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  • 1995-1999  (643)
  • 1998  (643)
  • General Chemistry  (643)
  • Inorganic Chemistry
  • 101
    Electronic Resource
    Electronic Resource
    Theoretical Comparison of the Electronic Structures of [PhN2]+ and [PhP2]+ - Can the Benzenediphosphonium Cation Exist in the Gas Phase? (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 1821-1825 
    Details
    ISSN: 1434-1948
    Keywords: Diazonium cations ; Diphosphonium cations ; Calculations ; Ab initio methods ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Ab initio quantum-chemical investigations are used to outline the main differences between the phenyldiazonium cation [PhN2]+ (1a,b) and its P analogue [PhP2]+ (2a,b). Our results show that in contrast to 1, 2b exists preferentially as a bridged structure. The phenyl ion affinity toward P2 has been determined and suggests that the phenyldiphosphonium cation should be stable in the gas phase and that it is probably accessible by reaction between P2 and Ph+.
    Additional Material: 6 Ill.
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  • 102
    Electronic Resource
    Electronic Resource
    Clusters as Ligands - Large Assemblies of Transition Metal Clusters (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 1835-1846 
    Details
    ISSN: 1434-1948
    Keywords: Clusters ; Catalysis ; Carboxylato complexes ; Hydrogenations ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A strategy of using functionalized clusters as ligands for cationic metal centers facilitates the construction of designed transition metal cluster assemblies. Examples of cluster metal carboxylates with conventional as well as novel structures are given and an application of these large molecular species to the generation of heterogeneous hydrogenation catalysts with unusual activities and selectivities is described.
    Type of Medium: Electronic Resource
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  • 103
    Electronic Resource
    Electronic Resource
    The 3,5-Dichlorotrifluorophenyl Ligand, a Useful Tool for the Study of Coordination Modes and Dynamic Behavior of Complexes of Palladium and Platinum (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 1745-1753 
    Details
    ISSN: 1434-1948
    Keywords: Palladium ; Platinum ; Aryl rotation ; Through-space coupling interactions ; Turnstile mechanism ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The square-planar complexes [MR2L2] (M = Pd, Pt; R = 3,5-C6Cl2F3) [L2 = OPPyPh2 (Py = 2-pyridyl); SPPyPh2; OPPy2Ph; DMBI (3,3′-dimethyl-2,2′-biindazole); OPPyPh(NHTol-p); p-TolNPPy2Ph] have been prepared by treating cis-[MR2(THF)2] (THF = tetrahydrofuran) with the appropriate chelate ligands. The 19F-NMR spectra of these complexes show the presence of intramolecular through-space F-F couplings between ortho-fluorine atoms of nonequivalent R groups, which provide information for the assignment of the different ortho-fluorine signals and can be used to study the dynamic behavior of the mentioned complexes such as: a) Rotation of the R group in either Pd or Pt complexes, at the same or at different rates for each R groups depending on the neutral ligand; and b) exchange of the coordination sites of the chelating ligand, either by Berry or by turnstile mechanisms. The activation parameters for some of the processes are given.
    Additional Material: 9 Ill.
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  • 104
    Electronic Resource
    Electronic Resource
    New Tripodal N3S Ligands and Some Zinc Complexes Thereof (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 1759-1764 
    Details
    ISSN: 1434-1948
    Keywords: Tripodal ligands ; Nitrogen-sulfur ligands ; Zinc complexes ; Structure determination ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Attachment of 2-pyridylmethyl units to cysteine amide and 2-mercaptobenzylamine leads to the new tripodal N3S ligands Nα-(4-methylbenzoyl)-L-cysteine-bis(2-pyridylmethyl)amide (CBPA-H) and 2-mercaptobenzyl-bis(2-pyridylmethyl)amine (MBPA-H). Their treatment with zinc halides yields the neutral complexes L · ZnHal (Hal = Cl, Br, I). With zinc perchlorate MBPA forms the ionic compound [L · Zn] ClO4, presumed to be a thiolate bridged dimer. Structure determinations of MBPA · ZnHal (Hal = Cl, Br) have confirmed the tripodal nature of the ligand in the trigonal-bipyramidal complexes.
    Additional Material: 1 Ill.
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  • 105
    Electronic Resource
    Electronic Resource
    Cyclophanes as Model Compounds for Permanent, Dynamic Aggregates - Induced Chirality with Strong CD Effects (1998)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 1915-1917 
    Details
    ISSN: 1434-193X
    Keywords: Cyclophanes ; Fluorescent dyes ; Perylenes ; Exciton coupling ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Dynamic processes, a bathochromically shifted fluorescence, and strong solvent-induced chirality effects are observed for the [12,12]-perylene-bis(imide)-cyclophane 3, which forms a “fixed supramolecule”.
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  • 106
    Electronic Resource
    Electronic Resource
    Reactivity of the 5-Hydroacenaphthylene Anion towards Electrophiles (1998)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 1907-1914 
    Details
    ISSN: 1434-193X
    Keywords: Reductive alkylation ; Acenaphthylene ; Carbanions ; Polycycles ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The dianion of acenaphthylene can be converted into the 5-hydroanion by protonation with one equivalent of methanol. Subsequent reaction with electrophiles such as allyl bromide and propargyl bromide occurs selectively at position 1, resulting in the formation of the novel 1-allylacenaphthene and 1-propargylacenaphthene. In addition to what was observed in the case of methyl iodide, the hitherto unknown 1,1-dialkylated acenaphthene derivatives are formed as minor products; probably the lower reactivity of the unsaturated bromides is responsible for this side reaction. From the products of the reactions with 3,3-dimethylallyl bromide and (bromomethyl)cyclopropane the mechanism was found to be SN2. Reaction of the hydroanion with benzyl bromide takes place at position 1 as well as at position 2a. The reactivity of carbon 2a towards the soft electrophile benzyl bromide is attributed to the high HOMO coefficient at this position.
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  • 107
    Electronic Resource
    Electronic Resource
    Kinetics of the [2+ + 4]-Cycloaddition Reactions of 1,3-Dithian-2-ylium Ions with 1,3-Dienes (1998)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 1919-1922 
    Details
    ISSN: 1434-193X
    Keywords: Heterocycles ; Carbocations ; Dienes ; Cycloadditions ; Kinetics ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The kinetics of the [2+ + 4] cycloadditions of 1,3-dithian-2-ylium ions (1) with 1,3-dienes was investigated photometrically in dichloromethane. The second-order rate constants determined for the reactions of 1 with 2,3-dimethyl-1,3-butadiene (2a) and isoprene (2b) were identical to those calculated for the first step of a stepwise cycloaddition pathway by the correlation lg k = s (E + N). Though a concerted cycloaddition pathway is not excluded by this finding, it is obvious that the transition states of these reactions are not noticeably stabilized by the simultaneous formation of two new σ bonds.
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  • 108
    Electronic Resource
    Electronic Resource
    Titanocene-Catalyzed Pinacol Couplings: Reagent-ControlledTransition-Metal-Catalyzed Radical Reactions (1998)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 1923-1927 
    Details
    ISSN: 1434-193X
    Keywords: Aldehydes ; Diastereoselectivity ; 1,2-Diols ; Radical reactions ; Reagent control ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The titanocene-catalyzed pinacol coupling of aromatic aldehydes proceeding in good yields and with high diastereoselectivity under reagent control is described.
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  • 109
    Electronic Resource
    Electronic Resource
    Sannamycin-Type Aminoglycoside Antibiotics - Efficient Syntheses - Biological Activity (1998)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 1935-1948 
    Details
    ISSN: 1434-193X
    Keywords: Sannamycin-type antibiotics ; Aminoglycoside syntheses ; Glycosylation ; Biological activity ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Shorter and more efficient routes to 6′-des(N-methyl)sannamycin A (1) and its 2′-epi analog 2 have been elaborated with the proven sannamine-type acceptor 10 and the glycosyl donors 5-8 featuring novel protecting patterns. With glycal 9 as glycosyl donor (and 10) an expedient access to 2′-desamino- (3) and 2′-desamino-2′-epi-hydroxysannamycin A (4) has been opened. For 4 a modest antibacterial activity was found, while 3 was inactive.
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  • 110
    Electronic Resource
    Electronic Resource
    Synthesis and Glycosidase Inhibitory Activity of Five Stereoisomers of 5-Amino-5-C-methyl-1,2,3,4-cyclopentanetetrol (1998)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 1929-1934 
    Details
    ISSN: 1434-193X
    Keywords: Cyclitols ; Aminocyclitols ; Glycosidase inhibitors ; α-Mannosidase inhibitors ; Aldol reaction ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In order to elucidate the essential core structure of potent α-mannosidase inhibitors, e.g. mannostatin A, 5-amino-5-C-methyl-1,2,3,4-cyclopentanetetrols 4-8 were designed and synthesized by a base-catalyzed nitro aldol condensation of nitroethane and the dialdehyde derived by periodate oxidation of DL-1,2-O-cyclohexylidene-myo-inositol, followed by reduction and deprotection. Biological assay of the five stereoisomers thus obtained for the six glycosidases has demonstrated the DL-(1,2/3,4,5) and (1,2,3,4,5/0) isomers to be moderate α-mannosidase inhibitors, suggesting that the all-cis configuration of the amino and three hydroxy groups on the cyclopentane ring plays a role in exhibiting inhibitory activity.
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  • 111
    Electronic Resource
    Electronic Resource
    A New Iron-Mediated Strategy for the Synthesis of α-Lipoic Acid and Analogues (1998)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 1949-1954 
    Details
    ISSN: 1434-193X
    Keywords: α-Lipoic acid ; Structural analogues ; Tricarbonyl(η5-pentadienyl)iron cations ; Carbonyliron complexes ; Diimide reduction ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Dithioester 10 was synthesized in 6 steps from tricarbonyl(diene)iron complex 3. Compound 10 is not only a key intermediate for the synthesis of methyl lipoate (13) but could also be of interest for the preparation of various labelled compounds and structural analogues.
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  • 112
    Electronic Resource
    Electronic Resource
    Highly Stereoselective trans Addition of π-Type Nucleophiles to a Bicyclic N-Acyliminium Ion - Application to the Synthesis of Indolizidine and Pyrrolizidine Alkaloids (1998)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 1955-1963 
    Details
    ISSN: 1434-193X
    Keywords: N-Acyliminium ; Pyrrolidine ; Indolizidine ; Pyrrolizidine ; Stereoselective ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Enantiopure bicyclic 5-ethoxytetrahydropyrrolo[1,2-c]oxazol-3-one 1b was prepared in two steps from the known tosylate 4, which is readily available from (S)-pyroglutamic acid. Trapping of the N-acyliminium ion (I), generated in situ from 1b in the presence of Lewis acid, with various silylated π-type nucleophiles gave rise selectively to trans adducts 2. The usefulness of this stereoselective access to trans-2,5-disubstituted pyrrolidines was illustrated by formal syntheses of 3,5-disubstituted indolizidine toxins, starting from 5-allyltetrahydropyrrolo[1,2-c]oxazol-3-one 2a. Moreover, an enantiodivergent synthesis of the pyrrolizidine alkaloids (+) and (-)-xenovenine was achieved starting from the same chiral building block 2a.
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  • 113
    Electronic Resource
    Electronic Resource
    Metal-Mediated Conversion of Methylcycloarsoxane (CH3AsO)n to Macrocyclic Octa- and Decanuclear Ligands -Trigonal Bipyramidal Coordination of Trivalent Arsenic (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 1999-2003 
    Details
    ISSN: 1434-1948
    Keywords: Arsenic ; Methylcycloarsoxane ; Ruthenium ; Platinum ; Macrocyclic ligands ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Reaction of cyclo-(CH3AsO)n with MCl3 · x H2O in acetonitrile at 100 °C affords [MCl2{cyclo-(CH3AsO)8}] [M = Ru (1), M = Os (2)] in which cyclooctamers (CH3AsO)8 are stabilised in a ĸ4As1,3,5,7 binding mode in the equatorial coordination sphere of the Group 8 metals. In contrast treatment of K2PtCl4 with alternatively AgNO3 or Ag2CO3 and cyclo-(CH3AsO)n at 100 °C in the same solvent leads to the formation of respectively octa- or decanuclear cagelike ligands in [Pt2{[cyclo-(As[CH3]OAs[NC(O)CH3]O)2]2}] (3) and [Pt2{[{CH3C(O)N}2As5(CH3)5O4]2}] (4) by metal-assisted reactions between cyclo-(CH3AsO)n and acetonitrile. λ5-AsIII atoms in these complexes participate in square-planar PtII coordination and themselves exhibit distorted trigonal bipyramidal coordination geometries.
    Additional Material: 6 Ill.
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  • 114
    Electronic Resource
    Electronic Resource
    Characterization, Crystal Structure of 2,4-Bis(triphenylphosphanimino)tetrazolo[5,1-a]-[1,3,5]triazine, and Improved Crystal Structure of 2,4,6-Triazido-1,3,5-triazine (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 2013-2016 
    Details
    ISSN: 1434-1948
    Keywords: Cyanuric azide ; Tetrazole ; Triazine ; Nitrogen compounds ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 2,4-Bis(triphenylphosphanimino)tetrazolo[5,1-a][1,3,5]triazine (1) was synthesized by reaction of cyanuric azide with triphenylphosphane. 1 is characterized by X-ray structural analysis, IR, Raman, and NMR spectroscopy. The obtained spectra showed that the remaining azide group in 1 reacts with the N4 atom of the triazine ring and forms a tetrazole. An improved crystal structure for 2,4,6-triazido-1,3,5-triazine (2) was determined and for the first time a 14N-NMR spectrum was obtained. CAUTION: 2 (Cyanuric azide) is explosive! The explosive nature increases with greater purity and crystal size.
    Additional Material: 3 Ill.
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  • 115
    Electronic Resource
    Electronic Resource
    17O-NMR, EPR and NMRD Characterization of [Gd(DTPA-BMEA)(H2O)]: A Neutral MRI Contrast Agent (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 2017-2021 
    Details
    ISSN: 1434-1948
    Keywords: MRI ; GdIII complexes ; NMR spectroscopy ; NMRD ; Lanthanides ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A study including variable-temperature and -pressure, multiple-field 17O NMR, EPR and NMRD has been performed on the MRI contrast agent, [Gd(DTPA-BMEA)(H2O)]. The water exchange rate [kex298 = (0.39 ± 0.02) × 106 s-1] and the activation volume (ΔV≠ = +7.4 ± 0.4 cm3 mol-1), hence the mechanism, are identical to those for [Gd(DTPA-BMA)(H2O)]. The longer rotational correlation time of [Gd(DTPA-BMEA)(H2O)], as obtained from a global analysis of 17O-NMR, EPR and NMRD data, and compared to that of [Gd(DTPA-BMA)(H2O)], can be explained by water molecules hydrogen-bonded to the ether oxygen atoms of the ligand side chain.
    Additional Material: 2 Ill.
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  • 116
    Electronic Resource
    Electronic Resource
    Intermediates and Side-Reactions in the Synthesis of Molecular Diphenolatonickel Compounds Containing Trimethylphosphane Ligands (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 2027-2032 
    Details
    ISSN: 1434-1948
    Keywords: Nickel(0) ; Oxidation ; Phenols ; Structure ; Ion pairs ; Hydrogen bonds ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Admission of molecular oxygen to a solution containing Ni(PMe3)4 and substituted phenols (ArOH) affords bisphenolatonickel compounds trans-Ni(OAr)2(PMe3)2 [ArOH = 2-chlorophenol (1), 2-bromophenol (2), 2,4,6-trichlorophenol (3)]. In the absence of dioxygen the phenols reversibly protonate the nickel complex to form ionic compounds [NiH(PMe3)4]+ Y- containing hydrogen-bonded anions Y = [H2(2-Cl-C6H4O)3] (4), [H(2-OH-C6H4COO)2] (5). As a side-reaction, formal insertion of nickel to give 2-hydroxyphenylnickel compounds Ni(Ar′)X(PMe3)3 [Ar′ = 2-OH-C6H4; × = Br (6), I (7)], trans-Ni(Ar′)Cl(PMe3)2 [Ar′ = 2-OH-3,5-Cl2-C6H2 (8)] and trans-Ni(OAr)Cl(PMe3)2 [Ar = 2,4,6-Cl3-C6H2 (9)] is observed. An X-ray crystal structure determination of 1 shows a trans square planar arrangement of donor atoms, that of 6shows a distorted square pyramid, while 4 contains tetrahedral nickel cations with a delocalized hydrogen atom and triphenolate anions H2(ArO)3-.
    Additional Material: 3 Ill.
