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  • General Chemistry  (14.926)
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  • 201
    Digitale Medien
    Digitale Medien
    Magnesiation of Triisopropylsilylphosphane: Synthesis and Structures of New Mg2nP2m Polyhedra (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 2215-2220 
    Details
    ISSN: 1434-1948
    Schlagwort(e): Magnesium ; Metalation ; Phosphorus ; Polyhedra ; X-ray structures ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The magnesiation of triisopropylsilylphosphane with dibutylmagnesium in toluene yields the octanuclear complex [Mg8(PSiiPr3)6{P(H)SiiPr3}4] (1) which consists of MgPSiiPr3 units forming a hexagonal Mg6P6 prism, with two opposite Mg2P2 moieties capped by additional Mg[P(H)SiiPr3]2 groups. If a small amount of THF is present during the metalation reaction [(THF)4Mg6(PSiiPr3)6] (2) also containing a hexagonal Mg6P6 prism can be isolated. The magnesiation of H2P-SiiPr3 in tetrahydrofuran leads to the formation of the tetrameric complex [(THF)MgPSiiPr3]4(3) with a slightly distorted Mg4P4 cubane-like structure.The structures depend strongly on the steric strain caused by the trialkylsilyl substituents and the neutral coligands at the magnesium center. The highest steric strain, which is induced by coordination to every magnesium atom, leads to the smallest MgnPn polyhedron - the central Mg4P4 heterocubane moiety. In compounds 1 and 2 the hexagonal Mg6P6 prism is formed, however, with reduced steric strain as observed for 2 where the Mg-P bond lengths become more similar.
    Zusätzliches Material: 4 Ill.
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  • 202
    Digitale Medien
    Digitale Medien
    Efficient Biomimetic-Type Synthesis of the Benzo[a]naphthacenequinone Antibiotics G-2A and G-2N (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 3099-3103 
    Details
    ISSN: 1434-193X
    Schlagwort(e): Antibiotics ; Biomimetic-type synthesis ; Polyketides ; Quinones ; Aldol reaction ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Trioxo ester 15 was prepared by attachment of two vicinal C-4 and C-6 ketide side chains on the anthraquinone core (6b). Mild base treatment of 15 initiated successive aldol condensations to produce the benzo[a]naphthacenequinone 16 regioselectively in one operation. Deprotection of 16 afforded the antibiotic G-2A (1) and decarboxylation of 1 lead to G-2N (2).
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  • 203
    Digitale Medien
    Digitale Medien
    Convenient Syntheses of Novel α- and β-Amino Acids with Spiropentyl Groups (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 3105-3115 
    Details
    ISSN: 1434-193X
    Schlagwort(e): Amino acids ; Spiro compounds ; Michael addition ; Copper reagents ; Curtius degradation ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Racemic spiropentylglycine (8) has been synthesized by sodium borohydride reduction of benzyl (E/Z)-2-chloro-2-spiropentylideneacetate (5-Bn), nucleophilic substitution of the chlorine in the product 6 with azide and hydrogenolytic deprotection of the resulting 7 (overall yield 15%). An alternative approach to 8 consisted of the coupling of the higher-order cuprate 10, generated by halogen-metal exchange from bromospiropentane (9), with the electrophilic glycine equivalent 11 followed by deprotection (overall yield 47%). Enantiomerically pure (1′-aminospiropentyl)acetic acid [(R)-16] (overall yield 16% from 5-Me) and 1-aminospiropentanecarboxylic acid [(R)-23] (29% from 5-Me) were obtained from the Michael adduct 14-Me of (4R,5S)-4,5-diphenyloxazolidin-2-one (13) and methyl (E/Z)-2-chloro-2-spiropentylideneacetate (5-Me). Racemic 1-aminospiropentanecarboxylic acid (R/S-23) was prepared by rhodium-catalyzed addition of dimethyl diazomalonate to methylenecyclopropane and subsequent Curtius degradation of the halfester 28 via the azide 29 (overall yield 14%). Upon standing in aqueous solution, 23 underwent complete rearrangement to the new 1-amino-2-methylenecyclobutanecarboxylic acid (24). The interesting derivative of azabicyclo[3.1.0]hexane-1-carboxylate 34 with an annelated spiropentane moiety and a β-amino acid fragment was incidentally obtained in a one-step intermolecular domino reaction starting with the addition of lithium benzylamide to methyl 2-chloro-2-cyclopropylideneacetate (32, 41% yield).
    Zusätzliches Material: 2 Ill.
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  • 204
    Digitale Medien
    Digitale Medien
    Mild Synthesis of Protected α-D-Glycosyl Iodides (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 3147-3150 
    Details
    ISSN: 1434-193X
    Schlagwort(e): Glycosyl iodides ; Triphenylphosphane-iodine complex ; Carbohydrates ; Glycosides ; Polymer bound reagents ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: α-D-Glycosyl iodides are stereoselectively obtained by iodine replacement of the free anomeric hydroxyl group of fully protected sugars treated with a polymer bound triarylphosphane-iodine complex and imidazole. High yields and mild conditions, compatible with all the common protecting groups used in carbohydrate chemistry, characterize the conversion.
    Zusätzliches Material: 1 Tab.
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  • 205
    Digitale Medien
    Digitale Medien
    An Efficient Synthetic Approach to Substituted Penta- and Hexahelicenes (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 3155-3163 
    Details
    ISSN: 1434-193X
    Schlagwort(e): Arenes ; Helical structures ; Cycloadditions ; NMR spectroscopy ; Semiempirical calculations ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: A two-step synthetic approach to penta- and hexahelicenes substituted at the terminal aromatic rings has been studied. This approach is based on the Diels-Alder reaction of 5,5′,8,8′-tetramethyl-3,3′,4,4′-tetrahydro-[1,1′]-binaphthalene (2b), 3-vinyl-1,2-dihydronaphthalene (5a), 5,8-dimethyl-3-vinyl-1,2-dihydronaphthalene (5b) and 3-vinyl-1,2-dihydrophenanthrene (15) followed by the aromatization of the cycloadducts. This method is flexible, efficient and of wide application to the synthesis of several benzenoid and nonbenzenoid penta- and hexahelicenes. The racemization energy barriers of helicenes 3, 9, 10, 13, 14, 17 and 18 were computed with the semiempirical quantum method AM1. The computed values show that, when methyl groups are introduced at the inner position of the terminal aromatic rings, the racemization barriers increase markedly. A structure analysis of the reaction products by 1H- and 13C-NMR spectroscopy is also presented.
    Zusätzliches Material: 1 Ill.
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  • 206
    Digitale Medien
    Digitale Medien
    A New Racemic Conglomerate and Its Characterization by the Melting Point Diagram - Formation of the Metastable Racemic Compound (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 3179-3183 
    Details
    ISSN: 1434-193X
    Schlagwort(e): Highly branched ester ; Partial optical resolution by mechanical manipulation ; Racemic conglomerate melting point diagram ; Enantiomer enthalpy and entropy of fusion ; Metastable racemic compounds ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The highly branched ester rac-1 has been prepared. It exists in the form of a conglomerate (m.p. 90-92 °C) in which the two enantiomers are present in separate crystal lattices, as indicated by the melting point diagram. Both enantiomers of 1 have been isolated by crystallization [m.p. 112-114 °C, [α]D22 = +24.4 ± 0.7 (c = 0.45, Et2O), -25.4 ± 0.8 (c = 0.44, Et2O)]; mechanical manipulation of the conglomerate provided samples enriched in one or the other enantiomer and subsequent recrystallization of these partially resolved samples furnished the isolated enantiomers. The high value of the enthalpy of fusion of enantiomers 1 (ΔHfenant = 8.8 ± 1.4 kcal mol-1) and the moderate value of the corresponding entropy (ΔSfenant = 23 ± 4 cal K-1 mol-1), both derived from the melting point diagram, are ascribed to the relative compactness of the highly branched molecule and to its reduced conformational flexibility, respectively. Ester rac-1 has been serendipitously obtained in the form of a racemic compound (m.p. 82-84 °C) by crystallization of the racemate. The racemic compound transforms into the conglomerate at 70 °C. This transformation may be regarded as a spontaneous optical resolution occurring in the solid crystalline state.
    Zusätzliches Material: 3 Ill.
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  • 207
    Digitale Medien
    Digitale Medien
    Photoelectron Spectra and Electronic Structures of a Series of Vinylogous Thioindigoid Compounds (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 3191-3197 
    Details
    ISSN: 1434-193X
    Schlagwort(e): Photoelectron spectroscopy ; Electronic structure ; Chromophores ; Dyes ; Ab initio calculations ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The molecular and the electronic structures of bi(4,4-dimethyl-3-oxotetrahydrothiophen-2-ylidene) (1), a compound comprising the basic chromophore of thioindigo dyes, and its two vinylogs 2 and 3 with two and three conjugated central double bonds, respectively, have been analyzed by B3LYP/6-31+G* calculations and UV photoelectron spectroscopy. The calculated structural parameters of 1-3 reveal no systematic variation. The first ionization potentials indicate no, or only a minor, increase in the energy of the highest occupied molecular orbital (HOMO) with the size of the chromophore. These findings are in accord with the corresponding characteristic optical properties of such indigoid compounds. For comparison, substituent effects on highest occupied (HOMO) and lowest unoccupied molecular orbital (LUMO) energies were analyzed by semi-empirical PM3 calculations in a series of α,ω-substituted linear conjugated polyenes. Systems with symmetrical substitution by two donor and two acceptor groups simulate the properties of 1-3, having rather constant energies for these molecular orbitals and a narrow separation. In addition, the long-wavelength absorption of 1-3, and probably of other indigoid compounds, is caused by the small overlap density of these molecular orbitals which are largely localized in different parts of the molecule.
    Zusätzliches Material: 3 Ill.
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  • 208
    Digitale Medien
    Digitale Medien
    Some Developments in the High Temperature Gas Phase Chemistry of Alkynes, Arynes and Aryl Radicals (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 3211-3222 
    Details
    ISSN: 1434-193X
    Schlagwort(e): Flash vacuum pyrolysis ; Alkynes ; Arynes ; Carbenes ; Radicals ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The discovery of the equilibration of alkynes with ylidenecarbenes at high temperatures has been followed by increasing use of the reactivity of such carbenes in the synthesis of polycyclic aromatic hydrocarbons. This has led to simple and elegant syntheses of fullerene fragments, and of cyclopenta-fused hydrocarbons. The related high-temperature equilibration of arynes with ring-contracted exocyclic carbenes has provided a further pathway for the transformation of polycyclic aromatic systems into less accessible cyclopenta-fused hydrocarbons. Some recent developments in the chemistry of aryl radicals have extended the scope of radical approaches to the synthesis of polycyclic hydrocarbons.
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  • 209
    Digitale Medien
    Digitale Medien
    Studies Directed Toward the Synthesis of Taxanes: Evaluation of the B-Ring Formation By an Intramolecular Nitrile Oxide Cycloaddition (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 3241-3249 
    Details
    ISSN: 1434-193X
    Schlagwort(e): Taxol ; Nitrile oxide ; Cycloaddition reactions ; Isoxazoline ; Macrocycles ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Several models for the formation of the 8-membered B-ring of taxanes by an intramolecular nitrile oxide [3+2] cycloaddition were prepared from the monoacetal of 2,2-dimethylcyclohexane-1,3-dione (5). The nitrile oxides were then generated under high-dilution conditions. In most cases only oligomers were obtained. The isoxazoline 19, containing a 9-membered ring, was formed from the nitrile oxide 17, and a bis(isoxazoline) 21was isolated from the reaction of the nitro compound 16c.
    Zusätzliches Material: 1 Tab.
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  • 210
    Digitale Medien
    Digitale Medien
    Matrix Isolation and Photochemistry of Tetrafluoro-p-xylylene (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 3287-3290 
    Details
    ISSN: 1434-193X
    Schlagwort(e): Cyclophanes ; Matrix isolation ; Photochemical reactions ; Quinodimethanes ; Parylene AF-4 ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Tetrafluoro-p-xylylene (3) has been generated by flash vacuum pyrolysis of octafluoro[2.2]paracyclophane (2) and subsequent trapping of the products in solid argon at 9 K. Xylylene 3 photochemically rearranges to the ring-expanded heptafulvene 5. Matrix-isolated species have been identified by comparison of experimental and calculated IR spectra. The temperature-dependence of the thermal fragmentation of paracyclophane 2 has been determined by mass spectrometric analysis of the pyrolysis products.
    Zusätzliches Material: 3 Ill.
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  • 211
    Digitale Medien
    Digitale Medien
    Thermochemical Study of Reduction and Oxidation Reactions of Molybdovanadophosphoric Heteropolyacids in Aqueous Solutions (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 1009-1014 
    Details
    ISSN: 1434-1948
    Schlagwort(e): Heteropolyacids ; Molybdovanadophosphates ; Hydrazine hydrate ; Reduction ; Oxidations ; Thermochemistry ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Differential enthalpies of reduction, -ΔrH4j, have been found at 343 K for 0.2 m aqueous heteropolyacids H3+xPVxMo12-xO40 (HPA-x, where 1 ≤ x ≤ 6) and their salts by hydrazine hydrate (HH). The -ΔrH4j values depend on x and m, where m = [VIV]/[HPA-x]. At m ≈ 0, the initial -ΔrH4j value is 436 ± 14 kJ mol-1 HH for all HPA-x. For HPA-x with 3 ≤ x ≤ 6, the curves -ΔrH4j = f(mj) have maxima associated with formation and reduction of the outer-sphere cation VVVIVO33+. A similar maximum is observed on reduction of 0.1 M VO2ClO4 in 4 M HClO4. No maxima are observed for the reduction of HPA-1, HPA-2, and salts of HPA-3. For HPA-3 salts, -ΔrH4j = f(mj) depends primarily on the pH of the salt solution, rather than on the nature of the cation. Reduction and oxidation of HPA-x and their salts are reversible reactions. In HPA-x solutions, VO2+ in the outer sphere is reduced first, and VV in the inner coordination sphere of the heteropoly anion is reduced next. Differential enthalpies for the oxidation of the reduced HPA-x by dioxygen (-ΔrH2j) have been calculated. The sequence of the oxidation of different VIV forms in the reduced HmHPA-x solutions is the reverse of that for the reduction of the VV forms in the initial HPA-x solutions.
    Zusätzliches Material: 4 Ill.
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  • 212
    Digitale Medien
    Digitale Medien
    Syntheses and Characterization by NMR Spectroscopy and X-ray Diffraction of Complexes Derived from Metals of Groups 2 and 13 and the Ligand Bis(3,5-di-tert-butyl-1-hydroxy-2-phenyl)amine (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 1021-1027 
    Details
    ISSN: 1434-1948
    Schlagwort(e): Alkaline earth metals ; Group-13 metals ; Coordination chemistry ; Bis(3,5-di-tert-butyl-1-hydroxy-2-phenyl)amine ligand ; Nonacoordinated strontium compound ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Reaction of 3,5-di-tert-butylcatechol and aqueous ammonia with boron, aluminum, gallium, or strontium chloride, or with calcium or barium acetate produce, under oxidizing conditions, neutral complexes of stoichiometric formulae ML (M = BCl), ML2, [M = Al (2), Ga (3), Ca (4), and Ba (5)], and ML3H [M = Sr (6)] [L = different oxidation states of bis(3,5-di-tert-butyl-1-hydroxy-2-phenyl)amine]. The structures of 1 and 4-6 were established by 1H- and 13C-NMR spectroscopy and of 2, 3, and 6 by X-ray diffraction. The coordination compound ClBL (1) was obtained by transmetallation of ZnL2 with BCl3. It is a tetracyclic compound with tetracoordinated boron and nitrogen atoms, the ligand being in the reduced form, bis(hydroxyphenyl)amine. The paramagnetic complexes 2 and 3 crystallized in the triclinic system and are hexacoordinated with two orthogonal planar ligands bonded to the metal atoms. The ligands appear in two different oxidation states: one as the monoanion and another as a radical dianion. Based on their X-ray diffraction molecular structures, it is deduced that both ligands have similar structures, confirming electronic delocalization and fast interconversion of their oxidation states. Ca and Ba complexes are diamagnetic and hexacoordinated, both ligands being monoanions The strontium complex crystallized in the monoclinic system, the metal atom is nonacoordinated, having two ligands as monoanions, and a third one is a neutral protonated diquinone. Its structure is a distorted helix with three paddles in a C3 geometry and its unexpected diamagnetic behaviour is due to the presence of a reduced protonated ligand.
    Zusätzliches Material: 4 Ill.
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  • 213
    Digitale Medien
    Digitale Medien
    Cycloisomerization of Alkynols at Transition Metal Templates (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 1057-1066 
    Details
    ISSN: 1434-1948
    Schlagwort(e): Alkynols ; Isomerizations ; Oxacycloalkylidene complexes ; Vinylidene complexes ; Transition metal templates ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The metal-assisted cycloisomerization of ω-alkynols to oxacycloalkylidene complexes is reviewed. A variety of low-valent coordinatively unsaturated transition metal templates from group 6 to 10 mediate the cyclization of ω-butynols, -pentynols, and -hexynols to give the corresponding oxacycloalkylidene complexes. In some cases kinetic hydroxyalkylvinylidene complex intermediates can be isolated and characterized.
    Zusätzliches Material: 2 Ill.
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  • 214
    Digitale Medien
    Digitale Medien
    Formation of Anionic PdX3(PPh3)- Complexes by Reaction of Halide Ions with PdX2(PPh3)2 (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 1081-1085 
    Details
    ISSN: 1434-1948
    Schlagwort(e): Palladium ; Anionic complexes ; Phosphane substitution ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Halide ions react with PdX2(PPh3)2 (X = Cl, Br, I) complexes in an equilibrated reaction in which the phosphane ligand is substituted by the halide X- to form anionic complexes PdX3(PPh3)- in THF and DMF. The equilibrium constants have been determined by cyclic voltammetry.
