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  • 1995-1999  (1,288)
  • 1998  (1,288)
  • Engineering  (644)
  • General Chemistry  (643)
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  • 201
    Electronic Resource
    Electronic Resource
    The Molecular Structure of Some Transition-Metal Complexes with 1,2,3,4-Tetrazole-5-thiolate Anions (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 93-99 
    Details
    ISSN: 1434-1948
    Keywords: 2-Methyl-1,2,3,4-tetrazole-5-thiolates ; 2-Phenyl-1,2,3,4-tetrazole-5-thiolates ; Palladium ; Platinum ; Copper ; Silver ; Gold ; Molecular structures ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The molecular structures of nine transition metal tetrazolethiolates have been determined by X-ray structure determinations. The ligand is invariably coordinated through its sulfur atom to the metal center [M = PdII, CuI, AgI, AuI, AuIII, and Hg]. The M-S-C bond angles vary considerably, but this cannot be correlated with variations in the C-S bond lengths. Intermolecular association occurs for Ph3PAu(SCN4Me) via Au-S contacts, leading to dimeric strands in the solid state. The copper compound (Ph3P)3Cu4(SCN4Me)4 (5), possesses a rather asymmetric structure: one Cu atom is tricoordinated by 3 sulfur atoms, the other three are tetracoordinated by P and N as well as by S atoms.
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  • 202
    Electronic Resource
    Electronic Resource
    Halogenation of Bis(phosphonio)isophosphindolide Salts: Oxidation versus Substitution (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 101-106 
    Details
    ISSN: 1434-1948
    Keywords: Phosphorus heterocycles ; Halogens ; Oxidations ; Electrophilic aromatic substitutions ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Bis(phosphonio)isophosphindolide iodide 1[I] reacts with an equimolar amount of I2 to yield the trihalide 1[I3], while treatment of 1[X] (X = Br, OTf) with excess Br2 furnishes the dibromophosphonium salt 6c[X]. The bromo-substituted bis- (phosphonio)isophosphindolide cations 5a and 5b are identified as intermediates in this reaction; 5b[Br] is also obtained in pure form by reaction of 6c[Br] with Zn or NEt3. Reaction of 1[OTf] with one equivalent of PhICl2 (7) affords the dichlorophosphonium salt 8a[OTf], which undergoes further substitution reactions in the presence of excess 7 and reacts with Me3SiI to give a mixture of 1[OTf] and I2 rather than a substitution product 9[OTf]. The results of a crystal-structure determination of 8a[OTf] are reported and the mechanistic aspects of the different oxidation/substitution reactions are discussed.
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  • 203
    Electronic Resource
    Electronic Resource
    Synthesis, Structure, and Dynamic Behaviour of Transition Metal Chelate Complexes with Atropisomeric Dithioether Ligands (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 113-118 
    Details
    ISSN: 1434-1948
    Keywords: S ligands ; Transition metals ; Fluxionality ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The preparation and characterization of RhI, PdII, and PtII complexes with chiral C2-symmetrical dithioether ligands derived from 1,1′-binaphthalene-2,2′-dithiol (BINAS) are reported. All complexes are fluxional in solution at room temp. Interconversion between the stereoisomers can take place through conformational equilibration of the chelate ring, and/or inversion of configuration at the stereogenic sulfur. In the solid state the palladium derivative of Me2BINAS shows a twisted chair conformation of the chelate ring, with both methyl groups in equatorial positions.
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  • 204
    Electronic Resource
    Electronic Resource
    Construction of One-Dimensional Multicomponent Molecular Arrays: Control of Electronic and Molecular Motions (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 1-14 
    Details
    ISSN: 1434-1948
    Keywords: One-dimensional multicomponent arrays ; Energy- and electron transfer ; Molecular motions ; Ruthenium ; Osmium ; Terpyridines ; Bis-terpyridines ; Bis-cyclometallating ligands ; Porphyrins ; Copper(I) rotaxane ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Transition metals are powerful three-dimensional templates, which can gather various functionalized ligands and orient them in a precise fashion so that complex multicomponent molecular systems can be obtained without constructing covalently-assembled edifices. The compounds thus prepared exhibit precise chemical or physical functions, which are governed by the design of the system. The construction of one-dimensional molecules around ruthenium(II) or osmium(II), using rigid ligands attached to the desired electroactive species, leads to systems that are able to undergo charge separation after photonic excitation. In other related compounds, a ruthenium(II)-based chromophore is, for example, connected to an osmium(II) complex by means of rod-like bridging ligand, thereby ensuring strict control over the Ru···Os distance. By tuning the length and the electronic properties of the bridge, one can control the efficiency of the electronic energy transfer between the two chromophores. In particular, the use of a bis-cyclometallating ligand is very conducive to energy transfer and allows the observation of this process up to a Ru…Os distance of ≈20 Å. By combining the building blocks of these inorganic systems with appropriate porphyrins, long-range (centre-to-centre distance between the donor and the acceptor porphyrins ≈30 Å) and relatively long-lived photoinduced charge separation has been demonstrated. Finally, with copper(I) as the template, compounds of the rotaxane family are obtained, which consist of a coordinating ring threaded by a string-like component. If this acyclic fragment is end-functionalized by two bulky stoppering groups and if it incorporates two different coordination sites (a bi- and a terdentate chelate site), novel dynamic properties are observed. The movement of a given fragment of the molecule is triggered by changing the metal oxidation state. This one-dimensional motion of the ring along the string on which it is threaded is controlled by redox manipulation, resulting in a primitive molecular machine.
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  • 205
    Electronic Resource
    Electronic Resource
    The Structural Chemistry of Aziridino- and Azetidinosilanes (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 107-112 
    Details
    ISSN: 1434-1948
    Keywords: Silicon ; Aminosilanes ; Aziridine ; Azetidine ; Molecular conformation ; Configuration determination ; Nitrogen ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In a continuation of structural investigations of poly(amino)silanes, a series of silicon derivatives of aziridine and azetidine have been prepared. Analogies with the isoelectronic phosphorus ylide species and the high barrier to inversion at nitrogen in small N heterocycles were suggestive of steeply pyramidal and rather rigid configurations at the N atoms in the title compounds. Tetrakis(N-aziridino)silane (1) and tetrakis(N-azetidino)silane (2) have been synthesized from SiCl4 and LiN(CH2)x (x = 2, 3). Compound 1 is also formed when LiN(CH2)2 and HSiCl3 are used as starting materials, but with free aziridine a non-volatile product (1a) is obtained. In neither case could any trace of HSi[N(CH2)2]3 be detected. In contrast, RSiCl3 (R = Me, Ph) could readily be converted into the corresponding tris(N-aziridino)silanes (3, 4) by treatment with excess aziridine. Tris(N-azetidino)silane (5) was accessible from HSiCl3 and excess azetidine, but the product was found to contain an unknown impurity. In order to determine the local symmetry and the dynamics of the aziridine rings, 1H-NMR spectra were recorded at low temperature (-80°C). No splitting of the signals was observed, indicating that the inversion barriers are extremely low, even in the highly strained three-membered heterocycles. Nevertheless, single-crystal X-ray diffraction studies of the N-triphenylsilyl derivatives of aziridine (6) and azetidine (7) revealed an aziridinyl group with a steeply pyramidal configuration at nitrogen in 6 (sum of the angles at N 313.32°), and an azetidinyl group with a flat geometry in 7 (sum of the angles at N 350.96°). The Si-N bond is significantly shorter in 7 as compared to that in 6.
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  • 206
    Electronic Resource
    Electronic Resource
    Five- and Six-Coordinate Nitrogen in Azaborane Clusters (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 143-153 
    Details
    ISSN: 1434-1948
    Keywords: Azaboranes ; Six-coordinate nitrogen ; Deltahedral clusters ; Cluster opening ; Cluster closure ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In the majority of known azaboranes NaBbHc and their derivatives, the coordination number of the nitrogen atoms within the cluster does not exceed the classical values of 3 or 4. In the azaboranes closo-NB9H10, nido-NB10H13, and closo-NB11H12 and in their derivatives, however, the nitrogen atoms are 5- or 6-coordinate and thus represent a novel bonding situation. The synthesis, structure, and reactivity of these azaboranes are reviewed in this article.
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  • 207
    Electronic Resource
    Electronic Resource
    [(Arene)(Diene)Fe] and [(Arene)(Diazadiene)Fe] Complexes: Preparation, Reactivity, and Catalytic Properties (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 119-126 
    Details
    ISSN: 1434-1948
    Keywords: Arene complexes ; Catalysis ; Diazadiene complexes ; Iron ; Metal vapour ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Two different routes to novel [(diene)(η6-2,6-dimethylpyridine)Fe] complexes are reported, both of which utilize metal vapour reactions. The presence of two small substituents on the 2,6-position of pyridine is essential for the η6-coordination of the heterocycle. Investigations on the reactivity and stability of the [(diene)(η6-arene)Fe] complexes are presented, including those of the benzene, phosphinine, and pyridine derivatives. These investigations give some hints to the relevant factors for determining the interaction between an iron atom and a π-coordinated neutral arene ligand, and their modification by a nitrogen or a phosphorus atom. Selective substitution of the 1,5-cyclooctadiene (COD) ligand of [(COD)(η6-arene)Fe] complexes by some 1,4-diaza-1,3-diene (DAD) derivatives is possible in the case of the benzene or phosphinine arene ligands, and [(DAD)(η6-arene)Fe] complexes are formed, but all DAD derivatives tested so far cause the complete disintegration of [(COD)(η6-2,6-dimethylpyridine)Fe]. [(DAD)(η6-arene)Fe] complexes exhibit a catalytic potential, which was evaluated by experiments on the catalytic cyclodimerization of 1,3-butadiene in the presence of [(Et2AlOEt)2] as a co-catalyst. This reaction yields up to 92% of 1,5-cyclooctadiene, and an almost quantitative butadiene conversion is possible in the presence of less than 0.1% of the catalyst. Structural investigations on [(N,N′-bis(cyclohexyl)ethylenediimine)(η6-toluene)Fe] 5a reveal some details of the Fe-DAD interaction. An effective electron back-donation from occupied iron d-orbitals into the π*-LUMO of the DAD is indicated.
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  • 208
    Electronic Resource
    Electronic Resource
    A Spectro- and Conductometric Study of the Reaction of Imidazoline-2-selone Derivatives with Bromine - Crystal Structure of 1,2-Bis(3-methyl-4-imidazolin-2-ylium dibromoselenanide)ethane (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 137-141 
    Details
    ISSN: 1434-1948
    Keywords: Bromine ; Imidazoline-2-selone ; Hypervalent Se compounds ; Dications ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The oxidative addition of Br2 to the imidazoline-2-selone derivatives 1a-c has been studied by spectrophotometric and conductometric techniques. The experimental results clearly indicate that this reaction involves the dications 2a-c, containing an Se-Se bond, as intermediates in the formation of the hypervalent 10-Se-3 selenium compounds 3a-c containing the Br-Se-Br group. The crystal structure of 1,2-bis(3-methyl-4-imidazolin-2-ylium dibromoselenanide)ethane (3c), a new stable hypervalent 10-Se-3 compound, is also reported.
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  • 209
    Electronic Resource
    Electronic Resource
    Light-Induced Codimerisation of Acetylene and Olefins at a Binuclear Tungsten Complex (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 127-135 
    Details
    ISSN: 1434-1948
    Keywords: Tungsten ; Ditungsten complexes ; Acetylene complex ; Tritungsten complex ; W-W single bond ; W-W triple bond ; Photochemistry ; C-C bond formations ; Olefins ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: [W2(η5-C5H5)2(CO)4(μ-η2:2-C2H2)] (1) and ethylene (A) react when irradiated with UV light at 253 K predominantly to [W2(η5-C5H5)2(CO)3(μ-η1:4-C4H5)(μ-H)] (3A), [W2(η5-C5H5)2(CO)4(μ-η1:3-C4H6)] (4A), and thermolabile [W2(η5-C5H5)2(CO)3(η4-C4H6)] (5A). Similarly, propene (B), 1-butene (C), and (E)-2-butene (D) yield mixtures of [W2(η5-C5H5)2(CO)3(μ-H)(μ-η1:4-1,3-dien-1-yl)] (3B, 3 C, 3D), [W2(η5-C5H5)2(CO)4(μ-η1:3-C4H5R] (4B, 4C), and [W2(η5-C5H5)2(CO)2(μ-η1:2-CO)(η4-1,3-diene) (5B, 5 C, 5D). With B and C also thermolabile [W2(η5-C5H5)2(CO)3(μ-η2:2-C2H2)(η2-C2H3R)] (2B, 2C) are formed. A by-product of the reaction of 1 with D is [W(η5-C5H5)(CO)(H){η4-(E)-C5H7CH3}], which is generated in two diastereomeric forms (6, 6′). In contrast, 1 yields no complexes with (Z)-2-butene (E) which contain ligands formed from coordinated acetylene and the olefin. From the reaction mixture only trinuclear [W3(η5-C5H5)3(CO)5(μ-η1:2-C2H3)] (7) was isolated, an alicyclic complex with a W-W single and a W-W triple bond. The crystal and molecular structures of 5D and 7 were determined by X-ray structure analysis. The constitutions of the other complexes were ascertained by IR and 1H-NMR spectroscopy.
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  • 210
    Electronic Resource
    Electronic Resource
    An Unusual Ring Structure of an Oligomeric Oxotitanium Alkoxide Carboxylate (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 159-161 
    Details
    ISSN: 1434-1948
    Keywords: Oxo clusters ; Titanium ; Metal alkoxides ; Sol-gel processes ; Carboxylato complexes ; Solid-state structures ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Ti9O8(OPr)4(methacrylate)16 was obtained by the reaction of Ti(OPr)4 with an excess of methacrylic acid and analyzed by X-ray diffraction. The compound consists of a ring of nine [TiO6] octahedra linked by six μ2- and only two μ3-oxide bridges.
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  • 211
    Electronic Resource
    Electronic Resource
    Coordination Behaviour of the New Multidentate Ligand 3,5-Bis(dimethylaminomethyl)pyridine with Palladium(II) and Platinum(II) Metal Centres (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 163-168 
    Details
    ISSN: 1434-1948
    Keywords: Pyridine ligands ; Bidentate bridging ligands ; Palladium ; Platinum ; N ligands ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The synthesis of the new potentially tridentate ligand 3,5-bis(dimethylaminomethyl)pyridine (3) is described. Coordination chemistry of this ligand has been investigated with PdII and PtII precursor compounds. Both a bidentate bridging bonding motif and a monodentate bonding mode is observed. The latter compounds incorporate 3 by coordination through the pyridinic N atom only. The former complexes contain ligand 3 bonded to 2 metal centres by bridging through coordination of one trialkyl N donor atom and the pyridinic N atom. The solid-state structure of a ligand bridged Pd dimer has been elucidated by single-crystal X-ray diffraction and corroborates with the solid-state IR data that suggested a trans-PdCl2 unit was present.
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  • 212
    Electronic Resource
    Electronic Resource
    Magnetic Interaction in Dinuclear Triphos-Cobalt Complexes with Co···Co Separations of 8 and 10 Å (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 183-189 
    Details
    ISSN: 1434-1948
    Keywords: Tripodal ligands ; Cobalt complexes ; Bridging ligands ; Exchange coupling ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Weak antiferromagnetic exchange interactions are observed in two CoII dimers of the general formula [{(triphos)Co}2(μ-dicarboxylato)](BF4)2 where the dicarboxylate is the dianion of fumaric acid [3 ·(BF4)2] or terephthalic acid [4 ·(BF4)2] and triphos is the tridentate phosphorus ligand 1,1,1-tris(diphenylphosphanomethyl)ethane. In these complexes the metal ions are separated by 8 and 10 Å, as determined by X-ray crystallography. Insight into the interaction pathway is gained through molecular orbital calculations performed on model compounds. The influence of bridging-ligand distortions and the stereochemistry around the two cobalt centres is discussed.
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  • 213
    Electronic Resource
    Electronic Resource
    A New and Easy Route to Polysilanylpotassium Compounds (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 221-226 
    Details
    ISSN: 1434-1948
    Keywords: Polysilanes ; Polysilyl anions ; Silylpotassium ; Silicon ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A method is presented for the synthesis of tertiary, secondary, and primary polysilylpotassium compounds. Reaction of potassium tert-butoxide, in either DME or THF, with a suitable precursor molecule, proceeds by cleavage of a trimethylsilyl- polysilanyl bond, and formation of trimethylsilyl tert-butyl ether and a polysilanylpotassium compound. This route allows easy and flexible access to a number of novel polysilanylpotassium compounds, avoiding the hitherto common use of poisonous mercury compounds.
