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  • General Chemistry  (1,656)
  • 1995-1999  (1,656)
  • 1995  (1,656)
  • 1
    Electronic Resource
    Electronic Resource
    Characterisation of the Intermediate C2H4…Cl2 in a Gaseous Mixture of Ethene and Chlorine by Rotational Spectroscopy: A Weak π-Type Complex (1995)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 1 (1995), S. 17-25 
    Details
    ISSN: 0947-6539
    Keywords: chlorine complexes ; ethene complexes ; intermediates ; rotational spectroscopy ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A complex of ethene and Cl2 has been characterised in the gas phase. Rotational spectra of the isotopomers C2H4…35Cl2, C2H4…35Cl37Cl and C2H4…37Cl35Cl were recorded by using a fast-mixing nozzle in an FT microwave spectrometer. Rotational constants, centrifugal distortion constants and Cl nuclear quadrupole coupling constants. χgg (Cl) are reported in each case. The complex is of the π-donor-acceptor type and has a C2v geometry in which Cl2 lies along the C2 axis perpendicular to the plane of the C2H4 nuclei. The binding is weak, and only small changes in the χgg (Cl) attend complex formation. A simple model attributes these changes to a transfer of around 0.02e from the inner to the outer Cl nucleus, thus confirming that the complex is of the Mulliken outer type. Similarities in the properties of C2H4… Cl2 and C2H4… HCl indicate that the angular geometry is in both cases determined mainly by the electrostatic part of the interaction. The distance from the π-bond midpoint to Cl decreases from C2H4… HCl to C2H4… Cl2; this suggests that Cl2 is “snub-nosed”.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19950010107
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  • 2
    Electronic Resource
    Electronic Resource
    5,10,15,20-Tetraphenylsapphyrin-Identification of a Pentapyrrolic Expanded Porphyrin in the Rothemund Synthesis (1995)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 1 (1995), S. 68-73 
    Details
    ISSN: 0947-6539
    Keywords: porphyrinoids ; Rothemund synthesis ; sapphyrin ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The Rothemund-type condensation of pyrrole and benzaldehyde yields, apart from 5,10,15,20-tetraphenylporphyrin (TPPH2) and inverted tetraphenylporphyrin 2-aza-21-carba-5,10,15,20-tetraphenylporphyrin (CTPPH2), a unique pentapyrrolic macrocyclic molecule with the aromatic nucleus of sapphyrin, namely, 5,10,15,20-tetraphenylsapphyrin (TPSH3). Its unorthodox structural skeleton with an inverted pyrrole ring lying opposite to the bipyrrole unit accounts for the spectroscopic properties of the novel sapphyrin. The diprotonation of TPSH3 acts as a trigger for a structural transformation involving a flip of the pyrrole units, which relocates the 27-NH pyrrolic nitrogen from the periphery into the center of the macrocycle. The formation of 5,10,15,20-tetraphenylsapphyrin proves that the pentapyrrolic product is accessible by the mechanism of the Rothemund synthesis.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19950010111
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  • 3
    Electronic Resource
    Electronic Resource
    A Tale of Two Complexes, [PtMen(RN=CH—CH=NR)] (n = 2 and n = 4, R = Cyclohexyl): Why do PtII and PtIV Complexes Exhibit Virtually Identical Redox Behavior and Colors? (1995)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 1 (1995), S. 95-99 
    Details
    ISSN: 0947-6539
    Keywords: charge transfer ; EPR spectroscopy ; organometallic compounds ; platinum compounds ; spectroelectrochemistry ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In spite of their very similar cyclic voltammograms, absorption spectra, and solvatochromic behavior, the two 1,4-diazabutadiene title complexes exhibit markedly different photoreactivities and underlying electronic structures, as evident from absorption and EPR spectra of the persistent anion radical forms. The lowest excited state of the nonphotoreactive PtII system [(CyN=CH—CH=NCy)-PtMe2] has MLCT (metal-to-ligand charge-transfer, 5d → π*) character, and the EPR spectrum of the corresponding anion radical at 〈g〉 = 2.016 exhibits sizable metal/ligand orbital mixing. On the other hand, the structurally characterized PtIV complex [(CyN=CH—CH=NCy)-PtMe4] (C2/c; a = 2021.6(2), b = 805.3(1), c = 1254.2(1) pm; β = 111.05(1)°; V = 1905.7(4) × 106 pm3; Z = 4) has a lowlying photoreactive LLCT (ligand-to-ligand charge-transfer, σPt—C → π*) excited state in which the axial Pt—C bonds are activated, as already suggested by the longer Pt—C(ax) bonds (214.0(8) pm) relative to Pt—C(eq) in the ground state (204.5(5) pm). The anion radical of the PtIV complex has lost the long-wavelength absorption band in the visible; it shows a well-resolved EPR spectrum at 〈g〉 = 1.9945 with π-ligand and 195Pt hyperfine structure and a small g anisotropy. A qualitative MO scheme is presented to account for the similar frontier-orbital energy differences despite dissimilar underlying electronic structures.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19950010114
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  • 4
    Electronic Resource
    Electronic Resource
    Linear and Cyclic Platinum σ-Acetylide Complexes of Tetraethynylethene (1995)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 1 (1995), S. 111-117 
    Details
    ISSN: 0947-6539
    Keywords: alkyne complexes ; carbon networks ; macrocycles ; platinum compounds ; tetraethynylethene ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The syntheses of the first organometallic mono- and dinuclear platinum complexes bearing the tetraethynylethene unit as an η1-ligand are reported. Structural characterization of two of the trans σ-bis(acetylide) derivatives by X-ray crystallography reveals coplanarity of the acetylenic π-ligands and indicates possible electronic delocalization across the metal center. This notion is further supported by comparing the electronic absorption spectra of the platinum-containing compounds with those of related tetraethynylethene derivatives without metals. The solidstate structure of a dinuclear complex with two iodoplatinum fragments attached to one set of geminal acetylenes of tetraethynylethene was also investigated by X-ray diffraction. Hay coupling of a mononuclear species leads to the incorporation of the σ-bis(acetylide) moiety into a diplatinated metallacycle. This macrocyclic compound represents a novel structural motif in the design of a transition metal linked carbon network based on tetraethynylethene.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19950010204