    Zusätzliches Material: 5 Ill.
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  • 215
    Digitale Medien
    Digitale Medien
    The Role of N-H···Cl Hydrogen Bonds in Gold(I) Complexes with Aliphatic Amine Ligands (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 1103-1110 
    Details
    ISSN: 1434-1948
    Schlagwort(e): Amines ; Aurophilicity ; Gold ; Hydrogen bonds ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Various gold(I) complexes of aliphatic amines have been prepared by the reaction of chloro(tetrahydrothiophene)gold(I) with the respective amines. The stability of these complexes can be attributed partly to the formation of hydrogen bonds involving the N-H functions, and partly to aurophilic interactions. Analysis of these secondary contacts suggests an inverse correlation between lengths of aurophilic interactions and hydrogen bonds.
    Zusätzliches Material: 11 Ill.
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  • 216
    Digitale Medien
    Digitale Medien
    Group-4 Metallocene Cation Complexes of Oligopeptides: Reaction of [Cp2ZrCH3(THF)+BPh4-] with Boc-Protected Di- and Tripeptide Esters (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 1111-1120 
    Details
    ISSN: 1434-1948
    Schlagwort(e): Bioorganometallic chemistry ; Zirconocene complexes ; Metallocene cations ; Group-4 metallocene peptide complexes ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: 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.
    Zusätzliches Material: 1 Ill.
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  • 217
    Digitale Medien
    Digitale Medien
    Gas-Phase Characterization of an Unhindered Germaimine by UV-Photoelectron Spectroscopy (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 1151-1153 
    Details
    ISSN: 1434-1948
    Schlagwort(e): Germacyclopentene ; Germaimine ; Photoelectron spectroscopy ; Ab initio calculations ; Germanium ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: An unhindered germaimine has been generated and characterized by the coupling of flash vacuum pyrolysis of two different precursors with UV-photoelectron spectroscopy. The Ge=N unit exhibits two ionizations in the low-energy region, corresponding to the ejection of an electron from the nitrogen atom lone pair and from the πGe=N orbital, respectively.
    Zusätzliches Material: 2 Ill.
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  • 218
    Digitale Medien
    Digitale Medien
    Combined Quantum Chemical and Mass Spectrometry Study of [Ge,C,H]+ and Its Neutral Counterpart (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 1203-1210 
    Details
    ISSN: 1434-1948
    Schlagwort(e): Organogermanium ions ; Mass spectrometry ; Ab initio theory ; NBO ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The cation [Ge,C,H]+ has been generated by the electron ionisation of trichloromethylgermane. Collisional activation experiments were used to establish a Ge-C-H connectivity in this species, for which a significant fraction of the ion population was found to survive neutralisation-reionisation mass spectrometry (NRMS) experiments. Thus, the neutral counterpart [Ge,C,H]0 is stable on a microsecond timescale. Becke's 3 parameter hybrid density functional (B3LYP) was used to map the ion and neutral potential-energy surfaces, in conjunction with double-zeta and triple-zeta basis sets. The computational results obtained using the triple-zeta basis sets suggest that, for the cation, the global minimum is the high spin 3Σ GeCH+, with the first Ge-C-H excited state, 1Σ GeCH+, approximately 39 kcal mol-1 less stable. The lowest energy ion structure with H-Ge-C connectivity is bent (3A′′HGeC+,∠H-Ge-C = 126.3) and 69 kcal mol-1 less stable than the global minimum. For the neutral, a doublet (2π) with Ge-C-H connectivity is predicted to be the global minimum. The classical barrier for the neutral 1,2-hydrogen shift reaction on the doublet surface is negligible (0.1 kcal mol-1), while the smallest barrier for the cation is 13.0 kcal mol-1, corresponding to (3A′′) HGeC+ → (3Σ) GeCH+. Natural bond order analysis has been used to establish the order of the metal-carbon bond for selected states of both the neutral and the ion. Neutral and cationic isomers with Ge-C triple bonds were found to be high-energy excited states, with the metal-carbon bonds in the cation and neutral ground states of order 2.0 and 2.5, respectively. The instability of Ge-C triple bonded species is attributed to the energy required for electronic promotion in the metal in order to achieve a hybrid configuration suitable for the formation of such a bond.
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  • 219
    Digitale Medien
    Digitale Medien
    Linear Five-Centred Chromium Multiple Bonds Bridged by Four tpda2- Ligands [tpda2- = tripyridyldiamido dianion] - Synthesis and Structural Studies (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 1243-1251 
    Details
    ISSN: 1434-1948
    Schlagwort(e): Metal string complexes ; Multicentered metal-metal multiple bond ; Quadruple bonds ; Metal-metal interactions ; Chromium ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The linear pentanuclear chromium complexes [CrII5(μ5-tpda)4Cl2] (1), [CrII5(μ5-tpda)4(NCS)2] (2), [CrIIICrII4(μ5-tpda)4F2](BF4) (3), and [CrIIICrII4(μ5-tpda)4F(OTf)](OTf) (4), with four all-syn tri(α-pyridyl)diamido dianion (tpda2-) ligands, have been prepared and structurally characterized. Compounds 1 and 2 possess a delocalized Cr(II)-Cr(II)-Cr(II)-Cr(II)-Cr(II) five-centred metal-metal bond of order 1.5. In both 1 and 2 two values for CrII-CrII bond lengths are found both; the outer ones connected with axial ligands are 2.284(1) and 2.285(2) Å, and the inner ones are 2.2405(8) and 2.246(1) Å, for 1 and 2, respectively. When compound 1 reacts with 2 equiv. of AgBF4 or Ag(OTf), a oxidation reaction takes place and one of the terminal chromium(II) ions is oxidized to produce [CrIIICrII4(μ5-tpda)4F2]BF4 (3) or [CrIIICrII4(μ5-tpda)4F(OTf)](OTf) (4). Two short Cr-Cr distances [1.969(2) and 2.138(2) Å for 3, 1.846(1) and 1.922(1) Å for 4] are found, with the presence of two quadruple bonds among four adjacent CrII ions. The fifth CrIII ion, which is separated from the neighboring CrII ion by 2.487(2) Å for 3 and 2.610(1) Å for 4, is simply a square pyramidal unit with no metal-metal bonding interaction.
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  • 220
    Digitale Medien
    Digitale Medien
    Synthesis and Characterization of the Heterometallic Aggregate Pb2Al5(μ3-O)(μ4-O)(μ-OiPr)9(OiPr)3(μ-OAc)3 (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 1291-1293 
    Details
    ISSN: 1434-1948
    Schlagwort(e): Aluminum ; Lead ; O ligands ; Alkoxy carboxylates ; Structure elucidation ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: A novel heterometallic aggregate Pb2Al5(μ3-O)(μ4-O)(μ-OiPr)9(OiPr)3(μ-OAc)3 obtained from the interaction of Pb(OAc)2 and Al(O-iPr)3 is the first structurally characterized example based on lead and aluminum. This compound has been isolated in high yield and examined by 1H-, 13C-, and 27Al NMR, and in the solid state by X-ray crystallography.
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  • 221
    Digitale Medien
    Digitale Medien
    Pyrazolato Metal Complexes - Synthesis, Characterization, and X-ray Crystal Structures of Heterotrimetallic Re-M2 Derivatives (M = Cu, Ag, Au) (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 1301-1307 
    Details
    ISSN: 1434-1948
    Schlagwort(e): Pyrazolato ligands ; Rhenium ; Group-11 metals ; Heterometallic complexes ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: By treating [(CO)3Re(Hpz)2(pz)] (Hpz = pyrazole) with [Cu(CH3CN)4]BF4, AgNO3, or [Au(tht)Cl] (tht = tetrahydrothiophene) in acetonitrile in the presence of Et3N, the corresponding trinuclear complexes {(CO)3Re(pz)3[M(CH3CN)]2} (1a-c) have been obtained. Treatment of complexes 1a-c with cyclohexyl isocyanide (c-C6H11NC) afforded the derivatives {(CO)3Re(pz)3[M(c-C6H11NC)]2} (2a-c). Complexes 2a-c have been characterized in solution by 1H-NMR spectroscopy and in the solid state by single-crystal X-ray diffraction analysis.
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  • 222
    Digitale Medien
    Digitale Medien
    Synthesis and Investigations on Nitrido(phthalocyaninato)rhenium Complexes (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 1309-1313 
    Details
    ISSN: 1434-1948
    Schlagwort(e): Phthalocyanines ; Rhenium ; Nitrido(octa-n-alkylphthalocyaninato)rhenium compounds ; Nucleophilic additions ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The reactions of nitrido(tetra-tert-butylphthalocyaninato)rhenium (1) with boron tribromide leading to (tBu4Pc)ReNBBr3 (4) and with acetone to give the imido complex (tBu4Pc)Re[NC(CH3)2CH2C(O)CH3]OH (2b) and its μ-oxo dimer 3 are reported. Starting from the corresponding 4,5-di-n-alkylphthalonitriles and ammonium perrhenate four soluble nitrido(octa-n-alkylphthalocyaninato)rhenium complexes 5-8 were synthesized. Nitrido(octa-n-pentylphthalocyaninato)rhenium (6) was treated with boron tribromide to afford [(C5H11)8Pc]ReNBBr3 (9).
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  • 223
    Digitale Medien
    Digitale Medien
    Synthesis, Chemistry, and Characterization of Perfluoroaromatic Selenium Derivatives (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 1359-1366 
    Details
    ISSN: 1434-1948
    Schlagwort(e): Selenium ; Fluorine ; Multinuclear NMR ; Raman spectroscopy ; X-ray crystallography ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The reaction of perfluoroaryllithium RC6F4Li, where R = F or 4-CF3C6F4O, respectively, with selenium gives the known diselanes (RC6F4Se)2 (1a, 1b). Redox reactions of 1 with hydrogen peroxide result in the formation of the seleninic acids RC6F4SeOOH which crystallize as hydrates (2a, 2b); with mercury give the bis(arylseleno)mercuries (RC6F4Se)2Hg (3a, 3b); with sulfuryl chloride or bromine give the selenenyl chlorides (4a, 4b) or selenenyl bromides (5a, 5b). Selenenyl chlorides (4a, 4b) react with a variety of trimethylsilyl reagents Me3SiX (X = Br, CN, NMe2, NEt2) to form 5a, 5b; selenocyanates RC6F4SeCN (6a, 6b); selenenyl amides RC6F4SeNMe2 (7a, 7b) and RC6F4SeNEt2 (8a, 8b). A new synthetic route to diorgano selanes is developed by reaction of 4a, 4b with perfluoroaryllithium to give the symmetric (RC6F4)2Se (9a, 9b). All derivatives are thoroughly characterized and in addition the molecular structures of 2a, 6a, and 9a are established by X-ray crystallography.
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  • 224
    Digitale Medien
    Digitale Medien
    Solvates of Sodium Bis(borane)dimethylamide (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 1373-1379 
    Details
    ISSN: 1434-1948
    Schlagwort(e): Sodium bis(borane)dimethylamide solvates ; X-ray structure ; Reduction ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The reaction of sodium metal with dimethylamine-borane in THF yields Na[(H3B)2NMe2] (1) which can be isolated as {Na[(H3B)2NMe2]}5·THF or as Na[(H3B)2NMe2]·15-crown-5 (2) and Na[(H3B)2NMe2]·benzo-15-crown-5 (3) after addition of the appropriate crown ether to the THF solution of 1. Reaction of 1 with ZrCl4 yields Me2HN-BH2-NMe2-BH3 (4), the structure of which has been determined. In THF solution, 1 reduces aldehydes, ketones, acyl chlorides, and esters to the corresponding alcohols. It also reacts slowly with nitriles and allylbenzene. Compound (1)5·THF crystallizes in an extended three-dimensional lattice, in which the Na atoms are coordinated by 6-9 hydridic H atoms, while 3 is a molecular compound in the solid state. Only one hydrogen atom of each BH3 group coordinates to the sodium center. On the other hand, 4 forms dimeric associates in the solid state through N-H···H-B interactions.
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  • 225
    Digitale Medien
    Digitale Medien
    Self-Assembly, Structure, and Physical Properties of Tetranuclear ZnII and CoII Complexes of [2 × 2] Grid-Type (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 1421-1428 
    Details
    ISSN: 1434-1948
    Schlagwort(e): Grid complexes ; Self-assembly ; Co ; Zn ; Coordination chemistry ; Bis(tridentate) ligands ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The tretrametallic [2 × 2] grid-type complexes 1-4 are formed by self-assembly of the bis(tridentate) ligands 5 and 6 with ZnII and CoII cations. They have been characterized by spectroscopic studies in solution as well as by crystal structure determination. The substituents in the central pyrimidine ring play an important role in terms of geometry and physical properties of the complexes. They induce an orthogonal orientation of the ligand in the complexes which is critical for the formation of ordered monolayers and extended self-organized arrays of grids. The physical properties of the complexes such as metal-metal interaction and π-π* stacking between the ligands may be modulated by changing these substituents.
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  • 226
    Digitale Medien
    Digitale Medien
    New Inorganic Metallacycles and the First Six-Membered Covalent “True” Heterocycle - Oxidation of RC(E)NHPPh2 (E = O or S; R = H2N, Ph, or Py) with O, S, or Se to Give RC(E)NHP(E′)Ph2 (E′ = O, S, Se) and Their Coordination Chemistry (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 1445-1452 
    Details
    ISSN: 1434-1948
    Schlagwort(e): Metallacycles ; Solid-state structures ; Heterocycles ; Oxidations ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Direct oxidation of PhC(O)NHPPh2, H2NC(S)NHPPh2, (C5H4N)C(S)NHPPh2 with O2, S8, or Se gives [PhC(O)NHP(O)Ph2] (1), [H2NC(S)NHP(S)Ph2] (2), [H2NC(O)NHP-(S)Ph2] (3), [PhC(O)NHP(S)Ph2] (4), [(C5H4N)C(S)NHP(S)Ph2] (5), and [H2NC(S)NHP(Se)Ph2] (6). Deprotonation of 1, 2, 4-6 with potassium tert-butoxide gives K[PhC(O)NP(O)Ph2] (7), K[H2NC(S)NP(S)Ph2] (8), K[PhC(O)NP(S)Ph2] (9), K[(C5H4N)C(S)NP(S)Ph2] (10), and K[H2NC(S)NP(Se)Ph2] (11). Reaction of 4with KOBu and [Cu(Ph3P)2][NO3] gives [Cu(Ph3P)(PhC(O)NP(S)Ph2)] (12) which is the first crystallographically characterised example of a non-ionic six-membered “true” heterocycle (i.e. a ring in which every heterocatom is different). 9 and 10 were treated with [PdCl2(COD)] to give [Pd{PhC(O)NP(S)Ph2}2] (13) and [Pd{(C5H4N)C(O)NP(S)Ph2}2] (14), respectively The anion of 8 coordinates to zinc forming [Zn{H2NC(S)NP(S)Ph2}2] (15). Treatment of 2 or 8 with [PtCl2(COD)] gives [Pt{H2NC(S)NP(S)Ph2}{H2NC(S)NHP(S)Ph2}]+Cl- (16) and [Pt{H2NC(S)NP(S)Ph2}2] (17), respectively. The X-ray structures of 12, 15-17are reported.
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  • 227
    Digitale Medien
    Digitale Medien
    Mechanism of the Catalytic Oxidation of Tertiary Alcohols by the Water-Soluble Mn-TMPyP/KHSO5 System: β-Fragmentation versus O-Neophyl Rearrangement (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 1467-1477 
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    ISSN: 1434-1948
    Schlagwort(e): Oxidations ; Tertiary alcohol ; Porphyrins ; Neophyl rearrangement ; Cleavage reactions ; β-Scission ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Oxidation of 4-(1-hydroxy-1-phenylethyl)benzoic acid HPEBA with a water-soluble metalloporphyrin as catalyst and KHSO5 as oxygen atom donor gives the major products, acetophenone AC and acetylbenzoic acid ABA, by a Caliph-CAr bond cleavage, but a minor product, benzoyloxybenzoic acid BOBA, requires the insertion of an oxygen atom to form the ester. This compound becomes the main oxidation product on increasing the amount of acetonitrile in the reaction medium, and its formation is oxygen-dependent. The conversion is drastically lowered by using D2O instead of H2O, suggesting that an alkoxyl radical is formed in the rate-determining step. Labeling experiments using 18O2 or H218O under different reaction conditions show that the carbonyl oxygen atoms of AC and ABA originate either from substrate, water or dioxygen. However, the carbonyl oxygen atom in the ester group of BOBA originates from dioxygen while the other oxygen atom of the ester remains unlabeled. These results can be explained by an O-neophyl rearrangement of the initial alkoxyl radical to afford a carbon-based radical which then reacts with dioxygen or MnIV-OH/water. In a competitive reaction pathway, direct β-scission of the alkoxyl radical leads to unlabeled products. The oxidation of other tertiary diaryl alcohols is also discussed.
