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  • 101
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 1933-1937 
    ISSN: 1434-193X
    Keywords: Fluoroalkenes ; Substitution ; Rearrangements ; γ-Unsaturated acids ; Lactones ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---A one-pot synthesis of α-bromo β-substituted γ-unsaturated acids via a diastereoselective Claisen rearrangement of allyl bromofluorovinyl ethers is described.
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  • 102
    ISSN: 1434-193X
    Keywords: Lanthanides ; Polydentate ligands ; Luminescence spectroscopy ; Near-infrared luminescence ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---A series of m-terphenyl-based ligands bearing three coordinating oxyacetate and two amido or two sulfonamido groups, (1a-b)H3 and (2)H3, respectively, have been synthesized and characterized. The structures of the corresponding neutral complexes have been studied using 1H-NMR spectroscopy and luminescence experiments. The photophysical properties of the (1a-b)Eu, (2)Eu, (1a)Tb, and (2)Tb complexes have been studied to determine the structure of the first coordination sphere in methanol. The first coordination sphere consists of eight donor atoms provided by the ligand (three chelating oxyacetate groups and two amide or sulfonamide oxygens), and one methanol molecule. The (1a)Dy and (1a)Sm complexes exhibited sensitized luminescence in the visible spectral region, but the luminescence intensity was very sensitive to quenching by C-H groups. The near-infrared emitting (1a)Ln and (2)Ln complexes exhibited sensitized luminescence at wavelengths (at 880, 1060, and 1330 nm for Nd3+, at 980 nm for Yb3+, and at 1550 nm for Er3+) of interest for applications in optical telecommunication devices. The luminescence lifetimes of these complexes in DMSO and [D6]DMSO are in the range of microseconds. The luminescent state of the NIR emitting lanthanide ions is very efficiently quenched by high frequency oscillators (such as C-H groups) in the solvent and the ligand.Supporting information for this article is available on the WWW under //http://www.wiley-vch.de/contents/jc_2046/2000/99457_s.pdf or from the author.
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  • 103
    ISSN: 1434-193X
    Keywords: Sulfur ; Halogens ; Hydrohalogenation ; Lewis acids ; Sulfoxides ; Sulfoxides ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The hydrohalogenation reaction of 1,2-allenic sulfoxides 1 afforded 2-haloallyl sulfoxides 2 with yields ranging from 56 to 89%. The influence of the ratio of AlCl3 and H2O on this reaction is discussed and the optimized ratio of allenic sulfoxides, AlCl3 and H2O is 1:0.55:1. For the hydroiodination reaction, a combination of excess NaI, AlCl3, and H2O was used. The reaction is probably mediated by the species formed from the reaction of AlX3 with H2O. Because of the steric hindrance of the substrates, the hydrohalogenation of 1-methyl-1-(methylsulfinyl)-1,2-propadiene (1e), (1-methyl-1,2-propadienylsulfinyl)benzene (1f), and (3-methyl-1,2-butadienylsulfinyl)benzene (1g) did not proceed under the same reaction conditions.
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  • 104
    ISSN: 1434-193X
    Keywords: Carbohydrates ; Glycosides ; Conformation analysis ; Molecular modeling ; Carbohydrates ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---The conformational behaviours of several nonhydrolizable lactose analogues, namely methyl α-thiolactoside (1), methyl β-carbalactoside (2) and methyl β-carbaiminolactoside (3) have been studied using a combination of NMR spectroscopy (J and NOE data) and molecular mechanics calculations. Analogies and differences with the natural compounds have been found.Supporting information for this article is available on the WWW under //http://www.wiley-vch.de/contents/jc_2046/2000/99592_s.pdf or from the author.
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  • 105
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 1959-1964 
    ISSN: 1434-193X
    Keywords: C-C coupling ; Palladium ; Silanes ; Catalysts ; Allylsilanes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---One of the main problems of the Heck reaction using acyclic substrates which lead to Pd intermediates with β- and β′-hydrogens is the lack of selectivity in the formation of the double bond as the last step of the catalytic cycle. The use of allylsilanes as the alkene moiety permits control of the elimination step. Thus, the Pd0-catalysed reaction of 1a-c and 2 leads exclusively to the corresponding bicyclic compounds 11a-c. In contrast, reaction of 7 yields a mixture of 12a, (E)-12b and (Z)-12b.
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  • 106
    ISSN: 1434-193X
    Keywords: Ion-pairing ; 23Na NMR ; Cation-anion interactions ; Ion association in 2-propanol ; Sodium thiolates in 2-propanol ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---Cation-anion interactions in 2-propanol solutions of sodium salts NaY (Y = MeS, iPrS, tBuS, iPrO, SCN, ClO4, Ph4B) have been studied by 23Na-NMR spectroscopy. The analysis involved measurements of chemical shift and T1 as a function of salt concentration in both the absence and presence of the Na+-complexing agent 18-crown-6. The results indicate that the interactions of Na+ with alkoxides and thiol anions are very different from those with charge-delocalized anions (SCN-, ClO4-, Ph4B-), and that the degree of association in NaSR salts is greater for R = tBu than for R = Me.
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  • 107
    ISSN: 1434-193X
    Keywords: Cup-shaped PAHs ; Host-guest compounds ; Host-guest chemistry ; Cyclizations ; Semiempirical calculations ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---Cyclotrimerisation of benzo-polycyclic bromostannylalkenes 8a-d with Cu(NO3)2·3H2O in THF affords benzotri(benzonorbornadienes) 3a-d as a mixture of the syn and anti isomers. The ratio of syn to anti is close to the 1:3 statistical value in most cases (i.e. in cyclotrimers 3a,b,d), but highly in favour of the anti isomer in 3c, where steric hindrance by the methoxy groups plays an important role in the stereochemistry of the cyclotrimerisation. The substrates for the cyclotrimerisation, i.e. the bromostannyl alkenes 8a-d, were prepared from bromoalkenes 7a-d by treatment with base (LDA) and quenching with trimethyltin chloride. In turn, bromoalkenes 7a-d were prepared from alkenes 5a-d by radical bromination-elimination. The reaction conditions used were designed to minimise Wagner-Meerwein rearrangements that would lead to unwanted bromo isomers. The cup-shaped syn cyclotrimers 3a-d exhibit high electron density within the cavity as determined by AM1 semiempirical calculations of their electrostatic potential surfaces and are valuable substrates for supramolecular chemistry. As an example, it is shown that fullerene C60 is drawn into solution in acetonitrile by complexation with both the syn and anti trimer of benzonorbornadiene 3a.
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  • 108
    ISSN: 1434-193X
    Keywords: Benzodiazepines ; Heterocycles ; Azeto[1,2-a]-1,5-benzodiazepines ; Cyclizations ; Cycloadditions ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---The reaction of o-phenylenediamine (4) with one, two or three equivalents of p-substituted 3-dimethylaminopropiophenone hydrochlorides 5a-e was studied. 4-Aryl-2,3-dihydro-1H-1,5-benzodiazepine derivatives 6a-e were obtained in good yields, along with the 1:2-adducts 7c-e and the unexpected 1:3-adducts rac-8c-e. The type of adduct formed is determined by the molar ratio of the reactants 4 and 5 and by the nature of the substituent in the para position of the propiophenone 5.
