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  • 1995-1999  (1.270)
  • 1960-1964  (1.966)
  • 1955-1959  (858)
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  • 1
    Digitale Medien
    Digitale Medien
    Studies of iron transport by arbuscular mycorrhizal hyphae from soil to peanut and sorghum plants (1998)
    Springer
    Mycorrhiza 8 (1998), S. 35-39 
    Details
    ISSN: 1432-1890
    Schlagwort(e): Key words Arbuscular mycorrhiza ; Iron ; Peanut ; Phosphorus ; Sorghum
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract  The influence of an arbuscular mycorrhizal (AM) fungus on phosphorus (P) and iron (Fe) uptake of peanut (Arachis hypogea L.) and sorghum (Sorghum bicolor L.) plants was studied in a pot experiment under controlled environmental conditions. The plants were grown for 10 weeks in pots containing sterilised calcareous soil with two levels of Fe supply. The soil was inoculated with rhizosphere microorganisms only or with rhizosphere microorganisms together with an AM fungus (Glomus mosseae [Nicol. & Gerd.] Gerdemann & Trappe). An additional small soil compartment accessible to hyphae but not roots was added to each pot after 6 weeks of plant growth. Radiolabelled P and Fe were supplied to the hyphae compartment 2 weeks after addition of this compartment. After a further 2 weeks, plants were harvested and shoots were analysed for radiolabelled elements. In both plant species, P uptake from the labelled soil increased significantly more in shoots of mycorrhizal plants than non-mycorrhizal plants, thus confirming the well-known activity of the fungus in P uptake. Mycorrhizal inoculation had no significant influence on the concentration of labelled Fe in shoots of peanut plants. In contrast, 59Fe increased in shoots of mycorrhizal sorghum plants. The uptake of Fe from labelled soil by sorghum was particularly high under conditions producing a low Fe nutritional status of the plants. These results are preliminary evidence that hyphae of an arbuscular mycorrhizal fungus can mobilise and/or take up Fe from soil and translocate it to the plant.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s005720050208
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  • 2
    Digitale Medien
    Digitale Medien
    Effect of root exudate fractions from P-deficient and P-sufficient onion plants on root colonisation by the arbuscular mycorrhizal fungus Gigaspora margarita (1998)
    Springer
    Mycorrhiza 8 (1998), S. 67-70 
    Details
    ISSN: 1432-1890
    Schlagwort(e): Key words Allium cepa ; Appressorium ; Arbuscular mycorrhiza ; Root colonisation ; Phosphorus
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract  The effect of root exudates from P-deficient onion on root colonisation by an arbuscular mycorrhizal fungus was examined. Onions (Allium cepa L.) were grown in solution culture at phosphorus concentrations of 0 (P0) and 2 (P2) mg P l–1. Root exudates were collected and fractionated with Amberlite XAD-4 resin to give EtOH and water soluble fractions. Onions inoculated with the arbuscular mycorrhizal fungus Gigaspora margarita Becker & Hall were grown with or without (control) root exudates and exudate fractions in a growth chamber. After 24 days, arbuscular mycorrhiza levels and appressoria formation had increased in plants treated with P0-root exudate or the P0-EtOH fraction when compared to corresponding P2 treatments or control plants. P0 and P2 water-soluble fractions did not significantly affect either aspect of fungal development. These results suggest that hydrophobic compounds found in root exudates from P-deficient onion increase appressorium formation and, therefore, enhance mycorrhiza development.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s005720050214
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  • 3
    Digitale Medien
    Digitale Medien
    Patterns of arbuscular mycorrhiza colonisation of the roots of Hyacinthoides non-scripta after disruption of soil mycelium (1998)
    Springer
    Mycorrhiza 8 (1998), S. 87-91 
    Details
    ISSN: 1432-1890
    Schlagwort(e): Key words Acaulospora ; Hyacinthoides non-scripta ; Bluebell ; Disturbance ; Glomus ; Fine endophytes ; Phosphorus ; Scutellospora
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract  Early-season colonisation of new roots of Hyacinthoides non-scripta (L.) Chouard ex Rothm. was investigated to determine how arbuscular mycorrhizal symbiosis is re-established after the annual root system is shed. During the rootless phase in summer, colonies of bulbs were removed and replanted after the soil around and below the bulb had been mixed (major disturbance) so as to disrupt the external mycelium of arbuscular mycorrhizal (AM) fungi. As a minor disturbance treatment, top soil was removed, bulbs were turned or not in their growth position with as little other disturbance as possible, and the top soil replaced. Control plants were left undisturbed. Half of the plants were harvested 3–4 weeks after the onset of root emergence. Populations of all AM fungi in roots were greatly reduced by major disturbance, whilst those in other treatments and controls were unaffected. At the second harvest, in spring, when shoots had emerged, root colonisation by fine endophytes and Scutellospora morphotypes developed in all treatments, whereas that of Acaulospora morphotypes remained low after major disturbance. Disturbance treatments delayed the appearance, at the second harvest, of mycorrhizas with degenerate arbuscules. Leaf phosphorus concentration was unaffected by soil disturbance, possibly due to partial recovery of AM fungal populations or buffering by resources stored in the bulb.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s005720050217
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  • 4
    Digitale Medien
    Digitale Medien
    Seasonal mycorrhizal colonization of winter wheat and its effect on wheat growth under dryland field conditions (1998)
    Springer
    Mycorrhiza 8 (1998), S. 139-144 
    Details
    ISSN: 1432-1890
    Schlagwort(e): Key words Winter wheat ; Mycorrhiza ; Phosphorus ; Dryland
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract  A field experiment was conducted to determine the seasonal patterns of arbuscular mycorrhiza (AM) in a dryland winter wheat (Triticum aestivum L.) system and to determine wheat growth and P uptake responses to inoculation with mycorrhizal fungus. Broadcast-incorporated treatments included (1) no inoculation with mycorrhizal fungus, with and without P fertilizer, and (2) mycorrhizal fungal inoculation at a rate of 5000 spores of Glomus intraradices (Schenck and Smith), per 30 cm in each row, with and without fertilizer P. Winter wheat was seeded within a day after treatments were imposed, and roots were sampled at five growth stages to quantify AM. Shoot samples were also taken for determination of dry matter, grain yield and yield components, and N and P uptake. No AM infection was evident during the fall months following seeding, which was characterized by low soil temperature, while during the spring, the AM increased gradually. Increases in wheat grain yields by enhanced AM were of similar magnitude to the response obtained from P fertilization. However, responses differed at intermediate growth stages. At the tillering stage, P uptake was mainly increased by P fertilization but not by fungal inoculation. At harvest, enhanced AM increased P uptake regardless of whether or not fertilizer P was added. The AM symbiosis increased with rising soil temperatures in the spring, in time to enhance late-season P accumulation and grain production.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s005720050226
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  • 5
    Digitale Medien
    Digitale Medien
    Effect of phosphate and the arbuscular mycorrhizal fungus Glomus intraradices on disease severity of root rot of peas (Pisum sativum) caused by Aphanomyces euteiches (1998)
    Springer
    Mycorrhiza 8 (1998), S. 169-174 
    Details
    ISSN: 1432-1890
    Schlagwort(e): Key words Peas ; Aphanomyces euteiches ; Phosphorus ; PAGE ; Isozymes
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract  The effects of inorganic phosphate levels and the presence of arbuscular mycorrhiza on disease severity of Aphanomyces euteiches in pea roots were studied. Disease severity on roots and epicotyl as well as the oospore number within infected root tissue were correlated with the phosphorus (P) level in the growth medium. The arbuscular mycorrhizal fungus Glomus intraradices increased P uptake and the P concentration in the plant but reduced disease development in peas. Polyacrylamide gel electrophoresis followed by densitometry of glucose-6-phosphate dehydrogenase specific to A.euteiches was used to measure the activity of the pathogen in roots. The enzyme activity increased with disease severity and disease incidence, except in plants supplemented with P at the highest level, where a peak in activity was seen 12 days after inoculation with the pathogen, followed by a decrease in activity. The epicotyl of mycorrhizal plants showed a reduction in disease severity although this part of the plants was not mycorrhizal. Thus, an induced systemic factor may be responsible for increased resistance in mycorrhizal plants.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s005720050230
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  • 6
    Digitale Medien
    Digitale Medien
    Edaphic factors as determinants for the distribution of intrinsic antibiotic resistance in a cowpea rhizobia population (1998)
    Springer
    Biology and fertility of soils 27 (1998), S. 386-392 
    Details
    ISSN: 1432-0789
    Schlagwort(e): Key words Rhizobia ; Cowpea ; Antibiotic resistance ; Phosphorus ; Aluminium
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Geologie und Paläontologie , Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft
    Notizen: Abstract  A large collection of cowpea rhizobia strains was obtained from soil samples collected from either a semi-arid or a tropical rain forest area located at about the same latitude in the north-eastern region of Brazil and evaluated for their intrinsic antibiotic resistance to eight commercial antibiotics. The aim of this study was to correlate antibiotic resistance of native rhizobia strains to edaphic-climatic factors as a way to establish suitable inoculants for specific areas. A large diversity regarding intrinsic antibiotic resistance was found, and 17 clusters were identified as varying from sensitive to gradually resistant up to 500 μg·ml–1 of the antibiotics tested. Clustering analysis did not show any pattern related to the geographic region where isolates have been obtained. On the other hand, an increase in the antibiotic-resistant rhizobia population was associated with an increase in soil P and Al contents. lsolates which were sensitive to spectinomycin, ampicillin, streptomycin, chloramphenicol and tetracycline were present at higher rates in soils devoid of Al. Rhizobia bacteria producing mucus type I (fluid and capable of spreading over the solid media) were found preferentially in soil with Al concentrations up to 36 mg·kg–1, diminishing quickly at higher levels.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s003740050448
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  • 7
    Digitale Medien
    Digitale Medien
    Soil-plant interactions in a neotropical mangrove forest: iron, phosphorus and sulfur dynamics (1998)
    Springer
    Oecologia 115 (1998), S. 553-563 
    Details
    ISSN: 1432-1939
    Schlagwort(e): Key words Mangrove species zonation ; Sulfate reduction ; Pyrite formation ; Phosphorus ; Decomposition
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract We examined soil porewater concentrations of sulfate, alkalinity, phosphorus, nitrogen, and dissolved organic carbon and solid phase concentrations of pyrite in relation to mangrove species distributions along a 3.1-km-long transect that traversed a 47.1-km2 mangrove forest in the Dominican Republic. Iron, phosphorus, and sulfur dynamics are closely coupled to the activity of sulfate-reducing bacteria, the primary decomposers in anoxic soils of mangrove ecosystems. Patterns in the chemistry data suggested that sulfate reduction rates and storage of reduced sulfur were greater in the inland basin forest dominated by Laguncularia racemosa than the Rhizophora mangle dominated forest of the lower tidal region. The distribution of Laguncularia was significantly correlated with concentrations of total phosphorus (r= 0.99) and dissolved organic carbon (r= 0.86), alkalinity (r= 0.60), and the extent of sulfate depletion (r= 0.77) in the soil porewater and soil pyrite concentrations (r= 0.72) across the tidal gradient. Leaf tissue chemistry of Laguncularia was characterized by lower C:N and C:P ratios that could fuel the higher rates of decomposition in the Laguncularia-dominated forest. We suggest that a plant-soil-microbial feedback contributes to the spatial patterning of vegetation and soil variables across the intertidal zone of many mangrove forest communities.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s004420050553
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  • 8
    Digitale Medien
    Digitale Medien
    Nutrient relations in calcareous grassland under elevated CO2 (1998)
    Springer
    Oecologia 116 (1998), S. 67-75 
    Details
    ISSN: 1432-1939
    Schlagwort(e): Key words Dinitrogen fixation ; Plant functional types ; legumes ; Nutrient limitation ; Phosphorus
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract Plant nutrient responses to 4 years of CO2 enrichment were investigated in situ in calcareous grassland. Beginning in year 2, plant aboveground C:N ratios were increased by 9% to 22% at elevated CO2 (P 〈 0.01), depending on year. Total amounts of N removed in biomass harvests during the first 4 years were not affected by elevated CO2 (19.9 ± 1.3 and 21.1 ± 1.3 g N m−2 at ambient and elevated CO2), indicating that the observed plant biomass increases were solely attained by dilution of nutrients. Total aboveground P and tissue N:P ratios also were not altered by CO2 enrichment (12.5 ± 2 g N g−1 P in both treatments). In contrast to non-legumes (〉98% of community aboveground biomass), legume C/N was not reduced at elevated CO2 and legume N:P was slightly increased. We attribute the less reduced N concentration in legumes at elevated CO2 to the fact that virtually all legume N originated from symbiotic N2 fixation (%Ndfa ≈ 90%), and thus legume growth was not limited by soil N. While total plant N was not affected by elevated CO2, microbial N pools increased by +18% under CO2 enrichment (P = 0.04) and plant available soil N decreased. Hence, there was a net increase in the overall biotic N pool, largely due increases in the microbial N pool. In order to assess the effects of legumes for ecosystem CO2 responses and to estimate the degree to which plant growth was P-limited, two greenhouse experiments were conducted, using firstly undisturbed grassland monoliths from the field site, and secondly designed `microcosm' communities on natural soil. Half the microcosms were planted with legumes and half were planted without. Both monoliths and microcosms were exposed to elevated CO2 and P fertilization in a factored design. After two seasons, plant N pools in both unfertilized monoliths and microcosm communities were unaffected by CO2 enrichment, similar to what was found in the field. However, when P was added total plant N pools increased at elevated CO2. This community-level effect originated almost solely from legume stimulation. The results suggest a complex interaction between atmospheric CO2 concentrations, N and P supply. Overall ecosystem productivity is N-limited, whereas CO2 effects on legume growth and their N2 fixation are limited by P.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s004420050564
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  • 9
    Digitale Medien
    Digitale Medien
    Lattice Monte Carlo simulations as link between ab-initio calculations and macroscopic behavior of dopants and defects in silicon (1998)
    Springer
    Journal of computer-aided materials design 5 (1998), S. 81-88 
    Details
    ISSN: 1573-4900
    Schlagwort(e): Aggregation ; Arsenic ; Diffusion ; Lattice Monte Carlo ; Phosphorus ; Silicon ; Vacancy
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract In this work, we show that lattice Monte Carlo simulations can be used to span the time and distance scales between underlying atomistic processes and macroscopic diffusion behavior. We use ab- initio calculations of binding energies versus configuration to calculate hopping rates of vacancies for use in lattice Monte Carlo (LMC) simulations of diffusion and aggregation in silicon. The LMC simulations consider the biased nature of vacancy hop frequencies in the neighborhood of dopants, with interactions up to sixth-nearest- neighbor distances included. We use these simulations to investigate the expected macroscopic diffusion behavior, as well as the process by which dopant/defect aggregation occurs. Specific phenomena investigated include collective behavior leading to greatly enhanced diffusivity at high doping levels, the time dependence of effective diffusivity due to the formation of dopant/vacancy clusters, and dopant fluxes in the presence of a vacancy gradient.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1008689130758
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  • 10
    Digitale Medien
    Digitale Medien
    Mapping of QTLs for phosphorus-deficiency tolerance in rice (Oryza sativa L.) (1998)
    Springer
    Theoretical and applied genetics 97 (1998), S. 777-783 
    Details
    ISSN: 1432-2242
    Schlagwort(e): Key words Rice ; QTL ; Phosphorus ; Use efficiency ; Deficiency tolerance
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract  Phosphorus (P) deficiency of soils is a major yield-limiting factor in rice production. Increasing the P-deficiency tolerance of rice cultivars may represent a more cost-effective solution than relying on fertilizer application. The objective of this study was to identify putative QTLs for P-deficiency tolerance in rice, using 98 backcross inbred lines derived from a japonica×indica cross and genotyped at 245 RFLP marker loci. Lines were grown on P-deficient soil and P uptake, internal P-use efficiency, dry weight, and tiller number were determined. Three QTLs were identified for dry weight and four QTLs for P uptake, together explaining 45.4% and 54.5% of the variation for the respective traits. Peaks for both traits were in good agreement which was to be expected considering the tight correlation of r=0.96 between dry weight and P uptake. For both traits the QTL linked to marker C443 on chromosome 12 had a major effect. Two of the three QTLs detected for internal P-use efficiency, including the major one on chromosome 12, coincided with QTLs for P uptake; however, whereas indica alleles increased P uptake they reduced P-use efficiency. We concluded that this was not due to the tight linkage of two genes in repulsion but rather due to an indirect effect of P uptake on P-use efficiency. Most lines with high use efficiency were characterized by very low P uptake and dry weight and apparently experienced extreme P-deficiency stress. Their higher P-use efficiency was thus the result of highly sub-optimal tissue-P concentrations and did not represent a positive adaptation to low P availability. The number of tillers produced under P deficiency is viewed as an indirect indicator of P-deficiency tolerance in rice. In addition to the major QTL on chromosome 12 already identified for all other traits, two QTLs on chromosome 4 and 12 were identified for tiller number. Their position, however, coincided with QTLs for tiller number reported elsewhere under P-sufficient conditions and therefore appear to be not related to P-deficiency tolerance. In this study P-deficiency tolerance was mainly caused by differences in P uptake and not in P-use efficiency. Using a trait indirectly related to P-deficiency tolerance such as tiller number, we detected a major QTL but none of the minor QTLs detected for P uptake or dry weight.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s001220050955
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  • 11
    Digitale Medien
    Digitale Medien
    Sutural mineralization of rat calvaria characterized by atomic-force microscopy and transmission electron microscopy (1998)
    Springer
    Cell & tissue research 294 (1998), S. 93-97 
    Details
    ISSN: 1432-0878
    Schlagwort(e): Key words Calvaria ; Mineralization ; Calcium ; Phosphorus ; Apatite ; Atomic-force microscopy ; Transmission electron microscopy ; Rat (Sprague Dawley)
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Medizin
    Notizen: Abstract  The application of transmission electron microscopy (TEM) and atomic-force microscopy (AFM) aid the acquisition of detailed structural information on the process of hard tissue formation. The sutural mineralization of rat calvaria is taken as a model for a collagen-related mineralization system. After cryofixation or chemical fixation an anhydrous tissue preparation technique with no staining procedures is used. The atomic-force microscope and the transmission electron microscope are used for structural analysis of the mineralizing region of the sutural tissue. With the application of AFM the collagen macroperiod is shown to be well represented in the unmineralized sutural tissue. At the mineralization front the collagen fibrils are found to be thickened and to change to a characteristic stacked platelet structure. Using TEM the macroperiod is faintly visible before mineral crystallites have formed and is more prominent after the apatite crystallization has started in the fibrils. In this step a needle-like structure of the newly formed apatitic crystals is visible.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s004410051159
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  • 12
    Digitale Medien
    Digitale Medien
    Comparison of nutrient losses into the water from rainbow trout culture based on fresh Baltic herring, moist and dry diets (1998)
    Springer
    Aquaculture international 6 (1998), S. 441-450 
    Details
    ISSN: 1573-143X
    Schlagwort(e): Cage culture ; Dietary lipid ; Dietary water ; Feeding frequency ; Moist diets ; Nitrogen ; Phosphorus ; Rainbow trout (Oncorhynchus mykiss)
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft
    Notizen: Abstract The nutrient losses into the water from rainbow trout (Oncorhynchus mykiss) cage culture using locally caught low-fat Baltic herring, herring-based moist diets and fishmeal-based dry diets were estimated. Feeding with herring led to nitrogen and phosphorus losses into the water twice as high as those feeding with dry pellets (78–162 versus 37–39 g N and 15–39 versus 7–18 g P per kg growth). This was supported by direct measurements of ammonia and phosphate excretion. Increasing feeding frequencies resulted in increased nutrient losses irrespective of diet. Increasing dietary lipid level had a more pronounced effect in reducing the expected nutrient losses in dry pellets than herring. The reduction within the herring was approximately 18% on average for nitrogen and 25% for phosphorus losses. Dietary water content did not affect the nutrient losses. © Rapid Science Ltd. 1998
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1009283401505
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  • 13
    Digitale Medien
    Digitale Medien
    Diastereomerically Pure 1,2-Diols by Nucleophilic Displacement Reactions of 3-Oxetanols - A Study Directed Towards the Identification of Suitable Nucleophiles and the Elucidation of Possible Side Reactions (1998)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 2161-2169 
    Details
    ISSN: 1434-193X
    Schlagwort(e): Photocycloaddition ; Ring opening ; Oxetanes ; 1,2-Diols ; Alkyldealkoxylation ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The ring opening of 3-isopropyl-2-phenyl-3-oxetanol (2a) by various nucleophiles has been studied. In the presence of BF3 as a Lewis acid, a clean reaction at the less substituted C-4 position was observed and the corresponding 1,2-diols 6-11 and 21-23 were isolated in diastereomerically pure form (47-97% yield). Alkyl-, aryl-, alkynyl- and alkenyllithium compounds proved to be suitable carbon nucleophiles. Deprotonated thiols were used as sulfur nucleophiles. An alkoxide derived from benzyl alcohol and an amide derived from benzylamine reacted less readily under these conditions, yielding the 1,2,3-trifunctional compounds 24 (42% yield) and 26 (54% yield). Other 2-phenyl-3-oxetanols such as 2b and 2c can also be employed as electrophiles, whereas 2-anisyl derivatives preferentially undergo rearrangement reactions, as exemplified by the conversion of oxetane 16 to the hydroxy ketone 17 (84% yield). The superior behaviour of 3-oxetanols as compared to their silyl derivatives in reactions with nucleophiles became evident from the reaction of 3-silyloxyoxetane 1a with alkyllithium reagents. A β elimination occurred upon treatment with nBuLi, which, after pericyclic ring opening and addition of nBuLi, yielded the allylic alcohol 20.
