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  • General Chemistry  (10,504)
  • Cell & Developmental Biology  (2,874)
  • 1995-1999  (9,359)
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  • 101
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 217-219 
    ISSN: 1434-1948
    Keywords: Nickel ; Iron ; Clusters ; Carbonyl complexes ; S ligands ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Upon reaction of the mononuclear nickel dithiolate complex [Ni(dsdm)] (H2dsdm = N,N′-dimethyl-N,N′-bis(2-sulfanylethyl)ethylenediamine) with K[HFe(CO)4] in ethanol a unique reshuffling of ligands and of oxidation states takes place. This results in the formation of a novel tetranuclear complex [FeII(dsdm)Ni0(CO)3]2, in which a linear array of Ni-Fe-Fe-Ni is formed. The inner core of this complex consists of the dinuclear [Fe(dsdm)]2, and two Ni(CO)3 groups are bound at the periphery through one of the thiolate sulfurs.
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  • 102
    ISSN: 1434-1948
    Keywords: Ruthenium ; Nitrogen heterocycles ; Hydrogen bonds ; Antitumor agents ; Crystal structures ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The X-ray structure of the potential antitumour complex trans-[RuCl3(H2O)(admtp)2] · H2O (admtp = 2-amino-5,7-dimethyl[1,2,4]triazolo[1,5-a]pyrimidine) shows unique and very interesting intramolecular hydrogen-bonding properties with the non-bridgehead pyrimidinic nitrogen atom of admtp acting as hydrogen acceptor and the amino group acting as hydrogen donor.Supporting information for this article is available on the WWW under http://www.wiley-vch.de/contents/jc_2005/1999/98348_s.pdf or from the author.
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  • 103
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 225-233 
    ISSN: 1434-1948
    Keywords: Arene complexes ; Chromium ; Sidechain functionalization ; Allenes ; Cuprates ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The cuprate addition to (arene)Cr(CO)3-substituted phosphorylallenes 1 gives rise to the regioselective formation of complexed allylphosphane oxide derivatives 3a-c and allylphosphonate derivatives 3d-j in good yields. In the case of racemic planar chiral ortho-substituted complexed (arylallenyl)phosphonates 1c, d the protonation of the intermediate allyl anion proceeds diastereoselectively due to the hindered rotation around the Cipso-Cα bond. This diastereoselective protonation is discussed on the basis of the conformational analysis as deduced from the X-ray structure analyses of the allenylphosphonate 1d and the allylphosphonates 3i, j.
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  • 104
    ISSN: 1434-1948
    Keywords: Dimolybdenum(III) complexes ; Azavinylidene ; C-C coupling ; Acetonitrile ligands ; X-ray crystal structure ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Removal of a proton from one of the two coordinated acetonitrile ligands in [Mo2Cp2(μ-SMe)3(CH3CN)2](BF4) (1) initiates its intramolecular condensation with the second of the acetonitrile ligands attached to the bimetallic [Mo2Cp2(μ-SMe)3] core, thereby giving rise to the novel μ-η1-azavinylidene complex {Mo2Cp2(μ-SMe)3[μ-η1-N=C(CH3)-CH2CN]} (2). Complex 2 has been characterized by NMR and X-ray methods.
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  • 105
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 247-253 
    ISSN: 1434-1948
    Keywords: Boron ; Fluorine ; Oxidation ; Nitrogen ; Molecular structures ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: (CF3)3B · NH3 (1) has been oxidized in aqueous solution using a platinum anode. At pH = 8-9 in CsOH/Cs2CO3 solution Cs[(CF3)3B-NO2] (2), Cs2[(CF3)3B-N(O)=N(O)-B(CF3)3] (3) and Cs2[(CF3)3B-N=N(O)-B(CF3)3] (4) are formed. Compound 3 slowly hydrolyses to yield the hydroxyborate Cs[(CF3)3B-OH] (5). Compound 2 and traces of 3 and 5 were also formed by oxidation of 1 or (CF3)3B · NHEt2 with ozone. The constitution of the novel borates has been deduced from multinuclear NMR, IR and mass spectra. The structures of 2-5 have been investigated by single-crystal X-ray diffraction.
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  • 106
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 235-245 
    ISSN: 1434-1948
    Keywords: TiO2 ; Growth ; Self-organisation ; Polytitanate ; Nanocrystals ; Nanostructure ; Superlattice ; Films ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Control over crystal structure, size, shape, and organization of TiO2 nanocrystals has been achieved by means of wet chemistry. Hydrolysis and polycondensation of titanium alkoxide [Ti(OR)4] has been performed in the presence of tetramethylammonium hydroxide (Me4NOH). This base both catalyzes the reaction and provides an organic cation that stabilizes the anatase polyanionic cores formed in this medium. These anatase clusters are organized so as to favour self-assembly into intermediate nanocrystals, which, in turn, self-assemble into superlattices. This self-assembling process has been exploited for the processing of highly structured titania films. Furthermore, larger anatase TiO2 nanocrystals of different sizes and shapes have been obtained by adjusting the relative concentrations of titanium alkoxide and Me4NOH, the reaction temperature, and the pressure. HRTEM, XRD, and EXAFS have been used to characterize the various samples and to elucidate the growth of titania anatase. Our observations are in accordance with theoretically predicted condensation and growth pathways. The formation of mesoscopic structures through a self-assembling process of the multiply charged polytitanate anions in the presence of Me4N+ is also discussed.
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  • 107
    ISSN: 1434-1948
    Keywords: Boron ; Small rings ; Trifluoromethyl group ; Crystal structure ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 1,1-Dimethyl-2,2-bis(trifluoromethyl)azoniaboratacyclopropanes, cyclo-(F3C)2B-CR1R2-NMe2 [R1 = R2 = C6H5 (2a); R1/R2 = C12H8 (2b); R1 = H, R2 = C6H5 (2c), 4-FC6H4 (2d), 3-FC6H4 (2e), 2-FC6H4 (2f), C6F5 (2g), iPr (2h), tBu (2i); R1 = Me, R2 = C(=O)OMe (2j), C(=O)OEt (2k)] have been obtained from (F3C)2BNMe2 (1) and diazomethanes R1R2CN2. In contrast to compound 2a, the B-N bonds of 2b-2k hydrolyze to form the zwitterionic species Me2NH-CR1R2-B(CF3)2OH (3b-3k). The diazoacetic acid esters HC(N2)C(=O)OMe and HC(N2)C(=O)OtBu react with 1 to form three-membered rings, which hydrolyze rapidly to form Me2NH-CR1R2-B(CF3)2OH [R1 = H, R2 = C(=O)OMe (3l), C(=O)OtBu (3m)]. F3CSiF3 reacts under elimination of CF2 with 1 to form the acyclic derivative (F3C)2BF-CF=NMe2 (4). The structures of 2a and 3ghave been investigated crystallographically. A nearly eclipsed conformation is found for the central B-C bond of 3g, which is 0.097(7) Å longer than the B-C bond length in the three-membered ring of 2a.
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  • 108
    ISSN: 1434-1948
    Keywords: Macrocyclic ligands ; N ligands ; Nickel complexes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Isomeric cis-2,9-bis(aminomethyl)-5,7,7,12,14,14-hexamethyl-1,4,8,11-tetraazacyclotetradecanes (6a and 6b) and their octahedral (4) and square-planar nickel(II) complexes (5) have been prepared and characterized. X-ray crystallographic investigations of the octahedral complexes have confirmed a folded conformation of the macrocyclic ring. Protonation of the pendant amino groups results in a change in the Ni configuration, which is accompanied by a concomitant change of the macrocycle conformation from a folded to a planar one. The structures of the protonated, square-planar complexes and of the free ligands have been established mainly on the basis of their 1H- and 13C-NMR spectra.
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  • 109
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 277-285 
    ISSN: 1434-1948
    Keywords: Nitric acid ; Nitrogen oxides ; Electrochemistry ; Thermodynamics ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Calculated diagrams, representing chemical and electrochemical properties of concentrated aqueous nitric acid mixtures, have been drawn for temperatures of 25 °C and 100 °C using vapor pressures and thermochemical data of related gaseous species. Electrochemical measurements have permitted the establishment of an experimental potential scale (referenced to the saturated mercurous sulfate electrode at 25 °C) incorporated in the diagram at 100 °C. These measurements also allowed the determination of the Gibbs free energy of formation of dissolved nitrous acid for various nitric acid solutions at 100 °C, leading to a value of ΔGf(HNO2) = -36.31 kJ mol-1, for the whole nitric acid concentration range.
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  • 110
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 269-276 
    ISSN: 1434-1948
    Keywords: Phthalocyanines ; Porphyrazines ; Macrocycles ; Chalcogen atom substitution ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A series of chalcogen atom substituted porphyrazines have been assembled and characterized. Oxygen and sulfur chalcogen atoms have been substituted for peripheral methylene groups. Heteroatom-enriched, seven-membered ring dinitriles (1-3) were synthesized and characterized by IR, MS, UV-vis, 1H NMR, elemental analysis, and X-ray analysis to examine the ring conformations. They were template cyclized in the presence of MgII to form the MgII containing porphyrazine macrocycles. The MgII and metal-free macrocycles (4-9) were synthesized for all peripherally substituted porphyrazines. The unchalcogen-substituted NiII, CuII, and ZnII containing porphyrazine derivatives (10-12) were also synthesized because of the higher solubility of the metal-free porphyrazine 7. The macrocycles were characterized and studied using such techniques as UV-vis, IR, elemental analysis, cyclic voltammetry, and electrical conductivity measurements.
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  • 111
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 287-293 
    ISSN: 1434-1948
    Keywords: MRI contrast agents ; Macrocyclic ligands ; Cyclodextrins ; Host-guest chemistry ; Lanthanides ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The interactions between α-, β-, and γ-CD and the TmIII chelates of the macrocyclic polyaminopolycarboxylates DOTA and NOTA were studied with the use of 1H- and 13C-NMR shift and relaxation rate measurements. Interactions were only observed between Tm(DOTA)- and γ-CD. The structure and the stability of the concerning supramolecular structures was elucidated by fitting of the NMR titration curves to a theoretical model. It appears that an inclusion compound is formed, where the hydrophobic macrocyclic part of the chelate sits in the γ-CD cavity. This inclusion compound binds a second Tm(DOTA)- molecule at the outside lower rim of the CD cone. The binding occurs probably via hydrogen bonds between non-chelated carboxylate oxygen atoms of the concerning Tm(DOTA)- and CH2OH groups of the γ-CD molecule, which are in a favorable position due to opening of the γ-CD cone angle as a result of the inclusion of the first γ-CD.
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  • 112
    ISSN: 1434-1948
    Keywords: Chromium ; Carboxylate complexes ; Metal-metal multiple bonds ; Molybdenum ; Rhenium ; Tungsten ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Reaction of Re2{μ-O2CC(CH3)3}4Cl2 with [(CO)5M-CN]Na (M = Cr, Mo, W) leads to tetranuclear complexes of formula Re2{μ-O2CC(CH3)3}4[-NC-M(CO)5]2 (M = Cr, Mo, W). These complexes were characterized by 1H-, 13C-, and 95Mo-NMR, IR and Raman spectroscopy, elemental analysis and examined by cyclic voltammetry. The applied methods show the donor capabilities of the [(CO)5M-CN]- ligands which shift electron density towards the Re centers weakening the Re-Re quadruple bond. The Re-Re bond lengths and the ν(Re-Re) force constants are estimated based on the FT-IR and Raman examinations. Photochemical examinations and TG/MS experiments have also been conducted. The latter method shows that the product complexes decompose around 100 °C, by first loosing their carbonyl substituents; as do the Cr, Mo, W precursor compounds. The dirhenium tetrapivalate unit decomposes only at higher temperatures in a distinct second step.
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  • 113
    ISSN: 1434-1948
    Keywords: Spectroelectrochemistry ; Cyclic voltammetry ; Photochemistry ; Copper(II) complexes ; Thiolate complexes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The electrochemical and photoredox properties of copper(II) thiopyrazolone Schiff base complexes 1-9 with imine and thiolate coordination, showing variable degrees of tetrahedral distortion, were investigated by means of combined electrochemical and spectroscopic techniques in the temperature range of 193-293 K. The cyclic voltammograms of 1-9 in butyronitrile revealed that the reduction and oxidation paths are strongly dependent on the geometry of the CuN2S2 moiety. Due to the strong delocalization of the singly occupied redox orbital (SOMO) the oxidations and reductions occur in a narrow potential range. The one-electron-reduced 1(r)-9(r) and oxidized 1(o)-9(o) products were electrogenerated and stabilized inside optically transparent thin-layer electrochemical (OTTLE) cells at variable temperatures and could be characterized for the first time by UV/Vis spectroscopy. The reduced formal d10 copper(I) species absorb only weakly in the visible region. The oxidized products 1(o)-9(o) show several strong absorptions in the visible region due to the presence of formal d8 copper(III) species. The spectral information allowed assignment of the initial photoproducts. Irradiations in donor media such as THF or EtOH initially produces 1(r)-9(r). No photoreduction was observed in tBuOH which cannot liberate reducing Hα. The primary oxidized species 1(o)-9(o) were formed in chlorinated acceptor solvents (CHCl3) on UV irradation. Fast relaxation to the ground state prevents the photoredox reactions from CT or LF excited states.
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  • 114
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 323-332 
    ISSN: 1434-1948
    Keywords: Semiconductors ; Germanium carbide ; Radiolysis ; Ab initio calculations ; Gas-phase reactions ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Gas-phase radical reactions of germane/ethylene mixtures have been investigated using theoretical calculations and radiolysis techniques. Ab initio quantum chemical calculations have been performed on reactions starting from GeHx (x = 0-3) radicals and C2H4. The geometrical structure and relative stability of isomeric GeC2Hn (n = 4-7) radicals have been investigated and restricted to the species in which a C-C bond is present, at the MP2(FROZEN) level of calculation with double-ζ quality basis sets. To better evaluate the relative stability of the investigated species, single-point calculations at the QCISD(T) level were performed with a 6-311G(3df,2p) basis set. Reaction enthalpies and heats of formation of the species have also been determined using theoretical calculations. From irradiation of GeH4/C2H4 mixtures, condensed products and volatile species were obtained. Composition, amount, and characteristics of the condensed phase products are reported. The volatile compounds were identified and their amounts determined. From experimental results and theoretical calculations some hypotheses on the reaction mechanisms are presented.