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  • 109
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 1983-1986 
    ISSN: 1434-193X
    Keywords: Radicals ; Dioxygen trapping ; Radical reactions ; Singlet-triplet splitting ; Thermochemistry ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---From the oxygen and temperature dependence of the trapping rate of 7,7-difluorobenzocyclopropene (1) in the range 180-240 °C, the energy profile of the equilibrium 1 →←2 has been obtained. From the heat of hydrogenation of 1, its heat of formation is derived (ΔHof = +3.8 kcal·mol-1), as a result of which the heat of formation of the singlet state of the diradical 2 is estimated as 25.7 kcal·mol-1. Whereas the trapping experiments demonstrate unambiguously a triplet ground state for 2, only a lower limit for the singlet-triplet splitting (〉 6 kcal·mol-1) can be given.
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  • 110
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 1977-1982 
    ISSN: 1434-193X
    Keywords: Biaryls ; Homogeneous catalysis ; Iron ; Addition reactions ; Quinones ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---Acceptor-substituted cycloalkenones 1 undergo an iron(III)-catalyzed vinylogous Michael reaction - a sequence of enone-dienol tautomerism, [4+2]-cycloaddition, and retro-aldol reaction - with quinone derivatives 3. A variety of products is obtained ranging from meta-terphenyl precursors 5 to dihydronaphthobenzofurans 7. Reaction of 1,2-naphthoquinone (3e) with vinylogous donors 1 yields cross-coupled products 12, which can be further converted into highly functionalized biaryl compounds 13 and 14.
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  • 111
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 1993-1999 
    ISSN: 1434-193X
    Keywords: Ketones ; Tautomerism ; Double bond migration ; Peptides ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---Treatment of 3-alkylidene or 3-benzylidene-2,5-piperazinediones 6 with catalytic amounts of acid gives rise to the formation of isomers 7 by migration of the C=C bond into the alkyl substituent at position 6, or results in mixtures of racemic 7 and E isomers 8. The existence of tautomeric equilibria is discussed.
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  • 112
    ISSN: 1434-193X
    Keywords: Nucleotides ; Thiophosphates ; Hydrolyses ; Reaction mechanisms ; Kinetics ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Hydrolysis of the cis-methyl ester of 3′-deoxy-3′-thiothymidine 3′-S,5′-O-cyclic(phosphorothiolate) (1a) has been followed by HPLC and MS. At pH 〈 2 hydrolysis of the thiophosphate triester moiety is acid-catalyzed (first order), while between pH = 2 and 5 the reaction is pH-independent and at pH 〉 5 first order in hydroxide ion. The uncatalyzed and acid-catalyzed reactions yield two thiophosphate diesters, the 3′-S,5′-O-cyclic phosphorothiolate 2 and 3′-S-phosphorothiolate methyl ester 3, in a 9:1 and 1:3 molar ratio, respectively. The hydroxide ion catalyzed reaction gives the endocyclic P-O and P-S bond-cleavage products (3 and 4, respectively) in a 1:2 molar ratio. The pH-independent reaction is suggested to take place by attack of a water molecule on the carbon atom and concomitant C-O bond rupture, whereas the alkaline and acidic reactions involve attack of the nucleophile on the phosphorus atom and formation of a pseudorotating thiophosphorane intermediate. Under acidic conditions, cleavage of the N-glycosidic linkage competes with the phosphoester hydrolysis, corresponding to 20% of the hydrolysis products at pH 〈 1.
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  • 113
    ISSN: 1434-193X
    Keywords: Addition reactions ; Octahydroacridine ; Polypyridines ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---A new octahydroacridine with a tert-butoxypropyl group in the 9-position was prepared and was used in the synthesis of new soluble annelated polypyridines. Quinquepyridine with 11 adjacent rings was prepared in 17-25% yield by condensation of an α-methylene ketone and an enolisable ketone in the presence of ammonium acetate under basic conditions.
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  • 114
    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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  • 115
    ISSN: 1434-1948
    Keywords: Arsenic ; UV photoelectron spectroscopy ; Ab initio calculations ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In this paper, we report the gas-phase characterization of two differently substituted amino(iminoarsanes), TmpAs=NSiMe3 and (SiMe2tBu)2NAs=N(SiMe2tBu), by coupling flash vacuum thermolysis (FVT) with UV photoelectron spectroscopy (PES). Quantum chemical calculations, using the DFT method (B3LYP) with the basis set 6-311G(d,p), have also been carried out on the R1As=NR2 unit with R1 = H, NH2, N(CH3)2, N(SiH3)2 and R2 = H, SiH3, in order to study the effect of substitution on the electronic properties and the thermodynamic stability of the As=N skeleton. Similarities with phosphorus analogues are also discussed.
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  • 116
    ISSN: 1434-1948
    Keywords: Clusters ; Steroids ; Protonation ; Carbocations ; Immunoassay ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The stabilization of carbenium ions by an adjacent organotransition metal moiety has been evaluated using the classical Deno's method as well as a new procedure based on DCI-MS spectrometry. The ability of transition metal clusters to enhance the stability of a proximate carbocationic center in 17α-alkynylestradiol-[OM] derivatives {[OM] = Co2(CO)6; Co2(CO)4(dppm); Mo2Cp2(CO)4; M3(CO)10, M = Ru, Os; HRu3(CO)9} has been related to their capacity to inactivate the estrogen receptor (affinity marker properties).
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  • 117
    ISSN: 1434-1948
    Keywords: Ion-molecule reactions ; Mass spectrometry ; Allene ; Germanium ; Silicon ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The gas-phase ion chemistry of germane/allene and silane/allene mixtures has been studied, with the aim of obtaining information on the experimental conditions leading to the formation of clusters of increasing size containing Ge or Si bonded to carbon atoms. Mechanisms of ion/molecule reactions have been elucidated by ion-trap mass spectrometry using single and multiple isolation steps. Rate constants for the most important reactions have been determined experimentally and compared with collisional rate constants. The germane/allene mixtures display a low reactivity and the most abundant germanium and carbon containing ion is GeCH3+. However, chain propagation proceeds after the first nucleation step, even if rather slowly, with the formation of large clusters such as Ge4C3H3+ at low abundance. In contrast, the silane/allene mixtures are very reactive and many different processes are observed, with the formation of several silicon and carbon containing ions with appreciable efficiency. Chain propagation proceeds mainly through reactions of silicon-containing ions with allene molecules and the subsequent formation of large clusters such as Si3C3H5+ and Si4C3H7+.
