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  • General Chemistry  (77,717)
  • Fisheries  (14,766)
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  • 1
    Publication Date: 2024-04-04
    Description: This eBook is a collection of articles from a Frontiers Research Topic. Frontiers Research Topics are very popular trademarks of the Frontiers Journals Series: they are collections of at least ten articles, all centered on a particular subject. With their unique mix of varied contributions from Original Research to Review Articles, Frontiers Research Topics unify the most influential researchers, the latest key findings and historical advances in a hot research area! Find out more on how to host your own Frontiers Research Topic or contribute to one as an author by contacting the Frontiers Editorial Office: frontiersin.org/about/contact
    Keywords: living marine resources ; Forecasting ; prediction ; fish ; Fisheries ; Seasonal to Decadal Prediction ; Climate services ; thema EDItEUR::P Mathematics and Science::PD Science: general issues ; thema EDItEUR::R Earth Sciences, Geography, Environment, Planning::RB Earth sciences::RBK Hydrology and the hydrosphere::RBKC Oceanography (seas and oceans)
    Language: English
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  • 2
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    Springer Nature | Palgrave Macmillan
    Publication Date: 2024-03-29
    Description: This open access book explores fishing livelihoods in the context of the wider contexts in which they are embedded. Drawing on case studies from across the Asia-Pacific region, the book highlights how fishing livelihoods are shaped by globalisation, social relationships and governance. The book concludes by showing how better understanding these relationships can contribute to governance for healthier ecosystems and social wellbeing. This is an open access book. This is an open access book.
    Keywords: Fisheries ; marine social science ; fishing livelihoods in the Asia-Pacific ; sustainable fishing ; environmental sustainability ; food security ; coastal conservation ; fish stocks ; fisheries governance ; Fishing livelihoods and social diversity ; Fishing livelihoods and wellbeing ; Open Access ; thema EDItEUR::J Society and Social Sciences::JP Politics and government::JPQ Central / national / federal government::JPQB Central / national / federal government policies ; thema EDItEUR::J Society and Social Sciences::JH Sociology and anthropology::JHB Sociology ; thema EDItEUR::R Earth Sciences, Geography, Environment, Planning::RN The environment ; thema EDItEUR::R Earth Sciences, Geography, Environment, Planning::RG Geography::RGB Physical geography and topography ; thema EDItEUR::R Earth Sciences, Geography, Environment, Planning::RN The environment::RNF Environmental management ; thema EDItEUR::R Earth Sciences, Geography, Environment, Planning::RG Geography::RGC Human geography
    Language: English
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  • 3
    ISSN: 1432-1009
    Keywords: Flushing ; Scouring ; Channel Maintenance ; Fisheries ; Trinity River
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering
    Notes: Abstract The operation of Trinity and Lewiston Dams on the Trinity River in northern California in the United States, combined with severe watershed erosion, has jeopardized the existence of prime salmonid fisheries. Extreme streamflow depletion and stream sedimentation below Lewiston have resulted in heavy accumulation of coarse sediment on riffle gravel and filling of streambed pools, causing the destruction of spawning, nursery, and overwintering habitat for prized chinook salmon (Salmo gairdnerii) and steelhead trout (Oncorhynchus tschawytscha). Proposals to restore and maintain the degraded habitat include controlled one-time remedial peak flows or annual maintenance peak flows designed to flush the spawning gravel and scour the banks, deltas, and pools. The criteria for effective channel restoration or maintenance by streambed flushing and scouring are examined here, as well as the mechanics involved. The liabilities of releasing mammoth scouring-flushing flows approximating the magnitude that preceded reservoir construction make this option unviable. The resulting damage to fish habitat established under the postproject streamflow regime, as well as damage to human settlements in the floodplain, would be unacceptable, as would the opportunity costs to hydroelectric and irrigation water users. The technical feasibility of annual maintenance flushing flows depends upon associated mechanical and structural measures, particularly instream maintenance dredging of deep pools and construction of a sediment control dam on a tributary where watershed erosion is extreme. The cost effectiveness of a sediment dam with a limited useful economic life, combined with perpetual maintenance dredging, is questionable.
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  • 4
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    Environmental management 7 (1983), S. 151-160 
    ISSN: 1432-1009
    Keywords: Grass carp ; Biological control ; Nuisance aquatic weeds ; Fisheries ; Aquaculture ; Reproductive requirements ; Arkansas management plan ; Sterile hybrids
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering
    Notes: Abstract Grass carp (Ctenopharyngodon idella Val.) were introduced into the United States in 1963 as potential biological control agents for nuisance aquatic weeds. Since that time an oftentimes bitter controversy has raged over its effects on sportfishing, and its possible natural reproduction and naturalization in North America. This review considers the history, ecology, and present status of grass carp in the United States in light of the voluminous scientific research conducted since its importation. Particular attention is given to the role of grass carp in the fisheries management plans of Arkansas. Recent development of a sterile, triploid grass carp hybrid may lead to widespread use of grass carp to control nuisance aquatic weeds in culturally eutrophicated waters of the United States.
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  • 5
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    Amsterdam : Elsevier
    Marine Policy 7 (1983), S. 197-211 
    ISSN: 0308-597X
    Keywords: Fisheries ; Management ; Property rights
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Political Science , Law
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  • 6
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    Amsterdam : Elsevier
    Marine Policy 6 (1982), S. 121-130 
    ISSN: 0308-597X
    Keywords: Atlantic ; Fisheries ; Management
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Political Science , Law
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  • 7
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    Amsterdam : Elsevier
    Marine Policy 6 (1982), S. 131-139 
    ISSN: 0308-597X
    Keywords: Economic measurements ; Fisheries ; Pacific
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Political Science , Law
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  • 8
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    Amsterdam : Elsevier
    Marine Policy 7 (1983), S. 267-278 
    ISSN: 0308-597X
    Keywords: Environment ; Fisheries ; Resource management
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Political Science , Law
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  • 9
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    Amsterdam : Elsevier
    Marine Policy 8 (1984), S. 239-258 
    ISSN: 0308-597X
    Keywords: Antarctica ; Fisheries ; Krill
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Political Science , Law
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  • 10
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    Amsterdam : Elsevier
    Marine Policy 9 (1985), S. 220-236 
    ISSN: 0308-597X
    Keywords: Fisheries ; Resource economics, UK
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Political Science , Law
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  • 11
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    Amsterdam : Elsevier
    Marine Policy 8 (1984), S. 137-150 
    ISSN: 0308-597X
    Keywords: Fisheries ; International organizations ; Management
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Political Science , Law
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  • 12
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    Amsterdam : Elsevier
    Marine Policy 9 (1985), S. 39-52 
    ISSN: 0308-597X
    Keywords: Ecology ; Fisheries ; Marine resources
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Political Science , Law
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  • 13
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    Amsterdam : Elsevier
    Marine Policy 6 (1982), S. 219-235 
    ISSN: 0308-597X
    Keywords: Canada ; Fisheries ; Foreign relations
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Political Science , Law
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  • 14
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    Amsterdam : Elsevier
    Marine Policy 9 (1985), S. 120-125 
    ISSN: 0308-597X
    Keywords: Exclusive Economic Zones ; Fisheries ; Law of the Sea
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Political Science , Law
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  • 15
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    Amsterdam : Elsevier
    Marine Policy 9 (1985), S. 126-133 
    ISSN: 0308-597X
    Keywords: Fisheries ; Government ; USA
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Political Science , Law
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  • 16
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    Amsterdam : Elsevier
    Marine Policy 6 (1982), S. 27-42 
    ISSN: 0308-597X
    Keywords: Fisheries ; International law ; United Nations Organization
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Political Science , Law
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  • 17
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    Amsterdam : Elsevier
    Marine Policy 6 (1982), S. 43-57 
    ISSN: 0308-597X
    Keywords: Atlantic ; Fisheries ; Management
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Political Science , Law
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  • 18
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    Amsterdam : Elsevier
    Marine Policy 6 (1982), S. 61-62 
    ISSN: 0308-597X
    Keywords: Fisheries ; Marketing ; UK
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Political Science , Law
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  • 19
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    Amsterdam : Elsevier
    Marine Policy 6 (1982), S. 66-68 
    ISSN: 0308-597X
    Keywords: Fisheries ; Regional government organizations ; West Africa
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Political Science , Law
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  • 20
    ISSN: 1432-1009
    Keywords: Fisheries ; Phosphorus ; Contaminants ; Ecosystem ; Management ; Simulation model ; Great Lakes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering
    Notes: Abstract A simulation model was developed to describe linkages among fish food web, nutrient cycling, and contaminant processes in the southern basin of Lake Michigan. The model was used to examine possible effects of management actions and an exotic zooplankter (Bythotrephes) on Lake Michigan food web and contaminant dynamics. The model predicts that contaminant concentrations in salmonines will decrease by nearly 20% ifBythotrephes successfully establishes itself in the lake. The model suggests that this decrease will result from lowered transfer efficiencies within the food web and increased flux of contaminants to the hypolimnion. The model also indicates that phosphorus management will have little effect on contaminant concentrations in salmonines. The modeling exercise helped identify weaknesses in the data base (e.g., incomplete information on contaminant loadings and on the biomass, production, and ecological efficiencies of dominant organisms) that should be corrected in order to make reliable management decisions.
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  • 21
    ISSN: 1432-1009
    Keywords: Reservoir ; Fisheries ; Breeding and wintering waterbirds ; Raising water levels ; Habitat change
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering
    Notes: Abstract A new, higher dam was installed at Kerkini Reservoir in 1982, causing habitat and landscape disruption. A decrease in the area of grassland and shallow water areas, the rapid disappearance of reedbeds, the appearance of beds ofNymphaea, and the disappearance of half the forest area were all observed between 1982 and 1991. With the new hydrological regime, a lacustrine system was created, with an extensive, rather deep (4–8 m), pelagic zone favorable for the development of coarse fish species throughout the year. After 1982, an increase in fishing effort and a change in the relative abundance of fish species in the catch, including the disappearance of eels and wels, were observed. The impact of the rise in the water level of breeding aquatic birds led to a general decline in species typical of marshy habitats in favor of species preferring deeper open water habitats. A decrease was recorded in bird species that feed largely on invertebrates and to a lesser extent fish (e.g., glossy ibis) and that require extensive shallow feeding areas. There was a decline in geese, whose nests were regularly flooded, and a major increase in piscivorous birds, particularly diving birds (e.g., cormorants), which prefer deeper open water and benefitted directly from the large increase in coarse fish biomass. The disappearance of birds breeding in flooded meadows (e.g., black-winged stilts) and of those restricted to reedbeds (e.g., marsh harrier) occurred from 1983. Over the same period, the changes in populations of wintering birds at Kerkini were different from those occurring in other wetlands in northern Greece. The changes recorded in the populations of wintering birds at Kerkini did not therefore result from overall regional trends but from the major habitat modifications that occurred to this wetland. As for breeding birds, strictly piscivorous species increased greatly as a result of the increased availability of fish, but also due to the appearance of many suitable night roosting sites (flooded trees) and to the great increase in the area of open water greater than 2 m deep. Today, Kerkini has become the most important breeding site in Greece for a majority of colonial waterbirds. In contrast, wintering shorebirds practically disappeared. The many changes recorded in the status of breeding and wintering birds at Kerkini can mostly be explained by the changes that occurred in the functioning of the ecosystem and in the habitat structure following the inauguration of the new hydrological regime. These changes did not all occur at the same time: some were immediate and others required a delay before they could be detected.
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  • 22
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    Environmental management 20 (1996), S. 523-539 
    ISSN: 1432-1009
    Keywords: Water control ; Floodplain ; Fisheries ; Bangladesh ; Chandpur
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering
    Notes: Abstract Bangladesh is a very flat delta built up by the Ganges—Brahmaputra—Meghna/Barak river systems. Because of its geographical location, floods cause huge destruction of lives and properties almost every year. Water control programs have been undertaken to enhance development through mitigating the threat of disasters. This structural approach to flood hazard has severely affected floodplain fisheries that supply the major share of protein to rural Bangladesh, as exemplified by the Chandpur Irrigation Project. Although the regulated environment of the Chandpur project has become favorable for closed-water cultured fish farming, the natural open-water fishery loss has been substantial. Results from research show that fish yields were better under preproject conditions. Under project conditions per capita fish consumption has dropped significantly, and the price of fish has risen beyond the means of the poor people, so that fish protein in the diet of poor people is gradually declining. Bangladesh is planning to expand water control facilities to the remaining flood-prone areas in the next 15–20 years. This will cause further loss of floodplain fisheries. If prices for closed-water fish remain beyond the buying power of the poor, alternative sources of cheap protein will be required.
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  • 23
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    Environmental management 3 (1979), S. 133-144 
    ISSN: 1432-1009
    Keywords: Coastal zone Management ; Fisheries ; Marshes ; Wetlands ; Louisiana
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering
    Notes: Abstract This paper examines causes and consequences of wetland losses in coastal Louisiana. Land loss is a cumulative impact, the result of many impacts both natural and artificial. Natural losses are caused by subsidence, decay of abandoned river deltas, waves, and storms. Artificial losses result from flood-control practices, impoundments, and dredging and subsequent erosion of artificial channels. Wetland loss also results from spoil disposal upon wetlands and land reclamation projects. Total land loss in Louisiana's coastal zone is at least 4,300 ha/year. Some wetlands are converted to spoil banks and other eco-systems so that wetland losses are probably two to three times higher. Annual wetland losses in the Barataria Bay basin are 2.6% of the wetland area. Human activities are the principal determinants of land loss. The present total wetland area directly lost because of canals may be close to 10% if spoil area is included. The interrelationship between hydrology, land, vegetation, substrate, subsidence, and sediment supply are complicated; however, hydrologic units with high canal density are generally associated with higher rates of land loss and the rate may be accelerating. Some cumulative impacts of land loss are increased saltwater intrusion, loss of capacity to buffer the impact of storms, and large additions of nutrients. One measure of the impact is that roughly $8–17 × 106 (U.S.A.) of fisheries products and services are lost annually in Louisiana. Viewed at the level of the hydrologic unit, land loss transcends differences in local vegetation, substrate, geology, and hydrology. Land management should therefore focus at that level of organization. Proper guideline recommendations require an appreciation of the long-term interrelations of the wetland estuarine system.
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  • 24
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    Agriculture and human values 17 (2000), S. 125-139 
    ISSN: 1572-8366
    Keywords: Environment ; Fisheries ; Fordism ; Nation-State ; Regulation ; Supranational State ; Transnational corporations ; Transnational State
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract This analysis uses an analytical frameworkgrounded in political economy perspectives of theglobalization of the agro-food sector combined with acase study approach focusing on the Marine StewardshipCouncil (MSC) to inform discussions regarding thecharacteristics of societal regulation in thepost-Fordist era. More specifically, this analysisuses the case of the emergence of the MSC toinvestigate propositions regarding the existence of,and location of, nascent forms of a transnationalState. The MSC proposes to regulate the certificationof sustainable fisheries at the global level throughan eco-labeling program. The MSC was created in 1996by the transnational environmental organization theWorld Wildlife Fund and the transnational corporationUnilever. The emergence of the MSC has generatedheated discussion in fisheries management circles thatis in general divided along North/South lines. Thisanalysis indicates that the case of the MSC providesvaluable insights into the possible characteristics ofsupranational regulatory mechanisms that might emulatethe role of the nation-State in the post-Fordist era.