    Materialart: Digitale Medien
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  • 14
    Digitale Medien
    Digitale Medien
    Fluorescence Quenching of Ester-Substituted DBO-Type Azoalkanes by Olefins and Arenes: Electronic and Steric Effects, Exciplex Formation and Hydrogen Abstraction (1998)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 2177-2179 
    Details
    ISSN: 1434-193X
    Schlagwort(e): Azoalkanes ; DBO ; Fluorescence quenching ; Exciplexes ; Hydrogen transfer ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The fluorescence of the DBO derivatives 1-3 is efficiently quenched by olefins and arenes, exciplex formation and hydrogen transfer operate as quenching mechanisms. The electron-accepting ester groups in the azoalkanes 1-3 promote significantly more effective quenching compared to the parent DBO. Steric hindrance accounts for the differences in the quenching efficiencies, but electronic effects dominate
    Materialart: Digitale Medien
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  • 15
    Digitale Medien
    Digitale Medien
    Fragmentation Reactions of Quaternized γ-Amino Alcohols - Diastereoselective Synthesis of Highly Functionalized Oxetanes and Unsaturated Aldehydes and Ketones with a (Z)-C—C Double Bond (1998)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 2185-2191 
    Details
    ISSN: 1434-193X
    Schlagwort(e): Mannich bases ; γ-Amino alcohols ; Grob fragmentation ; (Z)-Alkenes ; Oxetanes ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Quaternized γ-amino alcohols 5 derived from ternary iminium salts 2 are stereospecifically converted into both unsaturated aldehydes/ketones 6 with a (Z)-C—C double bond in a Grob-type fragmentation and highly functionalized oxetanes 7 by intramolecular substitution.
    Materialart: Digitale Medien
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  • 16
    Digitale Medien
    Digitale Medien
    An Asymmetric Domino Three-Component Synthesis of β-Lactams (1998)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 2201-2207 
    Details
    ISSN: 1434-193X
    Schlagwort(e): Antibiotics ; Asymmetric synthesis ; β-Lactams ; Michael additions ; Multicomponent reactions ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Lithium dialkylcuprates react either in a sequential one-pot or in a domino “three-component” fashion with chiral Michael acceptors, like Oppolzer's N-enoyl-2,10-camphorsultams 7 and 11 or ‘Evans’ N-enoyl-4-phenyl-1,3-oxazolidin-2-ones 8 and 13, and N-(methoxycarbonylmethylidene)(4-methoxyphenyl)amine 9 to afford the corresponding cis-3-alkyl-4-methoxycarbonyl-1-(4-methoxyphenyl)azetidin-2-ones 10, 14-15 in overall yields of 40-67% and enantiomeric excesses of 91-99%.
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  • 17
    Digitale Medien
    Digitale Medien
    Reactions of 3-Nitro-ν-benzylideneacetophenone with Carbanions Containing Leaving Groups (1998)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 2229-2235 
    Details
    ISSN: 1434-193X
    Schlagwort(e): 3-Nitro-ω-benzylideneacetophenone ; Carbanions ; Michael addition ; Intramolecular vicarious nucleophilic substitution of hydrogen ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: 3-Nitro-ω-benzylideneacetophenone (1) reacts with carbanions containing leaving groups to give addition products to the electrophilic side chain. As a result of conjugated addition and subsequent intramolecular vicarious nucleophilic substitution of hydrogen (VNS) in the nitroaromatic ring of 1 in the position para to the nitro group, 4-cyano-7-nitro-3-phenyl-1,2,3,4-tetrahydronaphthalen-1-one and 4-cyano-7-nitro-3-phenylnaphth-1-ol are obtained. Smooth intramolecular VNS in the position para to the nitro group was observed for 4-chloro-1-(3-nitrophenyl)-3-phenyl-4-(p-tosyl)butanol.
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  • 18
    Digitale Medien
    Digitale Medien
    Structure of the Dimers Obtained From the Reduction of 1-Benzyl-3,5-bis(dialkylcarbamoyl)pyridinium Ions - Models of NAD+ (1998)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 2237-2243 
    Details
    ISSN: 1434-193X
    Schlagwort(e): Conformation analysis ; Electrochemistry ; Nitrogen heterocycles ; Dimerization ; Mechanism ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: In aqueous media the one-electron reduction of the title compounds on a mercury pool generally gives rise to three dimers, which are distinguishable by HPL chromatography. From spectroscopic analyses it has been possible to propose a structure for these conformers and their stability has been studied. Two conformers are unstable, yielding the third conformer. A mechanism is proposed for this transformation.
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  • 19
    Digitale Medien
    Digitale Medien
    Nucleotide Delivery from cycloSaligenyl-3′-azido-3′-deoxythymidine Monophosphates (cycloSal-AZTMP) (1998)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 837-846 
    Details
    ISSN: 1434-193X
    Schlagwort(e): AZT ; cycloSal-pro-nucleotide ; Prodrugs ; Nucleotide delivery ; HIV chemotherapy ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The application of our cycloSaligenyl- (cycloSal) pronucleotide concept to the approved anti-HIV dideoxynucleoside 3′-azido-3′-deoxythymidine AZT (1) is reported. This pro-nucleotide concept has been designed to deliver the corresponding 3′-azido-3′-deoxythymidine monophosphate AZTMP (2) by selective chemical hydrolysis from the lipophilic precursors cycloSal-AZTMP 4a-h. All derivatives 4a-h were synthesized using differently substituted salicyl alcohols 7a-h as starting materials. In hydrolysis studies, compounds 4 decomposed selectively releasing AZTMP (2) and the salicyl alcohols 7 following the designed tandem reaction. Furthermore, due to the electronic properties introduced by substituents, the half-lives of the triesters 4 could be ajusted over a wide range. Phosphotriesters 4 exhibited considerable biological activity in HIV-1 and HIV-2 infected wild-type human T-lymphocyte (CEM/O) cells, whereas, contrary to our expectations, nearly all activity was lost in HIV-2 infected thymidine-kinase-deficient CEM cells.
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  • 20
    Digitale Medien
    Digitale Medien
    A Constrained Diketopiperazine as a New Scaffold for the Synthesis of Peptidomimetics (1998)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 853-859 
    Details
    ISSN: 1434-193X
    Schlagwort(e): N-Alkylation ; Diketopiperazine building block ; Peptidomimetics ; RGD analogues ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: As a new scaffold for peptidomimetic synthesis, a highly constrained bifunctional diketopiperazine, 4, has been prepared by smooth N-alkylation with tert-butyl bromoacetate. As a first application, we describe herein the synthesis of new peptidomimetics of the Arg-Gly-Asp (RGD) sequence. The product 30, which shows a selective platelet-aggregation inhibiting activity, can be used as a lead for the preparation of more potent products.
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  • 21
    Digitale Medien
    Digitale Medien
    On the Reaction of Aminoxyls with Dioxiranes (1998)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 871-876 
    Details
    ISSN: 1434-193X
    Schlagwort(e): Dioxirane ; Homolysis, induced ; Aminoxyl ; Oxidation ; Spin-trapping ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: In the reactions of dimethyldioxirane (1a) and methyl(trifluoromethyl)dioxirane (1b) with 2,2,6,6-tetramethylpiperidinyl-1-oxyl (2) (TEMPO) in acetone, the corresponding methoxyamine 1-methoxy-2,2,6,6-tetramethylpiperidine (5) is produced in ≥98% yield, both in air and under N2, and in the absence or presence of a hydrocarbon (adamantane). Kinetic experiments show that aminoxyl 2 triggers the radical decomposition of the dioxirane, in addition to scavenging methyl radicals derived therefrom. The reactions of an aminoxyl less prone to oxidation, namely 1,2-dihydro-2-methyl-2-phenyl-3H-indol-3-one-1-oxyl (4), with dioxiranes 1a and 1b in acetone have also been studied. In these cases, not only is the corresponding methoxyamine 8a produced (yield 12-16%), but quinoneimine-N-oxides 10 (yield 12-21%) and 11 (yield 18-19%) are also formed. Furthermore, significant amounts (8-14%) of the amine 9 (the product of deoxygenation of 4) can be isolated. These observations provide useful information concerning the free-radical mechanism that follows the initial attack by the aminoxyl at the dioxirane.
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  • 22
    Digitale Medien
    Digitale Medien
    A Blue Excitable Charge-Transfer Fluorescent Probe and Its Fluorogenic Derivative (1998)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 2373-2377 
    Details
    ISSN: 1434-193X
    Schlagwort(e): Charge-transfer fluorescence ; Fluorogenic probe ; Fluorescence labelling ; Maleimide group ; Solvatochromism ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Structural modification of the highly fluorescent donor-bridge-acceptor molecule “Fluoroprobe” (FP) is shown to extend the excitation window to longer wavelengths. The resulting “Fluorotrope” (FT) shows appreciable absorption in the 350-420-nm range, so that visible (blue) light can be used for excitation. Further functionalization with a maleimide group results in the novel fluorogenic reagent MaleimidoFluorotrope (MFT) which yields fluorescent adducts with amines, thiols and other reactive groups that add to the double bond of the maleimide. The fluorescence wavelength of these adducts is extremely sensitive to the polarity and mobility of the medium.
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
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  • 23
    Digitale Medien
    Digitale Medien
    Polylithiated β-Peptides: like-Selective C-Terminal Alkylation of Boc-β-HVal-β-HAla-β-HLeu-OMe (1998)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 2379-2387 
    Details
    ISSN: 1434-193X
    Schlagwort(e): β-Peptides ; Polylithiation of peptides ; Li-enolates of peptides ; Back-bone alkylation of β-peptides ; Diastereoselective alkylation of β-peptide enolates ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: A series of N-Boc-protected β-tripeptide derivatives with or without N-methyl groups and with free or Me-ester-protected C terminus has been prepared (8-14, 16, 17). As with α-peptides (→ A), the β-peptide derivatives can be polylithiated (→ B, C). No epimerization of stereogenic centers and no β elimination (exception 17 → 24) is observed upon treatment with bases as strong as tBuLi. The C terminal ester Li-enolate moiety of tetralithio β-tripeptides (cf. C) can be selectively alkylated with methyl, benzyl and allyl halides, and with tert-butyl bromoacetate in yields ranging from 35-80% (8 → 18, 14 → 20-23).
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  • 24
    Digitale Medien
    Digitale Medien
    Synthesis of Analogues of Brassinosteroids from Chenodeoxycholic Acid (1998)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 2405-2407 
    Details
    ISSN: 1434-193X
    Schlagwort(e): Natural products ; Steroids ; Chenodeoxycholic acid ; Brassinosteroid analogues ; Biological activity ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The synthesis and spectroscopic characterization of two new bioactive analogues of brassinosteroids with a 24-hydroxylated cholanic side chain, an A/B ring cis-junction and oxygenated functions in C-7 is described.
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  • 25
    Digitale Medien
    Digitale Medien
    Syntheses and Properties of S2-Bridged Benzidines (1998)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 2409-2416 
    Details
    ISSN: 1434-193X
    Schlagwort(e): Sulfur heterocycles ; Rearrangements ; Reductions ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The syntheses of 1,2-benzodithiino[5,4,3-cde][1,2]benzodithiin-2,7-diamine (1) and dithio-bridged benzidine 2 have been achieved. The starting material for the synthesis of 1 was 1,3-diiodo-5-nitrobenzene (15) which was transformed by conventional means into 1,2-bis[3,5-bis(ethylthio)phenyl]diazane (19). The benzidine rearrangement of 19 in the presence of HBF4 at -30 °C yielded 4,4′-diamino-2,2′,6,6′-tetraethylthiobiphenyl (20) in 50 % yield. Treatment of 20 with sodium in ammonia and work-up in the presence of air yielded 1. The latter compound could be reduced with LiAlH4 to the tetrathiol 20a. The starting material for the preparation of 2 was 3-chloro-1-iodo-5-nitrobenzene (23), a side product of the preparation of 15. It was transformed analogously to the preparation of 1 into 1,2-bis(3-ethylthiophenyl)diazane (28). The benzidine rearrangement of 28 in presence of HBF4 at -30 °C afforded 4,4′-diamino-2,2′-bis(ethylthio)biphenyl (29) in 49 % yield. Treatment of 29 with sodium in ammonia and work-up under aerobic conditions yielded 2. Quantitative reduction of 2 to the thiol 29a could be achieved with LiAlH4. The reversible electrochemical reduction of 1 on unmodified glassy carbon electrodes leads to a product to which the structure of 3 was assigned.
    Zusätzliches Material: 5 Ill.
    Materialart: Digitale Medien
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  • 26
    Digitale Medien
    Digitale Medien
    Stereoelectronic Inhibition of Deprotonation in the Radical Cation of N-Benzylpiperidine: a Contribution to the Debate on the Mechanism of N-Dealkylation of Tertiary Amines (1998)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 2425-2429 
    Details
    ISSN: 1434-193X
    Schlagwort(e): N-Heterocycles ; Porphyrins ; Radical cations ; N-Dealkylation ; Stereoelectronic effects ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Evidence for a stereoelectronic inhibition of deprotonation of the radical cation of N-benzylpiperidine is presented. This stereoelectronic effect, which is due to the cyclic structure of the precursor, provides a tool to differentiate hydrogen-atom- versus electron-transfer routes in the biomimetic oxidative N-dealkylation of tertiary amines: the electron-transfer route appears to be the operating mechanism.
    Zusätzliches Material: 1 Ill.