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  • 214
    Electronic Resource
    Electronic Resource
    Homoleptic Organometallic Compounds of Zinc, Cadmium, and Mercury, Intramolecularly Stabilized by Amine Ligands (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 245-252 
    Details
    ISSN: 1434-1948
    Keywords: Alkylamines ; Arylamines ; Zinc ; Cadmium ; Mercury ; X-ray diffraction ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Homoleptic intramolecularly stabilized organozinc, -cadmium, and -mercury compounds MR2, with R bearing an amino function, have been synthesized from the corresponding metal dichlorides MCl2 and the lithium salts LiC6H4CH2NEt2-2 (1), LiC6H3(CH2NMe2)2-2,6 (2), LiC6H3(CH2NEt2)2-2,6 (3), (LiCH2CH2CH2)2NMe (4), and LiCH2CH2CH2NC5H10 (5). The crystal structures of Hg(C6H4CH2NEt2-2)2 (1c), [M(CH2CH2CH2)2NMe]2 [M = Zn (4a), Hg (4c)], and of M(CH2CH2CH2NC5H10)2 [M = Zn (5a), Cd (5b)] have been determined by X-ray diffraction. 4a and 4c form dimers with an unusual coordination number (three) of the central metal.
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  • 215
    Electronic Resource
    Electronic Resource
    Synthesis and Spectroscopic Data of para-Substituted (3-Phenyl-2H-azaphosphirene)tungsten Complexes (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 257-261 
    Details
    ISSN: 1434-1948
    Keywords: Phosphorus heterocycles ; 2H-Azaphosphirene complexes ; Carbene complexes ; Tungsten ; Cyclizations ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: High-yield synthesis of para-substituted pentacarbonyl(3-phenyl-2H-azaphosphirene)tungsten complexes is reported, using a multi-step rearrangement reaction. Spectroscopic and mass-spectrometric data of these heterocyclic complexes are discussed; the 31P-NMR-chemical shifts clearly reflect the electronic influence of the para-phenyl substituents and the correlation with Hammett σp-constants is almost linear.
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  • 216
    Electronic Resource
    Electronic Resource
    Spectroscopic Evidence for Intramolecular MoVI(O2)····HO-C Hydrogen Bonding in Solution (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 275-281 
    Details
    ISSN: 1434-1948
    Keywords: Molybdenum ; Peroxo complexes ; Hydrogen bonds ; Catalysis ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The ring-opening reaction of epoxycyclohexane with 2-[3(5)-pyrazolyl]pyridine results in the formation of racemic trans-2-[3-(2-pyridyl)-1-pyrazolyl]cyclohexanol (1). Kinetic resolution with lipase B from candida antarctica gives the (1S,2S) enantiomer of 1, the solid-state structure of which was determined by X-ray crystallography, as an enantiomerically pure tridentate ligand. Investigation by NMR spectroscopy of the corresponding oxodiperoxomolybdenum complex 2, where 1 acts as a bidentate chelate, proves the formation of a weak intramolecular MoVI(O2)····HO-C bridge in CHCl3 solution. This H bonding is broken by solvents such as acetone, THF or DMF, which are capable of forming hydrogen bonds to alcohols. Intermolecular hydrogen bonds between the OH groups and molybdenum peroxo moieties are also found in the solid-state structure of 2, leading to a helical arrangement of the peroxo complexes.
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  • 217
    Electronic Resource
    Electronic Resource
    Synthesis and Structure of the First η1-Borazine Complexes (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 291-293 
    Details
    ISSN: 1434-1948
    Keywords: Boron ; Iron ; Boryl complexes ; η1-Coordinated borazine ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A series of η1-borazine complexes were obtained by the reaction of trichloroborazine with Na[(η5-C5R5)Fe(CO)2]. The compounds [{(C5R5)(CO)2Fe}nCl3-nB3N3H3] (1a, n = 1, R = Me; 1b, n = 2, C5R5 = C5H4Me; 1c, n = 3, R = H) have one to three iron-boron σ bonds and Fe-B π-interactions can be ruled out from the spectroscopic and structural results. All new borazine complexes were isolated as orange crystalline solids and characterized by multinuclear NMR methods and IR spectroscopy. The structure of 1b in the crystalline state was also determined by a single-crystal X-ray study.
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  • 218
    Electronic Resource
    Electronic Resource
    Group-13 Metal-Induced Coordination Variation of the Bis(2-pyridyl)amide Ligand in Solution and in the Solid State (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 311-317 
    Details
    ISSN: 1434-1948
    Keywords: Molecular recognition ; Amides ; Aluminium ; Thallium ; Structure elucidation ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Ligands containing aromatic nitrogen heterocycles play a leading role in the molecular self assembling processes that lead to macromolecular architectures. The inductive effect of various metal fragments on those building blocks has not yet been studied systematically. To evaluate this effect we synthesized the homologous series of Group-13 metal complexes [Me2AlPy2N] (1), [Me2GaPy2N] (2), [Me2InNPy2]2 (3), and [Me2TlNPy2]∞ (4) (Py = 2-NC5H4), and characterized them by low-temperature X-ray structure analysis and 15N-NMR spectroscopy in solution. The electronic equivalence of the central and the ring nitrogen atoms leaves the energetic hyperface of the anion quite flat, and the electron density is polarized according to the requirements of the metal. In the aluminum and the gallium complexes 1 and 2 the metal center is coordinated exclusively through the nitrogen atoms within the pyridyl rings. The complexes with these hard metals are close-contact ion pairs. In the indium complex 3 the cis-cis orientation gives rise to a dimeric structure, while the unprecedented cis-trans arrangement in the thallium compound 4 leads to a polymeric structure. The complexes 3 and 4 have to be regarded as separated ion pairs of Me2M+ cations and Py2N- anions without any covalent bonds between the anionic moiety and the dimethylmetal cations, even in the solid state. The series of complexes proves the bis(2-pyridyl)amide to be an excellent self-adapting ligand. These findings are substantiated by NMR-spectroscopic studies in solution. Not only do the steric requirements of N heteroaromatic ligands have to be considered in molecular self-assembling processes but also the inductive effect of the different metal fragments.
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  • 219
    Electronic Resource
    Electronic Resource
    Diastereoselective Substitution of PR3 for CO in Carbene(dicarbonyl)cyclopentadienyl Complexes of Manganese - Synthesis of (SMn)- and (RMn)-[Cp(CO)(PR3)Mn=C(OR*)R′] Complexes (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 339-347 
    Details
    ISSN: 1434-1948
    Keywords: Carbene complexes ; Carbyne complexes ; Asymmetric synthesis ; Carbohydrates ; Chiral auxiliaries ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Chiral carbene complexes [Cp(CO)2Mn=C(OR*)Ph] (4a-e) were prepared by reaction of [Cp(CO)2Mn=C(OAc)Ph] (2) with HOR* [HOR* = 1,2:3,4-di-O-isopropylidene-D-galactopyranose (3a), 2,3,4,6-tetra-O-acetyl-D-galactopyranose (3b), 2,3,4,6-tetra-O-acetyl-D-glucopyranose (3c), (S)- (3d) and (R)-1,2-O-isopropylideneglycerol (3e)]. The replacement of a CO ligand with PTol3 in 4a-e proceeded diastereoselectively to give [Cp(CO)(PTol3)Mn=C(OR*)Ph] (5a-e). The diastereoselectivity increased in the order a, b, c, d: de = 8% (5a), 33% (5b), 70% (5c), 〉 96% (5d). For (R)-5d the isomer with the (S) configuration at manganese (SMn) was formed predominantly. For (S)-5d, only (RMn,S)-5d was detected (de 〉 96%). Photolysis of (R)-4d in the presence of phosphites or phosphanes afforded (SMn)-[Cp(CO)(PR3)Mn=C(OR*)Ph] [PR3 = P(OPh)3 (8), P(OMe)3 (9), P(OMe)2Ph (10), P(OMe)Ph2 (11), PPh3 (12), P(C6H4Cl-p)3 (13)] with a de 〉 96%. Photolysis of (S)-4d in the presence of P(OMe)3 gave (RMn,S)-9. Complex (R)-14 [related to (R)-4d] was obtained from [Cp(CO)2Mn=C(OAc)Tol-p] and 3d. Replacement of CO by PR3 in (R)-14 gave (SMn,R)-[Cp(CO)(PR3)Mn=C(OR*)Tol-p] [R = Tol-p (15), OMe (16), C6H4Cl-p (17)] with a de 〉 96%. In solution, the PTol3-substituted complex 5d is configurationally stable whereas the P(OMe)3 complex 9 epimerizes slowly at room temperature in CH2Cl2, Et2O, and THF within about one week.
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    The Reactions of R2Ga-GaR2 and R2In-InR2 [R = CH(SiMe3)2] with Protic Reagents: Substituent Exchange versus Cleavage of the Element-Element Bond (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 355-360 
    Details
    ISSN: 1434-1948
    Keywords: Gallium ; Indium ; Low-valent compounds ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Tetrakis[bis(trimethylsilyl)methyl]digallane(4) (1) with a Ga-Ga single bond and the corresponding diindane(4) 2 with an In-In single bond were treated with different protic reagents: tert-Butyl alcohol did not react with 1 at all, while phenol gave a mixture of unknown products, which could not be separated. The more acidic pentafluorophenol did not react as an acid, but C-F bonds were cleaved to form almost quantitatively the dimer (R2GaF)2 5, which was characterized by a crystal-structure determination. Water and 1 yielded the dimeric dialkylgallium hydroxide 6. The Ga-Ga bond was also cleaved by the reaction of 1 with durylthiophenol (duryl = 2,3,5,6-tetramethylphenyl), which gave two main products: R2Ga(SDuryl) 7 and RGa(SDuryl)2 8. In contrast, the chelating acid dibenzoylmethane reacted by means of a substituent exchange, with the release of two equiv. of bis(trimethylsilyl)methane for each formula unit of 1, to form 9, in which the Ga-Ga bond is retained and each chelating 1,3-diphenyl-1,3-propanedionato ligand is in a terminal position bonded to only one Ga atom, in more than 80% yield. The Ga-Ga bond is shortened [244.1(1) pm] compared to that in the starting compound tetraalkyldigallane(4) 1. The In-In bond of diindane(4) 2 is, however, cleaved in a similar reaction with dibenzoylmethane, and only the fragmentation product dialkyl(1,3-diphenyl-1,3-propanedionato)indium 10 could be isolated.
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    The Reaction of Potassium Polyselenides with [CpW(CO)3Cl] in DMF - Formation and Crystal Structure of [CpW(CO)3SeC(O)NMe2] and {[CpW(CO)3]2Se4} (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 397-400 
    Details
    ISSN: 1434-1948
    Keywords: Polychalcogenides ; Selenium ; Selenocarbamato complexes ; 77Se NMR ; Crystal structure ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The reactions of the potassium polyselenides „K2Se6” and „K2Se8” with [CpW(CO)3Cl] and 18-crown-6 in DMF lead to a mixture of the selenido complexes {[CpW(CO)3]2Se4} 1 and [(18-crown-6)K]+[CpW(Se4)2]- 3 and the Se-bonded selenocarbamato complex [CpW(CO)3SeC(O)NMe2] 2 in yields depending on the selenium content of the used potassium polyselenides („K2Se6” or „K2Se8”). A similar reaction in THF produces {[CpW(CO)3]2Se4} as the main product. X-ray structures of 1 and 2 were determined. In 1 the Se4-chain is bonded in a μ2-η1 fashion, with corresponding W-Se bond lengths of 264.0(1) and 264.3(1) pm. The Se-Se bond lengths lie in the range 232 to 237 pm. The first example of an η1 Se-bonded selenocarbamato ligand is observed in the crystal structure of 2, with a W-Se bond length of 263.1(1) pm. The 77Se-NMR data are compared with the corresponding data of related complexes.
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    Specific Chelate Tuning of the Substitution Kinetics of Platinum(II) Complexes in Aqueous Solution (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 389-396 
    Details
    ISSN: 1434-1948
    Keywords: Substitution mechanism ; Platinum ; Pressure dependence ; Kinetics ; Dinuclear complex ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Both reaction steps observed for the substitution of water by thiourea in the complexes [Pt(en)(OH2)2]2+ and [Pt(phen)(OH2)2]2+ (en = ethylenediamine, phen = 1,10-phenanthroline) were investigated under pseudo-first-order conditions using the stopped-flow technique. The substitution of the second water molecule in each complex was also studied under high pressure. The observed pseudo-first-order rate constants kobs (s-1) obeyed the equation k1,2obs= k1,2[tu] (tu = thiourea), where “1” and “2” refer to the first and the second substitution reactions, respectively. Kinetic parameters associated with the substitution process are: k1en (25.0°C, pH = 3.0, I = 0.1 M) = 25.6 M-1 s-1, ΔH# = 51 kJ mol-1, ΔS# = -48 J K-1 mol-1; k2en (same conditions) = 12.1 M-1 s-1, ΔH# = 30 kJ mol-1, ΔS# = -124 J K-1 mol-1, ΔV# = -7 cm3 mol-1; k1phen (25.0°C, pH = 1.0, I = 0.1 M) = 2900 M-1 s-1, ΔH# = 41 kJ mol-1, ΔS# = -41 J K-1 mol-1; k2phen (same conditions) = 1170 M-1 s-1, ΔH# = 37 kJ mol-1, ΔS#= -61 J K-1 mol-1, ΔV# = -5 cm3 mol-1. The temperature and pressure dependence of all the processes studied suggest an associative substitution mechanism. The hydroxo-bridged dinuclear complex [{Pt(phen)(μ-OH)}2]2+ is formed from [Pt(phen)(OH2)2]2+ in aqueous solution unless the solution is very dilute and highly acidic. The X-ray structure of [{Pt(phen)(μ-OH)}2](F3CSO3)2 · 2 H2O was determined. It belongs to the triclinic space group P1­ and has one formula unit in the unit cell. The unit cell dimensions are a = 7.126(5), b = 9.665(5), c = 12.774(7) Å; α = 71.85(5), β = 85.52(5), γ = 73.12(5) deg; V = 799.9(8) Å3. The structure was solved with the Patterson method and refined to R = 0.061. A square planar coordination of the platinum centers is observed, with no deviations from planarity but distortions due to the small bite angle of phen and the four-membered ring. No significant lengthening of the Pt-O bond [mean value: 2.03(1) Å] is observed in comparison with [{Pt(NH3)2(μ-OH)}2]2+.
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    Ethylene Polymerization with Hydridotris(pyrazolyl)boratoniobium Complexes as Precursors (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 425-428 
    Details
    ISSN: 1434-1948
    Keywords: Ethylene polymerization ; Group 5 metal complexes ; Hydridotris(pyrazolyl)borates ; Alkyne ligands ; Migratory insertion ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Substituted hydridotris(pyrazolyl)borato (Tp′) niobium complexes of the type [Tp′NbMe2(PhC≡CMe)] polymerize ethylene (under 1 atm, at room temp. and in toluene) when treated with an equimolar amount of B(C6F5)3. A clear relationship is observed between the stereoelectronic nature of the complex and catalytic activity. This is discussed on the basis of electrochemical data for the dichloro complexes [Tp′NbCl2(PhC≡CMe)], and the rates of alkyl migration in [Tp′Nb(Cl)(R)(PhC≡CMe)] (R = CH2Me, CH2SiMe3). For a given electron density at the metal, the bulky TpMe2,4-Cl yields a catalyst which is more than 6 times as active as the unsubstituted Tp based catalyst.
