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  • 1
    ISSN: 1434-193X
    Keywords: Fullerenes ; Cycloadditions ; Donor-acceptor systems ; Cyclic voltammetry ; Photoinduced electron transfer ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---The new C60 and C70 adducts 1b, 1d-1k, 1m, 6d, 7d, and 8d have been synthesized by [2+3] cycloadditions of the appropriate nitrile oxides. Variations in the distance and geometry of the donor and acceptor substituents are seen to have an influence on the redox behavior of the fullerene adducts in cyclic voltammetry experiments. The isoxazolo-fullerenes 1c, 1d, and 1i show shifts of about 30 mV or 40 mV to more negative values compared with the reference compound 1a. On the other hand, strong acceptor properties are detected in the case of compound 1e, which shows a positive shift of 30 mV relative to 1a. Moreover, time-resolved fluorescence spectroscopy has shown that upon excitation of the fullerene moiety in the polar solvent benzonitrile, an electron is transferred from the donor substituent to the first excited singlet state of the fullerene, thereby reducing the excited-state lifetime. Our data demonstrate that the electron-transfer rate in donor-substituted fullerenes can be controlled by the electron-donating property of the substituent as well as the electronic structure and/or length of the spacer used. The C70 regioisomers 6d, 7d, and 8d exhibit differences in their spectroscopic characteristics.
    Additional Material: 3 Ill.
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  • 2
    ISSN: 1434-193X
    Keywords: Asymmetric synthesis ; Phosphazene base ; Pyridyl epoxide ; Furyl epoxide ; Pyridyl alcohol ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---trans-1-(2-Pyridyl)-, trans-1-(3-pyridyl)-, trans-1(2-furyl)-, and trans-1(3-furyl)-2-phenyl epoxides with enantiomeric purities ranging from 96.8 to 99.8% [in favor of the (+, EtOH)-isomer] are obtained in two steps from pure (R,R,R)-oxathiane which is recovered (85-90%) and reused. The chiral bidentate ligand 2-phenyl-(S)-1-(2-pyridyl)ethanol with 99.6% ee was obtained in three steps and 67% overall isolated yield.
    Additional Material: 1 Ill.
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  • 3
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 2000 (2000), S. 13-16 
    ISSN: 1434-1948
    Keywords: Pyrazole ; Titanium ; Redox reaction ; Mercury ; Amalgams ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The reduction of [L2TiCl2] (1) (L = 3,5-tert-butylpyrazolate) with 1% Na/Hg in tetrahydrofuran (THF) affords the complex [L2TiCl(THF)2] (2), which crystallizes from hexane in moderate yield. The analogous reduction carried out in toluene gives dimeric [(L2TiCl)2] (3) in high yield. If the reduction time is extended to 3 days, the complex [L3Ti] (4) is isolated as light blue crystals in low yield. An alternative procedure for preparing compound 4 requires mixing [TiCl3(THF)3] with 3 equivalents of potassium 3,5-tert-butylpyrazolate in toluene. Crystallization from hexane affords 4 in high yield. Crystallographic data for 2, 3 and 4 are presented.
    Additional Material: 3 Ill.
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  • 4
    ISSN: 1434-1948
    Keywords: Thiolato-bridged complexes ; Iron ; Ruthenium ; Mixed-valent compounds ; Mössbauer spectroscopy ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The reaction of [FeIIIL] with [RuIICl2(dmso)4] in methanol under argon, affords, upon addition of NaPF6, brown crystals of [LFeRuFeL](PF6)2· 3 CH3OH (1). Its one-electron oxidation product [LFeRuFeL](PF6)3 (2) [L = 1,4,7-(4-tert-butyl-2-mercaptobenzyl)-1,4,7-triazacyclononane] was generated by using one equivalent of [NO]BF4. The crystal structure determination of [LFeRuFeL](BPh4)2· CH3CN · 3 (CH3)2CO shows that 1 contains a trinuclear, face-sharing thiolato-bridged dication. Mössbauer spectroscopy established that the oxidation state distribution of 1 can best be described by Fe2.5RuIIIFe2.5 and 2 by FeIIIRuIIIFeIII. Complex 1 possesses a diamagnetic (St = 0) and 2 an St = 1/2 ground state. The electronic structures of 1 and 2 are rationalized by an MO picture involving Fe-Ru metal-metal bonds of bond order 0.5 in both species. Complex 1 is formally a mixed valence compound with complete delocalization of the “excess electron” (class III).