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  • 228
    Digitale Medien
    Digitale Medien
    Geminal Bis(hypersilyl) Compounds - The Reaction of Tris(trimethylsilyl)silyllithium with Dialkyl(chloromethylene)ammonium Chlorides (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 21-26 
    Details
    ISSN: 1434-1948
    Schlagwort(e): Silicon ; Silanes, sterically congested ; Tris(trimethylsilyl)silanes ; (Chloromethylene)ammonium chlorides ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Tris(trimethylsilyl)silyllithium (1) reacts with dialkyl(chloromethylene)ammonium chlorides (molar ratio 2:1) to give the (dialkylamino)bis(hypersilyl)methanes [(Me3Si)3Si]2CHNR2 (5a-c; a: R = Me, b: R = Et, c: R2 = [CH2]5). Due to the extreme bulkiness of the hemispherical (Me3Si)3Si substituents, the structures of these geminal bis(hypersilyl) derivatives are characterized by tremendous distortions of their molecular skeletons. This was confirmed by X-ray structural analyses of 5a and 5c, which revealed considerable elongations of the central Si-C bonds (5a: 2.01 and 1.95 Å; 5c: 1.99 and 1.97 Å) and an extreme widening of the Si-C-Si angles at the central sp3-carbon atoms (5a: 132.6°; 5c: 128.7°). By concentrated sulfuric acid, 5a is converted to give, after hydrolysis, the silanol (Me3Si)2Si(OH)-CH2Si(SiMe3)3 (13). The formation of 13 is discussed as proceeding through the transient silene (Me3Si)2Si=CHSi(SiMe3)3 (11), generated by a formal (dimethylamino)trimethylsilane elimination from 5a according to an acid-induced sila Peterson mechanism.
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  • 229
    Digitale Medien
    Digitale Medien
    Steric and Electronic Effects on the 103Rh NMR Chemical Shifts of RhI(cyclooctadiene) Compounds Bearing N-Donor Ligands (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 27-33 
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    ISSN: 1434-1948
    Schlagwort(e): 103Rh NMR ; Rhodium complexes ; Nitrogen ligands ; Chemical-shift computation ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: In order to study electronic and steric effects on δ(103Rh), the103Rh-NMR spectra of a series of [Rh(cod)L2] complexes (with L = nitrogen, oxygen, or chloride) have been measured by gradient-enhanced HMQC (1H,103Rh) NMR spectroscopy. Density functional computations of representative examples have been performed at the GIAO-B3LYP level of theory. The obtained experimental values of 103Rh shifts fit the generally observed trend of coordinating ligands in the first coordination sphere of the metal: P 〈 N 〈 O. Calculated 103Rh shifts agreed to within 8 % with experimental values. The computational results indicate that the Rh-N bond distance has a larger influence on the chemical shift than the N-Rh-N angle.
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  • 230
    Digitale Medien
    Digitale Medien
    A Versatile Fluorescent System for Sensing of H+, Transition Metals, and Aromatic Carboxylates (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 35-39 
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    ISSN: 1434-1948
    Schlagwort(e): Fluorescent sensors ; Molecular recognition ; Charge transfer excited states ; Metal complexes ; pH Sensors ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The fluorescent emission of the N,N-dimethylaniline fragment of the tetramine system 3varies with pH, displaying a maximum of the fluorescent intensity, IF, at pH = 5. Binding of transition metals (CuII, NiII) induces fluorescence quenching and modifies the IF vs. pH profile, giving rise to an OFF-ON-OFF type of sensor. The [ZnII(3)]2+complex recognises carboxylate anions, both aliphatic and aromatic. Recognition is signalled via fluorescence quenching only for aromatic carboxylates.
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  • 231
    Digitale Medien
    Digitale Medien
    Aromatic Phosphenium Cations (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 41-49 
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    ISSN: 1434-1948
    Schlagwort(e): Phosphorus heterocycles ; Aromaticity ; Phosphenium cations ; Ab initio calculations ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The aromatic stabilization of cyclic phosphenium cations (general type C2N2P+) was studied by experimental methods (synthesis, multinuclear NMR, single crystal X-ray crystallography) and quantum chemical calculations (ab initio methods). The structures of the 1,3,2-diazaphosphole derivatives [(tBuN-CH=CH-NtBu)P+]Cl- (1), (tBuN-CH2-CH2-NtBu)P-Cl (2), [(tBuN-CH=CH-NtBu)P]+PF6- (3) and [(tBuN-CH2-CH2-NtBu)]P+PF6- (4) were examined by single crystal X-ray diffraction. The chloro phosphane [(tBuN-CH=CH-NtBu)P]+Cl- (1) has an ionic P-Cl bond and contains an aromatically stabilized phosphenium cation [shortest distance P···Cl = 275.9(2) pm], while the CC-saturated compound (tBuN-CH2-CH2-NtBu)P-Cl (2) is covalent. The two chloro-phosphanes 1 and 2 differ sharply in their volatility and solubility in organic solvents. Compound 2 is soluble in hydrocarbons and sublimes readily at 90 °C/0.1 Torr but 1 is insoluble in hexanes and not volatile below 180 °C/0.1 Torr. The degree of aromatic stabilization in the phosphenium cation 1 was investigated by ab initio methods. For the model cations [RN-CH2-CH2-NR]P+ and [(RN-CH=CH-NR)P]+, thermochemical stabilization energies of 25.8 kcal · mol-1 (R = H) and 28.1 kcal · mol-1 (R = Me) were obtained from isodesmic hydrogenation reactions at the RHF/MP2/6-31G*//RHF/6-31G* level.
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  • 232
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    Digitale Medien
    Crystal Structure and Intercalation Properties of γ-Zr(AsO4)(H2AsO4) × 2 H2O (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 61-65 
    Details
    ISSN: 1434-1948
    Schlagwort(e): Zirconium arsenate ; Crystal structure ; Amine intercalation ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The crystalline structure of γ-Zr(AsO4)(H2AsO4) × 2 H2O (γ-ZrAs) has been refined by the Rietveld method. It has a monoclinic P21 layered structure built up from AsO4 tetrahedra and ZrO6 octahedra stacked along the 001 direction. The cell parameters are: a = 5.5752(6) Å, b = 6.8290(7) Å, c = 12.110(1) Å, and β = 103.03(1)°. The layered nature of γ-ZrAs is confirmed by the intercalation of n-alkylamines (CH3[CH2]nNH2; n = 0-5) as well as of cyclic amines (benzylamine, cyclohexylamine, piperidine, and pyridine). Among the linear amines, only with methyl-, ethyl-, and hexylamine is the maximum incorporation attained. With the cyclic amines, except in the case of pyridine, pure new phases are obtained, with the highest degree of intercalation being one mol of amine per mol of γ-ZrAs.
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  • 233
    Digitale Medien
    Digitale Medien
    Synthesis of the Stereoisomers of Methohexital by Palladium-Catalyzed Allylation (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 51-59 
    Details
    ISSN: 1434-1948
    Schlagwort(e): Asymmetric catalysis ; Allylic alkylation ; 1-Methyl-5-(1′-methylpent-2′-ynyl)barbituric acid ; Palladium catalysts ; Chiral phosphane imine ligands ; Methohexital ; Anesthetic dose ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Allylation of 1-methyl-5-(1′-methylpent-2′-ynyl)barbituric acid (MBS) with allyl acetate using in situ catalysts of palladium(II) acetylacetonate and chiral phosphane imine ligands resulted in the enantioselective formation of 5-allyl-1-methyl-5-(1′-methylpent-2′-ynyl)barbituric acid (Methohexital), an important anesthetic drug. Both, MBS and Methohexital contain two stereogenic carbon atoms. In MBS, the asymmetric centre in the barbiturate system is labile due to enolization. The asymmetric centre in the hexyne side chain is stable and racemic. The two asymmetric centres of Methohexital are stable and give rise to four stereoisomers, two diastereomeric racemates. An analysis of the isomers of MBS and Methohexital was established on the basis of 1H NMR and, in particular, GC including a base-line separation of the four stereoisomers of Methohexital. The stereoselectivity of the allylation is difficult to control, because the new quaternary asymmetric centre in the barbiturate ring of Methohexital is formed within the nucleophile, attacking the η3-allyl ligand of the catalyst from the side opposite to the palladium atom. Classical optically active ligands, such as diop or norphos, give only 2-6 % ee. Chiral phosphane imine ligands are a successful class of compounds, synthesized by Schiff base condensation of (2-formylphenyl)diphenylphosphane with optically active primary amines. The most efficient ligands have a hydroxymethyl and a bulky alkyl substituent at the asymmetric centre in the imine part, e.g. the L-iso-leucinol and the L-tert-leucinol derivatives 5 and 7. In the Pd-catalyzed allylation of MBS a kinetic resolution and the effect of the enantioselective catalyst interplay, the contributions of which are separated. For MBS the best stereoselectivity factor of the kinetic resolution s = kR/kS was 2.6 and 83 % “ee” were achieved. The corresponding values for Methohexital were s = 3.5 and 80 % ee in the α-dl pair. For 10 mixtures of Methohexital stereoisomers the anesthetic doses for rats were determined. With 9.1 mg/kg body weight of the animal the sample obtained from the catalysis with the D-α-phenylglycinol derivative 8 gave a much lower anesthetic dose than the widely used narcotic Brevimytal®Natrium, the sodium salt of the α-dl racemate of Methohexital, with 13.0 mg/kg body weight.
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  • 234
    Digitale Medien
    Digitale Medien
    Synthesis and Structure of the First [1]Boratitanocenophanes (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 69-73 
    Details
    ISSN: 1434-1948
    Schlagwort(e): Boron ; Titanium ; Metallocenophanes ; [1]Boratitanocenophanes ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: This paper presents two methods for the synthesis of the first [1]boratitanocenophanes. The novel biscyclopentadienylborane [(Me3Si)2NB(C5H5)2], the dilithio salt Li2[(Me3Si)2NB(C5H4)2] (1) of which was characterized by multinuclear NMR methods, was prepared in situ, and served as starting material for several [1]boratitanocenophanes. [Cl2Ti{(C5H4)2BN(SiMe3)2}] (2) was obtained in high yield by a convenient one-pot synthesis starting from 1 and [TiCl3(thf)3], followed by oxidation with PbCl2. The highly reactive [(Me2N)2Ti{(C5H4)2BN(SiMe3)2}] (3) was obtained by the reaction of [(Me3Si)2NB(C5H5)2], prepared in situ, with Ti(NMe2)4and converted into the chloro derivatives [(Me2N)ClTi{(C5H4)2BN(SiMe3)2}] (4) and [Cl2Ti{(C5H4)2BN(SiMe3)2}] (2) by treatment with one or two equivalents of a suitable diaminochloroborane. All [1]boratitanocenophanes were characterized in solution by multinuclear NMR spectroscopy, and in addition the structure of 2 in the crystalline state was determined by a single-crystal X-ray study.
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  • 235
    Digitale Medien
    Digitale Medien
    An Unusual Reaction of Hexafluoroacetone with Methylenediphosphanes: Facile Synthesis of Carbodiphosphoranes (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 1665-1671 
    Details
    ISSN: 1434-1948
    Schlagwort(e): Methylenediphosphane ; Hexafluoroacetone ; Carbodiphosphorane ; Ylides ; Carbenes ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The oxidation of the methylenediphosphanes 3a,b with hexafluoroacetone does not lead to the expected dioxaphospholane heterocycles, but yields quantitatively the carbodiphosphoranes 5a,b. Compounds 5a,b easily add HCl, HF or Cl2 to the ylidic bonds. The chloro derivative 14b, and its analogue 17 were used for the synthesis of phosphonium substituted carbenes.
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  • 236
    Digitale Medien
    Digitale Medien
    Nanostructuring Titania: Control over Nanocrystal Structure, Size, Shape, and Organization (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 235-245 
    Details
    ISSN: 1434-1948
    Schlagwort(e): TiO2 ; Growth ; Self-organisation ; Polytitanate ; Nanocrystals ; Nanostructure ; Superlattice ; Films ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Control over crystal structure, size, shape, and organization of TiO2 nanocrystals has been achieved by means of wet chemistry. Hydrolysis and polycondensation of titanium alkoxide [Ti(OR)4] has been performed in the presence of tetramethylammonium hydroxide (Me4NOH). This base both catalyzes the reaction and provides an organic cation that stabilizes the anatase polyanionic cores formed in this medium. These anatase clusters are organized so as to favour self-assembly into intermediate nanocrystals, which, in turn, self-assemble into superlattices. This self-assembling process has been exploited for the processing of highly structured titania films. Furthermore, larger anatase TiO2 nanocrystals of different sizes and shapes have been obtained by adjusting the relative concentrations of titanium alkoxide and Me4NOH, the reaction temperature, and the pressure. HRTEM, XRD, and EXAFS have been used to characterize the various samples and to elucidate the growth of titania anatase. Our observations are in accordance with theoretically predicted condensation and growth pathways. The formation of mesoscopic structures through a self-assembling process of the multiply charged polytitanate anions in the presence of Me4N+ is also discussed.
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  • 237
    Digitale Medien
    Digitale Medien
    Molybdenum(VI) Bisimidoaryl Phenoxide and Alkoxide Complexes: Molecular Structures of [Mo(NAr)2(OCMe2-2-py)(CH2SiMe3)] and [{Mo(NAr)2Me(OMe)}2] (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 1727-1733 
    Details
    ISSN: 1434-1948
    Schlagwort(e): Molybdenum ; Bisimidoaryl ; Alkoxide and phenoxide ligands ; Intramolecular coordination ; Imido complexes ; Chelates ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The synthesis and characterisation is reported of new, five-coordinate molybdenum(VI) bisimidoaryl complexes [Mo(NAr)2(O-N)(R)] [Ar = C6H3(iPr)2-2,6; O-N= 2-pyridyldiphenylmethoxide (a), 2-pyridyldimethylmethoxide (b), 8-quinolinolate (c); R = Cl, Me, CH2SiMe3] and the corresponding bisalkoxide (a, b) and bisphenolate [c, d = (OC6H4CH2NMe2-2)-] MoVI bisimidoaryl complexes [Mo(NAr)2(O-N)2]. These complexes can be formed by simple alcoholysis reactions between [Mo(NAr)2Cl2(DME)] and the appropriate alcohol in the presence of Et3N. The remaining chloride can be replaced by a methyl or trimethylsilylmethyl group by transmetallation with MeMgCl or LiCH2SiMe3. The solid state structure of [Mo(NAr)2(OCMe2-2-py)(CH2SiMe3)] (5) has been determined by single-crystal X-ray analysis. A similar synthetic procedure was used to synthesise and characterise [{Mo(NAr)2Me(OMe)}2] (7). The two methoxide ligands bridge between the two molybdenum(VI) nuclei. Compounds in which the ligand can form six-membered chelate rings {like [Mo(NAr)2(OC6H4CH2NMe2-2)2] (9) and analogues} are usually difficult to obtain in a pure form and yields are typically low.
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  • 238
    Digitale Medien
    Digitale Medien
    Deprotonation of Amides and Polyfunctional Imides Probed by Heteronuclear NMR and Quantum Chemical Calculations (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 287-295 
    Details
    ISSN: 1434-193X
    Schlagwort(e): Ab initio calculations ; Amides ; Imides ; Acidity ; NMR spectroscopy ; Deprotonation site ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: -The site of deprotonation of several types of amide acids (carboxylic amides and imides, sulfonamides, cyanamide, N-hydroxyurea) has been investigated by quantum chemical calculations and heteronuclear NMR measurements. Relative energies of tautomeric ions deriving from protonation at the various sites were determined both in the gas phase and in water (by the IPCM continuum solvation method). NMR properties (nuclear shielding and electric field gradient) of the involved heteronuclei were calculated and compared with experimental 14N, 17O and 33S chemical shifts and relaxation rates. It is shown that the combination of theoretical and experimental tools allows a reliable prediction of spectral parameters and ultimately of the deprotonation site of polyfunctional acids.Supporting information for this article is available on the WWW under -http://www.wileY-Vch.de/contents/jc_2046/1999/98401_s.pdf or from the author.
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  • 239
    Digitale Medien
    Digitale Medien
    Tetracarboxylatodirhenium Complexes Linked by Axial Cyano Bridges to Metalpentacarbonyl Ligands - Synthesis and Characterization (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 295-301 
    Details
    ISSN: 1434-1948
    Schlagwort(e): Chromium ; Carboxylate complexes ; Metal-metal multiple bonds ; Molybdenum ; Rhenium ; Tungsten ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Reaction of Re2{μ-O2CC(CH3)3}4Cl2 with [(CO)5M-CN]Na (M = Cr, Mo, W) leads to tetranuclear complexes of formula Re2{μ-O2CC(CH3)3}4[-NC-M(CO)5]2 (M = Cr, Mo, W). These complexes were characterized by 1H-, 13C-, and 95Mo-NMR, IR and Raman spectroscopy, elemental analysis and examined by cyclic voltammetry. The applied methods show the donor capabilities of the [(CO)5M-CN]- ligands which shift electron density towards the Re centers weakening the Re-Re quadruple bond. The Re-Re bond lengths and the ν(Re-Re) force constants are estimated based on the FT-IR and Raman examinations. Photochemical examinations and TG/MS experiments have also been conducted. The latter method shows that the product complexes decompose around 100 °C, by first loosing their carbonyl substituents; as do the Cr, Mo, W precursor compounds. The dirhenium tetrapivalate unit decomposes only at higher temperatures in a distinct second step.
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  • 240
    Digitale Medien
    Digitale Medien
    Synthesis, Electrochemistry, and Oxygen-Atom Transfer Reactions of Dioxotungsten(VI) and -molybdenum(VI) Complexes with N2O2 and N2S2 Tetradentate Ligands (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 313-321 
    Details
    ISSN: 1434-1948
    Schlagwort(e): Tungsten complexes ; Molybdenum complexes ; Tetradentate ligands ; Oxygen-atom transfer ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: A series of N2O2 tetradentate ligands with a range of substituents attached to the nitrogen atoms have been prepared (H2Ln) (n = 1-9). Treatment of these ligands and the N2S2 tetradentate ligand H2L10 with [WO2Cl2(DME)] (DME = 1,2-dimethoxyethane) in the presence of triethylamine leads to the formation of cis-dioxotungsten(VI) complexes [WO2(Ln)] (n = 1-10). Reaction of the N2O2 tetradentate ligands H2Ln (n = 1, 3-7) with ammonium molybdate tetrahydrate and dilute hydrochloric acid gives the corresponding molybdenum(VI) analogs [MoO2(Ln)] (n = 1, 3-7). These compounds have been spectroscopically characterized and the molecular structures of [WO2(Ln)] (n = 1, 2, 9) and [MoO2(L5)] have been established by X-ray diffraction analysis. These high-valent compounds participate in oxygen-atom transfer reactions and can catalyze the oxidation of benzoin with dimethyl sulfoxide. The complex [WO2(L10)], which contains an S-donor ligand, has lower reduction potential and higher reactivity toward oxo-transfer reactions than analogous tungsten complexes having N2O2 ligands. The kinetics of these catalytic processes along with the structure and electrochemistry of these dioxotungsten and -molybdenum complexes are described and compared.Supporting information for this article is available on the WWW under http://www.wiley-vch.de/contents/jc_2005/1999/98246_s.pdf or from the author.