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  • 117
    Electronic Resource
    Electronic Resource
    An Uncommon Derivative of 4H-Thiopyran-4-one: 4H,8H-Thiopyrano[3,2-b]thiopyran-4,8-dione: Synthesis, Redox Properties, and Calculations (1998)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 1989-1996 
    Details
    ISSN: 1434-193X
    Keywords: Synthesis design ; Sulfur heterocycles ; Electron transfer ; MO calculations ; Electrochemistry ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Starting from tetrahydrothiopyran-4-one (4d) a rational eight-step synthesis of 3a has been developed with 25 % overall yield. This route passes H4-3a and H2-3a which are compared with 3a and its dithione 3b by IR, UV/Vis, 13C-NMR spectra, redox behavior, and crystal structure (H4-3a and 3a). The very low solubility of 3a and 3b prevented further reactions.
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  • 118
    Electronic Resource
    Electronic Resource
    Synthesis of Chiral Rhenium Complexes Containing Functionalized Thiolate Ligands (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 2055-2061 
    Details
    ISSN: 1434-1948
    Keywords: N-Acetylcysteine ; Amino acids ; Captopril ; Rhenium ; S ligands ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Chiral racemic rhenium thiolate complexes [CpRe(NO)(PPh3)(SR)] were obtained under either acidic or basic conditions. Thus, when [CpRe(NO)(PPh3)(CH3)] (1) was treated with etheral HBF4 and HSR the thiolate complexes [CpRe(NO)(PPh3)(SR)] [SR = SCH2(2-furyl) (2), SCH2C(O)OEt (3)] were obtained after chromatographic workup. Ligand exchange reactions between [CpRe(NO)(PPh3)(OC4H8)]BF4 (4) and sodium thiolates yielded analogous complexes with SR = SH (5), SCH2CH2Ph (6), SCH2CH=CH2 (7). SR groups which tolerate strongly alkaline conditions may be introduced by treatment of 4 with HSR in the presence of sodium ethoxide as demonstrated by the high-yield synthesis of 2 as well as of complexes with SR = SCH2CH2NHAc (8), SCH2CH2C(O)OH (9). A milder synthesis using hydrated sodium carbonate as a base provided 8 and compounds with SR = SCH2CH2C(O)OMe (10), SCH2CH2C(O)NHCH2Ph (11) in high yields. Using similar methods, thiolate complexes of (R)-N-acetylcysteine (13), its methyl ester (14), (R)-N-phthaloylcysteine (16), and N-[(S)-3-mercapto-2-methylpropionyl]-S-proline (Captopril) (17) were obtained as diastereomeric pairs. The formation of 13 was preceded by the O-bonded isomer 12 which slowly rearranges in solution. 13 can be converted under acidic conditions into its methyl (14) or ethyl (15) esters. The diastereomers of 16 were separated by crystallization, and the structure of the (R,R)-isomer 16a determined.
    Additional Material: 1 Ill.
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  • 119
    Electronic Resource
    Electronic Resource
    Franz Fehér (1903-1991) (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 2089-2105 
    Details
    ISSN: 1434-1948
    Keywords: Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A Personal and Professional Portrait
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  • 120
    Electronic Resource
    Electronic Resource
    Some Silatetraazaspiroalkanes with [4 + 4] Octacoordinated Silicon (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 1967-1973 
    Details
    ISSN: 1434-1948
    Keywords: Sulfonamidosilanes ; [4 + 4] Octacoordinated silicon ; Capped tetrahedron ; X-ray structures ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Spirocyclic compounds containing an Si(N)4 core have been prepared from 1,2-ethane- and 1,3 propanediamines bearing the electron-withdrawing p-toluenesulfonyl groups at the four N atoms. According to the X-ray structure analysis of the compounds 8a and 13, the spirocyclic rings are almost perpendicular to each other. In both cases a distorted dodecahedral arrangement of a [4 + 4] octacoordinate Si atom is found in which one O atom of each of the four sulfonyl groups caps one of the planes defined by the Si(N)4 tetrahedron. The O···Si distances are 2.85-3.02 Å and the two O···Si···O angles are 145-159°. According to the X-ray structure analysis of the monocyclic compound 16, one O atom of the p-toluenesulfonyl group caps the plane defined by O1-N2-C13 of the distorted S(N2)(O)C tetrahedron.
    Additional Material: 3 Ill.
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  • 121
    Electronic Resource
    Electronic Resource
    Asymmetric Synthesis and Enantioselectivity of Binding of 1-Aryl-1,2,3,4-tetrahydroisoquinolines at the PCP Site of the NMDA Receptor Complex (1998)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 2019-2029 
    Details
    ISSN: 1434-193X
    Keywords: Asymmetric synthesis ; Nitrogen heterocycles ; N-Acyliminium ions ; PCP site ligands ; Pharmacological enantioselectivity ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A new method for the asymmetric synthesis of 1-substituted tetrahydroisoquinolines is presented. It is based on stereoselective addition reactions of organometallic compounds to the intermediate N-acyliminium ion 6, which is provided with an N-acyl group as a chiral auxiliary. In addition reactions with organomagnesium and organozinc reagents diastereoselectivities from 70:30 to 95:5 (for 7/8) were observed with the zinc reagents in general leading to markedly improved stereoselectivities. By catalytic hydrogenation of 7 and 8 and after removal of the chiral auxiliary the target compounds 11 and 12 were obtained. The enantiomerically pure 11c-g and 12c-g (ee 〉 99 %), 1-aryl-tetrahydroisoquinolines, were evaluated for their affinity to the PCP [1-(1-phenylcyclohexyl)piperidine] binding site of the NMDA (N-methyl D-aspartate) receptor. In each case the enantiomers 11 exhibited a higher affinity than those of 12, with the potencies of the enantiomers differing by a factor of 4 (11/12g) to 27 (11/12c). The absolute configuration of the more potent enantiomers 11 is in accordance with the stereochemical requirement found for FR115427 (3) which is a close analogue.
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  • 122
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    Electronic Resource
    Diels-Alder Reactions of tert-Butylphosphaethyne with 1,3,2-Diaza- and 1,2-Azaphosphinines (1998)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 2039-2045 
    Details
    ISSN: 1434-193X
    Keywords: Phosphorus heterocycles ; Nitrogen heterocycles ; Phosphinines ; Phosphaalkynes ; [4 + 2] Cycloadditions ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: tert-Butylphosphaethyne (2) undergoes a Diels-Alder reaction with the 1,3,2-diazaphosphinine 1 at room temperature to furnish the diazadiphosphabarrelene 3. In the presence of an excess of 2 in toluene under reflux compound 3 experiences elimination of a molecule of pivalonitrile to afford the 1-aza-2,4-diphosphinine 5 which, in turn, reacts with a further equivalent of 2 to form the transient azatriphosphabarrelene 6. Formation of the final product, the stable tetraphosphatetracyclic compound 4, is the result of a homo Diels-Alder reaction between 6 and yet another equivalent of 2. The structure of 4 has been confirmed by an X-ray crystallographic analysis of its pentacarbonyltungsten complex 7. As a consequence of the high steric overcrowding in 4, complexation occurs exclusively at its phosphaalkene phosphorus atom. The reactivity of 2 towards the four functionally substituted 1,2-azaphosphinines 8a-d has also been examined. At room temperature smooth [4 + 2] cycloaddition reactions proceed to yield the azadiphosphabarrelenes 9a-d. While thermolyses of the barrelenes 9a-c in toluene under reflux lead exclusively to the starting compounds 8a-c by a [4 + 2] cycloreversion process with concomitant elimination of 2, pyrolysis of 9d under the same conditions furnishes the 1,3-diphosphinine 10, also unambiguously identified by analysis of its tpentacarbonyltungsten complex 11.
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    Control of Asymmetry Through Conjugate Addition Reactions (1998)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 2051-2061 
    Details
    ISSN: 1434-193X
    Keywords: Asymmetric synthesis ; Chiral auxiliaries ; Michael addition ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The use of nucleophiles bearing chiral centres, the use of α,β-unsaturated systems with the chirality at the γ position and the presence of chiral ligands or other chiral mediators are the more common sources for the control of asymmetry through Michael addition reactions.
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  • 124
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    Generation and Diels-Alder Trapping of 4,5-Bis(bromomethylene)-4,5-dihydrothiazole (1998)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 2047-2050 
    Details
    ISSN: 1434-193X
    Keywords: Quinodimethanes ; Cycloadditions ; Thiazole derivatives ; Quinones ; Regioselectivity ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Treatment of 4,5-bis(dibromomethyl)thiazole (1a) with sodium iodide in DMF led to 4,5-bis(bromomethylene)-4,5-dihydrothiazole (2a). Trapping the latter in situ with dienophiles afforded directly the aromatized cycloadducts. Starting with 5-hydroxynaphthoquinone or its 2- and 3-bromo derivatives 6 gave a mixture of the tetracyclic quinones 10 + 11 from which the 1,6-regioisomer 10 predominates. Using acrylate dienophiles gave 6-substituted benzothiazoles 13 as the major products. The regiochemistry of the cycloadditions between 2a and naphthoquinones 6 agrees with the predictions of the frontier molecular orbital theory. In contrast, the regioselectivity observed from 2a and acrylate dienophiles 12, similar to that previously obtained with 5-bromomethylene-4-methylene-4,5-dihydrothiazole (2b), is opposite to that predicted and could be better accomodated by a competitive Michael addition followed by a cyclization-elimination step.
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  • 125
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    A General Route to the Monomeric Subunits of the Macrotetrolides - A Short Synthesis of Methyl Nonactate (1998)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 2073-2078 
    Details
    ISSN: 1434-193X
    Keywords: Sultones ; Intramolecular Diels-Alder reaction ; Desulfurization ; Heterocycles ; Actic acids ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A highly stereoselective and flexible sultone route to actic acids, the monomeric subunits of the macrotetrolides, has been developed and exemplified for nonactic acid (2a). Due to the extensive application of tandem transformations, only six steps were needed to secure methyl nonactate (20) from furan.
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  • 126
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    The Thermally and Photochemically Induced Ring Opening of cis-3,4-Dichlorocyclobutene and trans-3,4-Dichlorocyclobutene: New Insights from a Matrix-Spectroscopic Study (1998)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 2063-2072 
    Details
    ISSN: 1434-193X
    Keywords: Matrix isolation ; Ring opening ; Flash pyrolysis ; Photochemistry ; Cyclobutenes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The thermally induced ring opening of 1 and 5 proceeds with high stereospecifity in a conrotatory fashion in agreement with the Woodward-Hoffmann rules. Upon flash pyrolysis of 1 the matrix-isolated (Xe, 12 K) products 2a and 2b were found, whereas the corresponding reaction of 5 yielded 3a and 3b. The s-cis conformers 2b and 3b were identified for the first time by comparison of the experimental and calculated (BLYP-6-311G*) IR absorptions. A non-stereospecific photochemical reaction could be observed if matrix-isolated (Ar or Xe, 12 K) 1 was excited directly with λ = 193 nm. Products of the allowed disrotatory pathway as well as those of the forbidden conrotatory reaction were found, a behaviour that corresponds with the known photochemistry of cyclobutenes. A surprising reaction was found if 1 and 5 were irradiated in a xenon matrix with λ 〉 270 nm. The precursors, which were photostable in an argon matrix, opened the ring in a conrotatory fashion, the expected pathway for a thermal reaction. In this case the light is absorbed by the solid xenon in a cooperative process with the precursor molecules. A detailed discussion of the possible energy transfer mechanisms is given. Most probably, a hot ground-state reaction of vibrationally excited 1 and 5 occurs, although the reaction of the radical cations cannot be excluded.
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  • 127
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    Diastereo- and Enantioselective δ-H Abstraction in the Solid State of 1-Benzoyl-8-benzylnaphthalene - Absolute Asymmetric Synthesis Due to a Chiral Crystal Environment (1998)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 2079-2082 
    Details
    ISSN: 1434-193X
    Keywords: Asymmetric synthesis ; Hydrogen transfer ; Photochemistry ; Solid-state chemistry ; Topochemistry ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Due to the matrix effect of the crystal lattice, irradiation of ketone 1 yields 2 diastereoselectively as the main product (97% de). Furthermore, the chiral crystal environment in single crystals of 1 (space group P212121) also renders the reaction enantioselective (86% ee). Both enantiomers of alcohol 2 could be produced, depending on which enantiomorphic form of the chiral crystal was irradiated. As the ketone 1 is achiral and the chiral induction is caused exclusively by physical influences, this reaction represents a further example of an absolute asymmetric synthesis.
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    Naphthalene Isotopomers from Isotope-Labelled Phenyl-Annelated 1,3-Hexadien-5-ynes Facilitate an Evaluation of Competing Radical Cycloisomerization Pathways (1998)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 2135-2142 
    Details
    ISSN: 1434-193X
    Keywords: Pyrolysis ; 1,3-Hexadien-5-ynes ; Cyclization, radical ; 13C, D labelling ; Naphthalene isotopomers ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The thermal cycloisomerization of the isotope-labelled 1-phenyl-1-buten-3-ynes 1 {including the [3-13C,4-D]1-phenyl-1-buten-3-yne (6) and the [4-D]1-phenyl-1-buten-3-yne (9) formed as intermediates} has been studied. The investigations were performed in a quartz flow system at a temperature of 650 °C (1, 6) [and over the range 625-750 °C for (9)] at a reaction time of 0.3 s in the presence of different diluent gases (H2, N2, N2-toluene). Spectroscopic analyses of the naphthalene isotopomers formed allow the evaluation of competing radical reaction channels in addition to reactions occuring by electrocyclic and carbene-like ring closure.[1] A mechanistic analysis for the conversion of 1 undoubtedly suggests a predominant reaction course via phenyl-type radical intermediates (1c/6c), followed by their exocyclization to the indenylcarbenyl radicals 1f/6f and the homoallyl-like rearrangement of the latter to the 1,2-dihydronaphthyl radicals 1i/6i at 650 °C. With increasing temperature, other competing reactions (endocyclizations of vinyl- and phenyl-type radicals as well as neophyl-like rearrangements of the indenylcarbinyl radicals 1f/6f) gain in importance.
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    Oxidative Addition of α-Bromoglycine to Palladium(0) and Platinum(0) Complexes: α-Metallated Amino Acids as Models for Intermediates in the Metal-Catalyzed Hydrogenation of Dehydroamino Acids (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 375-379 
    Details
    ISSN: 1434-1948
    Keywords: α-Metallated amino acids ; Palladium ; Platinum ; Oxidative addition ; α-Bromoglycinate ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Oxidative addition of methyl N-benzoyl-2-bromoglycinate to bis(dibenzylideneacetone)palladium, in the presence of 2,2′-bipyridyl, and to (Ph3P)2Pt(η2-C2H4) gives the α-metallated glycine esters 1a and 2a. Abstraction of bromide from 1a, 2a, using AgSbF6 or AgBF4, affords the cationic C,O-chelate complexes [(bpy)Pd-CH(CO2Me)NHC(Ph)O]+ (1b,c) and [(Ph3P)2Pt-CH(CO2Me)NHC(Ph)O]+ (2b), respectively, featuring coordination of the amide O atom. The complexes 1b and 2b have been characterized by X-ray diffraction.
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  • 130
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    Mono- and Dinuclear Carbonyl Complexes of (1,4,7-Trimethyl-1,4,7-triazacyclononane)rhodium(I): Facile Migration of a C(O)OMe Ligand at a Dinuclear Rh(μ-CO)2Rh Core (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 401-406 
    Details
    ISSN: 1434-1948
    Keywords: Rhodium ; N ligands ; Carbonyl complexes ; Methoxycarbonyl ; Dinuclear complexes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The reaction of 1,4,7-trimethyl-1,4,7-triazacyclononane (Cn*) with [{(CO)2Rh(μ-Cl)}2] in methanol at 0°C, followed by the addition of NH4PF6, results in the formation of the mononuclear carbonyl complex [Cn*Rh(μ-CO)2]PF6 ([1]PF6), the dinuclear carbonyl complex [Cn*Rh(μ-CO)3RhCn*](PF6)2 {[2](PF6)2} and the dinuclear methoxycarbonyl complex [Cn*Rh(C(O)OMe)(μ-CO)2RhCn*]PF6 ([3]PF6). The reaction of [2](PF6)2 with NaOMe results in formation of [3]PF6 by the attack of the methoxide at a bridging carbonyl. Treatment of [3]PF6 with NH4PF6 regenerates [2](PF6)2, thus showing that the methoxylation of [2](PF6)2 is reversible. The structures of [1]PF6, [2](PF6)2 and [3]PF6 have been determined by single-crystal X-ray diffraction. For [3]PF6 an unprecendented facile, reversible, migration of the C(O)OMe ligand between the two rhodium centres of the Rh(μ-CO)2Rh core is observed.