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  • 5
    Electronic Resource
    Electronic Resource
    Asymmetric Control of 1,3-Dipolar Cycloaddition Reactions with Azomethine Ylides by Means of Proline Esters as Chiral Auxiliary Groups (1995)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 1 (1995), S. 150-154 
    Details
    ISSN: 0947-6539
    Keywords: asymmetric syntheses ; azomethine ylides ; chiral auxiliaries ; cycloadditions ; pyrrolidines ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Upon treatment with triethylamine or DBU in the presence of LiBr, aromatic and aliphatic imines of amino acid esters are converted to N-metalated azomethine ylides. These 1,3-dipoles undergo highly stereoselective cycloadditions with N-acryloyl-(S)-proline esters in THF at -78 to -40°C to afford highly substituted pyrrolidines with complete regiocontrol and good to excellent diastereomeric ratios. The chiral auxiliary groups can readily be removed from the cycloadducts by simple acid hydrolysis. To rationalize the observed stereoselectivity a transition-state model is proposed in which the lithium cation is coordinated to both the 1,3-dipole and the dipolarophile.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19950010209
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  • 6
    Electronic Resource
    Electronic Resource
    Synthesis of a Methyl Heptaglucoside with Phytoalexin Elicitor Activity Based on Oxidative Coupling of Glucals (1995)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 1 (1995), S. 161-164 
    Details
    ISSN: 0947-6539
    Keywords: block synthesis ; epoxidations ; glycosylations ; oligosaccharides ; selenoglycosides ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Several suitable building blocks for the construction of the phytoalexin elicitor α-methyl-32, 34-di-β-D-glucopyranosylgentiopentaoside (2) were readily accessible by oxidative coupling of glucals. Block coupling of trimeric phenylseleno- and ethylthioglucosyl donors 17 and 18 with tetrasaccharide 16 in the presence of the thiophilic promoter N-iodosuccinimide and catalytic trifluoromethanesulfonic acid furnished the desired heptaglucan 2 in high overall yield.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19950010304
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  • 7
    Electronic Resource
    Electronic Resource
    Cover Page (1995)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 1 (1995), S. cpi 
    Details
    ISSN: 0947-6539
    Keywords: Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19950010401
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  • 8
    Electronic Resource
    Electronic Resource
    Graphical Abstract (1995)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 1 (1995), S. i 
    Details
    ISSN: 0947-6539
    Keywords: Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19950010403
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  • 9
    Electronic Resource
    Electronic Resource
    Asymmetric syn-Selective Michael Addition of Enolates to Chiral 8-Phenylmenthyloxy Vinyl Chromium Carbene Complexes (1995)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 1 (1995), S. 236-242 
    Details
    ISSN: 0947-6539
    Keywords: asymmetric syntheses ; enol ethers ; Fischer carbenes ; Michael additions ; syn diastereoselectivity ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Michael addition reactions of ketone and ester lithium enolates to optically active Fischer vinylcarbene complexes derived from (-)-8-phenylmenthol take place with high syn selectivity and high levels of asymmetric induction. The initial Michael adducts can be further elaborated through diastereoselective addition of organometallic reagents to ketones and aldol reactions. Removal of the metal fragment and chiral auxiliary group leads to cyclic enol ethers with three or five contiguous stereogenic centers and of high enantiomeric purity.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19950010407
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  • 10
    Electronic Resource
    Electronic Resource
    Synthesis of a Fullerene[60] Cryptate and Systematic Langmuir-Blodgett and Thin-Film Investigations of Amphiphilic Fullerene Derivatives (1995)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 1 (1995), S. 243-251 
    Details
    ISSN: 0947-6539
    Keywords: amphiphiles ; C-glycosides ; cryptates ; fullerenes ; ionophores ; Langmuir-Blodgett films ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The synthesis of the first fullerene cryptate 7 with a sodium ion bound to a benzo[2.2.2]cryptand covalently attached to a methanofullerene[60] is described. The amphiphilic properties of 7 as well as of a variety of other covalent fullerene derivatives with polar functional groups and the ability of these compounds to form Langmuir monolayers at the air-water interface were investigated in a systematic study. Among these derivatives are Diels-Alder adducts of C60 and methanofullerenes, four of which are fullerene C-glycosides. The films at the water surface were characterized by their surface pressure versus molecular area isotherms, compression and expansion cycles, and optical light microscopy. UV/Vis spectroscopy and small-angle X-ray diffraction (SAXS) were employed for LB film characterization on solid substrates. Parameters influencing the spreading and monolayer character include (a) polarity, (b) balance of hydrophobicity to hydrophilicity, (c) size and bulkiness of the polar groups attached to the fullerene, and (d) presence of aromatic residues in these groups.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19950010408
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