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  • 1
    ISSN: 1434-1948
    Keywords: Diene complexes ; η3-Cyclooctatetraene metal complex ; B(C6F5)3 addition ; Tantalum ; Bicyclo[5.1.0]octadienyl metal complex ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The [(η4-diene)(η5-RCp)TaCl2] complexes 6a-e (diene = butadiene, isoprene or 2,3-dimethylbutadiene; RCp = pentamethylcyclopentadienyl, methylcyclopentadienyl or cyclopentadienyl) react with cyclooctatetraene dianion (employed as [(cot)Li2]) to yield the (η4-diene)(η3-cyclooctatetraene)(η5-RCp)tantalum complexes 7. The η3-cot coordination was confirmed by an X-ray crystal structure analysis of the compound [(supine-s-cis-η4-C4H6)(η3-cot)(η5-Cp*)Ta] 7a. In solution, the cot ligand of all the complexes 7 is fluxional. Two isomers [supine and proneorientation of the (diene)CpTa subunit] were found for the (η4-butadiene)(η3-cot)CpTa system (7e/7e′ = 95:5). Complex 7e cleanly adds the organometallic Lewis acid B(C6F5)3 to yield the betaine system [(η4-C4H6){C8H8B(C6F5)3}Cp*Ta] 8, which contains a substituted bicyclo[5.1.0]octadienyl ligand.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 76 (1993), S. 1216-1218 
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The INADEQUATE experiment for spin-1 nuclei has been extended to deuteron spin systems of the AX, AA′ XX′, and AA′MM′X type. Measurements with (3,3-D2)norcampher, 4-chloro(2,3,5,6-D4)pyridine, and (D5)pyridine revealed correlation peaks due to two-spin double quantum coherences and additional one-spin double quantum peaks with coordinates F1 = 2 ωi, F2 =(ωii = A, X) which were not observed in the 6Li, 6Li,-INADEQUATE experiment described earlier.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
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  • 3
    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.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1434-193X
    Keywords: Indolizino[3,4-b]quinoline ; Receptors ; Molecular tweezers ; Tentacle molecules ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A convenient diastereoselective synthetic route to the molecular tweezer bis(indolizino[3,4-b]quinolyl)methane 9 and the rigid indolizino[7′,8′:2,3]quinolino[8,7-h]indolizino[8,7-b]quinolines 14, 15 as potential receptor molecules has been developed, involving double imine condensation followed by Lewis acid catalyzed biscyclization of prolinal-derived bis(imines) 8 and 13, respectively. Whereas the use of SnCl4 leads to the formation of the planar polycycle 15, the corresponding concave product 14 is formed in the presence of EtAlCl2. Both compounds 14, 15, as well as tweezer 9 have been characterized by X-ray crystal-structure analysis. Although tris(imines) 20, 24 derived from 1,3,5-triaminobenzene (18) and tris(4-aminophenyl)amine (23) could be obtained similarly by molecular sieve-catalyzed condensation, the corresponding triscyclization could not be achieved. However, by attaching preformed indolizino[3,4-b]quinoline subunits 25 and 31 to an aromatic core, the bidentate receptors 30, 33 and the tentacle molecule 28 were accessible.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 31 (1993), S. 509-511 
    ISSN: 0749-1581
    Keywords: NMR ; 2H NMR ; 1D-TOCSY ; 2H-TOCSY ; Magnetization transfer Selective excitation ; Pyridine-d5 ; Deuteriated cyclohexanes ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The 1D-TOCSY experiment for 2H NMR is introduced and applications for signal assignments are illustrated with the spectra of pyridine-d5 and iodo- and chlorocyclohexane-d11. The potential of the method for the analysis of overlapping 2H spectra is demonstrated.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
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