    Materialart: Digitale Medien
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  • 27
    Digitale Medien
    Digitale Medien
    (-)-(M,7S)-Colchicine and (-)-(M,7S)-10-Ethylthiocolchicide/Alkyne Cycloaddition Reactions: Synthesis of Novel Colchicine Derivatives by Consecutive [4+2] and [3+2] Cycloadditions (1998)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 2451-2460 
    Details
    ISSN: 1434-193X
    Schlagwort(e): Colchicine ; 10-Ethylthiocolchicide, diene properties of ; π-Facial diastereoselectivity ; Consecutive [4+2],[3+2] cycloadditions ; Atropisomerism ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Cycloaddition reactions of the facially dissymmetric diene moiety of (-)-(M,7S)-colchicine (5) and (-)-(M,7S)-10-ethylthiocolchicide (9) to various alkynes have been studied. With 5 and the dienophilic benzyne (3), dimethyl acetylenedicarboxylate (DMAD) (4) and cyclooctyne (6) as starting materials all cycloadditions could be realized with high regioselectivity at the 8,12-positions of the alkaloid. The approach of the dienophiles preferentially occurred toward the syn π-face of the diene. In contrast to the cycloaddition mode of 5 the ethylthiocolchicide 9 surprisingly reacted in a different manner. With benzyne as starting material a novel [3+2] cycloaddition of the thioenol ether moiety of 9 towards the dipolarophilic benzyne is supposed, affording the unexpected colchicide 10 after [1,5]H shift of the primarily formed cycloadduct followed by cleavage of the C-S linkage. With DMAD (4) and cyclooctyne (6) the reaction course is more complex. In a consecutive [4+2]/[3+2] cycloaddition (or vice versa) followed by a thermally induced cycloreversion of a not identified intermediate DMAD (4) gives rise to the polycyclic thiophene derivative 13 and the novel allocolchicinoid 14. In a similar way cyclooctyne (6) yielded three products, the thiophene-annulated homobarrelenones 18 and 19 and the tetracyclic allocolchicinoid 21. The structures of the novel colchicine derivatives were assigned on the basis of spectral data, those of the cycloadducts 1 and 19 were verified by X-ray crystallography. For the unprecedented formation of the various allocolchicinoids by consecutive [4+2]/[3+2] cycloadditions plausible reaction pathways are suggested, as far as possible. In addition the inhibitory effects on the tubulin polymerization reaction in vitro of 10, 14, and 21 are reported.
    Zusätzliches Material: 2 Ill.
    Materialart: Digitale Medien
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  • 28
    Digitale Medien
    Digitale Medien
    Exploration of High-Pressure Cycloadducts of Furans and Citraconic Anhydride as Precursors for CD-Ring Fragments of Paclitaxel and Its Analogues (1998)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 2483-2492 
    Details
    ISSN: 1434-193X
    Schlagwort(e): Paclitaxel (Taxol®) ; Paclitaxel CD-ring ; High-pressure Diels-Alder reactions ; Furan cycloadditions ; Ether cleavage in 7-oxabicyclo[2.2.1]heptanes ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The high-pressure promoted Diels-Alder reactions between several furans and citraconic anhydride have been studied and the cycloadducts obtained have been explored in new straightforward routes to the CD-ring fragment of paclitaxel. The reaction between furan and citraconic anhydride afforded the exo cycloadduct diastereoselectively, whereas a variety of 2-substituted furans afforded approximate 1:1 mixtures of exo regioisomers. Separation of both regioisomers was accomplished after either diastereoselective esterification or regioselective reduction of the anhydride function. Ether cleavage of the bicyclic compounds by either high-pressure promoted ether cleavage or Boord elimination afforded several potential CD-ring precursors which can be used in the total synthesis of paclitaxel analogues.
    Zusätzliches Material: 2 Ill.
    Materialart: Digitale Medien
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  • 29
    Digitale Medien
    Digitale Medien
    An Improved Method for the endo-Fusion of Five-Membered Ring Lactones to the Bornane Ring System (1998)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 2507-2511 
    Details
    ISSN: 1434-193X
    Schlagwort(e): Camphoracetyl chloride ; Lactols, fused ; Lactones, fused ; Pseudoacid chlorides ; Reagents, stereoselective ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: endo-Fused lactone 3 was obtained in high yield from the camphoracetic acid 2 with thionyl chloride and a subsequent reduction of intermediate 5 with tributyltin hydride. The structure of 5 was elaborated and some aspects of the mechanism of its formation and reactivity were investigated. Lactone 3 serves as key intermediate for lactol 1 which is a useful reagent in racemate resolution and asymmetric synthesis.
    Zusätzliches Material: 1 Ill.
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  • 30
    Digitale Medien
    Digitale Medien
    Synthesis and Characterization of Novel Pyridines and 3,3′-Bridged Bipyridines Using 1,x-Cyclohexanediones (1998)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 2609-2615 
    Details
    ISSN: 1434-193X
    Schlagwort(e): Supramolecular chemistry ; Domino reactions ; Bipyridines ; 1,x-Cyclohexanediones ; Mannich bases ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: A one-pot reaction using 1,x-cyclohexanediones, a Mannich base (or its hydrochloride), and ammonium acetate delivers novel pyridines or 3,3′-bridged bipyridine compounds 8, 16, 18, 20, and 22. This strategy offers a great flexibility in the design of new building blocks, e.g. in supramolecular chemistry and underlines the efficiency of domino reactions.
    Zusätzliches Material: 1 Ill.
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  • 31
    Digitale Medien
    Digitale Medien
    Fluorinated Analogs of Retinoids: Stereocontrolled Synthesis Employing Fluoroisoprenoidal Horner Ylides (1998)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 2603-2607 
    Details
    ISSN: 1434-193X
    Schlagwort(e): Fluoro analogs of vitamin A ; Horner-Wittig reaction ; Fluoroisoprenoid building blocks ; Stereoselectivity ; Hydrolysis of chlorofluorocyclopropanes ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: An improved method for the preparation of ethyl 2-fluoro-3-methyl-2-butenoate (3) is described. The two stereoisomers [(E)-4 and (Z)-4] obtained after γ-bromination can be separated and can be individually converted into the corresponding diethyl phosphonates. The PO-ylides generated by α-deprotonation of the latter lose their stereochemical integrity by rapid torsional equilibration of the ester tail. Thus, Horner-Wittig reactions accomplished with benzaldehyde and (Z)- or (E)-(β-ionylidene)-acetaldehyde lead inevitably to stereorandomization at the terminal, ethoxycarbonyl-bearing double bond affording (E)- and (Z)-isomers in 50:50 to 15:85 ratios, depending on the reaction conditions. The new double bond, however, is formed with perfect trans-selectivity.
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  • 32
    Digitale Medien
    Digitale Medien
    Cyclization of 3-Aminoacrylates - Total Synthesis of Pumiliotoxin C and Related Stereoisomeric Compounds (1998)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 2641-2646 
    Details
    ISSN: 1434-193X
    Schlagwort(e): Alkaloids ; Total synthesis/Pumiliotoxin ; PTX-C ; PTX isomers ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: A method is described for the synthesis of pumiliotoxin C (1a) and related stereoisomeric compounds 1c-1f. Starting from (+)- or (-)-3-methylcyclohexanone (6a,b), the oxo esters 7a and 7b were prepared. Condensation with (+)- or (-)-3-aminohexanol (8a,b) gave the stereoisomeric 3-aminoacrylates 9a, 9b and 9c. The hydroxy group of the amino-acrylates was transformed into bromide using the tosylate method. Cyclization of the bromides led to unsaturated quinoline ring systems. Finally, decarboxylation and catalytic hydrogenation gave the different cis- and trans-fused stereoisomeric alkaloids of the pumiliotoxin C type. The structures were verified by X-ray analysis.
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  • 33
    Digitale Medien
    Digitale Medien
    Synthesis of 3,7-Disubstituted 9-Thiatricyclo[3.3.1.03,7]nonane-1,5-dithiol Derivatives and Crystal Structure of Tetramethyl 3(4aH)-Oxo-1,4-dihydrophenanthro[9,10-a]pentalene-1,2,4,4a-tetracarboxylate (1998)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 2647-2650 
    Details
    ISSN: 1434-193X
    Schlagwort(e): Lawesson's reagent ; Thiolation of cyclic ketones ; Anchimeric effect ; cis-Bicyclo[3.3.0]octane-3,7-diones ; 9-Thiatricyclo[3.3.1.03,7]nonane ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: A simple and efficient approach to the 9-thiatricyclo[3.3.1.03,7]nonane ring system (5) has been found by treating cis-bicyclo[3.3.0]octane-3,7-diones (1) with Lawesson's reagent or phosphorus pentasulfide. When dione 1 is treated with Lawesson's reagent tetramethyl 3(4aH)oxo-1,4-dihydrophenanthro[9,10-a]pentalene-1,2,4,4a-tetracarboxylate (6) is obtained as a by-product as shown by X-ray structural analysis.
    Zusätzliches Material: 1 Ill.
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  • 34
    Digitale Medien
    Digitale Medien
    Synthesis of Chiral 4-(ω-Hydroxyalkyl)pyrazolidin-3-ones by Ring-Chain Transformation of α-Alkylidenelactones with Hydrazines (1998)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 2667-2672 
    Details
    ISSN: 1434-193X
    Schlagwort(e): Pyrazolidin-3-ones ; Optical activity ; Asymmetric synthesis ; Ring transformation ; Hydrazines ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Enantiopure α-alkylidenelactones 7 were prepared by a Wittig reaction from α-bromolactones 4 and chiral aldehydes 6. Compounds 7 react with hydrazines 9 by stereoselective Michael-like addition and ring-chain transformation affording optically active 4-(ω-hydroxyalkyl)pyrazolidin-3-ones 11.
    Zusätzliches Material: 5 Ill.
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  • 35
    Digitale Medien
    Digitale Medien
    A Novel Concept for Transition-Metal-Catalyzed Reactions: Electron Transfer under Buffered Protic Conditions (1998)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 2673-2676 
    Details
    ISSN: 1434-193X
    Schlagwort(e): Aromatic aldehydes ; Pinacol coupling ; Radical reactions ; Reagent control ; Titanium ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: A novel concept for conductingtransition-metal-catalyzed radical reactions that allows highly diastereoselective titanocene-catalyzed pinacol couplings is described.
    Zusätzliches Material: 4 Ill.
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  • 36
    Digitale Medien
    Digitale Medien
    Synthesis of Spirolactones from the Limonene System (1998)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 2677-2682 
    Details
    ISSN: 1434-193X
    Schlagwort(e): Terpenoid lactones ; Antifeedants ; Limonene ; Claisen rearrangement ; Iodolactonization ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Four enantiomeric pairs of spirolactones were obtained in a four step synthesis from (+) and (-) limonene. The Claisen rearrangement and iodolactonization were the key steps of the syntheses presented. The structures of products were confirmed by X-ray crystallography of 11, 18b, and 19.
    Zusätzliches Material: 3 Ill.
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  • 37
    Digitale Medien
    Digitale Medien
    Functionalisation of the 1-Phosphanorbornadiene Structure at the C2 Position by Stille Cross-Coupling Reactions (1998)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 2683-2687 
    Details
    ISSN: 1434-193X
    Schlagwort(e): Phosphole ; Phosphanorbornadiene ; Stille cross-coupling ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The reaction of alkynylstannanes with 1-phenyl-3,4-dimethylphosphole at 150 °C affords the corresponding 2-stannyl-1-phosphanorbornadienes (2a, b), in fair yield. Oxidation under mild conditions affords the corresponding phosphane oxides (3a, b), whereas more drastic conditions (H2O2, 15% in toluene at 80 °C) induce the oxidative cleavage of the P-CH2 bond of the bridge to give a bicyclic phosphinate such as 4. Treatement of 4 by iodine leads to a tin → iodine exchange. The X-ray crystal structure analysis of the resulting 1-phospha-2-oxabicyclo[2.2.2]octa-5,7-diene 1-oxide confirms the functionalisation at the α-position and the relief of ring strain taking place upon insertion of oxygen into the P-CH2 bond of the norbornadiene. The 2-stannyl-1-phosphanorbornadiene 1-oxides (3a, b) readily undergo tin → iodine exchange. The resulting 2-iodo derivatives (6a, b) can be cross-coupled with 2-furyl-, 2-thienyl-, 2-pyrrolyl-, phenylethynyl-, and vinyl-tributylstannanes to give the corresponding 2-functional 1-phosphanorbornadiene 1-oxides in excellent yields (80-95%)
    Zusätzliches Material: 1 Ill.
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  • 38
    Digitale Medien
    Digitale Medien
    Stereoselective Intramolecular Hetero Diels-Alder Reactions of Cyclic Benzylidenesulfoxides and DFT Calculations on the Transition Structures (1998)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 2733-2741 
    Details
    ISSN: 1434-193X
    Schlagwort(e): Asymmetric synthesis ; Density functional calculations ; Cycloadditions ; Dihydropyrans ; Enantioselective oxidations ; Sulfur heterocycles ; Sulfoxides ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The 4-benzylidene-3-oxo[1,3]oxathiolan-5-ones 13-15, which were derived from the 3-oxo[1,3]oxathiolan-5-ones 9-11 by Knoevenagel condensation with the aldehydes 12, cyclize in an intramolecular hetero Diels-Alder reaction with high yield and excellent endo/exo as well as induced diastereoselectivity to give the hetero Diels-Alder adducts 16-18. The preferred formation of the Knoevenagel products 13-15 with a (Z) configuration was predicted with DFT calculations (B3LYP-6-311+G*) using the model systems 28 and 29. In addition B3LYP-6-31G*/sB3LYP/3-21G(*) calculations on transition structures for the hetero Diels-Alder reaction of 29 and 30 allowed a good correlation with the experimental results, which show that an endo attack of the dienophile syn to the S-O group in 13-15 leads to the main products.
    Zusätzliches Material: 2 Ill.
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  • 39
    Digitale Medien
    Digitale Medien
    Studies on Phosphorus Phthalocyanines and Triazatetrabenzcorroles (1998)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 2759-2767 
    Details
    ISSN: 1434-193X
    Schlagwort(e): Phosphorus phthalocyanines ; Triazatetrabenzcorroles ; Dihydroxyphosphorus(V) phthalocyanine hydroxides ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The previously reported reaction of phthalocyanines [H2(pc)] with PBr3, which was claimed to give a phosphorus(III) phthalocyanine “(PcPIII)”, has been reinvestigated in detail with both unsubstituted and alkyl-substituted phthalocyanines, 1-4. The products exhibit unusual electronic and mass spectra compared to normal phthalocyanines and have been identified as oxophosphorus(V) triazatetrabenzcorroles 5-8. The corresponding dihydroxyphosphorus(V) phthalocyanine hydroxides 9-12 have also been synthesized for the first time by insertion of phosphorus(V) into phthalocyanines and have been characterized in detail. The different reactivities of PBr3 and POX3 (X = Cl, Br) toward phthalocyanines are discussed.
    Zusätzliches Material: 3 Ill.
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  • 40
    Digitale Medien
    Digitale Medien
    A General Synthesis of Disubstituted Rubicenes (1998)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 2769-2773 
    Details
    ISSN: 1434-193X
    Schlagwort(e): Rubicenes ; Cyclization ; Polycyclic aromatic hydrocarbons ; Arenes ; Synthetic methods ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The synthesis of novel disubstituted rubicenes 1a-k is described. Starting from 1,5-dichloroanthraquinone and aryllithium reagents 3, the diol adducts 4 are reduced and the resulting diarylanthracenes 5 are cyclized to afford the title compounds in fair to good overall yield.
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  • 41
    Digitale Medien
    Digitale Medien
    Water-Soluble Tripodal Phosphane Ligands and Their Rhodium Complexes (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 37-41 
    Details
    ISSN: 1434-1948
    Schlagwort(e): Tripodal P ligands ; Rhodium ; Water-soluble complexes ; Immobilization ; Biphasic hydroformylation ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The synthesis of the water-soluble tripodal phosphane ligand cis,cis-1,3,5-(PPh2)3-1,3,5-[CH2(OCH2CH2)xOCH3]C6H6 (x = 30-160) (5) has been achieved in a four-step reaction sequence. The alcohol Mo(CO)3[cis,cis-1,3,5-(PPh2)3-1,3,5-(CH2OH)3C6H6] (1) is converted to the corresponding alcoholate 2, which forms the polyethylene glycol derivative 3 in a polyaddition reaction with oxirane. After methylation of the end groups of 3, the ligand 5 is obtained by a combined photochemical/oxidative demolybdenation reaction. The water-soluble tripodal phosphane 5 and the methoxymethyl functionalized tripodal ligand 6 react with Rh(PPh3)3(CO)H to form the water-soluble and water-insoluble rhodium carbonyl hydrido complexes 5a and 6a, respectively. The catalytic activity of the rhodium complex 5a in the hydroformylation of 1-hexene was found to be comparable in a single-phase system (1-hexene/methanol) with that in the biphasic system (1-hexene/water). Only traces of alcohol were found, which demonstrates that the catalyst 5a displays higher selectivity in hydroformylation than in hydrogenation.
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  • 42
    Digitale Medien
    Digitale Medien
    Metalloarsaalkene [(η5-C5Me5)(CO)2FeAs=C(NMe2)2] as a Ligand in Carbonylchromium, -iron, and -nickel Complexes (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 55-59 
    Details
    ISSN: 1434-1948
    Schlagwort(e): Arsaalkenes ; Arsenic ligands ; Carbonyl complexes ; Chromium ; Iron ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Reaction of equimolar amounts of the metalloarsaalkene [(η5-C5Me5)(CO)2FeAs=C(NMe2)2] (1) with the carbonyl complexes [Ni(CO)4], [Fe2(CO)9], and [{(Z)-cyclooctene}Cr(CO)5], respectively, affords the adducts [(η5-C5Me5)(CO)2FeAs{M(CO)n}=C(NMe2)2] with [M(CO)n] = [Ni(CO)3] (2); [Fe(CO)4] (3), and [Cr(CO)5] (4). These feature η1 coordination of the arsaalkene ligand via the arsenic atom. The molecular structures of the complexes 3 and 4 have been determined by X-ray diffraction analyses.