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  • 241
    Digitale Medien
    Digitale Medien
    Synthesis and Investigation of Chalcogen Atom Substituted Dinitriles and Porphyrazines (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 269-276 
    Details
    ISSN: 1434-1948
    Schlagwort(e): Phthalocyanines ; Porphyrazines ; Macrocycles ; Chalcogen atom substitution ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: A series of chalcogen atom substituted porphyrazines have been assembled and characterized. Oxygen and sulfur chalcogen atoms have been substituted for peripheral methylene groups. Heteroatom-enriched, seven-membered ring dinitriles (1-3) were synthesized and characterized by IR, MS, UV-vis, 1H NMR, elemental analysis, and X-ray analysis to examine the ring conformations. They were template cyclized in the presence of MgII to form the MgII containing porphyrazine macrocycles. The MgII and metal-free macrocycles (4-9) were synthesized for all peripherally substituted porphyrazines. The unchalcogen-substituted NiII, CuII, and ZnII containing porphyrazine derivatives (10-12) were also synthesized because of the higher solubility of the metal-free porphyrazine 7. The macrocycles were characterized and studied using such techniques as UV-vis, IR, elemental analysis, cyclic voltammetry, and electrical conductivity measurements.
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  • 242
    Digitale Medien
    Digitale Medien
    Interactions Between Cyclodextrins and TmIII Chelates of Polyazamacrocycles as Studied by NMR in Aqueous Solution (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 287-293 
    Details
    ISSN: 1434-1948
    Schlagwort(e): MRI contrast agents ; Macrocyclic ligands ; Cyclodextrins ; Host-guest chemistry ; Lanthanides ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The interactions between α-, β-, and γ-CD and the TmIII chelates of the macrocyclic polyaminopolycarboxylates DOTA and NOTA were studied with the use of 1H- and 13C-NMR shift and relaxation rate measurements. Interactions were only observed between Tm(DOTA)- and γ-CD. The structure and the stability of the concerning supramolecular structures was elucidated by fitting of the NMR titration curves to a theoretical model. It appears that an inclusion compound is formed, where the hydrophobic macrocyclic part of the chelate sits in the γ-CD cavity. This inclusion compound binds a second Tm(DOTA)- molecule at the outside lower rim of the CD cone. The binding occurs probably via hydrogen bonds between non-chelated carboxylate oxygen atoms of the concerning Tm(DOTA)- and CH2OH groups of the γ-CD molecule, which are in a favorable position due to opening of the γ-CD cone angle as a result of the inclusion of the first γ-CD.
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  • 243
    Digitale Medien
    Digitale Medien
    Some Silicon, Germanium, Tin, and Lead Analogues of Carbenes, Alkenes, and Dienes (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 373-381 
    Details
    ISSN: 1434-1948
    Schlagwort(e): Silicon ; Germanium ; Tin ; Lead ; Carbene analogues ; Multiple bonds ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The isolation and characterization of thermally stable diaminocarbenes and diaminosilylenes has reawakened interest in the low-coordinated compounds of group-14 elements. The existence of these species is presumably due to interactions between the free electron pairs on the nitrogen atoms and the carbene carbon atom or the silicon atom. The present review is mainly concerned with the heavier analogues R2Ge:, R2Sn:, and R2Pb:, systems without intramolecular donor stabilization that owe their existence principally to steric shielding by the voluminous alkyl or aryl groups R. Dimerizations of these electron-sextet molecules give rise to the double-bond systems of the digermenes, distannenes, and diplumbenes; the latter species have for a long time been considered as being incapable of existence. The properties of these molecules are compared with the results of quantum chemical calculations. A separate section is devoted to the isomers of Si4R6, which include novel tetrasilacyclobutenes and the diene analogues, the tetrasilabuta-1,3-dienes.
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  • 244
    Digitale Medien
    Digitale Medien
    Synthesis and Properties of Chiral Ruthenium Complexes Containing O-, S- and P-Functionalized Cp-Ligands (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 1919-1930 
    Details
    ISSN: 1434-1948
    Schlagwort(e): Ruthenium ; Chirality ; Cyclopentadienyl complexes ; Kinetics ; Asymmetric catalysis ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Novel, functionalized, chiral Cp-ligands with S- and P-donor atoms were designed. Together with known analogues containing ether side-chains they were complexed to ruthenium for use as chiral Lewis-acid catalysts. In the ether complexes [RuCl(η5-C5H4CH2CH2OR)(PPh3)2] {R = Me, (1S)-isobornyl, (1R)-menthyl, (1R)-fenchyl} the Cp-ligand is only η5-coordinated; all attempts to provoke a bidentate, Cp/O coordination were unsuccessful. The sulfide complex [Ru{η5:η1-C5H4CH2CH2S[(1R)-neomenthyl]}(PPh3)2][OTf] contains a bidentate Cp/S-coordinated ligand, but it is unstable. The stable phosphane complex [RuCl(η5:η1-C5H4CH2CH(Me)PPh2)(PPh3)] exists as a 77:23 mixture of diastereomers containing a strongly bidentate Cp/P ligand. The diastereomers interchange, with Ru-Cl bond cleavage as the rate-determining step.Supporting information for this article is available on the WWW under http://www.wiley-vch.de/contents/jc_2005/1999/99126_s.pdf or from the author.
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  • 245
    Digitale Medien
    Digitale Medien
    A Boron-Boron Double Bond in the Dianions of Tetra(amino)diborates (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 1931-1937 
    Details
    ISSN: 1434-1948
    Schlagwort(e): Diboron compounds ; B-B double bond ; Dilithium tetra(amino)diborates(2-) ; Structure elucidation ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: A series of mixed tetraaminodiborane(4) compounds bearing pyrrolyl, indolyl, and carbazolyl substituents besides dimethylamino groups has been prepared and subjected to reduction with elemental Li in the presence of diethyl ether. Tetraaminodiborates(2-) are formed, which feature a boron-boron double bond. The diborate anion acts as a double bidentate ligand coordinating pairwise through two of its nitrogen atoms to an Li center, which is tricoordinated by one O and the two N atoms. The new diborates are isoelectronic with tetraaminoethylenes and are expected to be electron-transfer reagents.
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  • 246
    Digitale Medien
    Digitale Medien
    The Interpretation of the Terminal ν(CO) Spectra of Some Tetranuclear Carbonyl Clusters (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 1957-1963 
    Details
    ISSN: 1434-1948
    Schlagwort(e): Cluster compounds ; Vibrational spectroscopy ; Spherical harmonics ; Carbonyl complexes ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The recently suggested spherical (SHM) and tensor (THM) harmonic models are applied to the interpretation of the terminal ν(CO) spectra of twenty six tetrahedral transition metal clusters containing between four and twelve terminal carbonyl groups. Although the SHM is perhaps the more generally relevant, there are species for which the THM is appropriate as a first approximation. The distinction between the two appears to be associated with a disruption of the band structure of the cluster either by the introduction of heterometal atoms or by the presence of a group - acetate ester, halide or hydride - presumably acting as an electronegative substituent.
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  • 247
    Digitale Medien
    Digitale Medien
    Efficient and Selective Photochemical Labilization of a Given Bidentate Ligand in Mixed Ruthenium(II) Complexes of the Ru(phen)2L2+ and Ru(bipy)2L2+ Family (L = Sterically Hindering Chelate) (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 383-386 
    Details
    ISSN: 1434-1948
    Schlagwort(e): Ruthenium ; Photochemistry ; Photosubstitution ; Diimine chelates ; Sterically hindered ligands ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Mixed ruthenium(II) complexes containing 1,10-phenanthroline (or 2,2′-bipyridine) and a sterically congested bidentate ligand such as 2,9-diphenyl-1,10-phenanthroline, 6,6′-dimethyl- or 6,6′-diphenyl-2,2′-bipyridine, or 1-(2′-pyridyl)-3,5-dimethylpyrazole undergo clean and selective ligand substitution under irradiation with visible light. For instance, Ru(phen)2(dmbp)2+ in CH3CN is quantitatively converted to Ru(phen)2(CH3CN)22+ in a photochemical reaction accompanied by expulsion of the sterically hindering chelate dmbp (phen = 1,10-phenanthroline; dmbp = 6,6′-dimethyl-2,2′-bipyridine). Interestingly, 2,2′-bipyridine was found to be photochemically ejected in one case, probably as a consequence of its greater flexibility.
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  • 248
    Digitale Medien
    Digitale Medien
    Syntheses, Structures, and Coordination of Diborylbipyridines and Bipyridinediborates (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 393-398 
    Details
    ISSN: 1434-1948
    Schlagwort(e): Boranes ; Bipyridine ; Crystal structures ; Donor-acceptor interaction ; Heterocycles ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: 6,6′-Bis(diethylboryl)-2,2′-bipyridine (1a) was obtained in low yield by in situ deprotonation of 2,2′-bipyridine in the presence of diethyl(methoxy)borane. 6,6′-Dilithio-2,2′-bipyridine reacts with various alkoxyboranes leading to bipyridinediborates 2 in good yields. The derivatives 2b and 2c allow the formation of the free diborylbipyridines 1b and 1c. The coordination properties of the diboryl-bipyridines as tetrafunctional donor-acceptor compounds have been used for the formation of the copper complex 4 and of the adduct 5 which is built from diborylbipyridine and a dihydroxydiboroxan derivative. The composition of the products follows from spectroscopic data and from X-ray structure analyses for 2f, 4, and 5.
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  • 249
    Digitale Medien
    Digitale Medien
    Addition of Stabilized Carbanions to Cationic (η6-Arene)tricarbonylmanganese Complexes: Syntheses of Homo (Mn-Mn) and Hetero (Mn-Cr) Dinuclear Complexes (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 421-433 
    Details
    ISSN: 1434-1948
    Schlagwort(e): Arene complexes ; Chromium ; Cyclohexadienyl complexes ; Dinuclear complexes ; Manganese ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The reaction of secondary α-cyano or α-sulfonyl carbanions with cationic (η6-arene)tricarbonylmanganese complexes affords neutral mono- and dinuclear tricarbonyl(η5-cyclohexadienyl)manganese complexes. The X-ray analyses of three (η5-cyclohexadienyl)Mn complexes (two mononuclear and one dinuclear) obtained by addition of α-cyano carbanion to cationic (η6-arene)manganese complexes are reported. The addition of benzylic carbanions of (η6-arene)tricarbonylchromium complexes to cationic (η6-arene)manganese complexes gives rise to the formation of the corresponding heterodinuclear [(η5-cyclohexadienyl)manganese-(η6-arene)chromium] complexes.
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  • 250
    Digitale Medien
    Digitale Medien
    Synthesis, Structure, Electrochemistry and Reactivity of the Bis(μ-σ-stannanediyl)dinickel Butterfly Cluster [{{(SiMe3)2CH}2Sn-Ni(η5-Cp)}2](Ni2-Sn2) (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 1987-1993 
    Details
    ISSN: 1434-1948
    Schlagwort(e): Cluster ; Nickel ; Tin ; Bimetallic complexes ; Electrochemistry ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Addition of stannylene [{(SiMe3)2CH}2Sn:] (2) to the unbridged homobimetallic Ni-Ni bond of [{PEt3Ni(η5-Cp)}2] (1) gives the heterobimetallic, tetranuclear compound [{{(SiMe3)2CH}2Sn-Ni(η5-Cp)}2] (3) with a butterfly arrangement and leaves the Ni-Ni bond of 1 intact. Elimination of both PEt3 ligands from the starting material 1 is observed, probably due to steric restraints. Compound 3 is formally related to the hypothetical closo-borane B4H42-. The Ni-Ni bond in 3 is only slightly elongated [2.454(3) Å] when compared to the starting material 1 [2.41(1) Å]. Compound 3 displays a butterfly arrangement with a hinge angle of 62.5°. An alternative route to 3 is by a direct reaction between nickelocene (5) and Lappert's stannylene [{(SiMe3)2CH}2Sn:] in 63% yield. Treating 3 with water results in the cleavage of an Ni-Sn bond and subsequent opening of the cluster cage of 3 to form the trinuclear compound [(η5-Cp)Ni{Sn(CH(SiMe3)2}2OH] (6) having an Sn-OH-Sn bridge. The hydroxy proton in 6 can be exchanged by deuterium within a few minutes, as determined by 1H-NMR spectroscopy, giving the monodeuterio product, [D1]-6. Compound 6 is reactive towards acetonitrile, leading to cleavage of one Ni-Sn bond, elimination of one [{(SiMe3)2CH}2Sn:] unit, and formation of the organotin hydroxo complex [{(SiMe3)2CH}2(OH)Sn-Ni(η5-Cp)(CH3CN)] (7). In this complex, acetonitrile is coordinated to Ni via its σ lone pair, bearing the OH ligand in a terminal bonding mode to tin.
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  • 251
    Digitale Medien
    Digitale Medien
    Difluorosilanethione F2Si=S by Flash Vacuum Thermolysis of (F3Si)2S and by Reaction of SiS with F2 - Matrix Studies and Ab initio Calculations (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 2013-2019 
    Details
    ISSN: 1434-1948
    Schlagwort(e): Ab initio calculations ; Flash pyrolysis ; Matrix isolation ; Silicon ; Multiple bonds ; IR spectroscopy ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Difluorosilanethione F2Si=S (1) has been synthesized by Flash Vacuum Pyrolysis of (F3Si)2S at ≥ 500 °C and trapped in an Ar matrix. Furthermore, 1 has been obtained by co-deposition of SiS and F2/Ar and by pyrolysis of a matrix-isolated SiS2-XeF2 complex under cryogenic conditions. All six vibrational fundamentals of 1 have been observed in the matrix IR spectrum. Ab initio calculations at the MP2 and CCSD(T) levels using large basis sets have been performed. These calculations have guided the detection of 1 and the vibrational assignment. The best estimate of the structure of 1 with C2v symmetry is: r(Si=S) 191.1(1) pm, r(SiF) 156.1(1) pm, ki(FSiF) 103.3(2)°.
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  • 252
    Digitale Medien
    Digitale Medien
    Photochemical Synthesis and Reactivity of New Chloro-Bridged Complexes with Tungstenocene (η5-C5H5)(η5-C5H4PPh2)WClX (X = H, Cl) and Tetracarbonylmetal (Cr, W) Units (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 2029-2035 
    Details
    ISSN: 1434-1948
    Schlagwort(e): Tungsten ; Sandwich complexes ; Bimetallic compounds ; Carbonyl complexes ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Chloro-bridged bimetallic complexes (η5-C5H5)[η5-C5H4PPh2M′(CO)4]W(μ-Cl)X [X = Cl (3), × = H (4); M′ = Cr, W] were prepared by photochemical irradiation of (η5-C5H5)[η5-C5H4PPh2M′(CO)5]WClX [X = Cl (1), × = H (2); M′ = Cr, W]. The reactivity of the chloro-bridged complexes towards Lewis bases was studied; by exposure to CO or phosphanes, a facile cleavage of the chloro bridge accompanied by regio- and stereospecific coordination at M′ occurs. The X-ray structure of complex 3 (M′ = W) is reported.
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  • 253
    Digitale Medien
    Digitale Medien
    The Lewis Basicity of Diaminocarbene - A Theoretical Study of Donor-Acceptor Complexes of C(NH2)2, NH3 and CO with the Lewis Acids EF3, ECl3 (E = B, Al, Ga, In), TiF4 and TiCl4 (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 2037-2045 
    Details
    ISSN: 1434-1948
    Schlagwort(e): Diaminocarbenes ; Lewis basicity ; Ab initio calculations ; Donor-acceptor complexes ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Quantum chemical calculations at the MP2 level using large valence basis sets up to TZ+2P quality have been carried out in order to predict the geometries and bond energies of the title compounds. The nature of the donor-acceptor bond has also been investigated. The calculations show clearly that diaminocarbenes are much stronger Lewis bases than amines. The complexation energies of C(NH2)2 have been calculated to be 14-27 kcal/mol higher than those of NH3. The most strongly bonded complex is Cl3Al-C(NH2)2, which has a theoretically predicted Al-C bond energy Do = 59.1 kcal/mol. In all the complexes, the strength of the Lewis bases is C(NH2)2 〉 NH3 〉 CO, but the ordering of Lewis acid strength of EX3 depends on the coordinated Lewis base. TiF4 and TiCl4 have similar Lewis acidities as BF3, but the titanium tetrahalides may bind one or two donor molecules with almost the same bond strength. The investigated donor-acceptor bonds have a high degree of ionic character. The largest covalent contributions are found for the diaminocarbene complexes. The covalent character of the X3E-CO bond increases on going from E = boron to the heavier Group 13 elements, while the opposite order is found for the X3E-NH3 and X3E-C(NH2)2 bonds.
