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  • Inorganic Chemistry  (25)
  • Organic Chemistry  (5)
  • Computational Chemistry and Molecular Modeling
  • 1985-1989  (29)
  • 1930-1934  (2)
  • 1989  (12)
  • 1987  (17)
  • 1932  (1)
  • 1931  (1)
Collection
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  • 1985-1989  (29)
  • 1930-1934  (2)
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  • 1
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The solubility of open-chain peptide derivatives (12 examples) in non-polar, ether-type organic solvents may be greatly increased by addition of salts (LiCl, LiBr, LiI, LiBF4, LiClO4, NaI, MgBr2 CaBr2, ZnCl2) or of titanates (Ti(OEt)4, Ti(OCHMe2)4). Examples are reported (Tables 2-6) in which this solubilizing effect leads to peptide concentrations more than one-hundred-fold those in the absence of salt (cf, Boc—Ala—Gly—Gly—Gly—OH in THF from 2g·1-1 to ≥ 300 g·1-1 with 6 equiv. of LiCl), 1H-NMR Spectra of one of these solutions are reported (Fig. 1). There are no indications for epimerizations of stereogenic centres on the peptide backbone. Possible applications of these solutions in peptide chemistry are discussed.
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  • 2
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Chiral Alkoxytitanium(iv) Complexes for Enantioselective Nucleophilic Additions to Aldehydes and as Lewis Acids in Diels-Alder ReactionsA Number of chiral 1,2-1,3 and 1,4-diols were prepared and used as alkoxy ligands on Ti for enantioselective nucleophilic transfer of methyl, butyl, cyclopropyl, allyl, alkinyl, and phenyl groups to aromatic aldehydes, as well as for the enantioselective[4+2]cycloaddition of acrylate to cyclopentadiene. The 1,2-diols were pinane diol 7 and 1,2:5.6-diacetonide-protected mannitol 9 (Scheme 3) and tartrates. The 1,3-diols were obtained from the yeast-reduction products of 2-oxocyclopentane- and 2-oxocyclohexanecarboxylates and excess MeLi, BuLi, or PhLi (or the corresponding Grignard reagents; see4-6.) As 1,4-diols, we used the products 2 and 3 from tartrate acetals and methyl or Pheny1 Grignard reagents, the bis(benzaldehyde) acetal 8 of d-mannitol and o,o'-binaphthol (22). These diols were attached to the Ti-atom by azeotropic removal of i-PrOH from a mixture with [TiCi(i-PrO)3]. Addition of various organometallic reagents R-metal (metal = Li, BR3, MgX, MnC1, CuLiR) was followed by combination with aldehydes at - 75., a warm up period, quenching with aqueous KF solution, and workup (for results see Tables 1-6 and Formulae 17-20). The enantiomeric excess of the secondary alcohols obtained varies greatly, certain combinations of chiral ligands, nucleophilic groups, and aldehyde substrates give rise to values as high as 90% ee; see e.g. Table 4. The Ti-complexes of the general formula [Ti(R*O)2Ci2] or [Ti(R*O)2(i-PrO)CI] induced the Diels-Alder addition of methyl acrylate to cyclopentadience to take place at -30.. The best enantioselectivity (50% ee) was observed with the binaphthol derivative (Table 7). The structures of the complexes involved in these reactions are unknown. The substitution on C(2) of the dioxolanes 2 and 3 (derived from tartaric acid) has a pronounced effect on the selectivities of both reactions studied here (Tables 2, 3, and 7). This remote effect (1,6-distance between the stereogenic acetal-C-atom and the Ti-centers) must be caused by conformational changes in the vicinity of the reactive site, i.e. the Ti—C bond in the nucleophilic addition reactions and the Ti-acrylate-oxygen complexation in the Diels-Alder reaction.
    Additional Material: 7 Tab.
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  • 3
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: We present the application of several homo- and heteronuclear 1D- and 2D-NMR techniques to assign the 1H-NMR chemical shifts of the dominant conformation of didemnin B (2; three different conformations in (D6)DMSO solution in the ratio 8:1:1) and its conformational analysis, as well as the solution conformation of didemnin A (1). The conformations were refined by restrained molecular-dynamics calculations using the GROMOS program and by MOMO, a novel personal-computer-based interactive molecular-graphics and molecular-mechanics package, using experimental distances (via a H…H pseudo potential function) as restraints. The solution structures of 1 and 2 obtained by GROMOS and MOMO calculations were compared with each other and related to the recently solved crystal structure of 2. Focusing on the main conformer, the two kinds of the distance-restrained conformational calculations for 2 yielded a ‘solution structure’ close to the crystal structure. Almost all of the 40 restrained H…H distances coincided (within the estimated standard deviations) with those observed in the crystal structure. One more hydrogen bond was detected in solution involving the lactoyl OH group (disordered in the crystal structure) and the dimethyltyrosine (Me2Tyr5) carbonyl O-atom. The macrocyclic ring system in the modeled solution structure of 1 exhibited a topology close to those of the solution and crystal structures of 2. The main difference between 1 and 2 could be traced back to a significant change in the Ψ angle of the N-methyl-D-leucine (MeLeu7) residue. In 1, the N-methyl moiety of MeLeu7 points inward within the macrocyclic ring toward the 1st and Hip region. We also tested the suitability of structures obtained from NMR data as ‘search fragments’ in the ‘Patterson search approach’ of crystal-structure analysis. It proved possible to resolve the crystal structure of 2 a posteriori with the Patterson search program PATSEE, in this way.