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  • 115
    ISSN: 1434-1948
    Keywords: Tungsten complexes ; Molybdenum complexes ; Tetradentate ligands ; Oxygen-atom transfer ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A series of N2O2 tetradentate ligands with a range of substituents attached to the nitrogen atoms have been prepared (H2Ln) (n = 1-9). Treatment of these ligands and the N2S2 tetradentate ligand H2L10 with [WO2Cl2(DME)] (DME = 1,2-dimethoxyethane) in the presence of triethylamine leads to the formation of cis-dioxotungsten(VI) complexes [WO2(Ln)] (n = 1-10). Reaction of the N2O2 tetradentate ligands H2Ln (n = 1, 3-7) with ammonium molybdate tetrahydrate and dilute hydrochloric acid gives the corresponding molybdenum(VI) analogs [MoO2(Ln)] (n = 1, 3-7). These compounds have been spectroscopically characterized and the molecular structures of [WO2(Ln)] (n = 1, 2, 9) and [MoO2(L5)] have been established by X-ray diffraction analysis. These high-valent compounds participate in oxygen-atom transfer reactions and can catalyze the oxidation of benzoin with dimethyl sulfoxide. The complex [WO2(L10)], which contains an S-donor ligand, has lower reduction potential and higher reactivity toward oxo-transfer reactions than analogous tungsten complexes having N2O2 ligands. The kinetics of these catalytic processes along with the structure and electrochemistry of these dioxotungsten and -molybdenum complexes are described and compared.Supporting information for this article is available on the WWW under http://www.wiley-vch.de/contents/jc_2005/1999/98246_s.pdf or from the author.
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  • 116
    ISSN: 1434-1948
    Keywords: Cleavage reactions ; C-S cleavage ; Ligand synthesis ; Osmium ; Ruthenium ; S ligands ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In search of a tetradentate thioether thiolate ligand that is more stable toward reductive C-S bond cleavage than the parent ligand ′S4′-H2 [′S4′-H2 = 1,2-bis(2-mercaptophenylthio)ethane], the novel tris-phenylene ligand ′tpS4′-H2 (3) [′tpS4′-H2 = 1,2-bis(2-mercaptophenylthio)phenylene] was synthesized via the nitro and amine compounds ′tpS2(NO2)2′ (1) and ′tpS2(NH2)2′ (2). The coordination of ′tpS4′2- to ruthenium centers resulted in the formation of six-coordinate [Ru(L)(PR3)(′tpS4′)] complexes (R = Et, L = PEt34; R = Ph, L = PPh35, CO 6, DMSO 7). The X-ray structure analyses of 4 and 6 revealed that the thiolate donors occupy trans positions; consequently the ′tpS4′2- ligand coordinates in the same way as the ′S4′2- ligand. The stability of the ′tpS4′2- ligand toward reductive C-S cleavage reactions was shown by the synthesis of [Os(PEt3)2(′tpS4′)] (8). In contrast to [Os(PEt3)2(′S4′)], 8 is stable for unlimited periods of time. The X-ray structure analysis of [Ru(Cl)2(PPh3)(′tpS2(NH2)2′)] (9) demonstrates that the potentially tetradentate ligand ′tpS2(NH2)2′ coordinates in 9 through three donors leaving one NH2 donor dangling.
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  • 117
    ISSN: 1434-1948
    Keywords: Copper clusters ; Cu(100) surface ; Chemical hardness ; Relaxation energy ; Size effect ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Density Functional Theory is used to study the influence of the size of copper clusters modeling the Cu(100) surface, on the electronic properties: ionization potential, electron affinity, electronic chemical potential, and chemical hardness. The model clusters are chosen to have a bilayer structure and range in size from 9 to 20 copper atoms. The chemical hardness being identified as the relaxation energy of the frontier levels when an electron is removed or added to the system, a simple expression is proposed to estimate its value from the eigenenergies of the frontier levels in neutral and partially ionized systems. A detailed comparison of the geometric and electronic structures is made between the model surface copper clusters, real copper clusters, and the actual metal surface; it is seen that the model surface clusters provide an easy extrapolation to the properties of the metal surface.
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  • 118
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    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 341-348 
    ISSN: 1434-1948
    Keywords: N ligands ; S ligands ; Iron ; Ruthenium ; Pentadentate ligands ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In order to obtain iron and ruthenium complexes which are analogous to [M(L)(′NHS4′)] and [M(L)(′N2H2S3′)] complexes [′NHS4′2- = 2,2′-bis(2-mercaptophenylthio)diethylamine(2-), ′N2H2S3′2- = 2,2′-bis(2-mercaptophenylamino)diethylsulfide(2-)] but have electron-richer metal centers, the new pentadentate amine thiolate ligand ′N3H3S2′-H2 [ = 2,2′-bis(2-mercaptophenylamino)diethylamine] (4) was synthesized. The dianion ′N3H3S2′2- reacted with FeII salts to give high-spin [Fe(′N3H3S2′)] (5) [μeff (293 K) = 3.94 μB], which yielded diamagnetic [Fe(CO)(′N3H3S2′)] (6) upon reaction with CO. Complex 6 exhibits a low-frequency ν(CO) band (1934 cm-1 in THF) indicating an electron-rich Fe center and a strong Fe-CO bond. In spite of this, 6 readily dissociated in solution to 5 and CO. The reaction of [RuCl2(PPh3)3] with ′N3H3S2′2- yielded [Ru(PPh3)(′N3H3S2′)] (7), which proved inert with respect to PPh3 substitution but could be methylated at the thiolate donors. The resulting [Ru(PPh3)(′N3H3S2′-Me2)]I2 (8) proved as inert towards substitution as 7. Complex 8 could reversibly be deprotonated to give [Ru(PPh3)(′N3H2S2′-Me2)]I (11), in the course of which the [RuPN3S2] cores rearrange from CS to C1 symmetry. Reversible protonation/deprotonation was also found with [Ru(NO)(′N3H2S2′)] (9) which formed from [RuCl3(NO)(PPh3)2] and ′N3H3S2′2- in the presence of one additional equivalent of LiOMe. Protonation of 9 with HBF4 gave [Ru(NO)(′N3H3S2′)]BF4 (10). The NMR spectra and the X-ray structure analysis of 8 proved that the [RuPN3S2] cores of 7 and 8 exhibit a CS-symmetrical meso structure. In all other complexes, however, the [MLN3S2] cores exhibit a C1-symmetrical structure. It results from the fac-mer coordination mode of the ′N3H3S2′2- ligand and favors the planarization of amide donors when NH functions are reversibly deprotonated.
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  • 119
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    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 361-371 
    ISSN: 1434-1948
    Keywords: Zeolites ; Transition metals ; Organometallic compounds ; Adsorption properties ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Molecular sieves can be modified by organometallic complexes using two different methods: (i) OMCVD (organometallic chemical vapor deposition), where a multilayered organometallic fragment is calcined and transformed into an oxide of rather indefinite composition, and (ii) SOMC (surface organometallic chemistry), where an organometallic fragment is grafted with retention of its molecular integrity. Both methods may lead to a grafting, which can occur at the external surface and/or inside the channels of the zeolites. In the case of SOMC, by judicious choice of both the reaction conditions and the organometallic complexes, it is possible to modify only the external surface of the sieve, for example, of a mordenite. This can lead to a decrease of the surface acidity, allowing greater selectivity in catalytic reactions (such as xylene isomerization). Another application is the modification of the pore openings of the channels by grafting organometallic compounds near the pore entrances. This results in a modification of the adsorption characteristics of the molecular sieve, allowing a fine tuning of its properties. Depending on the size of the adsorbed molecule, two effects can be observed: (i) a total exclusion of the molecule from the channels of the molecular sieve, due to steric effects (“thermodynamic” control); (ii) a modification of the adsorption kinetics of the adsorbed molecule, depending greatly on its size and on the size of the organometallic fragment (“kinetic” control). Finally, the grafting reaction can, in some cases, occur inside the channels, thereby leading to effects similar to those described above and to a reduction of the adsorption capacity due to the presence of the grafted organometallic moieties within the pores.
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  • 120
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    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 373-381 
    ISSN: 1434-1948
    Keywords: Silicon ; Germanium ; Tin ; Lead ; Carbene analogues ; Multiple bonds ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The isolation and characterization of thermally stable diaminocarbenes and diaminosilylenes has reawakened interest in the low-coordinated compounds of group-14 elements. The existence of these species is presumably due to interactions between the free electron pairs on the nitrogen atoms and the carbene carbon atom or the silicon atom. The present review is mainly concerned with the heavier analogues R2Ge:, R2Sn:, and R2Pb:, systems without intramolecular donor stabilization that owe their existence principally to steric shielding by the voluminous alkyl or aryl groups R. Dimerizations of these electron-sextet molecules give rise to the double-bond systems of the digermenes, distannenes, and diplumbenes; the latter species have for a long time been considered as being incapable of existence. The properties of these molecules are compared with the results of quantum chemical calculations. A separate section is devoted to the isomers of Si4R6, which include novel tetrasilacyclobutenes and the diene analogues, the tetrasilabuta-1,3-dienes.
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  • 121
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    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 393-398 
    ISSN: 1434-1948
    Keywords: Boranes ; Bipyridine ; Crystal structures ; Donor-acceptor interaction ; Heterocycles ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 6,6′-Bis(diethylboryl)-2,2′-bipyridine (1a) was obtained in low yield by in situ deprotonation of 2,2′-bipyridine in the presence of diethyl(methoxy)borane. 6,6′-Dilithio-2,2′-bipyridine reacts with various alkoxyboranes leading to bipyridinediborates 2 in good yields. The derivatives 2b and 2c allow the formation of the free diborylbipyridines 1b and 1c. The coordination properties of the diboryl-bipyridines as tetrafunctional donor-acceptor compounds have been used for the formation of the copper complex 4 and of the adduct 5 which is built from diborylbipyridine and a dihydroxydiboroxan derivative. The composition of the products follows from spectroscopic data and from X-ray structure analyses for 2f, 4, and 5.
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  • 122
    ISSN: 1434-1948
    Keywords: Ruthenium ; Photochemistry ; Photosubstitution ; Diimine chelates ; Sterically hindered ligands ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Mixed ruthenium(II) complexes containing 1,10-phenanthroline (or 2,2′-bipyridine) and a sterically congested bidentate ligand such as 2,9-diphenyl-1,10-phenanthroline, 6,6′-dimethyl- or 6,6′-diphenyl-2,2′-bipyridine, or 1-(2′-pyridyl)-3,5-dimethylpyrazole undergo clean and selective ligand substitution under irradiation with visible light. For instance, Ru(phen)2(dmbp)2+ in CH3CN is quantitatively converted to Ru(phen)2(CH3CN)22+ in a photochemical reaction accompanied by expulsion of the sterically hindering chelate dmbp (phen = 1,10-phenanthroline; dmbp = 6,6′-dimethyl-2,2′-bipyridine). Interestingly, 2,2′-bipyridine was found to be photochemically ejected in one case, probably as a consequence of its greater flexibility.
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  • 123
    ISSN: 1434-1948
    Keywords: Molybdenum ; Hydrazido complexes ; Organometallic complexes ; Phenanthroline ; X-ray structure determination ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: New organometallic compounds containing the cis-[MoO(NNPhR)]2+ core have been synthesized by means of a two-step procedure involving: (i) functionalization of the precursor [MoO2Br2(o-phen)] (1) with MePhNNH2 and Ph2NNH2 to afford the intermediates [MoO(NNMePh)Br2(o-phen)] (2) and [MoO(NNPh2)Br2(o-phen)] · MeCN (3), respectively, and (ii) reaction of these intermediates with Grignard reagents to give [MoO(NNPhR)Me2(o-phen)] [R = Me (4), R = Ph (5)], [MoO(NNPhMe)Ph2(o-phen)] (6), and [MoO(NNPh2)Ph2(o-phen)] · CH2Cl2 (7). These compounds have been characterized by 1H-NMR, IR, and UV/Vis spectroscopy and the crystal and molecular structures of 5 and 7 have been determined by X-ray diffraction analysis.
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  • 124
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    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 399-404 
    ISSN: 1434-1948
    Keywords: Boranes ; 1-Alkylpyrroles ; Porphyrinogenes ; Lithiation ; Tin-boron exchange ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Reactions of 2,5-dilithiated 1-methylpyrrole (1a) with ClB(NR2)2 lead to the novel 2,5-diboryl-1-methylpyrroles 2a and 2b. Accordingly, 2,5-diboryl-1-benzylpyrrole 2d is obtained. 1a and Cl2BNiPr2 form the aminochloroboryl-substituted derivative 2c and the di(5-boryl-2-pyrrolyl)borane 4 in 29% and 15% yield, respectively. The 2,5-distannyl-1-methylpyrrole 1c is used for the synthesis of the aryloxy-boryl derivative 2e. Reacting monolithiated 1-methyl- and 1-benzylpyrroles with Cl2BNiPr2 yields the di(2-pyrrolyl)boranes 3e and 3f, respectively. NMR and MS data are in agreement with the compositions of the compounds, which are confirmed by X-ray structure analyses for 2a, 2b, 2d, und 3e.
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  • 125
    ISSN: 1434-1948
    Keywords: Arene complexes ; Chromium ; Cyclohexadienyl complexes ; Dinuclear complexes ; Manganese ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The reaction of secondary α-cyano or α-sulfonyl carbanions with cationic (η6-arene)tricarbonylmanganese complexes affords neutral mono- and dinuclear tricarbonyl(η5-cyclohexadienyl)manganese complexes. The X-ray analyses of three (η5-cyclohexadienyl)Mn complexes (two mononuclear and one dinuclear) obtained by addition of α-cyano carbanion to cationic (η6-arene)manganese complexes are reported. The addition of benzylic carbanions of (η6-arene)tricarbonylchromium complexes to cationic (η6-arene)manganese complexes gives rise to the formation of the corresponding heterodinuclear [(η5-cyclohexadienyl)manganese-(η6-arene)chromium] complexes.
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  • 126
    ISSN: 1434-1948
    Keywords: Rhodium(III) complexes ; Tridentate ligand ; Oxidative addition ; Reductive elimination ; C-C coupling ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: As part of studies aimed at delineating the mechanism of the rhodium complex-catalyzed hydroamination of olefins, the model complexes [Rh(PNP)R] (R = CH31a, C6H51b) have been investigated with regard to oxidative addition reactions. The reaction of I2 with 1a leads to both trans- and cis-[Rh(PNP)(CH3)I2] (trans: 2a, cis: 2a′), whereas with 1b only trans-[Rh(PNP)(C6H5)I2] (2b) is obtained. The rhodium(III) complexes [Rh(PNP)(CH3)RI] (3a,b) are formed by the reaction of 1a,b with CH3I. The new organorhodium(III) complexes 2a,b and 3a,b have been characterized by 31P-, 1H-, and 13C-NMR spectrometry, as well as by EI mass spectrometry. The hydrocarbons RCH3 are reductively eliminated in the reaction of [Rh(PNP)(CH3)RI] (3a,b) with TlBF4 in acetone, while the reaction of 3b and TlBF4 in THF/CH3CN leads to the stable rhodium(III) complex [Rh(PNP)(CH3)(C6H5)(CH3CN)]BF4 (5). Complex 5 has been characterized by X-ray crystallography.