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    Synthesis and X-Ray Structures of Novel Lead(1+) and Indium(3+) Phosphazenide Complexes; Detailed 207Pb-NMR Spectra of the 207Pb-Labelled Dimeric Lead(1+) Species (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 437-444 
    Details
    ISSN: 1434-1948
    Keywords: Lead(1+) ; Indium(3+) ; Organylphosphanylamide complexes ; Phosphazene ; 207Pb-NMR spectra ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The reaction of PbCl2 with LiN(PPh2)2 (1) at -78°C affords the P-P coupled phosphazene Ph2P-N=PPh2-PPh2=N-PPh2 (2) as an oxidation product and, as a reduction equivalent, the novel lead(1+) complex [(Pb1+)2(μ-Ph2P···N···PPh2-)2](Pb-Pb) (3). The crystal structure determination of the red compound 3 shows a Pb-Pb bond length of 304.1(1) pm. The 31P- and 207Pb-NMR spectra of 3 are complicated due to the presence of a higher order spin system (AA′A′′A′′′X for the mono-207Pb isotopomer, AA′A′′A′′′XX′ for the bis-207Pb isotopomer). Simulations of the 31P and 207Pb spectra both on material with natural isotope abundance and on the 207Pb-labelled compound (3*) reveal a large Pb,Pb coupling constant of 7708 Hz, indicative of a covalent Pb-Pb bond. - Though InCl3 is diagonally related to PbCl2, no significant redox process is observed in the reaction between InCl3 and 1. The yellow crystals of [In3+(Ph2P···N···PPh2-)3] (4) that are obtained were also investigated by X-ray analysis. These show a propeller-like configuration of the three four-membered chelate rings with indium(3+) as the centre.
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    Boryl- and Bridging Boryleneiron Complexes from Aminodichloroboranes (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 465-468 
    Details
    ISSN: 1434-1948
    Keywords: Boron ; Iron ; Boryl complexes ; Borylene complexes ; Iron-boron bond ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Depending on the nature of the amino group bound to the boron atom, the reactions of various aminodichloroboranes R2NBCl2 with Na[(η5-C5R′5)Fe(CO)2] yield either boryl or bridging borylene complexes of iron. The compounds [(C5R′5)(CO)2Fe{BCl(NR2)}] (1a, C5R′5 = C5H5, R = Me; 1b, C5R′5 = C5H4Me, R = Me; 1c, C5R′5 = C5Me5, R = Me) and [(η-BNR2)(μ-CO){(C5R′5)Fe(CO)}2] (2a, C5R′5 = C5H5, R = SiMe3; 2b, C5R′5 = C5H4Me, R = SiMe3) were isolated as orange (1a-c) or red (2a, b) crystalline solids, and characterized by multinuclear NMR methods and IR spectroscopy. The structures of 1c and 2b in the crystalline state were determined by single-crystal X-ray studies.
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    Synthesis and Structural Characterization of Gold(I) and Silver(I) Complexes of the Multidonor Ligand 2-(Phenacylthio)pyridine - Crystal Structures of [(AuPPh3){py{SCH2C(O)Ph}-2}](ClO4) and [(AgPPh3)(OClO3){py{SCH2C(O)Ph}-2}] (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 511-516 
    Details
    ISSN: 1434-1948
    Keywords: Gold(I) ; Silver(I) ; S-donor and N-donor ligand ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The ligand properties of 2-(phenacylthio)pyridine towards gold(I) and silver(I) have been investigated. From the reactions of the ligand with acetone solutions of [M(PPh3)(acetone)]ClO4 (M = Ag, Au) under various experimental conditions, complexes [(AuPPh3)n{py{SCH2C(O)Ph}-2}](ClO)n, and [(AgPPh3)n(OClO3)n{py{SCH2C(O)Ph}-2}](n = 1-3) have been obtained. The crystal structures of the complexes [(AuPPh3){py{SCH2C(O)Ph}-2}]ClO4 and [(AgPPh3)(OClO3){py{SCH2C(O)Ph}-2}] have been determined by X-ray diffraction. In the cationic gold complex the metal is linearly coordinated to nitrogen and phosphorus, whereas the corresponding silver complex displays a trigonal planar geometry with pyridine, phosphane and perchlorato ligands.
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    Synthesis of the First Lanthanoid(II) Pyrazolate Complex by Redox Transmetallation from Thallium and Mercury Reagents (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 543-545 
    Details
    ISSN: 1434-1948
    Keywords: Lanthanoid(II) complexes ; Ytterbium ; Thallium ; η2-Pyrazolate complexes ; Diphenylmercury ; Redox transmetallation ; X-ray crystal structure ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Ytterbium metal reacts with thallium(I) 3,5-diphenylpyrazolate, or with diphenylmercury and 3,5-diphenylpyrazole (Ph2pzH) in tetrahydrofuran or 1,2-dimethoxyethane (DME) giving, after appropriate isolation, the first lanthanoid(II) pyrazolate complex, [Yb(Ph2pz)2(DME)2]. The molecular structure reveals eight coordinate ytterbium(II) with two cisoid η2-3,5-diphenylpyrazolate and two chelating 1,2-dimethoxyethane ligands.
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    Syntheses of 3-Phenyl-2H-Azaphosphirene Chromium and Molybdenum Complexes - First Evidence for Reaction Intermediates (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 571-574 
    Details
    ISSN: 1434-1948
    Keywords: Phosphorus heterocycles ; 2H-Azaphosphirene complexes ; Carbene complexes ; Chromium ; Molybdenum ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The synthesis of 3-phenyl-substituted 2H-azaphosphirene pentacarbonylchromium and pentacarbonylmolybdenum complexes is reported. New information on the rearrangement cascade, which finally leads to 2H-azaphosphirene ring formation, has been obtained through isolation of a reactive intermediate. A comparison of the 13C-, 15N-, 31P-NMR, and UV/vis spectroscopic data and single crystal X-ray structural data of 3-phenyl-substituted 2H-azaphosphirene chromium, molybdenum, and tungsten complexes is presented.
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    A New Class of Oligonuclear Platinum-Thallium Compounds with a Direct Metal-Metal Bond - 3. Unusual Equilibria in Aqueous Solution (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 565-570 
    Details
    ISSN: 1434-1948
    Keywords: Equilibrium ; Metal-metal bond ; Stability constants ; Platinum ; Thallium ; NMR ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A new series of four binuclear platinum-thallium cyano compounds containing a direct and unsupported by ligands metal-metal bond has been prepared in aqueous solution. These compounds are represented by the formula[(NC)5Pt-Tl(CN)n-1](n-1)- (n = 1-4 for compounds I, II, III IV, respectively) and [(NC)5Pt-Tl-Pt(CN)5]3- (for compound V). The oligonuclear complexes are synthesised according to the reaction mPt(CN)42- + Tl3+ + nCN- █[PtmTl(CN)4m+n]3-2-n. Thus, there occurs a change of the coordination number of the Pt center from four (square planar) to six (octahedral). Consequently, the formation of binuclear platinum-thallium cyano compounds involves at least two steps: (i) formation of metal-metal bond and (ii) formation of (NC)5Pt- unit by a cyanide transfer process. - The complexes exist in an equilibrium, which also includes the parent complexes Pt(CN)42- and Tl(CN)n3-n (n = 0-4), and can be controlled by varying the cyanide concentration and/or pH of the solution. The stability constants of the compounds βN =[PtmTl(CN)4m+n3-2m-n{[Pt(CN)42-]m · [Tl3+] · [CN-]n} have been determined by means of multinuclear NMR (195Pt, 205Tl): logβN = 19.9±0.4, 30.7±0.3, 38.6±0.3, and 44.8±0.2 for I, II, III and IV(m = 1, n = 1-4), and 32.1±0.3 for V(m = 2, n = 2), respectively, (in 1 M NaClO4 as ionic medium, at 25 oC). To our knowledge, the present work constitutes the first detailed equilibrium study of metal-metal bonded compounds; it indicates that also other cluster formation reactions described in the literature may represent real equilibria.
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    P-Alkylated (1S,2S)-Cyclopentane-1,2-diylbisphosphanes with Four Stereogenic Centers and Some Group 10 Metal(II) Complexes Containing the (1S,2S)-C5H8[P(CH3)C8H15-cyclo]2 Ligand (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 597-603 
    Details
    ISSN: 1434-1948
    Keywords: Chirality ; P ligands ; Nickel ; Palladium ; Platinum ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Radical-initiated P-H addition of (1S,2S)-C5H8(PH2)2 to cycloalkenes gave bis(secondary phosphanes), (1S,2S)-C5H8[P(H)CnH2n-1-cyclo]2 (n = 5-8), as mixtures of RP,RP′, SP,SP′, and RP,SP′ diastereomers. The three diastereomers of the peralkylated chiral P2 ligand (1S,2S)-C5H8[P(CH3)C8H15-cyclo]2 and its complexes with NiCl2, PdI2, and PtI2 were prepared. The structures of [(1S,2S)-C5H8{P(CH3)C8H15-cyclo(R)}2NiCl2] · [(1S,2S)-C5H8{P(CH3)C8H15-cyclo-(S)}2NiCl2],(1S,2S)-C5H8{P(CH3)C8H15-cyclo-(R)}2PdI2, and (1S,2S)-C5H8{P(CH3)C8H15-cyclo-(R)}2PtI2 were determined by X-ray diffraction.
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    The Conformational Flexibility of Oxidized Cytochrome c Studied through Its Interaction with NH3 and at High Temperatures (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 583-591 
    Details
    ISSN: 1434-1948
    Keywords: Cytochrome c ; Hyperfine shift ; Magnetic susceptibility anisotropy ; NMR spectroscopy ; Heme proteins ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The binding of ammonia to oxidized horse heart cytochrome c has been studied by 1H-NMR, EPR, and CD spectroscopy at pH = 8.0. The affinity constant of the ligand is in the range 1.5-4 M-1. The 1H-NMR spectra of the heme group have been found to be similar to those of the high-pH forms, high-temperature forms, and cyanide adduct of the Met80Ala mutant of S. cerevisiae iso-1-cytochrome c. The assignment of a number of signals has led to the determination of the values of the magnetic anisotropy and of the orientation of its axes. The latter are similar to those of the Met80Ala cyanide derivative. The assignment of the high-temperature species has been further pursued during this research. The analysis of the NMR data of the NH3 adduct leads to the conclusion that substitution of Met80 at high pH or high temperature occurs through a ligand with cylindrical symmetry. This supports the suggestion that Met80 is substituted by a lysine at high pH.
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    C-C Coupling Reactions of (Sulfene)ruthenium Complexes with Enolates (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 605-611 
    Details
    ISSN: 1434-1948
    Keywords: Enolates ; Nucleophilic additions ; Ruthenium ; S ligands ; Sulfenes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Sulfene complexes [CpRu(PR′3)2(RHC=SO2)]PF6 (2a-d) are obtained from the corresponding sulfur dioxide complexes 1a-c and diazomethane or -ethane. Reaction of [CpRu(dppm)(SO2)]Cl (1d) and phenyldiazomethane gives the chlorobenzylsulfinato complex [CpRu(dppm)(SO2CHPhCl)] (3). Alternatively, 2a may be synthesized by sulfur dioxide addition to the carbene complex [CpRu(dppm)(CH2)]PF6 (5) which, in turn, is obtained from the corresponding methyl complex [CpRu(dppm)(CH3)] and [Ph3C]PF6. Treatment of 2a-d or 3 with the enolates of cyclic 2-methyl-1,3-diketones, methyl malonates, open-chain cyano or β-oxo esters, and cyclic β-oxo esters gives the C-C coupling products 6a, b, 7a-e, 8a-c, 9a-c in high yields and, in one case, with high diastereoselectivity as well. The functionalized sulfinate ligands thus formed may be alkylated and subsequently removed from the metal center by ligand substitution with acetonitrile. After MeCN/SO2 exchange, the ruthenium complex can be recycled.
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    Replacement of One CO Unit in Dicarbonyl(η5-cyclopentadienyl)cobalt Derivatives by Bis(tert-butylsulfonyl)acetylene (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 629-632 
    Details
    ISSN: 1434-1948
    Keywords: Alkyne complexes ; Carbonyl complexes ; Cobalt ; CO replacement ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The reaction of dicarbonyl(η5-cyclopentadienyl)cobalt (1) and some of the Cp-ring substituted congeners with bis(tert-butylsulfonyl)acetylene (BTSA) results in the replacement of one CO group by the BTSA moiety. The variation of the yields and reaction times indicates a dependence of the reactivity of 1-6 with BTSA as a function of substituents. X-ray investigations of the products show that the alkyne unit is strongly bound to the metal.
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    2,3,4-Tricarba-nido-hexaboranes(7) with a Bridging B-Ethyl-B Moiety (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 633-637 
    Details
    ISSN: 1434-1948
    Keywords: Ab initio calculations ; Boron ; Carboranes ; NMR spectroscopy ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Hydroboration of diethyl(1-propynyl)borane 1 with tetraethyldiborane(6) in the presence of a catalytic amount of trimethyl- or tributyltin chloride gave two new organo-substituted carboranes 6 and 7 with 2,3,5-tricarba-nido-hexaborane(7) and 2,3,4-tricarba-nido-hexaborane(7) skeletons, respectively, along with polymeric material and the known organo-substituted 1-carba-arachno-pentaborane(10) (3) and pentaethyl-1,5-dicarba-closo-pentaborane(5) (4). Selective 11B(5,6) decoupled 13C-NMR spectra indicate an unprecedented B(5)-ethyl-B(6) bridge in 7. This structure is supported by the agreement between experimental and calculated 11B- and 13C-chemical shifts on a model compound 7d with methyl groups in the 1,2,3,5,6-positions and an ethyl group bridging B(5) and B(6).
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    How to Derive Force Field Parameters by Genetic Algorithms: Modelling tripod-Mo(CO)3 Compounds as an Example (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 693-702 
    Details
    ISSN: 1434-1948
    Keywords: Genetic Algorithms ; Force field calculations ; Refinement of force field parameters ; Tripod metal compounds ; Conformational analysis ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Force field parameters used to describe the conformation of coordination compounds involving transition metals are generally derived by a trial-and-error procedure, until a somehow satisfying agreement between the calculated and observed conformations of a few members of a class of related compounds is reached. It is shown in this paper that a more general and less biased alternative is available, applicable to many structures at a time. Genetic Algorithms will effectively optimize force field parameters in an automatic way, on the basis of a potentially exhaustive set of all the structural data available for a given class of compounds. The feasibility of this procedure has been demonstrated by the derivation of force field parameters describing the conformational behaviour of tripod-Mo(CO)3 compounds [tripod= RCH2C(CH2X)(CH2Y)(CH2Z), X,Y,Z = PR′R′′)] by simultaneous optimization based on the structure of ten individual molecules. With the force field parameters relevant to the organic part of these compounds taken from MM2*, the parameters involving contributions from the Mo center were refined. The agreement between observed and calculated structures is characterized by an rms deviation of around 0.3 Å for the ten structures contained in the data base. To assess the validity of this approach, the conformational space of CH3C(CH2PPh2)3Mo(CO)3 was explored exhaustively. A contour diagram representing the relative energy of the molecule with respect to the rotational positions of its phenyl groups was found to effectively reproduce the scatter of these conformational parameters as earlier derived from an analysis of 82 relevant compounds. - As a further assessment, the conformational space of CH3C[CH2P(o-Tol)2]3Mo(CO)3, which was not included in the data base, has been analyzed. It is found that the structure corresponding to the global energy minimum corresponds to that observed in the crystal with an rms deviation of only 0.3 Å. The novel approach to problems of this type - Genetic Algorithms had not previously been applied in this context - thus appears promising.
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    Four-Coordinate Group-14 Elements in the Formal Oxidation State of Zero - Syntheses, Structures, and Dynamics of [{(CO)5Cr}2Sn(L2)] and Related Species (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 703-720 
    Details
    ISSN: 1434-1948
    Keywords: Germanium ; Tin ; Lead ; 119Sn NMR ; Dynamic NMR ; Salt metathesis ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The sodium salts Na2[{(CO)5M}2EX2] (M = Cr, Mo, W; E = Ge, Sn, Pb; X = Cl, I, OOCCH3) react with 2,2′-bipyridine (bipy) to form neutral compounds [{(CO)5M}2E(bipy)] (E = Sn: 1a-1c; E = Ge: 3a; E = Pb: 4). 1,10-Phenanthroline (phen) analogues of compounds 1a-1c and 3a [{(CO)5M}2E(phen)] (E = Sn: 1d-1f, E = Ge: 3b) are as well accessible. The 2,2′-bipyridine ligand in 1 may be formally replaced by two pyridine (py) ligands resulting in [{(CO)5M}2Sn(py)2] (1g: M = Cr, 1h: M = W). The bis-bidentate ligand 2,2′-bipyrimidine (bpmd) is found to coordinate just one [{(CO)5M}2Sn] entity in [{(CO)5M}2Sn(bpmd)] (2b: M = Cr, 2c: M = W). The biimidazolato (biim) ligand binds two [{(CO)5Cr}2Sn] moieties in [{(CO)5Cr}2Sn(biim)Sn{Cr(CO)5}2]2-, 2a. It is shown by 1H-NMR that the pyrimidine entities in these compounds (2b, 2c) are able to rotate by a full 180° turn-around with respect to one another. This process must involve complete de-coordination of at least one of the two nitrogen donors in again at least one of the chelate cycles, the activation energy for this process being around 60 kJ/mol. By 119Sn-NMR spectroscopy of almost all of the tin compounds described it is shown that equilibria between [{(CO)5M}2Sn(L2)] and [{(CO)5M}2Sn(L)] + L exist in all cases. From the temperature dependence of the δ values it is concluded that the activation barriers for this association/dissociation process is below 10 kJ/mol. The structures of all new compounds are documented by X-ray analyses and all compounds are characterized by the usual analytical and spectroscopical techniques.