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  • 43
    Digitale Medien
    Digitale Medien
    The Effect of the Bite Angle of Diphosphane Ligands on Activity and Selectivity in Palladium-Catalyzed Cross-Coupling (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 155-157 
    Details
    ISSN: 1434-1948
    Schlagwort(e): Bite angle ; Catalysis ; P ligands ; Palladium ; Cross-coupling ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The effect of the natural bite angle (βn) of diphosphane ligands on catalyst selectivity and activity in the palladium-catalyzed cross-coupling of sec-butyl magnesium chloride with bromobenzene was investigated. The calculated natural bite angles range from 78° for dppe (1,2-bisdiphenylphosphanoethane) to 110° for Xantphos. The natural bite angle of diphosphane ligands has a large effect on catalyst selectivity and activity. Both rate and selectivity of the cross-coupling reaction increase with increasing bite angle and reach a maximum value with DPEphos (βn = 102.7° ). Larger bite angles of the diphosphane ligands result in a decreased selectivity and activity.
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  • 44
    Digitale Medien
    Digitale Medien
    Synthesis, Spectroscopy, and Magnetic Properties of Transition-Metal Complexes with the Diethyl 2-Quinolylmethylphosphonate (2-qmpe) Ligand - Crystal Structures of [Ni(2-qmpe)4(H2O)2](ClO4)2 and [Mn(2-qmpe)4(H2O)2](ClO4)2 Showing Unexpected O-Binding of the qmpe Ligands (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 169-175 
    Details
    ISSN: 1434-1948
    Schlagwort(e): Ligand field spectra ; Phosphonate complexes ; X-ray structures ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The synthesis and characterization of transition-metal coordination compounds containing the ligand diethyl 2-quinolylmethylphosphonate (2-qmpe) is described. Complexes of CoII, MnII, NiII, CdII, and ZnII were found to be mutually isomorphous according to their X-ray powder diffraction patterns and IR spectra. The new coordination compounds were identified and characterized by elemental analysis, magnetic measurements, infrared and ligand-field spectra. The crystal structures of the complexes [M(2-qmpe)4(H2O)2](ClO4)2 (M = Ni, 1; Mn, 2) reveal six-coordinate [M(2-qmpe)4(H2O)2] cations with the qmpe ligand coordinating via the oxygen rather than via the nitrogen atom, as well as lattice perchlorate anions. The metal ion is octahedrally surrounded by the four oxygen atoms of the four organic ligands. The non-participation of the pyridine nitrogen atom is unusual. The two water molecules occupy the fifth and the sixth coordination sites in a trans configuration. The coordinated water molecules are strongly hydrogen-bonded to the pyridine nitrogen atom of the 2-qmpe, further stabilizing the solid-state structure. The geometry of the metal ion can be described as distorted octahedral. For the CuII complex, a hydroxo-bridged dinuclear structure of the type [Cu(2-qmpe)2(OH)(H2O)2]2(ClO4)2 is proposed, based on its spectroscopic and magnetic properties. Ligand-field spectra of the Co and Ni compounds were found to be in agreement with the tetragonally distorted octahedral geometry.
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  • 45
    Digitale Medien
    Digitale Medien
    Polynuclear Complexes with Propynylidene C3-Bridges: General Synthetic Route to Bis-, Tris-, and Tetrakis(ethynylcarbene) Complexes (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 191-202 
    Details
    ISSN: 1434-1948
    Schlagwort(e): Polynuclear complexes ; Carbene complexes ; Bridging ligands ; Alkynyl complexes ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The sequential reaction of two equivalents of the dimethylamino(ethynyl)carbene complexes [(CO)5M=C(NMe2)C≡CH] [M = W (1a), Cr (1b)] with two equivalents of nBuLi and one equivalent of a transition metal dichloride, [Cl2M′(Ln)], affords trinuclear biscarbene complexes of the type [(CO)5M=C(NMe2)C≡C-M′(Ln)-C≡CC(NMe)2=M(CO)5] [M′(Ln) = Ni(PEt3)2 (2a, b), Pd(PEt3)2 (3a, b), Pt(PEt3)2 (4a, b), Fe(dmpe)2 (6a), Hg (8a), Ti(η5-C5H5)2 (9a, b)] [dmpe = 1,2-bis(dimethylphosphino)ethane]. Treatment of 1a with equimolar amounts of first nBuLi and then [Cl2M′(Ln)] results in the formation of the monosubstitution products [(CO)5W=C(NMe2)C≡CM′(Ln)] [M′(Ln) = trans-Pd(PEt3)2Cl (5a), trans-Fe(dmpe)2Cl (7a)]. Additionally, the synthesis of the heterobimetallicethynylcarbene complex [(CO)5W=C(NMe2)C≡CPd(PEt3)2C≡CH] (10a), starting from 1a and [ClPd(PEt3)2C≡CH], is described. When three equivalents of 1a are treated, first with three equivalents of nBuLi and then with one equivalent of the trihalides PCl3 or BBr3, the novel tris(ethynylcarbene) complexes [{(CO)5W=C(NMe2)C≡C}3E] [E = B (11a), P (12a)] are obtained. The reaction of four equivalents of 1a,b with four equivalents of nBuLi, followed by addition of one equivalent of a group 14 tetrachloride [M′Cl4], yields the novel tetrakis(ethynylcarbene) complexes [{(CO)5M=C(NMe2)C≡C}4M′] [M′ = Si (13a, b), Ge (14a), Sn (15a, b)]. The complexes 8a, 9a, 12a, and 15a were characterized by X-ray structural analyses. All spectroscopic and structural data suggest that the carbene fragments and the central transition metal or heteroatom in these new bis-, tris-, and tetrakis(ethynylcarbene) complexes interact only weakly.
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  • 46
    Digitale Medien
    Digitale Medien
    2-Oxacyclopentylidene, 2-Oxacyclohexylidene, and 2-Oxacycloheptylidene Rhenium Complexes by Reaction of ω-Alkynols with the [{MeC(CH2PPh2)3}Re(CO)2]+ Auxiliary (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 211-219 
    Details
    ISSN: 1434-1948
    Schlagwort(e): Rhenium ; Oxacyclocarbene complexes ; Vinylidene comlexes ; Alkynols ; Tripodal ligands ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Various β-, γ-, and δ-alkynols have been reacted with the 16e- fragment [(triphos)Re(CO)2]+ generated in situ by H2 elimination from [(triphos)Re(CO)2(η2-H2)]BF4 [triphos = MeC(CH2PPh2)3]. Irrespective of the length of the alkyl chain between the C≡C and OH functional groups in the ω-alkynol, 2-oxacyclocarbene complexes are obtained. These include the 2-oxacyclopentylidene derivatives [(triphos)Re(CO)2{=CCH2CH2CH2O}]BF4 and [(triphos)Re(CO)2{=CCH2CH2CH(Me)O}]BF4, the 2-oxacyclohexylidene dervivatives [(triphos)Re(CO)2{=CCH2CH2CH2CH2O}]BF4 and[(triphos)Re(CO)2{=CCH2CH2CH2CH(Me)O}]BF4, and the 2-oxacycloheptylidene complex [(triphos)Re(CO)2{=CCH2CH2- CH2CH2CH2O}]BF4. The latter compound contains a unprecedented seven-membered oxacarbene ring. The rhenium-assisted δ-alkynol to 2-oxacyloheptylidene rearrangement proceeds via the hydroxybutylvinylidene kinetic intermediate [(triphos)Re(CO)2{C=C(H)CH2CH2CH2CH2OH}]BF4, which has been characterized in both the solid state and solution. An X-ray analysis has been carried out on a single crystal of [(triphos)Re(CO)2{=CCH2CH2CH(Me)O}]BF4. The structure of this complex consists of [(triphos)Re(CO)2{=CCH2CH2CH(Me)O}]+ cations and tetrafluoroborate anions with no interspersed solvent molecules. A facial triphos ligand, two cis-disposed carbonyl groups and a 2-oxacyclopentylidene ligand coordinate the Re centre in a slightly distorted octahedral environment.
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  • 47
    Digitale Medien
    Digitale Medien
    Titanium Complexes with a Linked Amido-Cyclopentadienyl Ligand and a Bidentate Organyl Group: Synthesis, Structure, and Ethene Polymerization Activity (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 237-244 
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    ISSN: 1434-1948
    Schlagwort(e): Titanium complexes ; Amido-cyclopentadienyl ligand ; Titanium alkyl ; Intramolecular coordination ; Ethene polymerization ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Titanium complexes containing a linked isopropyl- or benzylamido(tetramethylcyclopentadienyl) ligand C5Me4SiMe2NR (R = iPr, CH2Ph,) and one bidentate organyl group C6H4(CH2NMe2)-2, CH2C6H4(NMe2)-2, and {η5-C5H3(CH2NMe2)-2}Fe(η5-C5H5) were prepared by salt metathesis of the corresponding dichloro complex Ti(η5:η1-C5Me4SiMe2NR)Cl2 with the lithium organyl. Single crystal X-ray structural analysis of Ti(η5:η1-C5Me4SiMe2NCH2Ph)- {C6H4(CH2NMe2)-2}Cl and of Ti(η5:η1-C5Me4SiMe2NiPr){CH2C6H4(NMe2)-2}Cl revealed the presence of intramolecular coordination with square pyramidal geometry around titanium. In the ferrocenyl derivative Ti(η5:η1-C5Me4SiMe2NCH2Ph)[{η5-C5H3(CH2NMe2)-2}Fe(η5-C5H5)]Cl the NMe2 group is not bonded at the titanium atom. Ethene polymerization catalyzed by these complexes upon activation with methylaluminoxane was examined.
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  • 48
    Digitale Medien
    Digitale Medien
    Hydrolytic Cleavage of Diphosphates, Sulfonatophosphates, and Disulfonates by (Pyrazolylborate)zinc Hydroxide Complexes (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 271-274 
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    ISSN: 1434-1948
    Schlagwort(e): Zinc complexes ; Pyrazolylborate ligands ; Hydrolytic cleavage ; Diphosphate ; Sulfonatophosphate ; Disulfonate ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Three (pyrazolylborate)zinc hydroxide complexes Tp*Zn-OH were used as hydrolytic reagents to cleave the P-O-P, P-O-S, and S-O-S linkages of organic diphosphates, sulfonatophosphates, and disulfonates. The resulting complexes of the types Tp*Zn-OPO(OR)2 and Tp*Zn-OSO2R could also be obtained by condensation reactions between Tp*Zn-OH and HO-PO(OR)2 or HO-SO2R. Two of them were characterized by structure determinations.
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  • 49
    Digitale Medien
    Digitale Medien
    K2AuPS4, Tl2AuPS4, K2AuAsS4, and KAu5P2S8: Syntheses, Structures, and Properties of Quaternary Gold Thiophosphate and Thioarsenate Compounds (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 283-289 
    Details
    ISSN: 1434-1948
    Schlagwort(e): Gold ; Chalcogenide ; Flux reaction ; Structure determination ; Metal-metal bonding ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The novel compounds K2AuPS4 (1), Tl2AuPS4 (2), K2AuAsS4 (3), and KAu5P2S8 (4) have been synthesized by direct reaction of the elements with a molten alkaline polythiophosphate(arsenate) flux at 550°C. The crystal structures of these compounds have been determined by single-crystal X-ray diffraction techniques. 1, 2, and 3 crystallize in the monoclinic space group P21/m. The structures of 1, 2, and 3 consist of infinite, one-dimensional anionic chains running along the crystallographic b axis. The chains are separated by potassium or thallium ions. Neighbouring Au atoms are bridged by MS43- tetrahedra (M = P, As) in a trans orientation. Compound 4 crystallizes in the space group P21/c. The anionic chains of 4 are built up from linear AuS2 dumbbell units and PS43- tetrahedra. The chains extend along the [110] and [110] direction and are separated by charge balancing K+ cations. Each of the compounds was investigated by differential thermal analysis, FT-IR, and solid-state UV/Vis diffuse reflectance spectroscopy.
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  • 50
    Digitale Medien
    Digitale Medien
    Dinuclear Molybdenum(III) and Tungsten(III) Calix[4]arene Complexes - Metal-Metal Triple Bonds Supported by Bridging Calix[4]arene Ligands (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 299-303 
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    ISSN: 1434-1948
    Schlagwort(e): Calix[4]arenes ; Calix[4]arene complexes ; Molybdenum ; Tungsten ; Metal-metal bonding ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Addition of p-tert-butylcalix[4]arene LH4 to the dinuclear compounds M2(NMe2)6 (M = Mo, W) results in the formation of [NH2Me2]2[L2M2] 1 (M = Mo) and 2 (M = W). Both compounds have been characterized by spectroscopic methods and single-crystal X-ray diffraction. The metal-metal distances of 1 and 2, of 2.194(1) Å and 2.293(1) Å, respectively, are consistent with the retention of the M≡M triple bond. Both „ate” complexes contain a [M≡M]6+ dimetal core, supported by two bridging μ2-κ2O,κ2O-calix[4]arene ligands in the solid state. These compounds are the first examples of a formally fourfold deprotonated calix[4]arene acting as a μ2-κ2O,κ2O bridging ligand for two transition metal centres. The calix[4]arenes in 1 and 2 are distorted from a cone conformation in the uncomplexed ligand, to an elliptical cone section. 1H-NMR data at variable temperatures suggest fluxional behaviour of 1 and 2 in solution.
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  • 51
    Digitale Medien
    Digitale Medien
    Bis(pentamethylcyclopentadienyl)-Substituted Phosphanes: Synthesis and Structure (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 331-337 
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    ISSN: 1434-1948
    Schlagwort(e): Bis(pentamethylcyclopentadienyl)phosphanes ; Aminobis(pentamethylcyclopentadienyl)phosphanes ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The bis(1,2,3,4,5-pentamethyl-1,3-cyclopentadien-1-yl)phosphanes 3-7 are formed in good yields by the reaction of the halogenophosphanes 2a or 2b with the appropriate nucleophile. Following another route, the dialkylaminobis(pentamethylcyclopentadienyl)phosphanes 11a-c have been synthesized by the treatment of dichloro(dialkylamino)phosphanes with two equivalents of (pentamethylcyclopentadienyl)lithium. The compounds 3-11 have been characterized by multinuclear NMR spectroscopy and 3, 5, 6, and 11a have also been characterized by single-crystal X-ray diffraction studies. The molecular structure of 11a is governed by steric congestion, which typically would lead to a parallel arrangement of the two pentamethylcyclopentadienyl ligands at the phosphorus atom. However, surprisingly, the crystal structure of the (dimethylamino)phosphane 11a, exhibits a tilted, rather than a parallel, conformation of the pentamethylcyclopentadienyl groups [tilt angle: 130.6(1)°].
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  • 52
    Digitale Medien
    Digitale Medien
    Monodentate and Bridging Coordination of 3,3′-Annelated 2,2′-Bipyridines in Zerovalent Palladium- and Platinum-p-quinone Complexes (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 319-330 
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    ISSN: 1434-1948
    Schlagwort(e): Palladium ; Platinum ; Bidentate nitrogen ligands ; p-Quinone ; Alkenes ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Compounds of the type M(N∩N-κN)(nq)2 and M2(μ2-N∩N)(μ2-pbq)2, in which nq = 1,4-naphthoquinone, pbq = 1,4-benzoquinone, and N∩N is a monodentate or bridging ligand of the α-diimine type, were obtained from reactions of Pd(dba)2 in toluene with the 3,3′-annelated-2,2′-bipyridines: 4,5-diazafluoren-9-one (dafo) and 4,5-diazafluorene (dafe) in the presence of the appropriate p-quinone. In the corresponding reactions with 2,2′-bipyridine (bpy), 1,10-phenanthroline (phen), 2,2′-bipyrimidine (bpym), N,N′-dicyclohexyl-1,4-diaza-1,3-butadiene (chex-dab), bis[N-(o,o′-diisopropyl)phenylimino]acenaphthene (o,o′-iPr2-bian) and 5,6-dihydro-1,10-phenanthroline (dh-phen) only complexes of the type M(N∩N-κ2N)(Q) were formed (Q = nq, pbq). The structures of the complexes have been established by NMR in solution and by X-ray diffraction in the solid state; crystal structures of Pd(bpy-κ2N)(η2-pbq) (1) Pd(dafo-κN)(η2-nq)2 (14) and Pd2(μ2-dafo)(μ2,η2:η2-pbq)2 (16) have been determined. Of the ligands, dafo and dafe are the only ones apt to form complexes containing a monodentate or bridging N∩N ligand. This behaviour is ascribed to the geometrical constraints of dafo and dafe; the annelation by one carbon atom at the 3,3′-positions in these ligands causes an increase in bite angle from approximately 77° to 82°.
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  • 53
    Digitale Medien
    Digitale Medien
    Soluble Chloro- and Aryl(phthalocyaninato)indium(III) Complexes: Synthesis and Characterization (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 367-373 
    Details
    ISSN: 1434-1948
    Schlagwort(e): Phthalocyanines ; Indium ; Indium-carbon bond ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The synthesis of highly soluble chloro(phthalocyaninato)indium(III) complexes RxPcInCl (3a: R1 = tert-butyl, R2 = H, x = 4 and 4a: R1 = R2 = n-pentyl, x = 8), and their reactions with R′MgBr [R′ = p-trifluoromethylphenyl- (b), m-trifluoromethylphenyl- (c), p-fluorophenyl- (d), perfluorophenyl- (e)] leading to the stable σ-bonded aryl(phthalocyaninato)indium(III) complexes 3b-e, 4b-e are described. All compounds were characterized by IR, UV/Vis, MS, 1H, 13C and 19F NMR as well as elemental analyses. Phenyl(phthalocyaninato)indium(III) (4f) was prepared by the reaction of (n-C5H11)8PcInCl (4a) with PhLi. The high solubility of the complexes 3a-e and 4a-f is, aside from the influence of the peripheral substituents, considered to be derived from the large dipole moments present which are due to the strongly electron withdrawing axial ligands, and from the lower tendency of axially substituted phthalocyaninato metal complexes to form aggregates.