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  • 127
    ISSN: 1434-1948
    Keywords: Epichlorohydrin ; Chiral diphos ligands ; Diphos rhodium complexes ; Conformation analysis ; Chelates ; Asymmetric synthesis ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Enantiomerically pure chelate ligands L2 = XCH2CH(OH)CH2Y (1) are obtained from epichlorohydrin in a two-step synthesis. × and Y may be different types of R2P donor groups, NR2 or SR donors. The OH function of 1 may be transformed into an ether function under specialized conditions. Ligands 1 react with [Rh(COD)Cl]2 in the presence of KPF6 to give the coordination compounds 2, [L2Rh(COD)]+PF6-, as orange, microcrystalline salts. The structures adopted by compounds 2 in the solid state have been analysed by X-ray crystallography in selected cases, and it has been found that the six-membered chelate cycles adopt twist as well as chair conformations depending on the nature of × and Y. In solution, compounds 2 generally show dynamic behaviour, which is in part due to the conformational flexibility of the six-membered cycles. In cases where one of the PR2 donor groups contains ortho-substituted phenyl substituents, rotational isomerism of these groups is an additional dynamic process. For some of these compounds, the nature of the dynamic behaviour has been analysed by variable-temperature NMR experiments. Compounds 2 are found to be precatalysts in the hydrogenation of (Z)-2-acetamidocinnamic acid. The rate of conversion is strongly influenced by the steric bulk of the substituents, with smaller substituents leading to higher rates. Enantiomeric discrimination is high only for those ligands that contain ortho-substituted aryl groups at their PR2 donors. The maximum enantiomeric excess observed was 85% for × = PPh2, Y = P(2-MeOPh)2.
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  • 128
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    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 447-454 
    ISSN: 1434-1948
    Keywords: Kinetics ; Oxidations ; Iron ; Oxygen ; High pressure ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The complicated oxidation kinetics of the reaction of [FeII(cdta)] [cdta = 1,2-(N,N′- cyclohexanediamine)tetraacetate] with molecular oxygen was investigated as a function of [FeII], [O2], pH, temperature and pressure. In the presence of an excess of [FeII(cdta)] three steps could be observed, for which the following rate constants were found at 25°C; k1 = 1080 ± 16 M-1 s-1, k2 = 103 ± 4 M-1 s-1 and k3 = 59 ± 5 M-1 s-1. These reaction steps can be accounted for in terms of the following mechanism: (1) [FeII(cdta)H2O]2- reacts with O2 by a substitution process to form [FeII(cdta)O2]2-; (2) electron-transfer to form an FeIII-superoxo species; (3) subsequent bridge formation followed by electron-transfer to give [(cdta)FeIII-O22--FeIII(cdta)]4-; and (4) a fast decomposition of the peroxide intermediate yielding the monomeric [FeIII(cdta)] and H2O2. Rate and activation parameters for these steps are reported and discussed in terms of the postulated mechanism and in reference to available literature data.Supporting information for this article is available on the WWW under http://www.wiley-vch.de/contents/jc_2005/1999/98232_s.pdf or from the author.
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  • 129
    ISSN: 1434-1948
    Keywords: Copper ; Nickel ; Manganese ; Carboxylate bridge ; Metal complexes ; Magnetic properties ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The reaction of M(hfac)2 with the tridentate Schiff base H2L (where H2L stands for the 1:1 condensation product of 2-imidazolecarboxaldehyde with β-alanine) leads to the complexes [M(HL)(hfac)]n [M = MnII, NiII, and CuII; hfac = hexafluoroacetylacetonate anion] (1-3). The structures of the complexes 1 and 3 have been solved by X-ray crystallographic methods. The structures are very similar and consist of infinite zig-zag chains, running parallel to the b axis, in which the metal ions are bridged sequentially by anti-anti carboxylate groups with intrachain metal-metal distances of 6.134 Å for 1 and 6.239 Å for 3. Each monodeprotonated HL ligand acts as a tridentate one to a metal(II) ion and as a monodentate one to a neighbouring metal(II) centre. Metal atoms exhibit distorted octahedral coordination spheres comprised of two oxygen atoms from the hexafluoroacetylacetonate ligand, three donor atoms from the HL ligand and the oxygen atom belonging to the carboxylate group of an adjacent molecule. The complexes 1-3 have been confirmed to be isomorphous and isostructural on the basis of X-ray powder diffraction and IR spectra. The magnetic properties of the three compounds were studied by susceptibility measurements as a function of the temperature and successfully analyzed in terms of the isotropic spin Hamiltonian for one-dimensional infinite chain systems to give the coupling parameters J = -0.91 cm-1, g = 2.03 (1); J = -13.2 cm-1, g = 2.24 (2); and J = 0.40 cm-1, g = 2.11 (3). The magnetic behaviour for all three complexes can be satisfactorily explained in terms of the conformation of the bridge and the interaction between the d orbitals of the metal centre and the bridge.
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  • 130
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    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 461-464 
    ISSN: 1434-1948
    Keywords: Germyllithium ; 2-(Dimethylamino)phenyl ligand ; Chelates ; Solid-state structures ; Solution structures ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: {Tris[2-(dimethylamino)phenyl]germyl}lithium (1) has been prepared. The X-ray analysis shows that 1 exists as a monochelated monomer in the solid state, where the lithium atom is coordinated to one of the amino groups and two THF molecules. The interaction between the lithium atom and the amino group induces the distortion of the geometry around the germanium atom. In solution, however, two species exist as evidenced by 1H-, 7Li-, and 13C-NMR spectra. The temperature-dependent behavior of these two species has been analyzed by variable-temperature NMR studies.
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  • 131
    ISSN: 1434-1948
    Keywords: Chemosensors ; Fluorescence ; Tripodal ligands ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The new tripodal ligand 1 containing the dansyl chromophore has been synthesized and characterized. The intense luminescence characteristic of the chromophore is maintained in the ligand structure, showing that no intramolecular interactions are present. This ligand has been shown to complex in acetonitrile/water solutions only with Cu2+, Co2+, Zn2+, and Cd2+ ions, with concomitant pronounced changes in the fluorescence spectra. The complexation is controlled by pH conditions: at neutral pH this ligand shows a remarkable selectivity towards Cu2+ ions, suggesting a possible use for 1 as a luminescent chemosensor for this ion.
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  • 132
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    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 465-469 
    ISSN: 1434-1948
    Keywords: Dipeptide ester ; Cyclic tetrapeptides ; Palladium complexes ; Coordination chemistry ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: trans-Bis(dipeptide ester)palladium 1-6 complexes with a deprotonated amide group were obtained by dehydrochlorination of trans-Cl2Pd(dipeptide ester)2 or by direct reaction of Na2PdCl4 with dipeptide ester in the presence of sodium methoxide. The structure of Pd(NH2CH2CONCH2CH2CO2CH3)2 (3) was determined by X-ray diffraction. Addition of NaOCH3 to Pd[NH2C(H)(R)NCH2CH2CO2CH3]2 [R = CH(CH3)24, CH2Ph 5] results in the formation of the corresponding complexes 7, 8 with cyclic tetrapeptides which also can be directly synthesized from the dipeptide ester and Na2PdCl4.
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  • 133
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    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 471-482 
    ISSN: 1434-1948
    Keywords: Quinine ; Cinchonine ; Palladium ; Platinum ; Silver ; Gold ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A series of metal complexes in which quinine (L1) and cinchonine (L2) are coordinated via the four possible donor atoms was prepared and characterized. Coordination of the tertiary N atom of quinine is observed in [L1MPPh3]+NO3- [M = Au (1), Ag (2)], [L1Pd(COD)(Cl)]+ NO3- (3) and L1Pd(Cl)(allyl) (4). The mono anion of quinine functions as N,O chelate ligand in (L1-H+)M(Cl)(PR3) (M = Pd, Pt, 5-10), [(L1-H+)Pd(en)]+NO3- (11) and (L1-H+)2TiCl2 (12). Protection of the tertiary N atom of quinine by methylation or protonation allows the synthesis of the quinoline complexes [(L1CH3+)M(Cl)2(PR3)]+ BF4- (M = Pd, Pt, 14-18), [(L1CH3+)Ir(Cl)2(Cp*)]+ BF4- (19), [(L1+H+)M(Cl)2(PR3)]+ CF3SO3- (M = Pd, Pt, 20-22) and (L2+H+)(ZnCl3-) (23). Quinine and cinchonine act as N,O-N bridge in the complexes (R3P)(Cl)M(μ-L1-H+)M(Cl)2(PR3) (M = Pd, Pt, 24, 25, 27, 28), (Cp*)(Cl)Ir(μ-L1-H1)Ir(Cl)2(Cp*) (29), (EtP3)(Cl)Pd(μ-L2-H+)Pd(Cl)2(PEt3) (26), and as N-N bridge in the complexes [(Ph3P)Au(μ-L1)Au(PPh3)]+NO3- (30) and (allyl)(Cl)Pd(μ-L1)Pd(Cl)(allyl) (31). Coordination of quinine via the C=C double bond occurs in [(L1+2 H+)PtCl3]+Cl- (32). The structures of 11, 13, 19, 23, 26 and 32 were determined by X-ray diffraction. In most cases the coordination mode and the conformation of quinine can also be derived from the 1H-NMR spectra.
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  • 134
    ISSN: 1434-1948
    Keywords: Rhenium ; N Ligands ; Nonlinear optics ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Carbonylrhenium bromide complexes fac-Br(OC)3ReL2 (3a,b, 4a,b) and cis-Br(OC)4ReL (5a,b) with conjugated pyridines L = Fc-CH=CH-p-C5H4N (1a), Fc-CH=CHC(CH3)=CHCH=CHCH=C(CH3)CH=CH-p-C5H4N (1b), 1,1′-Fc(-CH=CH-p-C5H4N)2 (1c), p-Me2N-C6H4-CH=CHCH=CH-p-C5H4N (2a), and p-Me2N-C6H4-CH=CHC(CH3)=CHCH=CHCH=C(CH3)-CH=CH-p-C5H4N (2b) have been synthesized. The structures of 4a and 5a have been determined by X-ray diffraction analysis. Compound 4a exhibits a remarkable quadratic hyperpolarizability.
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  • 135
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    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 499-504 
    ISSN: 1434-1948
    Keywords: Alkynes ; Heterocycles ; Cyclizations ; Cobalt ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The following monocyclic and bicyclic 14-membered diynes were treated with [CpCo(cod)]: 1-oxacyclotetradeca-4,11-diyne (2), 1,8-dioxacyclotetradeca-4,11-diyne (3), cyclotetradeca-4,11-diynone (4), cyclotetradeca-4,11-diyne-1,8-dione (5), 1,1,8,8-tetramethyl-1,8-disilacyclotetradeca-4,11-diyne (6), 1-allyl-1-azacyclotetradeca-4,11diyne (7), 1,8-dipropyl-1,8-diazacyclotetradeca-1,11-diyne (8), 1,8-diallyl-1,8-diazacyclotetradeca-4,11-diyne (9), 1,8-diazabicyclo[6.6.4]octadeca-4,11-diyne (10), 1,8-diazabicyclo[6.6.6]eicosa-4,11-diyne (11), 1,10-diazabicyclo[8.6.6]docosa-13,19-diyne (12) and 1,12-diazabicyclo[10.6.6]tetracosa-15,21-diyne (13). In all cases we obtained an intramolecular cyclobutadiene complex stabilized with a CpCo fragment (15-26). For 3 we could isolate, besides the cyclobutadiene complex 16, the trimerization product 28. In the cases of 15, 16, 18, 20, 23, 25, and 26 the structure of the cylobutadiene complexes could be confirmed by X-ray studies. Common to all structures is a boat-like conformation of the tricyclic unit containing the cyclobutadiene ring. The two cycloheptene units adopt a chair conformation in which the heteroatom is removed from the metal center.
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  • 136
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    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 505-507 
    ISSN: 1434-1948
    Keywords: Macrocycle ; Pyrazole ; N-Heterocycle ; Carbonate ; Copper ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The 22-membered macrocycle, spanning four endocyclic pyrazole groups, viz. 1,4,9,14,17,22,27,28,29,30-decaaza-5,13,18,26-tetramethylpentacyclo[24.2.1.14,7.111,14.117,20]triacontane-5,7(28),11(29),12,18,20(30),24(27),25-octaene (22Pz), rendered the tetranuclear compound [Cu4(22Pz)2(CO3)2(MeOH)2](ClO4)4(MeOH)4. The copper(II) ions are in distorted octahedral N3O3 environments. All four pyrazole groups of each macrocycle participate in the coordination of the copper(II) ions. The cationic part of this compound is in fact a dimer of two macrocyclic ligands, each containing two copper(II) ions bridged by two carbonate ions in the highly unusual pentacoordinating fashion.Supporting information for this article is available on the WWW under http://www.wiley-vch.de/contents/jc_2005/1999/98332_s.pdf or from the author.
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  • 137
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    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 491-497 
    ISSN: 1434-1948
    Keywords: Boron ; Diazaboroles ; Hydrides ; Tin ; Heterocycles ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 1,3-Di-tert-butyl-2,3-dihydro-1H-1,3,2-diazaborole (4a) and 1,3-bis(2,6-dimethylphenyl)-2,3-dihydro-1H-1,3,2-diazaborole (4b) were formed by the reaction of the corresponding 2-bromo or 2-iodo derivatives 1a and 2b with LiAlH4. Treatment of 1a with n-butyllithium afforded 2-n-butyl-1,3-di-tert-butyl-2,3-dihydro-1H-1,3,2-diazaborole (5a), whereas 1,3-di-tert-butyl-2-cyano-2,3-dihydro-1H-1,3,2-diazaborole (3a) was converted into the 2-tert-butyl derivative 6a or the 2-ethynyl-1,3,2-diazaborole 7a by means of tert-butyllithium or by the ethylenediamine adduct of lithium acetylide. Similarly, 1,3-di-tert-butyl-2-trimethylstannyl-2,3-dihydro-1H-1,3,2-diazaborole (8a) and 1,3-bis(2,6-dimethylphenyl)-2-trimethylstannyl-2,3-dihydro-1H-1,3,2-diazaborole (8b) were accessible from 1a or 2b and trimethylstannyllithium. In the complex 9a the compound 3a serves as an η1 ligand towards the [Cr(CO)5] unit via the cyano group. These novel compounds were characterized by 1H-, 11B-, 13C-, and 119Sn-NMR spectroscopy, as well as by X-ray structure analyses of 4b, 8a, and 9a.
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  • 138
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    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 509-515 
    ISSN: 1434-1948
    Keywords: Macrocyclic ligands ; Molecular modeling ; Schiff bases ; Helical structures ; Copper ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The structural properties of the dicopper(I) compounds of the two large macrocyclic Schiff base ligands para-222 and meta-222 with two dithiadiimine coordination sites, where the two sites are linked by two para- or two meta-xylylene spacer groups and all bridges between the donors of each site are ethylene groups (32- and 30-membered macrocycles for the para- or meta-xylylen-bridged para-222 and meta-222 species, respectively) are studied, in solution and by computer modeling. Solid-state structural data have been reported elsewhere. The coordination of the 32-membered macrocycle para-222 to two copper(I) centers leads to a helical figure-of-eight-shaped structure. Two diastereomeric pairs of enantiomers have been observed for this type of compound in solution. The crystallized form is more stable than the second isomer by approximately 6-10 kJ/mol (solution-NMR spectroscopy and force-field calculations). Both experimentally detected isomers are more than 15 kJ/mol more stable than the other five possible configurations (force-field calculations). For the meta-222 macrocycle (30-membered ring) an achiral structure has been observed in the solid while two of the 21 possible isomers have been detected in solution (3:1, NMR spectroscopy). The computed structures and isomer distributions (force-field calculations) are compared with the solid-state structures and with observed isomer distributions from NMR experiments, and dynamic processes are analyzed in detail.