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  • 118
    ISSN: 1434-1948
    Keywords: Tin ; Nucleotides ; NMR spectrometry ; Mass spectroscopy ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The interactions between diethyltin dichloride and 5′-CMP, 5′-dCMP, and 5′-UMP in aqueous solution were investigated by multinuclear 1D and 2D NMR techniques including 119Sn, 15N and 31P nuclei. These studies were combined with electrospray mass spectrometry, infrared spectroscopy, solid state 13C, 31P and 117Sn CP-MAS NMR, and elemental analysis. As demonstrated by 31P-1H HOESY spectroscopy, the diethyltin moiety interacts with the phosphate group of the pyrimidic mononucleotides in the pH range 0.5-3.5. Compound 8 (X = Cl), the solid isolated in this pH range from 5′-CMP, contains two tin atoms bridged by one oxygen and one chlorine atom, each tin atom being linked to the phosphate group of a nucleotide moiety. For 5′-UMP the solid isolated (12) has a dimeric structure with two different tin atoms; it can be formed by dimerization of compound 11 with the elimination of two water molecules. As demonstrated by 1H-119Sn HMQC correlation NMR data and the 2J(119Sn-O-117Sn) coupling constant of 156 Hz, the diethyltin moiety reacts with the O(2′) and O(3′) oxygen atoms of the nucleotides to form a dimeric diethyldioxastannolane at pH 〉 9.0. Between pH 5.0 and 9.0, no evidence for any interaction between the diethyltin moiety and the nucleotides was found.
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  • 119
    ISSN: 1434-1948
    Keywords: Coordination chemistry ; Gallium(III) ; Dynamik 19F NMR ; EXSY ; Kinetics of ligand exchange ; Bailar and Rây-Dutt mechanisms ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The rates of intramolecular rearrangement of the meridional isomer of the metal tris-chelate complex [Ga(fox)3, fox = 5-fluoro-8-hydroxyquinoline] in DMF solution were measured using 1D NMR line shape analysis and 2D EXSY spectra. The rates of exchange kab, kbc and kac between the three non-equivalent ligands a, b and c were determined. The values of the activation parameters were obtained. ΔH
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  • 120
    ISSN: 1434-1948
    Keywords: Pyrrolizinato complexes ; Tetracyanoethylene ; Phthalocyanines ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Complexes of NiII, CuII, ZnII, and CoIII containing the 1,2,6,7-tetracyano-3,5-dihydro-3,5-diiminopyrrolizinide (L) and the 2,4-tert-butylacetylacetonide (DPM) ligands have been synthesized and characterized. The absorption optical spectra of these species and of the corresponding ML2 complexes in coordinating solvents are compared with those of metal-phthalocyanines (MPc) and hydrogen-phthalocyanine (H2Pc), respectively. The comparison shows a close similarity, especially for the nickel-containing species, in the low-energy spectral region where the first π→π* transitions occur (Q band). The Q band position of the pyrrolizinato complexes is much more dependant on the metal than is the case for MPc. For the same metal, the Q band position is also dependant on the M-N bond lengths in the molecular plane. For M = Ni, a reduction of this distance causes a red-shift of the Q band and a decrease of its maximum intensity. These conclusions are based on the X-ray molecular structure of the solvent-free NiL(DPM) complex and its pyridine solvate NiL(DPM)(Pyr)2 · 2 Pyr and on their solvatochromism. A symmetry-based correlation diagram between the frontier orbitals of the pyrrolizinato-complexes and the phthalocyanines is proposed.
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  • 121
    ISSN: 1434-1948
    Keywords: Mesoporous materials ; MCM-41 ; MCM-48 ; Immobilisation ; Solid-state NMR ; Heterogeneous catalysis ; Titanium ; Titanocenes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Titanium(IV)-grafted mesoporous silicas have been prepared by diffusion of an excess of the ansa-bridged titanocene [SiMe2(η5-C5H4)2]TiCl2 into the channels of hexagonal MCM-41 and cubic MCM-48 in dichloromethane or tetrahydrofuran at room temperature. The choice of solvent determines the course of the reaction and hence the activity of the resulting materials as catalysts in the catalytic epoxidation of cyclooctene with tert-butylhydroperoxide. Magic-angle spinning (MAS) NMR (13C, 29Si) spectroscopy was used to characterise the local environment of the surface-bound titanium active sites. When dichloromethane is used, the dominant species anchored to the surface are isolated ansa-bridged titanocene fragments. When THF is used, the [SiMe2(η5-C5H4)2] unit is lost with the concomitant formation of surface-bound TiIV species coordinated by THF molecules. These materials showed the best catalytic performance per Ti atom for the conversion of cyclooctene. All materials were further characterised by means of elemental analysis, powder X-ray diffraction (XRD), N2 adsorption and FTIR spectroscopy.
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  • 122
    ISSN: 1434-1948
    Keywords: Macrocyclic ligands ; Copper ; EPR spectroscopy ; Electronic spectrophotometry ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Copper(II) mononuclear complexes with the polyazamacrocyclic ligands NOTA (1,4,7-triazacyclononane-N,N′,N″triacetate), DOTA (1,4,7,10-tetraazacyclo-dodecane-N,N′,N″,N″′-tetraacetate), NOTP [1,4,7-triazacyclononane-N,N′,N″-tris(methylenephosphonate)] and DOTP [1,4,7,10tetraazacyclododecane-N,N′,N″,N‴-tetrakis(methylenephosphonate)] were characterised in aqueous solution by electronic absorption spectrophotometry and electron paramagnetic resonance (EPR) spectroscopy. While two isomeric species were detected by EPR spectroscopy in frozen samples of the polycarboxylate complexes, only one complex form was found for the poly(methylenephosphonate) systems. The results obtained are in accordance with a six-coordinate pattern for the metal centre, yielding tetragonally distorted complexes in solution, in agreement with previously reported studies on CuII complexes, both in solution and in the solid state.
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  • 123
    ISSN: 1434-1948
    Keywords: Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 124
    ISSN: 1434-1948
    Keywords: Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 125
    ISSN: 1434-1948
    Keywords: Polyoxometalates ; Heteropolyanions ; Dawson-type structures ; Transition metal cations ; Electrochemistry ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The complexes formed by [(1)-2,3-P2Mo2W15O61]10- with vanadium(IV), manganese(II), cobalt(II), nickel(II), copper(II), and zinc(II) were synthesized. They were characterized by elemental analysis, IR, UV/Vis and 31P NMR spectroscopy. Their electrochemical studies are complemented by those of the previously synthesized iron(III)- and Mo(VI)-substituted complexes. Among the main conclusions from the electrochemistry of all these compounds, it can be pointed out that only the iron(III) and the copper(II) ions within the complexes are reducible in the same potential domain as the molybdenum(VI) moieties. In the case of the iron(III) complex, it has been possible to obtain a reversible overall three-electron process on the first wave of the oxometalate by varying the pH of the solution. In contrast, copper can be deposited from the corresponding complex. Substitution of [(1)-2,3-P2Mo2W15O61]10- with vanadium(IV), manganese(II), iron(III), cobalt(II), nickel(II), copper(II), zinc(II) and molybdenum(VI) gives a series of complexes in which the trimetallic moiety constituting one of the ‘‘caps’’ of the polyoxometalate contains cations different from the remaining tungsten skeleton. The electrochemical properties of these complexes are modulated by this particular constitution.
