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  • General Chemistry  (77,716)
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  • 1
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 2000 (2000), S. 801-818 
    ISSN: 1434-1948
    Keywords: Zeolites ; Microporous zeolites ; Titanosilicates ; Transition metal ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Stable microporous materials, such as zeolites, are extremely important for applications in catalysis, adsorption, ion-exchange, and separation. In this review we describe a new class of stable microporous materials that involves novel mixed octhaedral-tetrahedral framework oxides. The archetypal material is based on titanosilicates, although there is tremendous scope for introducing many other transition metals. These materials not only have potential novel applications in the fields normally associated with zeolites but also possible applications in the areas of optoelectronics, nonlinear optics, batteries, magnetic materials and sensors.
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  • 2
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 2000 (2000), S. 827-830 
    ISSN: 1434-1948
    Keywords: Ammonolysis ; Chlorine ; Nitrogen ; Silicon ; Silsesquiazane ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The ammonolysis of trichlorosilanes RSiCl3 [R = CH(SiMe3)2 (1a), Ph (1b), Et (1c)] leads to a series of condensed products such as six-membered rings [(Me3Si)2CHSi(OH)NH]3 (2a) and [PhSi(NH2)NH]3 (2b), disilazane [(Me3Si)2CHSi(NH2)2]2NH (3) and the cage compound (EtSi)6(NH)9 (4). The mixed Si-N-O compound 2a was obtained when liquid ammonia was not dried over sodium prior to use. The reaction with sodium gives NaCl instead of NH4Cl as a by-product which is easily removed by filtration.
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  • 3
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 2000 (2000), S. 835-837 
    ISSN: 1434-1948
    Keywords: Gold ; Clusters ; Quantum dots ; Monolayers ; Amphiphiles ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Extended ordered monolayers of ligand stabilized Au55 clusters are formed at the phase boundary between water and dichloromethane. The water phase, containing amphiphilic molecules like per-6-deoxy-6-thio-α-cyclodextrin (1) or poly(vinylpyrrolidone) (2), is covered by a thin film of a solution of [Au55(PPh3)12Cl6] in dichloromethane. The interaction of the cluster molecules with the thiol functions of 1 or the polymer chains of 2 form perfect cluster orders of hexagonal and cubic structure. The monolayers can be transferred onto solid substrates by a simple dipping process. The use of carbon coated copper grids allows the investigation of the monolayers by transmission electron microscopy (TEM). Electron diffraction experiments under a microscope prove the hexagonal and cubic arrangements. The reason for the formation of the one or the other modification is still unknown.
    Additional Material: 4 Ill.
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  • 4
    ISSN: 1434-1948
    Keywords: Triosmium cluster ; Biphosphinine ; Crystal structure ; Cyclic voltammetry ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The crystal structure of the novel cluster [Os3(CO)10(4,4′,5,5′-tetramethyl-2,2′-biphosphinine)] reveals an unprecedented coordination mode of the biphosphinine ligand that occupies a doubly-bridging position spanning the open osmium triangle. The cluster is photostable, pointing to a localization of the lowest-energy electronic transition largely on the negatively charged biphosphinine ligand.
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  • 5
    ISSN: 1434-1948
    Keywords: Photochemistry ; Electrochemistry ; Ruthenium compounds ; α-Diimine complexes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The photophysical, photochemical and redox properties of the title complexes were investigated. Resonance Raman measurements revealed the lowest-energy electronic transition to possess σ→π* character. At low temperatures, long-lived near-IR emission was observed. Irradiation in solution results in homolytic splitting of a Ru-Ru bond as the primary step, followed by secondary reactions of the radical fragments depending on the experimental conditions. (Spectro)electrochemical investigations of the title species proved that the axial [RuCp(CO)2] groups exert a stabilising influence on the corresponding radical cations, while destabilising the corresponding radical anions, compared to the redox behaviour of other ruthenium complexes of this type.
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  • 6
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 2000 (2000), S. 889-894 
    ISSN: 1434-1948
    Keywords: Rhodium hydride complexes ; Parahydrogen ; Tin ligands ; Hydrogenations ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The oxidative addition of dihydrogen to the [RhH(SnCl3)5]3-/PR3 system (PR3 = PPh3, PEtPh2, PEt3) leads to the formation of previously unknown dihydride complexes, the 1H-NMR spectra of which have been studied by means of the ParaHydrogen Induced Polarization (PHIP) method. The composition of the resulting complexes crucially depends on the type of the added phosphane. With PEt3 as the phosphane and acetonitrile as the solvent, a complex with a SnCl2L ligand (L = CD3CN) can be detected. All systems examined catalyze the hydrogenation of phenylacetylene. During these reactions, both the 1H-NMR resonances of the dihydride complexes and those of styrene, the hydrogenation product of phenylacetylene, can be detected simultaneously. In the case of SnBr3 ligands, hydrogen addition in the presence of phosphanes leads to similar dihydride complexes, which were also identified via 1H-NMR spectroscopy. Furthermore, a mixed complex of the structure [Rh(SnBr3)nBr6-n]3- has been isolated.
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  • 7
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 2000 (2000), S. 857-877 
    ISSN: 1434-1948
    Keywords: Crystal packing ; Neural networks ; Pattern recognition ; Organometallic compounds ; Close packing ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The crystal structures of hundreds of thousands of molecular compounds have now been determined with the quantitative information being stored in large databases. Chemists are generally interested in that specific part of this information which refers to individual molecules. The packing of molecules and their spatial relation to each other is not the focus of interest, even though the material properties of a molecular crystal are determined by both the packing arrangement of the molecules and their specific properties. The lack of interest in packing has at least one obvious reason. It is difficult for the non-expert to find the appropriate packing categories when looking at a principally infinite lattice. A tool performing this search for individual categories of packing in an automatic manner would therefore be of general importance. The development and application of such a tool is described in this paper. Novel strategies to extract a set of n points forming a specific n-point polyhedron from a set of p points (p 〉 n) is at its basis. Neural networks and second moment analysis are used as the methods of pattern recognition. In order to correlate packing and shape, second moment analysis of molecular shape is also used. This novel method is applied to three classes of organometallic compounds to determine whether the crystals formed by these compounds belong to any of the three classes fcc, bcc, or hcp in an idealized sense. A strong correlation is found between molecular shape and the membership or nonmembership of these classes. The corresponding program, including appropriate tools for visual representation, is available from the authors.
    Additional Material: 18 Ill.
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  • 8
    ISSN: 1434-1948
    Keywords: Arenetricarbonyl chromium complexes ; Palladium ; Cross coupling reaction ; Thiophenes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The cross coupling reaction of (p-chloroanisole)tricarbonylchromium complex (1) with thiophene derivatives under palladium-catalyzed conditions leads to the selective formation of tricarbonyl-η6-[(2-thiophenyl)arene]- or -η6-[(2-thiophenyl)carbonylarene]chromium complexes (2 or 3) depending on reaction conditions. The conformation of complexes 2 and 3 in the solid state as well as in solution are reported.
    Additional Material: 4 Ill.
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  • 9
    ISSN: 1434-1948
    Keywords: Ruthenium ; Phenanthroline ; Luminescence ; Sterically hindered ligands ; Terpyridine ; Cyclometallation ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Two series of cyclometallated and noncyclometallated ruthenium(II) complexes incorporating mono- or disubstituted 1,10-phenanthroline- and 2,2′:6′,2′′-terpyridine-type ligands have been synthesized and characterized. An X-ray crystal structure for one of the complexes, Ru(ttpy)(mapH)-(Cl)(PF6), has been obtained (mapH = 2-p-anisyl-1,10-phenanthroline; ttpy = 4′-tolyl-2,2′:6′,2′′-terpyridine). Distinct electrochemical and photophysical properties have been observed for the two series: a remarkable feature is the observation of relatively long-lived MLCT excited states (from 70 to 106 ns at room temperature in CH3CN) for three of the cyclometallated complexes. A discussion is given on the role of factors like sigma donation by the cyclometallating ligands, interligand steric hindrance and interligand π-π interactions that affect the electrochemical and spectroscopic properties.
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  • 10
    ISSN: 1434-1948
    Keywords: Polymeric copper complexes ; Group-subgroup relationships ; 2D-sheets ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The synthesis and characterisation of two new polymeric CuII complexes is described, i.e. {[Cu(btp)2(CH3CN)(H2O)](CF3SO3)2}n (1) and {[Cu(btp)2(CH3CN)2](ClO4)2}n (2), in which btp = [1,3-bis(1,2,4-triazol-1-yl)propane]. Compound 1 crystallizes in space group P21/c with a = 11.9337(15) Å, b = 20.108(6) Å, c = 12.748(6) Å, β = 92.247(14)°, and Z = 4. Compound 2 crystallizes in space group Pna21 with a = 18.770(8) Å, b = 12.648(8) Å, and c = 12.019(8) Å. The structures refined to R1 values of 0.0683 for 1 and 0.0846 for 2. In both structures the CuII ions are linked by the bridging ligands, resulting in two-dimensional networks. Two such curved layers are arranged on top of each other with center-to-center of layer distances of 2.12 Å in 1 and 1.98 Å in 2. Such double layers are separated from each other by 10.05 Å in 1 and 9.385 Å in 2. The space between the double layers is occupied with interstitial anions. No significant interaction between CuII ions is observed by EPR and magnetic susceptibility measurements. The compounds form a new class of a lattice engineered system held together by the CuII ions. - The coordination geometry of the copper ions is distorted octahedral, with the equatorial plane formed by the N4 nitrogens of the four triazole groups and the axial sites occupied by solvent molecules; acetonitrile and water in structure 1 and two acetonitrile molecules in structure 2. The two structures are related by a group-subgroup relationship, which appears to be the first such case in supramolecular chemistry. - The Cu-N vibrations in the FIR region are found at 274 cm-1 for 1, and at 276 cm-1 for 2. The ligand-field maxima are observed at about 16·103 cm-1, with a shoulder at about 12·103 cm-1. The νCN stretching vibrations of the acetonitrile molecules are found at 2303 and 2261 cm-1 for 1, and at 2313, 2294, 2278, and 2260 cm-1 for 2.Supporting information for this article is available on the WWW under -//_/_http://www.wiley-vch.de/contents/jc_2005/2000/99211_s.pdf or from the author.