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  • 139
    ISSN: 1434-1948
    Keywords: Palladium ; Azide ; Pyridine ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Palladium(II) azide (1) was synthesized by reaction of palladium nitrate and sodium azide. 1 was characterized by AAS, IR, and 14N-NMR spectroscopy. Bis(azido)bis(pyridine)palladium(II) (2) and tetramminepalladium tetraazidopalladate(II) (3) were synthesized by a high-yield reaction. Both were characterized by X-ray structural analysis, IR, Raman, and NMR spectroscopy.
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  • 140
    ISSN: 1434-1948
    Keywords: Self-assembly ; Tetranuclear CuII complex ; [2 × 2] grid-type complex ; Crystal structure ; Magnetic properties ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The ditopic ligand 3 has been synthesized. In its deprotonated form, it reacts with copper(II) ions to form a tetranuclear complex 1 of the [2 × 2] CuII4 grid type, the structure of which has been confirmed by X-ray crystallography. Magnetic studies of complex 1 indicate a very weak antiferromagnetic coupling between the phenoxo-bridged CuII ions.
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  • 141
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    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 533-537 
    ISSN: 1434-1948
    Keywords: Ab initio calculations ; Carboranes ; NMR ; X-ray analysis ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Hydroboration of bis(diethylboryl)ethyne (1) with tetraethyldiborane(6) leads to a B-ethyl-substituted tetracarba-nido-octaborane 2, a spiro-carborane 3, which belongs to the 2,3,5-tricarba-nido-carborane family, and a hexacarba-arachno-dodecaborane(12) 4, along with polymeric material. The X-ray structure analysis of carborane 2, determined here, is fully consistent with the structure deduced earlier from NMR data. The structure of 3 in solution was established by theoretical analysis of its NMR data. Ab initio calculations of the structures of 2b and 3b (b denotes the B-metyhl-substituted derivatives) and the comparison of calculated with experimental NMR data support the suggested structures of 2 and 3 in solution. The calculated structure of the carborane cage of 2a also agrees with the experimental geometry of 2.
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  • 142
    ISSN: 1434-1948
    Keywords: Lanthanides ; WAXS ; Ladder polymers ; Rare-earth compounds ; Supramolecular chemistry ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The compounds of formula Ln2[M(opba)]3·xH2O·yDMSO containing 4f LnIII and 3d MII ions have been synthesized; opba stands for ortho-phenylenebis(oxamato). These compounds crystallize poorly, and hence structural information has been obtained from the wide angle X-ray scattering (WAXS) technique. It has been shown that the compounds present the same ladder-like motif as that previously described for Tm2[Cu(opba)]3·4H2O·10DMF. Changing the LnIII and/or MII ions results in more or less pronounced distortions of the ladders. For a given MII ion, changing the LnIII ion from LaIII to LuIII results in a decrease of the Ln-M distance parallel to the lanthanide contraction. In the same way, for a given rare earth, changing the MII ion from CuII to NiII and ZnII ions also results in the decrease of the Ln-M distance in accord with the decreasing radii of the MII ions. The structural details have been analyzed and discussed.
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  • 143
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    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 539-546 
    ISSN: 1434-1948
    Keywords: Nickel ; Sulfur ligands ; Hydrogenases ; Bioinorganic chemistry ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The cis-dithiolate complex [N,N′-bis(2-mercaptoethyl-2-methylpropyl)-1,5-diazacyclooctane]nickel(II) (Ni-1*) reacts with stoichiometric amounts of iodoacetamide to yield S-alkylated, mono- and diacetamide complexes, [(AA)Ni-1*][I] and [(AA)2Ni-1*][I]2. Their molecular structures are established by X-ray crystallography and find the former in pseudo-square planar geometry with no additional coordination of the amide functionality, while the latter is an octahedral N2S2O2NiII complex. The assignment of the axial coordination ligands as amide oxygen atoms is consistent with IR-spectroscopic ν(C=O) results both in the solid and solution states. The complexes are further characterized by UV/Vis spectroscopy, conductance measurements, and electrochemical studies. Comparisons are drawn between the alkylation of these simple dithiolate complexes and the loss of [NiFe]hydrogenase activity upon addition of alkylating agents.
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  • 144
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    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 557-563 
    ISSN: 1434-1948
    Keywords: Bioinorganic chemistry ; Copper ; DNA cleavage ; Intercalation ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The synthesis of three novel derivatives [N-acetyl-Clip-Phen (1), Clip-Phen-hexylaminoacridine (4) and Clip-Phen-hexylchloromethoxyaminoacridine (5)] of the bis(phenanthroline) ligand “Clip-Phen”, are described. Complexation of these ligands with copper(II) afforded the 1:1 complexes as hexafluorophosphate salts. The relaxation of φX 174 DNA was used as a DNA cleavage assay, with the following results. [Cu(1)]2+ was found to show a diminished activity relative to the parent complex [Cu(Clip-Phen)]2+. However, the acridine-containing complexes [Cu(4)H]3+ and [Cu(5)H]3+ exhibited significantly enhanced cleavage efficiencies, which has been attributed to increased affinity of the complexes for DNA. UV/Vis-spectral data of the complexes in the presence of calf-thymus DNA was consistent with an intercalative mode of binding.
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  • 145
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    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 565-577 
    ISSN: 1434-1948
    Keywords: Microporous crystalline aluminophosphates ; Isomorphous substitution ; Synthesis ; Spectroscopy ; Heterogeneous catalysis ; Transition metal ion ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Microporous crystalline metalloaluminophosphates (MeAPO-n) represent an important group of molecular sieves because of their potential catalytic and adsorptive properties. Many transition metal ions are claimed to incorporate in the framework of these molecular sieves. Here, the concept of isomorphous substitution, and the different indirect and direct tools available to verify this substitution process for Co, Cr, V, Fe and Mn are reviewed taking the AlPO4-5 structure as an example. In addition, it will be shown that transition metal ions can be used as a probe to follow the hydrothermal synthesis process of microporous aluminophosphates.
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  • 146
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    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 547-555 
    ISSN: 1434-1948
    Keywords: Nucleotides ; Conformation analysis ; NMR spectroscopy ; Pseudorotational equilibrium ; Anomeric effect ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A conformational study is reported on 2′-deoxyguanosine 5′-methylmonophosphate [MepdG (1)] and 2′-deoxyguanosine 3′-methylmonophosphate [dGpMe (2)] and their interactions with Mg2+, Zn2+ and Hg2+ ions. The conformation of MepdG (1) and dGpMe (2) in D2O solution was inferred from vicinal proton-proton, proton-phosphorus and carbon-phosphorus NMR coupling constants and nuclear Overhauser effects (NOE). The chemical shift changes showed that hard Mg2+ ions interact preferentially with the phosphate oxygen atoms in MepdG (1), whereas in the case of dGpMe (2) the interaction with the phosphate oxygen atoms competes with the interaction to the C6=O carbonyl group. Softer Zn2+ and Hg2+ ions were found to show strong binding affinity towards N7 in both MepdG (1) and dGpMe (2). Analysis of J coupling constants and NOEs measured as a function of metal ion concentration revealed that: (i) N → S pseudorotational equilibria are biased towards C2′-endo pseudorotamers in M2+-free MepdG (1) and dGpMe (2) by 68% and 75% at 298K, respectively. Titration of MepdG (1) and dGpMe (2) with Mg2+ ions caused no observable changes in N → S pseudorotational equilibrium, whereas the interactions of Zn2+ and Hg2+ ions with N7 resulted in the shift towards N-type pseudorotamers which can be explained by the strengthening of the anomeric effect as softer metal ions bind to N7 and make the imidazole moiety less electron-rich. (ii) The binding of divalent metal ions to MepdG (1) and dGpMe (2) causes a shift of the syn → anti equilibrium towards anti, which is larger for softer Zn2+ than for harder Mg2+ ions. (iii) The conformational equilibrium across the C4′-C5′ bond (γ torsion) in dGpMe (2) is not affected by the increased concentration of M2+ ions. (iv) βt conformers are preferred by ca. 77% in aqueous solution of MepdG (1) and only small changes of ca. 1 percentage point in βt population have been found upon metal ion binding to MepdG (1). (v) The two-state εt → ε- conformational equilibrium is biased towards εt rotamers by 63.5% in dGpMe (2). Interaction of hard Mg2+ and softer Zn2+ or Hg2+ ions with dGpMe (2) resulted in the minor increase (〈 3 percentage points) in the population of εt conformers.
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  • 147
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    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 579-582 
    ISSN: 1434-1948
    Keywords: Lead ; Plumbylenes ; Plumbanediyles ; Diplumbene ; Plumbylene dimers ; Double-bond systems ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Treatment of the diarylplumbylene R2Pb: (R = 2,4,6-iPr3C6H2) with the disilylplumbylene R′2Pb: [R′ = Si(SiMe3)3] furnishes the heteroleptic plumbylene RR′Pb: which exists as the diplumbene RR′Pb=PbRR′ (7) in the solid state. The X-ray structure analysis of 7 reveals a trans-bent angle of 42.7° and a Pb-Pb bond length of 298.99(5) pm, the shortest observed so far for diplumbenes with a lead-lead double bond. Reaction of mesitylmagnesium bromide with PbCl2 yielded black crystals of an MgBr2 stabilized dimesitylplumbylene dimer with a large trans-bent angle of 71°, a lead-lead separation of 335.49(6) pm, and long Pb···Br contacts of 315.71(8) pm.
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  • 148
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    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 583-588 
    ISSN: 1434-1948
    Keywords: Dicarbonate ion ; Autodissociation constant ; Electrochemistry ; Potentiometric titration ; Acidity ; Basicity ; Anions ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The solubility of CO2 in the molten ternary eutectic mixture Li2CO3-Na2CO3-K2CO3 (43.5, 31.5, 25.0 mol.%) at 973 K has been determined by a titration technique. From the obtained titration curve, the solubility has been found to amount to 9.5·10-2 mol·L-1 (σ= 1.0) under a pressure of CO2 of 1 atm and the pKd value of the carbonate melt has been evaluated to 5.37 (σ5 = 0.24) if the concentrations of the solutes are expressed in mol·L-1. This pKd value is in good agreement with literature data but the solubility value reported in this work is much higher than most of those reported in the literature. A chemical dissolution of CO2 as C2O52- is proposed and the consequences of the occurrence of this species on the acidobasic properties of molten carbonates are discussed. It appears from the experimental results that the CO2/C2O52- equilibrium in the carbonate melt is a slow process.
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  • 149
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    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 589-592 
    ISSN: 1434-1948
    Keywords: Ab initio calculations ; Dicarbonate anion C2O52- ; Dicarbonate structure ; Dicarbonate stability ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A theoretical study of the structure and stability of the dicarbonate ion has been performed at the Hartree-Fock, MP2, and QCI/SD levels. A flexible 6-31+G(d) basis set was used to allow for the diffuse electron density appearing in the anions. A stable anion corresponding to two CO2 entities covalently bound to a central oxygen has been found. The formation reaction starting from the carbonate anion and carbon dioxide has also been studied. Its thermodynamic features favour the formation of the dicarbonate anion, which in turn may account for the impressive solubility of carbon dioxide in carbonate melts.
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  • 150
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    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 593-600 
    ISSN: 1434-1948
    Keywords: Tripodal ligands ; Cobalt ; Bridging ligands ; Mixed-valence compounds ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The spectroscopic and electrochemical properties of a series of dinuclear mixed-valence complexes containing two (triphos)Co units are reported: [(triphos)Co(L)Co(triphos)]+ (L = C6O4X2; × = H, Cl, Br, I, Me: 2a-e+; L = C14H4O4Me2: 4+). Complexes 2a-e+ are bridged by tetraoxybenzene ligands and exhibit very strong metal-metal interaction leading to delocalized class-III behaviour while in 4+ the extended tetraoxoanthracence bridging ligand leads to a partial electron localization. Additionally, the different oxidation behaviour of the parent dicationic complexes 1a-e2+ and 32+ have been investigated and are explained on the basis of a qualitative MO model.
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  • 151
    ISSN: 1434-1948
    Keywords: Phosphorus ; Ferrocenes ; Phosphorylated iminophosphoranes ; Dendrimers ; Cations ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Several R3P=N-P(X)R′2 and Fe[C5H4Ph2P=N-P(X)R′2]2 derivatives (X = S, O) are readily obtained from Staudinger reactions between phosphanes and N3-P(X)R′2. The P=N-P=X groups are easily alkylated on the × atom with methyl or isopropyl triflates. The alkylation induces a lengthening of the P-X bond, as shown by X-ray diffraction studies. This corresponds to a weakening of the P-X bond which can be cleaved with P(NMe2)3 to yield [P=N-P:] linkages. The presence of tricoordinated phosphorus atoms opens the way to a versatile reactivity, including the reaction with alkyl iodides and functionalized azides. These molecules are good models for screening which types of reagents and reactions could be used with macromolecules possessing also P=N-P=X linkages, such as dendrimers.
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  • 152
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    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 613-619 
    ISSN: 1434-1948
    Keywords: Rhodium ; Ketone complexes ; Vinylidene complexes ; Allenylidene complexes ; Ligand substitution reactions ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The complex [Rh(acetone)2(C8H14)2]PF6 (2), which is prepared from [RhCl(C8H14)2]2 and AgPF6 in acetone, reacts with PiPr3 to afford the PF6 salt 3 of the cation [Rh(acetone)2(PiPr3)2]+ containing the ketone and phosphane ligands in cis dispositions. Treatment of 3 with MeC≡CPh leads to the displacement of one acetone ligand and the formation of the corresponding π-alkyne complex 4. In contrast, from 3 and terminal alkynes such as HC≡CC6H4-4-Me or HC≡CCPh2OH the cationic vinylidenerhodium(I) compounds 5 and 6 are obtained. The latter, with C=CHCPh2OH as the ligand, is rather labile and even at room temperature eliminates water to give the cationic four-coordinate rhodium allenylidene 7. The molecular structure of this compound has been determined by X-ray crystallography. In the presence of pyridine or ammonia, the acetone ligand of 5 and 7 is readily displaced and the substitution products 8-10 are formed almost quantitatively. Anions such as acetate or hydroxide also displace the ketone unit of 7 and yield the neutral allenylidenerhodium(I) complexes trans-[RhX(=C=C=CPh2)(PiPr3)2] with × = OAc (11) and OH (12).