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  • 25
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    Environmental biology of fishes 2 (1977), S. 241-259 
    ISSN: 1573-5133
    Keywords: Production ; Fisheries ; Population dynamics ; Energetics ; Fishes ; Competition
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Synopsis Production rates of seven species of fishes were determined for one year in a 0.95 ha pond. Total annual production of all fishes in the pond was 209 g m−2y−1 (after the subtraction of 16.2 g m−2y−1 of negative production). Over 90% of the production occurred in the months of June through September, with young-of-the-year fishes contributing 84% of the total. When Y of Y fishes shifted to benthic diets in the spring, the small biomass of benthos available could not sustain the large biomas of fish. Severe competition for the available food then resulted in decreased production rates for the entire fish taxocene.
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  • 26
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    Environmental biology of fishes 27 (1990), S. 303-308 
    ISSN: 1573-5133
    Keywords: Fish introductions ; Africa ; Cichlids ; Barbus ; Haplochromis ; Lake management ; Fisheries
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Synopsis Cyprinid fishes apparently constituted the major part of the original fish fauna in Lake Luhondo, Rwanda, at least until 1934. At that time only three species, all cyprinids, were known from the lake:Barbus neumayeri, a small barbel, very common in the lake (described from the lake asBarbus luhondo) and two larger cyprinid species:Barbus microbarbis andVaricorhinus ruandae. These two large species were probably not very common in the lake. Between 1935 and 1938 some youngTilapia were introduced into Lake Luhondo. Since then and certainly since 1952 the large cyprinids seem to have disappeared completely from the lake. The smallBarbus neumayeri has become extremely rare; at present it survives only in some small tributaries of the lake. In the lake itselfTilapia andHaplochromis species are now the dominant fauna. A survey of the available information is given.
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  • 27
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    Environmental biology of fishes 30 (1991), S. 253-271 
    ISSN: 1573-5133
    Keywords: Rockfish ; Longevity ; Reproductive value ; Fisheries ; Scorpaenidae
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Synopsis The characteristics of lightly and heavily exploited Pacific ocean perch,Sebastes alutus, stocks are evaluated relative to the predictions of life history theory. These long-lived species (50–100 year lifespan) show limited phenotypic plasticity and have little buffering against the effects of reduced lifespan. Reduced stock abundance has generated some compensatory increase in growth rate. Length at first maturity varies only slightly with increased growth rate, although age at maturity may decrease by 1–4 years. Grooth increases yield larger (15–20%) size at age and increased reproductive effort at younger ages, but lower size-specific fecundity for these faster-growing fish. This suggests an energy allocation protocol favouring growth over reproduction in these long-lived animals. Rockfishes have late recruitment to fisheries (ages 10–15), and the detection time for results of management actions is equally long. Their vulnerability to overfishing means that indices of population changes, more representative of fishing effects than the catch rate index presently used, are required. Reproductive value indices are shown to be extremely sensitive and continuous with population abundance changes. Their incorporation into monitoring programs would permit more timely evaluation of management actions. Management policies developed for shorter-lived species are shown to be inappropriate for rockfishes. The need for an improved match in the time frame of the species' life history, and that of management strategies, is stressed.
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  • 28
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    Environmental biology of fishes 43 (1995), S. 381-391 
    ISSN: 1573-5133
    Keywords: Fisheries ; Irrigation ; Reproductive seasonality ; Sarotherodon galilaeus ; Species richness ; Water quality
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Synopsis A preliminary study of the ecology and commercial fish catches was carried out in the Toho-Todougba, Ahouangan and Dati lakes (1500 ha) in southern Benin (West Africa) over a period of 18 consecutive months. Water quality, species richness, and the reproductive biology of the dominant species, Sarotherodon galilaeus, were examined. Unlike Lagoon Toho-Todougba, lakes Ahouangan and Dati are less favourable for fish production because of their high total iron content and their relative low pH. The study revealed the existence of 19 species belonging to eleven (11) families: 16 species in Lagoon Toho-Todougba,12 in Lake Ahouangan, and 7 in Lake Dati. Lakes Ahouangan and Dati had a relatively high faunal similarity whereas Lagoon Toho-Todougba exhibited a relatively low faunal similarity with the former systems. In Lagoon Toho-Todougba, six cichlid species were the most important component of the fishery: Sarotherodon galilaeus, Tilapia guineensis, T. zillii, T. mariae, Chromidotilapia guntheri, Hemichromis fasciatus. Three catfish species Chrysichthys auratus, Clarias agboyiensis, and Clarias lazera were harvested in low abundances. Some other fish, such as Polypterus senegalus senegalus, Protopterus annectens and Heterotis niloticus were captured sporadically, with H. niloticus appearing more consistently in catches than the others. Although not abundant, Gymnarchus niloticus and the African pike, Hepsetus odoe, were almost always present in the catches. Ctenopoma kingsleyae appeared only in Ahouangan. Some predatory species, such as Notopterus afer and Xenomystus nigri, are encountered only in lakes Ahouangan and Dati. In Lagoon Toho-Todougba, Sarotherodon galilaeus had a sex ratio (♂: ♀) of 0.49:1, and size at maturation was estimated as 12.3 cm TL. The spawning period extended from May to September with the peak occurring in July. Fecundity was correlated to log-body length (r = 0.74) and log-body weight (r = 0.76). Fish catches were estimated at 389 kg ha−1 year−1; about 73% of which was Sarotherodon galilaeus. The overexploitation of juvenile fish and the use of this lagoon for the irrigation of palm tree plantations have reduced fish recruitment and mean size.
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  • 29
    ISSN: 1573-5133
    Keywords: Chondrichthyes ; Elasmobranchs ; Fisheries ; Ageing methods ; Growth rates ; Gestation periods ; Maturity ; Vertebral bands ; Weight-length relationships ; Life histories
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Synopsis The silky shark, Carcharhinus falciformis, and scalloped hammerhead, Sphyrna lewini, represent 〉80% of the shark by-catch of the winter swordfish/tuna longline fishery of the northwestern Gulf of Mexico. This catch represents a potential supplemental fishery, yet little is known of the life histories of the two species. This report relates reproductive biology data to age and growth estimates for 135 C. falciformis and 78 S. lewini. Unlike other regional populations, C. falciformis in the Gulf of Mexico may have a seasonal 12 month gestation period. Males mature at 210–220 cm TL (6–7 yr); females at 〉225 cm TL (7–9 yr). Application of age at length data for combined sexes produced von Bertalanffy growth model parameter estimates of L∞ = 291 cm TL, K = 0.153, t0 = −2.2 yr. Adult male S. lewini outnumbered adult females in catches because of differences in the distributions of the sexually segregated population. Males mature at 180 cm TL (10 yr); females at 250 cm TL (15 yr). von Bertalanffy parameter estimates for combined sexes of this species were L∞ = 329 cm TL, K = 0.073, to = −2.2 yr.
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  • 30
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    Environmental biology of fishes 23 (1988), S. 141-154 
    ISSN: 1573-5133
    Keywords: Cyanide ; Diversity ; Development ; Ecology ; Environment ; Fisheries ; Pollution
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Synopsis The biological diversity and productivity of Philippine coral reefs are threatened by siltation, destructive fishing methods, coral and shell collecting and overfishing. Destructive fishing includes: the widespread, illegal use of explosives; poisons such as sodium cyanide; muro-ami and kayakas fishing; and trawling. The recent decline in catch rates threatens the livelihood of 700 000 near-shore subsistence fishermen who catch 55% of the total landings. The new government under Corazon Aquino wishes to protect the marine environment through the creation of a viable marine conservation management plan, enforcement of existing laws and through cooperation between government, non-government and international agencies to provide education and research. The Department of Agriculture, which has the authority for fisheries, has designated the International Marinelife Alliance as the lead non-government agency involved with fund raising, net-training and finding alternatives to destructive fishing methods.
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    Environmental biology of fishes 35 (1992), S. 187-203 
    ISSN: 1573-5133
    Keywords: California ; Elasmobranchs ; Exploitation ; Fisheries ; Life history ; Tagging ; Triakidae
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Synopsis The age, growth, and sexual maturation of the leopard shark, Triakis semifasciata, from central California were studied. Growth band counts in vertebral centra of 162 leopard sharks produced von Bertalanffy growth curves with L∞, K. and to parameters of 1536 mm. 0.082, and -2.31, respectively, for both sexes combined. The L8 value for females (1602 mm TL) was slightly but insignificantly higher than for males (1499 mm TL), but the K and to values were almost identical. Seasonal changes in size modes of young-of-the-year leopard sharks, centrum edge characteristics, and growth and tetracycline mark-recapture from the field were used to validate annual deposition of vertebral centrum band pairs. Sexual maturity was evaluated by the gonads and presence of sperm and eggs; males mature at 7 yr and at about 63% of asymptotic length, and females mature at 10 yr, and at about 72% of asymptotic length. This slow growth, late maturity, and relatively low fecundity may increase their susceptibility to over-exploitation.
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    Environmental biology of fishes 45 (1996), S. 219-235 
    ISSN: 1573-5133
    Keywords: Ecology ; Behaviour ; Evolution ; Cichlids ; Fisheries ; Conservation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Synopsis Ecological conditions in tropical lacustrine systems are considered by focusing on the evolution, maintenance, exploitation and vulnerability of fish communities in the African Great Lakes. The exceptionally high biodiversities in the littoral/sublittoral zones of the very ancient, deep, clear, permanently stratified rift lakes Tanganyika and Malawi, are contrasted with the simpler systems in their pelagic zones, also with biodiversity in the much younger, shallower Victoria, the world's largest tropical lake.
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    Environmental biology of fishes 7 (1982), S. 177-180 
    ISSN: 1573-5133
    Keywords: Temperature ; Behavior ; Ecology ; Fisheries ; Fish ; Marine juveniles
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Synopsis Sixteen yearling winter flounder, tested individually for 3-day periods in electronic shuttleboxes, voluntarily occupied an 8–27°C range of temperature, with a modal final thermal preferendum of 18.5°C (mean 18.7°C, median 19°C, midpoint 17.5°C, s.d. 1.9°C, S k + 0.33). The locomotor activity pattern of the yearling fish in the laboratory was markedly nocturnal, with mean hourly nocturnal activity exceeding mean hourly diurnal activity by a factor of 3.4. Maximum activity occurred at 0300 EST, minimum activity at 1400 EST. While activity generally increased with temperature, a local activity minimum occurred at 18.7°C, coinciding with the 24-hour mean final thermal preferendum. Comparison of these laboratory data with previously published field data suggest that behavioral responses to temperature and light play significant roles in determining age- and size-specific differences in seasonal depth stratification and onshore-offshore distributions in this species.
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  • 34
    ISSN: 1573-5133
    Keywords: Cyprinids ; Ethiopia ; Morphotypes ; Food-niche ; Biodiversity ; Feeding ; Evolution ; Fisheries ; Resource partitioning ; Piscivory
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Synopsis In October–December 1990, the large barbs (Barbus) that contribute more than 35% of the catch in lake Tana (northern Ethiopia) were studied. Previous authors (Rüppell 1837, Boulenger 1902,1911, Bini 1940) described from 6 to 23 (sub)species for the lake. Banister (1973) lumped all of these into one subspecies: Barbus intermedius intermedius Rüppell,1837. We found that the Lake Tana Barbus could be readily categorized in at least 13 discrete morphotypes, some of which were already distinguished by local fishermen. None of the known descriptions are adequate to distinguish the barbs unambiguously, which is important for monitoring and management of developing fisheries. Intermediates between morphotypes were rare (〈 10%). By applying canonical discriminant analysis on a set of 17 morphometric characters (including some directly associated with feeding) our initial morphotype-distinction was confirmed. Also, differences between the morphotypes in distribution, related to depth and substratum were found, as well as differences in intestinal contents, a key to the food-niche. The high number of piscivorous morphotypes (8 out of 13) was striking as piscivory is relatively rare among cyprinids. Piscivory was found to be highly correlated with morphological (feeding related) characters. The presence of discrete morphotypes, that also differ in food-niche and distribution, strongly suggests that several distinct populations exist, that may be (partly or completely) reproductively segregated. Knowledge about these populations, that may represent separate units of fish stock, is of crucial importance for the management of sustainable fisheries and protection of the biodiversity in Lake Tana. It is possible that several species or even a unique cyprinid species flock are present, that urgently need protection.
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    Environment, development and sustainability 2 (2000), S. 277-304 
    ISSN: 1573-2975
    Keywords: Systems of Knowledge ; Local Knowledge ; Fisheries ; Resource Management
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Sociology
    Notes: Abstract During the last 20 years, the existence of rich systems of local knowledge, and their vital support to resource use and management regimes, has been demonstrated in a wide range of biological, physical and geographical domains, such as agriculture, animal husbandry, forestry and agroforestry, medicine, and marine science and fisheries. Local knowledge includes empirical and practical components that are fundamental to sustainable resource management. Among coastal-marine fishers, for example, regular catches and, often, long-term resource sustainment are ensured through the application of knowledge that encompasses empirical information on fish behaviour, marine physical environments, fish habitats and the interactions among ecosystem components, as well as complex fish taxonomies. Local knowledge is therefore an important cultural resource that guides and sustains the operation of customary management systems. The sets of rules that compose a fisheries management system derive directly from local concepts and knowledge of the resources on which the fishery is based. Beyond the practical and the empirical, it is essential to recognise the fundamental socio-cultural importance of local knowledge to any society. It is through knowledge transmission and socialisation that worldviews are constructed, social institutions perpetuated, customary practices established, and social roles defined. In this manner, local knowledge and its transmission, shape society and culture, and culture and society shape knowledge. Local knowledge is of great potential practical value. It can provide an important information base for local resources management, especially in the tropics, where conventionally-used data are usually scarce to non-existent, as well as providing a shortcut to pinpoint essential scientific research needs. To be useful for resources management, however, it must be systematically collected and scientifically verified, before being blended with complementary information derived from Western-based sciences. But local knowledge should not be looked on with only a short-term utilitarian eye. Arguments widely accepted for conserving biodiversity, for example, are also applicable to the intellectual cultural diversity encompassed in local knowledge systems: they should be conserved because their utility may only be revealed at some later date or owing to their intrinsic value as part of the world's global heritage. At least in cultures with a Western liberal tradition, more than lip-service is now being paid to alternative systems of knowledge. The denigration of alternative knowledge systems as backward, inefficient, inferior, and founded on myth and ignorance has recently begun to change. Many such practices are a logical, sophisticated and often still-evolving adaptation to risk, based on generations of empirical experience and arranged according to principles, philosophies and institutions that are radically different from those prevailing in Western scientific circles, and hence all-but incomprehensible to them. But steadfastly held prejudices remain powerful. In this presentation I describe the 'design principles' of local knowledge systems, with particular reference to coastal-marine fishing communities, and their social and practical usefulness. I then examine the economic, ideological and institutional factors that combine to perpetuate the marginalisation and neglect of local knowledge, and discuss some of the requirements for applying local knowledge in modern management.
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    Berichte der deutschen chemischen Gesellschaft 2000 (2000), S. 801-818 
    ISSN: 1434-1948
    Keywords: Zeolites ; Microporous zeolites ; Titanosilicates ; Transition metal ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Stable microporous materials, such as zeolites, are extremely important for applications in catalysis, adsorption, ion-exchange, and separation. In this review we describe a new class of stable microporous materials that involves novel mixed octhaedral-tetrahedral framework oxides. The archetypal material is based on titanosilicates, although there is tremendous scope for introducing many other transition metals. These materials not only have potential novel applications in the fields normally associated with zeolites but also possible applications in the areas of optoelectronics, nonlinear optics, batteries, magnetic materials and sensors.