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  • 11
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 2000 (2000), S. 217-224 
    ISSN: 1434-1948
    Keywords: Reaction mechanisms ; Cyclopalladation ; Acetic acid ; Pd-C bond stability ; Polynuclear species ; Palladium ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The processes operating during the synthetic cyclopalladation reactions of imines in acetic acid have been studied from a kinetico-mechanistic point of view. These reactions include a fast initial coordination to the palladium through the N-donor atom of the imine, followed by the proper C-H bond activation to produce the acetato bridged dimeric species. At this point, the lability of the bridging acetato groups, the hydrolysis of the C-Pd bonds, and/or the hydrolysis of C=N exo bonds contribute to the generation of dark red polynuclear compounds. The processes occurring after the C-H activation have been followed kinetically, both from palladium acetate plus imine, and the synthetically pure isolated acetato dimers as starting materials. The kinetic and activation parameters have been found identical within experimental error whatever the starting material was (k323 = 1.5 × 10-4 s-1; ΔH# = 51 kJ mol-1; ΔS# = -163 JK-1 mol-1 ΔV# = +19 cm3 mol-1 for the 4-ClC6H4-CH=N-CH2-C6H5 imine derivative 1a). Acidolysis of C-Pd bonds has been found to occur in these polynuclear species. When alternative monomeric Cbenzylic-Pd bond-containing complexes are possible follow ups of the reactions produce them as final dead-end complexes (k323 = 2.2 × 10-5 s-1; ΔH# = 61 kJ mol-1; ΔS# = JK-1 mol-1 ΔV# ≈ 0 cm3 cm-1 for the [2,4,6-(CH3)3]C6H2-CH=N-CH2-[2-(CH3]C6[H4] imine derivative 3d). The same study has been carried out with primary amines in order to check the validity of the data if C=N bond hydrolysis is taking place in the imine derivatives with exo C=N bonds. For complexes with similar type of metallacycles, the results agree reasonably well with the proposed mechanism [k323 = 1.2·10-4 s-1, ΔH# = 46 kJ·mol-1, ΔS# = -180 J·K-1mol-1, ΔV# = -16 cm3·mol-1 for the polynuclear formation of the C6H5-CH2-NH2 derivative 4e; k323 = 3.0·10-4 s-1, ΔH# = 55 kJ·mol-1, ΔS
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  • 12
    ISSN: 1434-1948
    Keywords: Phosphanylphenolate ; Cyclopentadienylnickel complexes ; Chelates ; Ethylene polymerization ; Crystal structure ; Polymerizations ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 2-Diphenylphosphanyl- and 2-alkylphenylphosphanyl-4-methylphenols 1 or their silyl ethers 2 and equimolar amounts of nickelocene react in benzene preferably to give orange-brown diamagnetic cyclopentadienylnickel chelate complexes [η-CpNi(P∩O)] (3). Addition of a second equivalent of 1 or 2 affords (RR) and (SS) diastereoisomers of cis-bis(P∩O-chelates) 4a-c (R = Ph, Me, iPr) or the unsymmetrical cis-bis(P∩O-chelate) 5, whereas with bulkier substituted derivatives 1d or 2d (R = tBu) the second step is hindered or retarded. The reactivity of 1d remains high towards nickel salts in polar solvents, but in contrast to 1a-c, yielding 4, a sparingly soluble green trans-bis(P-O-chelate) nickel complex 6d is formed. Complexes formed in situ from 1 or 2 and Ni(COD)2 in toluene catalyze the polymerization of ethylene. The cyclopentadienyl (P∩O) complexes 3, however, are too stable to be active in this process. The crystal and molecular structure of 3c and 4c are described.Supporting information for this article is available on the WWW under -//_/_http://www.wiley-vch.de/contents/jc_2005/2000/99035_s.pdf or from the author.
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  • 13
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 2000 (2000), S. 287-297 
    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: Reaction of the chiral racemic complex [CpRu(mppe)(SO2)]PF6 (1, mppe = Me2PC2H4PPh2) with diazomethane or -ethane gave the sulfene complexes [CpRu(mppe)(RHC/SO2)]PF6 (R = H, 2a; R = Me, 2b). Treatment of 2a with prochiral enamines or deprotonated β-oxo esters yielded C-C coupling products with 32-60% de. An analog of 2a, [NmcpRu(mppe)(H2C/SO2)]PF6 (8, Nmcp = neomenthylcyclopentadienyl) was prepared in a four-step synthesis starting from LiNmcp and [RuCl2(PPh3)3]. Repeated crystallization of the intermediate [NmcpRu(mppe)Cl] (6) provided diastereomerically pure 6′ which added methylene stereospecifically to give diastereomerically pure 8′. Compound 8 turned out to be much less reactive towards nucleophiles than 2a, but still added deprotonated ethyl 2-methyl-3-oxobutanoate with 44% de. The chiral, enantiomerically pure sulfur dioxide complex [CpRu(chir)(SO2)]PF6 [10, chir = (S,S)-Ph2PCHMeCHMePPh2] was synthesized from [CpRu(chir)Cl] and SO2 and was characterized by X-ray crystallography. Reaction of 10 with diazomethane gave the enantiomerically pure sulfene complex [CpRu(chir)(H2C/SO2)]PF6 (11). Addition reactions of 11 with N-(1-cyclopentenyl)morpholine, as well as with various enolates derived from β-oxo esters or 1,3-diesters proceeded with high yields and 20-90% de. The structure of a diastereomerically pure addition product, [CpRu(chir)(SO2CH2C(Me){C(O)Me}{C(O)OtBu}] (13d′), was determined crystallographically and was shown to have (R) configuration at the quaternary carbon atom. After alkylation of one of the S/O functions, the sulfinate ligand was cleaved from the metal center by ligand substitution with acetonitrile, and the resulting acetonitrile complex 15 was converted back into 10 by treatment with SO2.
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  • 14
    ISSN: 1434-1948
    Keywords: Metal-rich antimonides ; Magnetism ; Structure and bonding ; Conductivity ; LMTO ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The title compounds can be synthesized in quantitative yields by arc-melting of stoichiometric amounts of HfSb2, Hf and one of the 3d metals V, Cr, Mn, Fe, Co, Ni, and Cu. These antimonides crystallize in a substitution variant of the W5Si3 type, in which one position is statistically mixed, occupied by the 3d metal atom M or the Sb2 atom in different ratios. Within the linear (M,Sb) chain, the M:Sb ratio may vary between 3:1 and 2:3. According to calculations of the electronic structures of Hf10MδSb6-δ with δ = 1, these phases are metallic compounds stabilized by strong Hf-Hf, Hf-M, and Hf-Sb bonds, and to a smaller extent by bonding interactions within the linear (M,Sb) chain. The metallic character was confirmed by measurements of the electrical resistivity and the magnetism of selected samples. Whereas Pauli paramagnetism was observed experimentally for M = V, Co, and Ni, Hf10FeSb5 is apparently the only phase with localized magnetic moments and magnetic coupling. This is in agreement with the magnetic ground state obtained solely for the ordered structure model of Hf10FeSb5 with spin-polarized calculation within the local spin density approximation.
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  • 15
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 2000 (2000), S. 323-330 
    ISSN: 1434-1948
    Keywords: Amino acids ; Alkynes ; Ferrocene ; Palladium ; Catalysis ; Bioorganometallic chemistry ; Biosensors ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: This work describes a Pd-catalyzed coupling of ferrocene alkyne derivatives to iodo amino acids. Ferrocene carboxylic acid propargyl amides were easily obtained in high yield. The crystal structures of the propargyl amine derivative 3 and the 1,1-diethylpropargylamine derivative 4 have been determined by X-ray diffraction. Pd-catalyzed coupling to p-iodoanilide amino acids gave the corresponding ferrocene-labeled amino acid derivatives, which were easily purified by diethyl ether extraction in the case of the 1,1-diethyl derivatives 8. The coupling reaction did not require anhydrous solvents and tolerated a variety of functional groups present in peptides such as alcohols (8a, Ser), thioethers (8d, Met), disulfide bonds (cystine, 12) esters (as in the N-labeled Leu derivative 10) and of course amides. A minor by-product of the coupling reaction, namely the homo-dimer bis(ferrocene carboxylic acid propargylamide) 9, was identified in the crude reaction mixtures by mass spectrometry and independently synthesized by oxidative coupling (Glaser and Eglington) of 3. All new compounds were completely characterized spectroscopically, including 15N- and 2D NMR spectroscopy, Mössbauer spectroscopy and electrochemistry. This work introduces a versatile procedure for a selective functionalization of amino acids with organometallics at the C-terminus which is expected to be of general applicability to peptide chemistry.
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  • 16
    ISSN: 1434-1948
    Keywords: Palladium ; Insertion reactions ; Tridentate ligands ; Hydrazones ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Potentially tridentate hydrazonic ligands of the type HNNO have been used in the synthesis of some methyl palladium(II) complexes. Depending on the applied experimental conditions two different kinds of complexes are obtained. Thus, the reactions between HL1-HL5 and (COD)PdMeCl in diethyl ether led to the formation of bidentate methyl complexes of the type Pd(HNN)MeCl (1-5), where the ligands maintain a neutral character. However, in the presence of a base such as Et3N or NaOMe, the ligands are deprotonated with the consequent formation of tridentate methyl complexes of the type Pd(NNO)Me (7-10). In solution, complexes 1-5 tend to lose the hydrazonic proton with elimination of methane and formation of a tridentate chloride complex Pd(NNO)Cl (6); this tendency can be correlated with the acidity of the free ligands, which has been determined. On bubbling carbon monoxide through solutions of 1-5, the corresponding acetyl complexes Pd(HNN)[C(O)Me]Cl (11-15) are formed, in which both the cis and trans isomers are present. Their molar ratio is rationalised from the results of a molecular modelling study on the basis of electronic considerations. A remarkably different reactivity has been found in the carbonylation of the tridentate complexes 7-10: they decompose rapidly and quantitatively to palladium black and an organic product corresponding to the ligand with an acetyl group bonded to the hydrazonic nitrogen. The X-ray structures of a methyl complex (3) and its corresponding acetyl (13) derivative have been determined.
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  • 17
    ISSN: 1434-1948
    Keywords: Vanadyl arsenate ; Hydrates ; Layered compounds ; Vibrational spectroscopy ; X-ray scattering ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The course of the intercalation and deintercalation of water molecules in vanadyl arsenate has been studied by X-ray diffraction analysis and by infrared and Raman spectroscopies. The formation of VOAsO4 hydrates at ambient temperature has been found to depend on relative humidity (r.h.): VOAsO4 · 5 H2O (basal spacing c = 10.48 Å) is formed at r.h. above 76%, VOAsO4 · 3 H2O (c = 8.03 Å) at 43-76% r.h., VOAsO4 · 2 H2O (c = 7.33 Å) at 11-43% r.h.; dehydrated VOAsO4 (c = 4.18 Å) exists near 0% r.h. Like the thermal dehydration of VOPO4 · 2 H2O, the thermal dehydration of VOAsO4 · 3 H2O proceeds in a stepwise manner so that the dihydrate and monohydrate are formed en route to the anhydrous compound. The arsenate monohydrate is gradually dehydrated over a broad temperature range. The broad diffraction lines observed can be explained in terms of the existence of a disordered phase containing monohydrated and anhydrous forms of vanadyl arsenate. A similar phenomenon has been observed during the dehydration of VOAsO4 · 3 H2O over phosphorus pentoxide at ambient temperature. The hydration of VOAsO4 is different from that of VOPO4. The first step, i.e. the insertion of water that coordinates to the vanadium atoms, is very slow. On the contrary, the uptake of further water molecules with the formation of higher hydrates is fast. It thus seems likely that the filling of one interlayer space with water facilitates the intercalation of further water into neighboring interlayer spaces. Therefore, only higher hydrates together with the original anhydrous phase are observed. Impedance spectral measurements indicate that the conductivity of the trihydrate has a mixed ionic/electronic character.