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  • 153
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    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 621-632 
    ISSN: 1434-1948
    Keywords: (η2-Aldehyde)zirconocene complexes ; Metallaoxirane-stabilized group 4 metallocene hydride cations ; Nitrile insertion ; Isocyanate insertion ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Treatment of the [Cp2Zr(η2-acetaldehyde)/H(CH3)ZrCp2] adduct 8 with B(C6F5)3 yields the dimetallabicyclic salt [Cp2Zr(μ-η1-O:η2-C,O-OCHMe)(μ-H)(ZrCp2)]+[CH3B(C6F5)3]-18b. Similarly, hydride abstraction from the related neutral dimetallabicyclic [Cp2Zr(OCHR)/H2ZrCp2] adducts 11 (R = CH3) or 14 (R = C2H5) with B(C6F5)3 yields the systems [Cp2Zr(μ-η1-O:η2-C,O-OCHR)(μ-H)(ZrCp2)]+[HB(C6F5)3]- (18a, c) and the reaction of B(C6F5)3 with [Cp2Zr(OCHCH2Ph)/H(PhCH2)ZrCp2)]+17 gives [Cp2Zr(μ-η1-O:η2-C,O-(OCHCH2Ph)(μ-H)ZrCp2]+[PhCH2B(C6F5)3]-18d. A variety of nitriles R2-C≡N (R = CH3, CMe3, p-tolyl, or ethyl) cleanly reacts with the cations 18 by addition of the Zr2(μ-H) moiety to the nitrile functionality to yield the respective aldiminium-bridged cations [Cp2Zr(μ-η1-O:η2-C,O-(OCHR1)(μ-N=CHR2)ZrCp2]+ (21-24). Complex 24d (R1 = PhCH2, R2 = C2H5) was characterized by an X-ray crystal structure analysis. Similarly, treatment of the systems 18a-d with isocyanates RN=C=O (R = CMe3, SiMe3, p-tolyl, or adamantyl) gave the related μ-formamidato complexes 27-30.
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  • 154
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    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 651-654 
    ISSN: 1434-1948
    Keywords: Manganese ; Coordination modes ; 1-Hydronaphthalene complexes ; Trimethylphosphite addition ; Photochemistry ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Tricarbonyl(2-4,4a,8a-η-1-hydronaphthalene)manganese (1) reacts readily with trimethyl phosphite to afford tricarbonyl(2-4-η-1-hydronaphthalene)(trimethyl phosphite)manganese (2), by a simultaneous η5-η3-hapticity change. Upon UV irradiation, one carbonyl ligand is preferentially cleaved from 2 to yield dicarbonyl(2-4,4a,8a-η-1-hydronaphthalene)(trimethyl phosphite)manganese (3), with a η5-coordinated 1-hydronaphthalene ligand. In a similar fashion 3 also reacts with trimethyl phosphite and forms dicarbonyl(2-4-η-1-hydronaphthalene)bis(trimethyl phosphite)manganese (4), which loses carbon monoxide upon UV irradiation to afford carbonyl(2-4,4a,8a-η-1-hydronaphthalene)bis(trimethyl phosphite)manganese (5). All compounds were characterized by IR and NMR spectroscopy. The η5-1-hydronaphthalene complexes 1, 3 and 5 show hindered 1,4-H shifts of 1-Hendo. Considerable energy barriers were also found for the rotation of the 1-hydronaphthalene ligand in 2-5.
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  • 155
    ISSN: 1434-1948
    Keywords: Cobalt(III) complexes ; Tetrapodal pentadentate ligand ; Hydrolysis ; Kinetics ; Mechanism ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Multi-wavelength stopped-flow spectrophotometry was used to study the kinetics of base hydrolysis of the octahedral cobalt(III) complex CoLCl2+ (2), in which the tetrapodal pentadentate ligand L has an NN4 donor set and forms a square-pyramidal coordination cap [L = 2,6-bis(1′,3′-diamino-2′-methylprop-2′-yl)pyridine, 1]. The kinetic investigation, carried out at different temperatures, pressures and ionic strengths I, led to second-order kinetics, rate = kOH [2][OH-], with kOH = 0.139 ± 0.001 M-1s-1 (I = 0.1 M) and kOH = 0.0570 ± 0.0004 M-1s-1 (I = 1.0 M) at 298 K. The temperature and pressure dependence of kOH resulted in ΔH
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  • 156
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    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 1563-1566 
    ISSN: 1434-1948
    Keywords: Stannaborate cluster ; Transition metal complexes ; Tin ; Coordination modes ; Clusters ; Boron ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Reactions of the stannaborate salt [NBu4]2[SnB11H11] (1) with the organometallic electrophiles [CpFe(CO)2Br], [(C7H7)Mo(CO)2I], and [CpNi(PPh3)Cl] resulted in substitution of the halide to give the stannaborate coordination products [NBu4][CpFe(CO)2(SnB11H11)] (2), [NBu4][(C7H7)Mo(CO)2(SnB11H11)] (3), and [NBu4][CpNi(PPh3)(SnB11H11)] (4) in high yields. Single crystals of the air- and moisture-stable products have been characterized by X-ray crystal structure analyses.
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  • 157
    ISSN: 1434-1948
    Keywords: Metallamacrocycles ; Structure elucidation ; Supramolecular chemistry ; Tin(IV) compounds ; Vibrational spectroscopy ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Tetrakis[trimethyl(N-nitroso-N-phenylhydroxylaminato)tin(IV)] was synthesized by reaction of cupferron ([PhN(O)NO]NH4) with trimethyltin(IV) chloride. The complex was characterized by X-ray diffraction analysis, FT-IR and FT-Raman spectroscopy. An X-ray structural analysis of the title complex [Me3Sn(O2N2Ph)]4 reveals the first example of a bridging coordinated cupferronato ligand. This coordination pattern leads to an unprecedented inorganic 20-membered (carbon-free) metallamacrocycle Sn4O8N8 in which four Me3Sn and four PhN2O2 subunits are self-assembled.
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  • 158
    ISSN: 1434-1948
    Keywords: Phosphorus heterocycles ; 2H-Azaphosphirene complexes ; Water-soluble P ligands ; Tungsten ; Cyclizations ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Thermal ring-opening of [{2-bis(trimethylsilyl)methyl-3- phenyl-2H-azaphosphirene-ĸP}pentacarbonyltungsten(0)] (8a) in the presence of dimethyl acetylenedicarboxylate (DMAD) led to the 2,3-bifunctionalized 1H-phosphirene complex 9a and the 4-phenyl-substituted 2H-1,2-azaphosphole complex 10a, the latter as a by-product. If a small amount of benzonitrile was added, complex 10a was obtained as the main product, along with a small amount of the decomplexed 2H-1,2-azaphosphole 11, which could not be isolated. Reaction of complex 10a with elemental sulfur furnished the corresponding PV sulfide 13. When the ring-opening of complex 8a was performed in the presence of two equivalents of DMAD and two equivalents of dimethyl cyanamide, we obtained the 4-dimethylamino-substituted 2H-1,2-azaphosphole complex 10b, together with the diastereomeric Δ3-1,3,2-oxazaphospholene complexes 14a,b. On reaction of [{2-pentamethylcyclopentadienyl-3-phenyl-2H-azaphosphirene-ĸP}pentacarbonyltungsten(0)] (8b) and DMAD in toluene, the corresponding 1H-phosphirene complex 9b was only formed as a transient species and the P-coordinated P,C-cage compound 15 was the final product. Using benzonitrile as solvent, the 4-phenyl-substituted 2H-1,2-azaphosphole complex 10c was obtained, together with the 7-aza-1-phosphanorbornadiene complex 16, the latter through partial decomposition of 10c coupled with rearrangement and a Diels-Alder reaction; the ratio 10c/16 was found to depend strongly on the molar ratio of complex 8b to DMAD. A cycloaddition reaction of the 2,3-bifunctionalized 1H-phosphirene complex 9a with 2,3-dimethylbutadiene furnished the bicyclic phosphirane complex 19, along with a small amount of the noncoordinated bicyclic phosphirane 20. Reaction of complex 9a with diethylamine yielded the phosphirane complex 21 as a 1,2-addition product, the diorganophosphane complex 22 through ring-opening of 9a, and the 3,4-functionalized 1,2-dihydro-1-phosphet-2-one complex 23 through an unprecedented ring-expansion reaction; the products 21, 22, 23 were formed in a ratio of ca. 1:1:1. The structures of the 1H-phosphirene complex 9a, the 4-dimethylamino-substituted 2H-1,2-azaphosphole complex 10b, the bicyclic phosphirane complex 19, the phosphirane complex 21, and the 1,2-dihydro-1-phosphet-2-one complex 23 have been determined by single-crystal X-ray diffraction analysis.
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  • 159
    ISSN: 1434-1948
    Keywords: Rhodium ; Iridium ; N ligands ; Coordination modes ; Polymerizations ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Complexation of [RhI(cod)]+ and [IrI(cod)]+ by the new pyridine-amine-pyrrole ligands Py-CH2-N(R)-CH2-Pyr-H (HLR; R = H, Bzl, Bu) and the corresponding pyridine-amine-pyrrolate ligands [Py-CH2-N(R)-CH2-Pyr]- (LR-; R = H, Bzl, Bu, CH2Py) has been investigated. The neutral ligands HLR (R = H, Bu, Bzl) give [(HLR)MI(cod)]+ (M = Rh, Ir) in which HLR acts as a didentate ligand via the pyridine nitrogen (NPy) and the amine nitrogen (NRamine). The crystal structures of [(HLH)MI(cod)]PF6 (M = Rh: [1]PF6 and M = Ir: [2]PF6) have been determined. Deprotonation of [(HLR)MI(cod)]+ (M = Rh, Ir; R = H, Bzl, Bu) results in the neutral complexes [(LR)MI(cod)] (M = Rh, Ir) of the mono-anionic ligands LR- (R = H, Bzl, Bu). In square-planar [(LH)MI(cod)] (M = Rh: 3, M = Ir: 4), LH- is didentate via NHamine and the pyrrolate nitrogen (NPyr). The X-ray structures of 3 and 4 reveal that in both cases the uncoordinated NPy accepts a hydrogen bond from NHamine. The X-ray structures of [(LBzl)MI(cod)] (M = Rh: 5, M = Ir: 6), show that LBzl- is didentate via Namine and NPyr for M = Rh and tridentate for M = Ir. In solution LBzl- is tridentate for both M = Rh and M = Ir. The neutral complexes [{Py-CH2-N(R)-CH2-Pyr}MI(cod)] (M = Rh, Ir) cannot be oxidised selectively with H2O2. This is in marked contrast to the previously observed selective oxidation of the corresponding cationic complexes [{Py-CH2-N(R)-CH2-Py}RhI(cod)]+. Rhodium complex 5 is an active catalyst for the stereoregular polymerisation of phenylacetylene, whereas iridium complex 6 is inactive.
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  • 160
    ISSN: 1434-1948
    Keywords: Metallo-disilanes ; Ligand exchange at silicon ; Transition metal effect ; Raman spectroscopy ; Density functional theory ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Reaction of the sodium metalates Na[M(CO)2C5R5] [M = Fe, R = H (1a), Me (1b); M = Ru, R = H (1c), Me (1d)] with an equimolar amount of hexachlorodisilane yields the metallo-pentachlorodisilanes C5R5(OC)2M-SiCl2-SiCl3 (2a-d), which can be converted into the pentahydrido analogues C5R5(OC)2M-SiH2-SiH3 (3a-c) via Cl/H exchange with LiAlH4. Due to the activating effect of the transition metal fragment chlorination of 3a-c with CCl4 or HCCl3 occurs at the α-silicon to give C5R5(OC)2M-SiCl2-SiH3 (4a-c). The metallo-disilanes were characterised by 1H-, 13C-, 29Si-NMR, IR and especially Raman spectroscopy. The structures of C5H5(OC)2Fe-Si2Cl5 (2a) andC5Me5(OC)2Fe-Si2H5 (3b) have been determined by X-ray analysis; 2a,b, 3a,b were theoretically described by DFT calculations.
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  • 161
    ISSN: 1434-1948
    Keywords: Arsaalkenes ; Phosphaalkenes ; Aluminium ; Gallium ; Indium ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Reaction of equimolar amounts of the ferriophosphaalkene [(η5-C5Me5)(CO)2FeP=C(NMe2)2] (1a) or the ferrioarsaalkene [(η5-C5Me5)(CO)2FeAs=C(NMe2)2] (1b) with trimethylaluminium, trimethylgallium and trimethylindium afforded the adducts [(η5-C5Me5)(CO)2FeE{MMe3}C(NMe2)2] with E = P; M = Al (2a), Ga (3a), In (4a) and E = As; M = Al (2b), Ga (3b), and In (4b). These compounds feature η1-coordination of the phosphaalkene or the arsaalkene ligand towards the Lewis acid via the pnictogen atom. The molecular structures of 2a and 3a were elucidated by X-ray diffraction analyses.
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  • 162
    ISSN: 1434-1948
    Keywords: Indium ; Chalcogens ; Chelates ; Phosphazenes ; Metallacycles ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The ligands [Ph2(S)PNHP(X)Ph2]- (X = O, Se) react with InCl3 in a 3:1 ratio to give a tris-chelate [In{Ph2P(O)NP(S)Ph2-O,S}3]·0.75 C6H6 (2) and the unexpected pentacoordinate derivative [InCl{Ph2P(Se)NP(S)Ph2-Se,S}2] (3). These compounds have been characterized by means of IR, 1H- and 31P-NMR spectroscopy, positive-ion FAB mass spectrometry and elemental analysis. The molecular structures have been determined by single-crystal X-ray diffraction analysis. The coordination geometry in 2 resembles that observed in the three analogous tris-chelates incorporating the corresponding symmetrical oxygen, sulfur and selenium ligands. Compound 3 exhibits a very distorted trigonal-bipyramidal geometry at indium, where both the selenium and chlorine atoms are in equatorial positions, while the sulfur atoms are in axial positions.
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  • 163
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    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 1617-1642 
    ISSN: 1434-1948
    Keywords: Calculations ; Bond theory ; Electronic structure ; Molecular dynamics ; Kratzer ; Morse ; Potential energy curve ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: After decades of intensive research, the question remains whether or not a universal two- or three-parameter potential exists. For a large number of about 300 bonds, we now critically review the constraints for potentials and asymptotes, involved in three available scaling processes (Varshni, Calder-Ruedenberg, and Graves-Parr). We show that the covalent Sutherland parameter can never be a universal scaling factor. This implies that the usual constraint U(R) = -De at R = ∞ for potentials is only desirable and that the natural asymptote De is not even needed to explain the relations between the constants. We show that ionic potentials of generalized Kratzer-type (Varshni's Vth potential) and their ionic Coulomb-like asymptotes Ae2/Re (with A close to 1) behave as simple universal two-parameter potentials. For both αe and ωexe, this potential gives percentage deviations 2 to 3 times smaller than Morse's three parameter potential for hundreds of bonds. We also prove that the Graves-Parr scaling hypothesis is valid, despite these authors' own conclusion. We discuss various new relations between spectroscopic constants.Supporting information for this article is available on the WWW under http://www.wiley-vch.de/contents/jc_2005/1999/99005_s.pdf or from the author.