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    The π-Electron-Accepting Ability of the Boron Atom in Ethynylboranes and Related Compounds - An Approximate Weight Computation for Resonance Structures⋆ (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 733-744 
    Details
    ISSN: 1434-1948
    Keywords: Aminoboranes ; Ab initio calculations ; Valence-bond theory ; Resonance structures ; Alkynes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A theoretical analysis was performed to quantify the π-electron-accepting ability of the boron atom in ethynylboranes. An expansion technique was employed which permits to obtain a set of localized bonding schemes and their weights from a delocalized molecular orbital determinantal wavefunction. The derived manifold of bonding schemes is close to the classical resonance hybrid used in organic chemistry (valence-bond description). We quantified the π-electron transfer into the empty π-orbital of the boron atom by investigating nine model compounds where substituents with π-electron-donating ability are adjacent to a boron atom. This led to an ordering of the substituents according to their electron-donating ability towards boron. The boron atom hesitates to accept π-electrons from the ethynyl group in ethynylboranes in particular when good π-donors like amino groups are present. The π-electron donation from the vinyl group to the adjacent boron centre is slightly stronger than from the ethynyl group. Nitrogen lone-pair electrons are easily transferred to a neighbouring boron centre. Bonding schemes and their weights are in line with computed bond lengths and rotational barriers. Moreover, our theoretical results rationalize previous NMR and X-ray experiments and are in line with the reactivity of related compounds. It is demonstrated that bond lengths alone do not necessarily correlate with the degree of π-bonding and should be discussed with caution. The analysis is substantiated by showing that weights for covalent bonding schemes, as obtained from the simple restricted closed-shell MO determinant, correlate with bond strengths. Furthermore, a correlation of bonding-scheme weights with quantities based on the fragment orbital approach is presented. This novel correlation elucidates molecular properties which determine the extent of the π-electron transfer to the boron atom and permits a quantitative interpretation and prediction of intramolecular π-bonding.
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    Rh(I)-Catalysed Asymmetric Hydrosilylation using New Oxazoline Ligands with Potential Charge-transfer Properties (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 783-788 
    Details
    ISSN: 1434-1948
    Keywords: Enantioselective hydrosilylation ; Oxazoline ligands ; Charge-transfer ; 4,4-Bipyridine derivatives ; 2,5-Dimethoxyacetophenone ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Novel N′-methylated 2-(oxazolin-2-yl)-4,4′-bipyridinium salts, bearing a chiral oxazoline moiety, were tested in the Rh(I)-catalysed enantioselective hydrosilylation. After coordination to rhodium these electron-attracting ligands are supposed to exhibit charge-transfer effects with electron-donating substrates. Therefore, a new catalytic hydrosilylation reaction with 2,5-dimethoxyacetophenone as an electron-rich substrate was developed. The results were compared with those of the non-methylated 2-(oxazolin-2-yl)-4,4′-bipyridine and related ligands. In addition, the new ligands and Rh(I)-complexes were tested in the hydrosilylation of acetophenone.
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    Three-Dimensional Assemblies of Gold Colloids in Nanoporous Alumina Membranesast; (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 807-812 
    Details
    ISSN: 1434-1948
    Keywords: Gold colloids ; Self-assembly ; Nanoporous alumina ; Three-dimensional organization ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Examples of a new class of three-dimensionally arranged gold colloids have been prepared in the nanoscale pores of alumina membranes. Immobilization of the colloid particles was achieved by a modification of the inner walls with alkoxysilanes Y-(CH2)x-Si(OR)3 and Y-(CH2)x-SiR(OR)2 bearing suitable functional groups (Y = NH2, SH), followed by anchoring of the colloids by self-assembly onto the modified surface. This procedure gives tight and stable ensembles of colloids on the walls. TEM analyses revealed uniform and random colloidal dispersions on the walls in the form of sub-monolayers without any aggregation. UV/Vis spectra of the filled membranes showed an absorption maximum at ca. 525 nm arising from an excitation of the plasmon resonance of the gold colloids. The dimensions of the pores can be “tuned” and given the diverse range of different colloids available, routes to novel catalysts and sensors can be envisaged.
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    Synthesis, Structure, and Properties of Osmium Complexes Containing [Os(′S4′)] and [Os(′S2′)2] Fragments (′S4′2- = 1,2-Bis(2-mercaptophenylthio)ethane(2-), ′S2′2- = 1,2-Benzenedithiolate) (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 819-826 
    Details
    ISSN: 1434-1948
    Keywords: S ligands ; P ligands ; Osmium ; Solvent effects ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In search for osmium complexes with sulfur-dominated coordination spheres that potentially bind and activate or stabilize nitrogenase relevant small molecules, several osmium-sulfur complexes containing 1,2-bis(2-mercaptophenylthio)ethane(2-) (′S4′2-) and benzenedithiolate (′S2′2-) ligands were synthesized. [OsII(PR3)2(′S4′)] [R = Ph (1), Et (2)], [OsIV(PR3)2(′S2′)2] [R = Et (3), Pr(4), Me(5), Ph(6)], [OsIV(PCy3)(′S2′)2] (7), (PHCy3)[OsIII(′S2′)2] (8a), (NMe4)[OsIII(′S2′)2] (8b), and (NBu4)2[OsIV(′S2′)3] (9b) were obtained in reactions starting from commercially available osmium compounds and the sulfur and phosphane ligands. The presence or absence of reducing solvents strongly influenced these reactions. Octahedral (3), (4), and (PHCy3)2[OsIV(′S2′)3] (9a) were characterized by X-ray structure analysis, leading to the conclusion that despite the high oxidation state of the osmium centers, innocent dithiolate ligands are present. The stabilization of the OsIV centers is traced back to S→M π donation. Close inspection of 1 and 2 revealed a large influence of the phosphane ligands on the stability of OsII thioether complexes. While 1 is reasonable stable, 2 readily gives 3 and ethylene via intramolecular ′S4′2- ligand reduction and OsIII→ OsIV oxidation. UV-Vis spectra of 3-5 indicate phosphane dissociation in solution leading to pentacoordinate [Os(PR3)(′S2′)2] complexes. This was confirmed by the synthesis of pentacoordinate [Os(PCy3)(′S2′)2] (7).
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    Synthesis of Silylborazines and Their Utilization as Precursors to Silicon-Containing Boron Nitride⋆ (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 855-859 
    Details
    ISSN: 1434-1948
    Keywords: Borazines ; Silyl borazines ; Oligomers ; Pyrolysis ; Ceramics ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The reactions of LiSi(SiMe3)3 with Cl(Me)2B3N3(Me)3, Cl2(Me)B3N3(Me)3, (ClBNMe)3, and (ClBNH)3 result in the formation of molecular species (Me3Si)3Si(Me)2B3N3(Me)3, [(Me3Si)3Si]2(Me)B3N3(Me)3, [(Me3Si)3SiBNMe]3, and [(Me3-Si)3SiBNH]3. The new compounds have been characterized by spectroscopic techniques, and a single-crystal X-ray diffraction analysis for [(Me3Si)3SiBNMe]3 has been completed. The monomer (Me3Si)3Si(Cl)2B3N3H3 was also prepared and combined with (Me3Si)2NH in hexane to form an organic solvent soluble oligomer. Pyrolysis of this oligomer provides composites containing BN and an SiXNYCZ phase that suppresses the crystallization of BN.
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    (1S,2S)-Cyclopentane-1,2-diyl-bis(phosphonous dichloride), (1S,2S)-C5H8(PCl2)2 - A Versatile Optically Active Reagent (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 885-887 
    Details
    ISSN: 1434-1948
    Keywords: Chirality ; P ligands ; Synthetic methods ; Triphosgene ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Treatment of (1S,2S)-C5H8(PH2)2 (1) with OC(OCCl3)2 gave (1S,2S)-C5H8(PCl2)2 (2) as the first example of an optically active bis(phosphonous dichloride). 2 was converted to (1S,2S)-C5H8(PX2)2 [PX2 = P(OMe)2 (3), P(OPh)2 (4), P[OCH-(Me)Et-(S)]2 (5), P[2-OC10H6C10H6O-2′-(R)] (6), P(NC4H8O-cyclo)2 (7), P(C6H11-cyclo)2 (8)] by reactions with oxygen, nitrogen, and carbon nucleophiles.
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    Di-, Tri-, and Tetranuclear Cyclobutenylidene Complexes (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 1225-1234 
    Details
    ISSN: 1434-1948
    Keywords: Vinylidene complexes ; Cyclobutenylidene complexes ; Bridging ligands ; Cycloadditions ; Cross-coupling ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Pentacarbonyl(dimethylvinylidene)chromium, [(CO)5Cr=C=CMe2] (1), reacts with the butadiynyl complexes [Cp(CO)2FeC≡CC≡CR] [2; R = SiMe3 (a), nBu (b), Ph (c)] and [Cp(CO)(PPh3)FeC≡CC≡CSiMe3] (3a) by regiospecific cycloaddition of the Cα≡Cβ bond of the butadiynyl complexes to the C=C bond of 1 to form the 1,3-heterobinuclear cyclobutenylidene complexes 4a-c and 5a with an alkynyl substituent at C-2 of the bridging ring. Desilylation of the 2-C≡CSiMe3 substituent in 4a and 5a with tetrabutylammonium fluoride affords the 2-C≡CH-substituted complexes 6 and 7. Complex 4a reacts with HNMe2 and HN(CH2)5 by substitution of NR2 for the 3-Fe(CO)2Cp fragment to form the corresponding 3-aminocyclobutenylidene complexes 10 and 11. Sequential reactions of 4a with [nBu4N]F and nBu3SnNEt2 give the trinuclear 2-C≡CSnnBu3-substituted complex 12. Coupling of 12 with C6H4I2-p yields the 2-C≡CC6H4I-p-substituted complex 13. Coupling of 7 with C6H4I2-p yields a mixture of the mono-coupling product 14 and the tetranuclear C≡C-C6H4-C≡C-bridged bis(cyclobutenylidene) complex 15. Coupling of 7 with trans-[(Et3P)2MCl2] in the presence of CuI/[Pd(PPh3)4] gives the trinuclear 2-C≡C-M(PEt3)2X-substituted complexes 16 (M = Pd, × = I) and 17 (M = Pt, × = Cl). The spectroscopic data as well as the results of the X-ray-structural analysis of 5a indicate strong electronic communication between the metal centers. In the solid state, 5a exhibits a “butterfly” conformation.
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    Novel Nine-Membered Titanaheterocycles - Structure, ab initio Calculations, and Preparative Use towards the Selective Synthesis of Substituted Cyclopentanols (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 1253-1262 
    Details
    ISSN: 1434-1948
    Keywords: Cyclizations ; Cross-coupling ; Ab initio calculations ; Titanium ; Metallacycles ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Reactions of Cp2Ti(CO)2 (3) with two equivalents of α,β-unsaturated ketones 4 yield the novel titana-2,9-dioxacyclonona-3,7-dienes 5. Cross-coupling of 3 with two different ketones 4 and 6to give 7 can be achieved under certain reaction conditions. Hydrolysis of 5 or 7 may generate diketones 9, cyclopentanols 10/11, or cyclopentenes 12/13, depending on substituents and conditions. The X-ray crystal structure of 5a, the first nine-membered bis(η5-cyclopentadienyl)-substituted titanaheterocycle containing carbon, is presented. Ab initio calculations were performed for 5a and for titana-2-oxacyclopentene 1, a conceivable intermediate in the coupling reaction.
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    Cation Stabilities, Electrophilicities, and “Carbene Analogue” Character of Low Coordinate Phosphorus Cations (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 1087-1094 
    Details
    ISSN: 1434-1948
    Keywords: Phosphenium cations ; Cation stabilities ; Electrophilicity ; Carbene homologues ; Computer Chemistry ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The stabilities of low coordinated phosphorus cations can be expressed in the frame of the HSAB concept by the transferred charge density Δq(N) which a cation receives upon formation of a donor-acceptor adduct with a Lewis base N. This concept allows to differentiate between relative stabilities towards different reaction partners, and to compare the electrophilicities of phosphenium ions to those of isoelectronic carbenes and silylenes. An analysis of substituent influences on Δq(H) in cations [P(R)2]+suggests an increasing stabilizing power of substituents in the series R = Cl 〈 CH3 〈 OH, SH 〈 NH2. The same ordering was derived from isodesmic hydride transfer reactions. Interpretation of population analyses suggests that the individual substituent contributions to cation stabilities result from a balance between π-donation into the empty p(P) orbital and electrostatic stabilization by polar P-R σ-bonds. A further stabilizing effect, which is of similar magnitude as in isoelectronic carbenes or silylenes, may arise from cyclic π-conjugation between a diaminophosphenium fragment and an adjacent double bond. Substituent effects influence further the nature of the frontier orbitals of phosphenium ions, resulting in orbital sequences which resemble those of carbenes, allyl anions, or phospholides, respectively. The absence of frontier orbital related changes in reactivity patterns suggests that in all reactions, including metal complex formation, phosphenium ions behave as purely electrophilic rather than ambiphilic species.
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    The Aluminum-Nitrogen Bond in Monomeric Bis(amino)alanes: A Systematic Experimental Study of Bis(tetramethylpiperidino)alanes and Quantum Mechanical Calculations on the Model System (H2N)2AlY (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 1095-1114 
    Details
    ISSN: 1434-1948
    Keywords: Aminoalanes ; Alanes ; Ab initio calculations ; 27Al-NMR spectroscopy ; Structure elucidation ; Substituent effects ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Reactions of metallated nucleophiles MIY [Y = OR, SR, NR2, PR2, AsR2, CR3, Si(SiMe3)3, R = organyl, H] with bis(2,2,6,6-tetramethylpiperidino)aluminum halides [tmp2AlX, (X = Cl, Br, I)] offer facile access to a variety of bis(amino)alanes of the type tmp2AlY. As indicated by 27Al-NMR spectroscopy, mass spectrometry and X-ray crystal structure determina-tions, all of these compounds are monomeric in the solid state, in solution, and in the gas phase. Even Al-E single bonds (E = Si, P, As etc.) that are not commonly encountered are stabilized by the supporting tmp fragments. The results of a systematic analysis of the bonding parameters determined for the tmp2AlY compounds, combined with a quantum mechanical study on model compounds (H2N)2AlY, not only reveal the presence of a highly polar Al-N bond, but at the same time rule out AlN-pp(π) bonding, in contrast to the situation in the analogous tmp2BY compounds. It is shown that the Al-N bond length depends on the acidic character of the protic species HY: the shorter d(Al-N), the less basic is Y.
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    Preparation, Structure and Reactivity of 2-Chloro-, 2-Fluoro- and 2-Iodo-2,3-dihydro-1H-1,3,2-diazaboroles (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 1145-1152 
    Details
    ISSN: 1434-1948
    Keywords: Boron ; Diazaboroles ; Halogens ; Isocyanides ; Heterocycles ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A series of differently substituted 2-chloro-, 2-fluoro- and 2-iodo-2,3-dihydro-1H-1,3,2-diazaboroles have been prepared by various methods. 1,3-Di-tert-butyl-2-fluoro-2,3-dihydro-1H-1,3,2-diazaborole (3a), 1,3-di-tert-butyl-2-chloro-2,3-dihydro-1H-1,3,2-diazaborole (5a), 1,3-bis(2,6-dimethyl-phenyl)-2-chloro-2,3-dihydro-1H-1,3,2-diazaborole (5b), 2-chloro-4,5-dimethyl-1,3-dineopentyl-2,3-dihydro-1H-1,3,2-diazaborole (5c), and 1,3-di-tert-butyl-2-iodo-2,3-dihydro-1H-1,3,2-diazaborole (6a) were formed from the corresponding lithiated Z-1,2-diaminoethenes, by treatment with BF3·OEt2, BCl3, or BI3 in n-hexane. Compounds 3a, 5a, and 5b are also available by sodium amalgam reduction of the adduct (tBu)(BF3)N=CH-CH=N(BF3)(tBu) (2a), and the borolium salts [RNa=CH-CH=Nb(R)BCl2]X (Na-B) (4a: R = tBu, X = BCl4 and 4b: R = 2,6-Me2C6H2, X = Cl) respectively. The iodo derivative (2,6-Me2C6H2)-Na-CH=CH-Nb(2,6-Me2C6H2)BI (Na-B) (6b) was synthesized in a redox reaction between the 1,4-diazabutadiene 1b and BI3. The novel compounds were characterized by 1H-, 11B- and 13C-NMR spectroscopy, as well as by an X-ray structure analysis of 6b.Supporting information for this article is available on the WWW under http://www.wiley-vch.de/contents/jc_2005/1998/98047_s.pdf or from the author.