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  • 54
    Digitale Medien
    Digitale Medien
    Ylidylphosphanes and -diphosphanes (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 381-388 
    Details
    ISSN: 1434-1948
    Schlagwort(e): Phosphanes ; Phosphorus ylides ; Nucleophilic addition ; Structure elucidation ; NMR spectroscopy ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Chlorophosphanyl and dichlorophosphanyl alkylidene- and benzylidenephosphoranes 6 and 8 are converted by reaction with LiAlH4 to the respective phosphanes 7 and 9. The former can be isolated, but decompose on heating or on protonation to give the ylidyl diphosphane 11 and the phosphonium ylide or phosphonium salt, respectively. The final products are the cyclooligophosphanes 15-17. Only the C-tert-butyl derivative 7c is stable in both regards. The conformation of the RPH group in 7 as compared to that of the RPCl group in 6 clearly reflects their different interaction with the ylide moiety.
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  • 55
    Digitale Medien
    Digitale Medien
    Fluxionality and Phosphane Arm-off Reactions of Octahedral Ruthenium(II) Complexes with the Tripodal Polyphosphane MeC(CH2PPh2)3 (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 407-414 
    Details
    ISSN: 1434-1948
    Schlagwort(e): Ruthenium ; Phosphorus ; Triphos complexes ; Fluxionality ; Arm-off dissociation ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Structural fluxionality is apparent in the 1H- and 31P-NMR spectra of compounds of the type [Ru(L)(MeCN)(triphos)](CF3SO3), 2-5, at 25°C, where L represents a diorganyldithiocarbamate or a heterocyclic κ2N,S coordinating thioamide. In contrast, complexes [Ru(Et2NCS2)(Y)(triphos)]n+ (6, n = 1, Y = CO; 7, n = 0, Y = CN-; 8, n = 0, Y = H-) are stereochemically rigid in solution at this temperature, indicating that MeCN dissociation must occur for the crowded octahedral coordination spheres of 2-5. Reaction of [Ru(MeCN)3(triphos)](CF3SO3)2, 1, with Na(Et2NCS2) at a 1:2 molar ratio yields [Ru(Et2NCS2-κ2S)(Et2NCS2-κS)(triphos)], 9, which slowly converts to [Ru(Et2NCS2-κ2S)2(triphosO-κ2P)], 10, on recrystallization from ethanol/acetone under air [triphosO is O=P(Ph)2CH2C(CH3)(CH2PPh2)2]. A similar κ3P→κ2P arm-off dissociation leads to the formation of [Ru(mpy-κ2N,S)2(triphosO-κ2P)] (13) and [Ru(mmim-κ2N,S)2(triphosO-κ2P)] (14) (Hmpy = 2-mercaptopyridine, Hmmim = 2-mercapto-1-methylimidazole). Crystal structures are reported for [Ru(mbt-κ2N,S)(MeCN)(triphos-κ3P)](CF3SO3) (4) (Hmbt = 2-mercaptobenzothiazole), [Ru(mpym-κ2N,S)(mpym-κS)(triphos-κ3P)] (11) (Hmpym = 2-mercaptopyrimidine) and 14, the latter of which is present as the OC-6-13 isomer.
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  • 56
    Digitale Medien
    Digitale Medien
    Stability of Bridged and Unbridged η2-Alkyne-titanocene and -zirconocene Complexes - Influence of Metals, Alkyne Substituents, Cp Substitution and Additional Ligands (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 419-424 
    Details
    ISSN: 1434-1948
    Schlagwort(e): Alkyne complexes ; Titanium ; Zirconium ; Coordination mode ; Metallacycles ; Cyclopentadienes ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The influence of metals, alkyne substituents, Cp substitution and additional ligands on the stability of bridged and unbridged η2-alkyne-titanocene and -zirconocene complexes has been investigated. The reduction of the complex [(η5-C5H4)-SiMe2-(η5-C5H4)]TiCl2 with magnesium in the presence of tolan (PhC2Ph) does not give the expected alkyne-titanocene complex [(η5-C5H4)-SiMe2-(η5-C5H4)]Ti(η2-PhC2Ph) but by coupling of two tolan molecules the corresponding titanacyclopentadiene [(η5-C5H4)-SiMe2-(η5-C5H4)]TiC4Ph4 (1) was obtained. In the analogous reaction with Me3SiC2SiMe3 the stable η2-alkyne complex without additional ligands [(η5-C5H4)-SiMe2-(η5-C5H4)]Ti(η2-Me3SiC2SiMe3) (2) was formed, due to the sterical influence of the alkyne substituents. The compounds without additional ligands (thi)2Ti(η2-PhC2Ph) (3) and (thi)2Ti(η2- Me3SiC2SiMe3) (5) were isolated from the unbridged titanocene complex (thi)2TiCl2 (thi = tetrahydroindenyl). Two equivalents of complex 3 reacted with one equivalent of water to yield the dimeric alkylidene-μ-oxo complex [(thi)2Ti(CPh=CHPh)]2(μ-O) (6). The reaction of the unbridged zirconocene compound (thi)2ZrCl2 gave the alkyne complex (thi)2Zr(THF)(η2-Me3- SiC2SiMe3) (7) which is stabilized by THF. At higher temperature THF was eliminated from the orange complex 7 forming the green complex (thi)2Zr(η2-Me3SiC2SiMe3). This behaviour was investigated in detail using NMR spectroscopy and compared to similar complexes such as Cp2Zr(η2-Me3SiC2SiMe3) (not stable without THF), (ebthi)2Zr(η2-Me3SiC2SiMe3) (ebthi = ethylenebistetrahydroindenyl; stable without THF) and Cp*2Zr(η2-Me3SiC2SiMe3) (Cp* = pentamethyl-Cp, stable without THF). All complexes were characterized by spectroscopic methods. X-ray structural determinations were conducted for the complexes 1, 3 and 7. Compound 3 is the first example of a structurally characterized tolan-titanocene complex without additional ligands.
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  • 57
    Digitale Medien
    Digitale Medien
    Complexation Studies with a Calix[4]arene-Derived Phosphinite - Divergent Arrays of Cavities Linked by MCl2 Fragments (M = Pd, Pt) (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 451-457 
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    ISSN: 1434-1948
    Schlagwort(e): Calixarene ; Phosphinite ; Calixphosphane ; Transition metals ; X-ray diffraction ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: A cone-shaped calix[4]arene-derived monophosphinite, 25,27-di(ethoxycarbonylmethoxy)-26-hydroxy-28-(diphenylphosphinooxy)calix[4]arene (L1), has been prepared in two steps from calix[4]arene. Treatment of L1 with [AuCl(tetrahydrothiophene)] in tetrahydrofuran gave the phosphinite complex [AuClL1] (1). Reaction of [PdCl2(PhCN)2] with two equivalents of L1 gave selectively trans-[PdCl2L12] (2). Complex 2 · 2 CH2Cl2 crystallizes in the triclinic space group P1¯. The molecule is centrosymmetric, leading to a divergent array of the two calixarene moieties. The palladium atom resides outside both cones. As a result of steric interactions, the meta and para carbon atoms of the PPh2-bearing aryl ring are significantly pushed to the interior of the cavity. The related platinum complex trans-[PtCl2L122] (3), was obtained similarly from [PtCl2(PhCN)2] and presents in the solid state a structure which is isomorphous to that of 2. The diphosphinite 25,27-di(ethoxycarbonylmethoxy)-26,28-bis(diphenylphosphinoxy)calix[4]arene (cone) (L2) has also been prepared and reacts with [PtCl2(PhCN)2] to yield oligomeric material.
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  • 58
    Digitale Medien
    Digitale Medien
    Mesomorphic Cyclometalated (Cyclopentadienyl)palladium and -platinum Complexes (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 501-504 
    Details
    ISSN: 1434-1948
    Schlagwort(e): Metallomesogens ; Azo compounds ; Palladium ; Platinum ; Cyclopentadienyl complexes ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The mesogenic 4,4′-bis[4-(n-octyloxy)benzoyloxy]azobenzene (HL) ligand reacts with [(PhCN)2PdCl2] to give the dinuclear cyclometalated complex [(μ-Cl)(L)Pd]2 (1), from which the mononuclear half-sandwich [(η5-C5H5)(L)Pd] (2) species has been obtained by reaction with Tl(C5H5). The PtII analogue of 2, [(η5-C5H5)(L)Pt] (4), has been prepared in a similar manner starting from [(μ-Cl)(L)Pt]2 (3). Both dinuclear complexes 1 and 3 display a smectic C phase (SC) stable over 80°C. Whereas 4 is the first example of an 18-electron PtII mesogen, both mononuclear 2 and 4 are mesomorphic materials that exhibit a nematic phase spanning a wide temperature range.
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  • 59
    Digitale Medien
    Digitale Medien
    The “Coloring Problem” in Solids: How It Affects Structure, Composition and Properties (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 523-536 
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    ISSN: 1434-1948
    Schlagwort(e): Quantum chemistry ; Intermetallic compounds ; Transition metal cluster compounds ; Crystallography ; Electronic structure ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The “coloring problem,” as applied to the field of solid state chemistry, addresses the issues of structural preference as well as the distribution of different elements within a given structure. Both the connectivity and arrangement of elements in a solid affect physical and chemical properties, so a clear understanding of the forces controlling how elements will arrange themselves in a solid state structure creates the ability to predict structure-composition-property relationships. There are two fundamental energetic contributions that influence how elements in a structure order: the site energy and the bond energy. This review examines how these two parts of the total electronic energy work together to influence the observed structures, compositions, and properties of intermetallics and transition metal cluster compounds.
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  • 60
    Digitale Medien
    Digitale Medien
    Octanuclear Bis(triple-helical) Metal(II) Complexes (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 559-563 
    Details
    ISSN: 1434-1948
    Schlagwort(e): Metal(II) complexes ; Octanuclear complexes ; Supramolecular chemistry ; Zinc ; Cadmium ; Manganese ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The reaction of H2L1 and H2L2 with divalent metal ions leads to octanuclear bis(triple-helical) metal(II) complexes of the general composition [Zn8O2L26] (3) and [M8O2L16] (4: M = Cd2+; 5: M = Mn2+). NMR studies of the diamagnetic cadmium complex 4c show six equivalent ligands. Unambiguous characterisation of 5b was achieved by X-ray crystallographic analysis.
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  • 61
    Digitale Medien
    Digitale Medien
    Syntheses of 3-Heteroaryl-2H-Azaphosphirene Tungsten Complexes (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 575-578 
    Details
    ISSN: 1434-1948
    Schlagwort(e): Phosphorus heterocycles ; 2H-Azaphosphirene complexes ; Carbene complexes ; Tungsten ; Cyclizations ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The syntheses of 3-heteroaryl-substituted 2H-azaphosphirene pentacarbonyltungsten complexes are reported. The products were characterized by multinuclear NMR spectroscopy (1H, 13C, 15N, 31P, 183W); the structure of the 3-N-methylpyrryl-substituted 2H-azaphosphirene complex was determined by single-crystal X-ray structure analysis.
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  • 62
    Digitale Medien
    Digitale Medien
    Controlled Degradation of a Ligand-Deficient Complex: From [{Cd(C6F5)(STrt)}4] to [{Cd(C6F5)(STrt)}3(OH)]- and [Cd(C6F5)(STrt)2]- (Trt = Triphenylmethyl) (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 657-662 
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    ISSN: 1434-1948
    Schlagwort(e): Cadmium ; Crown compounds ; Pentafluorophenyl ; Potassium ; S ligands ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Bis(pentafluorophenyl)cadmium, [Cd(C6F5)2], reacts with equimolar amounts of triphenylmethanethiol, TrtSH, in toluene to give [{Cd(C6F5)(STrt)}4] · 1.5 tol (1). The cuboidal complex of 1 has been transformed into the heterometallic cuboidal complex [{Cd(C6F5)(STrt)}3(OH)K(THF)3] (2) by reaction with KOH in tetrahydrofuran. In the presence of 18-crown-6, the compound [K(18-crown-6)(THF)2][{Cd(C6F5)- (STrt)}3(OH)] · THF (3) has been obtained instead of 2. X-ray structure analysis shows the anion of 3 to be an incomplete cuboidal complex, which alternatively can be described as a cyclic trimer of the {Cd(C6F5)(STrt)} unit stabilized by a μ3-hydroxo ligand. The compound [K(18-crown-6)(THF)2][Cd(C6F5)(STrt)2] (4) has been isolated from reaction mixtures containing 1, KSTrt and 18-crown-6. The cadmium atom in 4 is three-coordinated, in contrast to the cadmium atoms in 1-3, which are situated in strongly distorted coordination tetrahedra. Intramolecular C6H5···C6F5···C6H5 stacks in 4 are interpreted as resulting from attractive ligand-ligand interactions. Spectroscopic data, particularly from 13C-NMR and IR spectra, are consistent with the order of ligand deficiency: 1 〉 2 〉 3 〉 4. The macrocyclic, eight-coordinate complex [K(18-crown-6)(THF)2]+ in 3 and 4 contains trans arranged THF ligands.
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  • 63
    Digitale Medien
    Digitale Medien
    Synthesis and Structure of Gallium/Silicon Heterocycles with a Ga2Si2 and a Ga3Si Framework⋆ (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 745-749 
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    ISSN: 1434-1948
    Schlagwort(e): Gallium ; Silicon ; Heterocycles ; Main group elements ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The reaction of Ga2X4· 2 dioxane with four equivalents of (Me3Si)3SiLi(thf)3 (= hypersilyllithium) affords for X = Br a 1,3,2,4-disiladigalletane together with tetrahedral hypersilylgallium(I). For X = Cl an anionic 1,2,3,4-silatrigalletanate, a four-membered heterocycle with a Ga3 unit, is isolated. These primary examples of gallium/group-14 heterocycles have been investigated by NMR spectroscopy as well as by X-ray single-crystal structure analysis. In addition, the synthesis and structure of bis(hypersilyl)gallium chloride is described. This monomeric molecule has a nearly T-shaped Si2GaCl framework.
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  • 64
    Digitale Medien
    Digitale Medien
    Novel Organoborane Lewis Acids via Selective Boron-Tin Exchange Processes Steric Constraints to Electrophilic Initiation by the Boron Halide (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 761-769 
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    ISSN: 1434-1948
    Schlagwort(e): Organometallics ; Boron ; Lithium ; Tin ; Metal-metal exchange ; Electrophilic reagents ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: With the purpose of preparing novel mono- and bidentate organoboron Lewis acids, the scope and limitations of synthesizing the requisite organoboranes by the boron-tin exchange between a boron halide and the appropriate organostannane have been examined in detail. The following organotin derivatives have been obtained either from the corresponding RMgBr or RLi reagent and MenSnCl4-n or from a Barbier procedure using the organic halide, Me3SnCl and magnesium metal: 1,2-bis(trimethylstannyl)ethyne, o-, m-, and p-bis(trimethyl-stannyl)benzenes, α,o-bis(trimethylstannyl)toluene, α,α-bis(trimethylstannyl)-o-xylene, and 2,2-dimethyl-2-stannaindane. The individual interaction of the 1,2-bis(trimethylstannyl)ethyne and the isomeric bis(trimethylstannyl)benzenes with Et2BBr produced the corresponding bis(diethylboryl)-derivatives. By contrast, with Et2BCl the α,o-bis(trimethylstannyl)toluene gave only o-diethylboryl-α-trimethylstannyltoluene and with BCl3 the α,α′-bis(trimethylstannyl)-o-xylene formed only,-bis-(chlorodimethylstannyl)-o-xylene. Furthermore, in the attempted double boron-tin exchange between o-bis(trimethylstannyl)benzene and BCl3, an unprecedented rearrangement of the 1-(dichloroboryl)-2-(trimethylstan-nyl)benzene intermediate into its 1-[chloro(methyl)boryl]-2-(chlorodimethylstannyl) isomer was observed. Likewise, o-bis(trimethylstannyl)benzene with PhBCl2 produced by a similar rearrangement 1-[methyl(phenyl)boryl]-2-(chloro-dimethylstannyl)benzene. The thermolysis of such boranes led variously to definite dimers or ill-defined oligomers. Preliminary studies of the properties of these organoboranes have identified the heightened Lewis acidity of 1,2-bis(diethylboryl)ethyne and the π-electron delocalization involving the 2pz-boron orbitals in the 9,10-dihydro-9,10-diboraanthracene system. Finally, an electronic mechanism for the boron-tin exchange has been developed to account for the selectivity of the boron halide's attack at unsaturated carbon-tin bonds.
