Mimicking reactive high-valent diiron--oxo intermediates of nonheme enzymes by an iron tetracarbene complex.

The first diiron(iii,iv)-μ2-oxo tetracarbene complex is isolated and characterized by SC-XRD, UV/Vis, EPR, Evans' NMR and elemental analysis. CV indicates the presence of a transient high-valent diiron(iv)-μ2-oxo species. Its formation and decay is investigated via UV/Vis kinetics and NMR.

Electronic Finetuning of a Bio-inspired Iron(II) tetra-NHC Complex by trans Axial Isocyanide Substitution.

The synthesis of trans axially substituted mono- (1 a) and bis(tert-butylisocyanide) (1 b) derivatives of the highly active homogeneous bio-inspired iron(II) olefin epoxidation (pre-)catalyst 1 bearing an equatorial macrocyclic tetra N-heterocyclic carbene and two trans axial labile acetonitrile ligands is reported. NMR spectroscopy and SC-XRD indicate a considerable π-backdonation from the iron(II) centres to the isocyanide ligand(s). The impact of isocyanide substitution on the electronic features of the complexes is studied by cyclic voltammetry revealing a significant increase in half-cell potential assignable to the reversible Fe(II)/Fe(III) redox couple with an increasing number of isocyanides as a result of their π-accepting properties: E =0.

Binding of molecular oxygen by an artificial heme analogue: investigation on the formation of an Fe-tetracarbene superoxo complex.

The dioxygen reactivity of a cyclic iron(ii) tetra-NHC-complex (NHC: N-heterocyclic carbene) is investigated. Divergent oxidation behavior is observed depending on the choice of the solvent (acetonitrile or acetone). In the first case, exposure to molecular oxygen leads to an oxygen free Fe(iii) whereas in the latter case an oxide bridged Fe(iii) dimer is formed.

Oxidative degradation of the organometallic iron(II) complex [Fe{bis[3-(pyridin-2-yl)-1H-imidazol-1-yl]methane}(MeCN)(PMe3)](PF6)2: structure of the ligand decomposition product trapped via coordination to iron(II).

Iron is of interest as a catalyst because of its established use in the Haber-Bosch process and because of its high abundance and low toxicity. Nitrogen-heterocyclic carbenes (NHC) are important ligands in homogeneous catalysis and iron-NHC complexes have attracted increasing attention in recent years but still face problems in terms of stability under oxidative conditions. The structure of the iron(II) complex [1,1'-bis(pyridin-2-yl)-2,2-bi(1H-imidazole)-κN(3)][3,3'-bis(pyridin-2-yl-κN)-1,1'-methanediylbi(1H-imidazol-2-yl-κC(2))](trimethylphosphane-κP)iron(II) bis(hexafluoridophosphate), [Fe(C17H14N6)(C16H12N6)(C3H9P)](PF6)2, features coordination by an organic decomposition product of a tetradentate NHC ligand in an axial position.

Formation of Highly Strained N-Heterocycles via Decomposition of Iron N-Heterocyclic Carbene Complexes: The Value of Labile Fe-C Bonds.

An unusual, highly-strained annulated 2,2'-biimdazole was isolated as decomposition product of the outer-sphere one-electron oxidation of an iron(II) N-heterocyclic carbene (NHC) complex bearing a tetradentate bis(NHC)-bis- (pyridine) ligand (NCCN). Reductive elimination leading to the 2,2'-biimdazole is a consequence of the lability of the FeC bonds in the transient species and also extends to complexes with modified ligands but the same coordination geometry. Closely related by a two-electron redox step to a family of less-strained tetraazafulvalenes, the obtained 2,2'-biimidazolium salts were studied electrochemically.

Structural diversity of late transition metal complexes with flexible tetra-NHC ligands.

The synthesis of copper, gold, nickel, palladium, platinum, and iron complexes with open chain tetra-N-heterocyclic carbene (NHC) ligands via transmetalation using silver NHC complexes is presented. The obtained complexes show differing coordination geometries depending on both ligand structure and metal. While the complexes of the coinage metals form di- or tetranuclear structures, the group 10 metal complexes exhibit a distorted square planar coordination geometry at the metal centers.