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  • 126
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    ISSN: 1434-1948
    Keywords: Organometallate complexes ; Zwitterionic states ; Transition metals ; Coordination modes ; Electrostatic interactions ; Ion pairs ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Whereas ion-pairing has been long recognized as playing a key role in organometallic chemistry, the zwitterionic feature of organotransition metal complexes has only recently become an influential factor in the design of cationic metal catalysts. The prospective situation of reversed polarity, with metal fragments formally bearing an integral negative charge, may be envisaged. Besides the well-documented zwitterionic complexes derived from phosphonium ylides, other examples of zwitterionic organometallate complexes, formulated as such on the basis of structural, spectroscopic, or chemical evidence, have been reported in the recent literature and are reviewed here. They are classified according to the nuclearity of the anionic core and the nature of the cationic moiety, which can be a phosphonium, an ammonium, an iminium, a sulfonium, or a cationic organometallic fragment. The stabilization of the non-solvated charge separation is shown to arise from resonance and partial hapticity effects, hydrogen-type bonding, and tight intramolecular ion-pairing made possible by a back-folding of the ligand onto the metal center.
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  • 127
    ISSN: 1434-1948
    Keywords: NLO materials ; Second harmonic generation ; Two-photon fluorescence ; Solvatochromism ; Electrochemistry ; Sesquifulvalene ; Sandwich complex ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In order to investigate nonlinear optical properties, in particular second harmonic generation (SHG) of organometallic complexes, numerous dipolar monocationic sesquifulvalene complexes of the general form [Mc-Z-C7H6]+ have been synthesised (Mc = metallocenyl), wherein the metallocenyl moiety Mc acts as an electron donor, and the tropylium cation C7H6+ as an electron acceptor. The mutual electronic influence of the donor and the acceptor groups is warranted by a linking spacer Z, which is a single bond [Mc = CpFeC5H4 (4a); Mc = CpRuC5H4 (4b)], an unsaturated bridge containing olefins [Z = (E-CH=CH)n: n = 1, Mc = CpFeC5H4 (25a), Mc = CpRuC5H4 (25b); n = 2, Mc = CpFeC5H4 (26); n = 3, Mc = CpFeC5H4 (27)], or thiophene units [Z = 2,5-C4H2S, Mc = CpFeC5H4 (28); Z = 5,5′-(2,2′-C4H2S)2, Mc = CpFeC5H4 (29); Z = 2-(5-E-CH=CH)C4H2S, Mc = CpFeC5H4 (30)]. For the salts of 4a·BF4, 4b·PF6 and 25a·PF6 X-ray structure determinations have been performed [4a·BF4: orthorhombic, Pnma, = 21.75(2), b = 9.900(2), c = 6.881(3) Å, V = 1482.0(15) Å3, Z = 4; 4b·PF6: monoclinic, P2(1)/c, a = 8.104(3), b = 18.206(14), c = 11.228(4) Å, β = 107.59(3), V = 1579.1(15) Å3, Z = 4; 25a·PF6: triclinic, P1bar, a = 10.067(6), b = 10.496(6), c = 11.418(6) Å, α = 94.07(4), β = 110.96(4), γ = 102.88(5)°, V = 1083.1(11) Å3, Z = 2]; the solid state structures indicate an almost coplanar arrangement of the organic π-system. Cyclic voltammetry studies reveal an irreversible one-electron reduction and an electrochemically reversible one-electron oxidation step for the ferrocenyl derivatives, whereas the ruthenocenyl derivatives demonstrate an irreversible two-electron oxidation. The redox potentials clearly indicate that the oxidation occurs at the metallocene unit, and the reduction is localised on the tropylium entity. In the electronic absorption spectra two intense bands are observed in the region 400 〈 λ 〈 900 nm which undergo strong negative solvatochromic shifts. The origin of the high-energy absorption band is assumed to be an interligand charge-transfer (LL-CT) transition, and the low-energy absorption band is assigned to a donor-acceptor charge-transfer (DA-CT) transition. Whereas the LL-CT is continuously shifted to lower energy with increasing spacer length, the energy of the DA-CT approaches a limiting value. A comparable phenomenon is also observed for the difference between the oxidation and reduction potentials obtained from electrochemical studies. Investigations concerning the nonlinear optical properties of the dipolar cationic sesquifulvalene complexes by means of hyper-Rayleigh scattering (HRS) indicate that the ferrocenyl derivatives fluoresce due to two-photon absorption whereas the ruthenocenyl congeners exhibit second harmonic generation with considerably larger first hyperpolarizability which is partly resonance-enhancement based.
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  • 128
    ISSN: 1434-1948
    Keywords: Perovskite phases ; Mixed conductors ; Materials science ; Neutron diffraction ; X-ray diffraction ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A new series of perovskite-type materials of general formula La1.33NaxMnxTi2-xO6 (x = 0.66, 0.55 and 0.44) was obtained and characterized. The common structure is rhombohedral (space group R3cbar) although a transition to orthorhombic (space group Ibmm) is observed between 400 and 600  K for the  x   = 0.66 phase. Complex impedance techniques and charge/discharge cycles show a different electrical behavior that varies from a purely electronic conductor (x = 0.66) to a mixed electronic-ionic behavior for the other phases.
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  • 129
    ISSN: 1434-1948
    Keywords: Hypercoordinated phosphorus ; Hypervalent phosphorus ; Phosphorus ; Diphosphonium compounds ; Ionomers ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Starting from R′R2P (R′ = 8-dimethylamino-1-naphthyl) containing a donor dimethylamino group, the new phosphonium salts [R′R2P(CH2Ph)]+Br- [R = Me (9) or Ph (10)] and [R′R2P(p-CH2C6H4CH2)PR2R′]2+[2Br]2- [R = Ph (12)] have been prepared. An interaction between the N and P atoms is evident from the X-ray crystal structure of 10 the N-P distance being less than the sum of the van der Waals radii of the 2 atoms. The geometry of 10 is that of a monocapped tetrahedron whereas the X-ray crystal structure determination shows essentially regular tetrahedral geometry for the analogous compound without the donor amino group, [(1-Np)Ph2P(CH2Ph)]+Br- (11). Treatment of 1,5-bis(dimethylamino)-2,6-dilithionaphthalene with chlorodiphenylphosphane gave 1,5-bis(dimethylamino)-2,6-bis(diphenylphosphanyl)naphthalene (8) which in the presence of methyl iodide afforded the diphosphonium salt [1,5-bis(dimethylamino)-2,6-bis(diphenylmethylphosphonium)naphthalene]2+[2I]2- (13). Similarly, treatment of 8 with 1 equivalent of benzyl bromide gave the monophosphonium salt [1,5-bis(dimethylamino)-2diphenylbenzylphosphonium-6-diphenylphosphanyl-naphthalene]+[Br]- (14) whereas in the presence of 2 equivalents of the same reagent [1,5-bis(dimethylamino)-2,6-bis(diphenylbenzylphosphonium)naphthalene]2+[2 Br]2- (15) was obtained. The ionomer poly([(1,5-bis{dimethylamino}2,6-bis{diphenylphosphonium}naphthalene)-(P,P-p-xylylene)]2+[2 Br]2-) (16), soluble in liquid SO2, was prepared by treatment of 8 with α,α′-dibromo-p-xylene.