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  • 65
    Digitale Medien
    Digitale Medien
    Oxovanadium(IV) and -(V) Complexes with Aminoalcohol Ligands: Synthesis, Structure, Electrochemical, and Magnetic Properties (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 799-805 
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    ISSN: 1434-1948
    Schlagwort(e): Aminoalcohol ligands ; Hydrogen bonds ; Magnetic properties ; Oxo complexes ; Vanadium ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The aminoalcohol ligands diethanolamine (H2dea) and triethanolamine (H3tea) react with [VO(acac)2] to yield the tetranuclear oxovanadium(IV) complexes [{VO(dea)}2{VO(acac)}2(μ2-OMe)2] (1) and [{VO(Htea)}2{VO(acac)}2(μ2-OMe)2] (2). In the case of the potentially bridging aminoalcohol ligands N,N,N′,N′-tetrakis(2-hydroxyethyl)ethylenediamine (H4edte) and N,N,N′,N′-tetrakis(2-hydroxypropyl)ethylenediamine (H4edtp) the corresponding oxovanadium(IV) complexes could not be isolated. Instead after air oxidation the ligand supported binuclear oxovanadium(V) complexes [{VO(acac)}2(edte)] (3) and [{VO(acac)}2(edtp)] (4) are obtained. The reaction of the ligand H4edtp with ammonium meta-vanadate in methanol solution leads to the methoxy bridged binuclear oxovanadium(V) complex [(VO)2(edtp)(μ2-OMe)2] (5). The tetranuclear oxovanadium(IV) complexes can be isolated as crystalline compounds 1 · 2 MeOH and 2 · 2 MeOH and have been characterized by IR, UV/Vis, and ESR spectroscopy as well as cyclic voltammetry and magnetic susceptibility measurements. Single-crystal diffraction studies reveal that the complexes 1 and 2 contain a tetranuclear {(VO)4(μ3-OR)2(μ2-OR)4}2+ core composed of three different types of edge-shared binuclear units, whereas the oxovanadium(V) complexes 3, 4, and 5 posses binuclear structures, that are either ligand supported as in the case of 3 and 4 or contain a μ2-methoxy bridged{(VO)2(μ2-OR)2}4+ core as in the case of 5. ESR and magnetic data indicate a singlet ground state for 1 · 2 MeOH and 2 · 2 MeOH, although competing ferromagnetic exchange interactions are operative within the tetranuclear core structure. In the solid state compounds 1 · 2 MeOH and 2 · 2 MeOH hydrogen bridged supramolecular structures are found. The hydrogen bonding scheme of both compounds leads to the formation of a similar chain arrangement of the tetranuclear complexes 1 and 2.
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  • 66
    Digitale Medien
    Digitale Medien
    The Triphosphide (tBu3Si)2P3Na: Formation, X-ray and Ab initio Structure Analyses, Protonation and Oxidation to Triphosphane (tBu3Si)2P3H and Hexaphosphanes (tBu3Si)4P6⋆ (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 833-841 
    Details
    ISSN: 1434-1948
    Schlagwort(e): Silicon ; Phosphorus ; Oligophosphides and -phosphanes ; NMR spectra ; X-ray structure analysis ; Ab initio calculations ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The violet THF adduct (tBu3Si)2P3Na(THF)4 (1a) of the triphosphide (tBu3Si)2P3Na (1) is prepared, (i) by protolysis of the tetraphosphide (tBu3Si)2P4Na2 (2) with an equimolar amount of CF3CO2H in THF (transformation of 2 into 1), (ii) by the reaction of tBu3SiNa and the oligophosphane (tBu3SiP3)n in THF (building-down of Pn), and (iii) by the action of tBu3SiNa on PCl3 in THF (building-up of Pn). According to X-ray structural analysis, the SiPPPSi skeleton of the anionic part [tBu3SiPPPSitBu3]- of 1a is W-shaped with two P-P 11/2 bonds; in addition, 1a contains a planar deltoid P3Na backbone with the 4 THF molecules coordinated to Na. The protolysis of 1a leads to cyclotriphosphane (tBu3Si)2P3H (11), and the oxidation of 1a leads to 1,1′-bicyclotriphosphane (tBu3Si)2P3-P3(SitBu3)2 (12) as the main product and bicyclo[3.1.0]hexaphosphane (tBu3Si)4P6 (13) as an isomer of 12. The structures of 11, 12, and 13 as well as the structure of 1a have been unambiguously determined by 31P-NMR studies. Ab initio structure and energy calculations show that the acyclic P3H2- with allylic conjugation and P-P 11/2 bonds is thermodynamically more stable than the cyclic isomer whereas, in contrast, the neutral compound P3H3 prefers the cyclic form. The exceptional downfield shift of the NMR signal of the central phosphorus in 1a is in agreement with DFT NMR calculations for a model compound [H3SiPPPSiH3]Na with P-P 11/2 bonds.
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  • 67
    Digitale Medien
    Digitale Medien
    A Trinuclear Palladium(II) Complex with Bridging 2-Hydroxyacetophenone N4-Ethylthiosemicarbazone Ligands - An Unusual Dimethylformamide Promoted Deprotonation and Aggregation (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 861-863 
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    ISSN: 1434-1948
    Schlagwort(e): Trinuclear triangulo palladium complex ; 2-Hydroxyacetophenone N4-ethylthiosemicarbazone ; Dimethylformamide aggregation ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The X-ray crystal structure of a palladium(II) complex of 2-hydroxyacetophenone N4-ethylthiosemicarbazone (H2Ap4E) shows it to be a triangular,trinuclear complex with bridging thiosemicarbazonato sulfur atoms. This species can be formed from a monomer on dissolution in DMF or directly from Li2PdCl4 and the thiosemicarbazone in methanol-ammonia solution.
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  • 68
    Digitale Medien
    Digitale Medien
    Zirconocene-(μ-Organyl)borate Betaines Derived by Treatment of a (σ-Alkenyl)(σ-alkynyl)zirconocene Complex with Tris(pentafluorophenyl)borane⋆ (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 889-895 
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    ISSN: 1434-1948
    Schlagwort(e): Zirconocene ; Metallocene cation ; Isonitrile insertion ; Isonitrile complex ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Hydrozirconation of propyne followed by treatment with propynyllithium yields the (σ-propenyl)(σ-propynyl)zir-conocene complex 11. Its treatment with the organometallic Lewis acid B(C6F5)3 results in transfer of the σ-propynyl group from zirconium to boron followed by insertion of the alkynylborate triple bond into the zirconium carbon bond of the remaining metallaallyl cation to furnish the zirconocene-(μ-hydrocarbyl)borate betaine complex 14. This reacts with three molar equivalents of tert-butyl isocyanide to give 16. Complex 16 contains a five-membered carbocyclic ring, formed by carbon-carbon coupling of the former propenyl and propynyl groups with the C≡N-R reagent, to which a (η2-iminoacyl)(ĸ-tert-butyl isocyanide)zirconocene moiety is attached. Complex 16 was characterized by an X-ray crystal structure analysis.
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  • 69
    Digitale Medien
    Digitale Medien
    A Methylene-Bridged Dialuminium Compound as a Chelating Lewis Acid: Complexation of Nitrite and Nitrate Anions by R2Al-CH2-AlR2[R = CH(SiMe3)2]⋆ (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 921-926 
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    ISSN: 1434-1948
    Schlagwort(e): Aluminium ; Chelates ; Lewis acids ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Sodium nitrite (NaNO2) dissolves readily in THF, when the methylene-bridged dialuminium compound R2Al-CH2-AlR2 [R = CH(SiMe3)2] 1 with two coordinatively unsaturated aluminium atoms is added. Compound 1 reacts as a chelating Lewis acid, and, as shown by a crystal structure deter-mination of the [Na([18]crown-6)(Et2O)]+ derivative 5c, a compound (5) is formed, in which one oxygen atom and the nitrogen atom of the nitrite ion are each coordinated by one aluminium atom to form a five-membered Al2CNO hetero-cycle. The second oxygen atom of the nitrite anion is not affected. Similarly, lithium nitrate (LiNO3) reacts with 1 to yield a THF soluble product (6a). Single crystals were obtain-ed of the [Li(N,N′,N′′-trimethyltriazinane)2]+ derivative 6c, whose structure shows each aluminium atom to be coordinated by one oxygen atom of the nitrate ion to give a six-membered Al2CNO2 heterocycle.
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  • 70
    Digitale Medien
    Digitale Medien
    Intramolecular Luminescence Quenching in Amino Acid Bridged Ruthenium(II)-Copper(II) Complexes with Negligible Ground-State Coupling (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 957-963 
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    ISSN: 1434-1948
    Schlagwort(e): Amino acids ; Bioinorganic chemistry ; Copper ; Luminescence ; Ruthenium ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: A series of heterobimetallic complexes [{Ru(bipy)2}m-AA{Cu(phen)(H2O)}](PF6)3 (m-AA = Nω-(4-carbonyl-4′-methyl-2,2′-bipyridyl)-L-α,ω-diamino acid; diamino acid (AA): 1b, L-2,3-diaminopropionic acid; 2b, L-2,4-diaminobutyric acid; 3b, L-ornithine, 4b, L-lysine) has been synthesized and characterized starting from the 2,2′-bipyridineruthenium(II)-substituted amino acids [{Ru(bipy)2}m-AA-αN-tBoc]2+ (αN-tBoc-1a-4a, αN-tBoc = Nα-tert-butoxycarbonyl). The metal centers in 1b-4b are bridged by insulating alkyl chains. Consequently, spectroscopic and electrochemical investi-gations confirmed the absence of any appreciable ground-state coupling between ruthenium(II) and copper(II). However, the luminescence of 1b-4b is significantly quenched compared to that of the parent compounds 1a-4a. Quenching was found to proceed only intramolecularly and to be most efficient in 1b with the shortest alkyl spacer. Equilibrium constants for the formation of 1b-4b were determined from luminescence titrations of the respective ruthenium-substituted amino acid with [Cu(phen)(NO3)2]. The complexes 2b-4b (K = 1.61-2.08 × 107M-1) were found to be significantly more stable than 1b (K = 5.7 × 106M -1). This is explained by a stronger electrostatic repulsion between the two metal centers in the latter compound.
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  • 71
    Digitale Medien
    Digitale Medien
    Phosphane Complexes of Alkaline Earth Metals (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 905-911 
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    ISSN: 1434-1948
    Schlagwort(e): Phosphane complexes ; Alkaline earth metal compounds ; Phosphanomethanides ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The reaction of lithium[bis(dimethylphosphanyl)(trimethyl-silyl)methanide] Li[(PMe2)2C(SiMe3)] with BeCl2 gave the homoleptic compound Be[(PMe2)2C(SiMe3)]2 (5) with four beryllium-phosphorus bonds constituting a distorted tetrahedron around the beryllium center. The reaction of MgCl2 with Li[(PMe2)2C(SiMe3)] resulted in the formation of the bis-chelate complex Mg[(PMe2)2C(SiMe3)]2 · 2 THF (7), where the distorted cis-octahedral magnesium center is additionally coordinated by two THF ligands. In the reaction of 7 with an additional equivalent of Li[C(PMe2)2(SiMe3)], THF is released and the magnesate anion {Mg[(PMe2)2C-(SiMe3)]3}- (8) was obtained. This compound is not only the first reported hexacoordinated magnesate, but also the first magnesium compound with six magnesium-phosphorus bonds. With CaCl2 and Li[C(PMe2)2(SiMe3)], a heptacoor-dinated complex Ca[(PMe2)2C(SiMe3)]2 · 3 THF (10) with three coordinating THF ligands was isolated. The complexes were characterized using 9Be{1H}-, 31P{1H}-, 1H-, 13C{1H}-NMR spectroscopy, and elemental analysis and by X-ray diffraction. The neutral compounds are highly soluble in nonpolar solvents.
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  • 72
    Digitale Medien
    Digitale Medien
    Structural Chemistry of Lithium Tetrahydroborate Ether Solvates⋆ (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 941-949 
    Details
    ISSN: 1434-1948
    Schlagwort(e): Lithium tetrahydridoborate diethyl ether (1:1) ; Lithium tetrahydridoborate diveron (1:1) ; Lithium tetrahydridoborate dimethoxyethane (1:2) ; Lithium tetrahydridoborate triglyme (1:1) ; Lithium tetrahydridoborate tetrahydrofuran (1:3) ; Lithium tetrahydridoborate 1,3-dioxolane (1:1) ; Hydride-bridge bonding ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: LiBH4 · OEt2 (1) and LiBH4 · O(Me)CMe3 (2) form double-stranded chains in the solid state. While 3 hydrides of the BH4 group in 1 bind to three different Li atoms through Li···H-B interactions, the fourth H atom interacts with three adjacent Li centers. In contrast, in compound 2 there are two single Li···H-B bonds and two doubly bridging hydrogen atoms, the latter again interacting with three lithium centers. Moreover, the arrangements of the ether molecules in 1 and 2 are different. LiBH4 · 2 DME (3) (DME = dimethoxyethane) forms a molecular lattice, in which the BH4- anions are present in Li···H2BH2 bridges. The same structural feature is present in LiBH4 · TG (4) (TG = triglyme = triethylene glycol dimethyl ether), but the TG molecule coordinates to two Li centers through two of its four oxygen atoms in such a manner that a chain structure results. The compound LiBH4 · 3 THF (5) exists as discrete molecules in the lattice. Its BH4- anion is triply bridging to the Li center. In contrast, LiBH4·C3H6O2 (6) (1,3-dioxolane) is polymeric. Due to the presence of two μ22-BH4 groups, a chain of the type ···Li(H2BH2)Li(H2BH2)··· is formed, and the 1,3-dioxolane molecules connect the chains through Li-O coordination to form a three-dimensional array. In spite of the variations in the bonding of the BH4 group to Li centers, the Li atoms are hexacoordinated in 3 to 6 but are heptacoordinated in 1 and 2.
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  • 73
    Digitale Medien
    Digitale Medien
    Synthesis and Properties of Silver(I) and Copper(I) Helicates with Imine-Bridged Oligobipyridine Ligands (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 977-982 
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    ISSN: 1434-1948
    Schlagwort(e): Helicates ; Oligobipyridine ligands ; Self-recognition ; NMR titration ; Self-assembly ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Oligobipyridine ligands containing one or two imine bridges were found to form double helicates by treatment with copper(I) or silver(I). The properties of the complexes are similar to those of oxapropylene-bridged oligobipyridines. Titration of a mixture of the bis(bipyridine) and the tris(bipyridine) ligands with silver(I) hexafluorophosphate showed that helicates formed with strict self-recognition.
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  • 74
    Digitale Medien
    Digitale Medien
    Generation of 1,3-Dithia-, 1-Selena-3-thia-, and 1,3-Diselena-2-tellurole by Neutralization-Reionization Mass Spectrometry⋆ (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 983-987 
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    ISSN: 1434-1948
    Schlagwort(e): Telluroles ; Neutralization-reionization mass spectrometry ; DFT calculations ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: 2,2-Dichloro-1,3-dichalcogena-2-telluroles of sulfur and selenium, C6H4[XTe(Cl)2Y] with X, Y = S, Se, serve as precursors to generate the cation radicals of 1,3-dichalcogena-2-telluroles C6H4[XTeY]+• as well as the corresponding neutral counterparts by means of neutralization-reionization mass spectrometry. These neutral 2-telluroles are intrinsically stable for at least 1 μs in the gas phase. The most abundant fragmentation channel at the neutral and cationic stages is due to loss of atomic tellurium to afford the corresponding benzo-1,2-dichalcogena-cyclobutenes. For the latter, partial isomerization to the related dichalcogena-ortho-quinones is indicated by the mass-spectrometric fragmentation pattern.
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  • 75
    Digitale Medien
    Digitale Medien
    π-Bond vs. Agostic Interaction in Three-Coordinated Alkoxy and Thiolate Derivatives of Aluminium, Boron and Cationic Carbon - An ab initio Study of H2X-YR Systems (X = Al, B, C+; Y = O, S; R = H, CH3) (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 1015-1023 
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    ISSN: 1434-1948
    Schlagwort(e): Ab initio calculations ; π interactions ; Agostic interactions ; Electronic structure ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Rotational barriers and π conjugation effects have been studied in H2X-YR systems (X = Al, B; Y = O, S; R = H, CH3) by means of ab initio calculations at the MP4/6-311G**//MP2/6-311G** level. In non-substituted systems H2X-YH, it is shown that the rotational barrier depends on three factors: (i) π conjugation strength between the X vacant p orbital and the Y p-lone pair; (ii) the opening ability of the Y-valence angle and (iii) a possible direct interaction between X and the Y hydrogen substituent. The conjugation stabilization has been estimated through Valence Bond calculations and is found to decrease in the order BO (22.6 kcal/mol), BS (16.6 kcal/mol), AlO (10.2 kcal/mol), and AlS (8.1 kcal/mol). Study of the methylated systems confirm the results found in unsubstituted species. The most important feature is the location of a deconjugated secondary minimum for H2B-SCH3 species. An acute B-S-C angle (69.6°) is found, thus evidencing a direct H···B agostic interaction with a four-membered (BSCH) heterocycle. To further evidence our analysis, additional calculations have been performed on carbocationic species H2C+-YR (Y = O, S; R = H, CH3) for which the H2C+ moiety is a strong π acceptor. As expected, the C+-O and C+-S conjugation are strong (about 60 kcal/mol). Only two minima have been located for the H2C+-OCH3 species. In the sulfur case, the Potential Energy Surface (PES) is more complicated and six stationary points have been characterized. A strong agostic interaction is found for a secondary deconjugated minimum for which an hydrogen symmetrically bridges the two carbon atoms. A schematic energy profile connecting the various extrema is given for this cationic species.
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  • 76
    Digitale Medien
    Digitale Medien
    Substituted Cyclopentadienides of Magnesium from the Reaction of Dialkylmagnesium with Fulvenes (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 965-971 
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    ISSN: 1434-1948
    Schlagwort(e): Cyclopentadienes ; Magnesium ; Metalations ; NMR spectroscopy ; Sandwich complexes ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The reaction of n/sec-dibutyl magnesium with 6-methyl-6-phenyl- and 6,6-dicyclopropylfulvene gives the β-hydride transfer products 1,1′-bis(1-phenylethyl)- and 1,1′-bis-(dicyclopropylmethyl)magnesocene, respectively. The latter crystallizes in the eclipsed conformation, whereas the first one shows an anti conformation in the solid state. Dimethyl-magnesium deprotonates 6-methyl-6-phenylfulvene with formation of 1,1′-bis(1-phenylethen-1-yl)magnesocene, which decomposes upon isolation. The deprotonation of 6,6-dicyclopropylfulvene with MgMe2 in thf solution yields [bis(tetrahydrofuran-O)][iro{cyclopropane-1,2′(1′-η5-cyclopentadienyl-1′,3′,3′-tricyclopropyl-1′,2′,3′,3a′-tetrahydropentalene)}-3a′-6′-η2-enyl]magnesium. In the absence of β-hydrogen atoms at the organometallic reagent as well as at the fulvene the addition reaction is the only possible reaction pathway. Thus, one Mg-C bond of MgMe2 adds to tetramethylfulvene to give quantitatively dimeric methylmagnesium ethyltetramethylcyclopentadienide. The bridging methyl groups are sterically shielded against further attack of the fulvene.