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  • 254
    Digitale Medien
    Digitale Medien
    Synthesis and Nonlinear Optical Properties of Carbonylrhenium Bromide Complexes with Conjugated Pyridines (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 483-490 
    Details
    ISSN: 1434-1948
    Schlagwort(e): Rhenium ; N Ligands ; Nonlinear optics ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Carbonylrhenium bromide complexes fac-Br(OC)3ReL2 (3a,b, 4a,b) and cis-Br(OC)4ReL (5a,b) with conjugated pyridines L = Fc-CH=CH-p-C5H4N (1a), Fc-CH=CHC(CH3)=CHCH=CHCH=C(CH3)CH=CH-p-C5H4N (1b), 1,1′-Fc(-CH=CH-p-C5H4N)2 (1c), p-Me2N-C6H4-CH=CHCH=CH-p-C5H4N (2a), and p-Me2N-C6H4-CH=CHC(CH3)=CHCH=CHCH=C(CH3)-CH=CH-p-C5H4N (2b) have been synthesized. The structures of 4a and 5a have been determined by X-ray diffraction analysis. Compound 4a exhibits a remarkable quadratic hyperpolarizability.
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  • 255
    Digitale Medien
    Digitale Medien
    Synthesis and Structure of 2-Hydro-, 2-Alkyl-, 2-Alkynyl-, and 2-Stannyl-2,3-dihydro-1H-1,3,2-diazaboroles (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 491-497 
    Details
    ISSN: 1434-1948
    Schlagwort(e): Boron ; Diazaboroles ; Hydrides ; Tin ; Heterocycles ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: 1,3-Di-tert-butyl-2,3-dihydro-1H-1,3,2-diazaborole (4a) and 1,3-bis(2,6-dimethylphenyl)-2,3-dihydro-1H-1,3,2-diazaborole (4b) were formed by the reaction of the corresponding 2-bromo or 2-iodo derivatives 1a and 2b with LiAlH4. Treatment of 1a with n-butyllithium afforded 2-n-butyl-1,3-di-tert-butyl-2,3-dihydro-1H-1,3,2-diazaborole (5a), whereas 1,3-di-tert-butyl-2-cyano-2,3-dihydro-1H-1,3,2-diazaborole (3a) was converted into the 2-tert-butyl derivative 6a or the 2-ethynyl-1,3,2-diazaborole 7a by means of tert-butyllithium or by the ethylenediamine adduct of lithium acetylide. Similarly, 1,3-di-tert-butyl-2-trimethylstannyl-2,3-dihydro-1H-1,3,2-diazaborole (8a) and 1,3-bis(2,6-dimethylphenyl)-2-trimethylstannyl-2,3-dihydro-1H-1,3,2-diazaborole (8b) were accessible from 1a or 2b and trimethylstannyllithium. In the complex 9a the compound 3a serves as an η1 ligand towards the [Cr(CO)5] unit via the cyano group. These novel compounds were characterized by 1H-, 11B-, 13C-, and 119Sn-NMR spectroscopy, as well as by X-ray structure analyses of 4b, 8a, and 9a.
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  • 256
    Digitale Medien
    Digitale Medien
    Bis(dipeptide ester-H+) Complexes of Palladium(II) - Precursors for the Formation of Cyclotetrapeptides (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 465-469 
    Details
    ISSN: 1434-1948
    Schlagwort(e): Dipeptide ester ; Cyclic tetrapeptides ; Palladium complexes ; Coordination chemistry ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: trans-Bis(dipeptide ester)palladium 1-6 complexes with a deprotonated amide group were obtained by dehydrochlorination of trans-Cl2Pd(dipeptide ester)2 or by direct reaction of Na2PdCl4 with dipeptide ester in the presence of sodium methoxide. The structure of Pd(NH2CH2CONCH2CH2CO2CH3)2 (3) was determined by X-ray diffraction. Addition of NaOCH3 to Pd[NH2C(H)(R)NCH2CH2CO2CH3]2 [R = CH(CH3)24, CH2Ph 5] results in the formation of the corresponding complexes 7, 8 with cyclic tetrapeptides which also can be directly synthesized from the dipeptide ester and Na2PdCl4.
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  • 257
    Digitale Medien
    Digitale Medien
    Cinchona Alkaloids as Versatile Ambivalent Ligands - Coordination of Transition Metals to the Four Potential Donor Sites of Quinine (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 471-482 
    Details
    ISSN: 1434-1948
    Schlagwort(e): Quinine ; Cinchonine ; Palladium ; Platinum ; Silver ; Gold ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: A series of metal complexes in which quinine (L1) and cinchonine (L2) are coordinated via the four possible donor atoms was prepared and characterized. Coordination of the tertiary N atom of quinine is observed in [L1MPPh3]+NO3- [M = Au (1), Ag (2)], [L1Pd(COD)(Cl)]+ NO3- (3) and L1Pd(Cl)(allyl) (4). The mono anion of quinine functions as N,O chelate ligand in (L1-H+)M(Cl)(PR3) (M = Pd, Pt, 5-10), [(L1-H+)Pd(en)]+NO3- (11) and (L1-H+)2TiCl2 (12). Protection of the tertiary N atom of quinine by methylation or protonation allows the synthesis of the quinoline complexes [(L1CH3+)M(Cl)2(PR3)]+ BF4- (M = Pd, Pt, 14-18), [(L1CH3+)Ir(Cl)2(Cp*)]+ BF4- (19), [(L1+H+)M(Cl)2(PR3)]+ CF3SO3- (M = Pd, Pt, 20-22) and (L2+H+)(ZnCl3-) (23). Quinine and cinchonine act as N,O-N bridge in the complexes (R3P)(Cl)M(μ-L1-H+)M(Cl)2(PR3) (M = Pd, Pt, 24, 25, 27, 28), (Cp*)(Cl)Ir(μ-L1-H1)Ir(Cl)2(Cp*) (29), (EtP3)(Cl)Pd(μ-L2-H+)Pd(Cl)2(PEt3) (26), and as N-N bridge in the complexes [(Ph3P)Au(μ-L1)Au(PPh3)]+NO3- (30) and (allyl)(Cl)Pd(μ-L1)Pd(Cl)(allyl) (31). Coordination of quinine via the C=C double bond occurs in [(L1+2 H+)PtCl3]+Cl- (32). The structures of 11, 13, 19, 23, 26 and 32 were determined by X-ray diffraction. In most cases the coordination mode and the conformation of quinine can also be derived from the 1H-NMR spectra.
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  • 258
    Digitale Medien
    Digitale Medien
    Reactions of 1,8-Diheterocyclotetradeca-4,11-diynes with (η4-Cycloocta-1,5-diene)(η5-cyclopentadienyl)cobalt (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 499-504 
    Details
    ISSN: 1434-1948
    Schlagwort(e): Alkynes ; Heterocycles ; Cyclizations ; Cobalt ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The following monocyclic and bicyclic 14-membered diynes were treated with [CpCo(cod)]: 1-oxacyclotetradeca-4,11-diyne (2), 1,8-dioxacyclotetradeca-4,11-diyne (3), cyclotetradeca-4,11-diynone (4), cyclotetradeca-4,11-diyne-1,8-dione (5), 1,1,8,8-tetramethyl-1,8-disilacyclotetradeca-4,11-diyne (6), 1-allyl-1-azacyclotetradeca-4,11diyne (7), 1,8-dipropyl-1,8-diazacyclotetradeca-1,11-diyne (8), 1,8-diallyl-1,8-diazacyclotetradeca-4,11-diyne (9), 1,8-diazabicyclo[6.6.4]octadeca-4,11-diyne (10), 1,8-diazabicyclo[6.6.6]eicosa-4,11-diyne (11), 1,10-diazabicyclo[8.6.6]docosa-13,19-diyne (12) and 1,12-diazabicyclo[10.6.6]tetracosa-15,21-diyne (13). In all cases we obtained an intramolecular cyclobutadiene complex stabilized with a CpCo fragment (15-26). For 3 we could isolate, besides the cyclobutadiene complex 16, the trimerization product 28. In the cases of 15, 16, 18, 20, 23, 25, and 26 the structure of the cylobutadiene complexes could be confirmed by X-ray studies. Common to all structures is a boat-like conformation of the tricyclic unit containing the cyclobutadiene ring. The two cycloheptene units adopt a chair conformation in which the heteroatom is removed from the metal center.
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  • 259
    Digitale Medien
    Digitale Medien
    A Dimeric Tetranuclear Copper(II) Compound Assembled through Pentacoordinating Carbonate Anions (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 505-507 
    Details
    ISSN: 1434-1948
    Schlagwort(e): Macrocycle ; Pyrazole ; N-Heterocycle ; Carbonate ; Copper ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The 22-membered macrocycle, spanning four endocyclic pyrazole groups, viz. 1,4,9,14,17,22,27,28,29,30-decaaza-5,13,18,26-tetramethylpentacyclo[24.2.1.14,7.111,14.117,20]triacontane-5,7(28),11(29),12,18,20(30),24(27),25-octaene (22Pz), rendered the tetranuclear compound [Cu4(22Pz)2(CO3)2(MeOH)2](ClO4)4(MeOH)4. The copper(II) ions are in distorted octahedral N3O3 environments. All four pyrazole groups of each macrocycle participate in the coordination of the copper(II) ions. The cationic part of this compound is in fact a dimer of two macrocyclic ligands, each containing two copper(II) ions bridged by two carbonate ions in the highly unusual pentacoordinating fashion.Supporting information for this article is available on the WWW under http://www.wiley-vch.de/contents/jc_2005/1999/98332_s.pdf or from the author.
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  • 260
    Digitale Medien
    Digitale Medien
    Characterization of Palladium(II) Azide and Crystal Structure of Bis(azido)bis(pyridine)palladium(II) and Tetramminepalladium Tetraazidopalladate(II) (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 523-526 
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    ISSN: 1434-1948
    Schlagwort(e): Palladium ; Azide ; Pyridine ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Palladium(II) azide (1) was synthesized by reaction of palladium nitrate and sodium azide. 1 was characterized by AAS, IR, and 14N-NMR spectroscopy. Bis(azido)bis(pyridine)palladium(II) (2) and tetramminepalladium tetraazidopalladate(II) (3) were synthesized by a high-yield reaction. Both were characterized by X-ray structural analysis, IR, Raman, and NMR spectroscopy.
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  • 261
    Digitale Medien
    Digitale Medien
    The Structures of a Tetracarba-nido-octaborane(8) and a Novel Spiro Derivative of a 2,3,5-Tricarba-nido-hexaborane(7) (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 533-537 
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    ISSN: 1434-1948
    Schlagwort(e): Ab initio calculations ; Carboranes ; NMR ; X-ray analysis ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Hydroboration of bis(diethylboryl)ethyne (1) with tetraethyldiborane(6) leads to a B-ethyl-substituted tetracarba-nido-octaborane 2, a spiro-carborane 3, which belongs to the 2,3,5-tricarba-nido-carborane family, and a hexacarba-arachno-dodecaborane(12) 4, along with polymeric material. The X-ray structure analysis of carborane 2, determined here, is fully consistent with the structure deduced earlier from NMR data. The structure of 3 in solution was established by theoretical analysis of its NMR data. Ab initio calculations of the structures of 2b and 3b (b denotes the B-metyhl-substituted derivatives) and the comparison of calculated with experimental NMR data support the suggested structures of 2 and 3 in solution. The calculated structure of the carborane cage of 2a also agrees with the experimental geometry of 2.
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  • 262
    Digitale Medien
    Digitale Medien
    Transition Metal Ions in Microporous Crystalline Aluminophosphates: Isomorphous Substitution (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 565-577 
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    ISSN: 1434-1948
    Schlagwort(e): Microporous crystalline aluminophosphates ; Isomorphous substitution ; Synthesis ; Spectroscopy ; Heterogeneous catalysis ; Transition metal ion ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Microporous crystalline metalloaluminophosphates (MeAPO-n) represent an important group of molecular sieves because of their potential catalytic and adsorptive properties. Many transition metal ions are claimed to incorporate in the framework of these molecular sieves. Here, the concept of isomorphous substitution, and the different indirect and direct tools available to verify this substitution process for Co, Cr, V, Fe and Mn are reviewed taking the AlPO4-5 structure as an example. In addition, it will be shown that transition metal ions can be used as a probe to follow the hydrothermal synthesis process of microporous aluminophosphates.
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  • 263
    Digitale Medien
    Digitale Medien
    Synthesis of Two Acridine Conjugates of the Bis(phenanthroline) Ligand “Clip-Phen” and Evaluation of the Nuclease Activity of the Corresponding Copper Complexes (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 557-563 
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    ISSN: 1434-1948
    Schlagwort(e): Bioinorganic chemistry ; Copper ; DNA cleavage ; Intercalation ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The synthesis of three novel derivatives [N-acetyl-Clip-Phen (1), Clip-Phen-hexylaminoacridine (4) and Clip-Phen-hexylchloromethoxyaminoacridine (5)] of the bis(phenanthroline) ligand “Clip-Phen”, are described. Complexation of these ligands with copper(II) afforded the 1:1 complexes as hexafluorophosphate salts. The relaxation of φX 174 DNA was used as a DNA cleavage assay, with the following results. [Cu(1)]2+ was found to show a diminished activity relative to the parent complex [Cu(Clip-Phen)]2+. However, the acridine-containing complexes [Cu(4)H]3+ and [Cu(5)H]3+ exhibited significantly enhanced cleavage efficiencies, which has been attributed to increased affinity of the complexes for DNA. UV/Vis-spectral data of the complexes in the presence of calf-thymus DNA was consistent with an intercalative mode of binding.
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  • 264
    Digitale Medien
    Digitale Medien
    A Heteroleptic Diplumbene and a Magnesium Dibromide Stabilized Plumbylene Dimer (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 579-582 
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    ISSN: 1434-1948
    Schlagwort(e): Lead ; Plumbylenes ; Plumbanediyles ; Diplumbene ; Plumbylene dimers ; Double-bond systems ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Treatment of the diarylplumbylene R2Pb: (R = 2,4,6-iPr3C6H2) with the disilylplumbylene R′2Pb: [R′ = Si(SiMe3)3] furnishes the heteroleptic plumbylene RR′Pb: which exists as the diplumbene RR′Pb=PbRR′ (7) in the solid state. The X-ray structure analysis of 7 reveals a trans-bent angle of 42.7° and a Pb-Pb bond length of 298.99(5) pm, the shortest observed so far for diplumbenes with a lead-lead double bond. Reaction of mesitylmagnesium bromide with PbCl2 yielded black crystals of an MgBr2 stabilized dimesitylplumbylene dimer with a large trans-bent angle of 71°, a lead-lead separation of 335.49(6) pm, and long Pb···Br contacts of 315.71(8) pm.
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  • 265
    Digitale Medien
    Digitale Medien
    Solubility and Solvation of Carbon Dioxide in the Molten Li2CO3/Na2CO3/K2CO3 (43.5:31.5:25.0 mol-%) Eutectic Mixture at 973 K I. Experimental Part (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 583-588 
    Details
    ISSN: 1434-1948
    Schlagwort(e): Dicarbonate ion ; Autodissociation constant ; Electrochemistry ; Potentiometric titration ; Acidity ; Basicity ; Anions ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The solubility of CO2 in the molten ternary eutectic mixture Li2CO3-Na2CO3-K2CO3 (43.5, 31.5, 25.0 mol.%) at 973 K has been determined by a titration technique. From the obtained titration curve, the solubility has been found to amount to 9.5·10-2 mol·L-1 (σ= 1.0) under a pressure of CO2 of 1 atm and the pKd value of the carbonate melt has been evaluated to 5.37 (σ5 = 0.24) if the concentrations of the solutes are expressed in mol·L-1. This pKd value is in good agreement with literature data but the solubility value reported in this work is much higher than most of those reported in the literature. A chemical dissolution of CO2 as C2O52- is proposed and the consequences of the occurrence of this species on the acidobasic properties of molten carbonates are discussed. It appears from the experimental results that the CO2/C2O52- equilibrium in the carbonate melt is a slow process.
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  • 266
    Digitale Medien
    Digitale Medien
    N-Thiophosphorylated and N-Phosphorylated Iminophosphoranes [R3P=N-P(X)R′2; × = O, S] as Models for Dendrimers: Synthesis, Reactivity and Crystal Structures (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 601-611 
    Details
    ISSN: 1434-1948
    Schlagwort(e): Phosphorus ; Ferrocenes ; Phosphorylated iminophosphoranes ; Dendrimers ; Cations ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Several R3P=N-P(X)R′2 and Fe[C5H4Ph2P=N-P(X)R′2]2 derivatives (X = S, O) are readily obtained from Staudinger reactions between phosphanes and N3-P(X)R′2. The P=N-P=X groups are easily alkylated on the × atom with methyl or isopropyl triflates. The alkylation induces a lengthening of the P-X bond, as shown by X-ray diffraction studies. This corresponds to a weakening of the P-X bond which can be cleaved with P(NMe2)3 to yield [P=N-P:] linkages. The presence of tricoordinated phosphorus atoms opens the way to a versatile reactivity, including the reaction with alkyl iodides and functionalized azides. These molecules are good models for screening which types of reagents and reactions could be used with macromolecules possessing also P=N-P=X linkages, such as dendrimers.