    Additional Material: 10 Ill.
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  • 4
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Gloeosporone, the germination self-inhibitor from the fungus Colletotrichum gloeosporioides f.sp. jussiaea, is shown by spectroscopic data and X-ray analysis to have the constitution and relative configuration as shown in Formula 2 (either (1S,6R,12R)-1-hydroxy-6-pentyl-5,15-dioxabicyclo[10.2.1]pentadecan-4,13-dione or its enantiomer), rather than the previously assigned constitution 1.
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  • 5
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 32 (1987), S. 457-468 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: With this work, we begin our treatment of the transition metal electron affinities. A procedure, REDUCE, for reducing the number of parental couplings per configuration present in the first order wave function from as many as 100 to only a few is introduced. Progress toward a comprehensive relativistic-correlation theory is discussed. Several states in Sc- were examined but none were found to be bound. Two new bound states were obtained for Cu-: 3d9 4s 4p2 5D and 3d8 4s 4P3 7F0, with electron affinities 0.109 and 1.052 eV, respectively.
    Additional Material: 6 Tab.
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  • 6
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 120 (1987), S. 889-893 
    ISSN: 0009-2940
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: The nucleophilic substitution of chloride in dichlorocyclobutenedione by carbonylmetallates gives the μ-(3,4-dioxo-1-cyclobutene-1,2-diyl) complexes LnM(C4O2)MLn 1 [MLn=Re(CO)5, Mn(CO)5, W(CO)3(η5-C5H5)] and the μ-(2-chloro-3,4-dioxo-1-cyclobuten-1-yl) complexes LnM— [MLn = Mn(Co)5, W(CO)3(η5-C5H5), Mo(CO)3(η5-C5H5)], respectively. The structure of the dirhenium complex (OC)5Re(C4O2)Re(CO)5 (1a) was determined by X-ray diffraction. The Re-C bonds are slightly shortened with respect to single bonds, Re-C=2.18(1)/2.17(1)Å [monoclinic, P21, a=7.031(1), b=11.532(1), c=11.418(1)Å, β=105.54(1)°, V=891.95Å3, dcalc=2.727 g/cm3 for Z=2, Rw=0.031 for 252 refined parameters and 3539 observables with I ≥ 2.0σ(I)].
    Notes: Die nucleophile Substitution von Chlorid in Dichlorcyclobutendion durch Carbonylmetallate liefert die μ-(3,4-Dioxo-1-cyclobuten-1,2-diyl)-Komplexe LnM(C4O2)MLn 1 [MLn=Re(CO)5, Mn(CO)5, W(CO)3(η5-C5H5)] bzw. die μ-(2-Chlor-3,4-dioxo-1-cyclobuten-1-yl)-Komplexe LnM— [MLn = Mn(Co)5, W(CO)3(η5-C5H5), Mo(CO)3(η5-C5H5)]. Nach der Röntgenstrukturanalyse des Dirhenium-Komplexes (OC)5Re-(C4O2)Re(CO)5 (1a) sind die Re-C-Bindungen gegenüber Einfachbindungen leicht verkürzt, Re-C=2.18(1)/2.17(1)Å [monoklin, P21, a=7.031(1), b=11.532(1), c=11.418(1)Å, β=105.54(1)°, V=891.95Å3, dber=2.727 g/cm3, Z=2, Rw=0.031 für 252 verfeinerte Parameter und 3539 Observablen mit I ≥ 2.0σ(I)].
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  • 7
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 120 (1987), S. 895-900 
    ISSN: 0009-2940
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: (OC)5ReFBF3 reacts with ethyl thiocyanate, malononitrile, cyanamide, and dicyandiamide (L) to give the ionic complexes [(OC)5ReL]+BF-4 (1). Two or three Re(CO)-3 cations, respectively, can be added to tetracyanoethene and tetracyano-p-quinodimethane (TCNQ) to give 2, 3. With the anions of tricyanoethenolate, TCNQ-, tricyanomethanide and dicyanamide (L-) the neutral compounds (OC)5ReL (4-7) are formed. The IR spectra and the X-ray structure analyses of [(OC)5Re(NCNC(NH2)2]+BF -4 (1d), (OC)5ReNCC(CN)2 (6), and of (OC)5ReNCNCN (7) show that the ligands are coordinated in all cases via the nitrile N-atom to the metal.