    Additional Material: 9 Ill.
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  • 5
    ISSN: 1434-1948
    Keywords: (R)-(+)-2,3-Epoxy-1-propanol ; 2,3-Dihydroxyalkyl phosphanes ; 1,3,2-Dioxaborolane ; 1,3-Dioxolane ring ; Enantiopure phosphanes ; Complexes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Reaction of (R)-(+)-2,3-epoxy-1-propanol with Ph2PH, Ph(Me)PH, or PhPH2 in the superbasic medium KOH/DMSO affords the novel chiral phosphanes 1a-1c. While 1a is obtained enantiomerically pure, 1b and the secondary phosphane 1c are formed as mixtures of diastereoisomers (RPRC, SPRC) with homochiral β carbon atoms. Derivatization of 1a with phenylboronic acid or 2,2-dimethoxypropane yields 2a and 3a with 1,3,2-dioxaborolane and 1,3-dioxolane ring systems, respectively. The X-ray structure of 2a (space group P21) reveals the presence of four molecules of R configuration in the unit cell. Nucleophilic phosphanylation of (R)-(-)-2,3-O-isopropylideneglycerol tosylate with Ph2PH, Ph(Me)PH, or PhPH2 yields chiral 3a-3d. Compound 3b was obtained enantiomerically pure. The secondary phosphane 3c has been employed in syntheses of the hydrophilic tertiary phosphanes 3e, 3f and of the novel bidentate phosphane ligands 3g, 3h, all of which have homochiral β carbon atoms. PdII complexes PdL2Cl2 of 1a, 2a, 3a (L) are formed as mixtures of cis/trans isomers. RhI complexes of 1a, 3a, and bidentate 3h have also been synthesized.
    Additional Material: 1 Ill.
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  • 6
    ISSN: 1434-193X
    Keywords: Hydroxyalkenoic acids ; Hydrogen bonds ; Crystal engineering ; Molecular assemblies ; Scanning force microscopy ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---The substituted 6-hydroxy-trans-3-hexenoic acids 2-4 have been prepared by a template coupling reaction between (butadiene)zirconocene, W(CO)6, and cyclobutanone, cyclodecanone, or cyclododecanone, respectively, followed by hydrolytic/oxidative demetallation of the resulting metallacyclic zirconoxycarbene tungsten complexes. The hydroxyalkenoic acids 2-4 have been found to form two novel fundamental types of associated supramolecular structural arrays in the solid state through intermolecular hydrogen bonding, which have been characterized by X-ray diffraction analysis. The cyclobutanone-derived compound 2 exhibits an infinitely extending sheet-like structure, which is composed of symmetrically alternating interconnected 12- and 36-membered rings, each being constructed from the functional groups or frameworks of four individual molecules of 2. In contrast, the cyclodecanone-derived compound 3 adopts a ribbon-type structure composed of C2-symmetrically arranged symmetry-equivalent 15-membered rings, each containing the functionalities from three individual molecules of 2. On the basis of scanning force microscopy studies, the cyclododecanone-derived compound 4 would appear to have a similar structure in the solid state. The structural features of the molecular assemblies that are formed by intermolecular hydrogen bonding of compounds 2-4 in the solid state are selectively controlled by the size and favoured conformations of the spiro-anellated carbocyclic rings at C6 of the 6-hydroxy-trans-3-hexenoic acid carbon chain.