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    New P,N-Chelate Ligands Based on Pyridyl-Substituted Phosphaferrocenes (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 1163-1168 
    Details
    ISSN: 1434-1948
    Keywords: Chelates ; P,N ligands ; Phosphaferrocene ; Catalysis ; Heterocycles ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The new pyridyl-substituted phosphaferrocene ligands 3 and 6 are prepared by addition of lithiated pyridine or α-picoline to 2-formyl-3,4-dimethylphosphaferrocene (1). The ligands 3 and 6 react with [Cp*RuCl]4 in THF to give the P,N-chelate complexes [Cp*RuCl·3] (9) and [Cp*RuCl·6] (10) with high diastereoselectivity. Addition of monodentate ligands like CO or PPh3 to the complexes leads by displacement of the Ru-bound pyridyl group to the respective carbonyl or phosphane complexes with monodentate P-coordinated phospha-ferrocene ligands. Reaction of the ligand 6 with [(C3H5)PdCl]2 and NH4PF6 gives the seven-membered chelate complex [(C3H5)Pd·6]PF6 (13) which was characterized by X-ray diffraction. The ligands 3 and 6 were tested in the palladium-catalyzed asymmetric alkylation of 1,3-diphenylallyl acetate.
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    Formation of a Constrained-Geometry Ziegler Catalyst System Containing a C1 Instead of the Usual Si1 Connection Between the Cyclopentadienyl and Amido Ligand Components (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 1153-1162 
    Details
    ISSN: 1434-1948
    Keywords: “Constrained-geometry” Ziegler catalysts ; Cp/amido zirconium complex ; 6-Aminofulvene deprotonation ; Ethene polymerization ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 6-Amino-6-methylfulvene (4) is cleanly N-acylated by treatment with pivaloylchloride/triethylamine to give the fulvene (C5H4)=C(CH3)NHCOCMe3 (5c). Treatment of 4 with trimethylchlorosilane similarly yields the mono-N-silylated fulvene (C5H4)=C(CH3)NHSiMe3 (7). Both 5c and 7 are cleanly doubly deprotonated e.g. by treatment with LDA to give ligand systems [(C5H4)C(=CH2)NR]Li2 [8a (R = COCMe3) and 8b (R = SiMe3), respectively]. Their treatment with MCl4 · 2 THF (M = Ti, Zr) yield the spiro-metallocenes [(C5H4)C(=CH2)NR]2M (9, 10). Complex 10a (M = Zr, R = COCMe3) was characterized by X-ray diffraction. The reaction of 8a with (Et2N)2ZrCl2 in THF gives rise to the formation of [(C5H4)C(=CH2)NCOCMe3]Zr(NEt2)2 (11) (70 % isolated), and the reaction of 8b with (Et2N)2ZrCl2 yields [(C5H4)C(=CH2)NSiMe3]Zr(NEt2)2 (12) (76 % isolated). Treatment of complex 12 with an excess of methylalumoxane (MAO) in toluene solution results in the generation of an active homogeneous Ziegler catalyst for the polymerization of ethene. A comparison with the usually employed [(Me5C4)SiMe2NCMe3]ZrCl2/MAO “constrained-geometry” Ziegler catalyst system reveals a similar catalyst activity and performance of this novel type of a C1-bridged “constrained-geometry” catalyst as it is exemplified by the [(C5H4)C(=CH2)NSiMe3]ZrX2 (12)/MAO combination.
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  • 250
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    The Acid-Induced Rearrangement of 1-Hydroxyalkyltris(trimethylsilyl)silanes (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 177-181 
    Details
    ISSN: 1434-1948
    Keywords: Silanes ; Rearrangements ; Polysilanes ; Hypersilylalcohols ; 1,2-Trimethylsilyl migration ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In the presence of strong acids, such as HCl or H2SO4, 1-hydroxyalkyltris(trimethylsilyl)silanes (Me3Si)3Si-C(OH)R1R2 (1a-f) isomerize by 1,2-Me3Si/OH exchange to give the trimethylsilylmethylsilanols (Me3Si)2Si(OH)-C(SiMe3)R1R2 (4a-f) [R1,R2: a: Me, Me; b: H, 4-MeC6H4; c: H, 4-iPrC6H4; d: H, Mes; e: H, 2-Me2NC6H4; f: H, 2,4,6-(MeO)3C6H2]. A mechanism for the isomerization is proposed. In the case of the reaction of 1d with sulfuric acid, the silylsulfate (Me3Si)2Si(OSO3H)-C(SiMe3)HMes (5) was isolated. 5 is the intermediate in the H2SO4-catalyzed isomerization of 1d and was converted in situ with methanol, acetic anhydride, HF or HCl to give the respective methoxysilane 6, acetoxysilane 7, fluorosilane 8, or chlorosilane 9. Deprotonation of 4a, d, f with sodium hydride causes a further rearrangement, a 1,3-C,O-trimethylsilyl migration, to give the siloxanes (Me3Si)2(Me3SiO)Si-CHR1R2 (11a, d, f).
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    Reactions of ε-Caprolactone with (Alkyne)zirconocene Complexes: Investigation of Elemental Steps in Catalytic Ring-Opening Polymerization of Lactones (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 1351-1357 
    Details
    ISSN: 1434-1948
    Keywords: ε-Caprolactone complexes ; Zirconocene ; Ring-opening polymerization ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The reactions of Cp2Zr(L)(η2-Me3SiC2SiMe3) (L = THF, pyridine) with ε-caprolactone, cyclohexanone and cycloheptanone result in an insertion of the carbonyl group into the zirconacyclopropene ring system of the alkyne complexes to yield the five-membered metallacyclic spiro-zirconadihydrofurane complexes 1, 3, 4. The product with ε-caprolactone is not stable at room temperature and was identified only by NMR spectra and chemical reactions. Starting from rac-(ebthi)Zr(η2-Me3SiC2SiMe3) with ε-caprolactone and ethylene carbonate under analogous conditions more stable complexes (2, 5) were obtained. Complexes 2 and 3 were characterized by X-ray crystal-structure analysis. Complexes 1 and 2 react with further ε-caprolactone in a catalytic ring-opening polymerization. The polymerization reactions were monitored by NMR spectroscopy.
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  • 252
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    Photoelectron-Spectrum and Electronic Structure of Perfluoro(2,4-dimethyl-3-oxa-2,4-diazapentane) (CF3)2N-O-N(CF3)2 (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 1377-1380 
    Details
    ISSN: 1434-1948
    Keywords: Ab initio calculations ; Electronic structure ; Photoelectron spectroscopy ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The electronic structure of the title compound 1 has been investigated by UV photoelectron spectroscopy and quantum chemical calculations. 1 has two nearly degenerate nN lone-pair orbitals which form the two highest occupied MOs. The third highest occupied MO is mainly localized at the oxygen atom (n0). All calculations indicate that the molecule has a twisted C2 conformation.
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  • 253
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    Tridentate Coordination Mode of N,N′-Dimethyl-2,11-diaza[3.3](2,6)pyridinophane in a Tricarbonylmolybdenum(0) Complex (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 1381-1385 
    Details
    ISSN: 1434-1948
    Keywords: Carbonyl complexes ; Coordination modes ; Fluxionality ; Macrocyclic ligands ; N ligands ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Tridentate coordination of the potentially tetradentate ligand N,N′-dimethyl-2,11-diaza[3.3](2,6)pyridinophane (L-N4Me2) has been structurally established in the tricarbonylmolybdenum(0) complex [Mo(L-N4Me2)(CO)3]. The fluxional behavior of the coordinated tetraazamacrocyclic ligand is demonstrated by a variable-temperature 1H-NMR study. The relevance of the tridentate coordination mode of the ligand is discussed with respect to its intermediacy in the reaction mechanism for the formation of cis octahedral metal complexes containing tetradentate 2,11-diaza[3.3](2,6)pyridinophane derivatives as ligands.
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  • 254
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    Chromium Sandwich Complexes of Polycyclic Aromatic Hydrocarbons: Triphenylene and Fluoranthene as η6 Ligands (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 1391-1401 
    Details
    ISSN: 1434-1948
    Keywords: Polycycles ; Sandwich complexes ; Site preference ; Cyclic voltammetry ; NMR and EPR spectroscopy ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The sandwich complexes bis(η6-triphenylene)chromium (12) and bis(η6-fluoranthene)chromium (13) have been prepared by means of metal atom/ligand vapor cocondensation. Whereas for triphenylene exclusive coordination to the peripheral rings is observed, the situation is more complicated for fluoranthene. According to NMR evidence initial metal coordination to the benzene (B) as well as to the naphthalene (N) section of the fluoranthene ligand occurs, leading to the isomers 13(I) (η6-B, η6-B), 13(II) (η6-B, η6-N) and 13(III) (η6-N, η6-N). Since the substitutional lability of the chromium-naphthalene bond largely exceeds that of the chromium-benzene bond, the isomer distribution depends on the workup conditions; 13(I) is clearly the most stable isomer. Crystal structure determinations performed for the salts [12][BPh4] and [13][I] point to the preference for syn orientation of the polycyclic aromatic hydrocarbons and to a minute metal slippage in the peripheral direction. The triphenylene complex 12 features the electrochemically reversible redox couples 12 (+/0, metal-centered), 12 (0/-, ligand-centered) and 12 (-/2-, ligand-centered), the latter displaying a redox splitting of 300 mV. Conversely, for the fluoranthene complex 13, secondary reduction 13 (-/2-) is irreversible. This finding is consistent with the larger redox splitting of ca. 480 mV which indicates more extensive interligand interaction in the dianion 132-, thereby favoring metal-ligand cleavage. While the radical cations 12+· and 13+· are amenable to EPR study, the radical anions 12-· and 13-· are too unstable. Instead, the radical anions of the free ligands are observed by EPR upon electrochemical reduction. In the case of 12, the temporary existence of the radical anion 12-· is indicated, however.
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    Thiolate and Thioether Functions as Donor Groups X, Y in Tripod Ligands RCH2C(CH2PPh2)(CH2X)(CH2Y) - Synthesis and Coordination Chemistry (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 1417-1424 
    Details
    ISSN: 1434-1948
    Keywords: Tripod ligands ; Molybdenum ; Mixed donor set ligands ; Thiole ligands ; Thiolate ligands ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Tripod ligands RCH2C(CH2PPh2)(CH2X)(CH2Y) (1) with X, Y = SAlkyl, SBzl selectively undergo reductive cleavage of the SBzl function with Li/NH3/THF at -40 °C to produce RCH2C(CH2PPh2)(CH2X)(CH2Y) (2) (X, Y = SAlkyl, SH). In these mixed donor set ligands the SH functions are the least coordinative ones such that [η2-{CH3C(CH2PPh2)(CH2SEt)(CH2SH)}(CO)4Mo] (5) is a stable compound with an uncoordinated SH function at the dangling arm of the ligand. If the SH functions of a potential tripod ligand are deprotonated the resulting thiolate functions are found to strongly coordinate in compounds such as [η3-{CH3C(CH2PPh2)2(CH2S)}(CO)3Mo]- which are obtained as their lithium and sodium salts 6. These highly reactive species may be stabilized by encapsulating their alkali counter ions in cryptands and the corresponding salts with [2,1,1]cryptand (7a) and [2,2,2]cryptand (7b) are far easier to handle than the cryptand-free progeners 6. Alkylation of the coordinatively bound thiolate function in 6 leads to the corresponding thioether derivatives [η3-{CH3C(CH2PPh2)2(CH2SR)}(CO)3Mo] (8).
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  • 256
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    New Synthetic Routes to Hydrotalcite-Like Compounds - Characterisation and Properties of the Obtained Materials (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 1439-1446 
    Details
    ISSN: 1434-1948
    Keywords: Layered double hydroxides ; Hydrotalcite-like compounds ; Magnesium ; Aluminium ; Intercalation ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Hydrotalcite-like anionic clays of general formula [M(II)1-xM(III)x(OH)2]x+[CO32-x/2]x- · m H2O with M(III) = Al and M(II) = Mg, Ni, Zn have been prepared by precipitation of the hydroxycarbonates from the “homogeneous” solution after the thermally induced hydrolysis of urea. The effect of the temperature of precipitation, of the total metal cations concentration, of the molar fraction M(III)/M(III) + M(II) and of the molar fraction urea/M(II) + M(III) in solution on the composition and on the crystallinity degree of the samples has been investigated. The optimum conditions are reported to obtain micro-crystalline powders with a narrow distribution of particle size in a short time with a simple procedure. The compounds obtained have been characterised for chemical composition, thermal behaviour, particle-size distribution and BET-surface area. In addition, the crystal structure of Mg0.67Al0.33(OH)2 (CO3)0.165 · 0.4 H2O has been refined by X-ray diffraction powder methods. The carbonate form has been converted into the chloride form by letting gaseous HCl flow over the hydrotalcite-like compounds, heated at 150 °C. The exchange of Cl- anions with some alkoxide anions in the presence of the respective alkanols has been investigated. The exchange reaction was driven by the segregation of NaCl crystals poorly soluble in alkanols and led to the co-intercalation of the alkoxide ions together with the alkanol with the formation of a bi-layer of extended alkyl chain in the interlayer region of the Mg-Al hydrotalcite. The intercalation compound, washed with water, produces a hydrotalcite with Cl- and OH- as balancing anions.
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    Amino Acid Derivatives of Layered Zirconium Phosphates - α-Zirconium L-(+)-Serinephosphate and Zirconium L-(+)-Serinephosphate Phosphates (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 1447-1452 
    Details
    ISSN: 1434-1948
    Keywords: Layered compounds ; Zirconium ; Amino acids ; Zirconium L-(+)-serinephosphates ; Intercalation ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A layered derivative of α-zirconium phosphate containing L-(+)-serine covalently attached to the inorganic layer has been prepared by allowing Zr fluoro complexes to decompose in the presence of L-(+)-phosphoserine. On the basis of thermogravimetric weight loss and C,H,N elemental analyses, the layered compound obtained has been formulated as Zr[HOOCCH(NH2)CH2OPO3]2. The X-ray powder diffraction pattern has been indexed with a monoclinic cell (a = 5.3737 Å, b = 9.3231 Å, c = 14.510 Å, β = 96.99°, Z = 2). FT-IR absorption spectra show that the serine groups attached to the inorganic layers are present as zwitterions. Thermal decomposition commences at ca. 250 °C and occurs in two steps: the first is due to a decarboxylation reaction, with the formation of the amino derivative Zr(NH2CH2CH2OPO3)2, while the second is associated with pyrolysis of the organic moiety, leading to ZrP2O7. Despite the presence of the amino acid function in the interlayer region, the compound does not show intercalation ability towards cations or anions or polar species. However, compounds with a certain degree of microporosity and possessing ion-exchange and adsorption properties have been obtained by replacing some of the phosphoserine groups of the compound by HPO4 groups, to produce the mixed layered derivatives Zr[HOOCCH(NH2)CH2OPO3]2-x-(HPO4)x.
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    X-ray Crystal Structures and Molecular Modelling Studies of Calix[4]dibenzocrowns-6 and Their Alkali Metal Cation Complexes (1998)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 1559-1568 
    Details
    ISSN: 1434-193X
    Keywords: X-ray crystal structure ; Calix crown ; Molecular dynamics ; Cesium selectivity ; Alkali metal cation complex ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: We present X-ray structures of complexes of KClO4·H2O and CsPic·H2O with a new calix[4]arene bearing a dibenzocrown-6 ether bridge. Alkali metal cation complexes with this macrocycle have been studied by molecular dynamics simulations in vacuo, taking account of the counterion, and in an explicit water phase, in order to compare the computed structures to those determined by X-ray crystallography. Two different sets of atomic charges were used in order to evaluate the influence of the electrostatic representation on the computed structures. The results obtained show that MNDO scaled charges give simulation results in better agreement with the available experimental data than MNDO/ESP.