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  • 18
    ISSN: 1434-1948
    Keywords: Coordination chemistry ; α-Imino ketones ; CO complexes ; Iron complexes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The reaction of Fe2(CO)9 at room temperature in THF or toluene with the α-imino ketones R1N=C(R2)-C(R3)=O (L) (R1 = alkyl, R2 = H, Me, Ph, R3 = Me, Ph) (a-k), initially results in the formation of the mononuclear chelate Fe(CO)3(α-imino ketone) complexes 6 which can be isolated in moderate (6h) to high (6e-g) yield. Under these reaction conditions, complexes 6 subsequently react with [Fe(CO)4] fragments or dimerise, to form the dinuclear complexes Fe2(CO)6(α-imino ketone) (7a-j) or Fe2(CO)4(L-L) (8a,b,k), respectively. The complexes 8 contain two α-imino ketone ligands C-C coupled at the ketone carbon atoms. Complexes 8a,b react with CO at elevated temperatures to quantitatively yield Fe(CO)3(α-imino ketone) (6a,b). This reaction can be reversed photochemically. Irradiation of a solution of 6a,b in the low-energy band results in the reformation of 8a,b in almost quantitative yield. The extremely air-sensitive complexes 6 and the dinuclear complexes 7 and 8 have been characterised spectroscopically (IR, UV/Vis, 1H and 13C NMR) and by elemental analysis. The solid state structures of complexes 6g and 8a have been determined by single-crystal X-ray diffraction. The molecular structure of 6g confirms the flat σ-O,σ-N chelate coordination of the α-imino ketone. The structure of 8a consists of two metal-metal-bonded Fe(CO)2 units, bridged by a formally 10e-donating dianionic C-C coupled (tBu-ADO) ligand. A mechanism for the formation of complexes 8 is discussed.Supporting information for this article is available on the WWW under -//_/_http://www.wiley-vch.de/contents/jc_2005/2000/99351_s.pdf or from the author.
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  • 19
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 2000 (2000), S. 929-932 
    ISSN: 1434-1948
    Keywords: Titanium ; Cyclopentadienes ; Arene complexes ; Cations ; Bridging ligands ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The half-sandwich titanium trimethyl complex (η5-C5H4CMe2Ar)TiMe3 (Ar = 3,5-Me2C6H3) reacts with the Lewis acid B(C6F5)3 to give the ionic TiIV ansa-cyclopentadienyl-arene complex [(η5,η6-C5H4CMe2Ar)TiMe2][MeB(C6F5)3]. In bromobenzene solvent, addition of more B(C6F5)3 leads to C6F5/Me exchange and, subsequently, to formation of an unusual dimeric TiIII dicationic species, {[(η5,η6-C5H4CMe2Ar)Ti(μ-Br)]2}[B(C6F5)4]2, which was structurally characterized. Its formation involves reduction of the transition-metal center, solvent C-Br cleavage and perfluoroaryl-group scrambling.Supporting information for this article is available on the WWW under -//_/_http://www.wiley-vch.de/contents/jc_2005/2000/99383_s.pdf or from the author.
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  • 20
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 2000 (2000), S. 939-941 
    ISSN: 1434-1948
    Keywords: Germanium ; Germanol ; Hydrogen bonds ; X-ray structure ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The hydrolysis of tBu2Ge(OEt)2 is described. Depending on the amount of water used either tBu2Ge(OH)2 (1) or a mixture of the latter and (tBu2GeOH)2O (2) were obtained. A cocrystallate consisting of 2tBu2Ge(OH)2, (tBu2GeOH)2O and water was the subject of a single crystal X-ray diffraction study. In the solid state the individual molecules are connected by hydrogen bonds giving rise to the formation of a polymeric double chain ribbon.
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  • 21
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 2000 (2000), S. 959-969 
    ISSN: 1434-1948
    Keywords: Bipyridyldiphosphane ligands ; Macrocycles ; Metallacyclophanes ; Platinum ; Supramolecular chemistry ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The 5,5′-bis(hydroxyalkyl)-2,2′-bipyridines 4a-c (Scheme 1) were prepared either in one step (4b, 4c) or in four steps (4a) starting with 5,5′-dimethyl-2,2′-bipyridine in each case. Reaction of 4a-c with mesyl chloride afforded the bis(mesylates) [-C5H3N-(CH2)n-CH2-OSO2Me]2 5a-c [n = 1 (a), 2 (b), 3 (c)], which could easily be transformed into the diphosphanes 6a-c by reaction with LiPPh2. Treatment of 6c, 6b with Cl2Pt(NCPh)2 and (RC6H4)2Pt(COD) according to the high-dilution method resulted in the formation of the tetraphosphadiplatinacyclophanes [-C5H3N-(CH2)4-PPh2PtCl2PPh2-(CH2)4-C5H3N-]2 (7c) and [-C5H3N-(CH2)3-PPh2Pt(C6H4R)2PPh2-(CH2)3-C5H3N-]2 (8b, 9b) (8b: R = H, 9b: R = tBu), respectively (Scheme 2). The molecular structures of 8b and 9b were elucidated by X-ray structural analyses. The noncoordinated bipyridine moieties in 8b were employed to encapsulate copper(I) to give the host/guest complex 10b (Scheme 3), which was investigated by FAB-MS, NMR spectroscopy, and cyclovoltammetry. 10b exhibited a quasi-reversible oxidation at E1/2 = -0.31 V and an electrodeposition-redissolution redox system at E1/2 = -0.79 V, owing to the formation of copper at the surface of the working electrode.
    Additional Material: 4 Ill.
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  • 22
    ISSN: 1434-1948
    Keywords: Lanthanides ; Ytterbium ; MRI contrast agents ; Solid-state structures ; Hydration ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The low temperature (-100 °C) X-ray structure of the complex K2[Yb(DTPA)(H2O)] has been determined. The metal ion is at the center of a tricapped trigonal prism and is nine-coordinate, binding to the three nitrogens and five oxygens of the ligand and one water molecule. From the structure obtained, three well-defined hydration shells can be observed consisting of: i) one coordinated water molecule; ii) several water molecules in the outer coordination sphere of the YbIII ion and iii) one water molecule surprisingly close to the metal center and hydrogen-bonded to proximate carboxylate groups. A variable-field and temperature NMRD study of the corresponding Gd complex has been performed and the data interpreted by taking into account the presence of second-sphere water molecule(s). The results of the analysis are in excellent agreement with the X-ray structural data.
    Additional Material: 3 Ill.
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  • 23
    ISSN: 1434-1948
    Keywords: Catalysis ; Densitiy functional theory ; Epoxidation ; Reaction mechanisms ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Seven-coordinated molybdenum oxobisperoxo complexes with chelate nitrogen donors like pyrazolylpyridines are catalysts for the epoxidation of olefins. An NMR spectroscopic and quantumchemical study on the fluxionality of the chelate ligand proves that during this process partial ligand dissociation takes place. This gave rise to a detailed theoretical study on the activation of CH3OOH at the model complex (NH3)2MoO(O2)2 including dissociation of one of the ammonia ligands and proton transfer from the hydroperoxide to one of the peroxo ligands.Supporting information for this article is available on the WWW under -//_/_http://www.wiley-vch.de/contents/jc_2005/2000/99429_s.pdf or from the author.
    Additional Material: 6 Ill.
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  • 24
    ISSN: 1434-1948
    Keywords: Palladium ; Tripodal ligands ; O ligands ; Fluxionality ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The reaction of [PdCl2(CH3CN)2] with the silver salt of the tripodal oxygen ligand L- = [(C5H5)Co{P(O)(OMe)2)}3]- yields the homoleptic oxygen ligand complex [PdL2] (1). The molecular structure of 1 was determined by single-crystal X-ray diffraction: monoclinic space group P21/n; a = 8.515(1), b = 13.627(2), c = 15.828(2) Å; β = 92.44(1)°; V = 1834.9(7) Å3; Z = 2. The complexes [Pd(PPh3)XL] [X = Cl (2a), Br (2b), I (2c)] have been prepared starting from 1. Complex 2a reacts with PPh3 to form [Pd(PPh3)2L]Cl (3a) and [Pd(PPh3)2L]L (3b). Treatment of 2a with CO in MeOH yields the carboxymethyl complex [{(PPh3)(COOMe)Pd(μ-Cl)}2] (4) and the protonated ligand HL. The carboxymethyl complex 4 shows some catalytic activity for the copolymerization of CO and ethene. Complex 4 reacts with AgL to yield [Pd(PPh3)(COOMe)L] (6). Alkylation of 2a with Me4Sn leads to the methyl complexes [Pd(PPh3)MeL] (7) and [Me2ClSnL] (8). CO insertion in the palladium-carbon bond of 7 gives the stable acetyl complex [Pd(PPh3){C(O)Me}L] (10). The palladium(II) complexes 1, 2, 3, 6, 7, and 10 of the tripodal oxygen ligand L are all fluxional molecules that have been studied by temperature-dependent 1H- and 31P-NMR spectroscopy.