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  • 130
    ISSN: 1434-1948
    Keywords: Autocatalysis ; Cyclic voltammetry ; Nitric acid ; Nitrogen oxides ; Reduction mechanism ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In order to explain and analyze the corrosion process of AISI 304 L stainless steel in the presence of nitric acid condensates, the reduction mechanism of nitric acid was studied on a platinum electrode in various nitric acid solutions (4 mol·L-1, 8 mol·L-1 and 12 mol·L-1) at 100 °C. Classical electrochemical techniques were used: cyclic voltammetry, chronoamperometry on a stationary electrode as well as on a rotating disk electrode. A reduction mechanism is proposed; this mechanism is autocatalytic and involves a charge-transfer step and a heterogeneous chemical reaction which regenerates the electroactive species at the electrode surface. The electroactive species is assumed to be nitrous acid which is a soluble species. The other compounds involved in the reduction mechanism are NO and NO2, which are supposed to be adsorbed. The nitric acid concentration influences the major product of the reduction process: NO for concentrations lower than 8 mol·L-1 and NO2 for higher concentrations.
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  • 131
    ISSN: 1434-1948
    Keywords: Calix[4]arenes ; Bipyridines ; Podands ; Cobalt complexes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Introduction of one or two 2,2′-bipyridine units at the upper rim of the calix[4]arene platform was performed by means of the Wittig reaction. The resulting alkenes were hydrogenated to give two new bipyridyl-based calixarene podands, which were studied as ligands for CoII cation. The mono-bipyridyldichlorocobalt complex was notably fully characterised by 1H-NMR and X-ray crystal structure analyses, which confirmed the tetrahedral coordination mode involving the bipyridyl subunit and the two chlorine atoms around the cobalt centre.
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  • 132
    ISSN: 1434-1948
    Keywords: Bridging ligands ; Nitrito bridge ; Copper ; Nickel ; Magnetic properties ; Supramolecular chemistry ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The reaction of NiX2 · 6 H2O (X = NO3-, ClO4-), bidentate amine, [Cu(oxpn)] [oxpn = N,N′-bis(3-aminopropyl)oxamide] and sodium nitrite in ethanolic solution, leads to the formation of new Cu2+-Ni2+ complexes of general formula [Cu(oxpn)Ni(NO2)(aa)]n(X)n [1, X = ClO4-, aa = N,N,N′-trimethylethylenediamine (trimen); 2, X = ClO4-, aa = N,N,N′N′- tetramethylethylenediamine (tmen); 3, X = ClO4-, aa = N,N-dimethyl-N′-ethylethylenediamine (dmeten); 4, X = PF6-, aa = trimen; 5, X = PF6-, aa = dmeten]. The structure of complex 1 consists of [Cu(oxpn)Ni(trimen)]2+ units linked by a nitrite group acting as a tridentate ligand, giving a one-dimensional system separated by ClO4- anions. In contrast, the structure of complex 2 consists of isolated [Cu(oxpn)Ni(NO2)(tmen)]+ dinuclear units and uncoordinated ClO4- anions. The nitrite group acts as a bidentate ligand. Variable-temperature magnetic susceptibility studies were performed on 1-5. The J value through the oxamidato bridge is close to -110 cm-1 in all five cases. For complex 1, considered as a chain, a simulation of the χMT vs T was performed with the CLUMAG program. These calculations revealed the influence of the magnetic interactions between the dinuclear entities through the nitrito bridging ligand, on the susceptibility curves at low temperatures.
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  • 133
    ISSN: 1434-1948
    Keywords: Germylene ; Stannylene ; Plumbylene ; Schiff base ; Transition metal complexes of M ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The syntheses, characterization, and reactivities of the new stable mono- and cis-disubstituted Group 14 metal(II) chromium and tungsten carbonyl complexes (salen)M=M′(CO)5 [salen = 2,2′-N,N′-bis(salicylidene)ethylenediamine; M′ = Cr, M = Ge (4), Sn (5), Pb (6); M′ = W, M = Ge (7), Sn (8), Pb (9)] and [(salen)M]2=M′(CO)4 [M′ = W, M = Ge (10), Sn (11), Pb (12); M′ = Cr, M = Sn (14), Ge (15)] are described. Complexes 4-9 were obtained in high yields by treatment of the M′(CO)5 · THF intermediates with the stable divalent species (salen)MII [M = Ge (1), Sn (2), Pb (3)]. Direct irradiation of mixtures of (salen)MII and M′(CO)6 resulted in formation of the monosubstituted compounds 4-9 together with the disubstituted species 10-12, 14, and 15 in ratios depending on the nature of both M and M′. Pure complexes 10-12 were obtained by two different synthetic approaches starting from the (salen)MII species or the (salen)M=M′(CO)5 complexes. Each of the new complexes has been characterized by 1H- and 13C-NMR, and by 119Sn-NMR in the case of 5, 8, 11, and 14, as well as by IR spectroscopy in all cases. The molecular structures of 5, 8, 11, and 14, determined by X-ray structure analyses, reveal a pentacoordinated tin atom. The tin-chromium distances are among the shortest (in particular that in 5, 2.557 Å) observed for transition metal divalent tin complexes and the tin lies about 0.99 Å above the plane defined by the O2N2 atoms of the salen ligand. All these complexes have been found to be unreactive towards water and organic acids. Simple phosphane monosubstitution of carbonyl in 8 using Ph3P led to the new complex 13. Reactions with 1,2-bis(diphenylphosphanyl)ethane and 3,5-di-tert-butyl-1,2-benzoquinone resulted in displacement of the divalent species from the carbonyl complexes 5 and 8.
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  • 134
    ISSN: 1434-1948
    Keywords: Ruthenium ; s-Triazole ; s-Triazoline ; Oxidations ; Crystal structure ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The chemical behavior of triazole, thiadiazole, and triazoline derivatives of thiocarbonohydrazide towards cis-[RuCl2(DMSO)4] (2) was studied. Reaction of 4-amino-5-methylthio-3-(2-pyridyl)-1,2,4-triazole (L1) with 2 gave two diastereomeric complexes, trans,cis-[RuCl2(DMSO)2(L1)] (3) and chiral cis,cis-[RuCl2(DMSO)2(L1)] (4). Reaction of 2 with 2-(2-formylhydrazino)-1,3,4-thiadiazole in MeOH gave the complex trans,cis-[RuCl2(DMSO)2(L2)] (5) with concomitant deformylation of the starting ligand. The process was catalyzed by RuII in very low yield. Synthesis of the Ru complexes of 4-amino-3-methyl-1,2,4-Δ2-triazoline-5-thione (L3) and 4-amino-3-ethyl-1,2,4-Δ2-triazoline-5-thione (L4) resulted in an interesting oxidation of the metal promoted by DMSO. Reaction of 2 with these ligands in a 6 N HCl solution led to the isolation of the complexes mer-[RuCl3(DMSO)(L3)]·1/2 H2O (6) and mer-[RuCl3(DMSO)(L4)]·1/2 H2O (7). The complex mer-[RuCl3(DMSO)(L4)]·CH3COOH·H2O (7′) was obtained by recrystallization of 7 from ethyl acetate. The complexes 6, 7, and 7′ were highly stable in HCl solutions and acetone but not in neutral aqueous solution. To the best of our knowledge this is the first report of RuIII complexes with an N-N-C-S chelating system.