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    An Efficient Method for Synthesizing Substituted Naphtho-1,3-dithiole-2-thiones from Tetrachlorotetrathionaphthalene and Sodium Trithiocarbonate (1998)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 1577-1581 
    Details
    ISSN: 1434-193X
    Keywords: Sulfur heterocycles ; Synthetic methods ; Conducting materials ; Desulfurization ; C-C coupling ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Two types of naphtho-fused 1,3-dithiole-2-thiones (2a-f and 4a-d) were obtained by the reaction of 3,4,7,8-tetrachloro-naphtho[1,8-cd:5,6-c′d′]bis(1,2-dithiole) (1) and sodium trithiocarbonate. The dechalcogenization of the thiones, using mercury acetate, leads to the corresponding naphtho-1,3-dithiol-2-ones (3a-d and 5a-d). The structures of 3a and 4a were confirmed by X-ray investigation. The tetrathiafulvalenes (TTFs) 6 and 7 were synthesized from 2d and 3c by coupling of the starting compounds with the help of triethyl phosphite. Using 2,3-dichloro-5,6-dicyano-benzoquinone (DDQ) the TTFs were converted into semiconducting charge-transfer complexes.
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  • 260
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    Synthesis and Anionically Induced Domino Reactions of Chiral α-Bromo α,β-Unsaturated Esters (1998)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 1569-1576 
    Details
    ISSN: 1434-193X
    Keywords: Asymmetric dihydroxylation (Sharpless-AD) ; Wittig olefination ; α-Bromo α,β-unsaturated esters ; Diastereoselective aprotic Michael domino reaction ; Tricyclo[3.2.1.02,7]octanes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The chiral α-bromo α,β-unsaturated esters 3 and 9 are prepared by asymmetric Sharpless dihydroxylation (AD) of 5 and from ester 7 and the chiral diols 8 by transacetalization, respectively. Both types of α-bromo α,β-unsaturated ester react with the kinetic lithium dienolates of enone 10 to give functionalized tricyclo[3.2.1.02,7]octanes 11. Esters 3 give one single diastereomer (de ≥ 95%), whereas mixtures of diastereomers (de 28 to 46%) are obtained with the esters 9.
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  • 261
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    Regio- and Stereoselective Cyclization Reactions of Unsaturated Silyl Enol Ethers by Photoinduced Electron Transfer - Mechanistic Aspects and Synthetic Approach (1998)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 1583-1596 
    Details
    ISSN: 1434-193X
    Keywords: Cyclizations ; Electron transfer ; High-pressure effects ; Radical cations ; Silyl enol ethers ; Solvent effects ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Oxidative photoinduced electron transfer (PET) reactions have been performed with various silyl enol ethers and silyloxy-2H-chromones bearing an olefinic or silylacetylenic side chain. The reactions result in regioselective ring closure with the formation of bi- to tetracyclic ring systems with a well-defined ring juncture, e.g. perhydrophenanthrenones 13 or benzo-annellated xanthenones 24. Our investigations have focussed on the optimization of this cyclization method with regard to irradiation time and product yield. The irradiation times could be reduced by using the cosensitized PET method. Modifying the substrate at the silyl group led to enhanced yields. In addition, we found that solvent and pressure dependences are important tools, allowing control of the regiochemistry. Both the synthesis of 6-endo products by radical cationic reaction pathways, as well as 5-exo ring closure by radical intermediates was achieved. Mechanistic details, including findings from deuterium labelling experiments, are discussed.
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    Monomeric N-Lithioaryl- and N-Lithioborylstannylamines from Distannylamines (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 1343-1349 
    Details
    ISSN: 1434-1948
    Keywords: Distannylamines ; N-Lithiostannylamines ; N-Lithioborylamines ; Amides ; Structure elucidation ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 8-Aminoquinoline reacts with (dimethylamino)trimethylstannane in a 2:1 molar ratio, undergoing transamination to the distannylamine 1a. The 9-[bis(trimethylstannyl)amino]-9-borabicyclo[3.3.1]nonane (1b) is obtained by the stannazane cleavage reaction of tris(trimethylstannyl)amine with 9-chloro-9-BBN. The cleavage of one Sn-N bond of the distannylamines 1a and 1b with MeLi yields the first two monomeric N-lithioaminostannanes, 2a and 2b, which can be stored at ambient temperature without decomposition. The molecular structures of 1a, 1b, 2a, and 2b have been determined by multinuclear magnetic resonance spectra in solution, as well as by X-ray structure analysis. Characteristic features are the intramolecular adduct formation of the quinoline ring nitrogen atom with one of the stannyl groups in 1a, as well as with the lithium cation in 2a, and the surprisingly short bonds between the central nitrogen atom and the adjacent elements [d(NSn): 2.02 Å, d(NB): 1.38 Å, d(NC): 1.34 Å, d(NLi): 1.95 Å] detected in the molecular structures of the lithium salts.
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  • 263
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    Stabilization of the New Antimonide Zr2V6Sb9 by V-V and Sb-Sb Bonding (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 1369-1375 
    Details
    ISSN: 1434-1948
    Keywords: Cluster ; Metal-rich antimonides ; Magnetism ; Sb-Sb bonds ; Structure and bonding ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The metal-rich antimonide Zr2V6Sb9 has been prepared by arc-melting of stoichiometric mixtures of Zr, V, and VSb2. Zr2V6Sb9 is the first example of a ternary ordered (filled) variant of the unusual V15Sb18 structure type. In addition to strong metal-antimony bonding, the crystal structure is significantly stabilized by bonding V-V and Sb-Sb interactions, whereas the Zr atoms do not form short metal-metal bonds. Band structure calculations using the Extended Hückel approximation reveal Zr2V6Sb9 being metallic, in agreement with the Pauli paramagnetism experimentally observed.
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    Preparation of P,N-Heterodifunctional Ferrocene-Coordinating Ligands by Selective Functionalization of Polyphosphanes by the Staudinger Reaction - Crystal and Molecular Structure of a New Cyclometallaphosphoraniminophosphane of Palladium(II) (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 1359-1368 
    Details
    ISSN: 1434-1948
    Keywords: β-Ferrocenylvinyl azide ; Polyphosphanes ; Iminophosphoranes ; P,N-Difunctional ligands ; Palladium ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Staudinger reactions of the β-ferrocenylvinyl azide 1 with several diphosphanes in a 1:1 molar ratio afford the monoiminophosphorane derivatives 2-4, whereas with a 2:1 stoichiometry these reactions afford the bis(iminophosphoranes) 5-7. Similar results are obtained for the reactions of 1 with tris(diphenylphosphanylmethyl)ethane (triphos) and tris[2-(diphenylphosphanyl)ethyl]phosphane (tetraphos). Reaction of these P,N-difunctional ferrocene ligands with dichlorobis(benzonitrile)palladium(II) leads to the PdII-metallacycle derivatives 13 and 14. The molecular structures of 5d and 13 have been established by X-ray crystallography.
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  • 265
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    Hemilabile Properties of Chelate Iron Complexes: Synthesis and Structure of Oxametallacycles (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 1387-1389 
    Details
    ISSN: 1434-1948
    Keywords: Carbene complexes ; Aromatic substitution / Chelate iron complexes ; Bond activation ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Oxametallacycles [Fe(C5Me5)(CO){C3(C6H4-o-Cl)(CO2Me)(R)Oa}(Fe-Oa)] (2, R = OMe; 4, R = Me) are accessible from the chelate (chloroaryl)carbene complex [Fe(C5Me5)(CO){C(OMe)C6H4-o-Cla}(Fe-Cla)][OTf] (1) upon treatment with the appropriate carbanions. Their formation arises from the lability of the chlorine atom. The related phosphonium salt [Fe(C5Me5)(CO){C3(C6H4-o-PMe3)(CO2Me)(OMe)Oa}(Fe-Oa)][OTf] (3) is formed only for the bis(ester) derivative, via Ar-Cl bond activation. No reaction occurs for 4, for which the coordination of the acetyl group has been supported by an X-ray analysis.
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  • 266
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    Dimethylphosphanylethylcyclopentadienyl Complexes of Lanthanum and Yttrium (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 1404-1406 
    Details
    ISSN: 1434-1948
    Keywords: Rare earth metal complexes ; Anionic phosphanes ; Phosphanylethylcyclopentadienyl complexes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The reactions of Li[C5H4(CH2)2P(CH3)2] (1) with La(CF3SO3)3 and Y(CF3SO3)3 are described. Three equivalents of 1 reacted with La(CF3SO3)3 under formation of La[C5H4(CH2)2P(CH3)2]3 (2). Two equivalents of 1 with one equivalent of Y(CF3SO3)3 in the presence of LiBr yielded BrY[C5H4(CH2)2P(CH3)2]2 (3). Both complexes 2and 3 have been characterized by X-ray structure analysis. In both cases an intramolecular coordination of the phosphanoethyl chain is established in the solid state by X-ray crystallography as well as in solution by NMR spectroscopy.
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    An Unprecedented, Copper-Mediated, In-Situ Multi-Step Ligand Formation - Synthesis, Structure, and Magnetism of Bis(μ-methoxo)bis[nitrato(2-methoxy- methylamino-3-methylpyridine)copper(II)] (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 1577-1579 
    Details
    ISSN: 1434-1948
    Keywords: Copper ; Methoxo-bridged complexes ; Crystal structure ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A novel chelating ligand, synthesized in situ within the coordination sphere of CuII from 2-amino-3-methylpyridine, MeOH, and dioxygen from the air, is found to form a strongly coupled, dinuclear methoxo-bridged CuII compound with the formula [Cu(L)(CH3O)(NO3)]2 (L = 2-methoxymethylamino-3-methylpyridine). The geometry around the copper atom is square pyramidal and the Cu-Cu distance within the dinuclear unit is 3.011(2) Å with an Cu-O-Cu angle of 103.13(8)°. Synthesis, X-ray crystal structure, and magnetism are reported.
    Additional Material: 1 Ill.
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  • 268
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    Solution Study, Crystal Structure and Relaxivity Properties of a Gd3+ Complex with an Uncharged Macrocyclic Ligand Bearing Four Amidic Side Arms (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 1581-1584 
    Details
    ISSN: 1434-1948
    Keywords: Gadolinium complexes ; Gadolinium ; Magnetic Resonance Imaging (MRI) ; Contrast agents ; Polyamino-polycarboxylic ligands ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Equilibrium data on the interaction of DTMA [(DTMA = DOTA tetrakis(methylammide)] with Gd3+ in aqueous solution, properties of the complexes formed in the pH range 0.6-11.8, water proton relaxation rate enhancement, and the crystal structure analysis of the [Gd(DTMA)H2O]3+ complex are reported. In the crystal structure the metal ion is bound to the nitrogen atoms of the tetraazamacrocyclic moiety, to the amidic oxygen atoms, and to an oxygen atom of a water molecule. The nine donors are located at the vertices of a distorted square antiprism, which is capped by the coordinated water oxygen atom in the axial position. In solution [Gd(DTMA)]3+ is not very stable [logKML = 12.8(1)] and gives rise to the formation of [Gd(DTMA)OH]2+ [pKa = 7.9(1)] and [Gd(HDTMA)]4+ [logK(ML+H) = 3.4(1)]. The proton solvent relaxivity of aqueous complex solutions assumes a constant value in the pH range 3-8, increasing at higher and lower pH. For pH 〉 3 the data are in good agreement with a previous study on the same compound. For pH 〈 3 a new interpretation is presented, based on the formation of [Gd(HDTMA)]4+ and the release of Gd3+.
    Additional Material: 2 Ill.
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    A Novel Route to Formaldehyde and Thioformaldehyde Rhodium Complexes (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 1605-1617 
    Details
    ISSN: 1434-1948
    Keywords: Rhodium ; Carbenoide metal complexes ; Formaldehyde complexes ; Thioformaldehyde complexes ; Cyclopentadienyl complexes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The acetoxymethyl rhodium compounds [(η5-C5R5)Rh(CH2OAc)(L)I] (4, 13-16) which were prepared from the chloromethyl derivatives [(η5-C5R5)Rh(CH2Cl)(L)I] and sodium acetate in benzene/acetic acid as solvent, reacted with AgPF6 to give the chelate complexes [(η5-C5R5)Rh{ĸ2-C,O-CH2OC(Me)O}(L)]PF6 (19-23) in excellent yields. Treatment of these complexes with KOH in methanol led to the elimination of the acetyl group and to the formation of the formaldehyde compounds [(η5-C5R5)Rh(η2-CH2O)(L)] (24-27). The related thioformaldehyde complexes [(η5-C5Me5)Rh(η2-CH2S)(L)] (46, 47) and [(η5-C5H5)Rh(η2-CH2S)(PMe3)] (50) were obtained on a similar route. Studies on the reactivity of the formaldehyde derivatives revealed that the Rh-CH2O bond is rather labile and the CH2O ligand easily converted to a CO group.
    Additional Material: 2 Ill.
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  • 270
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    Tricyclic Phosphorus-Carbon Compounds - Synthesis by Oligomerization of Kinetically Stabilized Phosphaalkynes (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 1597-1603 
    Details
    ISSN: 1434-1948
    Keywords: Phosphaalkynes ; Cooligomerization ; Phosphaalkyne cyclooligomers ; Cage compounds, phosphorus-carbon-aluminum ; Cage compounds, phosphorus-carbon-gallium ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: When trialkylaluminum reagents 2 bearing sterically demanding substituents are allowed to react with phosphaalkynes 1 a highly selective phosphaalkyne cyclotrimerization with incorporation of one organometal unit occurs (→ 5a-d). The resulting triphosphaalatricycloheptenes 5 are able to function as ligands in transition metal complexes (→ 6a,b), as illustrated by the reactions of 5a with nonacarbonyldiiron or the pentacarbonyltungsten tetrahydrofuran complex. When triethylgallium (7) is allowed to react with phosphaalkynes 1, tricyclic phosphorus-carbon-gallium compounds are generated (→ 8a,b).
    Additional Material: 1 Ill.
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    Synthesis, Structure, and Physical Properties of Tetraalkylammonium Bis(5,6-dihydro-1,4-dithiin-2,3-diselenolato)nickelate, (R4N)[Ni(ddds)2] (R = Me, Et, and nBu), and Neutral Complex [Ni(ddds)2]2 (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 1631-1639 
    Details
    ISSN: 1434-1948
    Keywords: Metal complexes ; Organic conductors ; Selenium ; Magnetic properties ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Novel metal complexes (R4N)[Ni(ddds)2] (R = Me, Et and nBu, ddds = 5,6-dihydro-1,4-dithiin-2,3-diselenolate) have been prepared and their crystal structures determined. The intraligand Se-Se distance is longer than that between the inner sulfur atoms of the five-member ring of the M(dddt)2- sulfur analogue and is almost equal to the S-S distance in the six-member ring. Consequently, two-dimensional intermolecular close contacts are expected, and observed in Ni(ddds)2 complexes. The neutral Ni(ddds)2 species was obtained by electrochemical oxidation from the monoanionic (nBu4N)[Ni(ddds)2] complex. X-Ray crystal structure analyses of this neutral species show that two Ni(ddds)2 are connected by the two Ni-Se bonds. Thus, the Ni(ddds)2entities form [Ni(ddds)2]2dimers which are arranged face-to-face and rotated by about 90° with respect to each other. The electrochemical behavior of (nBu4N)[Ni(ddds)2] indicates the possible formation of cation-radical species. The room temperature magnetic susceptibility measurements showed that the (R4N)[Ni(ddds)2] complexes are paramagnetic with μeff = 1.77-1.83 μB, corresponding to one unpaired electron per molecular formula. The temperature dependence of the magnetic susceptibility of (Et4N)[Ni(ddds)2] is indicative of weak long-range antiferromagnetic ordering below 9 K. The dimerization in [Ni(ddds)2]2results in a strong antiferromagnetic spin coupling within the dimer, and explain the non magnetic state observed for this compound.
    Additional Material: 8 Ill.
