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  • General Chemistry  (99)
  • 2010-2014
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  • 1997  (99)
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  • 2010-2014
  • 2000-2004
  • 1995-1999  (99)
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  • 1
    Digitale Medien
    Digitale Medien
    [(TptBu, Me)CrR]: A New Class of Mononuclear, Coordinatively Unsaturated Chromium(II) Alkyls with cis-Divacant Octahedral Structure (1997)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 3 (1997), S. 1668-1674 
    Details
    ISSN: 0947-6539
    Schlagwort(e): alkenes ; chromium ; cis-divacant octahedral geometry ; polymerizations ; tris(pyrazolyl)borate complexes ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Reaction of CrCl2 with TptBu, MeK yielded [TptBu, MeCr(3-tBu, 5-MepzH)Cl] (1) and [TptBu, MeCrCl] (2), while the same reaction in the presence of pyridine gave 1 and [TptBu, MeCr(py)Cl] (3). Alkylation of 3 with Grignard reagents produced the chromium(II) alkyls [TptBu, MeCrR] (4, R = Et; 5, R = Ph; 6, R = CH2SiMe3), which reversibly added to pyridine to form the five-coordinate adducts [TptBu, MeCr(py)R] (7, R = Et; 8, R = Ph; 9, R = CH2SiMe3). 1, 2, 4, and 5 were structurally characterized by X-ray diffraction. The four-coordinate molecules 2, 4, and 5 adopt a highly unusual cis-divacant octahedral coordination geometry, while 1 is the first five-coordinate TptBu, Me-complex of a first-row transition metal. Despite their coordinative unsaturation, chromium alkyls 4-6 do not polymerize ethylene, or even react with it. This observation is inconsistent with the catalytic activity commonly ascribed to divalent chromium in heterogeneous polymerization catalysts. Attempts to oxidize 4-6 (e.g., with [Cp2Fe]BPh4) to cationic chromium(II) alkyls failed, yielding [TptBu, MeCr(thf)][BPh4] (10) instead.
    Zusätzliches Material: 3 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/chem.19970031016
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  • 2
    Digitale Medien
    Digitale Medien
    Nickel Complexes of 21-Oxaporphyrin and 21, 23-Dioxaporphyrin (1997)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 3 (1997), S. 268-278 
    Details
    ISSN: 0947-6539
    Schlagwort(e): heterocycles ; heteroporphyrins ; nickel ; porphyrinoids ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The nickel(I) and nickel(II) complexes of 5,20-bis(p-tolyl)-10, 15-diphenyl-21-oxaporphyrin (ODTDPPH) and 5,10,15,20-tetraphenyl-21, 23-dioxaporphyrin (O2TPP) have been investigated. These oxa analogues of 5,10,15,20-tetraarylporphyrin, where one or two pyrrole rings are replaced by a furan moiety, have been synthesized by condensation of the respective precursors, namely 2,5-bis(arylhydroxymethyl)furan, pyrrole, and arylaldehyde. Insertion of nickel(II) into ODTDPPH or O2TPP yielded high-spin five- and six-coordinate ([(ODTDPP)NiIICl] and [(O2TPP)NiIICl2]) complexes, which can be reduced with moderate reducing reagents. The EPR spectra of [(ODTDPP)NiI] and [(O2TPP)NiICl] revealed the NiI oxa(dioxa)porphyrin rather than a NiI anion radical electronic structure. In the structures of [(ODTDPP)NiIICl], [(O2TPP)NiIICl2], and [(ODTDPP)NiI], determined by X-ray diffraction, the furan ring is planar and coordinates in the η1 fashion through the trigonal oxygen atom; the nickel ion lies in the furan plane for the latter two complexes, but slightly outside it in [(ODTDPP)NiIICl]. The Ni-N and Ni-O bond lengths decrease upon reduction of high-spin five-coordinate [(ODTDPP)NiIICl] to four-coordinate [(ODTDPP)NiI]. The pattern of downfield pyrrole resonances in 1H NMR spectra of [(ODTDPP)NiIICl] and [(O2TPP)-NiIICl2] has been established. The downfield positions of furan resonances are unusual for NiII heteroporphyrins; they have been accounted for by the nearly in-plane coordination of the furan moiety as opposed to the side-on coordination found for thiophene- or selenophene-containing heteroporphyrins. An example of ion-pair formation, [(O2TPPH)2][NiIICl4], was produced from [(O2TPP)NiIICl2] by acidification with HCl.