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    Berichte der deutschen chemischen Gesellschaft 2000 (2000), S. 827-830 
    ISSN: 1434-1948
    Keywords: Ammonolysis ; Chlorine ; Nitrogen ; Silicon ; Silsesquiazane ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The ammonolysis of trichlorosilanes RSiCl3 [R = CH(SiMe3)2 (1a), Ph (1b), Et (1c)] leads to a series of condensed products such as six-membered rings [(Me3Si)2CHSi(OH)NH]3 (2a) and [PhSi(NH2)NH]3 (2b), disilazane [(Me3Si)2CHSi(NH2)2]2NH (3) and the cage compound (EtSi)6(NH)9 (4). The mixed Si-N-O compound 2a was obtained when liquid ammonia was not dried over sodium prior to use. The reaction with sodium gives NaCl instead of NH4Cl as a by-product which is easily removed by filtration.
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    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 2147-2156 
    ISSN: 1434-1948
    Keywords: Tetrapodal pentadentate ligand ; Ligand periphery ; Polydentate amine complex ; Nickel ; Podand ; Schiff base ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The tetrapodal pentaamine ligand 2,6-bis(1′,3′-diamino-2′-methylprop-2′-yl)pyridine (1), which contains four equivalent primary amino groups, can be derivatised partly or completely by Schiff base condensation with suitable carbonyl compounds. The new ligands thus obtained are mononucleating, as shown by the X-ray crystal structures of their respective nickel(II) complexes. Reaction of 1 with 1 equiv. of salicylaldehyde and subsequent reduction allows the selective modification of one of the four sidearms. The resulting ligand 2 is hexadentate and uninegative in its nickel(II) complex {[(2)Ni]PF6} (3) with both the secondary amine and the phenoxide functionalities coordinated to the metal centre. The unreduced Schiff base form of the ligand, 4, does not form a complex with nickel(II) as readily, and only a small quantity of the mixed salt {[(4)Ni][(1)Ni(H2O)](Br)2(PF6)} (5)has been obtained. While the overall coordination of 4 resembles that of 2, there is considerably more strain in the appended chelate ring, due to the presence of the C=N double bond. Modification of one arm in 1 can also be achieved by condensation with 1 equiv. of acetylacetone, to give the new ligand 6 which, likewise, is hexadentate in its NiII complex {[(6)Ni](PF6)2} (7). In this case, however, the N/O-functional sidearm is not deprotonated. Rather, it is coordinated as the keto-imine tautomer, making 7 a rare example of a metal complex containing this structural fragment. Two-fold functionalisation of 1 is observed upon reaction with acetone, regardless of whether the ketone is present in stoichiometric amounts or in excess, to give the pentadentate ligand 8with two diagonally juxtaposed isopropylidene-imine units. The complex isolated with this ligand {[(8)Ni](PF6)2} (9) contains pentacoordinate NiII, the sixth coordination site being blocked by the rigidly positioned isopropylidene groups. When reacted with 4 equiv. of trans-cinnamaldehyde, all the primary amino groups in 1 condense to give the four-fold Schiff base 10, which acts as a pentadentate podand towards nickel(II). In this complex, {[(10)Ni(OH2)]Br2} (11), an aqua ligand completes the coordination octahedron. All ligands are stable towards hydrolysis when coordinated to the metal, despite the presence of alkyl-imine groups in some cases.
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    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 2157-2166 
    ISSN: 1434-1948
    Keywords: Septadentate N5S2-ligand ; Dinuclear complexes ; Nickel ; Reactivity ; Redox chemistry ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The coordination chemistry of a series of dinickel complexes of the new septadentate amine-thiolate ligand N,N′-bis[2-thio-3-aminomethyl-5-tert-butylbenzyl]diethylenetriamine, H29, has been investigated in the context of ligand binding and oxidation state changes. The complexes [Ni2(9)(L)][ClO4]2 (10), [Ni2(9)(Cl)][Cl] (11), [Ni2(9)(L)][BPh4]2 (12), and [Ni2(9)(NCS)][OH·OH2] (13) have central N2Ni(μ-SR)2NiN′3L cores [L = labile solvent molecule (10, 12), Cl- (11), and NCS- (13)] composed of dithiolate bridged planar NiN2S2 and six-coordinate NiN′3S2L units. This is demonstrated for 11 and 13 by crystal structure determinations and for 10 and 12 by UV/Vis spectroscopy and room temperature magnetic susceptibility measurements. Complexes 10, 11, or 12 readily add other co-ligands at the NiN′3S2L fragment by substitution of the solvent molecule L (10, 12) or the chloride substituent (11). The overall structure of the parent complexes is not affected by the substitution reactions. An electrochemical study has shown that complex 10 undergoes two successive one-electron oxidations at +0.88 and +0.41 V vs SCE. The oxidized species are not thermally stable, but electronic absorption spectra and EPR spectra are indicative of the presence of NiIII species.
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    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 2167-2172 
    ISSN: 1434-1948
    Keywords: Macrocyclic compounds ; Amine-Thiolate Donors ; Polynuclear Complexes ; Nickel ; Condensation reactions ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A novel route to macrocyclic amine-thiophenolate ligands is described. The new, air-stable thiophenolate precursor 1,2-bis(4-tert-butyl-2,6-diformyl-phenylsulfanyl)ethane (4) is readily condensed with two equivalents of 1,2-ethanediamine or 1,3-propanediamine under medium to high dilution conditions to give 2 × 4 condensation products. The smaller 1 × 2 macrocyclic compounds are not produced under these conditions. Subsequent reduction with NaBH4 (reduction of imine groups) and Na/NH3 (reductive cleavage of aryl-alkylsulfides) provides the 36- and 40-membered amine-thiophenolate ligands H46a and H46b. The macrocyclic compounds are versatile ligands for the preparation of polynuclear transition metal complexes. With divalent nickel H46a forms the di- and tetranuclear complexes [Ni2(6a)] (7) and [Ni4(6a)][ClO4]4 (8). Reaction of 8 with four equivalents of NH4SCN yields the novel isothiocyanate complex [Ni4II(6a)(NCS)4]·10MeCN (9). The structure consists of well-separated molecules of the tetranuclear complex [NiII4(6a)(NCS)4] (Ci symmetry). Two symmetry-related binuclear [N2Ni(μ2-SR)2NiN4] fragments composed of thiolate-bridged distorted planar {N2S2Ni}- and distorted cis-octahedral {(SCN)2N2S2Ni} units reside within the cavity of the macrocycle. The intramolecular distance between the two binuclear units is 6.144(1) Å.
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    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 2173-2185 
    ISSN: 1434-1948
    Keywords: EPR spectroscopy ; Metallocenylboranes ; Organovanadium radicals ; Redox chemistry (CV) ; X-ray diffraction ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The paramagnetic complexes di(mesityl)([5]trovacenyl)borane (5·), (mesityl)di([5]trovacenyl)borane (6··), and tri([5]trovacenyl)borane (7···) were prepared from [5]trovacenyllithium, (η5-C7H7)V(η5-C5H4Li), and (Mes)2BF, (Mes)BF2, and BF3, respectively. The propeller-shaped species 5·, 6··, and 7··· were subjected to X-ray diffraction with the aim of possibly correlating the twist angles with intramolecular intermetallic communication. Cyclic voltammetry points to successive vanadium-centered oxidation processes and boron-centered reduction, a small redox splitting δE1/2[(2+/+), (+/0)] being observed for 6··. According to EPR spectroscopy, performed in fluid solution, the exchange interaction J in the diradical 6·· approaches the fast-exchange region and is attenuated significantly by quaternization at boron in [6··-nBu]-. Although EPR spectroscopy of the triradical 7··· also indicates an extensive exchange interaction, the exchange parameters, derived from spectral simulation, follow the gradation J(7···) ≈ 1/3 J(6··). The magnetic susceptibility of 6·· and 7··· follows the same trend. As expected, compound 7··· exhibits spin frustration because it contains three antiferromagnetically coupled S = 1/2 systems that are arranged in an equilateral triangle.
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    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 2187-2199 
    ISSN: 1434-1948
    Keywords: Ansa compounds ; Cp-derived chelate ligands ; Neopentane chemistry ; Spiro compounds ; Tripodal ligands ; Cyclopentadienyl compounds ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The neopentane-derived functionalized oxetane O(CH2)2C(CH3)(CH2OMs), 1, reacts with indenyllithium (LiInd) or fluorenyllithium (LiFlu) to produce the derivatives O(CH2)2C(CH3)(CH2R) (R = indenyl, fluorenyl), 2. The oxetane ring of 2 undergoes nucleophilic ring-opening by reaction with LiPR′2 to give the chiral chelate ligands (HOCH2)(CH3)C(CH2R)(CH2PR′2) (R = indenyl, fluorenyl), 5. Nucleophilic ring-opening by LiInd or LiFlu is possible too, resulting in the functionalized ansa-Cp ligands (HOCH2)(CH3)C(CH2R)(CH2R′) (R, R′ = indenyl, fluorenyl), 12. Electrophilic ring-opening of 2 with HBr to give (HOCH2)(CH3)C(CH2R)(CH2Br) (R = indenyl, fluorenyl), 3, is also possible. The alcohol function of 3 may be activated directly, whereas activation of this group in 5 is only possible after BH3 protection of the phosphane function. The mesylates (MsOCH2)(CH3)C(CH2R)(CH2Br) (R = indenyl, fluorenyl), 4, undergo, under basic conditions, spiro cyclization to produce spirocyclobutane derivatives 9 with the α-carbons of the five-membered cycles acting as the spiro centres. Substitution of the mesylate group of 4 by PR2 nucleophiles is therefore not possible. Ansa-Cp derivative (MsOCH2)(CH3)C(CH2Ind)(CH2Flu), 12c also reacts with LiPPh2 with spiro cyclization to produce 9d, instead of giving the substitution product. Tripodal ligands (CH3)C(CH2R)(CHPPh2)2 (R = indenyl, fluorenyl), 11, are accessible by the reaction of (MsOCH2)(CH3)C(CH2PPh2)2 with LiInd or LiFlu. All compounds are fully characterized by the usual spectroscopic and analytical techniques including single-crystal X-ray analyses in several cases.
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    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 2201-2207 
    ISSN: 1434-1948
    Keywords: Carboxylate syn-anti ; N-centered tripodal ligand ; Manganese ; Imidazole ; Helicoïdal inorganic chiral chain ; Magnetism ; π-π interaction ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The crystal structure of an infinite inorganic chain consisting of MnII and an N-centered tripodal ligand N,N-(2-pyridylmethyl)[(1-methylimidazol-2-yl)-methyl]glycinate is presented. It exhibits a chiral helical structure with a pitch of two monomeric units (each monomeric unit containing one Mn atom). Each manganese is connected to its neighbor through a carboxylate bridge in a syn-anti geometry. Around each manganese center, two carboxylates bind in a cis geometry. This peculiar bridging geometry (syn-anticis) provides a broken-line chain, running in a zig-zag manner along the b axis of the P21 space group. The magnetic properties have been investigated. They show a pseudo-2D magnetic structure, with one major pathway along the chain and an inter-chain minor one. The intrachain coupling is a weak antiferromagnetic interaction (J/k = -0.25). This low value is entirely consistent with the geometry of the bridge. The interchain coupling is a weaker antiferromagnetic coupling (J′/k = -0.11) and could be mediated through π-π interactions between pyridine and imidazole from two adjacent helixes.
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    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 2221-2231 
    ISSN: 1434-1948
    Keywords: Calixarenes ; Inclusion compounds ; Imido Complexes ; Molybdenum ; Tungsten ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Syntheses, spectroscopic properties, molecular structures, and bonding of novel calix[4]arene imido compounds are described. Treatment of M(NtBu)2(NHtBu)2Ia (M = Mo), Ib (M = W) or M(NMes)2Cl2(dme) IIa (M = Mo), IIb (M = W) (Mes = 2,4,6-Me3-C6H2) with p-tBu-calix[4]arene LH4 affords calix[4]arene metal complexes LM(NR) 1a, b (M = Mo, W; R = tBu) and 2a, b (M = Mo, W; R = Mes). Analytical and spectroscopic data are consistent with monomeric structures for 1 and 2, retaining a local C4v symmetry for the calix[4]arene metal fragment. These complexes are well-suited to bind small molecules like acetonitrile, tBu-isonitrile, or water within their macrocyclic pockets. The spectroscopic data of some inclusion compounds and the crystal structures of LMo(NtBu)(NCMe) 1a(NCMe), LW(NtBu)(OH2) 1b(OH2), LW(NtBu)(CNtBu) 1b(CNt Bu), LMo(NMes)(NCMe) 2a(NCMe), and LW(NMes)(NCMe) 2b(NCMe) are reported. All complexes contain a group VI metal imido [M=NR] moiety mounted on the phenoxide rim of the calix[4]arene ligand as well as an incorporated guest molecule within the cavity. Some insights into the structures of complexes of the type L′W(NR′) (L′ = p-H-calix[4]arene; R′ = H, Me) and into bonding in these compounds are provided by density functional theory, applying the B-P86 density functional and an all SVP basis set within the RI-J-DFT approximation. At least one π bond is of importance for calix[4]arene-metal bonding in these compounds. The metal-imido bond can be described as a triple bond. A geometrically optimized minimum structure of L′W(NMe) 4 shows a calix[4]arene ligand only slightly distorted from a local C4v symmetry and an almost linear tungsten-imido moiety.
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  • 45
    ISSN: 1434-1948
    Keywords: Arsonium salts ; Superacidic systems ; Structure elicidation ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The reaction of trimethylarsane in the superacidic systems hydrogen/fluoride antimony pentafluoride and hydrogen fluoride/arsenic pentafluoride leads to trimethylarsonium fluorometallates. These salts are stable up to 60 °C and 5 °C, respectively. Structures were successfully elucidated in the cases of trimethylarsonium undecafluorodiarsenate and trimethylarsonium hexafluoroantimonate. (CH3)3AsH+As2F11- crystallizes in the monoclinic space group P21/n with four formula units per unit cell with the dimensions a = 7.362(1), b = 12.589(1), c = 13.598(1) Å and β = 95.37(1)°. (CH3)3AsH+SbF6- crystallizes in the monoclinic space group P21/m with four formula units per unit cell with the dimensions a = 8.313(1), b = 8.855(1), c = 13.285(1) Å and β = 94.358(1)°.
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    ISSN: 1434-1948
    Keywords: Molybdenum ; μ-Oxo ; Conformational equilibrium ; X-ray diffraction ; NMR spectroscopy ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A new thiocyanatomolybdenum(VI) dioxo-μ-oxo complex dimer bearing a 4,4′-di-tert-butyl-2,2′-bipyridine ligand (2) is shown to exist in the crystal cell unit as a meso (Mo-O-Mo angle of 180°) and d,l, pair (Mo-O-Mo angle of 155.7°). These conformers are in equilibrium in solution and have been observed clearly by 1H NMR spectroscopy.