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  • 25
    ISSN: 1434-1948
    Keywords: Tripod ligands ; Hindered rotation of vinylidene ligands ; CpML2 chelate ligands ; Ruthenium ; Carbenes ; Carbene-type ligands ; Cyclic voltammetry ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The tripodal ligand [CH3C(CH2C5H4)(CH2PPh2)2]- reacts with RuCl2(PPh3)3 to produce CH3C(CH2-η5-C5H4)(CH2-η1-PPh2)2RuCl, [tripodCpL2RuCl], 1. Complex 1 undergoes substitution of the chlorine function with various nucleophiles L′ to produce [tripodCpL2RuL′]+. The carbonyl derivative (L′ = CO) 2, isonitrile (L′ = RNC) 3, nitrile compounds (L′ = RCN) 4, and a tolane adduct (L′ = η2-PhC≡CPh) 5 are obtained when 1 is treated with the appropriate ligands in polar solvents. Halide acceptors (e.g. TlPF6) are generally needed to promote these reactions. The cyanide derivative tripodCpL2RuCN (3a) is alkylated by F3CSO3CH3 to give the isonitrile derivative [tripodCpL2RuCNMe]+3b. Terminal alkynes HC≡CR produce vinylidene compounds [tripodCpL2RuL′]+, where L′ = C=CHR (R = tBu, 7b; R = Ph, 7c), or allenylidene derivatives, L′ = C=C=CPh2 (6), depending on the nature of R (R = CPh2OH for synthesis of 6). Trimethylsilylacetylene gives the parent vinylidene species, L′ = C=CH2 (7a), which is transformed to the Fischer-type carbene compound, L′ = C(OMe)Me (8), upon treatment with methanol. The vinylidene species 7 are deprotonated by NaOMe to produce the alkynyl compounds tripodCpL2RuC≡CR (9). Methylation of 9 with F3CSO3CH3 results in the vinylidene derivatives L′ = C=C(Me)R (R = tBu, 7d; R = Ph, 7e), having two organic substituents at the terminal carbon centre. For all vinylidene compounds with two different substituents at their terminal carbon atom, hindered rotation of the single-faced vinylidene π-ligand about its Ru-C bond is observed. Analysis by 31P-NMR spectroscopic coalescence measurements as well as line-shape analyses reveals activation enthalpies of around 40 kJmol-1 for this rotation, with small activation entropies of around ±10 Jmol-1K-1. Solid-state structures of nine compounds of the type [tripodCpL2RuL′]+n (n = 0, 1) demonstrate the remarkable conformational rigidity of the tripodCpL2Ru template. They also show that the possible strain imposed by linking the Cp ligand and the two donor groups L in one and the same chelate scaffolding does not appear to impose a serious steric strain on these templates.
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  • 26
    ISSN: 1434-1948
    Keywords: (R)-(+)-2,3-Epoxy-1-propanol ; 2,3-Dihydroxyalkyl phosphanes ; 1,3,2-Dioxaborolane ; 1,3-Dioxolane ring ; Enantiopure phosphanes ; Complexes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Reaction of (R)-(+)-2,3-epoxy-1-propanol with Ph2PH, Ph(Me)PH, or PhPH2 in the superbasic medium KOH/DMSO affords the novel chiral phosphanes 1a-1c. While 1a is obtained enantiomerically pure, 1b and the secondary phosphane 1c are formed as mixtures of diastereoisomers (RPRC, SPRC) with homochiral β carbon atoms. Derivatization of 1a with phenylboronic acid or 2,2-dimethoxypropane yields 2a and 3a with 1,3,2-dioxaborolane and 1,3-dioxolane ring systems, respectively. The X-ray structure of 2a (space group P21) reveals the presence of four molecules of R configuration in the unit cell. Nucleophilic phosphanylation of (R)-(-)-2,3-O-isopropylideneglycerol tosylate with Ph2PH, Ph(Me)PH, or PhPH2 yields chiral 3a-3d. Compound 3b was obtained enantiomerically pure. The secondary phosphane 3c has been employed in syntheses of the hydrophilic tertiary phosphanes 3e, 3f and of the novel bidentate phosphane ligands 3g, 3h, all of which have homochiral β carbon atoms. PdII complexes PdL2Cl2 of 1a, 2a, 3a (L) are formed as mixtures of cis/trans isomers. RhI complexes of 1a, 3a, and bidentate 3h have also been synthesized.
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  • 27
    ISSN: 1434-1948
    Keywords: Macrocycles ; Nickel ; Redox chemistry ; Schiff bases ; S ligands ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A single crystal X-ray analysis of [Ni2L1](ClO4)2· MeCN · 1/4 H2O, 1a [formed directly from a mixture of nickel(II) template ions, 2,6-diformyl-4-methyl-thiophenolate, and 1,4-diaminobutane] reveals that the nickel(II) ions are in square-planar N2S2 environments and that the four “bowed” dinickel macrocycles in the asymmetric unit pack around a single central perchlorate template ion encapsulating it to form “star” clusters of stoichiometry {[Ni2L1]4(ClO4)}7+. These “stars” stack together, via π-π-stacking interactions, to form two-dimensional sheets, which are separated from one another by layers of the remaining perchlorate anions and solvent molecules. Reduction, by NaBH4, of the four imine bonds in [Ni2L2](ClO4)22a (analogous to 1a but formed from 1,3-diaminopropane not 1,4-diaminobutane) or [Ni2L2](CF3SO3)22b to amine bonds produces the corresponding tetra-amine complex, [Ni2L3](ClO4)23. These complexes are shown to contain diamagnetic nickel(II) ions by a combination of magnetic, NMR and UV/Vis spectroscopic results. The 1H NMR spectra of 1-3 run in [D3]MeNO2 and in [D3]MeCN are consistent with increasing axial binding ability in the order: 3 〈 2 〈 1. Thiocyanate ion binding studies reveal that 1 and 2 are able to coordinate two thiocyanate ions, forming [Ni2L1(NCS)2] 4 and [Ni2L2(NCS)2] 5 respectively, whereas 3 does not. Single crystal X-ray analyses of complexes 4· 2 MeCN and 5· MeCN show that adjacent square-planar and octahedral nickel(II) ions result. Two one-electron oxidations and two one-electron reductions are a feature of the electrochemistry of 1-3 in MeCN: curiously, the potentials for the oxidation processes are almost invariant whereas those for the reduction processes vary as anticipated. EPR spectroscopy shows that the first one-electron reduction process and the first one-electron oxidation process are metal centred. Spectroelectrochemical studies and redox titrations indicate that a purplish-coloured complex is produced by one-electron oxidation of 2 (λ = 870 nm, ε = 1320 L mol cm-1). The synthesis of a phenolate analogue, [Ni2L′(MeCN)4](ClO4)2 (6), of the thiophenolate complex 2a is also detailed. Complex 6 undergoes two one-electron oxidations in MeCN, but, in contrast to the thiophenolate complexes 1-3, these occur at much higher potentials. Only a single one-electron reduction process is observed and this occurs at a more negative potential than for any of 1-3.
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  • 28
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 2000 (2000), S. 195-203 
    ISSN: 1434-1948
    Keywords: Acid derivatives ; Cyclen and cyclam derivatives ; Phosphinic acid ; Potentiometry ; Protonation and stability constants ; 31P-NMR titration ; Hydrogen bonding ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Two phenylphosphinic acid derivatives of tetraaza macrocycles, (1,4,7,10-tetraazacyclododecanetetrayl)tetrakis(methylene)tetrakis(phenylphosphinic acid) [(H4L1) and (1,4,8,11-tetraazacyclotetradecanetetrayl)tetrakis(methylene)tetrakis(phenylphosphinic acid)] (H4L2), were synthesised and the crystal structures of H4L2 and its bis(1-adamantylammonium) salt were determined. In both the structures, the ring conformation is virtually the same and is stabilised by hydrogen bonds. Protonation constants of the acids and stability constants of their Zn2+ and Cd2+ complexes were determined pH-metrically at 25 °C and at an ionic strength of 0.1 mol dm-3 (KNO3). The pKA values found for both the compounds are lower than those for their carboxylic analogues and correspond to the expected electron-withdrawing ability of the -P(Ph)O2H moiety. The value pK1 of the last dissociation constant of H4L1 is surprisingly high. The complexes of Zn2+ and Cd2+ with (L1)4- and (L2)4- are less stable than those with other similar ligands, which is in accordance with lower overall basicity of H4L1 and H4L2. A pronounced drop in the stability of the complexes of H4L2 can be explained by partial coordination of the ligand to the metal ions. The solution properties of the ligands were also investigated by 31P-NMR spectroscopy. The spectra observed suggest stable (on the NMR time scale) conformations of the protonated ligands in solution. A comparison of NMR spectra in solution and CP/MAS-NMR spectra indicates that the structures of the conformers roughly correspond to the structures observed in the solid state. The conformations are stabilised by intramolecular hydrogen bonds and by hydrophobic interactions of phenylphosphinic moieties. The conformers are stable even at 90 °C, but not in the presence of complexing metal ions.Supporting information for this article is available on the WWW under -//_/_http://www.wiley-vch.de/contents/jc_2005/2000/99149_s.pdf or from the author.
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  • 29
    ISSN: 1434-1948
    Keywords: Rare earth complexes ; Naphthalocyaninato ligand ; Double-decker complexes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A series of rare earth(III) double-deckers RE[Nc(tBu)4]2 [RE = La, Ce, Pr, Nd, Eu, Gd, Tb, Y, Er; Nc(tBu)4 = dianion of tetra(tert-butyl)-2,3-naphthalocyanine] (1-9) have been prepared by treating RE(acac)3·n H2O (acac = acetylacetonate) with 6-tert-butylnaphthalonitrile in refluxing n-octanol in the presence of 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU). These novel sandwich-type complexes have been spectroscopically characterized. The electrochemical studies show that the first oxidation and the first reduction potentials increase with the size of the central metal ions with a relatively small separation (0.28-0.33 V), reflecting the narrow HOMO-LUMO gap.
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  • 30
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 2000 (2000), S. 229-239 
    ISSN: 1434-1948
    Keywords: Pyridine derivatives ; Bipyridine derivatives/Metal complexes ; Chromophores ; Nonlinear optics ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Metal complexes of pyridine and bipyridine-type ligands represent an important class of nonlinear optical (NLO) materials: (i) They can incorporate a variety of functionalised ligands with a wide range of metals which can give rise to tuneable NLO properties; (ii) they are generally associated with intense low-lying charge-transfer excitations such as metal to ligand charge-transfer (MLCT) or intraligand charge-transfer (ILCT); (iii) bipyridyl ligands are also good building blocks that allow the construction of octupolar complexes with a defined geometry and symmetry. This review describes the recent developments in the design of such dipolar and octupolar chromophores for second-order nonlinear optics.