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    Carbonyl and Benzene Complexes of Lithium: Transition-Metal-Like Behaviour of Lithium in Organolithium Compounds (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 537-541 
    Details
    ISSN: 1434-1948
    Keywords: Lithium ; (Benzene)lithium complex ; (Carbonyl)lithium complex ; Ab initio calculations ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Complexes of CO and aromatic compounds were believed to be an exclusive domain of transition metals caused by their ability of backbonding to these ligands. But recently, (benzene)lithium and (carbonyl)lithium complexes were characterized by X-ray structure analysis and IR spectoscopy. In order to determine geometries of the complexes and the bonding energies of the benzene and CO molecule to the organolithium starting compound suitable models were chosen in combination with high-level ab initio calculations. For the carbonyl derivative a reaction enthalpy of -8 kcal/mol was found while the interaction with benzene reached unexpectedly -21 kcal/mol. This underlines the ability of lithium to act like a transition metal in subcoordinated organyl compounds without having d orbitals available for bonding.
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    Formation of Metallocene-Stabilized Planar-Tetracoordinate Carbon Compounds by a Protonation Route (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 551-558 
    Details
    ISSN: 1434-1948
    Keywords: Planar-tetracoordinate carbon ; Zirconocene ; Acetylide complex ; Selective protonation ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Bis(alkynyl)zirconocene and -hafnocene complexes 4 react with (butadiene)zirconocene or -hafnocene, respectively, to yield the binuclear σ,π-acetylide bridged complexes [(Cp2M)2(μ-C≡C-R)2] 7 (M = Zr, Hf; R = CH3, C2H5, or CH2Ph). The complexes 7 are selectively protonated upon treatment with N,N-dimethylanilinium tetraphenylborate or tetrakis(pentafluorophenyl)borate to yield the dinuclear metallocene cation complexes [(Cp2M1)(μ-RCC1-H)(μ-C≡C-R)M2Cp2+] 13 (M1 = M2 = Zr, a-c; M1 = Zr, M2 = Hf, h; M1 = M2 = Hf, i) that contain a planar-tetracoordinate carbon atom (C1-H) bearing a hydrogen substituent. Complex 13a was characterized by X-ray diffraction. It reveals an agostic interaction of the C1-H moiety with the M2Cp2 unit. The planar-tetracoordinate carbon unit C1-H of 13a exhibits 13C/1H NMRchemical shifts of δ = 161.0 and -0.11 and a coupling constant of 1JCH = 103 Hz. Selective protonation of (μ-alkynyl)bis(group 4 metallocene) complexes containing other additional bridging ligands provides a rather general synthetic entry to planar-tetracoordinate carbon containing complexes of this type: [Cp2M1(μ-C≡C-CH3)(μ-Cl)M2Cp2] (10a-c, M1, M2 = Zr, Hf) and[Cp2M1(μ-C≡C-CH3)(μ-CH3)M2Cp2] (11a,b) selectively add a proton from [(HNMe2Ph)+(BAr4)-] at carbon atom C1 of the acetylide ligand to yield the corresponding “anti-van′t Hoff/LeBel complexes” [Cp2M1(μ-CH3CC1-H)(μ-X)M2Cp2+] (13d-g and k, X = Cl, CH3), respectively.
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    Synthesis and Structure of the First Carbyne Complex Functionalized Zwitterionic α-Carbenium Phosphinates [Tp′(CO)2M ≡ C-P(O)2-C(NR2)2] (M = Mo, W; R = Me, Et) (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 579-582 
    Details
    ISSN: 1434-1948
    Keywords: Carbyne complexes ; Molybdenum complexes ; Oxidations ; Tungsten ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Oxidation of the phosphaalkenyl-substituted carbyne complexes [Tp′(CO)2M≡C-P=C(NR2)2] (1a: M = Mo, R = Me; 1b: M = W, R = Me; 2a: M = Mo, R = Et; 2b: M = W, R = Et) with molecular dioxygen cleanly affords the orange carbyne complexes [Tp′(CO)2M≡C-P(O)2C(NR2)2] [3a: M = Mo, R = Me; 3b: M = W; R = Me; 4a: M = Mo, R = Et; 4b: M = W, R = Et; Tp′ = HB(3,5-Me2HC3N2)3], which are functionalized at the methylidyne carbon atom by an α-carbenium phosphinate moiety. The novel compounds have been characterized by IR, 1H-, 13C-, and 31P-NMR spectroscopy. In addition, the molecular structure of 4a has been determined by a single-crystal X-ray structure analysis.
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    Syntheses and Structures of Molecular Diphenolatonickel Compounds Containing Trimethylphosphane Ligands (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 621-627 
    Details
    ISSN: 1434-1948
    Keywords: Nickel ; Oxidation ; Phenols ; Structure ; Dynamic NMR spectroscopy ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The reaction of substituted phenols and dioxygen with Ni(PMe3)4 yields the low-spin tetracoordinate diphenolatonickel compounds Ni(OAr)2(PMe3)2 [ArOH = 2-tert-butylphenol (1), 2-tert-butyl-4-methylphenol (2), 2-tert-butyl-6-methylphenol (3), 2,4-di(tert-butyl)phenol (4), 2-tert-butyl-4-methoxophenol (5), 2-chloro-4-tert-butylphenol (6), 2-isopropylphenol (7), 3-tert-butylphenol (8)]. As is revealed by variable temperature 1H- and 13C-NMR spectroscopy the complexes constitute a mixture of two isomers, each of which can be observed separately at lower temperatures when interconversion is slower. An additional 6-carbaldehyde function transforms the phenolate into a chelating ligand, giving rise to a high-spin hexacoordinate compound Ni(OAr)2(PMe3)2 (9). X-ray crystal-structure determinations of 2 and 3 show a trans square-planar structure, and that of 9 shows a trans octahedral arrangement of donor atoms P2O4. Bulky substituents in the 3- or 4-position, or non-demanding substituents in the 2-position, are less effective in stabilizing molecular diphenolatonickel complexes.
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    Pyrazole as a Donor Function in Neopentane-Based Tripod Ligands RCH2C(CH2pyrazol-1-yl)3-n(CH2PR2)n - Synthesis and Coordination Chemistry (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 675-692 
    Details
    ISSN: 1434-1948
    Keywords: Tripodal ligands ; Pyrazolyl donors ; Molybdenum ; Hydrogen bonds ; 2D-NMR ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The chlorine functions of CH3C(CH2Cl)3, 1, may be replaced by pyrazolyl (pz) as well as imidazolyl (im) residues under the conditions of nucleophilic substitution leading to tripodal ligands CH3C(CH2X)3, X = pz, 2; X = im, 3. As a means of introducing two nitrogen donors and one phosphorus donor into a tripod ligand, substitution of the Br and OMs functions in O(CH2)2C(CH2Br)(CH2OMs), 8, by nitrogen nucleophiles and subsequent cleavage of the oxetane ring by a phosphide nucleophile to give HOCH2C(CH2PPh2)(CH2X)2 has been developed, furnishing 10a (X = pz) and 10d (X = NEt2), respectively. For the synthesis of 10a, K-pz was used as the nucleophile, while 10d was prepared using azide in the initial step, which then had to be transformed into NEt2 in two subsequent steps. The nucleophugic functions of the oxetane 8 undergo selective substitution by K-pz and KPPh2 in THF to produce O(CH2)2C(CH2PPh2)(CH2pz), 9b. Phosphide cleavage of the oxetane function leads to HOCH2C(CH2PPh2)(CH2PR2)(CH2pz), R = Ph, 10b; R = 3,5-Me2(C6H3), 10c. - The tris(pyrazolyl) tripod ligand 2 reacts with (MeCN)3Mo(CO)3to give 2 · Mo(CO)3(MeCN), 12a, in which only two of the three donor functions are coordinated. Upon reaction with 10a, the same reagent gives 10a · Mo(CO)4, 12b, with one pyrazolyl coordinated and the other involved in intramolecular hydrogen bonding to the CH2OH function (N···H-O distance 280 pm). Blocking of the OH function of 10a by etherification, i.e. to form EtOCH2C(CH2PPh2)(CH2pz)2, 11, does not dramatically affect the coordination capabilities with 11 · Mo(CO)3(MeCN), 12d, being formed upon treatment with (MeCN)3Mo(CO)3. Again only one pz function is coordinated to the metal. Bidentate coordination by two phosphorus donors of 10c is observed in 10c · Mo(CO)3(MeCN), 12d. The dangling arm pz donor function and the CH2OH group are intermolecularly hydrogen-bonded in this case. When the bulky P[3,5-Me2(C6H3)]2 substituent of 10c is replaced by the less sterically demanding PPh2 donor in 10b, η3-coordination is finally observed with the formation of 10b · Mo(CO)3, 13. The coordination capabilities of the new ligands are rationalized in terms of the size (six-, seven-, and eight-membered rings) and interference of the chelate cycles. All compounds have been characterized by the usual analytical and spectroscopic methods, with a complete assignment of the NMR data achieved by a combination of 2D-NMR techniques in some cases. The structures of the coordination compounds have additionally been deduced by X-ray methods.
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    Imidotitanium Complexes with Heteroallylic Ligands: Synthesis and Solid-State Structure (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 87-91 
    Details
    ISSN: 1434-1948
    Keywords: Imido complexes ; Titanium ; Heteroallylic ligands ; Benzamidinate ligands ; Diiminophosphinate ligands ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Treatment of Ti(NtBu)Cl2(py)2 (1, py = pyridine) with bulky heteroallylic ligands in a 1:1 molar ratio affords the monosubstituted derivatives [PhC(NSiMe3)2]Ti(NtBu)Cl(py)2 (2), [MeOC6H4C(NSiMe3)2]Ti(NtBu)Cl(py) (3), and [Ph2P(NSiMe3)2]Ti(NtBu)Cl(py) (4). Similarly, 2:1 reactions afforded the disubstitution products [PhC(NiPr)2]2Ti(NtBu)(py) (6) and [Ph2P(NSiMe3)2]2Ti(NtBu) (7). The bis(pyridine) adduct Ph2P(NSiMe3)2Li(py)2 (5) was isolated as a by-product during the preparation of 4. The molecular structures of 7 has been established by X-ray crystallography.
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    The Molecular Structure of Some Transition-Metal Complexes with 1,2,3,4-Tetrazole-5-thiolate Anions (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 93-99 
    Details
    ISSN: 1434-1948
    Keywords: 2-Methyl-1,2,3,4-tetrazole-5-thiolates ; 2-Phenyl-1,2,3,4-tetrazole-5-thiolates ; Palladium ; Platinum ; Copper ; Silver ; Gold ; Molecular structures ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The molecular structures of nine transition metal tetrazolethiolates have been determined by X-ray structure determinations. The ligand is invariably coordinated through its sulfur atom to the metal center [M = PdII, CuI, AgI, AuI, AuIII, and Hg]. The M-S-C bond angles vary considerably, but this cannot be correlated with variations in the C-S bond lengths. Intermolecular association occurs for Ph3PAu(SCN4Me) via Au-S contacts, leading to dimeric strands in the solid state. The copper compound (Ph3P)3Cu4(SCN4Me)4 (5), possesses a rather asymmetric structure: one Cu atom is tricoordinated by 3 sulfur atoms, the other three are tetracoordinated by P and N as well as by S atoms.
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    Halogenation of Bis(phosphonio)isophosphindolide Salts: Oxidation versus Substitution (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 101-106 
    Details
    ISSN: 1434-1948
    Keywords: Phosphorus heterocycles ; Halogens ; Oxidations ; Electrophilic aromatic substitutions ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Bis(phosphonio)isophosphindolide iodide 1[I] reacts with an equimolar amount of I2 to yield the trihalide 1[I3], while treatment of 1[X] (X = Br, OTf) with excess Br2 furnishes the dibromophosphonium salt 6c[X]. The bromo-substituted bis- (phosphonio)isophosphindolide cations 5a and 5b are identified as intermediates in this reaction; 5b[Br] is also obtained in pure form by reaction of 6c[Br] with Zn or NEt3. Reaction of 1[OTf] with one equivalent of PhICl2 (7) affords the dichlorophosphonium salt 8a[OTf], which undergoes further substitution reactions in the presence of excess 7 and reacts with Me3SiI to give a mixture of 1[OTf] and I2 rather than a substitution product 9[OTf]. The results of a crystal-structure determination of 8a[OTf] are reported and the mechanistic aspects of the different oxidation/substitution reactions are discussed.
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  • 139
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    Electronic Resource
    Synthesis, Structure, and Dynamic Behaviour of Transition Metal Chelate Complexes with Atropisomeric Dithioether Ligands (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 113-118 
    Details
    ISSN: 1434-1948
    Keywords: S ligands ; Transition metals ; Fluxionality ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The preparation and characterization of RhI, PdII, and PtII complexes with chiral C2-symmetrical dithioether ligands derived from 1,1′-binaphthalene-2,2′-dithiol (BINAS) are reported. All complexes are fluxional in solution at room temp. Interconversion between the stereoisomers can take place through conformational equilibration of the chelate ring, and/or inversion of configuration at the stereogenic sulfur. In the solid state the palladium derivative of Me2BINAS shows a twisted chair conformation of the chelate ring, with both methyl groups in equatorial positions.
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  • 140
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    Electronic Resource
    Construction of One-Dimensional Multicomponent Molecular Arrays: Control of Electronic and Molecular Motions (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 1-14 
    Details
    ISSN: 1434-1948
    Keywords: One-dimensional multicomponent arrays ; Energy- and electron transfer ; Molecular motions ; Ruthenium ; Osmium ; Terpyridines ; Bis-terpyridines ; Bis-cyclometallating ligands ; Porphyrins ; Copper(I) rotaxane ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Transition metals are powerful three-dimensional templates, which can gather various functionalized ligands and orient them in a precise fashion so that complex multicomponent molecular systems can be obtained without constructing covalently-assembled edifices. The compounds thus prepared exhibit precise chemical or physical functions, which are governed by the design of the system. The construction of one-dimensional molecules around ruthenium(II) or osmium(II), using rigid ligands attached to the desired electroactive species, leads to systems that are able to undergo charge separation after photonic excitation. In other related compounds, a ruthenium(II)-based chromophore is, for example, connected to an osmium(II) complex by means of rod-like bridging ligand, thereby ensuring strict control over the Ru···Os distance. By tuning the length and the electronic properties of the bridge, one can control the efficiency of the electronic energy transfer between the two chromophores. In particular, the use of a bis-cyclometallating ligand is very conducive to energy transfer and allows the observation of this process up to a Ru…Os distance of ≈20 Å. By combining the building blocks of these inorganic systems with appropriate porphyrins, long-range (centre-to-centre distance between the donor and the acceptor porphyrins ≈30 Å) and relatively long-lived photoinduced charge separation has been demonstrated. Finally, with copper(I) as the template, compounds of the rotaxane family are obtained, which consist of a coordinating ring threaded by a string-like component. If this acyclic fragment is end-functionalized by two bulky stoppering groups and if it incorporates two different coordination sites (a bi- and a terdentate chelate site), novel dynamic properties are observed. The movement of a given fragment of the molecule is triggered by changing the metal oxidation state. This one-dimensional motion of the ring along the string on which it is threaded is controlled by redox manipulation, resulting in a primitive molecular machine.
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  • 141
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    The Structural Chemistry of Aziridino- and Azetidinosilanes (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 107-112 
    Details
    ISSN: 1434-1948
    Keywords: Silicon ; Aminosilanes ; Aziridine ; Azetidine ; Molecular conformation ; Configuration determination ; Nitrogen ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In a continuation of structural investigations of poly(amino)silanes, a series of silicon derivatives of aziridine and azetidine have been prepared. Analogies with the isoelectronic phosphorus ylide species and the high barrier to inversion at nitrogen in small N heterocycles were suggestive of steeply pyramidal and rather rigid configurations at the N atoms in the title compounds. Tetrakis(N-aziridino)silane (1) and tetrakis(N-azetidino)silane (2) have been synthesized from SiCl4 and LiN(CH2)x (x = 2, 3). Compound 1 is also formed when LiN(CH2)2 and HSiCl3 are used as starting materials, but with free aziridine a non-volatile product (1a) is obtained. In neither case could any trace of HSi[N(CH2)2]3 be detected. In contrast, RSiCl3 (R = Me, Ph) could readily be converted into the corresponding tris(N-aziridino)silanes (3, 4) by treatment with excess aziridine. Tris(N-azetidino)silane (5) was accessible from HSiCl3 and excess azetidine, but the product was found to contain an unknown impurity. In order to determine the local symmetry and the dynamics of the aziridine rings, 1H-NMR spectra were recorded at low temperature (-80°C). No splitting of the signals was observed, indicating that the inversion barriers are extremely low, even in the highly strained three-membered heterocycles. Nevertheless, single-crystal X-ray diffraction studies of the N-triphenylsilyl derivatives of aziridine (6) and azetidine (7) revealed an aziridinyl group with a steeply pyramidal configuration at nitrogen in 6 (sum of the angles at N 313.32°), and an azetidinyl group with a flat geometry in 7 (sum of the angles at N 350.96°). The Si-N bond is significantly shorter in 7 as compared to that in 6.