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  • 47
    ISSN: 1434-1948
    Keywords: Macrocycles ; Lithium ; Fluorescence ; Cryptands ; Coordination ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Three aza-cages with the anthracene-containing photoactive groups L1, L2, and L3 have been synthesized. All compounds are able to selectively encapsulate a lithium ion and solid complexes have been isolated. The formation equilibria have been investigated by UV/Vis and 1H, 13C and 7Li NMR spectroscopic techniques. The fluorescence emission of both free ligands and lithium complexes have been investigated. Results indicate that the CHEF (chelation enhancement of the fluorescence) effect obtained by lithium coordination exits although lower than that occurring upon full protonation.
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  • 48
    ISSN: 1434-1948
    Keywords: Copper ; Trinuclear complexes ; Formamidines ; Magnetism ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Three new copper(II) linear trinuclear compounds are reported, all of which were synthesized in-situ, with the general formula [Cu3(L)4](CF3SO3)2(Y)x, where L is the dehydronated ligand: N,N′-bis(pyridine-2-yl)formamidine (abbreviated as Hpdf), N,N′-bis(pyrimidine-2-yl)formamidine (abbreviated as Hpmf) and N,N′-bis(5-methylpyridine-2-yl)formamidine (abbreviated as Hmpdf), Y = EtOH or H2O and x = 0.5-1.5. The compounds were characterized by X-ray diffraction, IR, LF, and EPR spectroscopy and by magnetic susceptibility down to 4 K. The structure of the compound [Cu3(pmf)4](CF3SO3)2(H2O)1/2 was determined by X-ray crystallography; it was found to crystallise in the triclinic space group P-1 with a = 8.529(5), b = 15.760(5), c = 19.639(5) Å, α = 101.793(5), β = 101.263(5), γ = 102.389(5)°, Z = 2. The structure [Cu-Cu-Cu angle 174.96(11)°] 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 with calculated J values, based on the Hamiltonian H = -2J(S1·S2 + S2·S3) - 2J′·S1·S3, of -174(1) cm-1, -120(1) cm-1, and -167(1) cm-1 for the compounds studied with L = pdf, pmf, and mpdf, respectively. These values are in agreement with an S = 1/2 ground state below temperatures of 120-160 K.
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  • 49
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    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 2277-2281 
    ISSN: 1434-1948
    Keywords: Boron ; Iron ; Nickel ; Carbyne complexes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The μ3-boryloxycarbyne complexes [{Fe(CO)3}3{μ3-COBCl{NtBu(SiMe3)}}2] (1) and [{(η5-C5H5)Ni}3{μ3-COBX(NR2)}μ3-CO] (2a: NR2 = NtBu(SiMe3), × = Cl; 2b: NR2 = N(SiMe3)2, × = Cl; 2c: NR2 = NMe2, × = BNMe2Cl) were obtained by reaction of the anionic complexes K2[{Fe(CO)3}3{μ3-CO}2] and K[{(η5-C5H5)Ni(CO)] with the corresponding chloroboranes Cl2BNR2 {NR2 = NtBu(SiMe3), N(SiMe3)2}, or 1,2-dichlorodiboranes(4) B2(NMe2)2Cl2, respectively. The products are formed by a nucleophilic attack of the CO oxygen atom at the boron centres with subsequent salt elimination. All compounds were characterized by IR and multinuclear NMR spectroscopy, and the structures of 1 and 2c in the solid state were determined by single-crystal X-ray diffraction studies.
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  • 50
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    Berichte der deutschen chemischen Gesellschaft 2000 (2000), S. 835-837 
    ISSN: 1434-1948
    Keywords: Gold ; Clusters ; Quantum dots ; Monolayers ; Amphiphiles ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Extended ordered monolayers of ligand stabilized Au55 clusters are formed at the phase boundary between water and dichloromethane. The water phase, containing amphiphilic molecules like per-6-deoxy-6-thio-α-cyclodextrin (1) or poly(vinylpyrrolidone) (2), is covered by a thin film of a solution of [Au55(PPh3)12Cl6] in dichloromethane. The interaction of the cluster molecules with the thiol functions of 1 or the polymer chains of 2 form perfect cluster orders of hexagonal and cubic structure. The monolayers can be transferred onto solid substrates by a simple dipping process. The use of carbon coated copper grids allows the investigation of the monolayers by transmission electron microscopy (TEM). Electron diffraction experiments under a microscope prove the hexagonal and cubic arrangements. The reason for the formation of the one or the other modification is still unknown.
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  • 51
    ISSN: 1434-1948
    Keywords: Triosmium cluster ; Biphosphinine ; Crystal structure ; Cyclic voltammetry ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The crystal structure of the novel cluster [Os3(CO)10(4,4′,5,5′-tetramethyl-2,2′-biphosphinine)] reveals an unprecedented coordination mode of the biphosphinine ligand that occupies a doubly-bridging position spanning the open osmium triangle. The cluster is photostable, pointing to a localization of the lowest-energy electronic transition largely on the negatively charged biphosphinine ligand.
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  • 52
    ISSN: 1434-1948
    Keywords: Photochemistry ; Electrochemistry ; Ruthenium compounds ; α-Diimine complexes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The photophysical, photochemical and redox properties of the title complexes were investigated. Resonance Raman measurements revealed the lowest-energy electronic transition to possess σ→π* character. At low temperatures, long-lived near-IR emission was observed. Irradiation in solution results in homolytic splitting of a Ru-Ru bond as the primary step, followed by secondary reactions of the radical fragments depending on the experimental conditions. (Spectro)electrochemical investigations of the title species proved that the axial [RuCp(CO)2] groups exert a stabilising influence on the corresponding radical cations, while destabilising the corresponding radical anions, compared to the redox behaviour of other ruthenium complexes of this type.
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  • 53
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    Berichte der deutschen chemischen Gesellschaft 2000 (2000), S. 889-894 
    ISSN: 1434-1948
    Keywords: Rhodium hydride complexes ; Parahydrogen ; Tin ligands ; Hydrogenations ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The oxidative addition of dihydrogen to the [RhH(SnCl3)5]3-/PR3 system (PR3 = PPh3, PEtPh2, PEt3) leads to the formation of previously unknown dihydride complexes, the 1H-NMR spectra of which have been studied by means of the ParaHydrogen Induced Polarization (PHIP) method. The composition of the resulting complexes crucially depends on the type of the added phosphane. With PEt3 as the phosphane and acetonitrile as the solvent, a complex with a SnCl2L ligand (L = CD3CN) can be detected. All systems examined catalyze the hydrogenation of phenylacetylene. During these reactions, both the 1H-NMR resonances of the dihydride complexes and those of styrene, the hydrogenation product of phenylacetylene, can be detected simultaneously. In the case of SnBr3 ligands, hydrogen addition in the presence of phosphanes leads to similar dihydride complexes, which were also identified via 1H-NMR spectroscopy. Furthermore, a mixed complex of the structure [Rh(SnBr3)nBr6-n]3- has been isolated.
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  • 54
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    Berichte der deutschen chemischen Gesellschaft 2000 (2000), S. 857-877 
    ISSN: 1434-1948
    Keywords: Crystal packing ; Neural networks ; Pattern recognition ; Organometallic compounds ; Close packing ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The crystal structures of hundreds of thousands of molecular compounds have now been determined with the quantitative information being stored in large databases. Chemists are generally interested in that specific part of this information which refers to individual molecules. The packing of molecules and their spatial relation to each other is not the focus of interest, even though the material properties of a molecular crystal are determined by both the packing arrangement of the molecules and their specific properties. The lack of interest in packing has at least one obvious reason. It is difficult for the non-expert to find the appropriate packing categories when looking at a principally infinite lattice. A tool performing this search for individual categories of packing in an automatic manner would therefore be of general importance. The development and application of such a tool is described in this paper. Novel strategies to extract a set of n points forming a specific n-point polyhedron from a set of p points (p 〉 n) is at its basis. Neural networks and second moment analysis are used as the methods of pattern recognition. In order to correlate packing and shape, second moment analysis of molecular shape is also used. This novel method is applied to three classes of organometallic compounds to determine whether the crystals formed by these compounds belong to any of the three classes fcc, bcc, or hcp in an idealized sense. A strong correlation is found between molecular shape and the membership or nonmembership of these classes. The corresponding program, including appropriate tools for visual representation, is available from the authors.
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  • 55
    ISSN: 1434-1948
    Keywords: Arenetricarbonyl chromium complexes ; Palladium ; Cross coupling reaction ; Thiophenes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The cross coupling reaction of (p-chloroanisole)tricarbonylchromium complex (1) with thiophene derivatives under palladium-catalyzed conditions leads to the selective formation of tricarbonyl-η6-[(2-thiophenyl)arene]- or -η6-[(2-thiophenyl)carbonylarene]chromium complexes (2 or 3) depending on reaction conditions. The conformation of complexes 2 and 3 in the solid state as well as in solution are reported.
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  • 56
    ISSN: 1434-1948
    Keywords: Ruthenium ; Phenanthroline ; Luminescence ; Sterically hindered ligands ; Terpyridine ; Cyclometallation ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Two series of cyclometallated and noncyclometallated ruthenium(II) complexes incorporating mono- or disubstituted 1,10-phenanthroline- and 2,2′:6′,2′′-terpyridine-type ligands have been synthesized and characterized. An X-ray crystal structure for one of the complexes, Ru(ttpy)(mapH)-(Cl)(PF6), has been obtained (mapH = 2-p-anisyl-1,10-phenanthroline; ttpy = 4′-tolyl-2,2′:6′,2′′-terpyridine). Distinct electrochemical and photophysical properties have been observed for the two series: a remarkable feature is the observation of relatively long-lived MLCT excited states (from 70 to 106 ns at room temperature in CH3CN) for three of the cyclometallated complexes. A discussion is given on the role of factors like sigma donation by the cyclometallating ligands, interligand steric hindrance and interligand π-π interactions that affect the electrochemical and spectroscopic properties.
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  • 57
    ISSN: 1434-1948
    Keywords: Polymeric copper complexes ; Group-subgroup relationships ; 2D-sheets ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The synthesis and characterisation of two new polymeric CuII complexes is described, i.e. {[Cu(btp)2(CH3CN)(H2O)](CF3SO3)2}n (1) and {[Cu(btp)2(CH3CN)2](ClO4)2}n (2), in which btp = [1,3-bis(1,2,4-triazol-1-yl)propane]. Compound 1 crystallizes in space group P21/c with a = 11.9337(15) Å, b = 20.108(6) Å, c = 12.748(6) Å, β = 92.247(14)°, and Z = 4. Compound 2 crystallizes in space group Pna21 with a = 18.770(8) Å, b = 12.648(8) Å, and c = 12.019(8) Å. The structures refined to R1 values of 0.0683 for 1 and 0.0846 for 2. In both structures the CuII ions are linked by the bridging ligands, resulting in two-dimensional networks. Two such curved layers are arranged on top of each other with center-to-center of layer distances of 2.12 Å in 1 and 1.98 Å in 2. Such double layers are separated from each other by 10.05 Å in 1 and 9.385 Å in 2. The space between the double layers is occupied with interstitial anions. No significant interaction between CuII ions is observed by EPR and magnetic susceptibility measurements. The compounds form a new class of a lattice engineered system held together by the CuII ions. - The coordination geometry of the copper ions is distorted octahedral, with the equatorial plane formed by the N4 nitrogens of the four triazole groups and the axial sites occupied by solvent molecules; acetonitrile and water in structure 1 and two acetonitrile molecules in structure 2. The two structures are related by a group-subgroup relationship, which appears to be the first such case in supramolecular chemistry. - The Cu-N vibrations in the FIR region are found at 274 cm-1 for 1, and at 276 cm-1 for 2. The ligand-field maxima are observed at about 16·103 cm-1, with a shoulder at about 12·103 cm-1. The νCN stretching vibrations of the acetonitrile molecules are found at 2303 and 2261 cm-1 for 1, and at 2313, 2294, 2278, and 2260 cm-1 for 2.Supporting information for this article is available on the WWW under -//_/_http://www.wiley-vch.de/contents/jc_2005/2000/99211_s.pdf or from the author.
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  • 58
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    Berichte der deutschen chemischen Gesellschaft 2000 (2000), S. 217-224 
    ISSN: 1434-1948
    Keywords: Reaction mechanisms ; Cyclopalladation ; Acetic acid ; Pd-C bond stability ; Polynuclear species ; Palladium ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The processes operating during the synthetic cyclopalladation reactions of imines in acetic acid have been studied from a kinetico-mechanistic point of view. These reactions include a fast initial coordination to the palladium through the N-donor atom of the imine, followed by the proper C-H bond activation to produce the acetato bridged dimeric species. At this point, the lability of the bridging acetato groups, the hydrolysis of the C-Pd bonds, and/or the hydrolysis of C=N exo bonds contribute to the generation of dark red polynuclear compounds. The processes occurring after the C-H activation have been followed kinetically, both from palladium acetate plus imine, and the synthetically pure isolated acetato dimers as starting materials. The kinetic and activation parameters have been found identical within experimental error whatever the starting material was (k323 = 1.5 × 10-4 s-1; ΔH# = 51 kJ mol-1; ΔS# = -163 JK-1 mol-1 ΔV# = +19 cm3 mol-1 for the 4-ClC6H4-CH=N-CH2-C6H5 imine derivative 1a). Acidolysis of C-Pd bonds has been found to occur in these polynuclear species. When alternative monomeric Cbenzylic-Pd bond-containing complexes are possible follow ups of the reactions produce them as final dead-end complexes (k323 = 2.2 × 10-5 s-1; ΔH# = 61 kJ mol-1; ΔS# = JK-1 mol-1 ΔV# ≈ 0 cm3 cm-1 for the [2,4,6-(CH3)3]C6H2-CH=N-CH2-[2-(CH3]C6[H4] imine derivative 3d). The same study has been carried out with primary amines in order to check the validity of the data if C=N bond hydrolysis is taking place in the imine derivatives with exo C=N bonds. For complexes with similar type of metallacycles, the results agree reasonably well with the proposed mechanism [k323 = 1.2·10-4 s-1, ΔH# = 46 kJ·mol-1, ΔS# = -180 J·K-1mol-1, ΔV# = -16 cm3·mol-1 for the polynuclear formation of the C6H5-CH2-NH2 derivative 4e; k323 = 3.0·10-4 s-1, ΔH# = 55 kJ·mol-1, ΔS
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  • 59
    ISSN: 1434-1948
    Keywords: Phosphanylphenolate ; Cyclopentadienylnickel complexes ; Chelates ; Ethylene polymerization ; Crystal structure ; Polymerizations ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 2-Diphenylphosphanyl- and 2-alkylphenylphosphanyl-4-methylphenols 1 or their silyl ethers 2 and equimolar amounts of nickelocene react in benzene preferably to give orange-brown diamagnetic cyclopentadienylnickel chelate complexes [η-CpNi(P∩O)] (3). Addition of a second equivalent of 1 or 2 affords (RR) and (SS) diastereoisomers of cis-bis(P∩O-chelates) 4a-c (R = Ph, Me, iPr) or the unsymmetrical cis-bis(P∩O-chelate) 5, whereas with bulkier substituted derivatives 1d or 2d (R = tBu) the second step is hindered or retarded. The reactivity of 1d remains high towards nickel salts in polar solvents, but in contrast to 1a-c, yielding 4, a sparingly soluble green trans-bis(P-O-chelate) nickel complex 6d is formed. Complexes formed in situ from 1 or 2 and Ni(COD)2 in toluene catalyze the polymerization of ethylene. The cyclopentadienyl (P∩O) complexes 3, however, are too stable to be active in this process. The crystal and molecular structure of 3c and 4c are described.Supporting information for this article is available on the WWW under -//_/_http://www.wiley-vch.de/contents/jc_2005/2000/99035_s.pdf or from the author.
