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Berlin Brandenburg

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  • 1
    Language: English
    In: Journal of the American Chemical Society, 02 April 2014, Vol.136(13), pp.4965-73
    Description: An isolated metal-monocatecholato moiety has been achieved in a highly robust metal-organic framework (MOF) by two fundamentally different postsynthetic strategies: postsynthetic deprotection (PSD) and postsynthetic exchange (PSE). Compared with PSD, PSE proved to be a more facile and efficient functionalization approach to access MOFs that could not be directly synthesized under solvothermal conditions. Metalation of the catechol functionality residing in the MOFs resulted in unprecedented Fe-monocatecholato and Cr-monocatecholato species, which were characterized by X-ray absorption spectroscopy, X-band electron paramagnetic resonance spectroscopy, and (57)Fe Mössbauer spectroscopy. The resulting materials are among the first examples of Zr(IV)-based UiO MOFs (UiO = University of Oslo) with coordinatively unsaturated active metal centers. Importantly, the Cr-metalated MOFs are active and efficient catalysts for the oxidation of alcohols to ketones using a wide range of substrates. Catalysis could be achieved with very low metal loadings (0.5-1 mol %). Unlike zeolite-supported, Cr-exchange oxidation catalysts, the MOF-based catalysts reported here are completely recyclable and reusable, which may make them attractive catalysts for 'green' chemistry processes.
    Keywords: Catechols -- Chemistry ; Metals -- Chemistry ; Organometallic Compounds -- Chemistry
    ISSN: 00027863
    E-ISSN: 1520-5126
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  • 2
    Language: English
    In: Journal of the American Chemical Society, 17 October 2012, Vol.134(41), pp.16921-4
    Description: Herein we report the one-pot synthesis of Fe(II) bis-terpyridine complexes with two peripheral square-planar Pt(II) bis-phosphinoalkylthioether moieties. These novel structures, which exhibit allosterically controllable electronic properties, are made by taking advantage of two orthogonal and high-yielding reactions. The prototypical complex can be structurally regulated through the reversible abstraction and introduction of chloride ions to the Pt(II) centers. This moves the Fe(II) center and two Pt(II) metal centers into and out of communication with each other, causing changes in the electronic structure of the complex and its corresponding optical and redox properties. The start and end points of the allosterically regulated system have been characterized by single-crystal X-ray diffraction and NMR, UV-vis, and (57)Fe Mößbauer spectroscopy.
    Keywords: Electrons ; Ferrous Compounds -- Chemical Synthesis ; Pyridines -- Chemistry
    ISSN: 00027863
    E-ISSN: 1520-5126
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  • 3
    Language: English
    In: Journal of the American Chemical Society, 18 April 2012, Vol.134(15), pp.6516-9
    Description: The reaction of TEMPO with the iron(I) synthon PhB(MesIm)(3)Fe(COE) leads to formation of the κ(1)-TEMPO complex PhB(MesIm)(3)Fe(TEMPO). Structural and spectroscopic data establish the complex contains divalent iron bound to a nitroxido anion and is isoelectronic to an iron(II) peroxo complex. Thermolysis of the complex results in N-O bond homolysis, leading to the formation of an iron(III) oxo intermediate. The oxo intermediate is active in oxygen atom transfer reactions and can be trapped by the triphenylmethyl radical to give the iron(II) alkoxo complex PhB(MesIm)(3)Fe(OCPh(3)).
    Keywords: Cyclic N-Oxides -- Chemistry ; Iron -- Chemistry
    ISSN: 00027863
    E-ISSN: 1520-5126
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  • 4
    Language: English
    In: Angewandte Chemie International Edition, 02 November 2015, Vol.54(45), pp.13431-13435
    Description: We report on an effective cluster expansion of CuBr‐linked aggregates by the increase of the steric bulk of the Cp ligand in the pentatopic molecules [CpFe(η‐P)]. Using [CpFe(η‐P)] (Cp=C(4‐BuCH)), the novel multishell aggregate [{CpFe(η‐P)}(CuBr)] is obtained. It shows topological analogy to the theoretically predicted I‐C fullerene molecule. The spherical cluster was comprehensively characterized by various methods in solution and in the solid state. : The change from Cp* to the sterically highly demanding ligand Cp in the pentaphosphaferrocenes resulted in an effective expansion of the aggregate giant spherical cluster which has a diameter of about 3.5 nm. It exhibits structural analogy to the hitherto unknown ‐C fullerene, a structural motif that has not yet been observed experimentally.