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  • 31
    ISSN: 1434-1948
    Keywords: Heterobimetallics ; Hydride complexes ; Alkenyl complexes ; μ-Isonitrile complexes ; Silicon ; Iron ; Platinum ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The heterobimetallic hydride complexes [(OC)3Fe{Si(OMe)3}(μ-Ph2PXPPh2)Pt(H)(PR3)] (1a: X = CH2, PR3 = PPh3; 1b: X = NH, PR3 = PPh3; 1c: X = CH2, PR3 = PMePh2) have been prepared by the oxidative addition of [(OC)3Fe(H){Si(OMe)3}(η1-Ph2PXPPh2)] to [Pt(H2C=CH2)(PPh3)2] or by reaction of K[(OC)3Fe{Si(OMe)3}(η1-dppm)] with trans-[Pt(Cl)(H)(PPh3)2]. The solid-state structure of compound 1b has been determined by single-crystal X-ray diffraction. 1-Alkynes such as methylpropiolate or phenylacetylene insert in a regiospecific manner into the Pt-H bond of 1 to yield the σ-alkenyl complexes [(OC)3Fe{μ-Si(OMe)2(OMe)}(μ-Ph2PXPPh2)Pt{C(R)=CH2}] (2a: X = CH2, R = CO2Me; 2b: X = NH, R = CO2Me; 3a: X = CH2, R = Ph). Addition of the Pt-H bond of 3a across the triple bond of [D1]phenylacetylene affords [(OC)3Fe{μ-Si(OMe)2(OMe)}(μ-dppm)Pt{C(Ph)=C(D)H}] (3a*) having the deuteron trans to platinum (cis addition). This insertion reaction is accompanied by dissociation of the platinum-bonded PR3 ligand and saturation of the vacant coordination site by a dative μ-η2-Si-O→Pt interaction. When 3 is treated with PR3 again, a subsequent phosphane-induced rearrangement leading to vinylidene-bridged complexes [(OC)3Fe{μ-C=C(H)R′}(μ-Ph2PXPPh2)Pt(PR3)] (4a: X = CH2, R′ = Ph, PR3 = PPh3; 4b: X = NH, R′ = Ph, PR3 = PPh3; 4c: X = CH2, R′ = Ph, PR3 = PMePh2; 4d: X = CH2, R′ = p-tolyl, PR3 = PPh3) occurs. Upon purging a solution of 3a with carbon monoxide, the labile CO adduct [(OC)3Fe{Si(OMe)3}(μ-dppm)-Pt(CO){C(Ph)=CH2}] 5a is formed, addition of 2,6-xylyl isocyanide to 2a and 3a affords the isonitrile adducts [(OC)3Fe{Si(OMe)3}(μ-dppm)Pt(CNxylyl){C(R)=CH2}] (5b: R = CO2Me; 5c: R = Ph), respectively. When hydride complex 1a is allowed to react with stoichiometric amounts of aromatic isonitriles, formal elimination of HSi(OMe)3 occurs, yielding the heterodinuclear isonitrile-bridged complexes [(OC)3Fe(μ-C=N-R)(μ-dppm)Pt(PPh3)] (6a: R = 2,6-xylyl; 6b: R = o-anisyl; 6c: R = p-anisyl; 6d: R = p-C6H4NH2) and the bis(isonitrile) complexes [(OC)2(RN≡C)Fe(μ-C=N-R)(μ-dppm)Pt(PPh3)] (7a: R = 2,6-xylyl; 7b: R = p-anisyl). Single-crystal X-ray diffraction studies perfomed on 6a and 6b reveal that the molecular structures of these μ-isonitrile complexes closely resemble the μ-vinylidene complexes 4. The two metal centers are bridged in a symmetric manner by strongly bent CNR ligands, the aromatic groups R being oriented towards the Fe(CO)3 moiety. Electrophilic addition of HBF4 to the basic nitrogen atom of the μ-CNR ligand transforms 6 to the cationic μ-aminocarbyne complexes [(OC)3Fe{μ-CN(H)R}(μ-dppm)Pt(PPh3)][BF4] (8a: R = 2,6-xylyl; 8b: R = p-anisyl; 8c: R = p-C6H4NH2).
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  • 32
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 2000 (2000), S. 253-264 
    ISSN: 1434-1948
    Keywords: Iron-sulfur clusters ; Crown ethers ; Electrochemical devices ; Host-guest chemistry ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A series of Fe4S4 cluster compounds, I, III, and V, in which the cuboidal cluster core is appended with four crown ether thiolate ligands, and II and IV, bearing thiolate ligands without crown ether parts, has been synthesized and characterized. The spectroscopic and electrochemical properties of these compounds are determined by the electronic nature of the thiolate ligands. Only in the case of III, where a very short α-thioacetyl linker was used to connect the crown ether ligands to the cluster core, was a restricted conformational freedom of the ligand observed. A detailed electrochemical study of the influence of alkali and earth alkali metal ions (Li+, Na+, K+, Mg2+, and Ba2+) on the reversible 2-/3- reduction of the cluster compounds was performed. In the case of the crown ether appended clusters I, III, and V, the addition of these metal ions resulted in an anodic shift, i.e. in positive direction, of the reduction potential (modulation effect) and to larger current responses (promotion effect). The magnitude of the modulation effects is determined by the binding affinity of the metal ions in the crown ether ligands, and by the distance between bound metal ions and the redox active cluster core. Variation of the linker between the cluster core and the metal ion binding site resulted in cluster compounds with almost inverse selectivities for e.g. K+ and Ba2+ in the case of I and III. For the large effects found for compound I a lariat binding mode is proposed.
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  • 33
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 2000 (2000), S. 281-285 
    ISSN: 1434-1948
    Keywords: NMR spectroscopy ; Zeolites ; Al-coordination ; Mordenite ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 27Al 3Q MAS NMR spectroscopy has been applied to study the coordination state of the species giving the 30 ppm Al NMR signal in the 27Al MAS NMR spectrum of activated mordenite materials. From the 27Al 3Q MAS NMR measurements it is evident that the broad peak at 30 ppm in the 27Al NMR spectrum of the mordenite calcined at temperatures up to 600 °C comes mainly from the distorted four-coordinated Al. By simulation a quadrupolar coupling constant of 5.8 MHz was estimated for the distorted tetrahedral Al. For samples calcined at 650 and 700 °C, a small amount of pentacoordinated Al emerges. The majority of the signal, however, arises from distorted tetrahedral Al. A two-step calcination results in a significant contribution of the pentacoordinated Al to the signal at 30 ppm. From the simulated line-shape, a quadrupole coupling constant of 6.2 MHz is obtained for the latter signal. These data show that during the calcination of the mordenite, the coordination environment at the Al centre gradually becomes distorted to give rise to the shoulder at 30 ppm. With the increase of the calcination temperature, pentacoordinated Al species form
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  • 34
    ISSN: 1434-1948
    Keywords: Copper ; Magnetic properties ; Supramolecular chemistry ; Three-dimensional architecture ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A novel three-dimensional copper(II) compound of the formula [Cu3(btre)5(H2O)2](ClO4)6·H2O (btre = 1,2-bis(1,2,4-triazol-4-yl)ethane) has been synthesized. The structure has been solved at 150 K by single-crystal X-ray analysis. The compound [C30H44Cu3N30O2·6(ClO4)·H2O] crystallizes in the triclinic space group P1bar with a = 12.488(1), b = 13.195(1), c = 19.756(2) Å, α = 78.959(8), β = 84.553(8), γ = 63.869(7)°, V = 2868.4(5) Å3, Z = 2 (trinuclear CuII units), 6484 reflections [I 〉 4σ(Ι)], RF = 0.0581, wR2 = 0.1214. The structure of this coordination polymer consists of a three-dimensional network built up from linear trinuclear CuII cations of formula [Cu3(btre)5(H2O)2]6+. This crystallographically independent unit comprises a linear array of three CuII ions linked by triple N1,N2-1,2,4-triazole bridges, yielding Cu1-Cu2 = 3.893(1) Å and Cu2-Cu3 = 3.889(1) Å. These linear trinuclear CuII units are linked by various pathways involving tridentate and tetradentate bridging btre ligands, which yields an unprecedented three-dimensional network. The CuII ions are weakly antiferromagnetically coupled with J = -1.01(2) cm-1 (based on the Hamiltonian: H = -J[SCu1·SCu2 + SCu2·SCu3] using the expression for the molar magnetic susceptibility S = 1/2 of a linear trinuclear system). The nature and the magnitude of the antiferromagnetic exchange have been discussed on the basis of the structural features.
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  • 35
    ISSN: 1434-1948
    Keywords: Alkenylcarbynes ; Dinuclear tungsten complexes ; Electrochemistry ; Tungsten NMR ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Neutral trans-cyanide alkenylcarbyne complexes 2a and 2b have been prepared by reaction of the complex 1a and 1b with NaCN or [Bu4N]CN. The reaction of complexes 2a and 2b with an equimolar amount of the acetonitrile complexes 1a and 1b in CH2Cl2 leads to the cationic cyanide-bridged bis(alkenylcarbyne) di-tungsten complexes 3a-d. Diisocyanide-bridged bis(alkenylcarbyne) di-tungsten complexes 4a and 4b have been synthesized by the reaction of complexes 1a and 1b with 0.5 equivalents of the diisocyanide 1,4-(CN)2C6H4. IR as well as 1H-, 31P{1H}-, 13C{1H}-, and 183W-NMR data are reported. The spectroscopic data show that in the dinuclear complexes 3a-d, the bridging CN group and the alkenylcarbyne units are located in trans positions, while in the dinuclear complexes 4a and b, the isocyanide groups of the bridging ligand 1,4-(CN)2C6H4 and the two alkenylcarbyne moieties are cis. The 183W chemical shifts of complexes 2a, 2b, 3a-d, 4a, and 4b were obtained through two-dimensional indirect 31P, 183W NMR recording techniques. A downfield shifting of 183W resonances of the cyanide-bridged dinuclear complexes 3a-d with respect to the mononuclear ones, 2a and 2b, was observed. The δ183W of isocyanide bridging dinuclear complexes 4a and 4b appear at higher field than those of the corresponding mononuclear cyanide 2a and 2b in accordance with the higher π-acceptor electron properties of the isocyanide ligand. The electrochemical behaviour of all the complexes has been investigated by cyclic voltammetry and controlled potential electrolysis in aprotic media and at a Pt (or vitreous C) electrode. Complexes 1, 2, or 3 undergo multi-electron irreversible oxidation processes involving anodically induced proton dissociation from the alkenylcarbyne ligands, and irreversible cathodic processes are also observed for all the complexes. The order of the redox potentials reflects that of the net electron π-acceptor/σ-donor character of the ligands and the ligating alkenylcarbynes are shown to behave as remarkably strong π-electron acceptors (even stronger than CO).
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  • 36
    ISSN: 1434-1948
    Keywords: Colloids ; Sol-gel processes ; Immobilization ; Heterogeneous catalysts ; Hydrogenations ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A bimetallic, fully alloyed Pd/Au colloid of 3.0 nm particle size, obtained by the co-reduction of Pd and Au salts with tetraalkylammonium triethylhydroborate, was embedded in a silica matrix employing a modified sol-gel procedure with THF as the solvent. The removal of the protecting tenside led to a mesoporous texture with a comparatively narrow pore distribution. The physical characterisation by a combination of several techniques has shown that the SiO2-embedded Pd/Au colloid preserves the size and the structural characteristics of the colloidal metal precursor. The new material exhibits catalytic properties in selective hydrogenation.
