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  • 1995-1999  (65)
  • 1900-1904
  • 1999  (65)
  • General Chemistry  (65)
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  • 1995-1999  (65)
  • 1900-1904
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Keywords
  • 1
    Electronic Resource
    Electronic Resource
    Diversity in Complexation of [RhI(cod)]+ and [IrI(cod)]+ by Pyridine-Amine-Pyrrole Ligands (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 1581-1592 
    Details
    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.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Homogeneous and Supported Copper Complexes of Cyclic and Open-Chain Polynitrogenated Ligands as Catalysts of Cyclopropanation Reactions (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 2347-2354 
    Details
    ISSN: 1434-1948
    Keywords: Cyclopropanation ; Copper ; N ligands ; Macrocycles ; Supported catalysts ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: CuI and CuII complexes of cyclic and open-chain polyaza compounds have been tested as catalysts in the benchmark cyclopropanation reaction of styrene with ethyl diazoacetate. In general, only small amounts of copper are needed to promote the reaction. The catalytic activity depends on the structure of the ligand, e.g. amine-amides are more efficient than polyamines, and on the oxidation state of copper, CuII being more active than CuI. Given that CuI is the active species, these changes of behavior must be related to the stabilities of the complexes. The nature of the counterion also has a noticeable influence on the catalytic activity, the role of which is discussed. XAS measurements suggest the formation of oligomeric species. Some of the chiral ligands lead to small enantiomeric excesses. Open-chain ligands can easily be supported on organic polymers and their complexes can be used as catalysts. Furthermore, cyclic and acyclic complexes can be supported on clays by cation exchange and the solids obtained tend to promote the reaction with a decrease in the trans/cis ratio.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Diastereoselective Conjugate Addition Reactions of 2′-Hydroxypropiophenone to 2′-Hydroxychalcones - Synthesis and Structural Characterization of the Diastereomers of (±)-3-Aryl-1,5-bis(2-hydroxyphenyl)-2,4-dimethyl-1,5-pentanediones (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 1739-1744 
    Details
    ISSN: 1434-193X
    Keywords: Addition reactions ; Diastereoselectivity ; 2′-Hydroxychalcones ; 3-Aryl-1,5-bis(2-hydroxyphenyl)-2,4-dimethyl-1,5-pentanediones ; NMR spectroscopy ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The diastereoselective synthesis of 3-aryl-1,5-bis(2-hydroxyphenyl)-2,4-dimethyl-1,5-pentanediones has been carried out by conjugate addition reactions of 2′-hydroxypropiophenone to 2′-hydroxy-α-methylchalcone derivatives, or in single one-pot reactions of 2′-hydroxypropiophenone with appropriate benzaldehyde derivatives. The structures and stereochemistry of the obtained diastereomers have been determined using various NMR techniques, and the factors determining their formation are investigated and discussed.