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  • 164
    ISSN: 1434-1948
    Keywords: Fractals ; Materials science ; Fluorapatite ; Collagen ; Intrinsic electric fields ; Core/shell assemblies ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The biomimetic growth of fluorapatite in gelatin matrices at ambient temperature (double-diffusion technique) starts with elongated hexagonal-prismatic seeds followed by self-similar branching (fractal growth) and ends up with anisotropic spherical aggregates. The chemical system fluorapatite/gelatin is closely related to in vivo conditions for bone or tooth formation and is well suited to a detailed investigation of the formation of an inorganic solid with complex morphology (morphogenesis). The fractal stage of the morphogenesis leads to the formation of closed spheres with diameters of up to 150 μm. The self-assembled hierarchical growth thereby shows immediate parallels to the topological branching criteria of the macromolecular starburst dendrimers. A second growth stage around the closed spheres of the first stage is characterized by the formation of concentric shells consisting of elongated prismatic fluorapatite units with nearly parallel orientation (maximum diameter of the complete core/shell spheres of 1 mm). The specific structure of the core/shell assembly is similar to the dentin/enamel structure in teeth. Together with the idea of the biological significance of electric fields (pyro-, piezoelectricity) during apatite formation under in vivo or biomimetic conditions the present paper considers the composite character of the material and the mechanisms of fractal growth (branching criteria and architecture, the influence of intrinsic electric fields etc.).
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  • 165
    ISSN: 1434-1948
    Keywords: Calcium ; Platinum Complexes ; Aminophosphonate ; Antitumor agents ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The presence of Ca2+ has a marked effect on the reaction kinetics of platinum phosphonate complexes with d(GpG). Compounds studied are [cis-Pt(NH3)2(bmpaa)] and [Pt(R,S-dach)(ntmp)]. The formation of GG-N7,N7 chelates and the release of the phosphonate ligand as observed by NMR is significantly accelerated by the presence of Ca2+, which is ascribed to its interaction with the phosphato groups in the ligands.
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  • 166
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    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 1665-1671 
    ISSN: 1434-1948
    Keywords: Methylenediphosphane ; Hexafluoroacetone ; Carbodiphosphorane ; Ylides ; Carbenes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The oxidation of the methylenediphosphanes 3a,b with hexafluoroacetone does not lead to the expected dioxaphospholane heterocycles, but yields quantitatively the carbodiphosphoranes 5a,b. Compounds 5a,b easily add HCl, HF or Cl2 to the ylidic bonds. The chloro derivative 14b, and its analogue 17 were used for the synthesis of phosphonium substituted carbenes.
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  • 167
    ISSN: 1434-1948
    Keywords: Ab initio studies ; Chirality ; Pentacoordinate silicon ; Stereochemistry ; Zwitterionic λ5Si-silicates ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The syntheses of the zwitterionic (molecular) spirocyclic λ5Si-silicates 5-9 are described. These chiral compounds contain a pentacoordinate (formally negatively charged) silicon atom and a tetracoordinate (formally positively charged) nitrogen atom. The stereochemistry and dynamic behavior of 5-9 were investigated. For this purpose, compounds 5-9 were studied by solution-state NMR spectroscopy (1H, 13C, 29Si; including VT 1H-NMR studies of 9) and solid-state NMR spectroscopy (13C CP/MAS, 29Si CP/MAS). In addition, compounds 5·H2O, 7, 8, 9·H2O, and 9·2CH3CN were structurally characterized by single-crystal X-ray diffraction, and ab initio investigations of the zwitterion 8 and the related anionic model species 10 were carried out.
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  • 168
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    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 1673-1684 
    ISSN: 1434-1948
    Keywords: Phosphazenes ; Polymers ; Chirality ; Urethanes ; TGA ; Thermochemistry ; Asymmetric synthesis ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The reaction of hexachlorocyclotriphosphazene with two equivalents of the chelating diols 2,2′-dioxybiphenyl and 2′,2′′-dioxy-1′,1′′-bi-2-naphthyl was investigated. Although a mixture of different stereoisomers may be expected, only the formation of the meso-compounds [(R,S)-(O,O)2Cl2P3N3] is found (O,O stands for the diolate). Interestingly, when the remaining PCl2 group undergoes reaction with hard nucleophiles like 4-methoxy phenolate, a change of configuration at one phosphorus center is observed and racemic mixtures of chiral [(R,R)-(O,O)2(RO)2P3N3] and [(S,S)-(O,O)2(RO)2P3N3] phosphazenes are observed. Enantiomerically pure cyclotriphosphazenes were obtaines from either the (R)- or (S)-form of 2′,2′′-dioxy-1′,1′′-bi-2-naphthyl. Soft nucleophiles like amines, however, do not affect the configuration at the phosphorus centers and allow the synthesis of meso-[(R,S)-(O,O)2(R1RN)2P3N3] compounds. the bifunctional cyclotriphosphazenes [(O,O)2(4-OH-C4H4O)2P3N3] and [(R,S)-(O,O)2(H2N)2P3N3] were used in polyaddition reactions with hexymethylene di(isocyanate) to give cyclolinea polymers of different stereochemical compositions corresponding to the stereochemistry of the phosphazene precursor (i.e. either a racemic mixture of homochiral polymer strands, enantiomerically pure polymers, or the meso-form of polymers was obtained). The properties of these polymers are discussed and a mechanism for the change of stereochemistry is proposed.
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  • 169
    ISSN: 1434-1948
    Keywords: Boranes ; Homogeneous catalysis ; Ab initio calculations ; Donor-acceptor systems ; X-ray analysis ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The catechol-substituted diboranes(4) 1 react with the catechol-substituted diborylacetylenes 2, in the presence of [Pt(PPh3)2(C2H4)] or [Pt(PPh3)4], to give tetra- and hexaborylethane derivatives. When [Pt(cod)2] is used as catalyst, the tetraborylethene 5a is formed exclusively. Catalytic hydrogenation of 5a affords the 1,1,1′,1′-tetraborylethane 4a, which has been studied by an X-ray structure analysis. Natural Bond Orbital (NBO) analyses for the RHF/3-21G optimized geometries of 4a and 5a reveal intramolecular stabilization of the boron pz orbital. This covers B-O, B-B, and agostic interactions. The photoelectron spectrum of 5a is reported
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  • 170
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    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 1701-1706 
    ISSN: 1434-1948
    Keywords: Ternary Tellurides ; Conductivity ; Electronic structure ; Layered compounds ; Low-dimensional metals ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The layered ternary tellurides NbNiTe5, TaNiTe5, TaPtTe5 and NbPdTe5 are all metallic, but the conductivity of the latter is between one and two orders of magnitude smaller. A tight binding study of the electronic structure of these phases suggests that the large conductivity difference results from the different Te···Te interlayer interactions and the Te → M (M = Nb, Ta) electron transfer that they induce.
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  • 171
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    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 1707-1713 
    ISSN: 1434-1948
    Keywords: Carbene complexes ; Carbonyl complexes ; Diazoalkanes ; Hydrido complexes ; Ruthenium ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The five-coordinate compound [RuHCl(CO)(PiPr2Ph)2] (1), which was prepared from RuCl3· 3 H2O and PiPr2Ph in methanol in the presence of NEt3, reacts with CO and with diazoalkanes RCHN2 (R = Ph, H) to give the six-coordinate complexes [RuHCl(CO)2(PiPr2Ph)2] (4) and [RuHCl(CO)(=CHR)(PiPr2Ph)2] (5, 6), respectively. If the reaction of 1 with CH2N2, which at -78 °C affords 6, is carried out at room temperature, the ionic compound [MePiPr2Ph][RuHCl2(CO)(PiPr2Ph)2] (7) is formed. The corresponding PPN salt was obtained from 1 and [PPN]Cl. The X-ray crystal structure analysis of 7 revealed, that the anionic species [RuHCl2(CO)(PiPr2Ph)2]- contains the chloro ligands in cis and the phosphanes in trans disposition. The Ru=CH2 bond of compound 6 is quite labile and, therefore, the CH2 unit is easily displaced by CO or pyridine. From 1 and pyridine, an isomeric mixture of [RuHCl(CO)(py)(PiPr2Ph)2] (9a, b) is formed. Treatment of 1 with HC≡CR (R = H, Ph) yields the five-coordinate vinylruthenium(II) complexes [Ru(CH=CHR)Cl(CO)(PiPr2Ph)2] (12, 13) by insertion of the alkyne into the Ru-H bond. The preparation of [RuHX(CO)-(PiPr2Ph)2] (X = CF3CO2, I) is also reported.
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  • 172
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    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 849-852 
    ISSN: 1434-1948
    Keywords: Azides ; Hydrazinium azide ; Hydrazine ; Nitrogen compounds ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: tert-Butylhydrazinium azide [tBuNH2NH2]+[N3]- (1) was prepared in a high yield reaction from tert-butylhydrazine and HN3. N,N,N-Trimethylhydrazinium azide [NH2N(CH3)3]+[N3]- (2) was prepared from the reaction of silver azide with N,N,N-trimethylhydraziniumiodide. Both were characterized by X-ray structural analysis, IR, Raman, and multinuclear (1H, 13C, 14N) NMR spectroscopy.
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  • 173
    ISSN: 1434-1948
    Keywords: Metallocenes ; Hydroselenide ligands ; Selenium ; Se coordination chemistry ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The reactions of [Cp#2NbBH4] (1) [Cp# = C5Me5 (Cp*) or C5Me4Et] and [Cp′2TaH3] (Cp′ = tBuC5H4) with elemental selenium give complexes of the general composition [Cp2MSe2H]. These exist in three isomeric forms, A-C, depending on the metal and the chalcogen. [Cp#2NbSe2H] (2) incorporates the novel η2-Se2H ligand (C), which is labile when exposed to light. Solutions of 2(Cp*) can be converted into [Cp*2NbSe2H] (3), which exists in two isomeric forms A or B, along with [Cp*2NbSe3H] (4) and [Cp*2NbO2H] (5). [Cp′2Ta(η2-Se2)H] (6) is the only isomer found for the Ta system. Se abstraction by means of P(OEt)3 gives [Cp′2Ta(=Se)H] (7). Complex 7 can be reduced with Na/Hg and subsequently hydrolysed to give [Cp′2Ta(SeH)H2] (8), which has also been observed during the formation of 6. Coordination of [W(CO)5THF] at the Se lone pair of 7 affords the heterobimetallic complex 9. All compounds have been characterized by means of 1H- and, in some cases, 77Se-NMR spectroscopy. Products 8 and 9 have also been subjected to X-ray diffraction analysis.
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  • 174
    ISSN: 1434-1948
    Keywords: Crystal structure ; Solution structure ; Homodinuclear lanthanide complexes ; Lanthanides ; Macrocyclic ligands ; Polyamine polycarboxylic acid ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The solid-state structures of the four homodinuclear chelate complexes, [Na2(Y2OHEC)(H2O)2] · 7 H2O · C2H5OH (1), [Na2(Gd2OHEC)(H2O)2] · 12 H2O (2), [Na2(Eu2OHEC)(H2O)2] · 11 H2O (3), and [Cs2(La2OHEC)(H2O)2] · 14 H2O (4) (H8OHEC = 1,4,7,10,14,17,20,23-octaazacyclohexacosane-1,4,7,10,14,17,20,23-octaacetic acid), were determined by X-ray crystal structure analysis. Each lanthanide(III) ion is ninefold coordinated by eight donor atoms of the ligand system and the oxygen atom of one water molecule. The structures are compared with those of DOTA- and TETA-coordinated complexes and the conformation of the OHEC ligand system with that of the parent amine and its dinuclear copper complex. NMR investigations of the diamagnetic complex 1indicate a very similar environment of the lanthanide cations in solution and in the solid state. Low-temperature and variable-temperature 1H-NMR measurements prove the existence of two isomers of 1 (3.5:1 ratio) which undergo conformational processes. The rate constants of these processes were deduced from a complete line shape analysis and were used to determine the activation parameters.Supporting information for this article is available on the WWW under http://www.wiley-vch.de/contents/jc_2005/1999/99081_s.pdf or from the author.
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  • 175
    ISSN: 1434-1948
    Keywords: Iron(II) ; Spin crossover ; Pentanuclear assembly ; Triazole ligand ; Structure elucidation ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A new iron(II) compound with the formula [Fe2(L)5(NCS)4]2[Fe(L)2(NCS)2(H2O)2] (I) [where L = 4-(p-tolyl)-1,2,4-triazole] has been synthesized and subjected to X-ray structure determination. Compound I crystallizes in the triclinic space group P-1 (no. 2) with a = 14.5785(11), b = 16.1253(11), c = 16.1963(8) Å, α = 80.930(5), β = 85.796(5), γ = 78.132(6)°, V = 3676.2(4) Å3. The structure refinement converged to wR2 = 0.172, RF = 0.084. The structure was found to consist of two types of iron-containing structural units, a mononuclear unit and a dinuclear one. The mononuclear unit has a crystallographic inversion centre, and is coordinated by two NCS anions, two triazole N1 nitrogen atoms, and two water molecules, each hydrogen-bonded to one of the two dinuclear units. The dinuclear units consist of two iron(II) ions bridged by three triazole ligands in a 1,2-fashion. The coordination spheres of both iron ions are completed by two NCS anions and one monodentate triazole ligand. The monodentate triazole ligands are connected through the non-coordinating N atom to the mononuclear iron unit by hydrogen bonds from its coordinated water molecule. Magnetic susceptibility measurements indicate a spin transition (ST) only for the iron ions in the dinuclear units, centred at around T1/2 = 111 K. The transition takes place within a relatively narrow T range. The mononuclear iron ion remains in the high-spin (HS) state even at very low temperature, yielding a ratio of 4:1 for the ST and HS iron ions. Temperature-dependent Mössbauer spectroscopy confirms these results.
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  • 176
    ISSN: 1434-1948
    Keywords: 2-Acetylpyridine 4-methylthiosemicarbazone ; Palladium ; Platinum ; Group-12 metal(II) complexes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Reaction of 2-acetylpyridine 4-methylthiosemicarbazone (H4ML) with halides of zinc(II), cadmium(II), and mercury(II) afforded complexes of the form [M(H4ML)X2] [M = ZnII (1-3), CdII (4-6) or HgII (7-9); × = Cl, Br, or I]. Reaction of H4ML with K2PdCl4 and K2PtCl4 gave compounds of the form [M(4ML)Cl] [M = PdII (10) or PtII (11)]. In all the new compounds, which were characterized by elemental analyses, conductance measurements, and electronic, IR and 1H- and 13C-NMR spectroscopy, and by 113Cd-, 195Pt-, or 199Hg-NMR spectroscopy when relevant, the ligand is N,N,S-tridentate, coordinating to the metal centre through its pyridine and azomethine nitrogen atoms and its thiocarbonyl sulfur atom, as was confirmed by X-ray diffraction studies in the cases of 4· 2 DMSO, 5· 2 DMSO, 6· 2 DMSO, 7· 2 DMSO, 10, and 11. In in-vitro assays, only [Zn(H4ML)Cl2] and [Zn(H4ML)Br2] showed some sign of antifungal activity against Aspergillus niger or Paecilomyces variotii.Supporting information for this article is available on the WWW under http://www.wiley-vch.de/contents/jc_2005/1999/98381_s.pdf or from the author.