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  • 142
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    Electronic Resource
    Five- and Six-Coordinate Nitrogen in Azaborane Clusters (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 143-153 
    Details
    ISSN: 1434-1948
    Keywords: Azaboranes ; Six-coordinate nitrogen ; Deltahedral clusters ; Cluster opening ; Cluster closure ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In the majority of known azaboranes NaBbHc and their derivatives, the coordination number of the nitrogen atoms within the cluster does not exceed the classical values of 3 or 4. In the azaboranes closo-NB9H10, nido-NB10H13, and closo-NB11H12 and in their derivatives, however, the nitrogen atoms are 5- or 6-coordinate and thus represent a novel bonding situation. The synthesis, structure, and reactivity of these azaboranes are reviewed in this article.
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  • 143
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    Electronic Resource
    [(Arene)(Diene)Fe] and [(Arene)(Diazadiene)Fe] Complexes: Preparation, Reactivity, and Catalytic Properties (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 119-126 
    Details
    ISSN: 1434-1948
    Keywords: Arene complexes ; Catalysis ; Diazadiene complexes ; Iron ; Metal vapour ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Two different routes to novel [(diene)(η6-2,6-dimethylpyridine)Fe] complexes are reported, both of which utilize metal vapour reactions. The presence of two small substituents on the 2,6-position of pyridine is essential for the η6-coordination of the heterocycle. Investigations on the reactivity and stability of the [(diene)(η6-arene)Fe] complexes are presented, including those of the benzene, phosphinine, and pyridine derivatives. These investigations give some hints to the relevant factors for determining the interaction between an iron atom and a π-coordinated neutral arene ligand, and their modification by a nitrogen or a phosphorus atom. Selective substitution of the 1,5-cyclooctadiene (COD) ligand of [(COD)(η6-arene)Fe] complexes by some 1,4-diaza-1,3-diene (DAD) derivatives is possible in the case of the benzene or phosphinine arene ligands, and [(DAD)(η6-arene)Fe] complexes are formed, but all DAD derivatives tested so far cause the complete disintegration of [(COD)(η6-2,6-dimethylpyridine)Fe]. [(DAD)(η6-arene)Fe] complexes exhibit a catalytic potential, which was evaluated by experiments on the catalytic cyclodimerization of 1,3-butadiene in the presence of [(Et2AlOEt)2] as a co-catalyst. This reaction yields up to 92% of 1,5-cyclooctadiene, and an almost quantitative butadiene conversion is possible in the presence of less than 0.1% of the catalyst. Structural investigations on [(N,N′-bis(cyclohexyl)ethylenediimine)(η6-toluene)Fe] 5a reveal some details of the Fe-DAD interaction. An effective electron back-donation from occupied iron d-orbitals into the π*-LUMO of the DAD is indicated.
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  • 144
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    Electronic Resource
    A Spectro- and Conductometric Study of the Reaction of Imidazoline-2-selone Derivatives with Bromine - Crystal Structure of 1,2-Bis(3-methyl-4-imidazolin-2-ylium dibromoselenanide)ethane (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 137-141 
    Details
    ISSN: 1434-1948
    Keywords: Bromine ; Imidazoline-2-selone ; Hypervalent Se compounds ; Dications ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The oxidative addition of Br2 to the imidazoline-2-selone derivatives 1a-c has been studied by spectrophotometric and conductometric techniques. The experimental results clearly indicate that this reaction involves the dications 2a-c, containing an Se-Se bond, as intermediates in the formation of the hypervalent 10-Se-3 selenium compounds 3a-c containing the Br-Se-Br group. The crystal structure of 1,2-bis(3-methyl-4-imidazolin-2-ylium dibromoselenanide)ethane (3c), a new stable hypervalent 10-Se-3 compound, is also reported.
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  • 145
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    Electronic Resource
    Light-Induced Codimerisation of Acetylene and Olefins at a Binuclear Tungsten Complex (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 127-135 
    Details
    ISSN: 1434-1948
    Keywords: Tungsten ; Ditungsten complexes ; Acetylene complex ; Tritungsten complex ; W-W single bond ; W-W triple bond ; Photochemistry ; C-C bond formations ; Olefins ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: [W2(η5-C5H5)2(CO)4(μ-η2:2-C2H2)] (1) and ethylene (A) react when irradiated with UV light at 253 K predominantly to [W2(η5-C5H5)2(CO)3(μ-η1:4-C4H5)(μ-H)] (3A), [W2(η5-C5H5)2(CO)4(μ-η1:3-C4H6)] (4A), and thermolabile [W2(η5-C5H5)2(CO)3(η4-C4H6)] (5A). Similarly, propene (B), 1-butene (C), and (E)-2-butene (D) yield mixtures of [W2(η5-C5H5)2(CO)3(μ-H)(μ-η1:4-1,3-dien-1-yl)] (3B, 3 C, 3D), [W2(η5-C5H5)2(CO)4(μ-η1:3-C4H5R] (4B, 4C), and [W2(η5-C5H5)2(CO)2(μ-η1:2-CO)(η4-1,3-diene) (5B, 5 C, 5D). With B and C also thermolabile [W2(η5-C5H5)2(CO)3(μ-η2:2-C2H2)(η2-C2H3R)] (2B, 2C) are formed. A by-product of the reaction of 1 with D is [W(η5-C5H5)(CO)(H){η4-(E)-C5H7CH3}], which is generated in two diastereomeric forms (6, 6′). In contrast, 1 yields no complexes with (Z)-2-butene (E) which contain ligands formed from coordinated acetylene and the olefin. From the reaction mixture only trinuclear [W3(η5-C5H5)3(CO)5(μ-η1:2-C2H3)] (7) was isolated, an alicyclic complex with a W-W single and a W-W triple bond. The crystal and molecular structures of 5D and 7 were determined by X-ray structure analysis. The constitutions of the other complexes were ascertained by IR and 1H-NMR spectroscopy.
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  • 146
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    Electronic Resource
    An Unusual Ring Structure of an Oligomeric Oxotitanium Alkoxide Carboxylate (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 159-161 
    Details
    ISSN: 1434-1948
    Keywords: Oxo clusters ; Titanium ; Metal alkoxides ; Sol-gel processes ; Carboxylato complexes ; Solid-state structures ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Ti9O8(OPr)4(methacrylate)16 was obtained by the reaction of Ti(OPr)4 with an excess of methacrylic acid and analyzed by X-ray diffraction. The compound consists of a ring of nine [TiO6] octahedra linked by six μ2- and only two μ3-oxide bridges.
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  • 147
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    Electronic Resource
    Coordination Behaviour of the New Multidentate Ligand 3,5-Bis(dimethylaminomethyl)pyridine with Palladium(II) and Platinum(II) Metal Centres (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 163-168 
    Details
    ISSN: 1434-1948
    Keywords: Pyridine ligands ; Bidentate bridging ligands ; Palladium ; Platinum ; N ligands ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The synthesis of the new potentially tridentate ligand 3,5-bis(dimethylaminomethyl)pyridine (3) is described. Coordination chemistry of this ligand has been investigated with PdII and PtII precursor compounds. Both a bidentate bridging bonding motif and a monodentate bonding mode is observed. The latter compounds incorporate 3 by coordination through the pyridinic N atom only. The former complexes contain ligand 3 bonded to 2 metal centres by bridging through coordination of one trialkyl N donor atom and the pyridinic N atom. The solid-state structure of a ligand bridged Pd dimer has been elucidated by single-crystal X-ray diffraction and corroborates with the solid-state IR data that suggested a trans-PdCl2 unit was present.
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  • 148
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    Electronic Resource
    Magnetic Interaction in Dinuclear Triphos-Cobalt Complexes with Co···Co Separations of 8 and 10 Å (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 183-189 
    Details
    ISSN: 1434-1948
    Keywords: Tripodal ligands ; Cobalt complexes ; Bridging ligands ; Exchange coupling ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Weak antiferromagnetic exchange interactions are observed in two CoII dimers of the general formula [{(triphos)Co}2(μ-dicarboxylato)](BF4)2 where the dicarboxylate is the dianion of fumaric acid [3 ·(BF4)2] or terephthalic acid [4 ·(BF4)2] and triphos is the tridentate phosphorus ligand 1,1,1-tris(diphenylphosphanomethyl)ethane. In these complexes the metal ions are separated by 8 and 10 Å, as determined by X-ray crystallography. Insight into the interaction pathway is gained through molecular orbital calculations performed on model compounds. The influence of bridging-ligand distortions and the stereochemistry around the two cobalt centres is discussed.
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  • 149
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    A New and Easy Route to Polysilanylpotassium Compounds (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 221-226 
    Details
    ISSN: 1434-1948
    Keywords: Polysilanes ; Polysilyl anions ; Silylpotassium ; Silicon ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A method is presented for the synthesis of tertiary, secondary, and primary polysilylpotassium compounds. Reaction of potassium tert-butoxide, in either DME or THF, with a suitable precursor molecule, proceeds by cleavage of a trimethylsilyl- polysilanyl bond, and formation of trimethylsilyl tert-butyl ether and a polysilanylpotassium compound. This route allows easy and flexible access to a number of novel polysilanylpotassium compounds, avoiding the hitherto common use of poisonous mercury compounds.
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  • 150
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    Electronic Resource
    Homoleptic Organometallic Compounds of Zinc, Cadmium, and Mercury, Intramolecularly Stabilized by Amine Ligands (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 245-252 
    Details
    ISSN: 1434-1948
    Keywords: Alkylamines ; Arylamines ; Zinc ; Cadmium ; Mercury ; X-ray diffraction ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Homoleptic intramolecularly stabilized organozinc, -cadmium, and -mercury compounds MR2, with R bearing an amino function, have been synthesized from the corresponding metal dichlorides MCl2 and the lithium salts LiC6H4CH2NEt2-2 (1), LiC6H3(CH2NMe2)2-2,6 (2), LiC6H3(CH2NEt2)2-2,6 (3), (LiCH2CH2CH2)2NMe (4), and LiCH2CH2CH2NC5H10 (5). The crystal structures of Hg(C6H4CH2NEt2-2)2 (1c), [M(CH2CH2CH2)2NMe]2 [M = Zn (4a), Hg (4c)], and of M(CH2CH2CH2NC5H10)2 [M = Zn (5a), Cd (5b)] have been determined by X-ray diffraction. 4a and 4c form dimers with an unusual coordination number (three) of the central metal.
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  • 151
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    Synthesis and Spectroscopic Data of para-Substituted (3-Phenyl-2H-azaphosphirene)tungsten Complexes (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 257-261 
    Details
    ISSN: 1434-1948
    Keywords: Phosphorus heterocycles ; 2H-Azaphosphirene complexes ; Carbene complexes ; Tungsten ; Cyclizations ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: High-yield synthesis of para-substituted pentacarbonyl(3-phenyl-2H-azaphosphirene)tungsten complexes is reported, using a multi-step rearrangement reaction. Spectroscopic and mass-spectrometric data of these heterocyclic complexes are discussed; the 31P-NMR-chemical shifts clearly reflect the electronic influence of the para-phenyl substituents and the correlation with Hammett σp-constants is almost linear.
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  • 152
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    Electronic Resource
    Spectroscopic Evidence for Intramolecular MoVI(O2)····HO-C Hydrogen Bonding in Solution (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 275-281 
    Details
    ISSN: 1434-1948
    Keywords: Molybdenum ; Peroxo complexes ; Hydrogen bonds ; Catalysis ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The ring-opening reaction of epoxycyclohexane with 2-[3(5)-pyrazolyl]pyridine results in the formation of racemic trans-2-[3-(2-pyridyl)-1-pyrazolyl]cyclohexanol (1). Kinetic resolution with lipase B from candida antarctica gives the (1S,2S) enantiomer of 1, the solid-state structure of which was determined by X-ray crystallography, as an enantiomerically pure tridentate ligand. Investigation by NMR spectroscopy of the corresponding oxodiperoxomolybdenum complex 2, where 1 acts as a bidentate chelate, proves the formation of a weak intramolecular MoVI(O2)····HO-C bridge in CHCl3 solution. This H bonding is broken by solvents such as acetone, THF or DMF, which are capable of forming hydrogen bonds to alcohols. Intermolecular hydrogen bonds between the OH groups and molybdenum peroxo moieties are also found in the solid-state structure of 2, leading to a helical arrangement of the peroxo complexes.
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  • 153
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    Synthesis and Structure of the First η1-Borazine Complexes (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 291-293 
    Details
    ISSN: 1434-1948
    Keywords: Boron ; Iron ; Boryl complexes ; η1-Coordinated borazine ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A series of η1-borazine complexes were obtained by the reaction of trichloroborazine with Na[(η5-C5R5)Fe(CO)2]. The compounds [{(C5R5)(CO)2Fe}nCl3-nB3N3H3] (1a, n = 1, R = Me; 1b, n = 2, C5R5 = C5H4Me; 1c, n = 3, R = H) have one to three iron-boron σ bonds and Fe-B π-interactions can be ruled out from the spectroscopic and structural results. All new borazine complexes were isolated as orange crystalline solids and characterized by multinuclear NMR methods and IR spectroscopy. The structure of 1b in the crystalline state was also determined by a single-crystal X-ray study.
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  • 154
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    Group-13 Metal-Induced Coordination Variation of the Bis(2-pyridyl)amide Ligand in Solution and in the Solid State (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 311-317 
    Details
    ISSN: 1434-1948
    Keywords: Molecular recognition ; Amides ; Aluminium ; Thallium ; Structure elucidation ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Ligands containing aromatic nitrogen heterocycles play a leading role in the molecular self assembling processes that lead to macromolecular architectures. The inductive effect of various metal fragments on those building blocks has not yet been studied systematically. To evaluate this effect we synthesized the homologous series of Group-13 metal complexes [Me2AlPy2N] (1), [Me2GaPy2N] (2), [Me2InNPy2]2 (3), and [Me2TlNPy2]∞ (4) (Py = 2-NC5H4), and characterized them by low-temperature X-ray structure analysis and 15N-NMR spectroscopy in solution. The electronic equivalence of the central and the ring nitrogen atoms leaves the energetic hyperface of the anion quite flat, and the electron density is polarized according to the requirements of the metal. In the aluminum and the gallium complexes 1 and 2 the metal center is coordinated exclusively through the nitrogen atoms within the pyridyl rings. The complexes with these hard metals are close-contact ion pairs. In the indium complex 3 the cis-cis orientation gives rise to a dimeric structure, while the unprecedented cis-trans arrangement in the thallium compound 4 leads to a polymeric structure. The complexes 3 and 4 have to be regarded as separated ion pairs of Me2M+ cations and Py2N- anions without any covalent bonds between the anionic moiety and the dimethylmetal cations, even in the solid state. The series of complexes proves the bis(2-pyridyl)amide to be an excellent self-adapting ligand. These findings are substantiated by NMR-spectroscopic studies in solution. Not only do the steric requirements of N heteroaromatic ligands have to be considered in molecular self-assembling processes but also the inductive effect of the different metal fragments.