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    New Syntheses of Flavones from Diels-Alder Reactions of 2-Styrylchromones with ortho-Benzoquinodimethanes (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 135-139 
    Details
    ISSN: 1434-193X
    Keywords: Flavones ; Chromones ; ortho-Benzoquinodimethanes ; Diels-Alder reactions ; NMR ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -The first reported cycloaddition reactions of 2-styrylchromones with ortho-benzoquinodimethane afforded 2-[2-(3-aryl-1,2,3,4-tetrahydronaphthyl)]chromones. These cycloadducts were converted into the corresponding 2-[2-(3-arylnaphthyl)]chromones (benzoflavone derivatives) by bromination/dehydrobromination processes. These benzoflavone derivatives were also obtained in one-pot cycloaddition reactions of 2-styrylchromones with ortho-benzoquinodibromomethane.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Interactions between Chromophore-Labelled Ammonium Surfactants and Hydrophobically Modified Polyelectrolytes (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 305-312 
    Details
    ISSN: 1434-193X
    Keywords: UV spectroscopy ; Poly(maleic acid-co-alkyl vinyl ether)s ; Azobenzene ; (Cyanobiphenylyl)oxy ; Cooperative binding ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -The interaction of poly(maleic acid-co-alkyl vinyl ether)s and poly(sulfonylethyl maleic acid monoamide-co-alkyl vinyl ether)s with and without (cyanobiphenylyl)oxy chromophores with N-[ω-(substituted azobenzoxy)alkyl]-N,N-dimethyl-N-hydroxyethylammonium bromide surfactants has been studied by UV spectroscopy. The azobenzene unit is functionalized at the 4′-position with a cyano or fluoro substituent and is connected to the surfactant headgroup via a decyl or dodecyl spacer. Upon addition of surfactants to poly(maleic acid-co-butyl vinyl ether) the absorption maxima (λmax) of the azobenzene chromophores immediately show their maximum blue shift. This indicates cooperative binding of surfactant to this polymer, and the formation of micelle-like aggregates surrounded by polyelectrolyte is assumed. Upon addition of the surfactants to the other polyelectrolytes λmax values of the azobenzoxy chromophores gradually shift to lower values indicating a lower cooperativity of surfactant binding. This is attributed to the formation of microdomains by the polyelectrolytes themselves. For these systems the formation of mixed micelles is assumed. The compactness of the microdomains of the maleic acid copolymers is influenced by the pH and binding with surfactants is also influenced by pH. The sulfonylethyl maleic acid monoamide copolymers show no pH dependence in binding above neutral pH. For these polyelectrolytes the cooperativity also becomes less with a longer spacer between backbone and chromophore. Upon elongation of the surfactant spacer or changing the end group from a cyano to the more hydrophobic fluoro substituent a lower λmaxis observed for the chromophores upon initial binding to the polyelectrolytes indicating more cooperative binding. When surfactants and polyelectrolytes are both labelled with chromophores, binding proceeds noncooperatively and the formation of mixed micelles is assumed.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Singly anti-anti Carboxylate-Bridged Zig-Zag Chain Complexes from a Carboxylate-Containing Tridentate Schiff Base Ligand and M(hfac)2 [M = MnII, NiII, and CuII]: Synthesis, Crystal Structure, and Magnetic Properties (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 441-445 
    Details
    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.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Crystal Structure and Intercalation Properties of γ-Zr(AsO4)(H2AsO4) × 2 H2O (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 61-65 
    Details
    ISSN: 1434-1948
    Keywords: Zirconium arsenate ; Crystal structure ; Amine intercalation ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The crystalline structure of γ-Zr(AsO4)(H2AsO4) × 2 H2O (γ-ZrAs) has been refined by the Rietveld method. It has a monoclinic P21 layered structure built up from AsO4 tetrahedra and ZrO6 octahedra stacked along the 001 direction. The cell parameters are: a = 5.5752(6) Å, b = 6.8290(7) Å, c = 12.110(1) Å, and β = 103.03(1)°. The layered nature of γ-ZrAs is confirmed by the intercalation of n-alkylamines (CH3[CH2]nNH2; n = 0-5) as well as of cyclic amines (benzylamine, cyclohexylamine, piperidine, and pyridine). Among the linear amines, only with methyl-, ethyl-, and hexylamine is the maximum incorporation attained. With the cyclic amines, except in the case of pyridine, pure new phases are obtained, with the highest degree of intercalation being one mol of amine per mol of γ-ZrAs.
    Additional Material: 5 Ill.