    Zusätzliches Material: 9 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/chem.19970030216
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  • 3
    Digitale Medien
    Digitale Medien
    A Joint Experimental and Theoretical Study of the Interaction between Aluminum and Electroluminescent Polymers: Cyano Derivatives of Poly(p-phenylene vinylene) (1997)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 3 (1997), S. 286-293 
    Details
    ISSN: 0947-6539
    Schlagwort(e): light-emitting diodes ; polymers ; semiempirical calculations ; electroluminescence ; polymer/metal interface ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The early stages of metal/polymer interface formation between aluminum and poly(2,5,2′,5′-tetrahexyloxy-8,7′-dicyanodi-p-phenylenevinylene) or their ring-substituted derivatives have been studied theoretically by using quantum-chemical calculations as well as experimentally by X-ray photoelectron spectroscopy and ultraviolet photoelectron spectroscopy. This class of conjugated polymer is of interest in the development of organic light-emitting diodes. The theoretical and experimental results indicate that aluminum preferentially reacts with the polymer by forming covalent bonds with the nitrogen and carbon atoms of the cyano groups. When the side chains of the phenylene rings include carbonyl groups, however, the theoretical results indicate that the carbonyl moiety is another preferred site of interaction.
    Zusätzliches Material: 10 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/chem.19970030218
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  • 4
    Digitale Medien
    Digitale Medien
    A New Strategy for Oligosaccharide Assembly Exploiting Cyclohexane-1,2-diacetal Methodology: An Efficient Synthesis of a High Mannose Type Nonasaccharide (1997)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 3 (1997), S. 431-440 
    Details
    ISSN: 0947-6539
    Schlagwort(e): carbohydrates ; glycoproteins ; HIV oligosaccharides ; protecting groups ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The high-mannose nonasaccharide 1 is part of the glycoprotein gp 120 of the viral coat of HIV-1. The mannan portion of this triantennary glycan was prepared by a number of consecutive glycosidation steps without the need for any protecting-group manipulation. This was achieved by carefully tuning the reactivity of the glycosyl donors by employing our cyclohexane-1,2-diacetal (CDA) methodology. The method was further extended with one-pot procedures for oligosaccharide synthesis, thus reducing the number of steps to form the protected nonasaccharide 21 from the monosaccharide building blocks to five.
    Zusätzliches Material: 1 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/chem.19970030315
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  • 5
    Digitale Medien
    Digitale Medien
    Molecular and Supramolecular Synthesis with Dibenzofuran-Containing SystemsMolecular meccano, part 18; for Part 17, see D. B. Amabilino, P. R. Ashton, S. E. Boyd, M. Gómez-López, W. Hayes, J. F. J. Org. Chem. 1997, 62, 3062-3075. (1997)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 3 (1997), S. 1136-1150 
    Details
    ISSN: 0947-6539
    Schlagwort(e): crystal engineering ; dibenzofuran ; molecular quadrilaterals ; supra-molecular chemistry ; template synthesis ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The template-directed syntheses of two new tetracationic cyclophanes, cyclobis(paraquat-2,8-dibenzofuran) and cyclobis(paraquat-3,7-dibenzofuran), incorporating dibenzofuran subunits has been accomplished. Initially, the cyclophanes were self-assembled around a macrocyclic polyether template, bis-p-phenylene[34]crown-10 (BPP34C10), to form catenanes: the mechanical bond order of the catenane formed determined the requisite “amacrocyclic” templates for synthesis of the free cyclophane. X-ray crystallography shows that both of the cyclophanes possess rectangular covalent frameworks. Furthermore, these cyclophanes form self-assembled tapes in the solid state, since the dibenzofuran moieties have a tendency to associate with each other through crossed ∞-∞ stacks. The dibenzofuran-containing catenanes also form two-dimensional supramolecular arrays in the solid state on account of extended ∞-∞ stacking interactions. In addition, the serendipitous discovery of a plerotopic tecton (consisting of a dibenzofuran nucleus covalently linked from the 2- and 8-positions by methylene groups to 4,4′-pyridylpyridinium (hydrogen bond acceptor) and protonated bipyridinium (hydrogen bond donor) units) has been made. The tecton dimerizes in the solid state to form a supramolecular macrocycle, since its complementary hydrogen bonding sites are oriented in a horseshoelike fashion by the 2,8-disubstituted dibenzofuran unit. However, this superstructure is not retained in the 1:1 complex of the tecton with BPP34C10: cocrystallization of the tecton with this crown ether opens the macrocyclic two-component supermolecule to afford a hydrogen-bonded pseudopolyrotaxane.