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  • 155
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    Diastereoselective Substitution of PR3 for CO in Carbene(dicarbonyl)cyclopentadienyl Complexes of Manganese - Synthesis of (SMn)- and (RMn)-[Cp(CO)(PR3)Mn=C(OR*)R′] Complexes (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 339-347 
    Details
    ISSN: 1434-1948
    Keywords: Carbene complexes ; Carbyne complexes ; Asymmetric synthesis ; Carbohydrates ; Chiral auxiliaries ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Chiral carbene complexes [Cp(CO)2Mn=C(OR*)Ph] (4a-e) were prepared by reaction of [Cp(CO)2Mn=C(OAc)Ph] (2) with HOR* [HOR* = 1,2:3,4-di-O-isopropylidene-D-galactopyranose (3a), 2,3,4,6-tetra-O-acetyl-D-galactopyranose (3b), 2,3,4,6-tetra-O-acetyl-D-glucopyranose (3c), (S)- (3d) and (R)-1,2-O-isopropylideneglycerol (3e)]. The replacement of a CO ligand with PTol3 in 4a-e proceeded diastereoselectively to give [Cp(CO)(PTol3)Mn=C(OR*)Ph] (5a-e). The diastereoselectivity increased in the order a, b, c, d: de = 8% (5a), 33% (5b), 70% (5c), 〉 96% (5d). For (R)-5d the isomer with the (S) configuration at manganese (SMn) was formed predominantly. For (S)-5d, only (RMn,S)-5d was detected (de 〉 96%). Photolysis of (R)-4d in the presence of phosphites or phosphanes afforded (SMn)-[Cp(CO)(PR3)Mn=C(OR*)Ph] [PR3 = P(OPh)3 (8), P(OMe)3 (9), P(OMe)2Ph (10), P(OMe)Ph2 (11), PPh3 (12), P(C6H4Cl-p)3 (13)] with a de 〉 96%. Photolysis of (S)-4d in the presence of P(OMe)3 gave (RMn,S)-9. Complex (R)-14 [related to (R)-4d] was obtained from [Cp(CO)2Mn=C(OAc)Tol-p] and 3d. Replacement of CO by PR3 in (R)-14 gave (SMn,R)-[Cp(CO)(PR3)Mn=C(OR*)Tol-p] [R = Tol-p (15), OMe (16), C6H4Cl-p (17)] with a de 〉 96%. In solution, the PTol3-substituted complex 5d is configurationally stable whereas the P(OMe)3 complex 9 epimerizes slowly at room temperature in CH2Cl2, Et2O, and THF within about one week.
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  • 156
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    The Reactions of R2Ga-GaR2 and R2In-InR2 [R = CH(SiMe3)2] with Protic Reagents: Substituent Exchange versus Cleavage of the Element-Element Bond (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 355-360 
    Details
    ISSN: 1434-1948
    Keywords: Gallium ; Indium ; Low-valent compounds ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Tetrakis[bis(trimethylsilyl)methyl]digallane(4) (1) with a Ga-Ga single bond and the corresponding diindane(4) 2 with an In-In single bond were treated with different protic reagents: tert-Butyl alcohol did not react with 1 at all, while phenol gave a mixture of unknown products, which could not be separated. The more acidic pentafluorophenol did not react as an acid, but C-F bonds were cleaved to form almost quantitatively the dimer (R2GaF)2 5, which was characterized by a crystal-structure determination. Water and 1 yielded the dimeric dialkylgallium hydroxide 6. The Ga-Ga bond was also cleaved by the reaction of 1 with durylthiophenol (duryl = 2,3,5,6-tetramethylphenyl), which gave two main products: R2Ga(SDuryl) 7 and RGa(SDuryl)2 8. In contrast, the chelating acid dibenzoylmethane reacted by means of a substituent exchange, with the release of two equiv. of bis(trimethylsilyl)methane for each formula unit of 1, to form 9, in which the Ga-Ga bond is retained and each chelating 1,3-diphenyl-1,3-propanedionato ligand is in a terminal position bonded to only one Ga atom, in more than 80% yield. The Ga-Ga bond is shortened [244.1(1) pm] compared to that in the starting compound tetraalkyldigallane(4) 1. The In-In bond of diindane(4) 2 is, however, cleaved in a similar reaction with dibenzoylmethane, and only the fragmentation product dialkyl(1,3-diphenyl-1,3-propanedionato)indium 10 could be isolated.
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  • 157
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    The Reaction of Potassium Polyselenides with [CpW(CO)3Cl] in DMF - Formation and Crystal Structure of [CpW(CO)3SeC(O)NMe2] and {[CpW(CO)3]2Se4} (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 397-400 
    Details
    ISSN: 1434-1948
    Keywords: Polychalcogenides ; Selenium ; Selenocarbamato complexes ; 77Se NMR ; Crystal structure ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The reactions of the potassium polyselenides „K2Se6” and „K2Se8” with [CpW(CO)3Cl] and 18-crown-6 in DMF lead to a mixture of the selenido complexes {[CpW(CO)3]2Se4} 1 and [(18-crown-6)K]+[CpW(Se4)2]- 3 and the Se-bonded selenocarbamato complex [CpW(CO)3SeC(O)NMe2] 2 in yields depending on the selenium content of the used potassium polyselenides („K2Se6” or „K2Se8”). A similar reaction in THF produces {[CpW(CO)3]2Se4} as the main product. X-ray structures of 1 and 2 were determined. In 1 the Se4-chain is bonded in a μ2-η1 fashion, with corresponding W-Se bond lengths of 264.0(1) and 264.3(1) pm. The Se-Se bond lengths lie in the range 232 to 237 pm. The first example of an η1 Se-bonded selenocarbamato ligand is observed in the crystal structure of 2, with a W-Se bond length of 263.1(1) pm. The 77Se-NMR data are compared with the corresponding data of related complexes.
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  • 158
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    Specific Chelate Tuning of the Substitution Kinetics of Platinum(II) Complexes in Aqueous Solution (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 389-396 
    Details
    ISSN: 1434-1948
    Keywords: Substitution mechanism ; Platinum ; Pressure dependence ; Kinetics ; Dinuclear complex ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Both reaction steps observed for the substitution of water by thiourea in the complexes [Pt(en)(OH2)2]2+ and [Pt(phen)(OH2)2]2+ (en = ethylenediamine, phen = 1,10-phenanthroline) were investigated under pseudo-first-order conditions using the stopped-flow technique. The substitution of the second water molecule in each complex was also studied under high pressure. The observed pseudo-first-order rate constants kobs (s-1) obeyed the equation k1,2obs= k1,2[tu] (tu = thiourea), where “1” and “2” refer to the first and the second substitution reactions, respectively. Kinetic parameters associated with the substitution process are: k1en (25.0°C, pH = 3.0, I = 0.1 M) = 25.6 M-1 s-1, ΔH# = 51 kJ mol-1, ΔS# = -48 J K-1 mol-1; k2en (same conditions) = 12.1 M-1 s-1, ΔH# = 30 kJ mol-1, ΔS# = -124 J K-1 mol-1, ΔV# = -7 cm3 mol-1; k1phen (25.0°C, pH = 1.0, I = 0.1 M) = 2900 M-1 s-1, ΔH# = 41 kJ mol-1, ΔS# = -41 J K-1 mol-1; k2phen (same conditions) = 1170 M-1 s-1, ΔH# = 37 kJ mol-1, ΔS#= -61 J K-1 mol-1, ΔV# = -5 cm3 mol-1. The temperature and pressure dependence of all the processes studied suggest an associative substitution mechanism. The hydroxo-bridged dinuclear complex [{Pt(phen)(μ-OH)}2]2+ is formed from [Pt(phen)(OH2)2]2+ in aqueous solution unless the solution is very dilute and highly acidic. The X-ray structure of [{Pt(phen)(μ-OH)}2](F3CSO3)2 · 2 H2O was determined. It belongs to the triclinic space group P1­ and has one formula unit in the unit cell. The unit cell dimensions are a = 7.126(5), b = 9.665(5), c = 12.774(7) Å; α = 71.85(5), β = 85.52(5), γ = 73.12(5) deg; V = 799.9(8) Å3. The structure was solved with the Patterson method and refined to R = 0.061. A square planar coordination of the platinum centers is observed, with no deviations from planarity but distortions due to the small bite angle of phen and the four-membered ring. No significant lengthening of the Pt-O bond [mean value: 2.03(1) Å] is observed in comparison with [{Pt(NH3)2(μ-OH)}2]2+.
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  • 159
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    Ethylene Polymerization with Hydridotris(pyrazolyl)boratoniobium Complexes as Precursors (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 425-428 
    Details
    ISSN: 1434-1948
    Keywords: Ethylene polymerization ; Group 5 metal complexes ; Hydridotris(pyrazolyl)borates ; Alkyne ligands ; Migratory insertion ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Substituted hydridotris(pyrazolyl)borato (Tp′) niobium complexes of the type [Tp′NbMe2(PhC≡CMe)] polymerize ethylene (under 1 atm, at room temp. and in toluene) when treated with an equimolar amount of B(C6F5)3. A clear relationship is observed between the stereoelectronic nature of the complex and catalytic activity. This is discussed on the basis of electrochemical data for the dichloro complexes [Tp′NbCl2(PhC≡CMe)], and the rates of alkyl migration in [Tp′Nb(Cl)(R)(PhC≡CMe)] (R = CH2Me, CH2SiMe3). For a given electron density at the metal, the bulky TpMe2,4-Cl yields a catalyst which is more than 6 times as active as the unsubstituted Tp based catalyst.
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  • 160
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    Synthesis and X-Ray Structures of Novel Lead(1+) and Indium(3+) Phosphazenide Complexes; Detailed 207Pb-NMR Spectra of the 207Pb-Labelled Dimeric Lead(1+) Species (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 437-444 
    Details
    ISSN: 1434-1948
    Keywords: Lead(1+) ; Indium(3+) ; Organylphosphanylamide complexes ; Phosphazene ; 207Pb-NMR spectra ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The reaction of PbCl2 with LiN(PPh2)2 (1) at -78°C affords the P-P coupled phosphazene Ph2P-N=PPh2-PPh2=N-PPh2 (2) as an oxidation product and, as a reduction equivalent, the novel lead(1+) complex [(Pb1+)2(μ-Ph2P···N···PPh2-)2](Pb-Pb) (3). The crystal structure determination of the red compound 3 shows a Pb-Pb bond length of 304.1(1) pm. The 31P- and 207Pb-NMR spectra of 3 are complicated due to the presence of a higher order spin system (AA′A′′A′′′X for the mono-207Pb isotopomer, AA′A′′A′′′XX′ for the bis-207Pb isotopomer). Simulations of the 31P and 207Pb spectra both on material with natural isotope abundance and on the 207Pb-labelled compound (3*) reveal a large Pb,Pb coupling constant of 7708 Hz, indicative of a covalent Pb-Pb bond. - Though InCl3 is diagonally related to PbCl2, no significant redox process is observed in the reaction between InCl3 and 1. The yellow crystals of [In3+(Ph2P···N···PPh2-)3] (4) that are obtained were also investigated by X-ray analysis. These show a propeller-like configuration of the three four-membered chelate rings with indium(3+) as the centre.
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  • 161
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    Boryl- and Bridging Boryleneiron Complexes from Aminodichloroboranes (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 465-468 
    Details
    ISSN: 1434-1948
    Keywords: Boron ; Iron ; Boryl complexes ; Borylene complexes ; Iron-boron bond ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Depending on the nature of the amino group bound to the boron atom, the reactions of various aminodichloroboranes R2NBCl2 with Na[(η5-C5R′5)Fe(CO)2] yield either boryl or bridging borylene complexes of iron. The compounds [(C5R′5)(CO)2Fe{BCl(NR2)}] (1a, C5R′5 = C5H5, R = Me; 1b, C5R′5 = C5H4Me, R = Me; 1c, C5R′5 = C5Me5, R = Me) and [(η-BNR2)(μ-CO){(C5R′5)Fe(CO)}2] (2a, C5R′5 = C5H5, R = SiMe3; 2b, C5R′5 = C5H4Me, R = SiMe3) were isolated as orange (1a-c) or red (2a, b) crystalline solids, and characterized by multinuclear NMR methods and IR spectroscopy. The structures of 1c and 2b in the crystalline state were determined by single-crystal X-ray studies.
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  • 162
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    Synthesis and Structural Characterization of Gold(I) and Silver(I) Complexes of the Multidonor Ligand 2-(Phenacylthio)pyridine - Crystal Structures of [(AuPPh3){py{SCH2C(O)Ph}-2}](ClO4) and [(AgPPh3)(OClO3){py{SCH2C(O)Ph}-2}] (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 511-516 
    Details
    ISSN: 1434-1948
    Keywords: Gold(I) ; Silver(I) ; S-donor and N-donor ligand ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The ligand properties of 2-(phenacylthio)pyridine towards gold(I) and silver(I) have been investigated. From the reactions of the ligand with acetone solutions of [M(PPh3)(acetone)]ClO4 (M = Ag, Au) under various experimental conditions, complexes [(AuPPh3)n{py{SCH2C(O)Ph}-2}](ClO)n, and [(AgPPh3)n(OClO3)n{py{SCH2C(O)Ph}-2}](n = 1-3) have been obtained. The crystal structures of the complexes [(AuPPh3){py{SCH2C(O)Ph}-2}]ClO4 and [(AgPPh3)(OClO3){py{SCH2C(O)Ph}-2}] have been determined by X-ray diffraction. In the cationic gold complex the metal is linearly coordinated to nitrogen and phosphorus, whereas the corresponding silver complex displays a trigonal planar geometry with pyridine, phosphane and perchlorato ligands.
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  • 163
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    Synthesis of the First Lanthanoid(II) Pyrazolate Complex by Redox Transmetallation from Thallium and Mercury Reagents (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 543-545 
    Details
    ISSN: 1434-1948
    Keywords: Lanthanoid(II) complexes ; Ytterbium ; Thallium ; η2-Pyrazolate complexes ; Diphenylmercury ; Redox transmetallation ; X-ray crystal structure ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Ytterbium metal reacts with thallium(I) 3,5-diphenylpyrazolate, or with diphenylmercury and 3,5-diphenylpyrazole (Ph2pzH) in tetrahydrofuran or 1,2-dimethoxyethane (DME) giving, after appropriate isolation, the first lanthanoid(II) pyrazolate complex, [Yb(Ph2pz)2(DME)2]. The molecular structure reveals eight coordinate ytterbium(II) with two cisoid η2-3,5-diphenylpyrazolate and two chelating 1,2-dimethoxyethane ligands.
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  • 164
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    Syntheses of 3-Phenyl-2H-Azaphosphirene Chromium and Molybdenum Complexes - First Evidence for Reaction Intermediates (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 571-574 
    Details
    ISSN: 1434-1948
    Keywords: Phosphorus heterocycles ; 2H-Azaphosphirene complexes ; Carbene complexes ; Chromium ; Molybdenum ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The synthesis of 3-phenyl-substituted 2H-azaphosphirene pentacarbonylchromium and pentacarbonylmolybdenum complexes is reported. New information on the rearrangement cascade, which finally leads to 2H-azaphosphirene ring formation, has been obtained through isolation of a reactive intermediate. A comparison of the 13C-, 15N-, 31P-NMR, and UV/vis spectroscopic data and single crystal X-ray structural data of 3-phenyl-substituted 2H-azaphosphirene chromium, molybdenum, and tungsten complexes is presented.
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  • 165
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    A New Class of Oligonuclear Platinum-Thallium Compounds with a Direct Metal-Metal Bond - 3. Unusual Equilibria in Aqueous Solution (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 565-570 
    Details
    ISSN: 1434-1948
    Keywords: Equilibrium ; Metal-metal bond ; Stability constants ; Platinum ; Thallium ; NMR ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A new series of four binuclear platinum-thallium cyano compounds containing a direct and unsupported by ligands metal-metal bond has been prepared in aqueous solution. These compounds are represented by the formula[(NC)5Pt-Tl(CN)n-1](n-1)- (n = 1-4 for compounds I, II, III IV, respectively) and [(NC)5Pt-Tl-Pt(CN)5]3- (for compound V). The oligonuclear complexes are synthesised according to the reaction mPt(CN)42- + Tl3+ + nCN- █[PtmTl(CN)4m+n]3-2-n. Thus, there occurs a change of the coordination number of the Pt center from four (square planar) to six (octahedral). Consequently, the formation of binuclear platinum-thallium cyano compounds involves at least two steps: (i) formation of metal-metal bond and (ii) formation of (NC)5Pt- unit by a cyanide transfer process. - The complexes exist in an equilibrium, which also includes the parent complexes Pt(CN)42- and Tl(CN)n3-n (n = 0-4), and can be controlled by varying the cyanide concentration and/or pH of the solution. The stability constants of the compounds βN =[PtmTl(CN)4m+n3-2m-n{[Pt(CN)42-]m · [Tl3+] · [CN-]n} have been determined by means of multinuclear NMR (195Pt, 205Tl): logβN = 19.9±0.4, 30.7±0.3, 38.6±0.3, and 44.8±0.2 for I, II, III and IV(m = 1, n = 1-4), and 32.1±0.3 for V(m = 2, n = 2), respectively, (in 1 M NaClO4 as ionic medium, at 25 oC). To our knowledge, the present work constitutes the first detailed equilibrium study of metal-metal bonded compounds; it indicates that also other cluster formation reactions described in the literature may represent real equilibria.