    Keywords: C 140 Fullerene ; Cp Big ; Giant Clusters ; Pentaphosphaferrocene ; Supramolecular Chemistry
    ISSN: 1433-7851
    E-ISSN: 1521-3773
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  • 5
    Language: English
    In: Journal of the American Chemical Society, 22 August 2012, Vol.134(33), pp.13651-61
    Description: The air stable complex [(PNP)FeCl(2)] (1) (PNP = N[2-P(CHMe(2))(2)-4-methylphenyl](2)(-)), prepared from one-electron oxidation of [(PNP)FeCl] with ClCPh(3), displays an unexpected S = 3/2 to S = 5/2 transition above 80 K as inferred by the dc SQUID magnetic susceptibility measurement. The ac SQUID magnetization data, at zero field and between frequencies 10 and 1042 Hz, clearly reveal complex 1 to have frequency dependence on the out-of-phase signal and thus being a single molecular magnet with a thermally activated barrier of U(eff) = 32-36 cm(-1) (47-52 K). Variable-temperature Mössbauer data also corroborate a significant temperature dependence in δ and ΔE(Q) values for 1, which is in agreement with the system undergoing a change in spin state. Likewise, variable-temperature X-band EPR spectra of 1 reveals the S = 3/2 to be likely the ground state with the S = 5/2 being close in energy. Multiedge XAS absorption spectra suggest the electronic structure of 1 to be highly covalent with an effective iron oxidation state that is more reduced than the typical ferric complexes due to the significant interaction of the phosphine groups in PNP and Cl ligands with iron. A variable-temperature single crystal X-ray diffraction study of 1 collected between 30 and 300 K also reveals elongation of the Fe-P bond lengths and increment in the Cl-Fe-Cl angle as the S = 5/2 state is populated. Theoretical studies show overall similar orbital pictures except for the d(z(2)) orbital, which has the most sensitivity to change in the geometry and bonding, where the quartet ((4)B) and the sextet ((6)A) states are close in energy.
    Keywords: Chemistry;
    ISSN: 00027863
    E-ISSN: 1520-5126
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  • 6
    Language: English
    In: Angewandte Chemie International Edition, 26 October 2018, Vol.57(44), pp.14597-14601
    Description: The 16‐valence electron species [Cp*Fe] (Cp*=η‐CMe), formally featuring a tetravalent iron ion, quantitatively binds CO in HF solution to form the stable, diamagnetic carbonyl species [Cp*Fe(CO)]. This dication forms salts in the presence of AsF and SbF that were crystallographically characterized. The molecular structure in crystals of [Cp*Fe(CO)](AsF) displays cyclopentadienyl rings that are clearly not parallel and an equatorially bound η‐CO ligand. The formal oxidation state +IV of iron was investigated by Fe Mössbauer spectroscopy and is supported by DFT computational analysis. A detailed spectroscopic characterization of the hitherto unprecedented high‐valent iron carbonyl compounds is reported. iron carbonyl complex [Cp*Fe(CO)](AsF), containing formally tetravalent iron, has been prepared by treating [Cp*Fe] with carbon monoxide in anhydrous HF. The complex was characterized by various spectroscopic techniques, including Fe Mössbauer spectroscopy and DFT computational analysis.
    Keywords: 57 Fe Mössbauer Spectroscopy ; Carbonyl Ligands ; Cyclopentadienyl Ligands ; Iron ; Metallocenes
    ISSN: 1433-7851
    E-ISSN: 1521-3773
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  • 7
    Language: English
    In: Angewandte Chemie International Edition, 16 October 2017, Vol.56(43), pp.13372-13376
    Description: Ferrocene, CpFe, is quantitatively protonated in a mixture of liquid HF/PF to yield [CpFeH](PF), which was characterized by H/C NMR and Fe Mössbauer spectroscopy as well as single‐crystal X‐ray diffraction analysis. X‐ray diffraction analysis at 100 K revealed a disordered, iron‐coordinated hydrido ligand, which was unambiguously located by aspherical atom refinement at 100 K, and by analyzing the non‐disordered crystal structure at 30 K, revealing a non‐agostic structure. , the mechanism of electrophilic substitutions on ferrocene was reinvestigated for the simplest electrophile, H, and the potential intermediate [CpFeH] was isolated. Single crystals of [CpFeH](PF) were obtained from an anhydrous HF/PF system. X‐ray diffraction analysis revealed a non‐agostic structure with an iron‐bound hydrido ligand.
    Keywords: Ferrocene ; Hydride ; Iron ; Superacids ; X-Ray Diffraction
    ISSN: 1433-7851
    E-ISSN: 1521-3773
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  • 8
    Language: English
    In: Inorganic chemistry, 20 July 2015, Vol.54(14), pp.6763-75
    Description: In an earlier study we investigated the reaction of iron(II) chloride with NO in a strongly coordinating ionic liquid 1-ethyl-3-methylimidazolium dicyanamide [emim][dca] and showed that the actual reactive species in solution was [Fe(II)(dca)5Cl](4-). For the present report we investigated in detail how this reaction could proceed in a noncoordinating ionic liquid 1-ethyl-3-methylimidazolium trifluoromethylsulfonate [emim][OTf]. The donor ability of OTf(-) is much lower than that of dca(-), such that the solubility of FeCl2 in [emim][OTf] strongly depended on other donors like water or chloride ions present or added to the ionic liquid. On increasing the chloride concentration in [emim][OTf], the tetrachloridoferrate complex [emim]2[FeCl4] was formed, as verified by X-ray crystallography. This complex undergoes reversible binding of NO, for which the UV-vis spectral characteristics of the green-brown nitrosyl product resembled that found for the corresponding nitrosyl complexes formed in water and [emim][dca] as solvents. A detailed analysis of the spectra revealed that the {Fe-NO}(7) species has Fe(II)-NO(•) character in contrast to Fe(III)-NO(-) as found for the other solvents. The formation constant, however, is much higher than in [emim][dca], lying closer to the value found for water as solvent. Surprisingly, the Mössbauer spectrum found in [emim][OTf] is very unusual and unsimilar to that found in water and [emim][dca] as solvents, pointing at a different electron density distribution between Fe and NO in {Fe-NO}.7 First, the high isomer shift points to the presence of iron(II) species in solution, thus indicating that upon NO binding no oxidation to iron(III) occurs. Second, the negligible quadrupole splitting suggests a high local symmetry around the iron center. The nitrosyl product is suggested to be [Fe(II)Cl3NO](-), which is supported by electron paramagnetic resonance (EPR) and IR measurements. The nature of the Fe(II) complexes formed in [emim][OTf] depends on the additives required to dissolve FeCl2 in this ionic liquid.
    Keywords: Iron Compounds – Chemical Properties ; X-Ray Crystallography – Usage ; Ionic Liquids – Research;
    ISSN: 00201669
    E-ISSN: 1520-510X
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  • 9
    Language: English
    In: Inorganic chemistry, 17 March 2014, Vol.53(6), pp.2763-5
    Description: A new family of C3-symmetric ligands, featuring phenolate donors and a secondary coordination sphere, have been synthesized. We report the synthesis and subsequent coordination chemistry of these new tripodal N-anchored tris(phenolate) chelates, [tris(5-tert-butyl-3-N-carboxamide-2-hydroxybenzyl)amines] (H3(R)SalAmi), to iron(II), iron(III), and zinc(II). These electron-rich complexes have intramolecular hydrogen bonds, and therefore the potential to stabilize biologically relevant substrates in small-molecule activation chemistry.
    ISSN: 00201669
    E-ISSN: 1520-510X
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  • 10
    Language: English
    In: Organometallics, 10/28/2013, Vol.32(20), pp.5935-5945
    ISSN: 0276-7333
    E-ISSN: 1520-6041
    Source: American Chemical Society (via CrossRef)
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