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  • 267
    Digitale Medien
    Digitale Medien
    Syntheses and Insertion Reactions of (η2-Aldehyde)zirconocene-Supported (Hydrido)zirconocene Cation Systems (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 621-632 
    Details
    ISSN: 1434-1948
    Schlagwort(e): (η2-Aldehyde)zirconocene complexes ; Metallaoxirane-stabilized group 4 metallocene hydride cations ; Nitrile insertion ; Isocyanate insertion ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Treatment of the [Cp2Zr(η2-acetaldehyde)/H(CH3)ZrCp2] adduct 8 with B(C6F5)3 yields the dimetallabicyclic salt [Cp2Zr(μ-η1-O:η2-C,O-OCHMe)(μ-H)(ZrCp2)]+[CH3B(C6F5)3]-18b. Similarly, hydride abstraction from the related neutral dimetallabicyclic [Cp2Zr(OCHR)/H2ZrCp2] adducts 11 (R = CH3) or 14 (R = C2H5) with B(C6F5)3 yields the systems [Cp2Zr(μ-η1-O:η2-C,O-OCHR)(μ-H)(ZrCp2)]+[HB(C6F5)3]- (18a, c) and the reaction of B(C6F5)3 with [Cp2Zr(OCHCH2Ph)/H(PhCH2)ZrCp2)]+17 gives [Cp2Zr(μ-η1-O:η2-C,O-(OCHCH2Ph)(μ-H)ZrCp2]+[PhCH2B(C6F5)3]-18d. A variety of nitriles R2-C≡N (R = CH3, CMe3, p-tolyl, or ethyl) cleanly reacts with the cations 18 by addition of the Zr2(μ-H) moiety to the nitrile functionality to yield the respective aldiminium-bridged cations [Cp2Zr(μ-η1-O:η2-C,O-(OCHR1)(μ-N=CHR2)ZrCp2]+ (21-24). Complex 24d (R1 = PhCH2, R2 = C2H5) was characterized by an X-ray crystal structure analysis. Similarly, treatment of the systems 18a-d with isocyanates RN=C=O (R = CMe3, SiMe3, p-tolyl, or adamantyl) gave the related μ-formamidato complexes 27-30.
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  • 268
    Digitale Medien
    Digitale Medien
    Kinetics and Mechanism of Base Hydrolysis in Cobalt(III) Complexes - The Case of a Complex CoLCl2+ where L has the Novel Topology of a Square-Pyramidal NN4 Coordination Cap (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 643-650 
    Details
    ISSN: 1434-1948
    Schlagwort(e): Cobalt(III) complexes ; Tetrapodal pentadentate ligand ; Hydrolysis ; Kinetics ; Mechanism ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Multi-wavelength stopped-flow spectrophotometry was used to study the kinetics of base hydrolysis of the octahedral cobalt(III) complex CoLCl2+ (2), in which the tetrapodal pentadentate ligand L has an NN4 donor set and forms a square-pyramidal coordination cap [L = 2,6-bis(1′,3′-diamino-2′-methylprop-2′-yl)pyridine, 1]. The kinetic investigation, carried out at different temperatures, pressures and ionic strengths I, led to second-order kinetics, rate = kOH [2][OH-], with kOH = 0.139 ± 0.001 M-1s-1 (I = 0.1 M) and kOH = 0.0570 ± 0.0004 M-1s-1 (I = 1.0 M) at 298 K. The temperature and pressure dependence of kOH resulted in ΔH
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  • 269
    Digitale Medien
    Digitale Medien
    Structural Characterization and Magnetic Behaviour of the Ferro-Antiferromagnetic Alternating Manganese-Azido Chain [Mn(3-Et,4-Mepy)2(μ-N3)2]n (3-Et,4-Mepy = 3-Ethyl-4-methylpyridine) (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 687-691 
    Details
    ISSN: 1434-1948
    Schlagwort(e): Bridging ligands ; Manganese ; Azido bridge ; Alternating chain ; Magnetic properties ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The ligands 3-ethyl-4-methylpyridine (3-Et,4-Mepy) and azide coordinate to MnII forming an alternating chain with the formula [Mn(3-Et,4-Mepy)2(μ-N3)2]n. This compound crystallizes in the space group P-1. The compound consists of chains of octahedrally coordinated manganese atoms alternately bridged by double end-to-end (μ1,3) and double end-on (μ1,1) azido bridges, which results in a structurally and magnetically alternating chain. The 3-ethyl-4-methylpyridine ligands are arranged trans, completing the six-fold coordination spheres of the manganese atoms. The Mn-Mn distances are distinctly different: Mn(1)-Mn(1A) = 5.149(3) Å (double end-to-end azido bridge) and Mn(1)-Mn(1B) = 3.402(2) Å (double end-on azido bridge). The magnetic properties of the compound, as studied in the temperature range 300-4 K, show bulk antiferromagnetic interaction. Fitting of the magnetic data by using an equation for alternating ferro-antiferromagnetic S = 5/2 1-D systems gives the parameters JAF = -13.7(1) cm-1, JF = 2.4(1) cm-1, g = 2.036(2).
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  • 270
    Digitale Medien
    Digitale Medien
    Cage-Structured Triplatinacyclophanes (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 679-685 
    Details
    ISSN: 1434-1948
    Schlagwort(e): Cage compounds ; Metallacyclophanes ; P ligands ; Platinum ; Supramolecular chemistry ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The synthesis of the tris(triflate) 4 (Scheme 1) has been achieved by means of a straightforward three-step reaction sequence. After initial lithiation of mesitylene, treatment of the obtained trilithium compound C6H3(CH2Li)3 (2) with oxirane results in the formation of 1,3,5-tris(3-hydroxypropyl)benzene (3), which is then transformed to 4 by reaction with (CF3SO2)2O in the presence of pyridine. Whereas 4 reacts with Na2[Os(CO)4] in a somewhat complicated manner, similar reactions with Na[Re(CO)5] and LiPPh2 give the hydrocarbon-bridged tris(rhenium) complex C6H3[(CH2)3Re(CO)5]3 (5) and the tris(phosphane) C6H3[(CH2)3PPh2]3 (6), respectively. Employing the high-dilution method, from 6 and Cl2Pt(NCPh)2 the nanoscaled tri- and hexaplatinacyclophanes 7 and 9 are available. Owing to the optimal geometry and flexibility of the cage in 7, 1,2-dichloroethane can be reversibly encapsulated. The molecular structure of 7 · 7 1,2-Cl2C2H4 was determined by an X-ray structure analysis. The utility of the reactive metal centers in 7 has been demonstrated by replacing the chloro ligands by acetonitrile to give the cationic platinacyclophane 8, in which, according to NMR studies, the cage-like structure is preserved.
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  • 271
    Digitale Medien
    Digitale Medien
    New Rare-Gas-Containing Neutral Molecules (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 729-737 
    Details
    ISSN: 1434-1948
    Schlagwort(e): Ab initio calculations ; Matrix isolation ; Rare-gas compounds ; Solid-state chemistry ; Photochemistry ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The synthesis of novel neutral rare-gas-containing molecules of type HXY, where × = Xe or Kr and Y is an electronegative atom or fragment, is discussed. The molecules are characterised experimentally by their vibrational spectra and computationally by extensive ab initio calculations. They are formed in low-temperature rare-gas solids from neutral reagents and their bonding consists of both covalent and ionic contributions. Our recent studies add to the previously known class of rare-gas chemical bonds in neutral ground-state molecules the new bonds Xe-H, Xe-I, Xe-Br, Xe-S, Kr-H, Kr-C, and Kr-Cl.
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  • 272
    Digitale Medien
    Digitale Medien
    Synthesis and Homomolecular Metalation of Trialkylsilylphosphanides of Calcium and Barium (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 743-750 
    Details
    ISSN: 1434-1948
    Schlagwort(e): Arsenic ; Barium ; Calcium ; Metalations ; NMR spectroscopy ; Phosphorus ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Metalation of triisopropylsilylphosphane with bis(tetrahydrofuran-O)calcium bis[bis(trimethylsilyl)amide] in tetrahydropyran (thp) in a molar ratio of 3:2 yields (Me3Si)2NCa[μ-P(H)SiiPr3]3Ca(thp)3 (1) containing a trigonal-bipyramidal Ca2P3 core, the metal atoms occupying apical positions. Reaction of two equivalents of triisopropylsilylphosphane or -arsane with bis(tetrahydrofuran-O)barium bis[bis(trimethylsilyl)amide] in tetrahydrofuran gives the corresponding bis(phosphanide) 2 and bis(arsanide) 3, compounds of the type (thf)3Ba[μ-E(H)SiiPr3]Ba(thf)2E(H)SiiPr3 with E = P, As. The equimolar reaction of (tri-tert-butylsilyl)phosphane with (thf)2Ba[N(SiMe3)2]2 in toluene yields heteroleptic dimeric (thf)2Ba[N(SiMe3)2][P(H)SitBu3] (4). Addition of a further equivalent of H2PSitBu3 leads to the formation of homoleptic (thf)nBa[P(H)SitBu3]2 (5). Dissolution of the latter in aromatic hydrocarbons leads to the elimination of H2PSitBu3, yielding dimeric (thf)Ba3(PSitBu3)2[P(H)SitBu3]2 (6). The inner core of 6 consists of the tetramer (BaPSitBu3)4 based on a Ba4P4 heterocubane unit, two opposite faces being capped with (thf)Ba[P(H)SitBu3]2 molecules.
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  • 273
    Digitale Medien
    Digitale Medien
    Synthesis and Structures of cisoidand transoidBis(1,2-dimethoxyethane)bis(η2-pyrazolato)lanthanoid(II) Complexes (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 751-761 
    Details
    ISSN: 1434-1948
    Schlagwort(e): Lanthanide(II) complexes ; Ytterbium ; Europium ; Samarium ; Redox transmetallation ; Thallium ; Diphenylmercury ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The complexes [Yb(bind)2(DME)2], [Yb(MePhpz)2(DME)2], [Yb(azin)2(DME)2], and [Eu(Ph2pz)2(DME)2] (bindH = 4,5-dihydro-2H-benz[g]indazole; MePhpzH = 3-methyl-5-phenylpyrazole; azinH = 7-azaindole; Ph2pzH = 3,5-diphenylpyrazole; DME = 1,2-dimethoxyethane) have been prepared by redox transmetallation between ytterbium or europium metal and the corresponding thallium(I) pyrazolate in tetrahydrofuran (THF) in the presence of mercury metal, followed by work up with DME. The thallium reagents were obtained by treatment of the appropriate pyrazole with thallium(I) ethoxide. Both [Yb(Ph2pz)2(DME)2] and [Sm(Ph2pz)2(DME)2] have been prepared by metathesis from LnI2(THF)2 and K(Ph2pz) in THF, whilst the former has also been obtained by redox transmetallation from [Hg(Ph2pz)2] and ytterbium metal and by reaction of 3,5-diphenylpyrazole with Yb(C6F5)2, and the latter from protolysis of [Sm{N(SiMe3)2}2(THF)2] with Ph2pzH, followed in each case by crystallisation of the crude product from DME. Europium(II) 3,5-di-tert-butylpyrazolate was synthesised by a redox transmetallation/ligand exchange reaction between europium metal chunks, diphenylmercury(II), and 3,5-di-tert-butylpyrazole (tBu2pzH) in the presence of mercury metal in THF, and [Eu(tBu2pz)2(DME)2] was isolated on crystallisation of the crude product from DME. The X-ray crystal structures of [Ln(L)2(DME)2] (Ln =Yb, L = bind or azin; Ln = Eu or Sm, L = Ph2pz; Ln = Eu, L = tBu2pz), each of a different crystallographic form, reveal eight-coordinate lanthanoid complexes with two η2-pyrazolate and two chelating DME ligands, but the structures differ in the relationship (cisoid or transoid) between the pyrazolate ligands. Thus cen-Ln-cen (cen = centre of the N-N bond) angles of 106.7° [Yb(bind)2(DME)2] (3a), 141.4° [Yb(azin)2(DME)2] (3c), 142.2° [Eu(Ph2pz)2(DME)2] (4a), 107.4° [Eu(tBu2pz)2(DME)2] (4b), and 102.1° [Sm(Ph2pz)2(DME)2] (5) are observed.
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  • 274
    Digitale Medien
    Digitale Medien
    Metallocenes of Nb and Ta with η2-Se2H, SeH, and Se Ligands - Crystal Structures of [Cp′2Ta(SeH)H2] and [Cp′2Ta(=Se)H·W(CO)5] (Cp′ = tBuC5H4) (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 843-848 
    Details
    ISSN: 1434-1948
    Schlagwort(e): Metallocenes ; Hydroselenide ligands ; Selenium ; Se coordination chemistry ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The reactions of [Cp#2NbBH4] (1) [Cp# = C5Me5 (Cp*) or C5Me4Et] and [Cp′2TaH3] (Cp′ = tBuC5H4) with elemental selenium give complexes of the general composition [Cp2MSe2H]. These exist in three isomeric forms, A-C, depending on the metal and the chalcogen. [Cp#2NbSe2H] (2) incorporates the novel η2-Se2H ligand (C), which is labile when exposed to light. Solutions of 2(Cp*) can be converted into [Cp*2NbSe2H] (3), which exists in two isomeric forms A or B, along with [Cp*2NbSe3H] (4) and [Cp*2NbO2H] (5). [Cp′2Ta(η2-Se2)H] (6) is the only isomer found for the Ta system. Se abstraction by means of P(OEt)3 gives [Cp′2Ta(=Se)H] (7). Complex 7 can be reduced with Na/Hg and subsequently hydrolysed to give [Cp′2Ta(SeH)H2] (8), which has also been observed during the formation of 6. Coordination of [W(CO)5THF] at the Se lone pair of 7 affords the heterobimetallic complex 9. All compounds have been characterized by means of 1H- and, in some cases, 77Se-NMR spectroscopy. Products 8 and 9 have also been subjected to X-ray diffraction analysis.
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  • 275
    Digitale Medien
    Digitale Medien
    Synthesis and Single-Crystal X-ray Diffraction Studies on New Methylindium(III) Alkoxides (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 1343-1350 
    Details
    ISSN: 1434-1948
    Schlagwort(e): Indium ; O ligands ; N ligands ; C ligands ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: New heteroleptic indium compounds have been synthesized starting from indium(III) halides and hexamethyldisilazyllithium to form MeXInN(SiMe3)2 [X = Cl (1), Br (2)], and then subsequent alcoholysis to afford the molecules [ClMeIn(OtBu)]2 (3), [BrMeIn(OtBu)]2 (4), {ClMeIn[O(C6H4)OMe]}2 (5), {[(SiMe3)2N]MeIn(OtBu)}2 (6) and [MeIn(OtBu)2]2 (7). The molecular structures of molecules 3-7 have been obtained by single crystal X-ray diffraction studies. The structures of the compounds 3-7 are almost identical: 3-5 crystallize in the monoclinic crystal system with two dimeric molecules per unit cell in the space group P21/c, 6 crystallizes in the monoclinic space group C2/c with four molecules per unit cell, and compound 7 crystallizes in the triclinic crystal system with one dimeric molecule per unit cell in the space group P-1. The central centrosymmetric In2O2 ring, common to all the compounds, is achieved by two bridging oxygen atoms. Due to the additional coordination by an oxygen atom of the methoxy group, the coordination number of the metal center rises from 4 to “4+1” if the OtBu ligand (compounds 3, 4, 6, and 7) is exchanged for a methoxyphenol ligand (compound 5). In addition to the In2O2 ring the compound 5 possesses two annealed five-membered InO2C2 rings. The common indium methyl group of all compounds, which is transfered by an original route from the silicon to the indium atom, is used to compare structural and spectroscopic properties of the molecules, as there is a correlation between the In-C bond length and the chemical shift of the methyl group which depends on the ligand system used.
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  • 276
    Digitale Medien
    Digitale Medien
    Synthesis, Mesomorphism, and Spectroscopic Characterization of Bis[4-(n-alkoxy)-5-(p-n-tetradecylphenylazo)]-Substituted (N,N′-Salicylidenediaminato)nickel(II) Complexes (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 1367-1372 
    Details
    ISSN: 1434-1948
    Schlagwort(e): Metallomesogens ; Nickel ; Salicylidenediamines ; Azo compounds ; (E)/(Z) photoisomerization ; Isomerizations ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The bis[4-(n-CmH2m+1O)-5-(p-C14H29C6H4N=N)]-substituted N,N′-salicylidenediamines H2[LN(m,14)] (N = 1: 1,2-diaminoethane; N = 2: 1,3-diaminopropane; N = 3: 1,3-diamino-2,2-dimethylpropane; m = 6 or 18) have been synthesized. Both the N = 2 and 3 series of compounds display a smectic C (SmC) mesophase, with clearing points well below 100 °C. By treating the H2[LN(m,14)] ligands with an NiII salt, liquid crystalline mononuclear complexes with “unconventional” (lateral-tailed) molecular shape form. These Ni[LN(m,14)] complexes, showing nematic and smectic disordered phases, are stable over a quite large temperature range and have been characterized by different spectroscopic techniques. The newly synthesized mesogens exhibit lower transition temperatures and higher thermal stability than homologous complexes Ni[LN(14)] with a “conventional” rod-like molecular geometry.
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  • 277
    Digitale Medien
    Digitale Medien
    Synthesis, Crystal Structure, Spectroscopy, and Theoretical Investigations of Tetrahedrally Distorted Copper(II) Chelates with [CuN2S2] Coordination Sphere (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 1393-1403 
    Details
    ISSN: 1434-1948
    Schlagwort(e): Copper chelates ; EPR spectroscopy ; Electronic structure ; Schiff base ligands ; Structure elucidation ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: A series of tetrahedrally distorted copper(II) complexes with thiolate and imine coordination were synthesized. Schiff bases derived from 4-benzoyl-3-methyl-1-phenyl-2-pyrazoline-5-thione and various diamines were used as tetradentate ligands to obtain tetrahedrally distorted metal chelates with [CuN2S2] complex units. Crystal structures of the complexes 1, 2, 5 and 6 and of ligand H25 have been determined by means of single-crystal X-ray structure analysis. The structure data show a strong influence of the diamine building blocks on the tetrahedral distortion of the copper(II) complexes. Results of Extended Hückel LCAO calculations correlate strongly with structural, electrochemical, UV/Vis- and EPR-spectroscopic features obtained experimentally. The calculations confirm for the whole complex series a strong delocalization of the frontier orbitals. The highest fully occupied molecular orbital shows a weak contribution, resulting from thiolate donor atoms, whereas the antibonding singly occupied molecular orbitals (SOMOs) are distributed between the copper(II) centre (ca. 35-40%) and the N2S2 donor set. The SOMO energy significantly lowers with increasing tetrahedral distortion of the coordination sphere. The influence of the tetrahedral distortion of copper(II) complexes on redox potentials, UV/Vis and EPR spectra is discussed.