Synthesis and characterization of an iron complex bearing a cyclic tetra-N-heterocyclic carbene ligand: an artifical heme analogue?

An iron(II) complex with a cyclic tetradentate ligand containing four N-heterocyclic carbenes was synthesized and characterized by means of NMR and IR spectroscopies, as well as by single-crystal X-ray structure analysis. The iron center exhibits an octahedral coordination geometry with two acetonitrile ligands in axial positions, showing structural analogies with porphyrine-ligated iron complexes. The acetonitrile ligands can readily be substituted by other ligands, for instance, dimethyl sulfoxide, carbon monoxide, and nitric oxide.

Application of open chain tetraimidazolium salts as precursors for the synthesis of silver tetra(NHC) complexes.

The synthesis of 3-((1H-imidazol-1-yl)methyl)-1-methyl-1H-imidazol-3-ium iodide 1 for the synthesis of multidentate tetra-N-heterocyclic carbene (NHC) structures is described. Two acyclic open chain tetra(NHC) precursors are synthesized together with their corresponding silver complexes. On the basis of nuclear magnetic resonance (NMR) spectroscopy and single crystal X-ray diffraction (XRD) data, the coordination geometry of the silver complexes is discussed.

Making oxidation potentials predictable: coordination of additives applied to the electronic fine tuning of an iron(II) complex.

This work examines the impact of axially coordinating additives on the electronic structure of a bioinspired octahedral low-spin iron(II) N-heterocyclic carbene (Fe-NHC) complex. Bearing two labile trans-acetonitrile ligands, the Fe-NHC complex, which is also an excellent oxidation catalyst, is prone to axial ligand exchange. Phosphine- and pyridine-based additives are used for substitution of the acetonitrile ligands.

Synthesis, characterization, and reactivity of furan- and thiophene-functionalized bis(N-heterocyclic carbene) complexes of iron(II).

The synthesis of iron(II) complexes bearing new heteroatom-functionalized methylene-bridged bis(N-heterocyclic carbene) ligands is reported. All complexes are characterized by single-crystal X-ray diffraction (SC-XRD), nuclear magnetic resonance (NMR) spectroscopy, and elemental analysis. Tetrakis(acetonitrile)-cis-[bis(o-imidazol-2-ylidenefuran)methane]iron(II) hexafluorophosphate (2a) and tetrakis(acetonitrile)-cis-[bis(o-imidazol-2-ylidenethiophene)methane]iron(II) hexafluorophosphate (2b) were obtained by aminolysis of [Fe{N(SiMe3)2}2(THF)] with furan- and thiophene-functionalized bis(imidazolium) salts 1a and 1b in acetonitrile.

Structure and catalytic activity of the ruthenium(I) sawhorse-type complex [Ru2{μ,η(2)-CF3(CF2)5COO}2(DMSO)2(CO)4].

The title compound, cis-di-μ-perfluoroheptanoato-κ(4)O:O'-bis[dicarbonyl(dimethyl sulfoxide-κS)ruthenium(I)](Ru-Ru), [Ru2(C7F13O2)2(C2H6OS)2(CO)4], is a sawhorse-type dinuclear ruthenium complex with two bridging perfluoroheptanoate ligands, and with two dimethyl sulfoxide (DMSO) ligands in the axial positions coordinating via the S atoms. It is a new example of a compound with an aliphatic fluorinated carboxylate ligand. The Ru-Ru bond distance of 2.

Combination of ionising irradiation and hyperthermia activates programmed apoptotic and necrotic cell death pathways in human colorectal carcinoma cells.

Purpose: The malignancy of tumor cells can be attenuated by interfering with cell death pathways. Since hyperthermia (HT) is a very potent radiosensitizer, the influence of HT (41.5 °C for 1 hour) alone and in combination with ionising irradiation (X-ray; 5 Gy or 10 Gy) on the form of cell death as well as on the expression of proteins known to be major components in tumor cells' apoptotic and necrotic pathways were examined in colorectal tumor cells.