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  • 37
    ISSN: 1434-1948
    Keywords: Thiacalixarene ; Trimetallic sandwich ; Cobalt ; Zinc ; Divergent receptors ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Reaction between deprotonated p-tert-butyltetrathiacalix[4]arene and CoII or ZnII under strictly defined conditions leads to the formation of sandwich species in which a trimetallic unit is held between two opposed, divergently oriented, staggered O- and S-bound calixarene ligands in the cone conformation. Despite the isomorphous nature of the crystalline compounds, there is a subtle difference in the coordination of CoII and ZnII, presumably related to the differences in metal radius and electron configuration combined with structural restrictions imposed by the calixarene framework, in that whereas all three Co atoms may be considered six-coordinate (and approximately octahedral), only two of the Zn atoms appear so, the third being five-coordinate and more nearly trigonal bipyramidal in its coordination geometry.
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  • 38
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 2000 (2000), S. 831-834 
    ISSN: 1434-1948
    Keywords: Metallo-calixarenes ; Gold complexes ; Tetraphosphane ; Stability constants ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Assemblage of the tetragold complex [L·(AuCl)4] from p-tert-butyl-calix[4]-(OCH2PPh2)4 (L) and [AuCl(tetrahydrothiophene)] was investigated by NMR and UV/Visible spectroscopic titrations. Three steps could be resolved and are assigned, respectively, to addition of one, two and four AuCl units to the macrocyclic ligand. At each stage of metallation, symmetrical species persist on the NMR time scale since the bound AuCl fragments migrate between the different phosphorus centers via both intra- and intermolecular processes. The derived stability constants (logβ1 = 4.4 ± 0.2, logβ2 = 7.0 ± 0.7, and logβ4 = 14.5 ± 2.0) indicate both positive and negative cooperativity during build-up of the tetranuclear species. An X-ray diffraction study made with crystals obtained from an L:Au (1:2) mixture revealed the formation of an unusual binuclear complex whose solid state structure comprises a polymeric chain of [L·AuCl] units linked by pseudo-tetrahedral Au+ ions, each generic unit containing a pendant linear PAuCl fragment. This polymeric species, with its two distinct binding modes, provides a simple rationale by which to explain the role of cooperativity in the overall assembly process.
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  • 39
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 2000 (2000), S. 839-842 
    ISSN: 1434-1948
    Keywords: Tris(pyrazolyl)borate ; Tantalum ; Agostic interactions ; Alkyne complexes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The synthesis of unprecedented alkyne hydrotris(3,5-dimethylpyrazolyl)borato (TpMe2) tantalum(III) complexes is reported. The parent dichloro complex TpMe2TaCl2(PhC≡ CCH3) (2) is obtained from TaCl3(DME)(PhC≡CCH3) and KTpMe2. 2 reacts with methyllithium to give the dimethyl complex TpMe2Ta(CH3)2(PhC≡CCH3) (3) and with ethylmagnesium chloride to give the X-ray characterized α-agostic ethyl complex TpMe2Ta(Cl)(μ-H-CHCH3)(PhC≡CCH3) (4). Reaction of 4 with methyllithium generates the mixed methyl ethyl complex TpMe2Ta(CH3)(μ-H-CHCH3)(PhC≡CCH3) (5) in solution. Spectroscopic data indicate that 5 is α-agostic at the ethyl group only.
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  • 40
    ISSN: 1434-1948
    Keywords: Sulfur ; Titanium ; Zinc ; Polysulfido complexes ; Sulfur heterocycles ; Polysulfides ; Polysulfanes ; Sulfenyl chlorides ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The preparation of seven novel organic polysulfanes is reported. Bis(n-octyl)heptasulfane R2S7 1 is formed upon reaction of RSCl with [Cp2TiS5], while the corresponding nonasulfane R2S9 2 is obtained by reaction of RSSCl with [Cp2TiS5]. The bis(n-octyl)pentasulfane R2S5 3 is obtained from RSCl and [(Cp′2TiCl)2S3] by transfer of the S3 ligand at 20 °C. The new alkyl polysulfanes 1-3 have been obtained in quantitative yields. They are liquids at 20 °C, having freezing points below -50 °C, but do not form mesogenic phases. Reactions of [Cp2TiS5] with 2-naphthyl- and 4-chlorophenyl sulfenyl chloride furnish the corresponding heptasulfanes 4 and 5, respectively, which are solids at 20 °C. 1,2-Benzodisulfenyl chloride C6H4(SCl)2 reacts with [(Cp′2TiCl)2S3] to give the known 1,2,3,4,5-benzopentathiepin C6H4S5 6, with [Cp2TiS5] to give the novel 1,2,3,4,5,6,7-benzoheptathionin C6H4S7 7, and with [(TMEDA)ZnS6] to give the novel 1,2,3,4,5,6,7,8-benzooctathiecin C6H4S8 8. The cyclic polysulfanes 6-8 are solids at 20 °C and have been recovered in yields of 60-83%. The orthorhombic structure of 1,2-C6H4S7 has been investigated by single-crystal X-ray diffraction analysis. The molecules are found to be located at sites of Cs symmetry and the motif of the C2S7 heterocycle is +-+-+-+-, with the torsion angle of zero at the carbon-carbon bond. The three internuclear SS distances measure 205.0(1), 203.7(1), and 205.7(1) pm.
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  • 41
    ISSN: 1434-1948
    Keywords: Palladium ; Platinum ; Dithiolenes ; Diselenolenes ; Sulfur ; Selenium ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The tetrachalcogenides [ME4(dppe)] (M = Pd, E = S; M = Pt, E = S, Se) react with the activated alkynes RO2CC≡CCO2R (R = Me, Et) to form the dithiolenes and diselenolenes [M{E2C2(CO2R)2}(dppe)]; the structures of the compounds with E = S, R = Et have been determined by X-ray crystallography; [PdS4(dppe)] also reacts with the carbene complex [W(CO)5{C(OEt)C≡CPh}] to yield the bimetallic dithiolene [Pd{S2C2[C(OEt)W(CO)5]Ph}(dppe)].
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  • 42
    ISSN: 1434-1948
    Keywords: Pyrazolate complexes ; Palladium ; Platinum ; N ligands ; Bridging ligands ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Trinuclear complexes containing pyrazolate bridging ligands of the type [NBu4]2[{(C6F5)2 M(μ-pz)(μ-X)}2M′] (M, M′= Pd or Pt; X = Cl, OH, or pz) (Hpz = pyrazole) have been prepared using [NBu4][M(C6F5)2(acac)] (acac = acetylacetonate) or [NBu4]2[M2(C6F5)4(μ-OH)2] and [M′Cl2(Hpz)2] or [M′(Hpz)4]2+ as starting materials. Asymmetric homo- and heterobimetallic complexes of the types [NBu4][R2M(μ-pz)2Pd(η3-allyl)] and [R2M(μ-pz)2M′L2] (allyl = C3H5 or C4H7; L2 = 2 PEt3 or bipy; R = C6F5 or C6Cl5; M, M′ = Pd or Pt) have been obtained starting from [NBu4][MR2(pzHpz)] and [Pd(η3-allyl)(acac)] or [M′L2Cl2], respectively. The identity of the new complexes has been established by NMR (1H, 19F and 31P) spectroscopy. The crystal structure of [{(C6F5)2Pd(μ-pz)(μ-Cl)}2Pd]2- has an inversion centre, with a bent appearance of the Pd3(μ-pz)2(μ-Cl)2 moiety. The crystal structure of [(C6F5)2Pd(μ-pz)2Pd(η3-C4H7)] has also been determined by single-crystal X-ray diffraction, where a boat conformation of the central “Pd2N4” six-membered rings is observed.
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  • 43
    ISSN: 1434-1948
    Keywords: Copper ; Nickel ; Amides ; Polynuclear complexes ; Magnetic properties ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: New homo- and heterometallic hexanuclear complexes of formula {[Cu(tmen)(H2O)]2[Cu(tmen)]2[Cu2L](H2O)}(ClO4)4 ·2 H2O [Cu6-tmen] {[Cu(pmdien)]4[Cu2L]}(ClO4)4 · 4 H2O [Cu6-pmdien] and {[Ni(cyclam)]4[Cu2L]}(ClO4)4 · 4 H2O [Cu2Ni4-cyclam] [H8L = tetrakis(aminomethylene)methanetetrakis(oxamic acid), tmen = N,N,N′,N′-tetramethylethylenediamine, pmdien = N,N,N′,N′,N″-pentamethyldiethylenetriamine, and cyclam = 1,4,8,11-tetraazacyclotetradecane] have been synthesized. The crystal structure of [Cu6-tmen] has been determined by single-crystal X-ray diffraction. The structure consists of cationic {[Cu(tmen)(H2O)]2[Cu(tmen)]2[Cu2L](H2O)}4+ hexanuclear units. The hexanuclear cation is made up of two symmetry-related oxamato-bridged trinuclear units connected through the central carbon atom C(6) of the L8- ligand. Variable-temperature magnetic susceptibility measurements (1.8-300 K) have been performed for these series of complexes including the dinuclear precursors of formula Na4[Cu2L] · 10.5 H2O [Cu2-Na], (NMe4)4[Cu2L] · 4 H2O [Cu2-NMe4] and (PPh4)4[Cu2L] · 6 H2O [Cu2-PPh4]. The magnetic data have been interpreted. Evidence of a weak intramolecular ferromagnetic interaction between the two CuII ions in [Cu2L]4- has been observed. For the hexanuclear species, the interaction through the oxamato bridge was found to be equal to -6790, -2650, and -1643 yJ (-342, -133, and -82 cm-1) for [Cu6-tmen], [Cu6-pmdien], and [Cu2Ni4-cyclam], respectively. In these complexes, the weak intramolecular ferromagnetic coupling between the two CuII ions within the dinuclear synthon was masked by intermolecular interactions or local anisotropy.
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  • 44
    ISSN: 1434-1948
    Keywords: Boron ; Transition metals ; Sandwich complexes ; Boratabenzene ; Pinene ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Complexes of pinene-fused boratabenzene ligands [(1R,9R)6,10,10-trimethyl-4-boratatricyclo[7.1.1.02,7]undeca-2,4,6trienes] C13H17BX (with a: X = NMe2; b: X = OMe; c: X = Me) are described. The lithium salt Li(C13H17BNMe2) [Li(1a)] reacts with [Cp*Fe(NCMe)3]PF6 and with Mn(CO)3Br(py)2 to give diastereomeric mixtures FeCp*(C13H17BNMe2) (4a) and Mn(CO)3(C13H17BNMe2) (7). The mixture 4a undergoes solvolysis in methanol to produce methoxy compounds 4b, which in turn react with LiMe in Et2O to give methyl derivatives 4c. The lithium salts Li(C13H17BX) [Li(1a-c)] react with ZrCl4 in toluene or Et2O to give exo,exo-ZrCl2(C13H17BX)2 complexes (8a-c). The dimethyl derivative exo,exo-ZrMe2(C13H17BNMe2)2 (9) can also be prepared from 8a/LiMe in Et2O. NOE difference spectra have been analyzed to determine the configurations of the diastereomers and to establish a chemical shift criterion for assessing the configuration of the metal-ligand coordination. An independent confirmation of the product stereochemistries has been obtained by single-crystal X-ray structure determinations of exo-4a and 8a.