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  • 278
    Digitale Medien
    Digitale Medien
    Intermediates and Products of the Hexachlorodisilane Cleavage of Group 14 Element Phosphanes and Amines - Molecular Structure of Di-tert-butyl(trichlorosilyl)phosphane in the Gas Phase Determined by Electron Diffraction and ab Initio Calculations (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 1381-1392 
    Details
    ISSN: 1434-1948
    Schlagwort(e): Phosphanes ; Disilanes ; Disilanylamines ; Germanes ; Stannanes ; Stannanes ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Reactions of dialkyl(trimethylsilyl)phosphanes RR′PSiMe3 (1:R, R′ = tBu; 3: R, R′ = iPr; 5: R = iPr, R′ = tBu) with Si2Cl6 provide stable trichlorosilylphosphanes RR′PSiCl3 (2, 4, 6); the reactions of silyl- and stannylamines of iPr2NMMe3 (M = Si: 11; M = Sn: 12) with Si2Cl6, however, provide the stable pentachlorodisilanylamine iPr2NSi2Cl5 (13). Heating of 1 with the technical mixture Me2(Cl)SiSiCl2Me/(MeCl2Si)2 yields the stable silylphosphane tBu2PSiMe2Cl (8) and the disilanylphosphane tBu2PSi(Me)(Cl)Si(Me)Cl2 (9). Methylation of 9 with MeLi gave tBu2PSi2Me510, which was isolated in a pure state. Reactions of tBu(iPr)PSiMe3 (5) and of organometal phosphanes tBu(iPr)PMR3 (14: M = Ge, R = Me; 17a-c: M = Sn; R = Me, Et, nBu) with Si2Cl6 were monitored by 31P, 29Si, and 119Sn NMR. - In the first step of these reactions, new tBu(iPr)PSi2Cl5 (7) is formed. 7 is accompanied by increasing amounts of tBu(iPr)PSiCl3 (6) and Me3GeSiCl3 (15)/(Me3Ge)2Si(SiCl3)2 (16) or traces of compounds R3SnSiCl3 (19a-c) that decompose providing (R3Sn)2Si(SiCl3)2 (18a-c) and nBu3SnSi(SiCl3)3 (20c). Subsequently, compounds 19a-c decompose providing increasing amounts of 18a-c. Stannylphosphane 17bis also cleaved by SiCl4 leading to 6 with liberation of Et3SnCl, whereas 17bis formedfrom the reaction of 5 with Et3SnCl under liberation of Me3SiCl. The suggestion of an extra stabilisation of P-Si bonds of trichlorosilylphosphanes was subjected to direct evidence through the structure determination of the trichlorosilylphosphane tBu2PSiCl3 (2) in the gas phase by electron diffraction. This crowded molecule has a “normal” P-Si bond length of 225.0(12) pm; its C1 symmetric conformation with both tBu groups and the SiCl3 group twisted about 17° from the perfectly staggered positions, and with each of the three groups tilted about 6° away from each other, allows to reduce steric strain.
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  • 279
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    Digitale Medien
    Dynamic Combinatorial Chemistry: Substrate H-Bonding Directed Assembly of Receptors Based on Bipyridine-Metal Complexes (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 1415-1420 
    Details
    ISSN: 1434-1948
    Schlagwort(e): Combinatorial chemistry ; Molecular recognition ; Functionalized bipyridine metal complexes ; Janus molecules ; Hydrogen bonding ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The functionalized ligands 1 and 2 bearing hydrogen-bonding recognition groups have been synthesized. Their assembly by metal ions such as CuI and PdII having different coordination geometries generates different receptor architectures for the binding of suitable substrates. Addition of the complementary bis(imide) Janus molecules (4-7) to [1a, 2a, CuTf] or to [1b, 2b, Pd(BF4)2] mixtures leads to a moderate selective increase of the fraction of the [(1a)2Cu]+ or [(1b)2Pd]2+ complex depending on the Janus substrate used. Largest enhancements are observed for those Janus substrates that may be expected to display highest geometrical complementarity with the two complexes. These results represent a process directed by target binding based on dynamic combinatorial chemistry.
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  • 280
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    Digitale Medien
    Chiral Rhenium Complexes of Functionalized Thioaldehydes (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 1435-1443 
    Details
    ISSN: 1434-1948
    Schlagwort(e): Captopril ; Cysteine ; Rhenium ; S ligands ; Thioaldehydes ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Chiral racemic rhenium thioaldehyde complexes [CpRe(NO)(PPh3)(η2-S=CHR)]PF6 (2a-g) bearing functionalized aliphatic groups R [R = CH2Ph (a), COOEt (b), CH2COOMe (c), CH2C(O)NHCH2Ph (d), (R)-CH(NC8H4O2)COOMe (e), (S,S)-CH(Me)C(O)NC4H7COOMe (f), C4H3O (g)] have been obtained by hydride abstraction from the corresponding thiolate complexes [CpRe(NO)(PPh3)(SCH2R)] (1a-g). With the exception of 2b, only single stereoisomers with like configurations at rhenium and the thioaldehyde carbon atom were obtained. In some cases, the corresponding sulfinate complexes [CpRe(NO)(PPh3)(SO2CH2R)] (3d-f) were formed as by-products. The analogous toluenesulfinate complex [CpRe(NO)(PPh3){SO2(4-C6H4CH3)}] (3a) has been prepared from [CpRe(NO)(PPh3)(THF)]BF4 (8), and the structure of 3e has been determined by X-ray crystallography. The use of phosphorus ligands other than PPh3 was briefly explored with the synthesis of [CpRe(NO)(PR′3)(η2-S=CHR)]PF6 (5a-d) [R′ = OPh, R = Ph (a), 4-C6H4Cl (b), R′ = iPr, R = Ph (c), H (d)]. Nucleophilic addition of NaSMe to [CpRe(NO)(PPh3){η2-S=CH(4-C6H4OMe)}]PF6 (5e) gave the dithioacetal complex [CpRe(NO)(PPh3){SCH(SMe)(4-C6H4OMe)}] (9) in high yield and with low diastereoselectivity. Diels-Alder additions of 5a, e with 2,3-dimethylbutadiene and 2,3-dimethoxy-butadiene gave complexes of cyclic thioethers (10a-c). From the relative rates of reaction (5a 〉〉 5e) and the low diastereoselectivity, it was concluded that the cycloadditions as well as the nucleophilic addition proceed via the linkage isomers [CpRe(NO)(PR′3)(η1-S=CHR)]PF6.
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  • 281
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    Digitale Medien
    Group 5 Metal Complexes with Cyclooctatetraene: Formation and Characterization of (Butadiene)(cyclooctatetraene)(cyclopentadienyl)tantalum Systems (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 1461-1466 
    Details
    ISSN: 1434-1948
    Schlagwort(e): Diene complexes ; η3-Cyclooctatetraene metal complex ; B(C6F5)3 addition ; Tantalum ; Bicyclo[5.1.0]octadienyl metal complex ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: 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.
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  • 282
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    Digitale Medien
    Histidine-Containing Bisperoxovanadium(V) Compounds: Insight Into the Solution Structure by an ESI-MS and 51V-NMR Comparative Study (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 1489-1495 
    Details
    ISSN: 1434-1948
    Schlagwort(e): Peroxo complexes ; Vanadium ; Mass spectrometry ; 51V-NMR spectroscopy ; Vanadium dependent bromoperoxidases ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: ESI mass spectrometry and 51V-NMR spectroscopy have been used to study the reactions occurring between bisperoxo vanadates and a number of histidine and histidine-like ligands, in aqueous alcoholic solutions. Coordination of one and two molecules of ligand is observed with all the compounds investigated affording [VO5L]- and [VO52L]-, respectively. Characterization of these species has been achieved by MSn experiments, which have allowed specific fragmentations of the peroxidic moiety to be distinguished. In particular, with [VO52L]-, two distinct modes of decomposition were observed, depending on the presence in the ligand of a free carboxylic function. - Possible biochemical implications related to vanadium haloperoxidase enzymes are discussed.
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  • 283
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    Digitale Medien
    Modified Bipyridines: 5,5′-Diamino-2,2′-bipyridine Metal Complexes Assembled into Multidimensional Networks via Hydrogen Bonding and π-π Stacking Interactions (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 1507-1521 
    Details
    ISSN: 1434-1948
    Schlagwort(e): 2,2′-Bipyridines ; Chelate complexes ; Hydrogen bonding ; π-π stacking ; Crystal structure ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: A new synthetic route for the synthesis of 5,5′-diamino-2,2-bipyridine (5) based on the coupling of 2-chloro-5-aminopyridine in the presence of NiCl2 × 6 H2O/PPh3/Zn in dimethylformamide is described. The reactions of the potentially ambidentate ligand 5 with salts of the transition metals Mn, Fe, Ni, Cu, Zn, Ag, and Cd gave a variety of 13 metal-ligand complexes depending on the anion, the crystallization conditions and the metal-to-ligand ratio. The complexes obtained were characterized by thermal analyses, NMR including 113Cd-NMR, IR, and for the iron complex 57Fe-Mößbauer spectroscopy. The structure of eight of the compounds was elucidated by X-ray crystallography. All of these metal complexes show a bipyridine-metal coordination. The amino functionality was never involved in metal coordination. The intermolecular arrangement is dictated by hydrogen bonding from the amino functionality and by π-π stacking of the bipyridine rings.Supporting information for this article is available on the WWW under http://www.wiley-vch.de/contents/jc_2005/1999/99078_s.pdf or from the author.
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  • 284
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    Digitale Medien
    A Tetranuclear Platinum Compound Designed to Overcome Cisplatin Resistance (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 1429-1433 
    Details
    ISSN: 1434-1948
    Schlagwort(e): Antitumor drugs ; Platinum ; DNA ; Dendrimers ; L1210 Mouse leukemia ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The synthesis and characterisation of the first generation of a poly(propyleneimine) dendrimer DAB(PA)4, substituted with four trans-diamminechloroplatinum moieties is reported. The compound DAB(PA-tPt-Cl)4 was designed to overcome two problems often associated with cisplatin resistance in cancer cells: (i) deactivation of the platinum species by intracellular thiolates and (ii) improved repair of crosslinks with DNA. The four-armed molecule can be expected to form crosslinks with DNA that are very different from the adducts formed by cisplatin. Also, the tetranuclear compound has four leaving groups, while cisplatin has only two. Therefore, DAB(PA-tPt-Cl)4 would be less susceptible towards inactivation by reaction with intracellular thiolates. A reaction with an excess of the model nucleobase guanosine 5′-monophosphate (GMP) confirmed that the tetranuclear compound is capable of binding a maximum of four nucleobases. Therefore, the inactivation of one or two arms would still leave the molecule with enough reactivity to form crosslinks with DNA. Cytotoxicity tests were performed on two mouse leukemia L1210 cell lines, both sensitive and resistant towards cisplatin, and in seven human tumor cell lines. In all cell lines, the tetranuclear compound showed a low cytotoxicity. It is suggested that the low activity is related to the structure of the compound. Probably the high charge (+6) at physiological pH and its branched structure hamper the molecule in crossing the cell membranes.
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  • 285
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    Digitale Medien
    Tungsten Carbonyl Complexes of 1H-Diphosphirenes and Diphosphirenylium Salts (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 1479-1488 
    Details
    ISSN: 1434-1948
    Schlagwort(e): Phosphorus heterocycles ; Cations ; Tungsten complexes ; Coordination modes ; Phosphaalkenes ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The 1,1,3-tris(diisopropylamino)diphosphirenium salt 1 reacts with lithium aluminium hydride leading to the P-hydrogeno-C-phosphinophosphaalkenes 2, which on treatment with a catalytic amount of BF3·OEt2 afford the 1,3-bis(diisopropylamino)-1H-diphosphirene 3. The corresponding η1-coordinated 1H-diphosphirene 6 can be prepared by treatment of 2 or 3 with one equivalent of [W(CO)5(thf)]. Alternatively, the diphosphirenium salt 1 reacts with an excess of [W(CO)5(thf)], affording the corresponding η1-coordinated diphosphirenium salt complex 4, which is converted into the P-hydrogenophosphaalkene complex 5 with lithium aluminium hydride. The dinuclear tungsten complexes 7 and 8 are obtained by treatment of the free 1H-diphosphirene 3 with two equivalents of [W(CO)5(thf)] or one equivalent of [W(CO)4(thf)2], respectively. Compound 6 reacts with two equivalents of hydrogen chloride, giving the 1-chloro-3-diisopropylamino-1H-diphosphirene 9, which can be subsequently converted into the 1-diisopropylamino-, 1-azido, or 1-phenyl-3-diisopropylamino-1H-diphosphirenes 6, 10 and 11 by nucleophilic substitution with diisopropylamine, azidotrimethylsilane or sodium tetraphenylborate, respectively. The [η2-(3-diisopropylaminodiphosphirenylium salt)·W(CO)5] complexes 12a-c can be prepared by reaction of 9 with silver trifluoromethanesulfonate, aluminium or gallium trichloride or, alternatively, by treatment of 6 with two equivalents of trifluoromethanesulfonic acid. Reaction of 12a with diisopropylamine, water, bis(triphenylphosphoranylidene)ammonium chloride or tetrabutylammonium fluoride gives the corresponding 1H-diphosphirene complexes 6, 13, 9, or 14, respectively. Compound 12a also reacts with one or two equivalents of [W(CO)5(thf)], leading to the di- and tri-nuclear complexes 15and 16, respectively.
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    Digitale Medien
    Porphyrazines with Annulated Diazepine Rings, 1 Synthesis and Characterization of Tetrakis-2,3-(5,7-diphenyl-6H-1,4-diazepino)porphyrazine and Its MgII, CuII, and ZnII Complexes - X-ray Crystal Structure of 2,3-Dicyano-5,7-diphenyl-6H-1,4-diazepine (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 2075-2084 
    Details
    ISSN: 1434-1948
    Schlagwort(e): Porphyrazines ; Diazepines ; Tetrakis(diazepino)porphyrazines ; Metal complexes ; Macrocyclic ligands ; Magnesium ; Copper ; Zinc ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: A new class of porphyrazine macrocycles carrying peripheral diazepine rings, i.e. tetrakis-2,3-(5,7-diphenyl-6H-1,4-diazepino)porphyrazine [Ph2DzPzH2](H2O)4, and its metal derivatives of formula [Ph2DzPzM](H2O)x=2-7 [M = MgII(H2O), CuII, ZnII] have been prepared and characterized. Single crystal X-ray work on the monomeric precursor 5,7-diphenyl-2,3-dicyano-6H-1,4-diazepine, Ph2(CN)2Dz, and NMR spectra (CDCl3, (CD3)2SO) and UV/Vis spectra in solution of different media (basic, neutral, acid) of the monomer and its macrocyclic derivatives have provided information on the conformational flexibility of the diazepine ring as well as on the structural and electronic features of the entire porphyrazine skeleton.
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  • 287
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    Digitale Medien
    The First Thioallenylidene Complexes from Ruthenium-Butatrienylidene Intermediates (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 2121-2126 
    Details
    ISSN: 1434-1948
    Schlagwort(e): Ruthenium ; Allenylidene complexes ; Butadiyne ; Electrochemistry ; Thio-Claisen rearrangements ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Ruthenium-butatrienylidene cations trans-[Cl(L2)2Ru=C=C=C=CH2]+ are key intermediates in the synthesis of the first thioallenylidene complexes trans-[Cl(L2)2Ru=C=C=C(SR)R′]+ (L2 = dppm, R = Et, R′ = Me: 3a, L2 = dppm, R = Me, R′ = C4H7: 3b, L2 = dppe, R = C3H5, R′ = C4H7: 3c). Spectroscopic and electrochemical data for 3a-c are presented and are compared with those of their aminoallenylidene analogues. Aminoallenylidene complexes are best represented by the iminiumalkynyl resonance form, while a true cumulene description is much more appropriate for thioallenylidene complexes 3a-c. Based on a combination of spectroscopic and electrochemical data, we present evidence that the NMR shifts of the carbon atoms of the unsaturated ligand in these allenylidene complexes are correlated to the HOMO-LUMO gap. In situ EPR-, UV/Vis-, and IR-spectro-electrochemistry reveals that the one-electron oxidation occurs at the metal center, while reduction occurs at the carbon-heteroatom terminus.
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  • 288
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    Digitale Medien
    Control of Reactivity of Dinuclear Nickel(II) Amine-Thiolate Complexes (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 2157-2166 
    Details
    ISSN: 1434-1948
    Schlagwort(e): Septadentate N5S2-ligand ; Dinuclear complexes ; Nickel ; Reactivity ; Redox chemistry ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The coordination chemistry of a series of dinickel complexes of the new septadentate amine-thiolate ligand N,N′-bis[2-thio-3-aminomethyl-5-tert-butylbenzyl]diethylenetriamine, H29, has been investigated in the context of ligand binding and oxidation state changes. The complexes [Ni2(9)(L)][ClO4]2 (10), [Ni2(9)(Cl)][Cl] (11), [Ni2(9)(L)][BPh4]2 (12), and [Ni2(9)(NCS)][OH·OH2] (13) have central N2Ni(μ-SR)2NiN′3L cores [L = labile solvent molecule (10, 12), Cl- (11), and NCS- (13)] composed of dithiolate bridged planar NiN2S2 and six-coordinate NiN′3S2L units. This is demonstrated for 11 and 13 by crystal structure determinations and for 10 and 12 by UV/Vis spectroscopy and room temperature magnetic susceptibility measurements. Complexes 10, 11, or 12 readily add other co-ligands at the NiN′3S2L fragment by substitution of the solvent molecule L (10, 12) or the chloride substituent (11). The overall structure of the parent complexes is not affected by the substitution reactions. An electrochemical study has shown that complex 10 undergoes two successive one-electron oxidations at +0.88 and +0.41 V vs SCE. The oxidized species are not thermally stable, but electronic absorption spectra and EPR spectra are indicative of the presence of NiIII species.