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  • 135
    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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  • 136
    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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  • 137
    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.
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  • 138
    ISSN: 1434-1948
    Keywords: Hydrogenation ; Isomerization ; Rhodium ; Iridium ; Hydrides ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The bulky β-diiminate ligands [(2,6-C6H3X2)NC(Me)CHC(Me)N(2,6-C6H3X2)]- (X = Me, LMe; X = Cl, LCl) have been found to be effective in stabilizing low coordination numbers (CN) in Rh and Ir complexes. The 14- complex LMeRh(COE) (COE = cyclooctene) has a three-coordinate T-shaped Rh environment and is nonagostic. Coordinative unsaturation is avoided by incorporation of a small ligand (e.g. N2, MeCN, olefins), by the intramolecular coordination of a chlorine atom in LClRh(COE), or by an agostic interaction in LMeRh(norbornene). In solution at room temperature, LMeRh(COE) undergoes rapid isomerization according to the allyl hydride mechanism; the corresponding 2,3-dimethylbutene complex actually prefers the allyl hydride structure. Rhodium(I) complexes of LMe and LCl catalyze olefin hydrogenation; hydrogenation of 2,3-dimethylbutene has been shown to be preceded by isomerization. The shielding properties of the bulky β-diiminate ligands allow direct observation of a number of reactive intermediates or their iridium analogues, including an olefin-dihydrogen complex (with Rh) and an olefin dihydride (with Ir). These observations, together with calculations on simple model systems, provide us with snapshots of a plausible hydrogenation cycle. Remarkably, hydrogenation according to this cycle appears to follow a 14-e/16-e path, in contrast to the more usual 16-e/18-e paths.
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  • 139
    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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  • 140
    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.
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  • 141
    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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  • 142
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    ISSN: 1434-1948
    Keywords: Linkage isomerization ; NMR spectroscopy ; Nucleobases ; Platinum ; Structure elucidation ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Bis(9-methyladenine) complexes of cis-PtII(NH3)2 undergo slow linkage isomerization from the N7 to the N1 site in aqueous solution at elevated temperatures. The ratio of the isomeric complexes during the isomerization process indicates that whilst PtII prefers the N(7) site in the adenine moiety kinetically, it is the N(1) coordination mode which is thermodynamically more stable. The crystal structures of the isomers do not reveal any unusual features; the few apparently structurally significant differences in the bond angles in the N(1)-bound bis(complex) merely reflect the poor quality of the crystal and/or crystal packing effects rather than a direct result emanating from the coordination mode of the ligand.
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  • 143
    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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  • 144
    ISSN: 1434-1948
    Keywords: Host-guest compounds ; Tin ; Mercury ; Pnictide halides ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A novel host-guest compound [Hg7As4I3](SnI3) has been prepared by a standard ampoule technique and its crystal structure was determined. It crystallizes in a cubic system [space group P213, a = 13.110(1) Å, Z = 4] with a unique structure type. The crystal structure comprises two parts: the three-dimensional [Hg7As4I3]1+ host network, and the SnI31- guest anions encapsulated in the cavities of the network. The network is built from the As2Hg7 bitetrahedra and As2Hg6 octahedra, which share corners, and contains an additional iodine atom connected to one of the mercury vertices. The SnI31- anion has the shape of a pyramid with the tin atom in a vertex. According to the quantum-chemistry calculations, the geometry of the anion deviates substantially from the equilibrium one, and is influenced by the distant mercury atoms of the host network.
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  • 145
    ISSN: 1434-1948
    Keywords: Iridium ; Amphiphiles ; N ligands ; Structure elucidation ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The reaction of 4′-functionalized 6′-phenyl-2,2′-bipyridine ligands (L-n) with the dimer [(ppy)2IrCl]2 (ppy = 2-phenylpyridine anion) and subsequent counterion exchange affords a new series of cationic orthometallated iridium(III) complexes, [(ppy)2Ir(L-n)][PF6] (1-5), which have been characterized by spectroscopic methods. These complexes have a large shape anisotropy and significant amphiphilic character. The crystal structure of 4 has been determined by X-ray diffraction.
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  • 146
    ISSN: 1434-1948
    Keywords: Molybdenum ; Fluxionality ; Pyridylphosphanes ; Phosphane oxides ; Polydentate ligands ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The pseudo-octahedral complexes [Mo(η3-allyl)Br(CO)2(PPynPh3-n-P,N)] (Py = 2-pyridyl; n = 2, 3) and [Mo(η3-allyl)Br(CO)2(OPPymPh3-m-O,N)] (m = 1, 2, 3) undergo three different dynamic processes in solution, depending on the chelating ligand. The complexes containing PPhPy2 and PPy3 as chelating P,N-donors undergo a novel “pivoted double switch” mechanism which scrambles two equatorial coordination sites with racemization, while maintaining the identity of the phosphorus atom trans to the allyl ligand. The complexes containing 2-pyridylphosphane oxides as chelating O,N-donors undergo a nondissociative intramolecular trigonal-twist (or turnstile) rearrangement which maintains the identity of the phosphane oxide oxygen atom coordinated in an equatorial position. All the complexes containing uncoordinated pyridyls undergo a slow dissociative exchange of pyridyls without coordination site scrambling. The structure of the complex [Mo(η3-allyl)Br(CO)2(OPPy3-O,N)] has been determined by X-ray diffraction.Supporting information for this article is available on the WWW under -//_/_http://www.wiley-vch.de/contents/jc_2005/2000/99363_s.pdf or from the author.
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  • 147
    ISSN: 1434-1948
    Keywords: Palladium ; Dithiadiazole ; Radicals ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Two new 1,2,3,5-dithiadiazoles, [4-(4′-C5H4N)CN2S2] (L1) and [4-(3′-C5H4N)CN2S2] (L2), with different pyridyl groups at the 4-position were prepared. As Lewis bases, the dithiadiazoles reacted with Lewis acids via their pyridyl groups to form acid-base adducts with retention of the five-membered dithiadiazole ring. Ligands L1 and L2 reacted with excess triethylborane to give L1BEt3 and L2BEt3 (1a and 1b) and with Mn(CO)5Br to give the fac-Mn(CO)3Br(L1)2 (2a) and fac-Mn(CO)3Br(L2)2 (2b) complexes. When reacted with Pd0 complexes, namely, Pd(PPh3)4 and a mixture of [Pd2(dba)3] and dppf, the dithiadiazoles underwent ring-opening reaction by reductive cleavage of the S-S bond of the dithiadiazole ring. The resulting formation of Pd-S bonds gave the corresponding trinuclear complexes [Pd3{μ-SNC(4′-C5H4N)NS-S,S′}2(PPh3)4] (3a), [Pd3{μ-SNC(3′-C5H4N)NS-S,S′}2(PPh3)4] (3b), and [Pd3{μ-SNC(4′-C5H4N)NS-S,S′}2(dppf)2] (4) [dba = dibenzylideneacetone, dppf = 1,1′-bis(diphenylphosphanyl)ferrocene]. Complexes 3a and 3b reacted with excess triethylborane to give the corresponding acid-base adducts [Pd3{μ-SNC(4′-C5H4NBEt3)NS-S,S′}2(PPh3)4] (5a) and [Pd3{μ-SNC(3′-C5H4NBEt3)NS-S,S′}2(PPh3)4] (5b.) Complex 3a reacted with Mn(CO)5Br to give {[Pd3{μ-SNC(4′-C5H4N)NS-S,S′}2(PPh3)4][MnBr(CO)3]}n (6). The structures of 3a, 5a, and 5b were established by X-ray crystallography.