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  • 60
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    Berichte der deutschen chemischen Gesellschaft 2000 (2000), S. 287-297 
    ISSN: 1434-1948
    Keywords: Enolates ; Nucleophilic additions ; Ruthenium ; S ligands ; Sulfenes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Reaction of the chiral racemic complex [CpRu(mppe)(SO2)]PF6 (1, mppe = Me2PC2H4PPh2) with diazomethane or -ethane gave the sulfene complexes [CpRu(mppe)(RHC/SO2)]PF6 (R = H, 2a; R = Me, 2b). Treatment of 2a with prochiral enamines or deprotonated β-oxo esters yielded C-C coupling products with 32-60% de. An analog of 2a, [NmcpRu(mppe)(H2C/SO2)]PF6 (8, Nmcp = neomenthylcyclopentadienyl) was prepared in a four-step synthesis starting from LiNmcp and [RuCl2(PPh3)3]. Repeated crystallization of the intermediate [NmcpRu(mppe)Cl] (6) provided diastereomerically pure 6′ which added methylene stereospecifically to give diastereomerically pure 8′. Compound 8 turned out to be much less reactive towards nucleophiles than 2a, but still added deprotonated ethyl 2-methyl-3-oxobutanoate with 44% de. The chiral, enantiomerically pure sulfur dioxide complex [CpRu(chir)(SO2)]PF6 [10, chir = (S,S)-Ph2PCHMeCHMePPh2] was synthesized from [CpRu(chir)Cl] and SO2 and was characterized by X-ray crystallography. Reaction of 10 with diazomethane gave the enantiomerically pure sulfene complex [CpRu(chir)(H2C/SO2)]PF6 (11). Addition reactions of 11 with N-(1-cyclopentenyl)morpholine, as well as with various enolates derived from β-oxo esters or 1,3-diesters proceeded with high yields and 20-90% de. The structure of a diastereomerically pure addition product, [CpRu(chir)(SO2CH2C(Me){C(O)Me}{C(O)OtBu}] (13d′), was determined crystallographically and was shown to have (R) configuration at the quaternary carbon atom. After alkylation of one of the S/O functions, the sulfinate ligand was cleaved from the metal center by ligand substitution with acetonitrile, and the resulting acetonitrile complex 15 was converted back into 10 by treatment with SO2.
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  • 61
    ISSN: 1434-1948
    Keywords: Metal-rich antimonides ; Magnetism ; Structure and bonding ; Conductivity ; LMTO ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The title compounds can be synthesized in quantitative yields by arc-melting of stoichiometric amounts of HfSb2, Hf and one of the 3d metals V, Cr, Mn, Fe, Co, Ni, and Cu. These antimonides crystallize in a substitution variant of the W5Si3 type, in which one position is statistically mixed, occupied by the 3d metal atom M or the Sb2 atom in different ratios. Within the linear (M,Sb) chain, the M:Sb ratio may vary between 3:1 and 2:3. According to calculations of the electronic structures of Hf10MδSb6-δ with δ = 1, these phases are metallic compounds stabilized by strong Hf-Hf, Hf-M, and Hf-Sb bonds, and to a smaller extent by bonding interactions within the linear (M,Sb) chain. The metallic character was confirmed by measurements of the electrical resistivity and the magnetism of selected samples. Whereas Pauli paramagnetism was observed experimentally for M = V, Co, and Ni, Hf10FeSb5 is apparently the only phase with localized magnetic moments and magnetic coupling. This is in agreement with the magnetic ground state obtained solely for the ordered structure model of Hf10FeSb5 with spin-polarized calculation within the local spin density approximation.
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  • 62
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    Berichte der deutschen chemischen Gesellschaft 2000 (2000), S. 323-330 
    ISSN: 1434-1948
    Keywords: Amino acids ; Alkynes ; Ferrocene ; Palladium ; Catalysis ; Bioorganometallic chemistry ; Biosensors ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: This work describes a Pd-catalyzed coupling of ferrocene alkyne derivatives to iodo amino acids. Ferrocene carboxylic acid propargyl amides were easily obtained in high yield. The crystal structures of the propargyl amine derivative 3 and the 1,1-diethylpropargylamine derivative 4 have been determined by X-ray diffraction. Pd-catalyzed coupling to p-iodoanilide amino acids gave the corresponding ferrocene-labeled amino acid derivatives, which were easily purified by diethyl ether extraction in the case of the 1,1-diethyl derivatives 8. The coupling reaction did not require anhydrous solvents and tolerated a variety of functional groups present in peptides such as alcohols (8a, Ser), thioethers (8d, Met), disulfide bonds (cystine, 12) esters (as in the N-labeled Leu derivative 10) and of course amides. A minor by-product of the coupling reaction, namely the homo-dimer bis(ferrocene carboxylic acid propargylamide) 9, was identified in the crude reaction mixtures by mass spectrometry and independently synthesized by oxidative coupling (Glaser and Eglington) of 3. All new compounds were completely characterized spectroscopically, including 15N- and 2D NMR spectroscopy, Mössbauer spectroscopy and electrochemistry. This work introduces a versatile procedure for a selective functionalization of amino acids with organometallics at the C-terminus which is expected to be of general applicability to peptide chemistry.
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  • 63
    ISSN: 1434-1948
    Keywords: Palladium ; Insertion reactions ; Tridentate ligands ; Hydrazones ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Potentially tridentate hydrazonic ligands of the type HNNO have been used in the synthesis of some methyl palladium(II) complexes. Depending on the applied experimental conditions two different kinds of complexes are obtained. Thus, the reactions between HL1-HL5 and (COD)PdMeCl in diethyl ether led to the formation of bidentate methyl complexes of the type Pd(HNN)MeCl (1-5), where the ligands maintain a neutral character. However, in the presence of a base such as Et3N or NaOMe, the ligands are deprotonated with the consequent formation of tridentate methyl complexes of the type Pd(NNO)Me (7-10). In solution, complexes 1-5 tend to lose the hydrazonic proton with elimination of methane and formation of a tridentate chloride complex Pd(NNO)Cl (6); this tendency can be correlated with the acidity of the free ligands, which has been determined. On bubbling carbon monoxide through solutions of 1-5, the corresponding acetyl complexes Pd(HNN)[C(O)Me]Cl (11-15) are formed, in which both the cis and trans isomers are present. Their molar ratio is rationalised from the results of a molecular modelling study on the basis of electronic considerations. A remarkably different reactivity has been found in the carbonylation of the tridentate complexes 7-10: they decompose rapidly and quantitatively to palladium black and an organic product corresponding to the ligand with an acetyl group bonded to the hydrazonic nitrogen. The X-ray structures of a methyl complex (3) and its corresponding acetyl (13) derivative have been determined.
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  • 64
    ISSN: 1434-1948
    Keywords: Vanadyl arsenate ; Hydrates ; Layered compounds ; Vibrational spectroscopy ; X-ray scattering ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The course of the intercalation and deintercalation of water molecules in vanadyl arsenate has been studied by X-ray diffraction analysis and by infrared and Raman spectroscopies. The formation of VOAsO4 hydrates at ambient temperature has been found to depend on relative humidity (r.h.): VOAsO4 · 5 H2O (basal spacing c = 10.48 Å) is formed at r.h. above 76%, VOAsO4 · 3 H2O (c = 8.03 Å) at 43-76% r.h., VOAsO4 · 2 H2O (c = 7.33 Å) at 11-43% r.h.; dehydrated VOAsO4 (c = 4.18 Å) exists near 0% r.h. Like the thermal dehydration of VOPO4 · 2 H2O, the thermal dehydration of VOAsO4 · 3 H2O proceeds in a stepwise manner so that the dihydrate and monohydrate are formed en route to the anhydrous compound. The arsenate monohydrate is gradually dehydrated over a broad temperature range. The broad diffraction lines observed can be explained in terms of the existence of a disordered phase containing monohydrated and anhydrous forms of vanadyl arsenate. A similar phenomenon has been observed during the dehydration of VOAsO4 · 3 H2O over phosphorus pentoxide at ambient temperature. The hydration of VOAsO4 is different from that of VOPO4. The first step, i.e. the insertion of water that coordinates to the vanadium atoms, is very slow. On the contrary, the uptake of further water molecules with the formation of higher hydrates is fast. It thus seems likely that the filling of one interlayer space with water facilitates the intercalation of further water into neighboring interlayer spaces. Therefore, only higher hydrates together with the original anhydrous phase are observed. Impedance spectral measurements indicate that the conductivity of the trihydrate has a mixed ionic/electronic character.
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  • 65
    ISSN: 1434-1948
    Keywords: Coordination chemistry ; α-Imino ketones ; CO complexes ; Iron complexes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The reaction of Fe2(CO)9 at room temperature in THF or toluene with the α-imino ketones R1N=C(R2)-C(R3)=O (L) (R1 = alkyl, R2 = H, Me, Ph, R3 = Me, Ph) (a-k), initially results in the formation of the mononuclear chelate Fe(CO)3(α-imino ketone) complexes 6 which can be isolated in moderate (6h) to high (6e-g) yield. Under these reaction conditions, complexes 6 subsequently react with [Fe(CO)4] fragments or dimerise, to form the dinuclear complexes Fe2(CO)6(α-imino ketone) (7a-j) or Fe2(CO)4(L-L) (8a,b,k), respectively. The complexes 8 contain two α-imino ketone ligands C-C coupled at the ketone carbon atoms. Complexes 8a,b react with CO at elevated temperatures to quantitatively yield Fe(CO)3(α-imino ketone) (6a,b). This reaction can be reversed photochemically. Irradiation of a solution of 6a,b in the low-energy band results in the reformation of 8a,b in almost quantitative yield. The extremely air-sensitive complexes 6 and the dinuclear complexes 7 and 8 have been characterised spectroscopically (IR, UV/Vis, 1H and 13C NMR) and by elemental analysis. The solid state structures of complexes 6g and 8a have been determined by single-crystal X-ray diffraction. The molecular structure of 6g confirms the flat σ-O,σ-N chelate coordination of the α-imino ketone. The structure of 8a consists of two metal-metal-bonded Fe(CO)2 units, bridged by a formally 10e-donating dianionic C-C coupled (tBu-ADO) ligand. A mechanism for the formation of complexes 8 is discussed.Supporting information for this article is available on the WWW under -//_/_http://www.wiley-vch.de/contents/jc_2005/2000/99351_s.pdf or from the author.
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  • 66
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    Berichte der deutschen chemischen Gesellschaft 2000 (2000), S. 929-932 
    ISSN: 1434-1948
    Keywords: Titanium ; Cyclopentadienes ; Arene complexes ; Cations ; Bridging ligands ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The half-sandwich titanium trimethyl complex (η5-C5H4CMe2Ar)TiMe3 (Ar = 3,5-Me2C6H3) reacts with the Lewis acid B(C6F5)3 to give the ionic TiIV ansa-cyclopentadienyl-arene complex [(η5,η6-C5H4CMe2Ar)TiMe2][MeB(C6F5)3]. In bromobenzene solvent, addition of more B(C6F5)3 leads to C6F5/Me exchange and, subsequently, to formation of an unusual dimeric TiIII dicationic species, {[(η5,η6-C5H4CMe2Ar)Ti(μ-Br)]2}[B(C6F5)4]2, which was structurally characterized. Its formation involves reduction of the transition-metal center, solvent C-Br cleavage and perfluoroaryl-group scrambling.Supporting information for this article is available on the WWW under -//_/_http://www.wiley-vch.de/contents/jc_2005/2000/99383_s.pdf or from the author.
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  • 67
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    Berichte der deutschen chemischen Gesellschaft 2000 (2000), S. 939-941 
    ISSN: 1434-1948
    Keywords: Germanium ; Germanol ; Hydrogen bonds ; X-ray structure ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The hydrolysis of tBu2Ge(OEt)2 is described. Depending on the amount of water used either tBu2Ge(OH)2 (1) or a mixture of the latter and (tBu2GeOH)2O (2) were obtained. A cocrystallate consisting of 2tBu2Ge(OH)2, (tBu2GeOH)2O and water was the subject of a single crystal X-ray diffraction study. In the solid state the individual molecules are connected by hydrogen bonds giving rise to the formation of a polymeric double chain ribbon.
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  • 68
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    Berichte der deutschen chemischen Gesellschaft 2000 (2000), S. 959-969 
    ISSN: 1434-1948
    Keywords: Bipyridyldiphosphane ligands ; Macrocycles ; Metallacyclophanes ; Platinum ; Supramolecular chemistry ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The 5,5′-bis(hydroxyalkyl)-2,2′-bipyridines 4a-c (Scheme 1) were prepared either in one step (4b, 4c) or in four steps (4a) starting with 5,5′-dimethyl-2,2′-bipyridine in each case. Reaction of 4a-c with mesyl chloride afforded the bis(mesylates) [-C5H3N-(CH2)n-CH2-OSO2Me]2 5a-c [n = 1 (a), 2 (b), 3 (c)], which could easily be transformed into the diphosphanes 6a-c by reaction with LiPPh2. Treatment of 6c, 6b with Cl2Pt(NCPh)2 and (RC6H4)2Pt(COD) according to the high-dilution method resulted in the formation of the tetraphosphadiplatinacyclophanes [-C5H3N-(CH2)4-PPh2PtCl2PPh2-(CH2)4-C5H3N-]2 (7c) and [-C5H3N-(CH2)3-PPh2Pt(C6H4R)2PPh2-(CH2)3-C5H3N-]2 (8b, 9b) (8b: R = H, 9b: R = tBu), respectively (Scheme 2). The molecular structures of 8b and 9b were elucidated by X-ray structural analyses. The noncoordinated bipyridine moieties in 8b were employed to encapsulate copper(I) to give the host/guest complex 10b (Scheme 3), which was investigated by FAB-MS, NMR spectroscopy, and cyclovoltammetry. 10b exhibited a quasi-reversible oxidation at E1/2 = -0.31 V and an electrodeposition-redissolution redox system at E1/2 = -0.79 V, owing to the formation of copper at the surface of the working electrode.
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  • 69
    ISSN: 1434-1948
    Keywords: Lanthanides ; Ytterbium ; MRI contrast agents ; Solid-state structures ; Hydration ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The low temperature (-100 °C) X-ray structure of the complex K2[Yb(DTPA)(H2O)] has been determined. The metal ion is at the center of a tricapped trigonal prism and is nine-coordinate, binding to the three nitrogens and five oxygens of the ligand and one water molecule. From the structure obtained, three well-defined hydration shells can be observed consisting of: i) one coordinated water molecule; ii) several water molecules in the outer coordination sphere of the YbIII ion and iii) one water molecule surprisingly close to the metal center and hydrogen-bonded to proximate carboxylate groups. A variable-field and temperature NMRD study of the corresponding Gd complex has been performed and the data interpreted by taking into account the presence of second-sphere water molecule(s). The results of the analysis are in excellent agreement with the X-ray structural data.