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  • 45
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 2000 (2000), S. 993-1000 
    ISSN: 1434-1948
    Keywords: Ruthenium ; Dihydrogen complexes ; Dihydrogen bonding ; Hydride protonation ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: in CD2Cl2 yielded, in a straightforward manner, the dicationic η2-dihydrogen complex [tpmRu(PPh3)2(H2)](BF4)2, which, as expected, is more acidic than its monocationic Tp [Tp = hydrotris(pyrazolyl)borate] analog [TpRu(PPh3)2(H2)]BF4 (pKa: 2.8 vs. 7.6). The complex [tpmRu(PPh3)2(H2)](BF4)2 is unstable towards H2 loss at ambient temperature. However, acidification of [tpmRu(PPh3)2H]BF4 with excess aqueous HBF4 or aqueous triflic acid in [D8]THF gave very interesting results. Variable-temperature 1H- and 31P-NMR studies revealed that the aqueous acid did not fully protonate the metal hydride to form the dihydrogen complex, but a hydrogen-bonded species was obtained. The feature of this species is that the strength of its Ru-H···H-(H2O)m interaction decreases with temperature; this phenomenon is unusual because other complexes containing dihydrogen bonds show enhanced M-H···H-X interaction as the temperature is lowered. Decrease of the dihydrogen-bond strength with temperature in the present case can be attributed to the decline of acidity that results from the formation of larger H+(H2O)n (n 〉 m) clusters at lower temperatures; steric hindrance of these large clusters also contribute to the weakening of the dihydrogen bonding interactions. At higher temperatures, facile H/H exchange occurs in Ru-H···H-(H2O)m via the intermediacy of a “hydrogen-bonded dihydrogen complex” Ru-(H2)···(H2O)m. To investigate the effect of the H+(H2O)m cluster size on the strength of the dihydrogen bonding in [tpmRu(PPh3)2H]+, molecular orbital calculations at the B3LYP level have been performed on model systems, [tpmRu(PH3)2H]+ + H+(H2O) and [tpmRu(PH3)2H]+ + H+(H2O)2. The results provide further support to the notion that the formation of larger H+(H2O)n clusters weakens the Ru-H····H(H2O)n dihydrogen bonding interaction.
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  • 46
    ISSN: 1434-1948
    Keywords: Imaging agents ; Lanthanides ; NMR spectroscopy ; DNA cleavage ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The hydration state of a series of [Ln(DO2A)(H2O)n]+ complexes in aqueous solution at pH = 6.4-7.0 was studied by measuring the lanthanide-induced 17O shifts (LIS) of water [Ln includes elements from Ce to Yb; DO2A = 1,7-bis(carboxymethyl)-1,4,7,10-tetraazacyclododecane]. Their contact contribution, obtained from Reilley plots, indicated a decrease in the inner-sphere water coordination number of the [Ln(DO2A)(H2O)n]+ complexes from n = 3 (Ce-Eu), to n = 2 (Tb-Yb). A temperature-dependent UV/Vis absorption study of the 578-582 nm 7F0 → 5D0 transition band of [Eu(DO2A)(H2O)n]+ in aqueous solution showed that this complex is present in an equilibrium between eight- and nine-coordinate species with n = 2 and n = 3, respectively. The hydration equilibrium parameters (2 ↔ 3), K2-3298 = 4.0 ± 0.2, ΔH2-30 = -12.1 ± 1 kJ mol-1 and ΔS2-30 = -28.9 ± 3 J mol-1 K-1,correspond to an average hydration number of 2.65-2.85 in the temperature range 273-363 K. A variable temperature, multiple field 17O NMR study combined with direct EPR measurements of the transverse electronic relaxation rates has been used to obtain the parameters characterizing water exchange, rotation and electronic relaxation, all influencing the proton relaxivity of [Gd(DO2A)(H2O)2-3]+. The small increase in the water exchange rate of [Gd(DO2A)(H2O)2-3]+ (kex298 = (10 ± 5) × 106s-1) relative to that of[Gd(DOTA)(H2O)]- (4.8 × 106 s-1) is a consequence of an unfavorable interplay of charge and hydration equilibria. The value of τR298 = 40 ± 1 ps is short, and the electronic relaxation rate (1/T2e ≍ 1.2 × 1010 s-1) is fast relative to [Gd(DOTA)(H2O)]- (1.3-2.4 × 109 s-1 for B = 0.34 T). These parameters negate to some extent the expected increase in proton relaxivity of the [Gd(DO2A)(H2O)2-3]+ complex.Supporting information for this article is available on the WWW under -//_/_http://www.wiley-vch.de/contents/jc_2005/2000/99338_s.pdf or from the author.
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  • 47
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 2000 (2000), S. 29-32 
    ISSN: 1434-1948
    Keywords: Arene complexes ; Ruthenium ; Benzimidazole ; Benzothiazole ; Benzoxazole ; Cycloisomerisation ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Fourteen ruthenium(II) complexes of the type [RuCl2(η6-arene)L], (arene = 1,4-MeC6H4Pri or C6Me6; L = benzimidazole derivative in which the NH group is substituted by N-alkyl or isoelectronic O or S atoms) have been prepared by cleavage of [RuCl2(η6-arene)]2 with the N-heterocycle L. Their spectroscopic and electrochemical properties are described. The effect of the nature of the benzazole (L) on the catalytic activity of these complexes for the intramolecular cyclization of (Z)-3-methylpent-2-en-4-yn-1-ol into 2,3-dimethylfuran has also been studied; the benzimidazole complexes were found to be the most active.
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  • 48
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 2000 (2000), S. 59-63 
    ISSN: 1434-1948
    Keywords: Phosphorane imine ; Sulfur ligands ; Nickel ; Palladium ; Platinum ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Reaction of the trinuclear [M(′S3′)]3 complexes {M = Ni (4), Pd (5), Pt (6); ′S3′2- = bis(2-mercaptophenyl)sulfide (2-)} with HNPnPr3 yielded the new phosphorane imine complexes [M(NHPnPr3)(′S3′)] {M = Ni (1), Pd (2), Pt (3)}. The complexes 1-3 have been completely characterized and are rare examples of mononuclear phosphorane imine complexes with late transition metals. Spectroscopic and structural results indicate that the HNPnPr3 ligands favor the ylidic structure when binding to [M(′S3′)] fragments. X-ray structure determinations showed that [M(NHPnPr3)(′S3′)] complexes associate through N-H···S(thiolate) bridges to give centrosymmetric dimers.
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  • 49
    ISSN: 1434-1948
    Keywords: Cages ; Synthesis ; Lithium ; Crystal structures ; Chromophores ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Three new macrocyclic cages 1, 2 and 3, able to selectively encapsulate the lithium ion, were studied. The synthesis and characterization of 2 and 3 are reported. The basicity behaviour of the three cages was investigated by spectrophotometry and by 1H and 13C NMR spectroscopy. The protonation constants were determined by potentiometric methods in aqueous solution (I = 0.15 mol dm-3 NMe4Cl, T = 298 ± 0.1 K) and were found to be logK1 = 11.67(5), 10.77(7), 11.17(7); logK2 = 7.76(5), 5.7(1), 5.6(1); logK3 = 1.3(1), 2.4(1), 1.9(1) for 1, 2, and 3, respectively. The lithium equilibrium complex formation Li+ + L = LiLH-1 + H+ was monitored by 13C and 7Li NMR spectroscopy, as well as by spectrophotometric and potentiometric techniques; log values of -9.1(1) and -8.0(1) were found for 1 and 3, respectively. For 2, precipitation of the lithium complex occurs. UV/Vis studies in aqueous solution show a significant shift towards high energy of the λmax in the lithium complex, indicating the potential for application of these ligands in colourimetric analysis. The crystal structure of 1 was examined by single crystal X-ray diffraction. Data collection was performed on two samples, namely 1a and 1b, obtained from two different crystallization procedures. Crystals of 1a are monoclinic, space group P21/n, while 1b crystallized in an orthorhombic space group Pc21b. The cell parameters are a = 12.423(3), b = 14.378(9), c = 28.436(7) Å, β = 93.74(2)° for 1a, and a = 10.674(4), b = 14.408(2), c= 17.034(2) Å for 1b. Molecular simulations were carried out on both conformational isomers 1a and 1b, with results indicating that the two isomers have essentially the same flexibility.
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  • 50
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 2000 (2000), S. 75-82 
    ISSN: 1434-1948
    Keywords: Macrocyclic ligands ; Conformational equilibria ; EXSY spectroscopy ; Lanthanide-induced shifts ; Solution structure ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The structure and the conformational equilibria in aqueous and methanolic solutions of YbDOTMA (DOTMA = (1R,4R,7R,10R)-α,α′,α′′,α′′′′-tetramethyl-1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid) are investigated and the dynamics studied by means of NMR methods. The presence of two isomeric forms in slow exchange is confirmed and quantitatively characterized by EXSY. The exchange peaks are assigned to the inversion of the conformation of the macrocycle ring. No evidence is obtained of a reorientation of the methyl acetate substituents. The protons switch between positions with the same geometrical factors, i.e. positions that would have the same pseudocontact shifts were it not for the different magnetic susceptibility anisotropies of the two species; steady-state NOE spectra on the major form allow unequivocal assignment of the conformations of the two isomers.Supporting information for this article is available on the WWW under -//_/_http://www.wiley-vch.de/contents/jc_2005/2000/99141_s.pdf or from the author.
    Additional Material: 5 Ill.