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  • 166
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    P-Alkylated (1S,2S)-Cyclopentane-1,2-diylbisphosphanes with Four Stereogenic Centers and Some Group 10 Metal(II) Complexes Containing the (1S,2S)-C5H8[P(CH3)C8H15-cyclo]2 Ligand (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 597-603 
    Details
    ISSN: 1434-1948
    Keywords: Chirality ; P ligands ; Nickel ; Palladium ; Platinum ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Radical-initiated P-H addition of (1S,2S)-C5H8(PH2)2 to cycloalkenes gave bis(secondary phosphanes), (1S,2S)-C5H8[P(H)CnH2n-1-cyclo]2 (n = 5-8), as mixtures of RP,RP′, SP,SP′, and RP,SP′ diastereomers. The three diastereomers of the peralkylated chiral P2 ligand (1S,2S)-C5H8[P(CH3)C8H15-cyclo]2 and its complexes with NiCl2, PdI2, and PtI2 were prepared. The structures of [(1S,2S)-C5H8{P(CH3)C8H15-cyclo(R)}2NiCl2] · [(1S,2S)-C5H8{P(CH3)C8H15-cyclo-(S)}2NiCl2],(1S,2S)-C5H8{P(CH3)C8H15-cyclo-(R)}2PdI2, and (1S,2S)-C5H8{P(CH3)C8H15-cyclo-(R)}2PtI2 were determined by X-ray diffraction.
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  • 167
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    The Conformational Flexibility of Oxidized Cytochrome c Studied through Its Interaction with NH3 and at High Temperatures (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 583-591 
    Details
    ISSN: 1434-1948
    Keywords: Cytochrome c ; Hyperfine shift ; Magnetic susceptibility anisotropy ; NMR spectroscopy ; Heme proteins ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The binding of ammonia to oxidized horse heart cytochrome c has been studied by 1H-NMR, EPR, and CD spectroscopy at pH = 8.0. The affinity constant of the ligand is in the range 1.5-4 M-1. The 1H-NMR spectra of the heme group have been found to be similar to those of the high-pH forms, high-temperature forms, and cyanide adduct of the Met80Ala mutant of S. cerevisiae iso-1-cytochrome c. The assignment of a number of signals has led to the determination of the values of the magnetic anisotropy and of the orientation of its axes. The latter are similar to those of the Met80Ala cyanide derivative. The assignment of the high-temperature species has been further pursued during this research. The analysis of the NMR data of the NH3 adduct leads to the conclusion that substitution of Met80 at high pH or high temperature occurs through a ligand with cylindrical symmetry. This supports the suggestion that Met80 is substituted by a lysine at high pH.
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  • 168
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    C-C Coupling Reactions of (Sulfene)ruthenium Complexes with Enolates (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 605-611 
    Details
    ISSN: 1434-1948
    Keywords: Enolates ; Nucleophilic additions ; Ruthenium ; S ligands ; Sulfenes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Sulfene complexes [CpRu(PR′3)2(RHC=SO2)]PF6 (2a-d) are obtained from the corresponding sulfur dioxide complexes 1a-c and diazomethane or -ethane. Reaction of [CpRu(dppm)(SO2)]Cl (1d) and phenyldiazomethane gives the chlorobenzylsulfinato complex [CpRu(dppm)(SO2CHPhCl)] (3). Alternatively, 2a may be synthesized by sulfur dioxide addition to the carbene complex [CpRu(dppm)(CH2)]PF6 (5) which, in turn, is obtained from the corresponding methyl complex [CpRu(dppm)(CH3)] and [Ph3C]PF6. Treatment of 2a-d or 3 with the enolates of cyclic 2-methyl-1,3-diketones, methyl malonates, open-chain cyano or β-oxo esters, and cyclic β-oxo esters gives the C-C coupling products 6a, b, 7a-e, 8a-c, 9a-c in high yields and, in one case, with high diastereoselectivity as well. The functionalized sulfinate ligands thus formed may be alkylated and subsequently removed from the metal center by ligand substitution with acetonitrile. After MeCN/SO2 exchange, the ruthenium complex can be recycled.
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  • 169
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    Replacement of One CO Unit in Dicarbonyl(η5-cyclopentadienyl)cobalt Derivatives by Bis(tert-butylsulfonyl)acetylene (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 629-632 
    Details
    ISSN: 1434-1948
    Keywords: Alkyne complexes ; Carbonyl complexes ; Cobalt ; CO replacement ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The reaction of dicarbonyl(η5-cyclopentadienyl)cobalt (1) and some of the Cp-ring substituted congeners with bis(tert-butylsulfonyl)acetylene (BTSA) results in the replacement of one CO group by the BTSA moiety. The variation of the yields and reaction times indicates a dependence of the reactivity of 1-6 with BTSA as a function of substituents. X-ray investigations of the products show that the alkyne unit is strongly bound to the metal.
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  • 170
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    2,3,4-Tricarba-nido-hexaboranes(7) with a Bridging B-Ethyl-B Moiety (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 633-637 
    Details
    ISSN: 1434-1948
    Keywords: Ab initio calculations ; Boron ; Carboranes ; NMR spectroscopy ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Hydroboration of diethyl(1-propynyl)borane 1 with tetraethyldiborane(6) in the presence of a catalytic amount of trimethyl- or tributyltin chloride gave two new organo-substituted carboranes 6 and 7 with 2,3,5-tricarba-nido-hexaborane(7) and 2,3,4-tricarba-nido-hexaborane(7) skeletons, respectively, along with polymeric material and the known organo-substituted 1-carba-arachno-pentaborane(10) (3) and pentaethyl-1,5-dicarba-closo-pentaborane(5) (4). Selective 11B(5,6) decoupled 13C-NMR spectra indicate an unprecedented B(5)-ethyl-B(6) bridge in 7. This structure is supported by the agreement between experimental and calculated 11B- and 13C-chemical shifts on a model compound 7d with methyl groups in the 1,2,3,5,6-positions and an ethyl group bridging B(5) and B(6).
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  • 171
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    How to Derive Force Field Parameters by Genetic Algorithms: Modelling tripod-Mo(CO)3 Compounds as an Example (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 693-702 
    Details
    ISSN: 1434-1948
    Keywords: Genetic Algorithms ; Force field calculations ; Refinement of force field parameters ; Tripod metal compounds ; Conformational analysis ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Force field parameters used to describe the conformation of coordination compounds involving transition metals are generally derived by a trial-and-error procedure, until a somehow satisfying agreement between the calculated and observed conformations of a few members of a class of related compounds is reached. It is shown in this paper that a more general and less biased alternative is available, applicable to many structures at a time. Genetic Algorithms will effectively optimize force field parameters in an automatic way, on the basis of a potentially exhaustive set of all the structural data available for a given class of compounds. The feasibility of this procedure has been demonstrated by the derivation of force field parameters describing the conformational behaviour of tripod-Mo(CO)3 compounds [tripod= RCH2C(CH2X)(CH2Y)(CH2Z), X,Y,Z = PR′R′′)] by simultaneous optimization based on the structure of ten individual molecules. With the force field parameters relevant to the organic part of these compounds taken from MM2*, the parameters involving contributions from the Mo center were refined. The agreement between observed and calculated structures is characterized by an rms deviation of around 0.3 Å for the ten structures contained in the data base. To assess the validity of this approach, the conformational space of CH3C(CH2PPh2)3Mo(CO)3 was explored exhaustively. A contour diagram representing the relative energy of the molecule with respect to the rotational positions of its phenyl groups was found to effectively reproduce the scatter of these conformational parameters as earlier derived from an analysis of 82 relevant compounds. - As a further assessment, the conformational space of CH3C[CH2P(o-Tol)2]3Mo(CO)3, which was not included in the data base, has been analyzed. It is found that the structure corresponding to the global energy minimum corresponds to that observed in the crystal with an rms deviation of only 0.3 Å. The novel approach to problems of this type - Genetic Algorithms had not previously been applied in this context - thus appears promising.
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  • 172
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    Four-Coordinate Group-14 Elements in the Formal Oxidation State of Zero - Syntheses, Structures, and Dynamics of [{(CO)5Cr}2Sn(L2)] and Related Species (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 703-720 
    Details
    ISSN: 1434-1948
    Keywords: Germanium ; Tin ; Lead ; 119Sn NMR ; Dynamic NMR ; Salt metathesis ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The sodium salts Na2[{(CO)5M}2EX2] (M = Cr, Mo, W; E = Ge, Sn, Pb; X = Cl, I, OOCCH3) react with 2,2′-bipyridine (bipy) to form neutral compounds [{(CO)5M}2E(bipy)] (E = Sn: 1a-1c; E = Ge: 3a; E = Pb: 4). 1,10-Phenanthroline (phen) analogues of compounds 1a-1c and 3a [{(CO)5M}2E(phen)] (E = Sn: 1d-1f, E = Ge: 3b) are as well accessible. The 2,2′-bipyridine ligand in 1 may be formally replaced by two pyridine (py) ligands resulting in [{(CO)5M}2Sn(py)2] (1g: M = Cr, 1h: M = W). The bis-bidentate ligand 2,2′-bipyrimidine (bpmd) is found to coordinate just one [{(CO)5M}2Sn] entity in [{(CO)5M}2Sn(bpmd)] (2b: M = Cr, 2c: M = W). The biimidazolato (biim) ligand binds two [{(CO)5Cr}2Sn] moieties in [{(CO)5Cr}2Sn(biim)Sn{Cr(CO)5}2]2-, 2a. It is shown by 1H-NMR that the pyrimidine entities in these compounds (2b, 2c) are able to rotate by a full 180° turn-around with respect to one another. This process must involve complete de-coordination of at least one of the two nitrogen donors in again at least one of the chelate cycles, the activation energy for this process being around 60 kJ/mol. By 119Sn-NMR spectroscopy of almost all of the tin compounds described it is shown that equilibria between [{(CO)5M}2Sn(L2)] and [{(CO)5M}2Sn(L)] + L exist in all cases. From the temperature dependence of the δ values it is concluded that the activation barriers for this association/dissociation process is below 10 kJ/mol. The structures of all new compounds are documented by X-ray analyses and all compounds are characterized by the usual analytical and spectroscopical techniques.
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  • 173
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    The π-Electron-Accepting Ability of the Boron Atom in Ethynylboranes and Related Compounds - An Approximate Weight Computation for Resonance Structures⋆ (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 733-744 
    Details
    ISSN: 1434-1948
    Keywords: Aminoboranes ; Ab initio calculations ; Valence-bond theory ; Resonance structures ; Alkynes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A theoretical analysis was performed to quantify the π-electron-accepting ability of the boron atom in ethynylboranes. An expansion technique was employed which permits to obtain a set of localized bonding schemes and their weights from a delocalized molecular orbital determinantal wavefunction. The derived manifold of bonding schemes is close to the classical resonance hybrid used in organic chemistry (valence-bond description). We quantified the π-electron transfer into the empty π-orbital of the boron atom by investigating nine model compounds where substituents with π-electron-donating ability are adjacent to a boron atom. This led to an ordering of the substituents according to their electron-donating ability towards boron. The boron atom hesitates to accept π-electrons from the ethynyl group in ethynylboranes in particular when good π-donors like amino groups are present. The π-electron donation from the vinyl group to the adjacent boron centre is slightly stronger than from the ethynyl group. Nitrogen lone-pair electrons are easily transferred to a neighbouring boron centre. Bonding schemes and their weights are in line with computed bond lengths and rotational barriers. Moreover, our theoretical results rationalize previous NMR and X-ray experiments and are in line with the reactivity of related compounds. It is demonstrated that bond lengths alone do not necessarily correlate with the degree of π-bonding and should be discussed with caution. The analysis is substantiated by showing that weights for covalent bonding schemes, as obtained from the simple restricted closed-shell MO determinant, correlate with bond strengths. Furthermore, a correlation of bonding-scheme weights with quantities based on the fragment orbital approach is presented. This novel correlation elucidates molecular properties which determine the extent of the π-electron transfer to the boron atom and permits a quantitative interpretation and prediction of intramolecular π-bonding.
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  • 174
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    Rh(I)-Catalysed Asymmetric Hydrosilylation using New Oxazoline Ligands with Potential Charge-transfer Properties (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 783-788 
    Details
    ISSN: 1434-1948
    Keywords: Enantioselective hydrosilylation ; Oxazoline ligands ; Charge-transfer ; 4,4-Bipyridine derivatives ; 2,5-Dimethoxyacetophenone ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Novel N′-methylated 2-(oxazolin-2-yl)-4,4′-bipyridinium salts, bearing a chiral oxazoline moiety, were tested in the Rh(I)-catalysed enantioselective hydrosilylation. After coordination to rhodium these electron-attracting ligands are supposed to exhibit charge-transfer effects with electron-donating substrates. Therefore, a new catalytic hydrosilylation reaction with 2,5-dimethoxyacetophenone as an electron-rich substrate was developed. The results were compared with those of the non-methylated 2-(oxazolin-2-yl)-4,4′-bipyridine and related ligands. In addition, the new ligands and Rh(I)-complexes were tested in the hydrosilylation of acetophenone.
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  • 175
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    Three-Dimensional Assemblies of Gold Colloids in Nanoporous Alumina Membranesast; (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 807-812 
    Details
    ISSN: 1434-1948
    Keywords: Gold colloids ; Self-assembly ; Nanoporous alumina ; Three-dimensional organization ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Examples of a new class of three-dimensionally arranged gold colloids have been prepared in the nanoscale pores of alumina membranes. Immobilization of the colloid particles was achieved by a modification of the inner walls with alkoxysilanes Y-(CH2)x-Si(OR)3 and Y-(CH2)x-SiR(OR)2 bearing suitable functional groups (Y = NH2, SH), followed by anchoring of the colloids by self-assembly onto the modified surface. This procedure gives tight and stable ensembles of colloids on the walls. TEM analyses revealed uniform and random colloidal dispersions on the walls in the form of sub-monolayers without any aggregation. UV/Vis spectra of the filled membranes showed an absorption maximum at ca. 525 nm arising from an excitation of the plasmon resonance of the gold colloids. The dimensions of the pores can be “tuned” and given the diverse range of different colloids available, routes to novel catalysts and sensors can be envisaged.
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  • 176
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    Synthesis, Structure, and Properties of Osmium Complexes Containing [Os(′S4′)] and [Os(′S2′)2] Fragments (′S4′2- = 1,2-Bis(2-mercaptophenylthio)ethane(2-), ′S2′2- = 1,2-Benzenedithiolate) (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 819-826 
    Details
    ISSN: 1434-1948
    Keywords: S ligands ; P ligands ; Osmium ; Solvent effects ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In search for osmium complexes with sulfur-dominated coordination spheres that potentially bind and activate or stabilize nitrogenase relevant small molecules, several osmium-sulfur complexes containing 1,2-bis(2-mercaptophenylthio)ethane(2-) (′S4′2-) and benzenedithiolate (′S2′2-) ligands were synthesized. [OsII(PR3)2(′S4′)] [R = Ph (1), Et (2)], [OsIV(PR3)2(′S2′)2] [R = Et (3), Pr(4), Me(5), Ph(6)], [OsIV(PCy3)(′S2′)2] (7), (PHCy3)[OsIII(′S2′)2] (8a), (NMe4)[OsIII(′S2′)2] (8b), and (NBu4)2[OsIV(′S2′)3] (9b) were obtained in reactions starting from commercially available osmium compounds and the sulfur and phosphane ligands. The presence or absence of reducing solvents strongly influenced these reactions. Octahedral (3), (4), and (PHCy3)2[OsIV(′S2′)3] (9a) were characterized by X-ray structure analysis, leading to the conclusion that despite the high oxidation state of the osmium centers, innocent dithiolate ligands are present. The stabilization of the OsIV centers is traced back to S→M π donation. Close inspection of 1 and 2 revealed a large influence of the phosphane ligands on the stability of OsII thioether complexes. While 1 is reasonable stable, 2 readily gives 3 and ethylene via intramolecular ′S4′2- ligand reduction and OsIII→ OsIV oxidation. UV-Vis spectra of 3-5 indicate phosphane dissociation in solution leading to pentacoordinate [Os(PR3)(′S2′)2] complexes. This was confirmed by the synthesis of pentacoordinate [Os(PCy3)(′S2′)2] (7).
