacetylpyridine (dap) and semioxamazide (sox) (in a 1:1:2 molar ratio). Hydrolysis, during which the semioxamazide amide group changed into a carboxyl group, resulted in the mu -oxo-diiron(III) complex [Fe(dapoamh)(H2O)(2)O . 3H(2)O (H(2)dapoamh = dioxo-2,6-pyridinediylbis(ethylidyne-1-hydrazinyl-2-ylidene)diacetic acid) with a doubly deprotonated acylhydrazone that retained its PBP geometry. The [Fe(dapsox)Cl].H2O complex obtained in the latter case has a square-pyramidal geometry with an asymmetrically coordinated, but still doubly deprotonated dapsox as a tetradentate. The structure of the [Fe(dapoamh)(H2O)(2)O . 3H(2)O complex determined by single-crystal X-ray analysis in this work represents the first mu -oxo-dimer of a PBP geometry with an acyclic polydentate. This is also the first diamagnetic Cl-oxo-diiron(III) complex ever obtained; this not only points to the super-exchange interaction over an ore-oxygen, but also to a significant interaction between the two low-spin Fe(III) ion d-orbitals. Based on the EPR spectra, it has been established that the monomer [Fe(dapsox)Cl].H2O complex is among the rare Fe(III) complexes with an intermediate spin state S = 3/2, and that a temperature decrease causes it to change to a low-spin complex, i.e. it demonstrates a cross-over (S = 3/2 reversible arrow S = 1/2). Further characterization has been done by IR and UV-VIS spectroscopy, and also by measuring the magnetic momentum at 293, 195 and 77 K. The results of this work, as well as of the previously synthesized Cu(II), Co(II) and Ni(II) complexes with H(2)dapsox, Hdapsox(-) and dapsox(2-), have led us to the conclusion that the doubly deprotonated acylhydrazone ligand has a considerably stronger field than its neutral or monoanionic forms. (C) 2001 Elsevier Science B.V. All rights reserved

Self-assembled M12L24 nanospheres as a reaction vessel to facilitate a dinuclear Cu(i) catalyzed cyclization reaction

The application of large M12L24 nanospheres allows the pre-concentration of catalysts to reach high local concentrations, facilitating reactions that proceed through dinuclear mechanisms. The mechanism of the copper(I)-catalyzed cyclization of 4-pentynoic acid has been elucidated by means of a detailed mechanistic study. The kinetics of the reaction show a higher order in copper, indicating the formation of a bis-Cu intermediate as the key rate determining step of the reaction. This intermediate was further identified during catalysis by CIS-HRMS analysis of the reaction mixture. Based on the mechanistic findings, an M12L24 nanosphere was applied that can bind up to 12 copper catalysts by hydrogen bonding. This pre-organization of copper catalysts in the nanosphere results in a high local concentration of copper leading to higher reaction rates and turnover numbers as the dinuclear pathway is favored

Structural Versatility and Supramolecular Isomerism in Redox-Active Tetra- and Hexaruthenium Macrocycles

We report on six macrocyclic tetra‐ and hexaruthenium complexes formed by the self‐assembly of 2,5‐divinylthiophene‐ or 2,5‑divinylfuran‐bridged diruthenium and 2,5‐thiophene‐, ‐furan‐ or ‑pyrroledicarboxylate linkers. All complexes were scrutinized by NMR spectroscopy and UHR ESI‐MS, cyclic and square wave voltammetry and, in five cases, by X‐ray diffraction analyses. Although the utilized building blocks differ only slightly with respect to their intrinsic bite angles, the resulting macrocycles exhibit remarkable structural versatility. Electrolysis inside an optically transparent electrochemical (OTTLE) cell provided their associated di‐/tri‐ and tetra‐/hexacations, which were studied by IR, UV/Vis/NIR and EPR spectroscopy. The divinylthiophene‐furandicarboxylate complex 2‑TF provides a rare example of supramolecular isomerism in metallamacrocyclic complexes. Thus, hexanuclear 2‑TF 6 is initially formed as a kinetic isomer, which subsequently transforms slowly and cleanly into tetranuclear 2‑TF 4 .publishe