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  • 51
    ISSN: 1434-1948
    Keywords: Ruthenium ; S ligands ; Hydrazine ; Diazene ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In the search for ruthenium complexes with sulfur-dominated coordination spheres that bind, activate, or stabilize nitrogenase relevant molecules, complexes containing the new and robust tetradentate ligand ‘tpS4’-H2 were synthesized. Treatment of [RuCl2(PPh3)3] with ‘tpS4’2- gives [Ru(PPh3)2(‘tpS4’)] (1), which contains two labile PPh3 ligands. The reaction of 1 with PEt3 or DMSO led to substitution of both PPh3 ligands, yielding [Ru(PEt3)2(‘tpS4’)] (2) and [Ru(DMSO)2(‘tpS4’)] (3), respectively. When treated with nitrogenous ligands, complex 1 lost only one PPh3 ligand to yield [Ru(L)(PPh3)(‘tpS4’)] complexes where L = py (7), NH3 (8), N2H4 (9), NH2NHMe (10), and CH3CN (12), all of which are labile. The labile acetonitrile complex [Ru(CH3CN)(PPh3)(‘tpS4’)] (12) proved to be particularly suited as a precursor for the syntheses of other [Ru(L)(PPh3)(‘tpS4’)] complexes. The 18 and 19 valence electron NO complexes [Ru(NO)(PPh3)(‘tpS4’)]BF4 (13) and [Ru(NO)(PPh3)(‘tpS4’)] (14), (NEt4)[Ru(N3)(PPh3)(‘tpS4’)] (15), [Ru(I)(PPh3)(‘tpS4’)] (16), and [Ru(N3)(PPh3)(‘tpS4’)] (17) were obtained starting from complex 12. The labile mononuclear hydrazine complex [Ru(N2H4)(PPh3)(‘tpS4’)] (9) gave the dinuclear complex [μ-N2H4{Ru(PPh3)(‘tpS4’)}2] (18) by dissociation of hydrazine. The dinuclear diazene complex [μ-N2H2{Ru(PPh3)(‘tpS4’)}2] (19) was obtained by oxidation of 9 and more readily from [Ru(CH3CN)(PPh3)(‘tpS4’)] (12) and N2H2, which was generated in situ from K2N2(CO2)2 and acetic acid. The molecular structures of 7, 13, 16, 18, and 19 were determined by X-ray structure analyses. The complexes 18 and 19 represent the first complexes containing the hydrazine/diazene couple, which enables us to compare both the bonding features and the formation of N-H···S bridges when hydrazine and diazene bind to transition metal sulfur sites.
    Additional Material: 5 Ill.
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  • 52
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 2000 (2000), S. 1097-1105 
    ISSN: 1434-1948
    Keywords: Fluorinated porphyrins ; Electrochemistry ; Manganese ; Oxidation catalysis ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The synthesis and characterization of manganese complexes of β-octafluoro-meso-tetraarylporphyrins are reported. The presence of the electron-withdrawing β-fluorine atoms induces a very large shift of the redox potential for the oxidation of the manganese(II) derivatives. With the meso-aryl group bearing two ortho-chlorine atoms (2,6-dichlorophenyl) or five fluorine atoms (pentafluorophenyl), metal complexation leads to the isolation of pure manganese(II) compounds. The stability and catalytic activity of these new derivatives have been studied using hydrogen peroxide and iodosylbenzene as oxidants, and standard substrates for epoxidation and hydroxylation reactions. The results are compared to those obtained with the β-hydrogenated analogs under the same conditions. In the case of hydrogen peroxide, the high level of porphyrin degradation prevents efficient catalytic activity. With iodosylbenzene as oxidant, both stability and epoxidation are similar to those of the β-hydrogenated porphyrins, however, a substantial improvement in the efficiency of the hydroxylation of cyclohexane is observed with up to 33 turnovers with (perfluorotetraphenylporphyrin)manganese(II).
    Additional Material: 8 Tab.
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  • 53
    ISSN: 1434-1948
    Keywords: Metallomesogens ; Liquid crystals ; Silver ; N ligands ; Amines ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The liquid crystalline properties of a series of ionic silver complexes [Ag(NH2n-CnH2n+1)2]X (X = NO3, n = 6, 8, 10, 12, 14; X = BF4, n = 8, 10, 12, 14), derived from silver nitrate or tetrafluoroborate and aliphatic amines, have been investigated by optical microscopy, DSC, and X-ray diffraction. The materials exhibit a birefringent fluid phase identified as a smectic A mesophase by optical microscopy and X-ray diffraction. Some of the complexes are liquid crystalline at temperatures close to room temperature. The X-ray results are consistent with the existence in the mesophase of a bilayer organization. The silver cations adopt a U-shape, which allows for the adoption of this bilayer arrangement, with alternating ionic and apolar regions and a short-range square-planar array inside the cationic sublayers. The thermodynamic parameters suggest that the melting transition clearly involves only disorder (melting) of the chains, whereas the clearing transition implies breaking the anion-cation arrangement.
    Additional Material: 6 Ill.
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  • 54
    ISSN: 1434-1948
    Keywords: Manganese ; Radicals ; Cyclic dimer complexes ; Exchange coupling parameters ; Spin states ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Temperature-dependent paramagnetic susceptibility data for two cyclic dimer complexes of bis(hexafluoroacetylacetonato)manganese(II) with 5-tert-butyl-1,3-phenylenebis(N-tert-butylaminoxyl) and 4-(N-tert-butyl-N-oxyamino)pyridine have been analyzed to obtain two sets of two intramolecular exchange coupling parameters J1 and J2. A previous model, based on one of these interactions being much weaker than the other, could not be explicitly correlated to these actual exchange-coupling parameters. However, the energy levels of the low-lying spin states were found to be reproduced reasonably well by the approximate method.
    Additional Material: 7 Ill.
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  • 55
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 2000 (2000), S. 331-340 
    ISSN: 1434-1948
    Keywords: Indenyl complexes ; Cyclopentadienyl complexes ; Molybdenocene ; Ring slippage ; Molybdenum ; DFT calculations ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Reduction of [IndCpMo(L)Br]Br (L = 1a, CO; 2, NCMe) with Cp2Co in the presence of two equivalents of the ligand L′ gives the ring-slipped neutral complexes [(η3-Ind)CpMoL′2] (L′ = 5, CO; 6, 1/2 dppe; 7, PMe3; 8, P(OMe)3; 9, CNtBu) in good yield. Products 7, 8, and 9, but not [IndCpMoL′], are also formed in the presence of only 1 equivalent of L′ in modest yields. In the case of the reduction of [IndCpMo(L)Br]Br [L = 2, NCMe; 3a, CNtBu; 4, P(OMe)3] mixtures of the complexes, [(η3-Ind)CpMoL2] (8, 9) and [(η5-Ind)CpMoL] [L = 11, P(OMe)3; 12, CNtBu] were obtained. The only product of formal type [(η5-Ind)CpMoL] that could be prepared by these methods was the alkyne complex [(η5-Ind)CpMo(η2-PhC≡CPh)] (10). These results contrast with the well-known reductions of similar bis-cyclopentadienyl cations [Cp2Mo(L)Br]+, which produce [Cp2MoL] complexes under the same conditions. The reduction of the dications [Cp2MoL2][BF4]2 [L = CO; P(OMe)3] with Cp2Co is now reported to afford the neutral complexes [CpMo(η3-C5H5)(CO)2] (13) and [Cp2Mo(P(OMe)3)] (14), respectively, showing that the stability of the ring-slipped complexes is dependent on the other ligands. From DFT and EHMO calculations used to probe the bonding and the energetics of these ring slippage processes it is concluded that weak π acceptor ligands favour η5-Ind → η3-Ind slippage and disfavour η5-Cp → η3-Cp slippage at the CpMoL2 fragment. Redox-induced ring slippages involve very similar energies for both indenyl and cyclopentadienyl complexes and should be able to produce more examples of the otherwise rare η3-Cp coordination mode.
    Additional Material: 1 Ill.
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  • 56
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 2000 (2000), S. 369-374 
    ISSN: 1434-1948
    Keywords: Phosphanylcarbenes ; Substituent effects ; Quantum chemical calculations ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A phosphanyl group exerts much less π-conjugation properties than an amino group. On this basis, corresponding carbene structures exhibit much smaller singlet-triplet energy separations. Of the various structures investigated quantum-chemically the largest singlet-triplet energy separations are predicted for cyclic diphosphanylcarbenes, in which the two functional groups are incorporated into a ring system and the phosphorus atoms are substituted by phosphoraniminato groups. Then the singlet-triplet energy separations become essentially larger than for the Bertrand-type (push-pull) carbenes.
    Additional Material: 1 Ill.
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  • 57
    ISSN: 1434-1948
    Keywords: Radicals ; Carbenium ions ; Clusters ; Cobalt ; Molybdenum ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Complexed α-CF3 propargyl alcohols of the general formula [(M2L6){μ-η2,η2-RC≡CCH(CF3)(OH)}] were prepared with M2L6 = Co2(CO)6, R = CH3(CH2)4- (1), R = C6H5- (2); M2L6 = Co2(CO)5P(C6H5)3, R = CH3(CH2)4- (3a,b), R = C6H5- (4a,b); M2L6 = Co2(CO)4dppm, R = C6H5- (5); M2L6 = Co(CO)3MoCp(CO)2, R = CH3(CH2)4- (6a,b), R = C6H5- (7a,b). An X-ray molecular structure of the propargyl-alcohol complex [{Co2(CO)4dppm}{μ-η2,η2-C6H5C≡CCH(CF3)(OH)}] (5) was also determined. The related carbenium ions [(M2L6){μ-η2,η3-RC≡CCH(CF3)}][BF4] (8-12) were obtained from the parent propargyl alcohol complexes by direct protonation with HBF4· Et2O in diethyl ether. These carbenium ions were reduced further by Zn in CH2Cl2 to give the alkyne adducts [(M2L6){μ-η2,η2-RC≡CCH2(CF3)}] (13-17), as confirmed by the X-ray molecular structure of [(Co2(CO)4dppm){μ-η2,η2-C6H5C≡CCH2(CF3)}] (17). Treatment of the carbenium ion complex [{Co(CO)3MoCp(CO)2}{μ-η2,η3-CH3(CH2)4C≡CCH(CF3)}][BF4] (8) with NaSMe unexpectedly afforded the reduced alkyne adduct [{Co(CO)3MoCp(CO)2}{μ-η2,η2-CH3(CH2)4C≡CCH2(CF3)}] (13), along with the alkyne-thioether diastereomers {Co(CO)3MoCp(CO)2}{μ-η2,η2-CH3(CH2)4C≡CCH(CF3)[(SMe)}] (18a,b). Presumably, all the reduction reactions proceed primarily by the formation of the transient radical species, which are subsequently transformed into the reduced alkyne complexes by hydrogen abstraction from the solvent medium. Interestingly, in the case of the complexed alcohols [{Co2(CO)5P(C6H5)3}{μ-η2,η2-RC≡CCH(CF3)(OH)}] (3a,b) and (4a,b), the reduction process occurs in acidic medium in THF/CH2Cl2. An extensive study of the electronic and steric factors that influence the stability and reactivity of the carbenium ions were performed, which allowed us to explain the behavior of the related radical species in solution during the reduction process.
    Additional Material: 4 Ill.
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  • 58
    ISSN: 1434-1948
    Keywords: Pyridyl carboxamides ; Carbonyl complexes ; Rhenium ; Metallotropic shifts ; NMR spectroscopy ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology