1,721,191 research outputs found
2,2'-Bipyridine Equipped with a Disulfide/Dithiol Switch for Coupled Two Electron and Proton Transfer
Full text link[1,2]dithiino[4,3-b:5,6-b´]dipyridine (1) and its protonated open form 3,3´-dithiol-2,2´-bipyridine (2) were synthesised and their interconversion investigated. The X-ray structure of 2 revealed an anti orientation of the two pyridine units and a zwitterionic form. In depth electrochemical studies in combination with DFT calculations lead to a comprehensive picture of the redox chemistry of 1 in the absence and presence of protons. Initial one electron reduction at E1 = −1.97 V results in the formation of the radical anion 1red with much elongated S-S bond, which readily undergoes further reduction at E2 = −2.15 V. Water triggers a potential inversion (E ≥ −1.9 V for the second reduction) as the radical anion 1red is protonated at its basic N atom. DFT studies revealed that S−S bond breaking and twisting of the pyridine units generally occurs after the second reduction step while the potential inversion induced by protonation is a result of charge compensation. The CV data were simulated to derive rate constants for the individual chemical and electrochemical reactions for both scenarios in the absence and presence of protons.Fil: Cattaneo, Mauricio. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tucumán. Instituto de Química del Noroeste. Universidad Nacional de Tucumán. Facultad de Bioquímica, Química y Farmacia. Instituto de Química del Noroeste; ArgentinaFil: Schiewer, Christine. Universität Göttingen; AlemaniaFil: Schober, Anne. Universität Göttingen; AlemaniaFil: Dechert, Sebastian. Universität Göttingen; AlemaniaFil: Siewert, Inke. Universität Göttingen; AlemaniaFil: Meyer, Franc. Universität Göttingen; Alemani
Non-innocence of N-heterocyclic carbene ligands: Intermolecular C-H activation in allyl palladium NHC complexes
No full textPolynuclear transition metal complexes of meta center dot center dot center dot metal-bridging compartmental pyrazolate ligands
No full textThe present article reviews the structures and properties of di-, oligo- and polynuclear transition metal complexes of substituted pyrazolate (pz) ligands with ligating side arms (D(n)) in which the N(2)-unit of the pyrazole ring acts as a bridge between two metal centres. Extensive literature surveys covering the literature until the beginning of 2008 of symmetrical 3,5-disubstituted ligands of the type D-pz-D-, D(2)-pz-D(2)- and D(3)-pz-D(3) with uni-, bi-and terdentate side arms, respectively, as well as of unsymmetrical 3,5-disubstituted ligands of the type D(n)(1)-pz-D(m)(2). are presented together with a comprehensive survey of the structurally characterised complexes thereof. Catalytic and/or stoichionnetric reactions of the dinuclear systems are discussed where appropriate. (C) 2009 Elsevier B.V. All rights reserved
Stereoselective Formation of C2-Symmetric ansa-Lanthanocenes by Reductive Coupling of Acenaphthylene with Activated Ytterbium or Samarium
No full textBridged dinucleating N-heterocyclic carbene ligands and their double helical mercury(II) complexes
No full textA series of six 3,6-bis(imidazolium-3-yl)pyridazine derivatives with different imidazole-N substituents have been synthesized and isolated as the salts [H2L]Cl-2 (1a)-(6a) and [H2L](PF6)(2) (1b)-(6b). Solid state structures have been determined crystallographically for eleven out of the twelve compounds, revealing diverse hydrogen bonding patterns that involve the imidazolium-(CH)-H-2 units and the anions. N-heterocyclic carbene (NHC) mercury(II) complexes [Hg2L2](PF6)(4) (7)A9) are readily formed in good yields from ligand precursors [H2L](PF6)(2) and Hg(OAc)(2), as long as imidazole-N substituents are not too bulky. X-ray crystallography reveals double helical bimetallic arrangements for the stable [Hg2L2](4+) cations. Ligand scrambling in [Hg2L2](4+) occurs only in the presence of free carbene precursor, presumably via an associative mechanism. (c) 2006 Elsevier B.V. All rights reserved
Highly Active and Readily Accessible Proline-Based Dizinc Catalyst for CO 2 /Epoxide Copolymerization
No full textBiomimetic Copper(I)-mediated Activation of Dioxygen and Unexpected Non-innocence in Copper(II) complexes of Bis(oxazolines)
No full textDicopper(I) oxalate complexes as molecular precursors for the deposition of copper compounds
No full textThe synthesis, characterization, and thermal decomposition behavior of dicopper(l) oxalato complexes L4Cu2(C2O4) (L = CNtBu (2a), CNCMe(2)CH(2)tBu (2b), CNC6H3Me2-2,6 (2c)) is reported. 2c can be prepared in a straightforward manner by the reaction of stoichiometric amounts of Cu2O and oxalic acid with four equivalents of CNC6H3Me2-2,6, while those complexes with aliphatic isocyanides are better prepared from a copper(l) oxalato complex with alkine capping ligands (Me3SiC equivalent to CSiMe3)(2)-Cu-2(C2O4) (1) via ligand exchange. Crystallographic and spectroscopic evidence for 2a-c confirms the anticipated dinuclear structure with the oxalate in a mu-1,2,3,4 bridging mode and an essentially sigma-character of the terminal isocyanicles. In solid form the complexes are stable at room temperature and can be handled in air for some time. Their decomposition was studied by thermal gravimetric analysis coupled with mass spectrometry, and the degradation pathway was shown to depend on the type of isocyanide capping ligand. Decomposition of 2a,b takes place between 150 and 200 degrees C to give CuCN in a clean process that involves isobutene elimination from the terminal ligands, with elimination of (CN)(2) and conversion to elemental copper at higher temperatures. Heating of 2c leads to CuO (and then to Cu2O) via release of the intact isocyanide, CO2, and CO in a well-behaved thermal process around 200-280 degrees C. (c) 2005 Elsevier B.V. All rights reserved
A versatile access to pyridazines with tethered imidazolium groups - new precursors for mono- and binucleating NHC/pyridazine hybrid ligands
No full textOne or two imidazolium groups have been attached to the 3- and 6-positions of the pyridazine heterocycle, providing valuable precursors for mono- and binucleating NHC/pyridazine hybrid ligands. For N-methyl imidazole with specific backbone substituents an unexpected methyl group transfer is observed, which defines the scope of the synthetic procedure. H-Bonding patterns in the solid state are elucidated by X-ray crystallography for seven chloride or PF6- salts of the new compounds. (c) 2007 Elsevier Ltd. All rights reserved
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