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  • 77
    Digitale Medien
    Digitale Medien
    Synthesis and Structural Characterization of Rare Earth Metal Disulfonamide Complexes⋆ (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 1009-1014 
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    ISSN: 1434-1948
    Schlagwort(e): Rare earth metals ; Lanthanides ; Chelating sulfonamides ; Silylamide route ; C2 symmetry ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The reaction of rare earth silylamides Ln[N(SiHMe2)2]3(thf)n [n = 1 for Sc (1a); n = 2 for Y (1b), La (1c), Nd (1d)] with trans-1,2-bis(2,4,6-triisopropylbenzenesulfonamido)cyclohexane (H2L, rac-2) in toluene at ambient temperature proceeds via an extended silylamide route, affording highly soluble complexes Sc(L)[N(SiHMe2)2] (3) and Ln(L)[N(SiHMe2)2](thf) (4a-c) in excellent yields. An X-ray crystallographic study performed on the solvent-free, dinuclear yttrium derivative 5 revealed an unusual μ2,η4:η1-coordination of the disulfonamide ligand, involving bridging S=O groups. In solution, equilibria between dimeric and monomeric forms, dependent on the presence of a donor molecule, were observed by NMR techniques.
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  • 78
    Digitale Medien
    Digitale Medien
    Synthesis, Molecular Structure, Fluxional Behavior, and Tricarbonyliron Transfer Reactions of (η4-1-Azabuta-1,3-diene)tricarbonyliron Complexes (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 993-1007 
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    ISSN: 1434-1948
    Schlagwort(e): Azabutadienes ; Tricarbonyliron complexes ; Transfer reagents ; Molecular structure ; Fluxionality ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The (η4-1-azabuta-1,3-diene)tricarbonyliron complexes 10 are easily prepared in high yield by condensation of the corresponding arylamines 7 with the cinnamaldehydes 8 and subsequent ultrasound-promoted complexation of the resulting 1-azabuta-1,3-dienes 9 with nonacarbonyldiiron. The complexes 10 are shown to represent excellent reagents for the transfer of the tricarbonyliron fragment onto cyclohexa-1,3-diene (1a). The structural characterization for the complexes 10 is achieved by IR, 1H-NMR, and 13C-NMR spectroscopy, as well as X-ray crystallography of 10b, 10c, and 10l. Using variable temperature 13C-NMR spectroscopy the fluxionality of the complexes 10a, 10b, 10c, 10e, and 2 is investigated and the activation barrier for the turnstile rotation of the tricarbonyliron fragment is determined. The transfer reaction and the structural factors influencing the transfer of the tricarbonyliron fragment are extensively investigated.
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  • 79
    Digitale Medien
    Digitale Medien
    Formation of a Stable Adduct of Ethoxycarbonyldithiocarbamic Acid and a Dimer of Ethoxycarbonyl Isothiocyanate (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 1025-1028 
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    ISSN: 1434-1948
    Schlagwort(e): Sulfur heterocycles ; Hydrolyses ; Isothiocyanate ; Dithiocarbamic acids ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The reaction of ethoxyxcarbonyl isothiocyanate with water in the absence of a solvent has yielded the new compound [EtO2CN=CS2C{N(H)CO2Et}{S2CN(H)CO2Et}] (1) in 76% yield that has been isolated in a crystalline form that con-tains one equivalent of ethoxyxcarbonyl isothiocyanate. Compound 1 can be viewed as an adduct of a dimer of EtO2CN=C=S and the dithiocarbamic acid 2. Compound 1 dissociates in solution to yield 2 and free ethoxyxcarbonyl isothiocyanate. Compound 2 can be isolated chromatog-raphically, but it is slowly oxidized when allowed to stand in the open air to form the thiuram disulfide 3. Compounds 1 and 3 were characterized crystallographically. Compound 1 contains an imino-substituted dithietane ring with a dithiocarbamate substitutent bonded to one of the ring carbon atoms. Compound 3 is a thiuram disulfide which has C2 crystallographic symmetry.
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  • 80
    Digitale Medien
    Digitale Medien
    Novel Syntheses of Mono- and Bisphosphonated Aromatic Phosphanes by Consecutive Pd-Catalyzed P-C Coupling Reactions and Nucleophilic Phosphanylation - X-ray Structure of Ph2P-C6H4-m-PO3Na2 · 5.5 H2O · iPrOH (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 1029-1034 
    Details
    ISSN: 1434-1948
    Schlagwort(e): Pd-catalyzed P-C coupling ; Nucleophilic phosphanylation ; Mono- and bisphosphonated phosphanes ; Monoesters ; Water solubility ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The triphenylphosphane derivatives 2a and 5, bearing one and two phosphonic ester groups, are accessible in high yields by consecutive Pd-catalyzed P-C coupling reactions of p-bromoiodobenzene with Ph2PH and PhPH2, respectively, and then with diethyl phosphite. Ester hydrolysis yields the highly water-soluble sodium salts of mono- and bis-phosphonated triphenylphosphane, 3a and 6, respectively. On reaction of the p- and m-fluorophenylphosphonic diethyl esters 7a, 7b with Ph2PK and subsequent ester hydrolysis the isomeric disodium (diphenylphosphano)phenylphosphonates 3a, 3b were obtained. The X-ray structure of Ph2P(C6H4-m-PO3Na2) · 5.5 H2O · iPrOH (space group Cmc21) has been determined. In the solid state, it forms a layer structure with hydrophilic (PO32-, H2O, iPrOH) and hydrophobic (Ph2P) compartments, in which the PO32- anionic groups are not engaged in coordination of the sodium cations.
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  • 81
    Digitale Medien
    Digitale Medien
    Conformational Flexibility of the Square-Pyramidal Coordination Cap in a Series of Octahedral Nickel(II) Pentaamine Complexes - Magnetochemical Characterization of the Singly μ-Cl-Bridged Nickel(II) Dimer [(pyN4)Ni-Cl-Ni(pyN4)](PF6)3 [pyN4 = 2,6-Bis(1′,3′-diamino-2′-methylprop-2′-yl)pyridine] (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 1041-1049 
    Details
    ISSN: 1434-1948
    Schlagwort(e): Tetrapodal pentadentate ligand ; Square pyramidal coordination cap ; Pentaamine ; Nickel(II) complexes ; Magnetochemistry ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The architecture of the tetrapodal pentaamine ligand 2,6-bis(1′,3′-diamino-2′-methylprop-2′-yl)pyridine (pyN4, 1) allows it to coordinate to nickel(II) as a square pyramidal coordination cap. The pyridine nitrogen atom occupies an apical position of the coordination octahedron, while four equivalent pendent primary amino groups occupy the equatorial positions, with a sixth coordination site remaining for a monodentate ligand. Exchange of this ligand is facile, and a series of complexes [(1)NiX]n+ (X = OH2, OClO3, NCS, N3, {Cl-Ni(pyN4)}) has been prepared and characterised by elemental analysis, IR and UV/Vis spectroscopies (as applicable), and X-ray structure determination. While the solid state structures show varying degrees of distortion of the ligand cap 1 from C2v symmetry, a polynucleating coordination mode has not been observed. The ligand enables the synthesis of dinuclear nickel(II) complexes containing a single bridging ligand, as exemplified by the singly -chloro bridged complex [(1)Ni-Cl-Ni(1)](PF6)3. This complex has an antiferromagnetically coupled ground state of total spin ST = 0, as determined from variable-temperature magnetic susceptibility measurements.
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  • 82
    Digitale Medien
    Digitale Medien
    The 1,3-Sn2O2-Heterocycle as a Ligand in Organometallic Compounds - Dimerization of the Inidene Species [{(CO)5M}2SnOR]- (M = Cr, W) (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 1057-1066 
    Details
    ISSN: 1434-1948
    Schlagwort(e): Pentacarbonylmetal-tin bonding ; Alkoxytin compounds ; Inidene compounds ; 119Sn NMR ; Bonding ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Dimerized inidene complexes [(CO)5M-Sn(OR)-M(CO)5]22- (M = Cr, W; R = Et, iPr), 1, are obtained from [{(CO)5M}2SnCl2]2- by different routes. Dimerization occurs via alkoxy-donor tin-acceptor bonding by which a planar Sn2O2 ring is formed. The Sn-{M(CO)5} bonds are made in a plane vertical to this ring such that, with the R-O groups being almost coplanar with the Sn2O2 ring, the overall geometry of the compounds shows idealized D2h symmetry. - The 119Sn-NMR resonances of 1 are found at rather low fields (M = Cr: δ ≈ 1400; M = W: δ ≈ 1170) indicating a low-lying tin-centered orbital in the LUMO range. Correspondingly EHT analyses show that the 3-center-4π system, which characterizes monomeric inidene species [LnM-E(X)-MLn]n, is still prevalent in the dimeric species 1. The low-lying π*-type LUMOs of 1 are the rationale for the observed 119Sn-NMR low-field shifts of 1. The dimeric compounds 1 react with 2,4-pentanedione to form chelate compounds of the same type as those characteristically obtained from monomeric inidene complexes: [{(CO)5Cr}2SnOEt]22- (1a) reacts to give [{(CO)5Cr}2Sn(acac)]- (2). The experimental results are verified by X-ray analyses in addition to the usual spectroscopic and analytical investigations.
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  • 83
    Digitale Medien
    Digitale Medien
    Reaction of a Stable Silylene with Divalent Group 14 Compounds (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 1067-1070 
    Details
    ISSN: 1434-1948
    Schlagwort(e): Silylene ; N Heterocycles ; Carbene analogs ; Tin ; Subvalent compounds ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The reaction of the stable silylene 1 (L′Si:) with CO, SnCl2, PbCl2, the stable carbene L′C: (2) and the stable germylene L′Ge: (3) was investigated as a possible approach for the synthesis of hetero-polysilanes (poly-carbosilanes, poly-germasilanes, poly-stannasilanes). The silylene 1 was found to be inert towards all substrates except SnCl2 and PbCl2. Reaction with SnCl2 led to the formation of the yellow, tris(silyl)stannane [(L′SiCl)3SnCl] (5) and elemental tin. The photolabile (5) was characterized by multinuclear NMR (1H, 13C, 29Si, 119Sn) and single crystal X-ray diffraction: C30H60Cl4N6Si3Sn, M = 849.60, orthorhombic, space group Pca21. The bond angles of 115.89 ° (ave. Si-Sn-Si) and 101.87 ° (ave. Cl-Sn-Si) show a slightly flattened tetrahedral geometry around the tin atom. - Thermolysis of 5 at 100 °C led to the deposition of thin films of tin; photolysis resulted in the formation of tin powder. All thermolysis products could be isolated and were characterized as SnCl2, elemental tin, L′Si: (1), L′SiCl2 (6) and the new disilane L′Si(Cl)-(Cl)SiL′ (7). Photolysis led to a reduced product spectrum (formation of Sn + SnCl2 + 7). Reaction of 1 with PbCl2 gave elemental lead and L′SiCl2 as the only products.
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  • 84
    Digitale Medien
    Digitale Medien
    Preparation, Structures, and Properties of Dinuclear Ni and Pd Complexes of Tridentate Amine-Chalcogenolate Ligands (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 1071-1077 
    Details
    ISSN: 1434-1948
    Schlagwort(e): Dinuclear complexes ; Nickel ; Palladium ; Amine-thiolate ligands ; Amine-selenolate ligands ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The preparation and characterization of dinuclear NiII and PdII complexes of the tridentate amine-chalcogenolate ligands 4-tert-butyl-2,6-di(aminomethyl)thiophenol (4a) and 4-tert-butyl-2,6-di(aminomethyl)selenophenol (4b) are re-ported. Reaction of 4a,b with Ni(ClO4)2·6 H2O or (COD)PdCl2 in a 1:1 molar ratio yields 1:1 complexes of composition [M2(L)2][BPh4]2·CH3CN·CH3OH [M = Ni, L = 4a,b (5a,b); M = Pd, L = 4a,b (6a,b)]. The palladium complex 6a is isomorphous with 5a as shown by X-ray crystal structure analysis. NMR studies reveal that both complexes retain their solid-state structure in solution and that the selenolate complexes are isostructural with the thiolate complexes. All complexes undergo electrochemically reversible one-electron transfer processes in the potential range -1.0 to -0.8 V vs. SCE ascribed to metal-centered reductions with formation of mixed-valent MI,II species [M2(L)2]+. Further reduction at more negative potentials then leads to the neutral [M2(L)2] species, which are not stable on the time scale of the CV experiment. The spectroscopic properties of the thiolate and selenolate complexes are very similar indicating electronically similar properties of the tridentate amine-chalcogenolate ligands.
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  • 85
    Digitale Medien
    Digitale Medien
    Oxidation of Polycyclic Aromatic Hydrocarbons Catalyzed by Iron Tetrasulfophthalocyanine FePcS: Inverse Isotope Effects and Oxygen Labeling Studies (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 1269-1281 
    Details
    ISSN: 1434-1948
    Schlagwort(e): Oxidation ; Catalysis ; Phthalocyanine ; Iron ; Anthracene ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Iron(III) tetrasulfophthalocyanine (FePcS) was shown to catalyze the oxidation of polycyclic aromatic hydrocarbons by H2O2. Benzo[a]pyrene and anthracene were converted to the corresponding quinones while biphenyl-2,2′-dicarboxylic acid was the main product of phenanthrene oxidation. The mechanism of the anthracene oxidation by H2O2 in the presence of FePcS or by KHSO5 with iron(III) meso-tetrakis(3,5-disulfonatomesityl)porphyrin (FeTMPS) (see Figure 1 for catalyst structures) has been investigated in details by using kinetic isotope effects (KIEs) and 18O labeling studies. KIEs measured on the substrate consumption in the competitive oxidation of [H10]anthracene and [D10]anthracene by FePcS/H2O2 and FeTMPS/KHSO5 were essentially the same, 0.75 ± 0.02 and 0.76 ± 0.06, respectively. These inverse KIEs on the first oxidation step can be explained by the sp2-to-sp3 hybridization change during the addition of an electrophilic oxoiron complex to the sp2 carbon center of anthracene to form a σ adduct (this inverse KIE being enhanced by stronger stacking interactions between the perdeuterated substrate with the macrocyclic catalyst). Although the first oxidation step seems to be the same, different distribution of the oxidation products of anthracene and very different 18O incorporation into anthrone and anthraquinone in catalytic oxidations performed in the presence of H218O suggested that different active species should be responsible for anthracene oxidation in both catalytic systems. All the results obtained are compatible with an involvement of TMPSFeV=O (or TMPS+FeIV=O), having two redox equivalents above the iron(III) state of the metalloporphyrin precursor, while PcSFeIV=O (one redox equivalent above FeIII state of FePcS) was proposed to be the active species in the metallophthalocyanine-based system.
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  • 86
    Digitale Medien
    Digitale Medien
    Structure/Chiroptics Relationships of Planar Chiral and Helical Molecules (1998)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 1491-1509 
    Details
    ISSN: 1434-193X
    Schlagwort(e): Chirality ; Circular dichroism ; Cyclophanes ; Theoretical calculations ; Strained molecules ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The chiroptical properties of planar-chiral and helical molecules without stereogenic centres and with well-defined structure, strain, electronic properties and chirality are investigated by experimental and theoretical circular dichroism spectroscopy. We report on the synthetic and theoretical achievements made during the past 10 years in the field of rigid [2.2]metacyclophane propellers, as well as in the area of [n]para- and [n]metacyclophanes containing aliphatic parts like adamantane or unsaturated bridges. Results for carbo and hetero helicenes and helicene-related molecules like twisted phenanthrenes are presented. It is demonstrated how reliable theoretical calculations using configuration interaction and time-dependent methods in combination with density functional theory today are and how useful the interplay between theory and experiment stimulates the development of chiral molecules optimized for this purpose. Even for large molecules it is routinely possible to assign Cotton effects to electronic transitions, to evaluate chromophore contributions, to determine absolute configurations and conformational equilibria, and to discover intramolecular charge transfer effects.
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  • 87
    Digitale Medien
    Digitale Medien
    2,3-Dihydroimidazol-2-ylidene (1998)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 1517-1520 
    Details
    ISSN: 1434-193X
    Schlagwort(e): Nucleophilic carbenes ; Heterocycles ; Decarboxylation ; Photochemistry ; Matrix isolation ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Irradiation of imidazole-2-carboxylic acid (3) - matrix-isolated in argon at 10 K - with a wavelength of 254 nm leads to decarboxylation and the formation of a complex between 2,3-dihydroimidazol-2-ylidene and carbon dioxide (1·CO2). Upon irradiation of 2,3-dihydroimidazol-2-ylidene (1) with λ = 254, 193, and 185 nm no imidazole can be detected. On the other hand flash vacuum pyrolysis of imidazole-2-carboxylic acid (3) produces imidazole and carbon dioxide. 2,3-Dihydroimidazol-2-ylidene (1) - the possible intermediate - cannot be trapped under these conditions.