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  • 289
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    Digitale Medien
    The Mono-, Di-, and Tri([5]trovacenyl)boranes: A Study of Intermetallic Communication Across an sp2-Hybridized Boron Atom (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 2173-2185 
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    ISSN: 1434-1948
    Schlagwort(e): EPR spectroscopy ; Metallocenylboranes ; Organovanadium radicals ; Redox chemistry (CV) ; X-ray diffraction ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The paramagnetic complexes di(mesityl)([5]trovacenyl)borane (5·), (mesityl)di([5]trovacenyl)borane (6··), and tri([5]trovacenyl)borane (7···) were prepared from [5]trovacenyllithium, (η5-C7H7)V(η5-C5H4Li), and (Mes)2BF, (Mes)BF2, and BF3, respectively. The propeller-shaped species 5·, 6··, and 7··· were subjected to X-ray diffraction with the aim of possibly correlating the twist angles with intramolecular intermetallic communication. Cyclic voltammetry points to successive vanadium-centered oxidation processes and boron-centered reduction, a small redox splitting δE1/2[(2+/+), (+/0)] being observed for 6··. According to EPR spectroscopy, performed in fluid solution, the exchange interaction J in the diradical 6·· approaches the fast-exchange region and is attenuated significantly by quaternization at boron in [6··-nBu]-. Although EPR spectroscopy of the triradical 7··· also indicates an extensive exchange interaction, the exchange parameters, derived from spectral simulation, follow the gradation J(7···) ≈ 1/3 J(6··). The magnetic susceptibility of 6·· and 7··· follows the same trend. As expected, compound 7··· exhibits spin frustration because it contains three antiferromagnetically coupled S = 1/2 systems that are arranged in an equilateral triangle.
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  • 290
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    Digitale Medien
    Synthesis, X-ray Crystal Structures and Reactivity Towards Alkynes of Gold(I)-Phosphinine Complexes (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 2233-2241 
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    ISSN: 1434-1948
    Schlagwort(e): Phosphorus ; Heterocycles ; Phosphinines ; Gold ; Cycloadditions ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The coordination behaviour of 2,6-disilyl-substituted phosphinines towards gold(I) has been examined. The reaction of the bis(trimethylsilyl)phosphinine 1 with [AuCl(SMe2)] gives the corresponding AuCl derivative 2. X-ray crystal structure analysis reveals that the aromaticity of the phosphinine ring is slightly reduced as a result of the poor π-back bonding ability of the AuCl fragment. The same phenomenon is observed in the cationic complex [Au(1)2][GaCl4] (3) which was readily prepared by reaction of two equivalents of 1 with [AuCl(SMe2)] followed by treatment with GaCl3 at low temperature. Reaction of 2,6-bis(phenylethynyldimethylsilyl)phosphinine (4) with the same precursor leads similarly to the complex [AuCl(4)] (5). Interestingly, this complex dimerizes upon crystallization to give the bis(phosphabarrelene) complex 6, also structurally characterized. The formation of 6 results from a [4 + 2] cycloaddition between one alkynyl group of each phosphinine with the other phosphinine subunit. The formation of the cationic complex [Au(4)][GaCl4] (8) occurs under classical conditions but it disproportionates to give the cationic complex [Au(4)2][GaCl4] (9) and colloidal gold deposition. The formation of 9 has been ascertained by treating 8 with one equivalent of ligand 4. Additionally, 9 can also be obtained in a straightforward fashion by treating two equivalents of 4 with [AuCl(SMe2)] followed by treatment with GaCl3 at low temperature. The structure of 9 has been elucidated. Despite a particular arrangement of the alkyne groups which encapsulate the gold coordination sphere, no gold-alkyne interactions are visible.
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    Digitale Medien
    Selective Lithium Complexation by Photoactive Aza-Cages Bearing the Anthracene Function (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 2261-2268 
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    ISSN: 1434-1948
    Schlagwort(e): Macrocycles ; Lithium ; Fluorescence ; Cryptands ; Coordination ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Three aza-cages with the anthracene-containing photoactive groups L1, L2, and L3 have been synthesized. All compounds are able to selectively encapsulate a lithium ion and solid complexes have been isolated. The formation equilibria have been investigated by UV/Vis and 1H, 13C and 7Li NMR spectroscopic techniques. The fluorescence emission of both free ligands and lithium complexes have been investigated. Results indicate that the CHEF (chelation enhancement of the fluorescence) effect obtained by lithium coordination exits although lower than that occurring upon full protonation.
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  • 292
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    Digitale Medien
    Enantioselective Organic Syntheses Using Chiral Transition Metal Complexes, 9 Atropo-Diastereoselective Ring Opening of Biaryl Thionolactones Using [CpRu{(S,S)-CHIRAPHOS}]+ as a Chiral Auxiliary (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 1745-1756 
    Details
    ISSN: 1434-1948
    Schlagwort(e): Biaryls ; Lactones ; Nucleophilic additions ; Ruthenium ; S ligands ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The substitution-labile thiophene complex [CpRu{(S,S)-CHIRAPHOS}(SC4H4)]BF4 (2) [(S,S)-CHIRAPHOS = (2S,3S)bis(diphenylphosphanyl)butane], prepared from [CpRu{(S,S)-CHIRAPHOS}Cl] (1), thiophene, and AgBF4, reacted with the biaryl-thionolactones 3a-f to give the corresponding S-coordinated complexes 4a-f in high yields. The structure of 4c, which crystallized as the pure (S,S,P) diastereoisomer, was determined by X-ray crystallography. Coordination of the ruthenium fragment caused an elongation of the C=S bond, a contraction of the C-O bond within the lactone ring and a flattening of that ring. Single hydride transfer with LiBEt3H converted 4a-f into the thiolactolate complexes 5a-f in good yields and diastereoselectivities. An X-ray structure determination of the major isomer of 5a revealed it to be the (S,S,S,P) diastereoisomer. Protonation with NH4PF6 converted 5a-f into the corresponding ring-opened thioaldehyde complexes 6a-f. Alkylation of 5a with methyl iodide resulted in Ru-S cleavage to give the oxothioacetal 7a and [CpRu{(S,S)-CHIRAPHOS}I] (8). Full reduction of 4a-f with LiAlH4 produced the thiolate complexes 9a-f in high yields and 6-74% de. Methylation at sulfur converted 9a-c into the corresponding thioether complexes 10a-c, which were cleaved to 8 and the free methyl thioethers 11a-c without isomerization of the biaryl axis.
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  • 293
    Digitale Medien
    Digitale Medien
    A Simple New Structural Force Field for the Computation of Linear Metallocenes (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 1787-1792 
    Details
    ISSN: 1434-1948
    Schlagwort(e): Molecular mechanics ; Metallocenes ; Ferrocene ; Points on a sphere ; Rotation barrier ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: A new structural force field for metallocenes is presented, which involves harmonic bonding potentials from the metal center to each of the carbon atoms, no angular potentials around the metal ion, inter-ligand 1,3-non-bonded interactions, and transferable parameters for the ligand backbones. The model has been parameterized for ferrocene, ruthenocene, and osmocene derivatives and the force field has been validated with relevant structures from the CSD files (Fe: 34, Ru: 10, Os: 2). The conformational space [rotation of the Cp (cyclopentadienyl) rings] has been searched with a cartesian stochastic search routine and energy barriers have been computed by scanning the pseudo-torsional angles involving the centroids of the two Cp rings. The computed energy barriers are smaller than those determined experimentally, but the predicted increase in transition energy upon substitution of the Cp rings is in agreement with experiment and the torsional angles for the minimum structures are computed accurately. It is suggested that the underestimated barrier height is due to the neglect of solvation.Supporting information for this article is available on the WWW under http://www.wiley-vch.de/contents/jc_2005/1999/99092_s.pdf or from the author.
    Zusätzliches Material: 3 Ill.
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  • 294
    Digitale Medien
    Digitale Medien
    Kinetics and Mechanism of the Outer-Sphere Oxidation of Horse-Heart Cytochrome c by an Anionic Chromium(v) Complex - Kinetic Evidence for Precursor Formation and a Late Electron-Transfer Transition State (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 1805-1812 
    Details
    ISSN: 1434-1948
    Schlagwort(e): Cytochrome c ; Chromium(v) ; Saturation kinetics ; Separation of K and kET ; Volume profile ; Kinetics ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The irreversible outer-sphere electron-transfer reaction between trans-bis(2-ethyl-2-hydroxybutanoato(2-))oxochromate(v) and cytochrome cII was investigated as a function of pH, concentration, temperature and pressure. The plot of the observed pseudo-first order rate constant as a function of the CrV concentration shows a clear trend towards saturation at higher CrV concentrations, from which the precursor formation constant and the electron-transfer rate constant could be separated (K = 37 ± 5 M-1 and kET = 1510 ± 180 s-1 at pH 4.8 and 279 K). In the low CrV concentration range the second-order electron-transfer rate contants were measured as a function of temperature (ΔH# = 20.9 ± 0.6 kJ mol-1; ΔS# = -79.9 ± 2.1 J K-1 mol-1; ΔG# (279 K) = 43.2 kJ mol-1). High-pressure experiments were performed at two different pH values. The kinetic (stopped-flow) and thermodynamic (electrochemical) measurements as a function of pressure enabled the construction of a volume profile for the system at 279 K. The activation volumes for the redox process are -9.2 ± 0.2 (pH 5.0) and -11.1 ± 0.8 cm3 mol-1 (pH 4.7), and the overall reaction volumes were estimated to be -7 ± 2 (pH 5.0) and -10 ± 2 cm3 mol-1 (pH 4.7) . The transition state of the redox reaction lies to a large extent on the product side and can be described as “late”. The results are discussed in comparison to earlier measurements using cobalt and ruthenium complexes as reaction partners for cytochrome c.
    Zusätzliches Material: 7 Ill.
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  • 295
    Digitale Medien
    Digitale Medien
    Mono- and 1,1′-Disubstituted Aza Ferrocenyl Compounds: Evidence for an Original Electroactive Fluorescent Species (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 1821-1825 
    Details
    ISSN: 1434-1948
    Schlagwort(e): Ferrocenyl ligands ; Electrochemistry ; Fluorescence ; Azaalkyl compounds ; Crown compounds ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: New azaalkyl or azacrown ferrocenyl compounds containing a C5H4COCC- linkage are accessible from mono- or diacetylferrocene upon treatment with the appropriate aldehydes (CHOC6H4-p-R, R = NEt2, N-aza-15-crown-5). Preliminary results concerning the electrochemical behaviour of complexes [(C5H5)Fe(C5H4COCH=CHC6H4NEt2)] (3a), [Fe(C5H4COCH=CHC6H4NEt2)2] (5a), the novel ferrocenophane [Fe(C5H4COCH2)2CHC6H4NEt2] (6a) and its protonated species [Fe(C5H4COCH2)2CHC6H4NHEt2][BF4] (7a), are reported. The ferrocenyl ligand 5a is a rare example of a molecule which is both electroactive and fluorescent.
    Zusätzliches Material: 3 Ill.
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  • 296
    Digitale Medien
    Digitale Medien
    Formation and Structural Characterisation of an Unusual Cyclic HexamericOxotitanium Complex (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 1847-1849 
    Details
    ISSN: 1434-1948
    Schlagwort(e): Titanium ; Amino alcohols ; Metal alkoxide ; Oxo alkoxide ; Metallacycles ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Ti6O6(MDEA)6·2CH2Cl2 (MDEA = N-methyldiethoxoamine) was obtained by the controlled hydrolysis of the Ti(MDEA)2 complex and analysed by X-ray diffraction. The compound consists of a ring of six [TiO5N] octahedra, edge bridged by μ2-oxide and a μ2-alkoxide arm of the aminoalkoxide ligand.
    Zusätzliches Material: 2 Ill.
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  • 297
    Digitale Medien
    Digitale Medien
    Novel μ3-Coordination of Urea at a Nickel(II) Site: Structure, Reactivity and Ferromagnetic Superexchange (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 1851-1854 
    Details
    ISSN: 1434-1948
    Schlagwort(e): Urea ; Nickel ; Coordination modes ; Cooperative effects ; Magnetic properties ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: A tetranuclear mixed-spin nickel(II) complex featuring two urea molecules in an unprecedented μ3-ĸN:ĸN′:ĸO coordination mode has been structurally characterized. The two central high-spin nickel(II) ions exhibit ferromagnetic coupling (J = +3.4 cm-1) mediated by the NH2-C-O linkages of the bridging urea. In solution the temperature dependence of the UV/Vis optical absorption and of the magnetic moment indicate that, upon cooling, additional solvent molecules bind to the terminal low-spin metal ions and a concomitant spin change occurs. In the solid state the coordinated urea ligands can be thermally degraded to cyanate within the grip of the multimetallic nickel(II) site.
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
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  • 298
    Digitale Medien
    Digitale Medien
    Synthesis and Structure of the First Fullerene Complex of Titanium Cp2Ti(η2-C60) (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 1855-1857 
    Details
    ISSN: 1434-1948
    Schlagwort(e): Fullerenes ; Titanium ; Complexes ; X-ray analysis ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The first fullerene complex of titanium Cp2Ti(η2-C60) has been synthesized by reaction of the bis(trimethylsilyl)-acetylene complex of titanocene Cp2Ti(η2-Me3SiC2SiMe3) with an equimolar amount of fullerene-60 in toluene at room temperature under argon. An X-ray diffraction study of the complex has shown that it has the structure of a titanacyclopropane derivative.
    Zusätzliches Material: 1 Ill.
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  • 299
    Digitale Medien
    Digitale Medien
    Structural and Energetical Characterization of the Methylbutadiene-Fe(CO)3 Isomers and Related Reactive Intermediates with Quantum Chemical Methods (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 1869-1880 
    Details
    ISSN: 1434-1948
    Schlagwort(e): Density functional calculations ; 1,3-Diene-Fe(CO)3 ; Conformational analysis ; Iron ; Organometallic chemistry ; Reactive intermediates ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: A theoretical investigation of isoprene-Fe(CO)3 (2), (E)-1,3-pentadiene-Fe(CO)3 (3), (Z)-1,3-pentadiene-Fe(CO)3 (4), and reactive intermediates derived from these complexes was undertaken, employing the HF/DFT hybrid functional Becke3LYP, and the results are presented. Special emphasis is placed on cationic, anionic, and radical intermediates formally derived by abstraction of a hydride, a proton, or a hydrogen atom from the methyl group of the parent complexes. The geometry, energy, and electronic situation of the calculated species are discussed in the context of experimental facts. This leads to a better mechanistic understanding of the chemistry of acyclic butadiene-Fe(CO)3 complexes, provides insights into structural details of the intermediates involved, and allows the evaluation of possible resonance formulae. The calculation of transition states of isomerization (or racemization) processes even permits a quantitative description of energy profiles. In this way, the configurational stability of relevant cationic, anionic and radical intermediates can be estimated.Supporting information for this article is available on the WWW under http://www.wiley-vch.de/contents/jc_2005/1999/99146_s.pdf or from the author.
    Zusätzliches Material: 15 Ill.
    Materialart: Digitale Medien
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  • 300
    Digitale Medien
    Digitale Medien
    1D- and 2D-Coordination Polymers from Self-Complementary Building Blocks: Co-Crystallization of (P)- and (M)-Single-Stranded Diastereoisomers (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 1859-1867 
    Details
    ISSN: 1434-1948
    Schlagwort(e): Coordination polymers ; Helical structures ; Copper ; Self-assembly ; Supramolecular chemistry ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Reaction of methanolic copper(II) acetate solution with oxazolidine 21 (HL7) led to the formation of the one-dimensional coordination polymer 1D-∞1[CuL27] 23. On the contrary, reaction of copper(II) acetate in methanol with pyrrolidine 24 (HL8) yielded the two-dimensional coordination polymer 2D-∞2[CuL28] 26. A common feature of 23 and 26 are the C2h-symmetric coordinatively unsaturated building blocks 22 and 25. In 1D-∞1[CuL27] 23, the cyano groups are linked to copper in a side-on fashion and the monomers 22 are oriented parallel to one another, whereas in 2D-∞2[CuL28] 26 the cyano groups are bound to copper in the end-on mode and the monomers 25 are oriented at an angle of 117° to one another. In both 1D-23 and 2D-26, copper has a distorted octahedral coordination sphere. On the other hand, reaction of methanolic copper(II) acetate solution with enantiomerically pure (5S)-pyrrolidine 27 (HL9(S)) led to the formation of the diastereomeric helical strands (M)-/(P)-1D-∞1[CuL29] 29. (M)- and (P)-29 are present in pairs in the infinite unit cell. In helical 1D-29, copper is tetragonal-pyramidally coordinated and the C2-symmetric monomers 28 (CuL29) are linked through only one cyano group. Moreover, it has been shown that the reaction of chiral racemic pyrrolidine 30 (HL10(R,S)) with copper(II) acetate via the intermediate Ci-symmetric building blocks 31 (CuL10(R)L10(S)) furnishes one-dimensional 1D-∞1[CuL10(R)L10(S)] 32. Single-crystal X-ray diffraction analyses of the supramolecular species 23, 26, 29, and 32 unequivocally establish the structures of these coordination polymers.
    Zusätzliches Material: 4 Ill.
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