A broad view at the complexity involved in water oxidation catalysis based on Ru-bpn complexes

A new Ru complex with the formula [Ru(bpn)(pic)2]Cl2 (where bpn is 2,2′-bi(1,10-phenanthroline) and pic stands for 4-picoline) (1Cl2) is synthesized to investigate the true nature of active species involved in the electrochemical and chemical water oxidation mediated by a class of N4 tetradentate equatorial ligands. Comprehensive electrochemical (by using cyclic voltammetry, differential pulse voltammetry, and controlled potential electrolysis), structural (X-ray diffraction analysis), spectroscopic (UV-vis, NMR, and resonance Raman), and kinetic studies are performed. 12+ undergoes a substitution reaction when it is chemically (by using NaIO4) or electrochemically oxidized to RuIII, in which picoline is replaced by an hydroxido ligand to produce [Ru(bpn)(pic)(OH)]2+ (22+). The former complex is in equilibrium with an oxo-bridged species {[Ru(bpn)(pic)]2(μ-O)}4+ (34+) which is the major form of the complex in the RuIII oxidation state. The dimer formation is the rate determining step of the overall oxidation process (kdimer = 1.35 M−1 s−1), which is in line with the electrochemical data at pH = 7 (kdimer = 1.4 M−1 s−1). 34+ can be reduced to [Ru(bpn)(pic)(OH2)]2+ (42+), showing a sort of square mechanism. All species generated in situ at pH 7 have been thoroughly characterized by NMR, mass spectrometry, UV-Vis and electrochemical techniques. 12+ and 42+ are also characterized by single crystal X-ray diffraction analysis. Chemical oxidation of 12+ triggered by CeIV shows its capability to oxidize water to dioxygen

Halide coordinated homoleptic [Fe4S4X4](2-) and heteroleptic [Fe4S4X2Y2](2-) clusters (X, Y = Cl, Br, I)-alternative preparations, structural analogies and spectroscopic properties in solution and solid state

New facile methods to prepare iron sulphur halide clusters [Fe4S4X4](2-) from [Fe(CO)(5)] and elemental sulphur were elaborated. Reactions of ferrous precursors like tetrahalidoferrates(II) or simple ferrous halides with [Fe(CO)(5)] and sulphur turned out to be efficient methods to prepare homoleptic [Fe4S4X4](2-) (X = Cl, Br) and heteroleptic clusters [Fe4S4X4-nYn](2-) (X = Cl, Br; Y = Br, I). Solid materials were obtained as salts of BTMA(+) (= benzyltrimethylammonium); the new compounds containing [Fe4S4Br4](2-) and [Fe4S4X2Y2](2-) (X, Y = Cl, Br, I) were all isostructural to (BTMA)(2)[Fe4S4I4] (monoclinic, Cc) as inferred from synchrotron X-ray powder diffraction. While the solid materials contain defined heteroleptic clusters with a halide X : Y ratio of 2 : 2, dissolving these compounds leads to rapid scrambling of the halide ligands forming mixtures of all five possible [Fe4S4X4-nYn](2-) clusters as could be shown by UHR-ESI MS. The variation of X and Y allowed assignment of the absorption bands in the visible and NIR; the long-wavelength bands around 1100 nm were tentatively assigned to intervalence charge transfer (IVCT) transitions

Two Unsupported Terminal Hydroxido Ligands in a mu-Oxo-Bridged Ferric Dimer: Protonation and Kinetic Lability Studies

Zimmermann T, Limpke T, Orth N, et al. Two Unsupported Terminal Hydroxido Ligands in a mu-Oxo-Bridged Ferric Dimer: Protonation and Kinetic Lability Studies. INORGANIC CHEMISTRY. 2018;57(16):10457-10468