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  • 70
    ISSN: 1434-1948
    Keywords: Catalysis ; Densitiy functional theory ; Epoxidation ; Reaction mechanisms ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Seven-coordinated molybdenum oxobisperoxo complexes with chelate nitrogen donors like pyrazolylpyridines are catalysts for the epoxidation of olefins. An NMR spectroscopic and quantumchemical study on the fluxionality of the chelate ligand proves that during this process partial ligand dissociation takes place. This gave rise to a detailed theoretical study on the activation of CH3OOH at the model complex (NH3)2MoO(O2)2 including dissociation of one of the ammonia ligands and proton transfer from the hydroperoxide to one of the peroxo ligands.Supporting information for this article is available on the WWW under -//_/_http://www.wiley-vch.de/contents/jc_2005/2000/99429_s.pdf or from the author.
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  • 71
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    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 1271-1279 
    ISSN: 1434-1948
    Keywords: Chirality ; Dinuclear complexes ; Rhodium ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Dinuclear and polynuclear metal complexes with octahedral centers coordinated to di- or polydentate ligands are often obtained as complicated mixtures of various stereoisomers. Stereospecific synthesis of such species is therefore of high current interest. Chiral derivatives of pyridine can be used for this purpose. Dinuclear μ-chloro-bridged RhIII complexes with two didentate, cyclometalated thienylpyridine-type ligands at each metal center are formed stereoselectively when pinene groups are fused to the pyridine rings. The two octahedral RhIII centers have homochiral configurations, ΔΔ and ΛΛ. The heterochiral diastereomer ΔΛ is not observed. With (8R,10R)-2-(2′-thienyl)-4,5-pinenopyridine [Hth4,5-(R,R)ppy] the ΔΔ to ΛΛ ratio is 9:1 when the separation eluent contains NaCl. Modeling the ΛΛ and the ΔΛ isomers of the dinuclear species shows crowding of the pinene groups in both cases; however, the strain can be released by relatively small distortions only in the case of the ΛΛ isomer. NO3- cleaves the dichloro bridge, yielding the mononuclear species Δ[Rh(L2)2(NO3)] (2) in a completely stereoselective manner when NaCl is replaced by KNO3 in the eluent mixture. The molecular structure has been determined by X-ray structure analysis for both the ΔΔ and the mononuclear complex Δ[Rh(L2)2(NO3)] (2) in order to confirm the configuration at the metal center. 1H-NMR, 13C-NMR and CD spectra were measured and the latter shows that the CD activity is solely due to the chirality at the metal center.
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  • 72
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    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 1281-1289 
    ISSN: 1434-1948
    Keywords: Phosphaalkynes ; Dimerization mechanism ; Diphosphacyclobutenes ; Density functional theory ; Ab initio calculations ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The dimerization of phosphaalkynes (R-C≡P, R = H, Me, tBu) without and with the presence of transition metal fragments, including CpCo (Cp = cyclopentadienyl) and COT-Ti (COT = cyclooctatetraene), has been probed using density functional theory calculations (B3LYP with different basis sets). MP2 and CCSD(T) calculations were also performed for the [H2C2P2] systems. In an attempt to address the exciting controversy and uncertainty about phosphaalkyne dimerization, a number of dimer formation mechanisms proposed in the literature have been examined. Some new and plausible intermediates have also been identified.
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  • 73
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    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 1315-1324 
    ISSN: 1434-1948
    Keywords: Ab initio calculations ; EHMO ; Vinylidene complexes ; Cobalt ; Rhodium ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The transformation of acetylene into vinylidene, as promoted by the metal fragment [(pp3)Co]+ [pp3 = P(CH2CH2PPh2)3], is unimolecular and features the hydride-acetylide species as an intermediate. The paper describes a detailed ab initio study of the reaction, in particular with regard to the step involving 1,3-H shift. The best computational results are obtained by mimicking the pp3 ligand with actual ethylenic chains rather than with single PH3 molecules. The keypoints along the two-step reaction path (π-acetylene, hydride-acetylide, and vinylidene complexes, as well as intermediate transition states) have been optimized for CoI and RhI derivatives at the MP2 level. For the fragment [(pp3)Co]+, the barrier associated with transformation of the hydride-acetylide intermediate to vinylidene (20.6 kcal/mol) is easier to surmount compared to that for reversion to the reactants (28.6 kcal/mol). The situation is reversed for the analogous RhI system, with the initial π-acetylene adduct being slightly more stable. Although higher in energy, the hydride-acetylide species is the experimentally detected product of the reaction of acetylene with the fragment [(pp3)Rh]+. The salient chemical aspects of the 1,3-H shift are discussed in terms of perturbation theory arguments. Parallel EHMO calculations, which have provided a relatively good consistency with the ab initio results, allow the proposal of an orbital rationale for the mode of migration of the hydride ligand along the substantially linear Co-Cα-Cβ grouping.
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  • 74
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    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 1335-1342 
    ISSN: 1434-1948
    Keywords: Photolysis ; Alkynes ; Matrix isolation ; DFT ; Oxygenations ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Photolytically-induced reactions of chromyl chloride with acetylene and but-2-yne (dimethylacetylene) in low-temperature argon matrices yield end-on ketene and dimethylketene complexes of O=CrCl2, respectively. The product formation probably results from an electrophilic attack of a Cr=O linkage on the C≡C triple bonds, leading to radical-like transition states or intermediates, which subsequently rearrange through 1,2-H or 1,2-methyl shifts. Consequently, allene is attacked at its central carbon and the allyl radical thus generated undergoes subsequent ring-closure to give a cyclopropanone complex of O=CrCl2.
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  • 75
    ISSN: 1434-1948
    Keywords: Copper chelates ; EPR spectroscopy ; Electronic structure ; Schiff base ligands ; Structure elucidation ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A series of tetrahedrally distorted copper(II) complexes with thiolate and imine coordination were synthesized. Schiff bases derived from 4-benzoyl-3-methyl-1-phenyl-2-pyrazoline-5-thione and various diamines were used as tetradentate ligands to obtain tetrahedrally distorted metal chelates with [CuN2S2] complex units. Crystal structures of the complexes 1, 2, 5 and 6 and of ligand H25 have been determined by means of single-crystal X-ray structure analysis. The structure data show a strong influence of the diamine building blocks on the tetrahedral distortion of the copper(II) complexes. Results of Extended Hückel LCAO calculations correlate strongly with structural, electrochemical, UV/Vis- and EPR-spectroscopic features obtained experimentally. The calculations confirm for the whole complex series a strong delocalization of the frontier orbitals. The highest fully occupied molecular orbital shows a weak contribution, resulting from thiolate donor atoms, whereas the antibonding singly occupied molecular orbitals (SOMOs) are distributed between the copper(II) centre (ca. 35-40%) and the N2S2 donor set. The SOMO energy significantly lowers with increasing tetrahedral distortion of the coordination sphere. The influence of the tetrahedral distortion of copper(II) complexes on redox potentials, UV/Vis and EPR spectra is discussed.
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  • 76
    ISSN: 1434-1948
    Keywords: Half-sandwich complexes ; Molybdenum ; Optically active complexes ; Rhenium ; Tungsten ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The synthesis of (η5-PinCp*)Re(CO)3 [PinCp* = tetramethyl(pinanyl)cyclopentadienyl] is described. Successive substitution of two CO ligands by NO+ and PPh3 generates a 1:1 diastereomeric mixture of chiral-at-metal [(SRe)/(RRe)-(PinCp*)Re(CO)(NO)(PPh3)]BF4. The diastereomers are converted with sodium methoxide into the derivative “esters” (SRe)/(RRe)-(PinCp*)Re(COOCH3)(NO)(PPh3), and then with (+)-(R)-(1-naphthylethyl)amine to the “amides” (SRe)/(RRe)-(PinCp*)Re(NO)(PPh3)[CONHCH(CH3)C10H7] [(SRe)/(RRe) = 1:1]. Fractional crystallisation separates the (SRe) isomer with an optical purity of 〉 98%. The latter compound has been characterized by X-ray structure analysis. By treating the (SRe)-amide with CF3CO2H and NaBF4, (SRe)-(PinCp*)Re(CH3)(NO)(PPh3) can be generated. Protolysis of this compound with HBF4/Et2O in CD2Cl2 at -78 °C leads to the solvent-stabilized complex (SRe)-[(PinCp*)Re(NO)(PPh3)(ClCD2Cl)]+BF4-. The thermal and configurational stability of this chiral Lewis acid is investigated at various temperatures. The syntheses of [PinCp*RhCl2]2, PinCp*TiCl3 and PinCp*M(CO)2(NO) (M = Mo, W) are also described. Starting with PinCp*M(CO)2(NO), the relatively stable 16-VE complexes PinCp*MCl2(NO) and PinCp*W(CH2SiMe3)2(NO) are synthesized.
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  • 77
    ISSN: 1434-1948
    Keywords: 2,2′-Bipyridines ; Chelate complexes ; Hydrogen bonding ; π-π stacking ; Crystal structure ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A new synthetic route for the synthesis of 5,5′-diamino-2,2-bipyridine (5) based on the coupling of 2-chloro-5-aminopyridine in the presence of NiCl2 × 6 H2O/PPh3/Zn in dimethylformamide is described. The reactions of the potentially ambidentate ligand 5 with salts of the transition metals Mn, Fe, Ni, Cu, Zn, Ag, and Cd gave a variety of 13 metal-ligand complexes depending on the anion, the crystallization conditions and the metal-to-ligand ratio. The complexes obtained were characterized by thermal analyses, NMR including 113Cd-NMR, IR, and for the iron complex 57Fe-Mößbauer spectroscopy. The structure of eight of the compounds was elucidated by X-ray crystallography. All of these metal complexes show a bipyridine-metal coordination. The amino functionality was never involved in metal coordination. The intermolecular arrangement is dictated by hydrogen bonding from the amino functionality and by π-π stacking of the bipyridine rings.Supporting information for this article is available on the WWW under http://www.wiley-vch.de/contents/jc_2005/1999/99078_s.pdf or from the author.
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  • 78
    ISSN: 1434-1948
    Keywords: Iron(III) ; Peroxo Complexes ; Kinetics ; Hydrogen Peroxide ; Catalase ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The new diiron complex [Fe2(tbpo){O2As(CH3)2}(CH3O)(CH3OH)](ClO4)3 · 5 CH3OH · 2 H2O (1) containing a (μ-alkoxo)(μ-dimethylarsinato)diiron(III) core was synthesized using the heptadentate ligand N,N,N′,N′-Tetrakis(2-benzimidazolylmethyl)-1,3-diamino-2-propanol (Htbpo). The complex was characterized structurally by X-ray crystallography. 1reproduces the coordination mode and the stoichiometry of the proposed purple acid phosphatase-arsenate inhibitor complex. More importantly, 1 is a good functional model for the activation of small molecules, since the solvent molecule in the coordination sphere of each iron ion can be substituted very easily by a small substrate molecule. This is confirmed by the comparatively high pH-dependent catalase-like activity of 1. In order to study the influence of the cacodylate bridge on the formation of the metastable adduct with hydrogen peroxide, the analogous hydroxo-bridged complex [Fe2(tbpo)(OH)(NO3)2](NO3)2 · CH3OH · 2 H2O (2) was employed. The reactions of 1and 2 with H2O2 were studied as a function of [H2O2], pH, temperature, and pressure, and the kinetic results including the activation parameters are reported. In the case of compound 2 the reaction proceeds in one step, and the observed first order rate constant, kobs, shows a linear dependence on the hydrogen peroxide concentration with a zero intercept. For complex 1 the kinetic traces could be fitted to two exponential functions. One of the observed pseudo-first-order rate constants, kobs1, exhibits a linear dependence on the hydrogen peroxide concentration with a zero intercept, whereas the other rate constant, kobs2, was independent of the hydrogen peroxide concentration. A mechanistic interpretation is presented.Supporting information for this article is available on the WWW under http://www.wiley-vch.de/contents/jc_2005/1999/99068_s.pdf or from the author.
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  • 79
    ISSN: 1434-1948
    Keywords: Ruthenium ; Coordination chemistry ; Paramagnetic complexes ; Magnetic properties ; Ion exchange ; Antitumor agents ; Colon tumors ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Indazolium trans-tetrachlorobis(indazole)ruthenate(III) exhibits excellent results against different tumor models in vitro and in vivo. To improve the water solubility necessary for the introduction of this tumor-inhibiting compound into clinical trials, we synthesized the corresponding sodium salt in a two-step ion exchange via the tetramethylammonium salt. The sodium salt shows a 35-fold higher solubility in water relative to the indazolium salt. We also synthesized the n-butylammonium, n-octylammonium, and tetraphenylphosphonium salts, all of which showed improved solubility in organic solvents. The X-ray crystal structure of the latter could be solved, proving the trans configuration of the complex anion. In spite of the paramagnetic RuIII center an assignement of the coordinated indazole protons could be made with the help of a COSY experiment.
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  • 80
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    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 2355-2368 
    ISSN: 1434-1948
    Keywords: Phosphane complexes ; Lithium ; Aminophosphanes ; Hydrazides ; (N-lithioamino)diorganophosphanes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Butyllithium (nBuLi) deprotonates Ph2P-NHtBu in ether to give (Ph2P-NLitBu)2·OEt2. There is no Li···P interaction in this molecule. Three compounds of the type R′P(NLiR)2 have been obtained by lithiation of R′P(NHR)2, isolated as [BuP(NLitBu)2·OEt2]2, [PhP(NLiPh)2·OEt2]2 and [PhP(NLiPh)2]2. Reaction of nBuLi with MeP(NHiPr)2 in hexane/THF leads to [MeP{N(Li)iPr]2·THF}4 with an asymmetric cluster structure comprising one LiP3, three LiPN2, three LiP2N and one LiN3 cluster units. The molecular structures of these compounds as determined by X-ray structure analysis show that they are best depicted as N-lithioaminophosphanes and not as the isomeric P-lithioiminophosphoranes.
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  • 81
    ISSN: 1434-1948
    Keywords: Alkylation ; Carbonyl complexes ; Lewis acids ; Phosphaalkenes ; Protonation ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The reaction of the carbonyl-functionalized phosphaalkenes RC(O)P=C(NMe2)2 [R = tBu (2a), Ph (2b)] with protic acids and alkylating reagents occurred at the two-coordinate phosphorus atom to give the phosphanyl-substituted carbocations 3a,b and 4a,b. In contrast, treatment with Me3SiOSO2CF3 resulted in attack at the oxygen atom by the silyl group, and the formation of [RC(OSiMe3)=PC(NMe2)2]SO3CF3 (5a,b). Similarly, the Lewis acids B(C6F5)3, Al(tBu)2Cl and AlMe3 were ligated to the oxygen atom of the carbonyl group. Two equivalents of GaMe3 were added to the oxygen and phosphorus atom of the phosphaalkene to yield the thermolabile complexes [RC(OGaMe3)=P(GaMe3)C(NMe2)2] (10a,b). In contrast, one molecule of InMe3 was bound to the phosphorus center of the phosphorus compound. Reaction of the phosphaalkenes with [Ni(CO)4], [Fe2(CO)9] or [{(Z)-cyclooctene}Cr(CO)5] also took place at the pnictogen atom, resulting in complexes of the type [RC(O)P{M(CO)n}C(NMe2)2] (R = tBu, Ph; M = Ni, n = 3; Fe, n = 4; Cr, n = 5). The chemical transformations reported here underline the versatile chemistry of phosphaalkenes and emphasize a relationship between carbonyl-functionalized phosphaalkenes and the well-investigated class of phosphorus ylides. X-ray structures of compounds 6b, 7b*, 10a, 11a and 12a are reported.