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  • 8
    Electronic Resource
    Electronic Resource
    Amino Alcohol Coordination in Ruthenium(II)-Catalysed Asymmetric Transfer Hydrogenation of Ketones (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 2335-2341 
    Details
    ISSN: 1434-1948
    Keywords: Asymmetric catalysis ; Transfer hydrogenation ; Ruthenium ; Amino alcohol ligands ; X-ray structure ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The nature of ruthenium-amino alcohol precursors in the catalytic cycle of asymmetric hydrogen transfer reactions was studied using two C2-symmetrical tetradentate ligands (1 and 2) that were synthesised from (nor)ephedrine. The structure of the catalyst precursor was examined through catalysis and NMR experiments. It was shown that the active catalyst contains one ligand per metal, which coordinates in a didentate N,O fashion (9). In addition, a RuIICl2 complex, in which N,N′-bis(2-hydroxy-1-methyl-2-phenylethyl)-1,2-diaminoethane (1) coordinates through two nitrogen atoms, was structurally characterised by X-ray diffraction (8). - Based on the results of this study a series of new amino alcohol ligands was synthesised from easily available starting materials. Optimisation of the amino alcohol ligand structure resulted in the most effective chiral amino alcohol ligand (5) so far that is capable of reducing acetophenone at 0 °C with up to 97% ee in the RuII-catalysed transfer hydrogenation.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Diastereoselective Self-Assembly of [2]Catenanes (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 995-1004 
    Details
    ISSN: 1434-193X
    Keywords: Catenanes ; Diastereoselectivity ; Molecular Recognition ; Self-Assembly ; Template-Directed Synthesis ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -Two chiral π-electron-rich crown ethers incorporating either a binaphthol or two D-mannitol units have been synthesized and their abilities to bind bipyridinium guests demonstrated. Both crown ethers could be interlocked mechanically with cyclobis(paraquat-p-phenylene) to afford two chiral [2]catenanes. Furthermore, these crown ethers were also mechanically interlocked with a tetracationic cyclophane incorporating a 2,2′-dihydroxy-1,1′-binaphthyl spacer to afford mixtures of diastereoisomeric [2]catenanes. The composition of these mixtures was determined by 1H-NMR-spectroscopic and HPLC analyses which revealed that modest diastereoselection (56:44-67:33) occurs during the kinetically controlled self-assembly of the catenanes. The free energy barriers (12.8-16.8 kcal mol-1) associated with the circumrotation of one macrocyclic component through the cavity of the other and vice versa were determined by variable-temperature 1H-NMR spectroscopy. In addition, another dynamic process involving the “rocking” of the mean planes of the mechanically interlocked macrocycles with respect to each other was also identified and the associated free energy barriers (10.3-10.4 kcal mol-1) determined.
    Additional Material: 6 Ill.
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  • 10
    Electronic Resource
    Electronic Resource
    Synthesis of 8-Substituted Xanthines and Their Oxidative Skeleton Rearrangement to 1-Oxo-2,4,7,9-tetraazaspiro[4,5]dec-2-ene-6,8,10-triones (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 2419-2428 
    Details
    ISSN: 1434-193X
    Keywords: 1,3,7-Trialkyl-8-(dialkylamino)xanthines ; 1,3,7-Trialkyl-8-(2′,2′,2′-trifluoroethoxy)xanthines ; 8-(Dialkylaminomethyl)caffeines ; 1-Oxo-2,4,7,9-tetraazaspiro[4,5]dec-2-ene-6,8,10-triones ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The synthesis of a number of 8-(dialkylamino)- and 8-alkoxyxanthines (3 and 6, respectively) is described. Treatment of 3 with m-chloroperoxybenzoic acid (m-CPBA) gave by a novel rearrangement 3-(disubstituted amino)-4,7,9-trimethyl-1-oxo-2,4,7,9-tetraazaspiro[4,5]dec-2-ene-6,8,10-triones 10. Also, the corresponding 3-alkoxy-subtituted spiro compounds 12 were obtained by an analogus treatment of 8-alkoxyxanthines 6. In attempts to elucidate a tentative mechanism for this rearrangement 8-[(dialkylamino)methyl]caffeines 7 when treated with m-CPBA did not undergo the rearrangement but only yielded the expected N-oxide derivatives 16. This result seems to indicate that a necessary structure element for this rearrangement to occur is an atom with an unshared pair of electrons to be attached to the 8-position of the investigated xanthines. In agreement with this statement is the fact that N-oxides of 8-[(dialkylamino)methyl]caffeines 16 do not undergo the novel rearrangement but rather give the expected Meisenheimer rearrangement or the Cope elimination depending upon reaction conditions.
    Additional Material: 5 Ill.
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