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  • 148
    ISSN: 1434-1948
    Keywords: Relaxivity ; Nuclear magnetic relaxation dispersion ; Imaging agents ; NMR spectroscopy ; MRI contrast agents ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Dipolar interaction between the metal ion and proximate water molecules represents an efficient mechanism for solvent relaxation in Gd3+ complexes currently employed as MRI contrast agents. Besides inner sphere (metal bound) and outer sphere hydration molecules, a well-defined second coordination shell may provide an additional mechanism for paramagnetic relaxation leading to a strong enhancement of the relaxivity of the complexes. Through a careful choice of hydrogen-bond-acceptor groups on the ligand we may: (1) promote the formation of a strong interaction; (2) increase the number of water molecules in the second hydration shell; (3) decrease their average distance from the paramagnetic metal center. These possibilities have been explored by considering complexes bearing phosphinate, phosphonate and carboxoamide pendant arms, by exploiting the formation of ion-pairs with cationic substrates and inclusion compounds of these adducts with -cyclodextrin. Finally, the contribution of this relaxation mechanism to the relaxivity of the commercially available MRI contrast agents is discussed and the NMRD data reevaluated and compared with crystallographic data.β
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  • 149
    ISSN: 1434-1948
    Keywords: Functionalized zirconocenes ; Half-sandwich complexes ; Hydroboration ; Propene polymerization/Homogeneous catalysis ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 6-Amino-6-methylfulvene has been coupled with benzoic acid by treatment with 7-azahydroxybenzotriazole and DCC. Subsequent two-fold deprotonation, at the NH and 6-methyl groups, generated the vinylidene-bridged Cp/benzoylamido ligand 5. Treatment of 5 with ZrCl4(THF)2 gave the spiro-metallocene complex 3a (characterized by X-ray crystal structure analysis), while reaction of 5 with (Et2N)2ZrCl2(THF)2 yielded the bridged half-sandwich complex 3b. Treatment of 3a with two molar equivalents of the strongly electrophilic borane HB(C6F5)2 resulted in hydroboration of the exocyclic C=C double bond with concomitant intramolecular N-B adduct formation to yield the azaboretidine-type systems 7 (three diastereoisomers, one of which has been characterized by X-ray diffraction analysis). Similarly, hydroboration of 3b with HB(C6F5)2 yielded the azaboretidine derivative 9. Activation of the complexes 7 and 9 with methylalumoxane led to active homogeneous Ziegler-type propene polymerization catalysts.
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  • 150
    ISSN: 1434-1948
    Keywords: Phosphorus ; Benzynezirconocenes ; Azazirconacyclopentenes ; Exchange reactions ; 1,2-Azaphosphindole ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The first 1,2-azaphosphindoles 14a,b, 15a,b were obtained in a straightforward manner upon heating diphenylzirconocene in the presence of a cyanophosphane, which afforded azazirconacyclopentenes 11a,b which can be reacted with various dichlorophosphanes. The use of the tetrachlorodiphosphane Cl2P(CH2)2PCl2 instead of a dichlorophosphane allowed the preparation of the bis(1,2-azaphosphindoles) 19, 19′. The monosulfur adduct of the azaphosphindole 14a, i.e. 16a, was characterized by X-ray structure analysis. Alkylation of 14a or 16a with methyltrifluoromethane sulfonate occurred selectively on the intracyclic phosphorus atom or on the sulfur atom, giving the salts 20 or 21, respectively.
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  • 151
    ISSN: 1434-1948
    Keywords: Ruthenium ; Sulfur ligands ; Exchange reactions ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In a quest for ruthenium complexes having [RuNS4] cores, a non-fluxional configuration, trans-thiolate donors, and exchangeable coligands L, [Ru(L)(‘pyS4’)] complexes have been synthesized [‘pyS4’2- = 2,6-bis(2-mercaptophenylthio)dimethylpyridine(2-)]. Treatment of [RuCl2(PPh3)3] with ‘pyS4’2- gave [Ru(PPh3)(‘pyS4’)] (1). Alkylation of 1 with excess MeI yielded [Ru(PPh3)(‘pyS4’-Me2)]I2 (2). [Ru(DMSO)(‘pyS4’)] (3) was obtained from [RuCl2(DMSO)4] and ‘pyS4’2-. The PPh3 or DMSO coligands in 1, 2, and 3 proved to be very inert to substitution. Only the DMSO could be displaced by CO under drastic conditions yielding [Ru(CO)(‘pyS4’)] (4). Treatment of [RuCl2(CH3CN)4] with ‘pyS4’2- yielded [Ru(‘pyS4’)]2 (5); in the presence of PEt3 or N2H4 mononuclear [Ru(PEt3)(‘pyS4’)] (6) and [Ru(N2H4)(‘pyS4’)] (7) were formed. Template alkylation of NBu4[Ru(NO)(S2C6H4)2] with 2,6-bis(tosyloxymethyl)pyridine gave [Ru(NO)(‘pyS4’)]Tos (8). Complex 8 proved to be the best suited precursor for L exchange reactions. Under reducing conditions, 8 releases its NO ligand and the resulting [Ru(‘pyS4’)] fragments can combine either with each other to give 5, or with PEt3 and N2H4 to yield 6 and 7, respectively. All complexes have been characterized by spectroscopic methods and elemental analysis; 1, 2, 3, and 4 have also been submitted to X-ray structure analysis.