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  • 82
    ISSN: 1434-1948
    Keywords: Palladium ; Tripodal ligands ; O ligands ; Fluxionality ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The reaction of [PdCl2(CH3CN)2] with the silver salt of the tripodal oxygen ligand L- = [(C5H5)Co{P(O)(OMe)2)}3]- yields the homoleptic oxygen ligand complex [PdL2] (1). The molecular structure of 1 was determined by single-crystal X-ray diffraction: monoclinic space group P21/n; a = 8.515(1), b = 13.627(2), c = 15.828(2) Å; β = 92.44(1)°; V = 1834.9(7) Å3; Z = 2. The complexes [Pd(PPh3)XL] [X = Cl (2a), Br (2b), I (2c)] have been prepared starting from 1. Complex 2a reacts with PPh3 to form [Pd(PPh3)2L]Cl (3a) and [Pd(PPh3)2L]L (3b). Treatment of 2a with CO in MeOH yields the carboxymethyl complex [{(PPh3)(COOMe)Pd(μ-Cl)}2] (4) and the protonated ligand HL. The carboxymethyl complex 4 shows some catalytic activity for the copolymerization of CO and ethene. Complex 4 reacts with AgL to yield [Pd(PPh3)(COOMe)L] (6). Alkylation of 2a with Me4Sn leads to the methyl complexes [Pd(PPh3)MeL] (7) and [Me2ClSnL] (8). CO insertion in the palladium-carbon bond of 7 gives the stable acetyl complex [Pd(PPh3){C(O)Me}L] (10). The palladium(II) complexes 1, 2, 3, 6, 7, and 10 of the tripodal oxygen ligand L are all fluxional molecules that have been studied by temperature-dependent 1H- and 31P-NMR spectroscopy.
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  • 83
    ISSN: 1434-1948
    Keywords: Tripod ligands ; Hindered rotation of vinylidene ligands ; CpML2 chelate ligands ; Ruthenium ; Carbenes ; Carbene-type ligands ; Cyclic voltammetry ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The tripodal ligand [CH3C(CH2C5H4)(CH2PPh2)2]- reacts with RuCl2(PPh3)3 to produce CH3C(CH2-η5-C5H4)(CH2-η1-PPh2)2RuCl, [tripodCpL2RuCl], 1. Complex 1 undergoes substitution of the chlorine function with various nucleophiles L′ to produce [tripodCpL2RuL′]+. The carbonyl derivative (L′ = CO) 2, isonitrile (L′ = RNC) 3, nitrile compounds (L′ = RCN) 4, and a tolane adduct (L′ = η2-PhC≡CPh) 5 are obtained when 1 is treated with the appropriate ligands in polar solvents. Halide acceptors (e.g. TlPF6) are generally needed to promote these reactions. The cyanide derivative tripodCpL2RuCN (3a) is alkylated by F3CSO3CH3 to give the isonitrile derivative [tripodCpL2RuCNMe]+3b. Terminal alkynes HC≡CR produce vinylidene compounds [tripodCpL2RuL′]+, where L′ = C=CHR (R = tBu, 7b; R = Ph, 7c), or allenylidene derivatives, L′ = C=C=CPh2 (6), depending on the nature of R (R = CPh2OH for synthesis of 6). Trimethylsilylacetylene gives the parent vinylidene species, L′ = C=CH2 (7a), which is transformed to the Fischer-type carbene compound, L′ = C(OMe)Me (8), upon treatment with methanol. The vinylidene species 7 are deprotonated by NaOMe to produce the alkynyl compounds tripodCpL2RuC≡CR (9). Methylation of 9 with F3CSO3CH3 results in the vinylidene derivatives L′ = C=C(Me)R (R = tBu, 7d; R = Ph, 7e), having two organic substituents at the terminal carbon centre. For all vinylidene compounds with two different substituents at their terminal carbon atom, hindered rotation of the single-faced vinylidene π-ligand about its Ru-C bond is observed. Analysis by 31P-NMR spectroscopic coalescence measurements as well as line-shape analyses reveals activation enthalpies of around 40 kJmol-1 for this rotation, with small activation entropies of around ±10 Jmol-1K-1. Solid-state structures of nine compounds of the type [tripodCpL2RuL′]+n (n = 0, 1) demonstrate the remarkable conformational rigidity of the tripodCpL2Ru template. They also show that the possible strain imposed by linking the Cp ligand and the two donor groups L in one and the same chelate scaffolding does not appear to impose a serious steric strain on these templates.
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  • 84
    ISSN: 1434-1948
    Keywords: (R)-(+)-2,3-Epoxy-1-propanol ; 2,3-Dihydroxyalkyl phosphanes ; 1,3,2-Dioxaborolane ; 1,3-Dioxolane ring ; Enantiopure phosphanes ; Complexes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Reaction of (R)-(+)-2,3-epoxy-1-propanol with Ph2PH, Ph(Me)PH, or PhPH2 in the superbasic medium KOH/DMSO affords the novel chiral phosphanes 1a-1c. While 1a is obtained enantiomerically pure, 1b and the secondary phosphane 1c are formed as mixtures of diastereoisomers (RPRC, SPRC) with homochiral β carbon atoms. Derivatization of 1a with phenylboronic acid or 2,2-dimethoxypropane yields 2a and 3a with 1,3,2-dioxaborolane and 1,3-dioxolane ring systems, respectively. The X-ray structure of 2a (space group P21) reveals the presence of four molecules of R configuration in the unit cell. Nucleophilic phosphanylation of (R)-(-)-2,3-O-isopropylideneglycerol tosylate with Ph2PH, Ph(Me)PH, or PhPH2 yields chiral 3a-3d. Compound 3b was obtained enantiomerically pure. The secondary phosphane 3c has been employed in syntheses of the hydrophilic tertiary phosphanes 3e, 3f and of the novel bidentate phosphane ligands 3g, 3h, all of which have homochiral β carbon atoms. PdII complexes PdL2Cl2 of 1a, 2a, 3a (L) are formed as mixtures of cis/trans isomers. RhI complexes of 1a, 3a, and bidentate 3h have also been synthesized.
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  • 85
    ISSN: 1434-1948
    Keywords: Macrocycles ; Nickel ; Redox chemistry ; Schiff bases ; S ligands ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A single crystal X-ray analysis of [Ni2L1](ClO4)2· MeCN · 1/4 H2O, 1a [formed directly from a mixture of nickel(II) template ions, 2,6-diformyl-4-methyl-thiophenolate, and 1,4-diaminobutane] reveals that the nickel(II) ions are in square-planar N2S2 environments and that the four “bowed” dinickel macrocycles in the asymmetric unit pack around a single central perchlorate template ion encapsulating it to form “star” clusters of stoichiometry {[Ni2L1]4(ClO4)}7+. These “stars” stack together, via π-π-stacking interactions, to form two-dimensional sheets, which are separated from one another by layers of the remaining perchlorate anions and solvent molecules. Reduction, by NaBH4, of the four imine bonds in [Ni2L2](ClO4)22a (analogous to 1a but formed from 1,3-diaminopropane not 1,4-diaminobutane) or [Ni2L2](CF3SO3)22b to amine bonds produces the corresponding tetra-amine complex, [Ni2L3](ClO4)23. These complexes are shown to contain diamagnetic nickel(II) ions by a combination of magnetic, NMR and UV/Vis spectroscopic results. The 1H NMR spectra of 1-3 run in [D3]MeNO2 and in [D3]MeCN are consistent with increasing axial binding ability in the order: 3 〈 2 〈 1. Thiocyanate ion binding studies reveal that 1 and 2 are able to coordinate two thiocyanate ions, forming [Ni2L1(NCS)2] 4 and [Ni2L2(NCS)2] 5 respectively, whereas 3 does not. Single crystal X-ray analyses of complexes 4· 2 MeCN and 5· MeCN show that adjacent square-planar and octahedral nickel(II) ions result. Two one-electron oxidations and two one-electron reductions are a feature of the electrochemistry of 1-3 in MeCN: curiously, the potentials for the oxidation processes are almost invariant whereas those for the reduction processes vary as anticipated. EPR spectroscopy shows that the first one-electron reduction process and the first one-electron oxidation process are metal centred. Spectroelectrochemical studies and redox titrations indicate that a purplish-coloured complex is produced by one-electron oxidation of 2 (λ = 870 nm, ε = 1320 L mol cm-1). The synthesis of a phenolate analogue, [Ni2L′(MeCN)4](ClO4)2 (6), of the thiophenolate complex 2a is also detailed. Complex 6 undergoes two one-electron oxidations in MeCN, but, in contrast to the thiophenolate complexes 1-3, these occur at much higher potentials. Only a single one-electron reduction process is observed and this occurs at a more negative potential than for any of 1-3.
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  • 86
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    Berichte der deutschen chemischen Gesellschaft 2000 (2000), S. 195-203 
    ISSN: 1434-1948
    Keywords: Acid derivatives ; Cyclen and cyclam derivatives ; Phosphinic acid ; Potentiometry ; Protonation and stability constants ; 31P-NMR titration ; Hydrogen bonding ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Two phenylphosphinic acid derivatives of tetraaza macrocycles, (1,4,7,10-tetraazacyclododecanetetrayl)tetrakis(methylene)tetrakis(phenylphosphinic acid) [(H4L1) and (1,4,8,11-tetraazacyclotetradecanetetrayl)tetrakis(methylene)tetrakis(phenylphosphinic acid)] (H4L2), were synthesised and the crystal structures of H4L2 and its bis(1-adamantylammonium) salt were determined. In both the structures, the ring conformation is virtually the same and is stabilised by hydrogen bonds. Protonation constants of the acids and stability constants of their Zn2+ and Cd2+ complexes were determined pH-metrically at 25 °C and at an ionic strength of 0.1 mol dm-3 (KNO3). The pKA values found for both the compounds are lower than those for their carboxylic analogues and correspond to the expected electron-withdrawing ability of the -P(Ph)O2H moiety. The value pK1 of the last dissociation constant of H4L1 is surprisingly high. The complexes of Zn2+ and Cd2+ with (L1)4- and (L2)4- are less stable than those with other similar ligands, which is in accordance with lower overall basicity of H4L1 and H4L2. A pronounced drop in the stability of the complexes of H4L2 can be explained by partial coordination of the ligand to the metal ions. The solution properties of the ligands were also investigated by 31P-NMR spectroscopy. The spectra observed suggest stable (on the NMR time scale) conformations of the protonated ligands in solution. A comparison of NMR spectra in solution and CP/MAS-NMR spectra indicates that the structures of the conformers roughly correspond to the structures observed in the solid state. The conformations are stabilised by intramolecular hydrogen bonds and by hydrophobic interactions of phenylphosphinic moieties. The conformers are stable even at 90 °C, but not in the presence of complexing metal ions.Supporting information for this article is available on the WWW under -//_/_http://www.wiley-vch.de/contents/jc_2005/2000/99149_s.pdf or from the author.
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  • 87
    ISSN: 1434-1948
    Keywords: Rare earth complexes ; Naphthalocyaninato ligand ; Double-decker complexes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A series of rare earth(III) double-deckers RE[Nc(tBu)4]2 [RE = La, Ce, Pr, Nd, Eu, Gd, Tb, Y, Er; Nc(tBu)4 = dianion of tetra(tert-butyl)-2,3-naphthalocyanine] (1-9) have been prepared by treating RE(acac)3·n H2O (acac = acetylacetonate) with 6-tert-butylnaphthalonitrile in refluxing n-octanol in the presence of 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU). These novel sandwich-type complexes have been spectroscopically characterized. The electrochemical studies show that the first oxidation and the first reduction potentials increase with the size of the central metal ions with a relatively small separation (0.28-0.33 V), reflecting the narrow HOMO-LUMO gap.
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  • 88
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    Berichte der deutschen chemischen Gesellschaft 2000 (2000), S. 229-239 
    ISSN: 1434-1948
    Keywords: Pyridine derivatives ; Bipyridine derivatives/Metal complexes ; Chromophores ; Nonlinear optics ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Metal complexes of pyridine and bipyridine-type ligands represent an important class of nonlinear optical (NLO) materials: (i) They can incorporate a variety of functionalised ligands with a wide range of metals which can give rise to tuneable NLO properties; (ii) they are generally associated with intense low-lying charge-transfer excitations such as metal to ligand charge-transfer (MLCT) or intraligand charge-transfer (ILCT); (iii) bipyridyl ligands are also good building blocks that allow the construction of octupolar complexes with a defined geometry and symmetry. This review describes the recent developments in the design of such dipolar and octupolar chromophores for second-order nonlinear optics.
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  • 89
    ISSN: 1434-1948
    Keywords: Heterobimetallics ; Hydride complexes ; Alkenyl complexes ; μ-Isonitrile complexes ; Silicon ; Iron ; Platinum ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The heterobimetallic hydride complexes [(OC)3Fe{Si(OMe)3}(μ-Ph2PXPPh2)Pt(H)(PR3)] (1a: X = CH2, PR3 = PPh3; 1b: X = NH, PR3 = PPh3; 1c: X = CH2, PR3 = PMePh2) have been prepared by the oxidative addition of [(OC)3Fe(H){Si(OMe)3}(η1-Ph2PXPPh2)] to [Pt(H2C=CH2)(PPh3)2] or by reaction of K[(OC)3Fe{Si(OMe)3}(η1-dppm)] with trans-[Pt(Cl)(H)(PPh3)2]. The solid-state structure of compound 1b has been determined by single-crystal X-ray diffraction. 1-Alkynes such as methylpropiolate or phenylacetylene insert in a regiospecific manner into the Pt-H bond of 1 to yield the σ-alkenyl complexes [(OC)3Fe{μ-Si(OMe)2(OMe)}(μ-Ph2PXPPh2)Pt{C(R)=CH2}] (2a: X = CH2, R = CO2Me; 2b: X = NH, R = CO2Me; 3a: X = CH2, R = Ph). Addition of the Pt-H bond of 3a across the triple bond of [D1]phenylacetylene affords [(OC)3Fe{μ-Si(OMe)2(OMe)}(μ-dppm)Pt{C(Ph)=C(D)H}] (3a*) having the deuteron trans to platinum (cis addition). This insertion reaction is accompanied by dissociation of the platinum-bonded PR3 ligand and saturation of the vacant coordination site by a dative μ-η2-Si-O→Pt interaction. When 3 is treated with PR3 again, a subsequent phosphane-induced rearrangement leading to vinylidene-bridged complexes [(OC)3Fe{μ-C=C(H)R′}(μ-Ph2PXPPh2)Pt(PR3)] (4a: X = CH2, R′ = Ph, PR3 = PPh3; 4b: X = NH, R′ = Ph, PR3 = PPh3; 4c: X = CH2, R′ = Ph, PR3 = PMePh2; 4d: X = CH2, R′ = p-tolyl, PR3 = PPh3) occurs. Upon purging a solution of 3a with carbon monoxide, the labile CO adduct [(OC)3Fe{Si(OMe)3}(μ-dppm)-Pt(CO){C(Ph)=CH2}] 5a is formed, addition of 2,6-xylyl isocyanide to 2a and 3a affords the isonitrile adducts [(OC)3Fe{Si(OMe)3}(μ-dppm)Pt(CNxylyl){C(R)=CH2}] (5b: R = CO2Me; 5c: R = Ph), respectively. When hydride complex 1a is allowed to react with stoichiometric amounts of aromatic isonitriles, formal elimination of HSi(OMe)3 occurs, yielding the heterodinuclear isonitrile-bridged complexes [(OC)3Fe(μ-C=N-R)(μ-dppm)Pt(PPh3)] (6a: R = 2,6-xylyl; 6b: R = o-anisyl; 6c: R = p-anisyl; 6d: R = p-C6H4NH2) and the bis(isonitrile) complexes [(OC)2(RN≡C)Fe(μ-C=N-R)(μ-dppm)Pt(PPh3)] (7a: R = 2,6-xylyl; 7b: R = p-anisyl). Single-crystal X-ray diffraction studies perfomed on 6a and 6b reveal that the molecular structures of these μ-isonitrile complexes closely resemble the μ-vinylidene complexes 4. The two metal centers are bridged in a symmetric manner by strongly bent CNR ligands, the aromatic groups R being oriented towards the Fe(CO)3 moiety. Electrophilic addition of HBF4 to the basic nitrogen atom of the μ-CNR ligand transforms 6 to the cationic μ-aminocarbyne complexes [(OC)3Fe{μ-CN(H)R}(μ-dppm)Pt(PPh3)][BF4] (8a: R = 2,6-xylyl; 8b: R = p-anisyl; 8c: R = p-C6H4NH2).