Halide coordinated homoleptic [Fe4S4X4]2- and heteroleptic [Fe4S4X2Y2]2- clusters (X, y = Cl, Br, I) - Alternative preparations, structural analogies and spectroscopic properties in solution and solid state

New facile methods to prepare iron sulphur halide clusters [Fe4S4X4]2- from [Fe(CO)5] and elemental sulphur were elaborated. Reactions of ferrous precursors like tetrahalidoferrates(ii) or simple ferrous halides with [Fe(CO)5] and sulphur turned out to be efficient methods to prepare homoleptic [Fe4S4X4]2- (X = Cl, Br) and heteroleptic clusters [Fe4S4X4-nYn]2- (X = Cl, Br; Y = Br, I). Solid materials were obtained as salts of BTMA+ (= benzyltrimethylammonium); the new compounds containing [Fe4S4Br4]2- and [Fe4S4X2Y2]2- (X, Y = Cl, Br, I) were all isostructural to (BTMA)2[Fe4S4I4] (monoclinic, Cc) as inferred from synchrotron X-ray powder diffraction. While the solid materials contain defined heteroleptic clusters with a halide X : Y ratio of 2 : 2, dissolving these compounds leads to rapid scrambling of the halide ligands forming mixtures of all five possible [Fe4S4X4-nYn]2- clusters as could be shown by UHR-ESI MS. The variation of X and Y allowed assignment of the absorption bands in the visible and NIR; the long-wavelength bands around 1100 nm were tentatively assigned to intervalence charge transfer (IVCT) transitions.Fil: Schüren, Andreas Oskar. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Química, Física de los Materiales, Medioambiente y Energía. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Química, Física de los Materiales, Medioambiente y Energía; Argentina. Universität zu Köln; AlemaniaFil: Gramm, Verena K.. Universität zu Köln; AlemaniaFil: Dürr, Maximilian. Friedrich-Alexander-Universität Erlangen-Nürnberg; AlemaniaFil: Foi, Maria Ana. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Química, Física de los Materiales, Medioambiente y Energía. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Química, Física de los Materiales, Medioambiente y Energía; ArgentinaFil: Ivanovic Burmazovic, Ivana. Friedrich-Alexander-Universität Erlangen-Nürnberg; AlemaniaFil: Doctorovich, Fabio. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Química, Física de los Materiales, Medioambiente y Energía. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Química, Física de los Materiales, Medioambiente y Energía; ArgentinaFil: Ruschewitz, Uwe. Universität zu Köln; AlemaniaFil: Klein, Axel. Universität zu Köln; Alemani

Catalytic H2O2 Activation by a Diiron Complex for Methanol Oxidation.

Zimmermann TP, Orth N, Finke S, et al. Catalytic H2O2 Activation by a Diiron Complex for Methanol Oxidation. Inorganic chemistry. 2020;59(21):15563–15569.In nature, C-H bond oxidation of CH4 involves a peroxo intermediate that decays to the high-valent active species of either a "closed" {FeIV(mu-O)2FeIV} core or an "open" {FeIV(O)(mu-O)FeIV(O)} core. To mimic and to obtain more mechanistic insight in this reaction mode, we have investigated the reactivity of the bioinspired diiron complex [(susan){Fe(OH)(mu-O)Fe(OH)}]2+ [susan = 4,7-dimethyl-1,1,10,10-tetrakis(2-pyridylmethyl)-1,4,7,10-tetraazadecane], which catalyzes CH3OH oxidation with H2O2 to HCHO and HCO2H. The kinetics is faster in the presence of a proton. 18O-labeling experiments show that the active species, generated by a decay of the initially formed peroxo intermediate [(susan){FeIII(mu-O)(mu-O2)FeIII}]2+, contains one reactive oxygen atom from the mu-oxo and another from the mu-peroxo bridge of its peroxo precursor. Considering an FeIVFeIV active species, a "closed" {FeIV(mu-O)2FeIV} core explains the observed labeling results, while a scrambling of the terminal and bridging oxo ligands is required to account for an "open" {FeIV(O)(mu-O)FeIV(O)} core