    Notes: (OC)5ReFBF3 setzt mit Ethylthiocyanat, Malononitril, Cyanamid und Dicyandiamid (L) zu den ionogenen Verbindungen [(OC)5ReL]+BF-4 (1) um. An Tetracyanethen sowie an Tetracyan-p-chinodimethan lassen sich zwei bzw. drei Re(CO)-3-Kationen unter Bildung von 2 und 3 addieren. Mit den Anionen Tricyanethenolat, TCNQ-, Tricyanmethanid und Dicyanamid (L-) entstehen die Neutral-Komplexe (OC)5ReL (4-7). Die IR-Spektren sowie die Röntgenstrukturanalysen von [(OC)5Re(NCNC(NH2)2]+BF -4 (1d), (OC)5ReNCC(CN)2 (6) und (OC)5ReNCNCN (7) zeigen, daß die Liganden in allen Fällen über das Nitril-N-Atom an das Metall koordiniert sind.
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  • 8
    ISSN: 0009-2940
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 9
    ISSN: 0009-2940
    Keywords: Heterobimetallic complexes, alkyne-bridged ; Carbonyl complexes ; Molybdenum ; Tungsten ; Rhenium ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Hydrocarbon-Bridged Metal Complexes, XII.  -  Nucleophilic Addition of Carbonylmetallates to Cationic Alkyne Molybdenum Complexes: A Rational Way to Heterobimetallic Tetrahedranes MM′C2 (M = Mo, W; M′ = Re, Mn, Mo)The reactions of cationic alkyne complexes [Cp(L1)(L2)M(RC≡CR)]+ (L1 = CO, PR3, P(OMe)3; L2 = C2Me2, CO, P(OMe)3; M = Mo, W) with [Re(CO)5]- or [Mn(CO)5]- give heterobimetallic tetrahedranes Cp(OC)2M(μ2-η2:η2-RC≡CR)M′(CO)3L1 (M = Mo, W; M′ = Re, Mn) and Cp(OC)2Mo(μ2-η2:η2-MeC≡CMe)Re(CO)2[P(OMe)3]2. Similarly, the reaction of [Cp(OC)Mo(RC≡CR)2]+ or [Cp(Ph3P)(OC)Mo(RC≡CR)]+ with [CpW(CO)3]- provides a rational synthesis of Cp(OC)2Mo(μ2-η2:η2-RC≡CR)W(CO)2Cp. The dimetallatetrahedranes contain a semibridging CO group. The structures of Cp(OC)2Mo(μ2-η2:η2-H3CC≡CCH3)Re(CO)4 and Cp(OC)2Mo(μ2-η2:η2-H3CC≡CCH3)Re(CO)2[P(OMe)3]2 have been determined by X-ray crystallography.
    Notes: Die Umsetzung der kationischen Alkin-Komplexe [Cp-(L1)(L2)M(RC≡CR)]+ (L1 = CO, PR3, P(OMe)3; L2 = C2Me2, CO, P(OMe)3, M = Mo, W) mit [Re(CO)5]- oder [Mn(CO)5]- liefert die heterodimetallischen Tetrahedrane Cp(OC)2M(μ2-η2:η2-RC≡CR)M′(CO)3L1 (M = Mo, W;M′ = Re, Mn) und Cp(OC)2-(μ2-η2:η2-MeC≡CMe)Re(CO)2[P(OMe)3]2. Ebenso lassen sich in gezielter Weise aus [Cp(OC)Mo(RC≡CR)2]+ oder [Cp(Ph3P)-(OC)Mo(RC≡CR)]+ und [CpW(CO)3]- die Alkin-verbrückten Komplexe Cp(OC)2Mo(μ2-η2:η2-RC≡CR)W(CO)2Cp aufbauen. Die Dimetallatetrahedrane enthalten stets eine semiverbrückende CO-Gruppe. Die Strukturen von Cp(OC)2Mo(μ2-η2:η2-H3C-C≡CCH3)Re(CO)4 und Cp(OC)2Mo(μ2-η2:η2-H3CC≡CCH3)-Re(CO)2[P(OMe)3]2 wurden röntgenographisch bestimmt.
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  • 10
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 120 (1987), S. 253-254 
    ISSN: 0009-2940
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Addition of the 16-electron system Re(CO)+5 [as (OC)5ReFBF3] to acetylpentacarbonylchromate and -tungstate (as NMe+4[M(CO)5C(Me)O]-, M=Cr, W) leads to the acetyl-bridged complexes (OC)5M-C(Me)-O-Re(CO)5 (1a,b). This reaction is analogous to the classic synthesis of Fischer carbene complexes from acylcarbonylmetallates and oxonium salts and provides a further example for the isolobal concept. The chromium compound 1a has been characterized by single crystal X-ray diffraction analysis.
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