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  • 88
    Digitale Medien
    Digitale Medien
    cis- and trans-2-(Isocyanomethyl)-5,5-dimethyl-2-oxo-4-phenyl-1,3,2-dioxaphosphorinane - Synthesis and Structure of the First Chiral Isocyanomethylphosphonate Synthons (1998)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 1511-1516 
    Details
    ISSN: 1434-193X
    Schlagwort(e): Chiral isocyanomethylphosphonates ; Phosphorus heterocycles ; Chiral auxiliaries ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Both cis-2-(isocyanomethyl)-5,5-dimethyl-2-oxo-4-phenyl-1,3,2-dioxaphosphorinane (1a) and the trans epimer 1b have been prepared as potentially useful chiral isocyanomethylphosphonate synthons. 2-Methoxy-1,3,2-dioxaphosphorinanes 5 and the corresponding 2-ethoxy analog 6 were prepared from 2,2-dimethyl-1-phenyl-1,3-propanediol (2) and were converted in an Arbuzov-type reaction to 2-(formamidomethyl)oxo-1,3,2-dioxaphosphorinane 7, which upon dehydration gave 1a. Thus, both (±)-1a and (2S,4S)-(-)-1a were prepared, and their molecular structures were determined by single-crystal X-ray analysis. Treatment of (2S,4S)-(-)-1a with KF gave a 1:3 equilibrium mixture of the phosphorus epimers 1a and 1b, from which the predominant trans epimer (2S,4R)-(-)-1b was isolated by column chromatography and crystallization.
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  • 89
    Digitale Medien
    Digitale Medien
    The Twofold Heck Reaction on 1,2-Dihalocycloalkenes and Subsequent 6π-Electrocyclization of the Resulting (E, Z, E)-1,3,5-Hexatrienes: A New Formal {2+2+2}-Assembly of Six-Membered Rings (1998)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 1521-1534 
    Details
    ISSN: 1434-193X
    Schlagwort(e): Heck reaction ; Cross coupling ; Palladium ; Catalysis ; 6π-Electrocyclization ; Cyclohexa-1,3-dienes ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: 1,6-Disubstituted (E, Z, E)-1,3,5-hexatrienes (4 and 5) were prepared by vicinal twofold Heck coupling reactions from 1,2-dibromocyclopentene (1), 1,2-dibromocyclohexene (2), 1,2-diiodocyclopentene (8), 1,2-diiodocyclohexene (9), 1-bromo-2-trifluoromethanesulfonyloxycyclohex-1-ene (11), or 1-chloro-2-nonafluorobutanesulfonyloxycyclohex-1-ene (19) with alkenes 3, e. g. methyl, tert-butyl, menthyl, 8-phenylmenthyl acrylate, styrene, and alkenylsilanes, respectively, in moderate to mostly good and very good yields (20-92 %). The coupling of alkenylsilanes 3f-k could only be achieved with the 1,2-diiodocycloalkenes 8 and 9, respectively. The corresponding hexatrienes 5 with two different substituents in the 1- and 6-positions were prepared by a sequence of two coupling reactions with different alkenes from 1-chloro-2-nonafluorobutanesulfonyloxycyclo-hex-1-ene (19) or by Wittig-Horner-Emmons olefination of 2-bromocyclohexene-1-carbaldehyde (24) and subsequent Heck reaction of the resulting (E,Z)-bromodienes 25. Several of the hexatrienes (4aa, ee, 5aa, ee, al, am, el) readily underwent a 6π-electrocyclization upon heating in an inert atmosphere to give the 5- or 6-ring-annelated cis-5,6-disubstituted cyclohexadienes 26, 27 (50-95 %). Starting from 5am 2,3-disubstituted tetrahydronaphthalene 28am was formed under oxidative conditions (air) in the reaction and in the work-up procedure. The bissilyl-substituted derivatives 4ff, jj, 5ff did not cyclize under thermal conditions, apparently due to the steric demand of the two silyl substituents which would have to end up cis with respect to each other in the cyclohexadiene products.
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  • 90
    Digitale Medien
    Digitale Medien
    Synthesis of N-Fused “Lactendiynes” (1998)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 1543-1548 
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    ISSN: 1434-193X
    Schlagwort(e): Enediynes ; β-Lactams ; Cycloaromatization ; Anticancer compounds ; Lactendiynes ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: New “lactendiynes”, characterized by the fusion at C-4 and N-1 of a β-lactam with a hydroxylated 10-membered cyclic enediyne, were synthesized. Studies on their reactivity have shown that this type of fusion with the azetidinone represents a sufficient “safety-catch” against cycloaromatization. These compounds are relatively reactive toward basic hydrolysis, affording monocyclic enediynes which undergo fast cycloaromatization at room temperature.
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  • 91
    Digitale Medien
    Digitale Medien
    Surprisingly Facile Addition of Thiols to the Double Bonds of Bicyclopropylidene and Other Methylenecyclopropanes (1998)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 1535-1542 
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    ISSN: 1434-193X
    Schlagwort(e): Radical reactions ; Spiro compounds ; Additions ; Sulfides ; Amino acids ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The addition of thiols 8a-h onto the double bonds of bicyclopropylidene (1) and methylenespiropentane (2) proceeds quantitatively in benzene at 20 to 75 °C in the absence of catalysts or radical initiators to give products 9, 10 with complete retention of both three-membered rings. Methylenespiropentane (2) yields exclusively the anti-Markovnikov adduct 10. The unsubstituted methylene-cyclopropane (3) gives 9% of the ring-opened compound 12 in addition to the anti-Markovnikov adduct 11. The addition of thiols to n-heptylbicyclopropylidene (13), methylenecyclopropylacetic acid (15), and the amino acids 17, 19 containing bicyclopropylidene or methylenespiropentane fragments, does not proceed stereoselectively, though in all cases the mercapto function adds to the double bond with retention of the cyclopropane ring to give interesting new amino acids containing bicyclopropyl and spiropentyl fragments, respectively. The probable mechanism of this thiol addition is discussed in the light of a test with the cyclizing intramolecular addition of 2-(2-methylenecyclopropyl)ethanethiol 27.
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  • 92
    Digitale Medien
    Digitale Medien
    Chromophore-Appended C60 and C70 Fullerenes: Anthracene and Pyrene Derivatives - Syntheses, Cyclic Voltammetry, and Spectra (1998)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 1549-1557 
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    ISSN: 1434-193X
    Schlagwort(e): Functionalized fullerenes ; Cyclic voltammetry, spectroelectrochemistry ; Ions and radical ions ; Absorption and emission spectra ; Intramolecular energy transfer ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: C60 and C70 adducts containing spacer-linked phenyl (BK1), 9-anthracenyl (BK2), 4-(9-anthracenyl)phenyl (BK3), and 1-pyrenyl groups (BE1 and FE1) have been studied. Two different synthetic pathways were employed based on the [4+2] cycloaddition of fullerenes with 2-trimethylsiloxy-1,3-butadienes (TB). Spectroscopic data for the new compounds are given. Electrochemical and optoelectrochemical studies were undertaken by using cyclic voltammetry and spectroelectrochemical methods. The fluorescence emission spectra of BK2, BK3, BE1, and FE1 are reported. Intramolecular energy transfer from the excited fluorophore to the fullerene subunit is shown to occur.
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  • 93
    Digitale Medien
    Digitale Medien
    Electronic Communication in [Co2(CO)6]2-Diyne and [Co2(CO)4(dppm)]2-Diyne Complexes (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 1473-1477 
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    ISSN: 1434-1948
    Schlagwort(e): Electrochemistry ; Mixed-valent compounds ; Alkynecobalt complexes ; Through-bond interactions ; Through-space interactions ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The electrochemical behaviour of the [Co2(CO)6]2(μ-R-C≡C-L-C≡C-R) and [Co2(CO)4(dppm)]2(μ-R-C≡C-L-C≡C-R) series is reported. Qualitative evidence suggests that both through-space and through-bond interactions are operating with different relative weight depending on the spacer L.
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  • 94
    Digitale Medien
    Digitale Medien
    The Photochemistry of M3(CO)12 (M = Ru, Os) with Pyrazole and Its Substituted Derivatives (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 1479-1483 
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    ISSN: 1434-1948
    Schlagwort(e): Photochemistry ; Ruthenium ; Osmium ; Clusters ; Nitrogen heterocycles ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The photochemistry of M3(CO)12 [M = Ru (1a), Os (1b)] with pyrazole, 3,5-dimethylpyrazole, and 3,5-diphenylpyrazole is documented. With 1a, photolysis with pyrazole leads to the substitution product HRu3(CO)10(C3H3N2) (2a). In the case of 1b, the initial product is the ortho-metallated species HOs3(CO)10(C3H3N2) (3b), heating of which yields HOs3(CO)10(C3H3N2) (2b). Photolysis of 1a and 1b with 3,5-dimethylpyrazole yields HRu3(CO)10(C3HMe2N2) (4a) and HOs3(CO)10(C3HMe2N2) (4b), respectively. The molecular structure of 4b has been determined by X-ray crystallography. There is no reaction on photolysis of 1a and 1b with 3,5-diphenylpyrazole.
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  • 95
    Digitale Medien
    Digitale Medien
    β-Diiminato Complexes of VIII and TiIII - Formation and Structure of Stable Paramagnetic Dialkylmetal Compounds (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 1485-1494 
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    ISSN: 1434-1948
    Schlagwort(e): Titanium ; Vanadium ; Polymerizations ; Diimine ; Dialkylmetal compounds ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: (Mono-β-diiminato)titanium(III) and -vanadium(III) dichlorides LMCl2 [L = ArNC(R)CHC(R)NAr-] are easily accessible from the metal trichlorides and LLi in THF. The crystal structures of LVCl2 (Ar = 2,6-iPr2C6H3, R = Me) and LTiCl2 (Ar = 2,4,6-Me3C6H2, R = Me and Ar = 2,4,6-Me3C6H2, R = tBu) reveal tetrahedral metal environments. Treatment of LVCl2 with alkyllithium reagents affords surprisingly stable dialkylvanadium(III) compounds; the structure of LV(nBu)2 (Ar = 2,6-iPr2C6H3, R = Me) is similar to that of the dichloride. The corresponding dialkyltitanium(III) compounds are less stable; only the dimethyl derivatives could be obtained in pure form (from LTiCl2 and MeMgI), and only for ligands bearing 2,6-disubstituted aryl groups. The structure of LTiMe2 (Ar = 2,4,6-Me3C6H2, R = Me) is also similar to that of the dichloride. Reaction of LTiMe2 with B(C6F5)3 produces a catalyst for α-olefin polymerization, but the corresponding VIII derivatives are inactive.
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  • 96
    Digitale Medien
    Digitale Medien
    Tuning Metal Stoichiometry in Heterometal Alkoxides: First Structurally Characterised Molecular Precursor to BaZrO3 (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 1327-1332 
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    ISSN: 1434-1948
    Schlagwort(e): Barium ; Zirconium ; O ligand ; Heterometal alkoxides ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Manipulable metal ratios are accessible in a series of heterometal Ba-Zr alkoxides by changing the size and the charge of the ligands. The synthesis and characterisation of four mixed-metal Ba-Zr species [BaZr2(OtBu)10] (1), [Ba2Zr(OtBu)8(tBuOH)(THF)2] (2), [BaZr(OtBu)6(THF)2] (3) and [BaZr(OH)(OiPr)5(iPrOH)3]2 (4), based on different Ba/Zr stoichiometries, are reported. The molecular structures of 1, 2, and 4 have been determined by single-crystal X-ray diffraction studies. 1 exhibits a bow-tie structural motif in which a trigonally distorted six-coordinate barium atom is chelated by two bipyramidal {Zr(OtBu)5}- units. 2 reveals a triangular “Ba2Zr(μ3-OtBu)2(μ2-OtBu)3” core structure formed by the fusion of three octahedra built about two Ba atoms and a Zr atom. The structure is unique in terms of the distribution of terminal ligands at each of the metal centers. One of the barium atoms possesses one -OtBu and one tBuOH as terminal ligands, while the terminal ligands on the second barium atom are two THF molecules; the zirconium center bears -OtBu groups as the terminal ligands. Hydrolysis of compound 3 with one equivalent of water, followed by alcoholysis (iPrOH) of the resulting product, gave 4. The structure of 4 shows a planar tetrametallic Ba2Zr2 frame capped by two μ3-hydroxo ligands. The coordination figure of the zirconium atoms resembles a distorted octahedron, whereas the geometry of the barium centers is best described as capped trigonal prisms. Both 3 and 4 are excellent precursors to morphologically pure BaZrO3 ceramic by the sol-gel process.
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  • 97
    Digitale Medien
    Digitale Medien
    A Unique Copper-Controlled Template Synthesis of Tetradentate N4-Donor Ligands and Their Propeller-Type Linear Trinuclear CuII Complexes (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 547-549 
    Details
    ISSN: 1434-1948
    Schlagwort(e): Copper ; Trinuclear ; Formamidines ; Magnetism ; Crystal structure ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: In situ reaction of CuII triflate with aminopyridine or aminopyrimidine and triethylorthoformate in ethanol results in unique linear trinuclear CuII complexes with the general formula [Cu3(L-)4](CF3SO3)2(EtOH)x (L = dehydronated ligand N,N′-bis(pyridine-2-yl)formamidine or the new ligand N,N′-bis(pyrimidine-2-yl)formamidine). The structure [Cu-Cu-Cu angle 175.19(2)°] consists of four nearly flat molecules of the ligand which contribute to the propeller-type structure around the Cu-Cu-Cu axis. A strong antiferromagnetic interaction between the CuII ions is observed, resulting in an S = 1/2 ground state below 100 K.
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  • 98
    Digitale Medien
    Digitale Medien
    Cyclopentadienyl Complexes of Yttrium Aminotroponiminates: An Example for an Improved Alternative Ligand System (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 593-596 
    Details
    ISSN: 1434-1948
    Schlagwort(e): Yttrium ; Aminotroponiminate ; Cyclopentadienyl ; Dynamic NMR ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Mixed aminotroponiminate ([ATI]-) cyclopentadienyl complexes were prepared using two different synthetic routes. Reaction of [[(iPr)2ATI]YCl2(THF)2]2 (1) with KCp* (Cp* = C5Me5) or Li[C5H3(SiMe3)2] affords [(iPr)2ATI]YCp2* (2a) and [(iPr)2ATI]Y[C5H3(SiMe3)2]2 (2b), respectively. Moreover, [(iPr)2ATI]YCp2* has also been obtained from the reaction of Cp2*Y(μ-Cl)2Li(OEt2)2 (3) and [(iPr)2ATI]K. The single crystal X-ray structure of [(iPr)2ATI]YCp2* shows that the steric demand of the [(iPr)2ATI]- ligand is somewhat similar to that of the well-known cyclopentadienyl group and diazadiene ligand. [(iPr)2ATI]Y[C5H3(SiMe3)2]2 shows a dynamic behavior in solution (1H NMR), which is essentially caused by rotation of the cyclopentadienyl group rather than by migration of the [(iPr)2ATI]- ligand.
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  • 99
    Digitale Medien
    Digitale Medien
    New Imidazabole Derivatives: Dimers of Carbene-Borane Adducts (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 1547-1553 
    Details
    ISSN: 1434-1948
    Schlagwort(e): Imidazaboles ; Carbene-borane adducts ; Azole-borane adducts ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The preparation and characterization of five new imidazabole derivatives is reported: 1,5-dibenzyl-4,4,8,8-tetrahydroimidazabole (2), 4,4,8,8-tetrafluoro-1,5-dimethylimidazabole (3), 4,4-difluoro-8,8-dihydro-1,5-dimethylimidazabole (4), 4,4,8,8-tetrachloro-1,5-dimethylimidazabole (5), and 4,4,8,8-tetraethyl-1,5-dimethylimidazabole (6). The structures of compounds 2-6 as dimeric carbene-borane adducts rather than dimeric N-borane adducts are discussed on the basis of NMR (2-6) and X-ray diffraction data (2, 3, 5 and 6).
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  • 100
    Digitale Medien
    Digitale Medien
    Schiff-Base Podates - X-ray, NMR and Ab Initio Molecular-Orbital Studies of the Cadmium(II) Complexes of Linear and Three-Armed Podands in Solution and Solid State (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 1555-1562 
    Details
    ISSN: 1434-1948
    Schlagwort(e): Schiff-bases ; Helical structures ; Structure elucidation ; NMR spectroscopy ; Ab initio calculations ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Cadmium(II) complexes of two Schiff bases, 1,3-di(pyridine-2-carboxaldimino)propane (C15H16N4, L1)[1] and tris[4-(2′-pyridyl)-3-aza-3-butenyl]amine (C24H27N7, L2)[2] are described. An efficient route utilising molecular sieves for the synthesis of Schiff bases is presented. The ligands L1 and L2 can be described as linear and three-armed podands, respectively, L1 being conformationally flexible and L2 preorganised. Cadmium perchlorate in methanol with L1 yields a crystalline complex [Cd(L1)2](ClO4)2 (1), the structure of which was determined by X-ray structure analysis. The complex 1 has an unusual nonsymmetrical 8-coordinated helical structure and crystallizes in an acentric space group (Cc, no. 9) as a pure enantiomer due to spontaneous resolution. Solution studies of 1 in CHCl3/DMSO (10:1) and pure DMSO were performed using 1H-, 13C-, 113Cd-NMR and 1H,15N z-GS HMBC spectroscopy and they suggest a reorientation of 1 into the more symmetrical 4-coordinate complex due to the flexible nature of L1. The preorganised, potentially tetra-, hexa- or heptadentate, three-armed podand L2 and its in situ complexation with the Cd2+ cation were investigated by 1H-, 13C-, 113Cd-NMR and 1H,15N z-GS HMBC spectroscopy. The results support the formation of a highly symmetrical helical 6-coordinate podate [CdL2](NO3)2 (2). The structure of 2 has also been verified by ab initio HF-MO calculations using a standard 3-21G* basis set (Lan2DZ for Cd).
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