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  • 7
    ISSN: 1434-193X
    Keywords: Tetrakis(dimethylamino)naphthalenes ; Basicity ; Hydrogen bonds ; Cyclicvoltammetry ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---For comparison to the recently described 2,3,6,7-tetrakis(dimethylamino)naphthalene (1) the three isomers 2,3, and 4 were synthesized. The basicities of this group of isomers are strongly dependent upon the different mutual orientations of the pairs of dimethylamino substituents: only the isomers 3 and, partially, 4, both with dimethylamino groups in adjacent peri-positions of the naphthalene, are strong “proton sponges”. For the isomers 1 and 2 with the same number and kind of twofold dimethylamino substituents in neighbouring ortho-positions, however, no significant basicity increase is observed. To explain this difference between the two groups of isomers it is suggested that in the ortho-pairs of 1 and 2 the C-N bonds diverge considerably, leading to an increased N···N distance and consequently to less stable [N···H···N]+ hydrogen bonds in contrast to the parallel C-N bonds in the peri-substituted isomers 3 and 4. X-ray crystal structure analyses of the bases and of some of the salts derived therefrom were solved and are discussed. Cyclic voltammetry indicates that 1 to 4 are strong electron donors, reacting easily to radical cations or dications which with suitable acids have been obtained as salts.
    Additional Material: 3 Ill.
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  • 8
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 1647-1651 
    ISSN: 1434-193X
    Keywords: Fullerenes ; Anthracene ; Photooxidations ; Photochemistry ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---Anthracene groups have been linked to [60]fullerene by the [3+2] cycloaddition of the corresponding nitrile oxides or by esterification with a [60]fullerenol. The anthryl groups of the fullerene derivatives 3, 7, and 10 react readily with singlet oxygen to form the 9,10-epidioxides 4, 8, and 12 under photooxidation. The anthryl moiety of the fullerenol ester 10 also reacts with the fullerene skeleton to form the stable intramolecular Diels-Alder adduct 11.
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  • 9
    ISSN: 1434-193X
    Keywords: Amide linkage ; Phosphodiester ; Hammerhead ribozyme ; Oligonucleotides ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---A nucleoside dimer in which the natural phosphodiester bond is replaced by an isosteric amide linkage has been prepared. This dimer analogue was subsequently incorporated chemically at the cleavage position of a hammerhead ribozyme substrate. Although the resulting substrate analogue exhibited a high affinity for the ribozyme as shown by gel retardation assays, the amide bond proved to be fully resistant to cleavage under standard conditions of ribozyme cleavage activity.
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  • 10
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 2000 (2000), S. 323-330 
    ISSN: 1434-1948
    Keywords: Amino acids ; Alkynes ; Ferrocene ; Palladium ; Catalysis ; Bioorganometallic chemistry ; Biosensors ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: This work describes a Pd-catalyzed coupling of ferrocene alkyne derivatives to iodo amino acids. Ferrocene carboxylic acid propargyl amides were easily obtained in high yield. The crystal structures of the propargyl amine derivative 3 and the 1,1-diethylpropargylamine derivative 4 have been determined by X-ray diffraction. Pd-catalyzed coupling to p-iodoanilide amino acids gave the corresponding ferrocene-labeled amino acid derivatives, which were easily purified by diethyl ether extraction in the case of the 1,1-diethyl derivatives 8. The coupling reaction did not require anhydrous solvents and tolerated a variety of functional groups present in peptides such as alcohols (8a, Ser), thioethers (8d, Met), disulfide bonds (cystine, 12) esters (as in the N-labeled Leu derivative 10) and of course amides. A minor by-product of the coupling reaction, namely the homo-dimer bis(ferrocene carboxylic acid propargylamide) 9, was identified in the crude reaction mixtures by mass spectrometry and independently synthesized by oxidative coupling (Glaser and Eglington) of 3. All new compounds were completely characterized spectroscopically, including 15N- and 2D NMR spectroscopy, Mössbauer spectroscopy and electrochemistry. This work introduces a versatile procedure for a selective functionalization of amino acids with organometallics at the C-terminus which is expected to be of general applicability to peptide chemistry.
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