    Zusätzliches Material: 15 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/chem.19970030720
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  • 6
    Digitale Medien
    Digitale Medien
    Adsorption of Ionophores and of Their Cation Complexes at the Water/Chloroform Interface: A Molecular Dynamics Study of a [2.2.2]Cryptand and of Phosphoryl-Containing Podands (1997)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 3 (1997), S. 552-560 
    Details
    ISSN: 0947-6539
    Schlagwort(e): extraction ; interfaces ; ionophores ; molecular dynamics ; counterion effect ; solvation ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: We report molecular dynamics simulations on ionophores of different topologies and on their complexes with alkali and alkaline-earth cations, with or without counterion, at the water/chloroform interface. As ionophores we consider two phosphoryl-containing podands (the “chainlike” monopodand MP and the “octopuslike” tripodand TP) and the bicyclic cryptand 222. We find that all the solutes behave as surfactants: they remain adsorbed at the interface, without migrating to bulk phases. Their precise location and solvation depend on the nature and conformation of the ionophore, of the cation and of the counterion. Schematically, two types of solutes can be distinguished, depending on their hydrophilic/hydrophobic character. The first type (cryptand 222 and its complexes, or the [MP⋅K+] complex), which have a hydrophobic exterior, stay on the chloroform side of the interface and are partially hydrated by “water fingers”. The second type (free MP and TP, [MP⋅K+]Pic- and [MP⋅Sr2+](Pic-)2 complexes), which are more hydrophilic, are partitioned to a greater extent between the two liquid phases. The status of the ion pairs at the interface depends on the interplay between cation … anion and anion … solvent interactions. When cation-anion interactions are strong enough (as in [MP⋅Sr2+](Pic-)2), the ion pairs remain intimate. Otherwise they dissociate, leading to solvent-separated ion pairs adsorbed at the interface (in the [222⋅K+] Pic- complex) or to the migration of the anion to the water phase (in the [222⋅K+] Cl- complex).
    Zusätzliches Material: 5 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/chem.19970030410
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  • 7
    Digitale Medien
    Digitale Medien
    Synthesis of Glycodendrimers by Modification of Poly(propylene imine) DendrimersSynthetic carbohydrate dendrimers, part 3. For part 2, see: P. R. Ashton, S. E. Boyd, C. L. Brown, N. Jayaraman, J. F. Stoddart, Angew. Chem. Int. Ed. Engl. 1997, 36, issue 7. A list of abbreviations used in this paper is given in ref. [37]. (1997)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 3 (1997), S. 974-984 
    Details
    ISSN: 0947-6539
    Schlagwort(e): carbohydrates ; dendrimers ; glycosides ; neoglycoconjugates ; polymers ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The use of preformed poly-(propylene imine) dendrimers (DAB-dendr-(NH2)x) for the rapid and facile construction of high molecular weight carbohydrate-coated dendrimers (glyco-dendrimers) is presented. An efficient attachment of spacer-armed derivatives of D-galactose and lactose to the primary amino end groups of DAB-dendr-(NH2)x has been achieved by means of amide bond formation, using the N-hydroxysuccinimide coupling procedure. Acetate protecting groups have been employed in order to avoid side reactions at the coupling stage. Deacetylation leads to the target glycodendrimers. The reactivity of all the available DAB-dendr-(NH2)x (generations 1-5) has been investigated and a series of homologous carbohydrate-coated dendrimers have been synthesized. In addition, the attachment of larger saccharide moieties has been demonstrated by the condensation of a trisgalactoside cluster with DAB-dendr-(NH2)x carrying both four and eight primary amino groups. The regularity of the glycodendrimers has been proven by NMR spectroscopy, and the molecular weights of the low-generation carbohydrate-coated dendrimers have been determined by mass spectrometry. Modifications of DAB-dendr-(NH2)x with biologically active carbohydrates affords a new and simple approach to high molecular weight compounds that may be considered as neoglycoconjugates with perfectly symmetrical structures and that offer much promise as multivalent ligands involved in carbohydrate-protein interactions.