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    Synthesis of Silylborazines and Their Utilization as Precursors to Silicon-Containing Boron Nitride⋆ (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 855-859 
    Details
    ISSN: 1434-1948
    Keywords: Borazines ; Silyl borazines ; Oligomers ; Pyrolysis ; Ceramics ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The reactions of LiSi(SiMe3)3 with Cl(Me)2B3N3(Me)3, Cl2(Me)B3N3(Me)3, (ClBNMe)3, and (ClBNH)3 result in the formation of molecular species (Me3Si)3Si(Me)2B3N3(Me)3, [(Me3Si)3Si]2(Me)B3N3(Me)3, [(Me3Si)3SiBNMe]3, and [(Me3-Si)3SiBNH]3. The new compounds have been characterized by spectroscopic techniques, and a single-crystal X-ray diffraction analysis for [(Me3Si)3SiBNMe]3 has been completed. The monomer (Me3Si)3Si(Cl)2B3N3H3 was also prepared and combined with (Me3Si)2NH in hexane to form an organic solvent soluble oligomer. Pyrolysis of this oligomer provides composites containing BN and an SiXNYCZ phase that suppresses the crystallization of BN.
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  • 178
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    (1S,2S)-Cyclopentane-1,2-diyl-bis(phosphonous dichloride), (1S,2S)-C5H8(PCl2)2 - A Versatile Optically Active Reagent (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 885-887 
    Details
    ISSN: 1434-1948
    Keywords: Chirality ; P ligands ; Synthetic methods ; Triphosgene ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Treatment of (1S,2S)-C5H8(PH2)2 (1) with OC(OCCl3)2 gave (1S,2S)-C5H8(PCl2)2 (2) as the first example of an optically active bis(phosphonous dichloride). 2 was converted to (1S,2S)-C5H8(PX2)2 [PX2 = P(OMe)2 (3), P(OPh)2 (4), P[OCH-(Me)Et-(S)]2 (5), P[2-OC10H6C10H6O-2′-(R)] (6), P(NC4H8O-cyclo)2 (7), P(C6H11-cyclo)2 (8)] by reactions with oxygen, nitrogen, and carbon nucleophiles.
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    Di-, Tri-, and Tetranuclear Cyclobutenylidene Complexes (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 1225-1234 
    Details
    ISSN: 1434-1948
    Keywords: Vinylidene complexes ; Cyclobutenylidene complexes ; Bridging ligands ; Cycloadditions ; Cross-coupling ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Pentacarbonyl(dimethylvinylidene)chromium, [(CO)5Cr=C=CMe2] (1), reacts with the butadiynyl complexes [Cp(CO)2FeC≡CC≡CR] [2; R = SiMe3 (a), nBu (b), Ph (c)] and [Cp(CO)(PPh3)FeC≡CC≡CSiMe3] (3a) by regiospecific cycloaddition of the Cα≡Cβ bond of the butadiynyl complexes to the C=C bond of 1 to form the 1,3-heterobinuclear cyclobutenylidene complexes 4a-c and 5a with an alkynyl substituent at C-2 of the bridging ring. Desilylation of the 2-C≡CSiMe3 substituent in 4a and 5a with tetrabutylammonium fluoride affords the 2-C≡CH-substituted complexes 6 and 7. Complex 4a reacts with HNMe2 and HN(CH2)5 by substitution of NR2 for the 3-Fe(CO)2Cp fragment to form the corresponding 3-aminocyclobutenylidene complexes 10 and 11. Sequential reactions of 4a with [nBu4N]F and nBu3SnNEt2 give the trinuclear 2-C≡CSnnBu3-substituted complex 12. Coupling of 12 with C6H4I2-p yields the 2-C≡CC6H4I-p-substituted complex 13. Coupling of 7 with C6H4I2-p yields a mixture of the mono-coupling product 14 and the tetranuclear C≡C-C6H4-C≡C-bridged bis(cyclobutenylidene) complex 15. Coupling of 7 with trans-[(Et3P)2MCl2] in the presence of CuI/[Pd(PPh3)4] gives the trinuclear 2-C≡C-M(PEt3)2X-substituted complexes 16 (M = Pd, × = I) and 17 (M = Pt, × = Cl). The spectroscopic data as well as the results of the X-ray-structural analysis of 5a indicate strong electronic communication between the metal centers. In the solid state, 5a exhibits a “butterfly” conformation.
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    Novel Nine-Membered Titanaheterocycles - Structure, ab initio Calculations, and Preparative Use towards the Selective Synthesis of Substituted Cyclopentanols (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 1253-1262 
    Details
    ISSN: 1434-1948
    Keywords: Cyclizations ; Cross-coupling ; Ab initio calculations ; Titanium ; Metallacycles ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Reactions of Cp2Ti(CO)2 (3) with two equivalents of α,β-unsaturated ketones 4 yield the novel titana-2,9-dioxacyclonona-3,7-dienes 5. Cross-coupling of 3 with two different ketones 4 and 6to give 7 can be achieved under certain reaction conditions. Hydrolysis of 5 or 7 may generate diketones 9, cyclopentanols 10/11, or cyclopentenes 12/13, depending on substituents and conditions. The X-ray crystal structure of 5a, the first nine-membered bis(η5-cyclopentadienyl)-substituted titanaheterocycle containing carbon, is presented. Ab initio calculations were performed for 5a and for titana-2-oxacyclopentene 1, a conceivable intermediate in the coupling reaction.
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    Cation Stabilities, Electrophilicities, and “Carbene Analogue” Character of Low Coordinate Phosphorus Cations (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 1087-1094 
    Details
    ISSN: 1434-1948
    Keywords: Phosphenium cations ; Cation stabilities ; Electrophilicity ; Carbene homologues ; Computer Chemistry ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The stabilities of low coordinated phosphorus cations can be expressed in the frame of the HSAB concept by the transferred charge density Δq(N) which a cation receives upon formation of a donor-acceptor adduct with a Lewis base N. This concept allows to differentiate between relative stabilities towards different reaction partners, and to compare the electrophilicities of phosphenium ions to those of isoelectronic carbenes and silylenes. An analysis of substituent influences on Δq(H) in cations [P(R)2]+suggests an increasing stabilizing power of substituents in the series R = Cl 〈 CH3 〈 OH, SH 〈 NH2. The same ordering was derived from isodesmic hydride transfer reactions. Interpretation of population analyses suggests that the individual substituent contributions to cation stabilities result from a balance between π-donation into the empty p(P) orbital and electrostatic stabilization by polar P-R σ-bonds. A further stabilizing effect, which is of similar magnitude as in isoelectronic carbenes or silylenes, may arise from cyclic π-conjugation between a diaminophosphenium fragment and an adjacent double bond. Substituent effects influence further the nature of the frontier orbitals of phosphenium ions, resulting in orbital sequences which resemble those of carbenes, allyl anions, or phospholides, respectively. The absence of frontier orbital related changes in reactivity patterns suggests that in all reactions, including metal complex formation, phosphenium ions behave as purely electrophilic rather than ambiphilic species.
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    The Aluminum-Nitrogen Bond in Monomeric Bis(amino)alanes: A Systematic Experimental Study of Bis(tetramethylpiperidino)alanes and Quantum Mechanical Calculations on the Model System (H2N)2AlY (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 1095-1114 
    Details
    ISSN: 1434-1948
    Keywords: Aminoalanes ; Alanes ; Ab initio calculations ; 27Al-NMR spectroscopy ; Structure elucidation ; Substituent effects ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Reactions of metallated nucleophiles MIY [Y = OR, SR, NR2, PR2, AsR2, CR3, Si(SiMe3)3, R = organyl, H] with bis(2,2,6,6-tetramethylpiperidino)aluminum halides [tmp2AlX, (X = Cl, Br, I)] offer facile access to a variety of bis(amino)alanes of the type tmp2AlY. As indicated by 27Al-NMR spectroscopy, mass spectrometry and X-ray crystal structure determina-tions, all of these compounds are monomeric in the solid state, in solution, and in the gas phase. Even Al-E single bonds (E = Si, P, As etc.) that are not commonly encountered are stabilized by the supporting tmp fragments. The results of a systematic analysis of the bonding parameters determined for the tmp2AlY compounds, combined with a quantum mechanical study on model compounds (H2N)2AlY, not only reveal the presence of a highly polar Al-N bond, but at the same time rule out AlN-pp(π) bonding, in contrast to the situation in the analogous tmp2BY compounds. It is shown that the Al-N bond length depends on the acidic character of the protic species HY: the shorter d(Al-N), the less basic is Y.
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    Preparation, Structure and Reactivity of 2-Chloro-, 2-Fluoro- and 2-Iodo-2,3-dihydro-1H-1,3,2-diazaboroles (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 1145-1152 
    Details
    ISSN: 1434-1948
    Keywords: Boron ; Diazaboroles ; Halogens ; Isocyanides ; Heterocycles ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A series of differently substituted 2-chloro-, 2-fluoro- and 2-iodo-2,3-dihydro-1H-1,3,2-diazaboroles have been prepared by various methods. 1,3-Di-tert-butyl-2-fluoro-2,3-dihydro-1H-1,3,2-diazaborole (3a), 1,3-di-tert-butyl-2-chloro-2,3-dihydro-1H-1,3,2-diazaborole (5a), 1,3-bis(2,6-dimethyl-phenyl)-2-chloro-2,3-dihydro-1H-1,3,2-diazaborole (5b), 2-chloro-4,5-dimethyl-1,3-dineopentyl-2,3-dihydro-1H-1,3,2-diazaborole (5c), and 1,3-di-tert-butyl-2-iodo-2,3-dihydro-1H-1,3,2-diazaborole (6a) were formed from the corresponding lithiated Z-1,2-diaminoethenes, by treatment with BF3·OEt2, BCl3, or BI3 in n-hexane. Compounds 3a, 5a, and 5b are also available by sodium amalgam reduction of the adduct (tBu)(BF3)N=CH-CH=N(BF3)(tBu) (2a), and the borolium salts [RNa=CH-CH=Nb(R)BCl2]X (Na-B) (4a: R = tBu, X = BCl4 and 4b: R = 2,6-Me2C6H2, X = Cl) respectively. The iodo derivative (2,6-Me2C6H2)-Na-CH=CH-Nb(2,6-Me2C6H2)BI (Na-B) (6b) was synthesized in a redox reaction between the 1,4-diazabutadiene 1b and BI3. The novel compounds were characterized by 1H-, 11B- and 13C-NMR spectroscopy, as well as by an X-ray structure analysis of 6b.Supporting information for this article is available on the WWW under http://www.wiley-vch.de/contents/jc_2005/1998/98047_s.pdf or from the author.
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    New P,N-Chelate Ligands Based on Pyridyl-Substituted Phosphaferrocenes (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 1163-1168 
    Details
    ISSN: 1434-1948
    Keywords: Chelates ; P,N ligands ; Phosphaferrocene ; Catalysis ; Heterocycles ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The new pyridyl-substituted phosphaferrocene ligands 3 and 6 are prepared by addition of lithiated pyridine or α-picoline to 2-formyl-3,4-dimethylphosphaferrocene (1). The ligands 3 and 6 react with [Cp*RuCl]4 in THF to give the P,N-chelate complexes [Cp*RuCl·3] (9) and [Cp*RuCl·6] (10) with high diastereoselectivity. Addition of monodentate ligands like CO or PPh3 to the complexes leads by displacement of the Ru-bound pyridyl group to the respective carbonyl or phosphane complexes with monodentate P-coordinated phospha-ferrocene ligands. Reaction of the ligand 6 with [(C3H5)PdCl]2 and NH4PF6 gives the seven-membered chelate complex [(C3H5)Pd·6]PF6 (13) which was characterized by X-ray diffraction. The ligands 3 and 6 were tested in the palladium-catalyzed asymmetric alkylation of 1,3-diphenylallyl acetate.
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    Formation of a Constrained-Geometry Ziegler Catalyst System Containing a C1 Instead of the Usual Si1 Connection Between the Cyclopentadienyl and Amido Ligand Components (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 1153-1162 
    Details
    ISSN: 1434-1948
    Keywords: “Constrained-geometry” Ziegler catalysts ; Cp/amido zirconium complex ; 6-Aminofulvene deprotonation ; Ethene polymerization ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 6-Amino-6-methylfulvene (4) is cleanly N-acylated by treatment with pivaloylchloride/triethylamine to give the fulvene (C5H4)=C(CH3)NHCOCMe3 (5c). Treatment of 4 with trimethylchlorosilane similarly yields the mono-N-silylated fulvene (C5H4)=C(CH3)NHSiMe3 (7). Both 5c and 7 are cleanly doubly deprotonated e.g. by treatment with LDA to give ligand systems [(C5H4)C(=CH2)NR]Li2 [8a (R = COCMe3) and 8b (R = SiMe3), respectively]. Their treatment with MCl4 · 2 THF (M = Ti, Zr) yield the spiro-metallocenes [(C5H4)C(=CH2)NR]2M (9, 10). Complex 10a (M = Zr, R = COCMe3) was characterized by X-ray diffraction. The reaction of 8a with (Et2N)2ZrCl2 in THF gives rise to the formation of [(C5H4)C(=CH2)NCOCMe3]Zr(NEt2)2 (11) (70 % isolated), and the reaction of 8b with (Et2N)2ZrCl2 yields [(C5H4)C(=CH2)NSiMe3]Zr(NEt2)2 (12) (76 % isolated). Treatment of complex 12 with an excess of methylalumoxane (MAO) in toluene solution results in the generation of an active homogeneous Ziegler catalyst for the polymerization of ethene. A comparison with the usually employed [(Me5C4)SiMe2NCMe3]ZrCl2/MAO “constrained-geometry” Ziegler catalyst system reveals a similar catalyst activity and performance of this novel type of a C1-bridged “constrained-geometry” catalyst as it is exemplified by the [(C5H4)C(=CH2)NSiMe3]ZrX2 (12)/MAO combination.
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  • 186
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    Electronic Resource
    The Acid-Induced Rearrangement of 1-Hydroxyalkyltris(trimethylsilyl)silanes (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 177-181 
    Details
    ISSN: 1434-1948
    Keywords: Silanes ; Rearrangements ; Polysilanes ; Hypersilylalcohols ; 1,2-Trimethylsilyl migration ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In the presence of strong acids, such as HCl or H2SO4, 1-hydroxyalkyltris(trimethylsilyl)silanes (Me3Si)3Si-C(OH)R1R2 (1a-f) isomerize by 1,2-Me3Si/OH exchange to give the trimethylsilylmethylsilanols (Me3Si)2Si(OH)-C(SiMe3)R1R2 (4a-f) [R1,R2: a: Me, Me; b: H, 4-MeC6H4; c: H, 4-iPrC6H4; d: H, Mes; e: H, 2-Me2NC6H4; f: H, 2,4,6-(MeO)3C6H2]. A mechanism for the isomerization is proposed. In the case of the reaction of 1d with sulfuric acid, the silylsulfate (Me3Si)2Si(OSO3H)-C(SiMe3)HMes (5) was isolated. 5 is the intermediate in the H2SO4-catalyzed isomerization of 1d and was converted in situ with methanol, acetic anhydride, HF or HCl to give the respective methoxysilane 6, acetoxysilane 7, fluorosilane 8, or chlorosilane 9. Deprotonation of 4a, d, f with sodium hydride causes a further rearrangement, a 1,3-C,O-trimethylsilyl migration, to give the siloxanes (Me3Si)2(Me3SiO)Si-CHR1R2 (11a, d, f).
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  • 187
    Electronic Resource
    Electronic Resource
    Reactions of ε-Caprolactone with (Alkyne)zirconocene Complexes: Investigation of Elemental Steps in Catalytic Ring-Opening Polymerization of Lactones (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 1351-1357 
    Details
    ISSN: 1434-1948
    Keywords: ε-Caprolactone complexes ; Zirconocene ; Ring-opening polymerization ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The reactions of Cp2Zr(L)(η2-Me3SiC2SiMe3) (L = THF, pyridine) with ε-caprolactone, cyclohexanone and cycloheptanone result in an insertion of the carbonyl group into the zirconacyclopropene ring system of the alkyne complexes to yield the five-membered metallacyclic spiro-zirconadihydrofurane complexes 1, 3, 4. The product with ε-caprolactone is not stable at room temperature and was identified only by NMR spectra and chemical reactions. Starting from rac-(ebthi)Zr(η2-Me3SiC2SiMe3) with ε-caprolactone and ethylene carbonate under analogous conditions more stable complexes (2, 5) were obtained. Complexes 2 and 3 were characterized by X-ray crystal-structure analysis. Complexes 1 and 2 react with further ε-caprolactone in a catalytic ring-opening polymerization. The polymerization reactions were monitored by NMR spectroscopy.