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  • 177
    ISSN: 1434-1948
    Keywords: Europium ; Ytterbium ; Indium ; Intermetallic compounds ; Ferromagnetism ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The new compounds EuPdIn2 (1), YbPdIn2 (2), and YbAuIn2 (3) have been synthesized by high-frequency melting of the elements in sealed tantalum tubes and subsequent annealing at about 900 K. Their crystal structures have been determined by single-crystal X-ray diffraction techniques. Compounds 1, 2, and 3 crystallize with the MgCuAl2-type structure (space group Cmcm), a ternary ordered version of the Re3B type. Structural elements in these compounds are transition metal centered trigonal prisms made up of the rare earth and indium atoms. The transition metal (T) and indium atoms form a three-dimensionally infinite [TIn2] polyanionic network in which the large rare earth metal atoms occupy one-dimensional pentagonal tubes. A semiempirical band structure calculation on 1 reveals a non-vanishing density-of-states (DOS) at the Fermi level. The strongest bonding interactions are found for the In-In and Pd-In contacts; the Eu-Pd and Eu-In interactions are much weaker. Magnetic investigations indicate divalent character of the ytterbium atoms in 2, showing negative susceptibilities below room temperature. Compound 1 exhibits Curie-Weiss behavior above 50 K with an experimental magnetic moment of 7.8(1) μB, thus indicating divalent europium. Ferromagnetic ordering was observed at TC = 14.5(5) K, with a saturation moment of 6.8(1) μB/Eu at 5.5 T and 4 K, as determined from magnetization measurements. Compounds 1 and 2 are found to be metallic conductors.
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  • 178
    ISSN: 1434-1948
    Keywords: Peroxo complexes ; Iron ; Nonheme iron ; Iron ; EPR spectroscopy ; Mass spectrometry ; UV/Vis spectroscopy ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Some nonheme hydroperoxoiron(III) species have been recently characterized by several groups. The reported examples were obtained by adding H2O2 in excess to an FeII complex with a neutral polypyridine ligand. We show here that on deprotonation, the purple low-spin hydroperoxoiron(III) complex [L5FeIIIOOH]2+ [L5 = N-methyl-N,N′,N′-tris(2-pyridylmethyl)ethane-1,2-diamine] gives a blue high-spin species which we characterized as the η2-peroxoiron(III) species [L5FeIIIO2]+. It seems that with such an auxiliary ligand, the hydroperoxo group is acidic in contrast with its basicity when it is coordinated to a heme group.
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  • 179
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    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 981-992 
    ISSN: 1434-1948
    Keywords: Cobaloximes ; Vitamin B12 ; Semiempirical calculations ; Force field ; Conformation analysis ; Cone angles ; Crystal structure ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Molecular mechanics force field constants have been derived for alkylcobaloximes, (alkyl)Co(DH)2L (DH = monoanion of dimethylglyoxime and L = planar N-donor ligand), implementing the AMBER force field. Atomic charges have been calculated by the semiempirical ZINDO/1 method. Stretching and bending constants have been calculated by the Badger and Halgren equations, with the introduction of simple functions for the description of the electronic influence of the axial ligands on the coordination geometry. 26 parameters have been optimized, by the Simplex method, to fit 4523 bond lengths and angles of 52 alkylcobaloxime accurate crystal structures. In spite of the oversimplification of the adopted method for the description of the electronic effects, this approach provides a good description of the metal coordination geometries. The root-mean-square deviations of the calculated bond lengths and angles from the experimental values average to 0.023 Å and 1.4°, respectively. The molecular mechanics results are discussed in terms of the steric properties of the axial ligands and correlated with their calculated cone angles. The force field has been used to analyse some conformational features of these compounds, such as the influence of the rotation of the axial ligands on their coordination geometry. The calculated energy for the Co-N rotational barrier agrees well with the experimetal ones derived from dynamic and saturation 1H-NMR spectroscopy in (alkyl)Co(DH)2(2-NH2-py). In order to have more experimental data for this analysis, the crystal structures of two new cobaloximes, (CH2Cl)Co(DH)2L with L = py, 1, and 1-Me-Im, 2) have been determined. The results of a conformational analysis on ribosyl-imidazole derivatives, taken as a suitable vitamin B12 coenzyme model, suggest that the 1-Me-imidazole-like ligands have a significantly greater rotation freedom with respect to the benzimidazole-like ones, but cause similar stretchings of the Co-C bond, and a significantly less stretching of the Co-N one. Implications for the recent findings on the binding mode of the coenzyme B12 in the enzyme active site are discussed.Supporting information for this article is available on the WWW under http://www.wiley-vch.de/contents/jc_2005/1999/98399_s.pdf or from the author.
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  • 180
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    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 997-999 
    ISSN: 1434-1948
    Keywords: Rhenium ; Clusters ; Solid-state structures ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The first two Re4 chalcogenide halide clusters (Pr4N)2Re4Q4(CH3CONH)2Cl8 (Q = S, Se) with ionic molecular structures have been synthesized by treatment of neutral molecular clusters Re4Q4Cl8(TeCl2)4 (Q = S, Se) with Pr4NCl in refluxing CH3CN. During the reaction acetonitrile solvent molecules are converted into acetamido ligands, coordinated as dinucleating ligands to Re-Re bonds.
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  • 181
    ISSN: 1434-1948
    Keywords: Cyclotriphosphazenes ; Oxypyridine ; Carbonyltungsten compounds ; NMR spectroscopy ; Heterocycles ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The reactions of [N3P3(dobp)2Cl2] and [N3P3(dobp)Cl4] with a mixture of HOC5H4N-4 and K2CO3 in acetone give the cyclotriphosphazenes [N3P3(dobp)2(OC5H4N-4)2] and [N3P3(dobp)(OC5H4N-4)4], respectively. These compounds react with [W(MeOH)(CO)5] in methanol to give mixtures of the polymetallic complexes [N3P3(dobp)2(OC5H4N-4)2{W(CO)5}x] (x = 1, 2) and [N3P3(dobp)(OC5H4N-4)4{W(CO)5}x] (x = 1-4), which are unstable in solution, slowly undergoing loss of the pentacarbonyl moiety. A complete characterization by multinuclear 1H, 15N, 31P, 183W magnetic resonance has revealed that the complexation of the N atom of one 4-oxypyridine ligand by the W(CO)5 fragment has a measurable effect on other parts of the phosphazene molecule very far away from the coordination site. The changes observed in δ183W have been used to identify the components in mixtures of compounds incorporating different numbers of tungsten atoms in the molecule. The characterization of less sensitive nuclei has been accomplished by means of indirect detection methods.
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  • 182
    ISSN: 1434-1948
    Keywords: Pyridine N-oxide ; Pyridine ; Asymmetric catalysis ; Amino acids ; Amino alcohols ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Starting from picolinic acids 3 and 4, the amino acid-derived 2-aminoacylpyridine N-oxides 1a,c-e and 2,6-bis(aminoacyl)pyridine N-oxides 2b-e can be prepared in two steps by the coupling of picolinic acid N-oxides 5 and 6 under Appel conditions with the corresponding L-amino acid ester or (1R,2S)-norephedrine. Compounds 1 and 2 were used as chiral ligands in two different asymmetric catalyses. In the catalytic addition of diethylzinc to benzaldehyde 11, low enantioselectivities (2-29% ee) were obtained regardless of the amino acid moiety. However, the corresponding 2,6-bis(aminoacyl)pyridines 7 and 8 led to increased ee values (55% ee). In the catalytic reduction of ketones 9a-c to alcohols 10a-c low enantioselectivities were observed for alanine-, valine-, and leucine-derived N-oxides 1a,c and 2b,c. An increase of selectivity was observed for bis-methionine ligand 2d (32-38% ee) relative to that of mono-methionine ligand 1d (7-16% ee). However, mono-norephedrine ligand 1e (≤ 64% ee) and the corresponding bis-norephedrine ligand 2e (≤ 51% ee) displayed the highest selectivities. The influence of the N-oxide moiety on the enantioselectivity was demonstrated by the observation that 2,6-bis(aminoacyl)pyridines 7 and 8 gave much lower selectivities than the corresponding pyridine N-oxides 2d and e.
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  • 183
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    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 1931-1937 
    ISSN: 1434-1948
    Keywords: Diboron compounds ; B-B double bond ; Dilithium tetra(amino)diborates(2-) ; Structure elucidation ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A series of mixed tetraaminodiborane(4) compounds bearing pyrrolyl, indolyl, and carbazolyl substituents besides dimethylamino groups has been prepared and subjected to reduction with elemental Li in the presence of diethyl ether. Tetraaminodiborates(2-) are formed, which feature a boron-boron double bond. The diborate anion acts as a double bidentate ligand coordinating pairwise through two of its nitrogen atoms to an Li center, which is tricoordinated by one O and the two N atoms. The new diborates are isoelectronic with tetraaminoethylenes and are expected to be electron-transfer reagents.
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  • 184
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    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 1919-1930 
    ISSN: 1434-1948
    Keywords: Ruthenium ; Chirality ; Cyclopentadienyl complexes ; Kinetics ; Asymmetric catalysis ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Novel, functionalized, chiral Cp-ligands with S- and P-donor atoms were designed. Together with known analogues containing ether side-chains they were complexed to ruthenium for use as chiral Lewis-acid catalysts. In the ether complexes [RuCl(η5-C5H4CH2CH2OR)(PPh3)2] {R = Me, (1S)-isobornyl, (1R)-menthyl, (1R)-fenchyl} the Cp-ligand is only η5-coordinated; all attempts to provoke a bidentate, Cp/O coordination were unsuccessful. The sulfide complex [Ru{η5:η1-C5H4CH2CH2S[(1R)-neomenthyl]}(PPh3)2][OTf] contains a bidentate Cp/S-coordinated ligand, but it is unstable. The stable phosphane complex [RuCl(η5:η1-C5H4CH2CH(Me)PPh2)(PPh3)] exists as a 77:23 mixture of diastereomers containing a strongly bidentate Cp/P ligand. The diastereomers interchange, with Ru-Cl bond cleavage as the rate-determining step.Supporting information for this article is available on the WWW under http://www.wiley-vch.de/contents/jc_2005/1999/99126_s.pdf or from the author.
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  • 185
    ISSN: 1434-1948
    Keywords: Palladium ; Bidentate nitrogen ligands ; Carbohydrates ; Alkenes ; Enantioselectivity ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Chiral N,N-chelates of formula 6-Me-pyridine-2-CH=N-R (1) and R-N=CH-CH=N-R (2) (R = 6-deoxy-α-D-glucoside or 6-deoxy-α-D-mannoside residue) and their palladium(0) complexes [Pd(N,N-chelate)(olefin)] (I) were prepared. Symmetrical type 2 ligands induced higher enantioselectivity in the coordination of prochiral olefins. The ability of a type 1 chelate to promote a stereoselective process was also assessed, i.e. dimethylfumarate inserted into the Pd-Me bond formed upon methylation of a type I complex with 50% ee. Finally, a water-soluble Pd0 complex was also prepared by deprotecting the alcoholic functions on the sugar residue, and its molecular structure determined through X-ray diffractometry.
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  • 186
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    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 1957-1963 
    ISSN: 1434-1948
    Keywords: Cluster compounds ; Vibrational spectroscopy ; Spherical harmonics ; Carbonyl complexes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The recently suggested spherical (SHM) and tensor (THM) harmonic models are applied to the interpretation of the terminal ν(CO) spectra of twenty six tetrahedral transition metal clusters containing between four and twelve terminal carbonyl groups. Although the SHM is perhaps the more generally relevant, there are species for which the THM is appropriate as a first approximation. The distinction between the two appears to be associated with a disruption of the band structure of the cluster either by the introduction of heterometal atoms or by the presence of a group - acetate ester, halide or hydride - presumably acting as an electronegative substituent.
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  • 187
    ISSN: 1434-1948
    Keywords: Palladium ; Carbenes ; Metallacycles ; 1,2,4-Triazole ; Coordination modes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Mononuclear palladium carbene complexes 2a-c and 3 derived from 1,1′-methylenebis(4-alkyl-4,5-dihydro-1H-1,2,4-triazole-5-ylidene) have been obtained by the reaction of 1,1′-methylenebis(4-alkyl-1,2,4-triazolium) diiodides 1a-d with palladium acetate under mild conditions. The mononuclear complexes 2a-c have been transformed into their corresponding trans-binuclear complexes 4a-c. All compounds were characterized by spectroscopic techniques and the dynamic behavior of 2a-cand 4a-c has been studied. The X-ray structures of 2a and 4c are reported.
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  • 188
    ISSN: 1434-1948
    Keywords: Phosphanylethyl-functionalized cyclopentadienyl ligands ; Intramolecular coordination ; Spiro compounds ; Zirconium ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The five-step synthesis of the first transition metal complex with the C5(CH3)4CH2CH2PPh2 ligand [η5:η1-C5(CH3)4CH2CH2PPh2]ZrCl3·THF (11), starting from the known compound [2-(dimethylamino)ethyl]tetramethylcyclopentadiene (4) via 4,5,6,7-tetramethylspiro[2,4]hepta-4,6-diene (7), is reported. Lithium cyclopentadienide LiC5(CH3)4CH2CH2PPh2 (9), silylated cyclopentadiene (CH3)3SiC5(CH3)4CH2CH2PPh2 (10) and cyclopentadiene HC5(CH3)4CH2CH2PPh2 (12) were isolated and characterised as pure substances. The crystal structure of the zirconium complex 11 was established by X-ray diffraction analysis.