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  • 152
    ISSN: 1434-1948
    Keywords: Methylnickel complexes ; 2-Phosphanylphenolate ; Chelates ; Homogeneous catalysis ; Oligomerization ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Reactions of various substituted 2-phosphanylphenols 1a-f with half-molar amounts of cis-[MeNi(μ-OMe)(PMe3)]2 have been found to yield square-planar methyl(2-phosphanylphenolato)(trimethylphosphane)nickel(II) complexes 2a-f. 2JPP coupling constants of 305-316 Hz at low temperature indicate a trans-configuration for the products, while broad 31P-NMR signals at room temperature can be attributed to rapid dissociation of PMe3. Reaction with excess 1 gave rigid bis(2-phosphanylphenolato)nickel(II) complexes as exemplified by 3e, whereas addition of PMe3 to 2a led to the pentacoordinate methyl(2-phosphanylphenolato)bis(trimethylphosphane)nickel(II) complex 4a. Higher yields of 4a and 4d were obtained by reactions of 1a and 1d with Me2Ni(PMe3)3. Single-crystal X-ray diffraction analyses of 3e and 4a have revealed the structures as square-planar trans-bis- and trigonal-bipyramidal mono(2-phosphanylphenolato)nickel(II) P1O-chelate complexes, respectively. The methylnickel complexes 2 and 4 have been found to be effective one-component catalysts for the oligomerization of ethene. High conversions (〉 96%) were achieved with the P-basic derivatives 2e, 2f, and 4d bearing one or two branched alkyl groups (isopropyl, tert-butyl), whereas the diphenylphosphanyl derivatives were less active; 4d gave shorter oligomers than 2e or 2f.
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  • 153
    ISSN: 1434-1948
    Keywords: Zinc ; Metalloporphyrins ; Porphyrins ; Cations ; Radicals ; ESR ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Zinc(II) complexes of substituted tetraphenylporphyrins, Zn[T(X-P)P], where X = H, p-F, p-Cl, m-Cl, p-CH3O, and m-CH3O, have been synthesized and characterized. Peripheral substitution shows marked changes in the chemical shifts of the phenyl proton resonances and E1/2 values of the redox couples in the anodic region while the UV/Vis spectra are unaffected. The monocation radicals of these complexes are generated by chemical oxidation with bromine. The ESR spectra reveal the formation of two types of radical species, Zn[T(X-P)P]+·Br- (species I) and Zn[T(X-P)(Brn-P)]+·Br- (species II): Species I at 298 K shows a spectrum, with well-resolved bromine hyperfine features, characteristic of a 2A2u electronic ground state while species II, except for the complex with X = m-CH3O, shows a featureless, isotropic resonance attributable to a 2A1u state. Zn[T(m-CH3O-P)(Brn-P)]+·Br-, on the other hand, exhibits nine resolved nitrogen hyperfine features corresponding to a 2A2u state. Variable temperature ESR spectra (77-298 K) indicate reduction in the bromine and nitrogen hyperfine coupling constants and an increase in the g value of species I from 2.0049 to 2.0060 with lowering temperature and suggest a labile electronic ground state for species I. The p-CH3O substituted complex exhibits an electronic transformation from 2A2u to 2A1u while the remaining complexes, including m-CH3O, show a transformation from 2A2u to an admixed 2A1u/2A2u state. The effect of substitution on the variable temperature ESR spectra are discussed.
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  • 154
    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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  • 155
    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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  • 156
    ISSN: 1434-1948
    Keywords: Cadmium(II) pyrazolonates ; Thiosemicarbazones ; Cyclizations ; 2-[Amino(thioxo)methyl]-3-pyrazolone ; 1H-, 13C-, 113Cd-NMR spectra ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Acetoacetanilide- and methylacetoacetate thiosemicarbazones (HTSC1 and HTSC2, respectively) react with cadmium(II) acetate in methanol, giving complexes containing the ligand 2-[amino(thioxo)methyl]-5-methyl-2,3-dihydro-1H-3-pyrazolonate (L-). An X-ray diffraction study of the structures of HTSC1, HTSC2, HL, and [CdL2Py], identified the main structural changes in the cyclization process. Additionally, the coordination of the metal in the complexes [CdL(AcO)] · 2 MeOH and [CdL2] · 3 H2O was analyzed using IR spectroscopy in the solid state and 1H-, 13C-, and 113Cd-NMR spectroscopy in solution. On reaction with aqueous trifluoroacetic acid, both complexes releases the free pyrazolone, which can be easily isolated.
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  • 157
    ISSN: 1434-1948
    Keywords: Photocatalysis ; Polyoxotungstates ; Catalytic oxidations ; Iron porphyrins ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Photoexcitation of (nBu4N)4W10O32 is a suitable mean of oxidizing cyclohexene and cyclooctene with O2 at room temperature and pressure. This process can be carried out in homogeneous solution as well as using the decatungstate in a dispersed form after its heterogenisation on silica. Cyclohexene and cyclooctene are mainly oxidized to the corresponding hydroperoxides as a consequence of primary photoprocesses which lead to the formation of allylic radicals. The presence of the FeIII[meso-tetrakis(2,6-dichlorophenyl)porphyrin] chloride as cocatalyst strongly affects the photocatalytic properties of (nBu4N)4W10O32, playing a key role in the allylic-hydroperoxide dependent oxidation of the cycloalkenes. In the photooxidation of cyclohexene, the porphyrin increases the photocatalytic efficiency of the decatungstate in terms of total turnover number and catalyses the decomposition of cyclohexenyl hydroperoxide with the selective formation of cyclohex-2-en-1-ol. On the other hand, its presence during the photoinduced oxidation of cyclooctene favours the formation of cyclooctene epoxide by addition of ROO· and RO· radicals to the double bond. In the case of cyclooctene, the heterogenisation of the decatungstate on the solid support also affects the chemoselectivity of the photocatalytic process in the absence of the iron porphyrin complex.
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  • 158
    ISSN: 1434-1948
    Keywords: Mesoporous materials ; MCM-48 ; Immobilization ; (1,1′-Ferrocenediyl)dimethylsilane ; 13C and 29Si solid-state NMR ; Sandwich-complexes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The walls of the cubic mesoporous silicate MCM-48 have been grafted with ferrocenyl end groups by a ring-opening reaction of the ansa-bridged ferrocene [Fe{(η-C5H4)2SiMe2}], carried out in a pentane solution at room temperature. The orange product has been characterized by elemental analysis, powder X-ray diffraction, 13C and 29Si solid-state NMR, N2 adsorption measurements, and Fe K-edge EXAFS. A high loading has been obtained (8.18 mass % Fe) and, as a result of the inclusion of the organometallic moiety, the N2 adsorption isotherm exhibits a lower uptake. Direct structural evidence for the surface attachment of both single ferrocenyl and short chain oligo(ferrocenyl) fragments has been obtained.
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  • 159
    ISSN: 1434-1948
    Keywords: Carbaalanes ; Cluster compounds ; Electron deficiency ; Aluminium ; Boron ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Cluster chemistry in the third main group has long been restricted to compounds of the lightest element boron. However, about 30 years ago the first compounds were synthesized and characterized in which single aluminium atoms adopted positions of high connectivity in polyhedral borane or carbaborane clusters. The next successful step in these efforts to establish a chemistry analogous to that of the polyboranes with the heavier elements of the third main-group was the synthesis of closo-dodecaaluminate [Al12iBu12]2- at the beginning of the nineties, which was the first homonuclear aluminium analogue of a polyborate anion and had a core exclusively formed by aluminium atoms. Another class of interesting new aluminium compounds was formed by the carbaalanes, which were synthesized and characterized for the first time only recently. They have clusters of aluminium and carbon atoms, and are similar to the carbaborane analogues in that their structures seem to be determined by the number of electron pairs in their molecular centers in accordance with the Wade rules.
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  • 160
    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.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
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