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    How to Predict Conformations Accessible to a Molecule in Solution: Validation of a Force Field-Based Prediction of NOE Distances by Comparison with the Experimental Data for the Series of Compounds CH3C[CH2P(Bzl)R]3Mo(CO)3 (R = Ph, m-Xyl) (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 1641-1653 
    Details
    ISSN: 1434-1948
    Keywords: tripodMolybdenum(CO)3 compounds ; Conformational ensembles in solution ; Modelling NOE contacts ; MM2* Force field calculations ; Packing forces ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: NMR-NOE analysis of the three compounds (RRS/SSR)-CH3C(CH2PPhBz)3Mo(CO)3 (1), (RRR/SSS)-CH3C(CH2PPhBz)3Mo(CO)3 (2), and (RRR/SSS)-CH3C[CH2P(m-Xyl)Bz]3Mo(CO)3 (3), leads to experimental values for a number of intramolecular H···H contacts in each case. By the very nature of the NOE method, and with the type of molecules studied here, these values have to be understood as a Boltzmann weighted average over all the conformations accessible to the molecules in solution. - A Boltzmann weighted force field approach is used to predict these values on the basis of sets of force field parameters derived earlier for this class of compounds. The agreement between observed and calculated NOE distances is highly satisfactory in each case (rms = 0.2 Å to 0.3 Å). By a statistical analysis it is shown that the predictions made by applying this Boltzmann weighted force field approach are highly significant. There is only a chance of 3 in 100 000 that this quality of prediction might be obtained by chance. This is taken as a validation, albeit indirect, of the energy scale reproduced by the force field parameters as developed. The methods described give a detailed insight into the conformational flexibility of molecules of the type studied. Solid state structures of the molecules are also correctly modelled by the force field used.
    Additional Material: 14 Ill.
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  • 273
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    Selective Catalytic Oxidation of Alcohols by a Ruthenium-Copper Bifunctional System Using Molecular Oxygen (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 1673-1675 
    Details
    ISSN: 1434-1948
    Keywords: Ruthenium ; Copper ; Oxidations ; Catalysis ; Alcohols ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The oxidation of allylic and benzylic alcohols to aldehydes can be carried out at room temperature with molecular oxygen, in the presence of the bifunctional ruthenium-copper system (nPr4N)(RuO4)-CuCl acting as the catalyst.
    Additional Material: 1 Tab.
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    Head-to-Head versus Head-to-Tail Dimerizations of Transient Silenes - The Solvent-Dependent Regiospecifity of the Dimerization of 2-(2-Methoxyphenyl)-1,1-bis(trimethylsilyl)silene (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 1667-1672 
    Details
    ISSN: 1434-1948
    Keywords: Silicon ; Silenes ; 1,2-Disilacyclobutanes ; 1,3-Disilacyclobutanes ; Eliminations ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The regiospecifity of the dimerization of the transient 2-(2-methoxyphenyl)-1,1-bis(trimethylsilyl)silene (6), synthesized by base-initiated trimethylsilanolate elimination from (2-methoxyphenyl)[tris(trimethylsilyl)silyl]methanol (5) according to a modified Peterson mechanism, decisively depends on the donating ability of the solvent in which the silene is generated. In ether, 6 undergoes a formal [2 + 2] dimerization to afford 3,4-bis(2-methoxyphenyl)-1,1,2,2-tetrakis(trimethylsilyl)-1,2-disilacyclobutane (12), whereas in toluene the head-to-tail [2 + 2] cyclodimer, 2,4-bis(2-methoxyphenyl)-1,1,3,3-tetrakis(trimethylsilyl)-1,3-disilacyclobutane (13) was obtained. 1,1-Bis(trimethylsilyl)-2-(2,4,6-trimethoxyphenyl)silene (18), similarly made by a modified Peterson reaction, under the same conditions reacted with the eliminated trimethylsilanolate with readdition at the polar Si=C bond to give, after hydrolysis, 2-(2,4,6-trimethoxybenzyl)-1,1,1,3,3,3-hexamethyl-2-(trimethylsiloxy)trisilane (19). A possible mechanism explaining the solvent-dependent regiospecificity of the dimerization of 6 is discussed. The structures of 12 and 13 were determined on the basis of NMR and MS data as well as X-ray structural analyses.
    Additional Material: 3 Ill.
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  • 275
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    Synthesis, Structure, and Properties of Twofold Bridged Sesquinorbornenes (1998)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 1759-1762 
    Details
    ISSN: 1434-193X
    Keywords: Alkenes ; Cycloadditions ; Cage compounds ; Ab initio calculations ; Double-bond pyramidalization ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The twofold bridged sesquinorbornenes 2 and 6 were prepared using sequential [4 + 2] cycloadditions of benzoquinone with 1,5-dihydropentalenes 1 and 5. These syntheses were improved using dilution conditions or a more reactive substituted benzoquinone. Results from semiempirical and ab initio DFT calculations indicated remarkably high pyramidalization angles (φ = 46-47°) for the central C-C double-bond atoms. The chemical reactivity with triplet and singlet oxygen, dimethyldioxirane and N-methyl-1,2,4-triazoline-3,5-dione supports these structural assignments.
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  • 276
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    Synthesis and Characterisation of Macrobicyclic Tetrathiafulvalene-Bridged Cage Molecules (1998)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 1743-1757 
    Details
    ISSN: 1434-193X
    Keywords: Cyclophanes ; Electrochemistry ; Tetrathiafulvalenes ; Macrocycles ; Crystal structure ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A series of new macrobicyclic tetrathiafulvalenophanes of type 1 and 2 with three tetrathiafulvalene bridges has been prepared under high-dilution conditions using a stepwise selective protection-deprotection of tetrathiafulvalenethiolates. All the macrobicyclic tetrathiafulvalenes, along with the intermediate compounds 5 and 6 and the unexpected tetrathiafulvalene pentamers 17, were studied by cyclic voltammetry. An electrochemical investigation using the Bard-Anson equation and thin-layer cyclic voltammetry has been carried out, allowing an estimate of the number of electrons involved in each redox process of these multi-redox compounds. The X-ray crystal structure showing the unusual crystal packing of 2a is also presented.
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    A New Method for the Selective Bridge Functionalization of [2.2]Paracyclophanediene - Indenyl-Annelated [2.2]Paracyclophanedienes and Their Iron Complexes (1998)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 1763-1770 
    Details
    ISSN: 1434-193X
    Keywords: Carbanions ; [2.2]Paracyclophanes ; Ring annelation ; Pericyclic reactions ; Metallocenes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: [2.2]Paracyclophane-1,9-diene (1) is readily deprotonated at its vinylic positions with BuLi to give the monolithium derivative 2 and - in the presence of TMEDA - even the 1,9-/1,10-dilithium derivatives 1,9-/1,10-6. Reaction of 2 with a variety of electrophiles including benzaldehyde and ethyl formate led to bridge-substituted derivatives 3a-d (71-89% yields) and 4, 5 (95 and 91%, respectively). Electrophilic substitution of 1,9-/1,10-6 with benzaldehyde gave the bis(vinylbenzyl) alcohols 1,9-/1,10-8 in 39% yield. The vinylbenzyl alcohols 5 and 1,9-/1,10-8 underwent cyclization upon treatment with zinc(II) chloride in 1,2-dichloroethane to give the indene-annelated [2.2]paracyclophane 9 (72%) and the bis(indene)-annelated compounds syn-11 and anti-11 (39%, ratio 19:1). Both 9 and syn-11, when treated with FeCl2•(THF)2 after deprotonation with methyllithium in the presence of excess lithium cyclopentadienide gave mixed-ligand ferrocene-type complexes 12 (63%) and syn-/anti-16 (46%). The bis(indeno[2.2]paracyclophane-9-ene) complex 13 was obtained from deprotonated 9 in 61% yield and characterized by an X-ray crystal structure analysis.
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    A One-Pot Synthesis of New Macrocyclic Compounds with Tetraaminoethene Substructure (1998)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 1803-1810 
    Details
    ISSN: 1434-193X
    Keywords: Oxalic amidines ; Lithium diamides ; Tetraaminoethenes ; Reduction ; Macrocycles ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A convienent one-pot synthesis of macrocycles containing a tetraaminoethene substructure is described. Starting from oxalic amidines 1, reduction with lithium and subsequent addition of phenyl isothiocyanate afforded the anionic bis(thiocarbamoyl) derivatives 3. In the final step, a ring-closure reaction using a large number of α,ω-dielectrophilic building blocks yields the new macrocyclic compounds 6-14.
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    Diastereo- and Enantioselective Synthesis of N-Protected 2-Amino 1,4-Diols by an Oxa Michael Addition/1,3-Dipolar Cycloaddition Protocol (1998)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 1793-1802 
    Details
    ISSN: 1434-193X
    Keywords: Amino alcohols ; Asymmetric synthesis ; Oxa Michael addition ; 1,3-Dipolar cycloaddition ; Nitrile oxides ; C-O bond cleavage ; Nitro alkenes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: An enantioselective synthesis of N-protected amino diols has been accomplished by employing a diastereoselective inter- and intramolecular 1,3-dipolar cycloaddition reaction of optically active nitrile oxides as a key step. The nitro alkane starting materials were obtained by diastereoselective oxa Michael addition of (1R,2S)-(-)-N-formylnorephedrine (1) to aliphatic (E)-nitro alkenes 2, 6a, b (de = 96 - ≥ 98%). Subsequent diastereo- and regioselective cycloaddition reactions to highly substituted 4,5-isoxazolines 5a-e, 8a, b (52-81%) and reductive ring opening led - after cleavage of the auxiliary - to amino diols 13, 14 in good overall yields (27-40%, over five steps) and with excellent diastereomeric and enantiomeric excesses (de,ee ≥ 96%).
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    Diastereo- and Enantioselective Synthesis of Vicinal Amino Alcohols by Oxa Michael Addition of N-Formylnorephedrine to Nitro Alkenes (1998)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 1771-1792 
    Details
    ISSN: 1434-193X
    Keywords: Amino alcohols ; Asymmetric synthesis ; Oxa Michael addition ; Nitro alkenes ; C-O bond cleavage ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The first intermolecular asymmetric oxa Michael additions with removable chirality information within the hydroxide source are reported. As enantiopure oxygen nucleophile functioning as chiral hydroxide equivalent N-formylnorephedrine (7) was used and conjugate additions to aliphatic (E)-nitro alkenes 2a-j were carried out in good yields (35-87%) and excellent diastereomeric excesses (de = 94-≥98%). After reduction of the nitro group and protection of the amino function (11a-h, 73-87%, both steps), the cleavage of the auxiliary occurred without epimerisation (69-99%) using Na/NH3. The Boc-protected 2-amino alcohols 12a-h could be obtained in good overall yields (30-58 %, four steps) and excellent diastereomeric and enantiomeric excesses (de, ee = 94-≥98%). Transition states explaining the overall stereochemical outcome are presented based on the absolute configuration determined by X-ray structure analysis on 8b.
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    Activation of Aryl and Vinyl Triflates by Palladium and Electron Transfer - Electrosynthesis of Aromatic and α,β-Unsaturated Carboxylic Acids from Carbon Dioxide (1998)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 1811-1821 
    Details
    ISSN: 1434-193X
    Keywords: Aryl triflates ; Vinyl triflates ; Palladium(0) catalyst ; Carbon dioxide ; Electron transfer ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The electrochemical reduction of aryl and vinyl triflates in the presence of CO2 and a catalytic amount of palladium results in the formation of aromatic and α,β-unsaturated carboxylic acids. Aryl and vinyl triflates usually undergo palladium-catalysed cross-coupling reactions with nucleophiles. Their reactivity has been reversed in the presence of an electron source, so that they react with electrophiles such as CO2. The reaction proceeds through an activation of the C-O bond of the aryl or vinyl triflate by oxidative addition to a palladium(0) complex, followed by an activation by electron transfer of the thus formed aryl- or vinylpalladium(II) complexes.
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    A Short Synthesis of Polyhydroxylated Piperidines by Aldol Reaction of Chelated Amino Acid Ester Enolates (1998)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 1833-1840 
    Details
    ISSN: 1434-193X
    Keywords: Amino acids ; Chelated enolates ; Aldol reactions ; Glycosidase inhibitors ; Piperidine alkaloids ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Aldol reactions of a chelated glycine ester enolate with a chiral aldehyde gives rise to the corresponding polyhydroxylated amino acid with excellent induced diastereoselectivity. These oxygenated amino acids can be converted into polyhydroxylated pipecolinic acids and azasugars by cyclization using the Mitsunobu reaction. An interesting epimerization was observed during the cyclization. The potential glycosidase inhibitor 1-deoxyaltronojirimycin (8b) was synthesized by this approach in a highly stereoselective fashion.
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    The Importance of Electrostatic Interactions in the Stereoselective 1,3-Dipolar Cycloadditions of Nitrones to Chiral Allyl Ethers: An Experimental and Force Field Approach (1998)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 1823-1832 
    Details
    ISSN: 1434-193X
    Keywords: Nitrones ; 1,3-Dipolar cycloadditions ; Chiral allyl ethers ; Transition state modeling ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The 1,3-dipolar cycloaddition of formaldehyde N-benzylnitrone with β′-alkoxy- and γ-alkoxy-α,β-unsaturated esters was investigated. The stereochemical outcome of these reactions was nicely rationalized on the basis of an interpretation of the inside alkoxy theory emphasizing the electrostatic interactions in the reaction TS. The force field approach previously developed for evaluating the stereoselection in nitrile oxide cycloadditions to chiral alkenes was successfully extended to nitrones′ reactions.
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    Oxidative Cycloaddition of Thiophenophanes - [n](2.5)Parathiophenophane (n = 8,10-12,14), [8](2,4)Metathiophenophane and [2.2](2,5)Parametathiophenophane (1998)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 1841-1850 
    Details
    ISSN: 1434-193X
    Keywords: Thiophenophanes ; Oxidative Diels-Alder reaction ; Thiophenophane S-monoxide ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The oxidative cycloaddition of 3,4-dibromo-[n](2,5)thiophenophanes 12b-e and (2,4)[8]thiophenophane 16 with dienophiles gave stereoselectively O=S-bridged cycloadducts 18, 19 and 24. The X-ray analysis of cycloadduct 18a shows it to have a rigid conformation. The molecules can be regarded as a new series of paddlanes. Under the same oxidative conditions, 3,4-dibromo-[8](2,5)thiophenophane (12a) gave the two dimers 29 and 30. The results of the X-ray analysis of 29 are discussed.
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    The Role of Ate Complexes in Halogen(Metalloid)-Metal Exchange Reactions: A Theoretical Study (1998)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 1851-1860 
    Details
    ISSN: 1434-193X
    Keywords: Ate complexes ; Halogen(metalloid)-metal exchange reactions ; Theoretical study ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Correlated electronic structure calculations predict that [(CH3)n+1X]- methyl ate anions, where X is an element of the main groups 14, 15, 16, or 17 up to Bi, possess widely varying stabilities that are governed by the electronegativities of their central atoms X. These stabilities correlate well with the propensities of the elements in question to undergo exchange with lithium and magnesium halide, except in the cases where steric hindrance in the transition states of the exchange reactions is important. These findings are nicely confirmed by calculations of the transition states [(CH3)2XLi]# (X = Cl, Br, I) and [(CH3)3SeLi]# of the corresponding degenerate exchange reactions CH3X (X = Cl, Br, I) + CH3Li and (CH3)2Se + CH3Li, respectively. The computed relative stabilities of the mixed [R-I-CH3]- ate anions of iodine (where R = phenyl, ethynyl, vinyl, ethyl, or cyclopropyl) are in excellent agreement with the experimentally observed equilibria of the corresponding lithium-iodine exchange reactions. The recent experimental observation of a highly stable α-iodine-substituted iodine ate complex as an intermediate in an iodine-magnesium bromide exchange reaction is also corroborated by our studies. Thus, the present calculations provide strong evidence for ate complexes being key intermediates in halogen(metalloid)-lithium(magnesium halide) exchange reactions.Supporting information for this article is available on the WWW under http://www.wiley-vch.de/contents/jc_2046/1998/98047_s.pdf or from the author.