    Zusätzliches Material: 6 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/chem.19970030620
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  • 8
    Digitale Medien
    Digitale Medien
    Zinc(II)-Catalyzed Disproportionation in Rubber: The mechanism of Sulfur Vulcanization Revisited (1997)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 3 (1997), S. 1846-1851 
    Details
    ISSN: 0947-6539
    Schlagwort(e): disproportionations ; dithiocarba-mate ; homogeneous catalysis ; vulcanization ; zinc ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Model studies have shown that cross-link precursors, that is, intermediates in the sulfur vulcanization of rubber, are transformed into cross-links by a nonsymmetric but regioselective disproportionation mechanism. Thus, two equivalents of the crosslink precursor of the type R—S—S—X are transformed into X—S—X and the actual cross-link R—S—S—S—R. Exchange of sulfur atoms is a prerequisite. A mechanism involving an SNi′ reaction with an allylic moiety, suggested in the literature, has not been observed. The disproportionation reaction is catalyzed by rubber-soluble zinc-dithiocarbamate complexes, an important class of vulcanization accelerators. By virtue of ligand-functional-group exchange reactions these complexes serve to transport and exchange sulfur atoms.
    Zusätzliches Material: 3 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/chem.19970031117
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  • 9
    Digitale Medien
    Digitale Medien
    From Dendrimers to Knedel-like StructuresKnedel is a polish word to describe a food of meat surrounded by a dough layer. (1997)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 3 (1997), S. 1397-1399 
    Details
    ISSN: 0947-6539
    Schlagwort(e): dendrimers ; polymers ; micelles ; nanospheres ; supramolecular chemistry ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Shell-crosslinked knedels are nanometer-sized (5-200 nm diameters), amphiphilic core-shell spheres that are prepared by the self-assembly of amphiphilic block copolymers into polymer micelles, followed by crosslinking of side chain functionalities along the block composing the shell of the polymer micelles. Such structures resemble dendrimers in the basic structural components, and have the advantages of a rapid synthetic approach and the production of larger and broader size ranges.
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/chem.19970030904
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  • 10
    Digitale Medien
    Digitale Medien
    A Novel Synthetic Route to Tantalum-Zinc Neophylidyne Complexes Stabilized by ortho-Chelating Arylamine Ligands; the X-Ray structure of [TaCl2(μ-C6H4CH2NMe2-2)(μ-CCMe2Ph)ZnCl(THF)] (1997)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 3 (1997), S. 817-822 
    Details
    ISSN: 0947-6539
    Schlagwort(e): bridging ligands ; intramolecular coordination ; organometallic complexes ; tantalum ; zinc ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: A dimeric tantalum-zinc neophylidyne complex proposed to be [{{TaCl2(μ-CCMe2Ph)(μ-Cl)(THF)2}{Zn(μ-Cl)}}2](5a), which can be prepared easily on a scale of 50 mmol, is an ideal starting material for the synthesis of mono- and bis(ortho)-chelated arylamine alkylidyne species such as the red Ta-Zn neophylidyne complexes [TaCl2(μ-C6H4CH2NMe2-2)(μ-CCMe2Ph)ZnCl(THF)] (6) and [TaCl2-{μ-C6H3(CH2NMe2)2-2,6}(μ-CCMe2Ph)ZnCl] (7), which have been isolated in high yields. Reaction of 7 with tmeda affords the Tav alkylidene complex [TaCl(=CHCMe2Ph){C6H3(CH2N(Me)CH2)-2-CH2NMe2)-6}] (8), which shows catalytic activity in the ring-opening metathesis polymerization of norbornene.
    Zusätzliches Material: 3 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/chem.19970030522
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