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  • 189
    ISSN: 1434-1948
    Keywords: MS-325 ; Angiography ; MRI contrast agent ; NMR spectroscopy ; Interaction with HSA ; Gadolimium ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The physicochemical characterization of MS-325 [trisodium {4-(R)-[(4,4-diphenylcyclohexyl)phosphanooxymethyl]-3,6,9-triaza-3,6,9-tris(methoxycarbonyl)undecanedioato}gadolinium(III)], a new derivative of Gd-DTPA {Magnevist®: dimeglumin [{3,6,9-triaza3,6,9-tris(methoxycarbonyl)undecanedioato}gadolinium(III)], presented as a potentially useful angiographic contrast agent, was carried out in various media. Water solution, protein-containing solution, phosphorylated metabolites solution, and Zn2+-containing solution were investigated using different NMR techniques such as water 1H nuclear magnetic relaxation rates, water 17O transverse relaxation rates, and 31P longitudinal relaxation rates of phosphorylated metabolites. The proton relaxivity of MS-325 in water was found to be higher than that of the parent compound Gd-DTPA; this can be attributed to the longer rotational correlation time (τR) of the hydrated complex, and possibly to an apparently shorter mean distance (r) between the protons of the coordinated water molecule and the gadolinium ion. The kinetic and thermodynamic stability of MS-325 in solutions containing phosphorylated metabolites (ATP, phosphocreatine and inorganic phosphate) were measured by 31P relaxation rate analysis and found to be higher than for Gd-DTPA. Similarly, the Zn2+ transmetallation process studied by proton relaxometry is slower than for the same reference compound. Finally, an analysis of the noncovalent binding of MS-325 to serum proteins by proton relaxometry showed that MS-325 interacts with human serum albumin (HSA) and that the association constant of this interaction is equal to 6100 ± 2130 M-1. A peak relaxivity of approx. 50 s-1mM-1 was determined at 25 MHz for the protein-bound paramagnetic complex. This value is lower than the maximal relaxivity predicted for a paramagnetic center totally immobilized at the surface of the protein.
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  • 190
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    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 1981-1985 
    ISSN: 1434-1948
    Keywords: Pyrazole ; Silver ; Metallacycles ; Macrocycles ; Self-assembly ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The 2,6-bis(pyrazolyl)pyrazine ligand 1 forms a 2,2-metallamacrocycle 3, composed of two ligands and two cations, in the presence of the Ag+ cation. In the crystalline phase, the 1,3,5-tris(pyrazolyl)benzene ligand 2 leads to an infinite metallatubular network in the presence of the Ag+ cation, composed of the 2,2-metallamacrocycle 4, which is formed from two molecules of 2 and two cations. This infinite network is formed by double interconnection of consecutive metallamacrocycles through binding of Ag+ centers by the free pyrazolyl moieties.
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  • 191
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    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 1095-1102 
    ISSN: 1434-1948
    Keywords: Silanorbornenes ; Silanorbornanes ; Silicon-functionalized olefins ; Silacyclobutanes ; Hydrogenations ; Heterocycles ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Catalytic hydrogenation of olefins containing functionalized silicon groups affords the saturated products in good yields. Chloro and alkoxy substituents at the silicon atom remain unaffected and, in the case of heterocyclic compounds, the cyclic or bicyclic moieties remain intact. The 2-silanorbornanes 4, 5, and 6 were synthesized from the corresponding 2-silanorbornenes 1, 2, and 3, and organosilanes 13 and 14 possessing the cyclopentyl group, were prepared from the cyclopentenyl-substituted precursors 10 and 12. The 3-vinyl-substituted silacyclobutanes 15, 17, and 18 were also hydrogenated in a simple apparatus with diethyl ether or THF as solvent, and Pd/C as a recoverable catalyst system. A basic organosilicon compound, trichloro(vinyl)silane, is hydrogenated in a nearly quantitative yield to form the saturated trichloro(ethyl)silane; this emphasizes the general applicability of this method.
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  • 192
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    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 1103-1110 
    ISSN: 1434-1948
    Keywords: Amines ; Aurophilicity ; Gold ; Hydrogen bonds ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Various gold(I) complexes of aliphatic amines have been prepared by the reaction of chloro(tetrahydrothiophene)gold(I) with the respective amines. The stability of these complexes can be attributed partly to the formation of hydrogen bonds involving the N-H functions, and partly to aurophilic interactions. Analysis of these secondary contacts suggests an inverse correlation between lengths of aurophilic interactions and hydrogen bonds.
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  • 193
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    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 1121-1132 
    ISSN: 1434-1948
    Keywords: Coordination chemistry ; Rhodium ; Aminations ; Hydroaminations ; Oxidative aminations ; Vinylpyridines ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Cationic rhodium complexes catalyze the amination of 2- and 4-vinylpyridine with secondary amines. Depending on the substrate and the reaction conditions either oxidative amination to yield the corresponding enamines 1a-8a or hydroamination to give 2-aminoethylpyridines 1b-8b occurs. In all cases products with anti-Markovnikov regioselectivity are obtained. For mechanistic studies novel cationic complexes of rhodium(I)-containing cyclooctadiene and vinylpyridine 12 as well as complexes containing cyclooctadiene, vinylpyridine, and morpholine 13 were prepared and characterized by NMR spectroscopy and X-ray diffraction analysis.
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  • 194
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    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 1141-1149 
    ISSN: 1434-1948
    Keywords: C-C coupling ; Metallacycles ; Metallacyclobutane ; Ruthenium ; Tripodal ligands ; Vinylidene complexes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Selective coupling of olefins and terminal acetylenes is shown to be effected in the coordination sphere of RuII by the successive intermediacy of vinylidene and ruthenacyclobutane complexes. Subsequent deprotonation of one of the β-hydrogen atoms of the latter by NaOEt yields η3-butadienyl complexes, while in the presence of Cl- rearrangement takes place to give neutral η2-butadiene complexes by a β-hydrogen elimination/reductive elimination sequence. [Ru(tp)(COD)Cl] and [Ru(tp){η3-(P,C,C)-Ph2PCH=CHC(Ph)=CH2}Cl] were the starting materials which were treated with HC≡CR (R = Ph, C6H9, ferrocenyl, CH2Ph, nBu). The η3-butadienyl complexes are nucleophilic at the enynyl carbon atom reacting readily with the electrophiles H+ and I2 to give the corresponding η2-butadienyl complexes. X-ray structures of representative products are given.
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  • 195
    ISSN: 1434-1948
    Keywords: Ruthenium ; Thiolate ligands ; Dithiolate ligands ; Substitution reactions ; Electrophilic additions ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The known dithiolate-bridged ruthenium(I) complex [Ru2(μ-bdt)(CO)6] (1) (bdt = benzene-1,2-dithiolate) has been prepared in fair yield (55%) by the sequential treatment of RuCl3·nH2O with carbon monoxide, benzene-1,2-dithiol and zinc in a one-pot reaction. Complex 1 reacts readily with monodentate phosphanes to give, stepwise, the penta- and tetracarbonyl derivatives [Ru2(μ-bdt)(CO)6-n(PR3)n] (n = 1, 2; R = Ph, Cy, iPr). However, the reaction of 1 with one equivalent of bis(diphenylphosphanyl)methane (dppm) affords a mixture of complex 1 and the disubstituted derivative [Ru2(μ-bdt)(CO)4(η1-dppm)2], in which the dppm ligands are monodentate. This mixture is subsequently transformed into a polymeric material of formula [{Ru2(μ-bdt)(CO)4}(μ-dppm)]n, which consists of binuclear {Ru2(μ-bdt)(CO)4} units linked to each other by bridging dppm ligands. The use of two equivalents of dppm leads to [Ru2(μ-bdt)(CO)4(η1-dppm)2] in quantitative yield. The X-ray diffraction structure of [Ru2(μ-bdt)(CO)4(PiPr3)2] (3c) confirms that the phosphane ligands are located in axial positions, cis to both sulfur atoms, and that the Ru-Ru distance is short [2.6753(7) Å]. A comparative study of the reactivity of complexes 1 and 3c with the electrophiles H+, [Au(PPh3)]+, and HgCl2 has allowed the isolation of the derivatives [Ru2(μ-H)(μ-bdt)(CO)6-n(PiPr3)n][BF4] (n = 0, 2), [Ru2Au(μ-bdt)(CO)6-n(PiPr3)n(PPh3)][BF4] (n = 0, 2) and [Ru2HgCl2(μ-bdt)(CO)6-n(PiPr3)n] (n = 0, 2), respectively.
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  • 196
    ISSN: 1434-1948
    Keywords: Bioorganometallic chemistry ; Zirconocene complexes ; Metallocene cations ; Group-4 metallocene peptide complexes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The dipeptide derivatives Boc-Gly-Val-OMe (2) and Boc-Ala-Val-OMe (3) selectively add the methylzirconocene cation 1 to the carbonyl oxygen atom of the N-terminal amino acid residue (ĸ-C4=O coordination) upon treatment with [Cp2ZrCH3(THF)+BPh4-] in dichloromethane at low temperature (〈 0 °C) to generate the complexes 2-I and 3-I, respectively. Above 0 °C methane is eliminated to give the stable chelate peptide metallocene cation complexes 2-A and 3-A, respectively, both featuring a combined C1=O/N2/C4=O coordination to the zirconium center. Complex 3-A was characterized by X-ray diffraction. The analogous tripeptide derivatives Boc-Gly-Val-Val-OMe (6), Boc-Ala-Ala-Val-OMe (7), Boc-Ala-Val-Val-OMe (8), and Boc-Val-Val-Gly-OMe (9) all form analogous ĸ-C4=O Cp2ZrCH3+ cation adducts (6-9)-I under kinetic control and after subsequent loss of CH4 C1=O/N2/C4=O chelate complexes (6-9)-A under thermodynamic control, both involving selective bonding of the organometallic cation to the terminal amino acid residue of the respective peptide derivatives. Thermolysis of the primary adduct 7-I (〉 0 °C) resulted in methane elimination and formation of a mixture of the isomers 7-B and 7-A (isolated in a 3:4 ratio). According to the detailed NMR analysis 7-A shows the favored chelate coordination at the N-terminus involving C1=O/N2/C4=O bonding, whereas the cation complex 7-B exhibits a similar chelate structure at the internal Ala moiety, characterized by C4=O/N5/C7=O coordination to the zirconium center. Similarly, methane liberation from 8-I and 9-I gave mixtures of the respective cationic chelate complex isomers 8-A/8-C (2:3) and 9-A/9-C (1:1), respectively. The (8,9)-A isomers have the zirconium ion bonded at the N-terminus, whereas (8,9)-C exhibit the Cp2Zr+ unit at the C-terminus of the peptide chain, involving the ester carbonyl group in forming the chelate framework (C7=O/N8/C10=O coordination). The (6-9)-A isomers are thermodynamically favored. The cation complexes 7-B, 8-C, 9-C rearrange to the A-type isomers upon prolonged standing at temperatures 〉 0 °C in dichloromethane solution.
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  • 197
    ISSN: 1434-1948
    Keywords: Zirconium ; Metallocenes ; Triflate ; Hydrosulfido ; Rhodium ; Early-late complex ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The bishydrosulfido zirconium metallocene compound [Cptt2Zr(SH)2] (2) containing the bulky η5-1,3-di-tert-butylcyclopentadienyl (Cptt) ligand is readily accessible from [Cptt2Zr(CH3)2] (1) upon treatment with H2S. Reaction of 2 with methyltriflate gives the monohydrosulfido complex [Cptt2Zr(SH)(OSO2CF3)] (3) which exists as two isomers in solution, and has been characterized by X-ray diffraction methods. Complex 2 is an effective metallaligand for the controlled synthesis of new trinuclear early-late heterobimetallic complexes (ELHB) with a ZrRh2 core such as [Cptt2Zr(μ3-S)2{Rh(CO)2}2] (4).
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  • 198
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    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 2021-2027 
    ISSN: 1434-1948
    Keywords: Aluminium ; Hydrazides ; Alanes ; Lithium ; Imino compounds ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Di(tert-butyl)aluminium chloride reacted with dilithium bis(trimethylsilyl)hydrazide with the formation of a novel Al2Li2N4 cage compound 1. Its structure consists of a dimeric iminoalane RAl(μN-SiMe3)2AlR (R = CMe3), which is bridged by a dilithiumhydrazido ligand with an intact N-N bond. A heterocubane-type molecule is formed, in which two vertices are occupied by Al atoms, two by Li atoms and four by N atoms. One face of the cube is strongly distorted due to the short N-N distance of the hydrazido group. A similar compound, 3, was formed with bis(neopentyl)aluminium chloride but it was isolated in very poor yield. The reaction of Li2N2(SiMe3)2 with (Me3C)2AlCl in the presence of THF yielded an adduct 2, in which each Li atom of the cage is additionally coordinated via Li-Cl-Al bridges to the ligand (Me3Al)2Cl·THF. The reaction of dilithium bis(trimethylsilyl)hydrazide with tert-butylaluminium dichloride gave, by complete cleavage of the hydrazido groups, a dimeric iminoalane [Me3C(THF)AlNSiMe3]2 (4), in which each aluminium atom is coordinated to one THF molecule. Its uncoordinated, solvent-free form 5 was obtained by heating solid 4 to 150 °C in vacuo for several hours. It was identified as the tetrameric iminoalane (Me3CAlNSiMe3)4, which does not adopt the expected heterocubane-type structure, but consists of three anellated four-membered Al2N2 heterocycles in a kind of ladder structure. Remarkably, the cage compound 1 could not be obtained by the reaction of an excess of lithium hydrazide with the iminoalanes 4 and 5. All compounds 1-5 were characterized by crystal structure determinations.
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  • 199
    ISSN: 1434-1948
    Keywords: Diaminocarbenes ; Lewis basicity ; Ab initio calculations ; Donor-acceptor complexes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Quantum chemical calculations at the MP2 level using large valence basis sets up to TZ+2P quality have been carried out in order to predict the geometries and bond energies of the title compounds. The nature of the donor-acceptor bond has also been investigated. The calculations show clearly that diaminocarbenes are much stronger Lewis bases than amines. The complexation energies of C(NH2)2 have been calculated to be 14-27 kcal/mol higher than those of NH3. The most strongly bonded complex is Cl3Al-C(NH2)2, which has a theoretically predicted Al-C bond energy Do = 59.1 kcal/mol. In all the complexes, the strength of the Lewis bases is C(NH2)2 〉 NH3 〉 CO, but the ordering of Lewis acid strength of EX3 depends on the coordinated Lewis base. TiF4 and TiCl4 have similar Lewis acidities as BF3, but the titanium tetrahalides may bind one or two donor molecules with almost the same bond strength. The investigated donor-acceptor bonds have a high degree of ionic character. The largest covalent contributions are found for the diaminocarbene complexes. The covalent character of the X3E-CO bond increases on going from E = boron to the heavier Group 13 elements, while the opposite order is found for the X3E-NH3 and X3E-C(NH2)2 bonds.
    Additional Material: 6 Ill.
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  • 200
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 2057-2061 
    ISSN: 1434-1948
    Keywords: Sulfur ; Sulfanes ; Acidity ; Ab initio MO calculations ; Hyperconjugation ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The gas-phase acidities ΔGacid(298 K) of the sulfanes H2Sn (n = 1-4) have been calculated by ab initio molecular orbital theory using the G2 and G2(MP2) methods, which were applied to the geometries of lowest energy. The results show that the higher sulfanes are surprisingly strong proton donors. The acidities (in kJ mol-1) are as follows: H2S (1444), H2S2 (1406), H2S3 (1370), H2S4 (1347). The latter three values may be compared to those of other strong Brønsted acids like gaseous HNO2 (1396), HCl (1371), and HBr (1332). The monoanions HSn- exhibit an interesting bond length distribution as a consequence of the charge delocalization by hyperconjugation, which in turn may be responsible for the high acidities of the sulfanes.
    Additional Material: 3 Ill.
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