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  • 286
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    Aza-Crown Tetrathiafulvalene Derivatives: Synthesis, X-ray Structure, and Metal Complexation Study (1998)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 1861-1865 
    Details
    ISSN: 1434-193X
    Keywords: Tetrathiafulvalene ; Macrocyclic ligands ; Receptors ; Crystal structure ; Mass spectrometry ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The synthesis of new aza-macrocyclic tetrathiafulvalene (TTF) derivatives is described, with a view to limiting the structural distortion of the redox-active TTF moiety and to favour metal complexation. An X-ray diffraction determination of one of these crown systems is provided. The electrochemical properties of these redox-active macrocyclic ligands are studied by cyclic voltammetry. Their complexing ability towards silver ions is evaluated by FAB mass spectrometry.
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  • 287
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    Palladium-Catalyzed Cyclization of Silyl-Substituted Bis(homo)propargylic Alcohols to 2,3-Dihydrofurans (1998)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 1873-1878 
    Details
    ISSN: 1434-193X
    Keywords: Oxiranes ; Alkynols ; 2,3-Dihydrofurans ; Furans ; Palladium catalysis ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Ring-opening of oxiranes 1 by the silicon- and sulfur-functionalized propargyl anions 2 yields the corresponding alk-4-yn-1-ols 3. Cyclization of 3 to 2,3-dihydro-4-phenylthiofurans 5 is achieved by reaction with palladium(II) acetate. The corresponding furans 7 are obtained when copper(II) chloride is added to the reaction mixtures.
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  • 288
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    Kinetics of the Enolisation Reactions of 3-Acetyl-2,5-dimethylfuran and of 2-Acetylselenophene (1998)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 1867-1872 
    Details
    ISSN: 1434-193X
    Keywords: Catalysis ; Metal ion catalysis ; Kinetics ; 3-Acetyl-2,5-dimethylfuran ; 2-Acetylselenophene ; Enolisation reaction ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Rate constants for the enolisation reactions of title compounds have been measured by their rates of halogenation at 25 °C in water, in several buffers, in dilute hydrochloric acid, in dilute sodium hydroxide, and in the presence of some metal ion salts. The results have been compared with those previously obtained from the corresponding reactions of acetophenone and a number of other acetyl heterocycles. Electronegativity of the heteroatoms and the “π-excessive” nature of the heterocyclic rings appear to be the main factors determining the relative reactivities in the acid-catalysed reactions. Brønsted β values and isotope effects, kH/kD, point to a more symmetrical transition state for the investigated acetyl heterocycles than that for acetophenone in the general base-catalysed reaction. Metal-activating factors (MAF), i.e. the catalytic constant for metal-ion (Cu2+, Zn2+, and Ni2+) catalysis, kM, relative to that for proton catalysis, kH, are discussed as an empirical measure of the “hard or soft” character of the carbonyl groups in acyl heterocycles.
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  • 289
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    Synthesis of Specifically Labelled Ganglioside [1c-13C]-GM3 (1998)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 1895-1899 
    Details
    ISSN: 1434-193X
    Keywords: Gangliosides ; Carbohydrates ; Sialic acid ; Tumor therapy ; Glycosides ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Glycosidation of the lactose derivative 4 with [1-13C]-sialyl xanthate 3, prepared from enzymatically obtained [1-13C]-sialic acid gave the trisaccharide 5 which was transformed into [1c-13C]-GM3 ([1c-13C]-1).
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  • 290
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    Synthesis of Neolacto Ganglioside LM1 (1998)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 1887-1894 
    Details
    ISSN: 1434-193X
    Keywords: Carbohydrates ; Cancer ; Gangliosides ; Trichloroacetimidates ; Sialyl xanthates ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The synthesis of the ganglioside LM1 (1) has been performed by glycosidation of 2 with azidosphingosine 3, followed by reduction of the azido group, acylation with stearine anhydride (4), and solvolysis. 2 was obtained from sialyl xanthate 5 and tetrasaccharide 6 in the presence of phenylsulfenyl triflate. The tetrasaccharide acceptor 6 was prepared from the lactose derivatives 7 and 8.
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  • 291
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    Synthesis of Spacer-Armed Glucodendrimers Based on the Modification of Poly(propylene Imine) Dendrimers (1998)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 1879-1886 
    Details
    ISSN: 1434-193X
    Keywords: Amphiphiles ; Carbohydrates ; Dendrimers ; Cluster glucosides ; Neoglycoconjugates ; Polymers ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The use of preformed poly(propylene imine) dendrimers [DAB(Pa)x] with reactive primary amine end groups proved to be very useful for the construction of saccharide surface-coated dendrimers. For this purpose, amide bonds were introduced by a reaction between the primary amine end groups of the dendrimers with N-succinimidyl-activated esters of spacer-armed acetyl-protected thioglucopyranoside units. The linear alkyl chain spacers between the dendrimer surface and the saccharide units was increased in length with 1, 5 and 10 carbon atoms. These spacer arms were introduced to determine the influence of local saccharide surface concentration variations on the dendrimer properties. After modification of the dendrimers with these saccharide units, the acetyl protecting groups were removed. Purification of these derivatives was accomplished by using dialysis either in water or in aqueous methanol. The solubility behavior of the resulting glucodendrimers proved to be strongly dependent on the hydrophobic part, i.e. the alkyl chain spacers in the molecule. Therefore, these nanosized multivalent structures, appropriate for studying carbohydrate-protein interactions, are also proposed useful for investigating amphiphilic properties.
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  • 292
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    Oxidation of Terminal Olefins by Dioxygen in the Presence of PdII(NH3)x-CuII-LiI-Cl- or PdII (or Pd0)/Zeolites/CuII-LiI-Cl- Systems and a Coreducer (Ethanol) (1998)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 1901-1906 
    Details
    ISSN: 1434-193X
    Keywords: Alkenes ; Ketones ; O-O activation ; Palladium ; Zeolites ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Simple ammonia complexes {cis-[PdCl2(NH3)2], [Pd(NH3)4]Cl2 or [Pd(NO2)2(NH3)2]} with copper(II) chloride and LiCl or PdII (or Pd0) inserted into zeolite (faujasite Y or mordenite Z)/CuII-LiI-Cl- precursors in anhydrous ethanol catalyse the oxidation of terminal olefins to methyl ketones by dioxygen. One oxygen atom is incorporated into the olefinic substrate, while the other is involved in a cooxidation process of the solvent leading to the formation of water. With 1-octene and ethanol, octan-2-one can be obtained selectively (up to 99 %), acetaldehyde and diethyl acetal being the main cooxidation products. Chorohydridopalladium species are key intermediates in the isomerization of 1-alkenes; it appears that the introduction of NH3, NO2- or zeolite ligands reduces the extent of isomerization and subsequently the formation of isomeric ketones (octan-3-one and octan-4-one). Although homogeneous catalysis cannot be ruled out, the improved selectivities and variations of selectivity and conversion with different zeolites suggest that a “ship-in-a-bottle” catalysis may be important.
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  • 293
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    NMR Investigation on the Solution Structure and Dynamic Behaviour of 1,2-Diphenyl-1,2-bis(trimethylsilyl)ethanediyldilithium (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 1771-1774 
    Details
    ISSN: 1434-1948
    Keywords: Dianions ; Organolithium compounds ; Reductive metallation ; HOESY ; Lithium NMR ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 1,2-Diphenyl-1,2-bis(trimethylsilyl)ethene (5) undergoes a smooth reductive metallation with metallic lithium to yield the corresponding dilithioethane derivative (Li2·5). The structure of this new compound in [D8]THF solution was determined by NMR spectroscopy (1H, 13C, 6Li, 7Li NMR and 6Li,1H-HOESY). It is shown that the phenyl rings have a high quinoid character and that the lithium cations are relatively mobile.
    Additional Material: 3 Ill.
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  • 294
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    Highly Regioselective Benzylic Deprotonation of Some (η6-Tetralin)- and (η6-trans-Octahydroanthracene)Cr(CO)3 Derivatives: Is the Regioselectivity Stereoelectronically Controlled? (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 1883-1905 
    Details
    ISSN: 1434-1948
    Keywords: (Arene)tricarbonylchromium complexes ; Benzylic deprotonation ; Stereoelectronic effects ; Conformational analysis ; Stereoselective synthesis ; Arene complexes ; Chromium ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The regioselectivity of benzylic deprotonation of a number of conformationally restricted (arene)Cr(CO)3 complexes has been examined in order to ascertain whether stereoelectronic effects play a role in such reactions. The complexes rac-5, rac-6, rac-7, rac-8 and rac-9 were diastereoselectively synthesized from the corresponding C2-symmetric ligands (2,3-disubstituted trans-1,2,3,4-tetrahydronaphthalene and trans-1,2,3,4,4a,9,9a,10-octahydroanthracene derivatives). Due to the desymmetrization caused by the Cr(CO)3 complexation, all four benzylic protons could be distinguished by 1H NMR and were assigned in all cases by a combination of H,H-COSY spectra and the observation of H/D exchange at both exo positions (tert-BuOK/[D6]DMSO). Deprotonation (n-butyllithium)/deuteration (D2O or CF3CO2D) experiments revealed a very high, unforeseen regioselectivity in the cases of rac-5 and rac-7, while the other substrates showed a low selectivity (rac-6) or could not be deuterated at all under these conditions (rac-8, rac-9). In the case of rac-5, the regioselectivity of the deprotonation was further confirmed by acylation (AcCl) or alkylation (MeI) of the lithiated intermediate. These results clearly rule out the notion that the regioselectivity is due to the preferred abstraction of pseudoaxially oriented benzylic hydrogen atoms. The crystal structures of rac-1, rac-5 and rac-7 suggest a possible link between the preferred conformation of the Cr(CO)3 tripod and the regioselectivity of the benzylic deprotonation. In analogy to a commonly accepted picture often used to explain the regioselectivity of nucleophile additions to (arene)Cr(CO)3 complexes, it was anticipated that those benzylic positions which are activated by an eclipsed CO ligand should be preferentially deprotonated (kinetically controlled). This (new) stereoelectronic model was corroborated by experiments using complexes rac-60 and rac-62, which were regioselectively deprotonated at the predicted position. In summary, it has been shown for the first time that the preferred conformation of the Cr(CO)3 tripod may have a directing influence on the regioselectivity of benzylic deprotonation in (arene)Cr(CO)3 complexes, at least in conformationally unambiguous situations where no obvious electronic effects are operative.
    Additional Material: 12 Ill.
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  • 295
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    An Expeditious Synthesis of Heteroarenes through Carbanion-Induced Ring Transformation Reactions of Suitable Functionalized Pyran-2-ones (1998)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 2083-2088 
    Details
    ISSN: 1434-193X
    Keywords: Heteroarenes ; Carbanions ; Pyran-2-ones ; Regioselectivity ; Ring transformation reaction ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Pyrazolo[1,5-a]pyridines (3) and pyrano[4,3-d]pyrazolo[1,5-a]pyridines (4) have been synthesized from the reaction of pyran-2-one (1) and 5-aryl-3-cyanomethyl-1H-pyrazole (2) through carbanion-induced ring transformation reactions. A regioselective synthesis of highly functionalized polysubstituted pyrazolo[1,5-a]pyridines (6, 7) has also been achieved from the reaction of 2 with polarised ketene dithioacetals (5) and arylidenemalononitrile, respectively. An analogous reaction of 1 with 2-cyanomethyl-1H-benzimidazole (8) has also afforded the fused heterocycles 9 and 10. The cyano function in 9 has been exploited for acid-catalysed cyclization with thiosemicarbazide to obtain 11 in high yield.
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  • 296
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    Novel Tetraphosphabarrelene and -semibullvalene Derivatives by Reactions of 2,4,6-Tri-tert-butyl-1,3,5-triphosphabenzene with Phosphaalkynes⋆ (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 2071-2074 
    Details
    ISSN: 1434-1948
    Keywords: Phosphorus heterocycles ; Phosphaalkynes ; Triphosphabenzene ; Tetraphosphabarrelenes ; Tetraphosphasemibullvalene ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 2,4,6-Tri-tert-butyl-1,3,5-triphosphabenzene 4 reacts with phosphaalkynes P≡C-R [R = tBu (5a), tPen (5b)] at room temperature in a formal [4 + 2] cycloaddition to yield the corresponding 1,3,5,7-tetraphosphabarrelene derivatives 8a and 8b, respectively. The analogous reaction of 4 with the aminophosphaethyne P≡C-N(iPr)2 (9) unexpectedly leads to the 1,3,4,7-tetraphosphasemibullvalene derivative 10 as the only product. The single-crystal X-ray analysis of 10 exhibits a diphosphirane unit with a very long PP distance of 2.274(1) Å together with a large extension of the PCP angle in the three-membered ring to 75.3(1)°.
    Additional Material: 1 Ill.
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  • 297
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    Ligand Synthesis and Metal Complex Formation of 1,2,3-Triaminopropane (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 2079-2086 
    Details
    ISSN: 1434-1948
    Keywords: N Ligands ; Copper ; Coordination polymers ; Stability constants ; Solid-state structures ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A series of linear primary polyamines H2N-CH2-(CH-NH2)n-CH2-NH2 (1 ≤ n ≤ 3) was prepared from the corresponding polyalcohols. The polyamines were isolated as HCl adducts and the acidity constants in aqueous solution were determined. The crystal structure of the fully protonated tetraamine (n = 2) was elucidated by an X-ray diffraction study. Complex formation of the triamine (n = 1) with Ni2+, Cu2+, Zn2+, Cd2+ was re-investigated in aqueous solution. The pH-dependent formation of a variety of species MxLyHz was established by potentiometric titrations and was compared with previous reports. The crystal structure of the Cu complex [CuL2]Cl2 exhibited a chain structure with a five-coordinate CuII centre in which two amino groups of the triamine ligands are coordinated to one Cu centre, while the third amino group of one of the ligands is bonded to a neighbouring Cu atom. The compound shows weak antiferromagnetic coupling interactions between the CuII centres within the chain.
    Additional Material: 4 Ill.
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  • 298
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    Adducts of Ferrocenylboranes and Pyridine Bases: Generation of Charge-Transfer Complexes and Reversible Coordination Polymers (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 2087-2087 
    Details
    ISSN: 1434-1948
    Keywords: Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Table 1 contains a wrong header for the last three lines.
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  • 299
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    Nucleophilic Phosphanylation of Fluoroaromatic Compounds with Carboxyl, Carboxymethyl, and Aminomethyl Functionalities - an Efficient Synthetic Route to Amphiphilic Arylphosphanes (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 73-82 
    Details
    ISSN: 1434-1948
    Keywords: Nucleophilic phosphanylation ; Phosphanylphthalic acid ; Phosphanylphenylacetic acid ; Benzylaminophosphanes ; Water solubility ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Chiral- and multiply-carboxylated phosphanes and phosphanyl derivatives of benzoic and phthalic acids (1-9) are accessible in high yields by nucleophilic phosphanylation of potassium or lithium salts of commercially available fluorobenzoic and 3-fluorophthalic acids with Ph2PH, Ph2PK, PhPLi2 Ph(K)P-(CH2)3-P(K)Ph in superbasic media (DMSO/KOH) or in THF and DME. The hitherto unknown phosphanylphenylacetic acids (10-13) and phosphanylbenzylamines RR′P-C6H4-CH2- NH2 (14-19, R, R′ = H, Me, Ph) with unsubstituted amino groups were also synthesized by this method. The diphenylphosphanyl derivatives 14-16 (R, R′ = Ph) are accessible by an alternative method involving LiAlH4 reduction of the phosphanylbenzonitriles (20-22), which were obtained in high yields by nucleophilic phosphanylation of the corresponding fluoro- or chlorobenzonitriles. The novel bidentate phosphanylbenzonitrile 23 has also been obtained using this synthetic route. All compounds were completely characterized by elemental analysis, NMR spectroscopy, and mass spectrometry.
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  • 300
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    Synthesis and Crystal Structures of P-Halogeno(imino)methylenephosphoranes X-P(=NtBu3C6H2)=C(SiMe3)2 (X = Cl, Br, I) (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 83-85 
    Details
    ISSN: 1434-1948
    Keywords: Phosphorus ylides ; Bis(ylene)phosphoranes ; Halogenophosphoranes ; X-ray structure analysis ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The iminophosphane (Me3Si)3C-P=N-Mes* (1) reacts with iodine to form the imino(methylene)phosphorane I-P(=N-Mes*)=C(SiMe3)2 (2). Upon subsequent treatment with AgCl, the corresponding chloro derivative 3 is obtained. Chlorine/bromine exchange in 3 with bromotrimethylsilane affords the bromo analogue 4. The structures of 2, 3 and 4 were confirmed by X-ray crystal structure analysis; each of the compounds features a trigonal-planar phosphorus atom.
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