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  • 188
    Electronic Resource
    Electronic Resource
    Photoelectron-Spectrum and Electronic Structure of Perfluoro(2,4-dimethyl-3-oxa-2,4-diazapentane) (CF3)2N-O-N(CF3)2 (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 1377-1380 
    Details
    ISSN: 1434-1948
    Keywords: Ab initio calculations ; Electronic structure ; Photoelectron spectroscopy ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The electronic structure of the title compound 1 has been investigated by UV photoelectron spectroscopy and quantum chemical calculations. 1 has two nearly degenerate nN lone-pair orbitals which form the two highest occupied MOs. The third highest occupied MO is mainly localized at the oxygen atom (n0). All calculations indicate that the molecule has a twisted C2 conformation.
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  • 189
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    Electronic Resource
    Tridentate Coordination Mode of N,N′-Dimethyl-2,11-diaza[3.3](2,6)pyridinophane in a Tricarbonylmolybdenum(0) Complex (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 1381-1385 
    Details
    ISSN: 1434-1948
    Keywords: Carbonyl complexes ; Coordination modes ; Fluxionality ; Macrocyclic ligands ; N ligands ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Tridentate coordination of the potentially tetradentate ligand N,N′-dimethyl-2,11-diaza[3.3](2,6)pyridinophane (L-N4Me2) has been structurally established in the tricarbonylmolybdenum(0) complex [Mo(L-N4Me2)(CO)3]. The fluxional behavior of the coordinated tetraazamacrocyclic ligand is demonstrated by a variable-temperature 1H-NMR study. The relevance of the tridentate coordination mode of the ligand is discussed with respect to its intermediacy in the reaction mechanism for the formation of cis octahedral metal complexes containing tetradentate 2,11-diaza[3.3](2,6)pyridinophane derivatives as ligands.
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  • 190
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    Electronic Resource
    Chromium Sandwich Complexes of Polycyclic Aromatic Hydrocarbons: Triphenylene and Fluoranthene as η6 Ligands (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 1391-1401 
    Details
    ISSN: 1434-1948
    Keywords: Polycycles ; Sandwich complexes ; Site preference ; Cyclic voltammetry ; NMR and EPR spectroscopy ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The sandwich complexes bis(η6-triphenylene)chromium (12) and bis(η6-fluoranthene)chromium (13) have been prepared by means of metal atom/ligand vapor cocondensation. Whereas for triphenylene exclusive coordination to the peripheral rings is observed, the situation is more complicated for fluoranthene. According to NMR evidence initial metal coordination to the benzene (B) as well as to the naphthalene (N) section of the fluoranthene ligand occurs, leading to the isomers 13(I) (η6-B, η6-B), 13(II) (η6-B, η6-N) and 13(III) (η6-N, η6-N). Since the substitutional lability of the chromium-naphthalene bond largely exceeds that of the chromium-benzene bond, the isomer distribution depends on the workup conditions; 13(I) is clearly the most stable isomer. Crystal structure determinations performed for the salts [12][BPh4] and [13][I] point to the preference for syn orientation of the polycyclic aromatic hydrocarbons and to a minute metal slippage in the peripheral direction. The triphenylene complex 12 features the electrochemically reversible redox couples 12 (+/0, metal-centered), 12 (0/-, ligand-centered) and 12 (-/2-, ligand-centered), the latter displaying a redox splitting of 300 mV. Conversely, for the fluoranthene complex 13, secondary reduction 13 (-/2-) is irreversible. This finding is consistent with the larger redox splitting of ca. 480 mV which indicates more extensive interligand interaction in the dianion 132-, thereby favoring metal-ligand cleavage. While the radical cations 12+· and 13+· are amenable to EPR study, the radical anions 12-· and 13-· are too unstable. Instead, the radical anions of the free ligands are observed by EPR upon electrochemical reduction. In the case of 12, the temporary existence of the radical anion 12-· is indicated, however.
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  • 191
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    Electronic Resource
    Thiolate and Thioether Functions as Donor Groups X, Y in Tripod Ligands RCH2C(CH2PPh2)(CH2X)(CH2Y) - Synthesis and Coordination Chemistry (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 1417-1424 
    Details
    ISSN: 1434-1948
    Keywords: Tripod ligands ; Molybdenum ; Mixed donor set ligands ; Thiole ligands ; Thiolate ligands ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Tripod ligands RCH2C(CH2PPh2)(CH2X)(CH2Y) (1) with X, Y = SAlkyl, SBzl selectively undergo reductive cleavage of the SBzl function with Li/NH3/THF at -40 °C to produce RCH2C(CH2PPh2)(CH2X)(CH2Y) (2) (X, Y = SAlkyl, SH). In these mixed donor set ligands the SH functions are the least coordinative ones such that [η2-{CH3C(CH2PPh2)(CH2SEt)(CH2SH)}(CO)4Mo] (5) is a stable compound with an uncoordinated SH function at the dangling arm of the ligand. If the SH functions of a potential tripod ligand are deprotonated the resulting thiolate functions are found to strongly coordinate in compounds such as [η3-{CH3C(CH2PPh2)2(CH2S)}(CO)3Mo]- which are obtained as their lithium and sodium salts 6. These highly reactive species may be stabilized by encapsulating their alkali counter ions in cryptands and the corresponding salts with [2,1,1]cryptand (7a) and [2,2,2]cryptand (7b) are far easier to handle than the cryptand-free progeners 6. Alkylation of the coordinatively bound thiolate function in 6 leads to the corresponding thioether derivatives [η3-{CH3C(CH2PPh2)2(CH2SR)}(CO)3Mo] (8).
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  • 192
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    Electronic Resource
    New Synthetic Routes to Hydrotalcite-Like Compounds - Characterisation and Properties of the Obtained Materials (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 1439-1446 
    Details
    ISSN: 1434-1948
    Keywords: Layered double hydroxides ; Hydrotalcite-like compounds ; Magnesium ; Aluminium ; Intercalation ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Hydrotalcite-like anionic clays of general formula [M(II)1-xM(III)x(OH)2]x+[CO32-x/2]x- · m H2O with M(III) = Al and M(II) = Mg, Ni, Zn have been prepared by precipitation of the hydroxycarbonates from the “homogeneous” solution after the thermally induced hydrolysis of urea. The effect of the temperature of precipitation, of the total metal cations concentration, of the molar fraction M(III)/M(III) + M(II) and of the molar fraction urea/M(II) + M(III) in solution on the composition and on the crystallinity degree of the samples has been investigated. The optimum conditions are reported to obtain micro-crystalline powders with a narrow distribution of particle size in a short time with a simple procedure. The compounds obtained have been characterised for chemical composition, thermal behaviour, particle-size distribution and BET-surface area. In addition, the crystal structure of Mg0.67Al0.33(OH)2 (CO3)0.165 · 0.4 H2O has been refined by X-ray diffraction powder methods. The carbonate form has been converted into the chloride form by letting gaseous HCl flow over the hydrotalcite-like compounds, heated at 150 °C. The exchange of Cl- anions with some alkoxide anions in the presence of the respective alkanols has been investigated. The exchange reaction was driven by the segregation of NaCl crystals poorly soluble in alkanols and led to the co-intercalation of the alkoxide ions together with the alkanol with the formation of a bi-layer of extended alkyl chain in the interlayer region of the Mg-Al hydrotalcite. The intercalation compound, washed with water, produces a hydrotalcite with Cl- and OH- as balancing anions.
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  • 193
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    Electronic Resource
    Amino Acid Derivatives of Layered Zirconium Phosphates - α-Zirconium L-(+)-Serinephosphate and Zirconium L-(+)-Serinephosphate Phosphates (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 1447-1452 
    Details
    ISSN: 1434-1948
    Keywords: Layered compounds ; Zirconium ; Amino acids ; Zirconium L-(+)-serinephosphates ; Intercalation ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A layered derivative of α-zirconium phosphate containing L-(+)-serine covalently attached to the inorganic layer has been prepared by allowing Zr fluoro complexes to decompose in the presence of L-(+)-phosphoserine. On the basis of thermogravimetric weight loss and C,H,N elemental analyses, the layered compound obtained has been formulated as Zr[HOOCCH(NH2)CH2OPO3]2. The X-ray powder diffraction pattern has been indexed with a monoclinic cell (a = 5.3737 Å, b = 9.3231 Å, c = 14.510 Å, β = 96.99°, Z = 2). FT-IR absorption spectra show that the serine groups attached to the inorganic layers are present as zwitterions. Thermal decomposition commences at ca. 250 °C and occurs in two steps: the first is due to a decarboxylation reaction, with the formation of the amino derivative Zr(NH2CH2CH2OPO3)2, while the second is associated with pyrolysis of the organic moiety, leading to ZrP2O7. Despite the presence of the amino acid function in the interlayer region, the compound does not show intercalation ability towards cations or anions or polar species. However, compounds with a certain degree of microporosity and possessing ion-exchange and adsorption properties have been obtained by replacing some of the phosphoserine groups of the compound by HPO4 groups, to produce the mixed layered derivatives Zr[HOOCCH(NH2)CH2OPO3]2-x-(HPO4)x.
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  • 194
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    Electronic Resource
    X-ray Crystal Structures and Molecular Modelling Studies of Calix[4]dibenzocrowns-6 and Their Alkali Metal Cation Complexes (1998)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 1559-1568 
    Details
    ISSN: 1434-193X
    Keywords: X-ray crystal structure ; Calix crown ; Molecular dynamics ; Cesium selectivity ; Alkali metal cation complex ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: We present X-ray structures of complexes of KClO4·H2O and CsPic·H2O with a new calix[4]arene bearing a dibenzocrown-6 ether bridge. Alkali metal cation complexes with this macrocycle have been studied by molecular dynamics simulations in vacuo, taking account of the counterion, and in an explicit water phase, in order to compare the computed structures to those determined by X-ray crystallography. Two different sets of atomic charges were used in order to evaluate the influence of the electrostatic representation on the computed structures. The results obtained show that MNDO scaled charges give simulation results in better agreement with the available experimental data than MNDO/ESP.
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  • 195
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    Electronic Resource
    An Efficient Method for Synthesizing Substituted Naphtho-1,3-dithiole-2-thiones from Tetrachlorotetrathionaphthalene and Sodium Trithiocarbonate (1998)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 1577-1581 
    Details
    ISSN: 1434-193X
    Keywords: Sulfur heterocycles ; Synthetic methods ; Conducting materials ; Desulfurization ; C-C coupling ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Two types of naphtho-fused 1,3-dithiole-2-thiones (2a-f and 4a-d) were obtained by the reaction of 3,4,7,8-tetrachloro-naphtho[1,8-cd:5,6-c′d′]bis(1,2-dithiole) (1) and sodium trithiocarbonate. The dechalcogenization of the thiones, using mercury acetate, leads to the corresponding naphtho-1,3-dithiol-2-ones (3a-d and 5a-d). The structures of 3a and 4a were confirmed by X-ray investigation. The tetrathiafulvalenes (TTFs) 6 and 7 were synthesized from 2d and 3c by coupling of the starting compounds with the help of triethyl phosphite. Using 2,3-dichloro-5,6-dicyano-benzoquinone (DDQ) the TTFs were converted into semiconducting charge-transfer complexes.
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  • 196
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    Electronic Resource
    Synthesis and Anionically Induced Domino Reactions of Chiral α-Bromo α,β-Unsaturated Esters (1998)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 1569-1576 
    Details
    ISSN: 1434-193X
    Keywords: Asymmetric dihydroxylation (Sharpless-AD) ; Wittig olefination ; α-Bromo α,β-unsaturated esters ; Diastereoselective aprotic Michael domino reaction ; Tricyclo[3.2.1.02,7]octanes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The chiral α-bromo α,β-unsaturated esters 3 and 9 are prepared by asymmetric Sharpless dihydroxylation (AD) of 5 and from ester 7 and the chiral diols 8 by transacetalization, respectively. Both types of α-bromo α,β-unsaturated ester react with the kinetic lithium dienolates of enone 10 to give functionalized tricyclo[3.2.1.02,7]octanes 11. Esters 3 give one single diastereomer (de ≥ 95%), whereas mixtures of diastereomers (de 28 to 46%) are obtained with the esters 9.
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  • 197
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    Electronic Resource
    Regio- and Stereoselective Cyclization Reactions of Unsaturated Silyl Enol Ethers by Photoinduced Electron Transfer - Mechanistic Aspects and Synthetic Approach (1998)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 1583-1596 
    Details
    ISSN: 1434-193X
    Keywords: Cyclizations ; Electron transfer ; High-pressure effects ; Radical cations ; Silyl enol ethers ; Solvent effects ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Oxidative photoinduced electron transfer (PET) reactions have been performed with various silyl enol ethers and silyloxy-2H-chromones bearing an olefinic or silylacetylenic side chain. The reactions result in regioselective ring closure with the formation of bi- to tetracyclic ring systems with a well-defined ring juncture, e.g. perhydrophenanthrenones 13 or benzo-annellated xanthenones 24. Our investigations have focussed on the optimization of this cyclization method with regard to irradiation time and product yield. The irradiation times could be reduced by using the cosensitized PET method. Modifying the substrate at the silyl group led to enhanced yields. In addition, we found that solvent and pressure dependences are important tools, allowing control of the regiochemistry. Both the synthesis of 6-endo products by radical cationic reaction pathways, as well as 5-exo ring closure by radical intermediates was achieved. Mechanistic details, including findings from deuterium labelling experiments, are discussed.
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  • 198
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    Electronic Resource
    Monomeric N-Lithioaryl- and N-Lithioborylstannylamines from Distannylamines (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 1343-1349 
    Details
    ISSN: 1434-1948
    Keywords: Distannylamines ; N-Lithiostannylamines ; N-Lithioborylamines ; Amides ; Structure elucidation ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 8-Aminoquinoline reacts with (dimethylamino)trimethylstannane in a 2:1 molar ratio, undergoing transamination to the distannylamine 1a. The 9-[bis(trimethylstannyl)amino]-9-borabicyclo[3.3.1]nonane (1b) is obtained by the stannazane cleavage reaction of tris(trimethylstannyl)amine with 9-chloro-9-BBN. The cleavage of one Sn-N bond of the distannylamines 1a and 1b with MeLi yields the first two monomeric N-lithioaminostannanes, 2a and 2b, which can be stored at ambient temperature without decomposition. The molecular structures of 1a, 1b, 2a, and 2b have been determined by multinuclear magnetic resonance spectra in solution, as well as by X-ray structure analysis. Characteristic features are the intramolecular adduct formation of the quinoline ring nitrogen atom with one of the stannyl groups in 1a, as well as with the lithium cation in 2a, and the surprisingly short bonds between the central nitrogen atom and the adjacent elements [d(NSn): 2.02 Å, d(NB): 1.38 Å, d(NC): 1.34 Å, d(NLi): 1.95 Å] detected in the molecular structures of the lithium salts.
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  • 199
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    Electronic Resource
    Stabilization of the New Antimonide Zr2V6Sb9 by V-V and Sb-Sb Bonding (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 1369-1375 
    Details
    ISSN: 1434-1948
    Keywords: Cluster ; Metal-rich antimonides ; Magnetism ; Sb-Sb bonds ; Structure and bonding ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The metal-rich antimonide Zr2V6Sb9 has been prepared by arc-melting of stoichiometric mixtures of Zr, V, and VSb2. Zr2V6Sb9 is the first example of a ternary ordered (filled) variant of the unusual V15Sb18 structure type. In addition to strong metal-antimony bonding, the crystal structure is significantly stabilized by bonding V-V and Sb-Sb interactions, whereas the Zr atoms do not form short metal-metal bonds. Band structure calculations using the Extended Hückel approximation reveal Zr2V6Sb9 being metallic, in agreement with the Pauli paramagnetism experimentally observed.
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  • 200
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    Electronic Resource
    Preparation of P,N-Heterodifunctional Ferrocene-Coordinating Ligands by Selective Functionalization of Polyphosphanes by the Staudinger Reaction - Crystal and Molecular Structure of a New Cyclometallaphosphoraniminophosphane of Palladium(II) (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 1359-1368 
    Details
    ISSN: 1434-1948
    Keywords: β-Ferrocenylvinyl azide ; Polyphosphanes ; Iminophosphoranes ; P,N-Difunctional ligands ; Palladium ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Staudinger reactions of the β-ferrocenylvinyl azide 1 with several diphosphanes in a 1:1 molar ratio afford the monoiminophosphorane derivatives 2-4, whereas with a 2:1 stoichiometry these reactions afford the bis(iminophosphoranes) 5-7. Similar results are obtained for the reactions of 1 with tris(diphenylphosphanylmethyl)ethane (triphos) and tris[2-(diphenylphosphanyl)ethyl]phosphane (tetraphos). Reaction of these P,N-difunctional ferrocene ligands with dichlorobis(benzonitrile)palladium(II) leads to the PdII-metallacycle derivatives 13 and 14. The molecular structures of 5d and 13 have been established by X-ray crystallography.
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