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  • 90
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    Berichte der deutschen chemischen Gesellschaft 2000 (2000), S. 253-264 
    ISSN: 1434-1948
    Keywords: Iron-sulfur clusters ; Crown ethers ; Electrochemical devices ; Host-guest chemistry ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A series of Fe4S4 cluster compounds, I, III, and V, in which the cuboidal cluster core is appended with four crown ether thiolate ligands, and II and IV, bearing thiolate ligands without crown ether parts, has been synthesized and characterized. The spectroscopic and electrochemical properties of these compounds are determined by the electronic nature of the thiolate ligands. Only in the case of III, where a very short α-thioacetyl linker was used to connect the crown ether ligands to the cluster core, was a restricted conformational freedom of the ligand observed. A detailed electrochemical study of the influence of alkali and earth alkali metal ions (Li+, Na+, K+, Mg2+, and Ba2+) on the reversible 2-/3- reduction of the cluster compounds was performed. In the case of the crown ether appended clusters I, III, and V, the addition of these metal ions resulted in an anodic shift, i.e. in positive direction, of the reduction potential (modulation effect) and to larger current responses (promotion effect). The magnitude of the modulation effects is determined by the binding affinity of the metal ions in the crown ether ligands, and by the distance between bound metal ions and the redox active cluster core. Variation of the linker between the cluster core and the metal ion binding site resulted in cluster compounds with almost inverse selectivities for e.g. K+ and Ba2+ in the case of I and III. For the large effects found for compound I a lariat binding mode is proposed.
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  • 91
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    Berichte der deutschen chemischen Gesellschaft 2000 (2000), S. 281-285 
    ISSN: 1434-1948
    Keywords: NMR spectroscopy ; Zeolites ; Al-coordination ; Mordenite ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 27Al 3Q MAS NMR spectroscopy has been applied to study the coordination state of the species giving the 30 ppm Al NMR signal in the 27Al MAS NMR spectrum of activated mordenite materials. From the 27Al 3Q MAS NMR measurements it is evident that the broad peak at 30 ppm in the 27Al NMR spectrum of the mordenite calcined at temperatures up to 600 °C comes mainly from the distorted four-coordinated Al. By simulation a quadrupolar coupling constant of 5.8 MHz was estimated for the distorted tetrahedral Al. For samples calcined at 650 and 700 °C, a small amount of pentacoordinated Al emerges. The majority of the signal, however, arises from distorted tetrahedral Al. A two-step calcination results in a significant contribution of the pentacoordinated Al to the signal at 30 ppm. From the simulated line-shape, a quadrupole coupling constant of 6.2 MHz is obtained for the latter signal. These data show that during the calcination of the mordenite, the coordination environment at the Al centre gradually becomes distorted to give rise to the shoulder at 30 ppm. With the increase of the calcination temperature, pentacoordinated Al species form
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  • 92
    ISSN: 1434-1948
    Keywords: Copper ; Magnetic properties ; Supramolecular chemistry ; Three-dimensional architecture ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A novel three-dimensional copper(II) compound of the formula [Cu3(btre)5(H2O)2](ClO4)6·H2O (btre = 1,2-bis(1,2,4-triazol-4-yl)ethane) has been synthesized. The structure has been solved at 150 K by single-crystal X-ray analysis. The compound [C30H44Cu3N30O2·6(ClO4)·H2O] crystallizes in the triclinic space group P1bar with a = 12.488(1), b = 13.195(1), c = 19.756(2) Å, α = 78.959(8), β = 84.553(8), γ = 63.869(7)°, V = 2868.4(5) Å3, Z = 2 (trinuclear CuII units), 6484 reflections [I 〉 4σ(Ι)], RF = 0.0581, wR2 = 0.1214. The structure of this coordination polymer consists of a three-dimensional network built up from linear trinuclear CuII cations of formula [Cu3(btre)5(H2O)2]6+. This crystallographically independent unit comprises a linear array of three CuII ions linked by triple N1,N2-1,2,4-triazole bridges, yielding Cu1-Cu2 = 3.893(1) Å and Cu2-Cu3 = 3.889(1) Å. These linear trinuclear CuII units are linked by various pathways involving tridentate and tetradentate bridging btre ligands, which yields an unprecedented three-dimensional network. The CuII ions are weakly antiferromagnetically coupled with J = -1.01(2) cm-1 (based on the Hamiltonian: H = -J[SCu1·SCu2 + SCu2·SCu3] using the expression for the molar magnetic susceptibility S = 1/2 of a linear trinuclear system). The nature and the magnitude of the antiferromagnetic exchange have been discussed on the basis of the structural features.
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  • 93
    ISSN: 1434-1948
    Keywords: Alkenylcarbynes ; Dinuclear tungsten complexes ; Electrochemistry ; Tungsten NMR ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Neutral trans-cyanide alkenylcarbyne complexes 2a and 2b have been prepared by reaction of the complex 1a and 1b with NaCN or [Bu4N]CN. The reaction of complexes 2a and 2b with an equimolar amount of the acetonitrile complexes 1a and 1b in CH2Cl2 leads to the cationic cyanide-bridged bis(alkenylcarbyne) di-tungsten complexes 3a-d. Diisocyanide-bridged bis(alkenylcarbyne) di-tungsten complexes 4a and 4b have been synthesized by the reaction of complexes 1a and 1b with 0.5 equivalents of the diisocyanide 1,4-(CN)2C6H4. IR as well as 1H-, 31P{1H}-, 13C{1H}-, and 183W-NMR data are reported. The spectroscopic data show that in the dinuclear complexes 3a-d, the bridging CN group and the alkenylcarbyne units are located in trans positions, while in the dinuclear complexes 4a and b, the isocyanide groups of the bridging ligand 1,4-(CN)2C6H4 and the two alkenylcarbyne moieties are cis. The 183W chemical shifts of complexes 2a, 2b, 3a-d, 4a, and 4b were obtained through two-dimensional indirect 31P, 183W NMR recording techniques. A downfield shifting of 183W resonances of the cyanide-bridged dinuclear complexes 3a-d with respect to the mononuclear ones, 2a and 2b, was observed. The δ183W of isocyanide bridging dinuclear complexes 4a and 4b appear at higher field than those of the corresponding mononuclear cyanide 2a and 2b in accordance with the higher π-acceptor electron properties of the isocyanide ligand. The electrochemical behaviour of all the complexes has been investigated by cyclic voltammetry and controlled potential electrolysis in aprotic media and at a Pt (or vitreous C) electrode. Complexes 1, 2, or 3 undergo multi-electron irreversible oxidation processes involving anodically induced proton dissociation from the alkenylcarbyne ligands, and irreversible cathodic processes are also observed for all the complexes. The order of the redox potentials reflects that of the net electron π-acceptor/σ-donor character of the ligands and the ligating alkenylcarbynes are shown to behave as remarkably strong π-electron acceptors (even stronger than CO).
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  • 94
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    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 2127-2134 
    ISSN: 1434-1948
    Keywords: Gallium ; Azides ; Chemical vapour deposition ; Gallium nitride ; Single source precursors ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The synthesis, properties and X-ray single crystal structure analysis of the intramolecularly adduct-stabilised organogallium bisazide (N3)2Ga[(CH2)3NMe2] (1), the mono azide (N3)Ga[(CH2)3NMe2]2 (2) and the trialkylamine adducts of triazidogallium of the type (N3)3Ga(NR3) (3a-d; R = alkyl) are reported. An unusual isomer 1b of compound 1 is described, which was obtained by slow cooling of the analytically pure neat liquid compound 1 to 0 °C. The new and unusual structure 1b can be regarded as a weak associate of dimers linked together by head-to-tail azide bridges. In contrast, compounds 2 and 3a-b (R = CH3, C2H5) are monomeric in the solid state. The suitability of the volatile compounds 1 and 2 as single source precursors to grow GaN thin films by chemical vapour deposition is compared, showing that preferentially oriented crystalline films can be obtained from compound 2 on sapphire substrates at 600-700 °C in vacuo (0.1 Pa). However the films have a grey rather than a transparent appearance, which is presumably due to N-deficiency owing to the lower N-content of the single molecule precursor 2 relative to 1.
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  • 95
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    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 2135-2145 
    ISSN: 1434-1948
    Keywords: Density functional calculations ; Epoxidation ; Peroxo complexes ; Titanium ; Transition states ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Epoxidation of olefins by TiIV peroxo and hydroperoxo (alkylperoxo) complexes was investigated using a hybrid DFT method (B3LYP). Reaction energies and activation barriers for direct oxygen transfer to ethylene as a model olefin were computed for various model complexes to compare the epoxidation activity of Ti(η2-O2) and TiOOR (R = H, CH3) moieties. The activity of complexes with a Ti(O2) peroxo group is shown to be essentially quenched when the coordination sphere of the complex is saturated by strongly basic (σ-donor) ligands. In contrast, the activity of a TiOOH functional group depends only weakly on the saturation of the coordination sphere of the Ti center. Substitution of methyl for hydrogen in a TiOOH group is found to slightly increase the activation barrier of epoxidation. The computational results give preference to reaction paths that involve TiOOR species. The factors governing the activity of Ti(O2) and TiOOR groups, in particular the effects of donor ligands, are discussed on the basis of a molecular orbital analysis.
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  • 96
    ISSN: 1434-1948
    Keywords: Colloids ; Sol-gel processes ; Immobilization ; Heterogeneous catalysts ; Hydrogenations ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A bimetallic, fully alloyed Pd/Au colloid of 3.0 nm particle size, obtained by the co-reduction of Pd and Au salts with tetraalkylammonium triethylhydroborate, was embedded in a silica matrix employing a modified sol-gel procedure with THF as the solvent. The removal of the protecting tenside led to a mesoporous texture with a comparatively narrow pore distribution. The physical characterisation by a combination of several techniques has shown that the SiO2-embedded Pd/Au colloid preserves the size and the structural characteristics of the colloidal metal precursor. The new material exhibits catalytic properties in selective hydrogenation.
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  • 97
    ISSN: 1434-1948
    Keywords: Thiacalixarene ; Trimetallic sandwich ; Cobalt ; Zinc ; Divergent receptors ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Reaction between deprotonated p-tert-butyltetrathiacalix[4]arene and CoII or ZnII under strictly defined conditions leads to the formation of sandwich species in which a trimetallic unit is held between two opposed, divergently oriented, staggered O- and S-bound calixarene ligands in the cone conformation. Despite the isomorphous nature of the crystalline compounds, there is a subtle difference in the coordination of CoII and ZnII, presumably related to the differences in metal radius and electron configuration combined with structural restrictions imposed by the calixarene framework, in that whereas all three Co atoms may be considered six-coordinate (and approximately octahedral), only two of the Zn atoms appear so, the third being five-coordinate and more nearly trigonal bipyramidal in its coordination geometry.
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  • 98
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    Berichte der deutschen chemischen Gesellschaft 2000 (2000), S. 831-834 
    ISSN: 1434-1948
    Keywords: Metallo-calixarenes ; Gold complexes ; Tetraphosphane ; Stability constants ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Assemblage of the tetragold complex [L·(AuCl)4] from p-tert-butyl-calix[4]-(OCH2PPh2)4 (L) and [AuCl(tetrahydrothiophene)] was investigated by NMR and UV/Visible spectroscopic titrations. Three steps could be resolved and are assigned, respectively, to addition of one, two and four AuCl units to the macrocyclic ligand. At each stage of metallation, symmetrical species persist on the NMR time scale since the bound AuCl fragments migrate between the different phosphorus centers via both intra- and intermolecular processes. The derived stability constants (logβ1 = 4.4 ± 0.2, logβ2 = 7.0 ± 0.7, and logβ4 = 14.5 ± 2.0) indicate both positive and negative cooperativity during build-up of the tetranuclear species. An X-ray diffraction study made with crystals obtained from an L:Au (1:2) mixture revealed the formation of an unusual binuclear complex whose solid state structure comprises a polymeric chain of [L·AuCl] units linked by pseudo-tetrahedral Au+ ions, each generic unit containing a pendant linear PAuCl fragment. This polymeric species, with its two distinct binding modes, provides a simple rationale by which to explain the role of cooperativity in the overall assembly process.
    Additional Material: 1 Ill.
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  • 99
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 2000 (2000), S. 839-842 
    ISSN: 1434-1948
    Keywords: Tris(pyrazolyl)borate ; Tantalum ; Agostic interactions ; Alkyne complexes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The synthesis of unprecedented alkyne hydrotris(3,5-dimethylpyrazolyl)borato (TpMe2) tantalum(III) complexes is reported. The parent dichloro complex TpMe2TaCl2(PhC≡ CCH3) (2) is obtained from TaCl3(DME)(PhC≡CCH3) and KTpMe2. 2 reacts with methyllithium to give the dimethyl complex TpMe2Ta(CH3)2(PhC≡CCH3) (3) and with ethylmagnesium chloride to give the X-ray characterized α-agostic ethyl complex TpMe2Ta(Cl)(μ-H-CHCH3)(PhC≡CCH3) (4). Reaction of 4 with methyllithium generates the mixed methyl ethyl complex TpMe2Ta(CH3)(μ-H-CHCH3)(PhC≡CCH3) (5) in solution. Spectroscopic data indicate that 5 is α-agostic at the ethyl group only.
    Additional Material: 1 Ill.
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  • 100
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 2289-2294 
    ISSN: 1434-1948
    Keywords: Intercalations ; Vanadyl phosphate ; Ethanol ; Hydration ; Kinetics ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The course of the replacement of ethanol by water molecules in the VOPO4·2C2H5OH intercalate, and of water by ethanol in VOPO4·2H2O has been studied by X-ray diffraction and infrared and Raman spectroscopy. Formation of mixed phase VOPO4·C2H5OH·H2O was not observed. The shape of the kinetics curves indicates a transition of at least one reaction zone through the crystal. A delay in formation of the product in comparison with the decrease in the amount of starting material can be explained by the existence of non-diffracting advancing phase boundary. In a VOPO4/ethanol/water system, VOPO4·2C2H5OH is formed as the only product when the system contained more than 96 vol% of ethanol, whereas in the system with less than 94 vol% of ethanol only VOPO4·2H2O is present.
    Additional Material: 7 Ill.
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