Kooperativer Bibliotheksverbund

Berlin Brandenburg

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  • 1
    Language: English
    In: Forest Ecology and Management, 01 August 2015, Vol.349, pp.94-105
    Description: Improved knowledge concerning nutrient removals through harvesting in former coppice forests is crucial for the sustainable management of these forests. This is especially true if the resumption of coppicing is being considered to serve increasing fuel wood demands. In this study the nutrient contents of various tree compartments of sessile oak ( (Mattuschka) Liebl.) and hornbeam ( L.) from two sites differing in soil fertility were determined using allometric equations to calculate nutrient removal associated with different harvesting intensities. Stand level nutrient contents in tree compartments were comparable between both study sites. The results for exchangeable base cations, plant available P, and total N indicate that coppicing is not a priori an unsustainable forest management system. On sites with large soil nutrient pools, even whole trees may be harvested without substantial reductions in ecosystem nutrient pools. However, on sites with a low nutrient capital, current harvesting practices would result in relatively high rates of nutrient export. In these stands, harvesting intensity should be based on careful selection of the tree compartments removed, e.g. stem only, to conserve nutrients on site. This study describes the impact of simulated tree harvesting on soil nutrient pools in aged coppice forest for the first time. Based on our findings, general assumptions related to soil sustainability of coppicing are replaced by clear recommendations regarding silvicultural nutrient management. Considering the large areas of aged coppice forests in Europe this study provides a methodological template which is needed to enhance their sustainable management.
    Keywords: Aged Coppice ; Oak ; Hornbeam ; Nutrient Content ; Nutrient Export ; Harvesting Intensity ; Forestry ; Biology
    ISSN: 0378-1127
    E-ISSN: 1872-7042
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  • 2
    In: Dalton Transactions, Journal of the Chemical Society, Dalton Transactions, 2004, Issue.22, pp.3883-3892
    Description: Chromium and ruthenium complexes of the chelating phosphine borane H 3 B·dppm are reported. Addition of H 3 B·dppm to [Cr(CO) 4 (nbd)] (nbd = norbornadiene) affords [Cr(CO) 4 (η 1 -H 3 B·dppm)] in which the borane is linked to the metal through a single B–H–Cr interaction. Addition of H 3 B·dppm to [CpRu(PR 3 )(NCMe) 2 ] + (Cp = η 5 -C 5 H 5 ) results in [CpRu(PR 3 )(η 1 -H 3 B·dppm)][PF 6 ] (R = Me, OMe) which also show a single B–H–Ru interaction. Reaction with [CpRu(NCMe) 3 ] + only resulted in a mixture of products. In contrast, with [Cp*Ru(NCMe) 3 ] + (Cp* = η 5 -C 5 Me 5 ) a single product is isolated in high yield: [Cp*Ru(η 2 -H 3 B·dppm)][PF 6 ]. This complex shows two B–H–Ru interactions. Reaction with L = PMe 3 or CO breaks one of these and the complexes [Cp*Ru(L)(η 1 -H 3 B·dppm)][PF 6 ] are formed in good yield. With L = MeCN an equilibrium is established between [Cp*Ru(η 2 -H 3 B·dppm)][PF 6 ] and the acetonitrile adduct. [Cp*Ru(η 2 -H 3 B·dppm)][PF 6 ] can be considered as being “operationally unsaturated”, effectively acting as a source of 16-electron [Cp*Ru(η 1 -H 3 B·dppm)][PF 6 ]. All the new compounds (apart from the CO and MeCN adducts) have been characterised by X-ray crystallography. The solid-state structure of H 3 B·dppm is also reported.
    ISSN: 1477-9227
    ISSN: 14779226
    E-ISSN: 1477-9235
    E-ISSN: 14779234
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  • 3
    Language: English
    In: Chemistry – A European Journal, 18 February 2013, Vol.19(8), pp.2776-2783
    Description: The β‐diketiminato magnesium alkyl complex [LMgBu] (L=CH{CMe(NDipp)}, Dipp=diisopropylphenyl) is shown to be a highly effective precatalyst for the hydroboration of alkyl and aryl substituted aldimines and ketimines with pinacol borane (HBpin). Catalysis is proposed to occur through a sequence of MgN/BH metathesis and rate‐determining MgH/NC insertion steps, a proposal strongly supported by stoichiometric studies and kinetic analysis. The reactions are observed to proceed through the intermediacy of well‐defined magnesium amides, two examples of which have been isolated and structurally characterized. Mechanistic investigations suggest that the catalytic rate‐determining process occurs at an isolated magnesium center and requires the presence of two molecules of the imine substrate for effective turnover. This latter observation is rationalized as a requirement for the secondary substrate molecule to displace HBpin from the coordination sphere of the catalytic magnesium center. : The heteroleptic magnesium alkyl complex [CH{C(Me)NDipp}MgBu] (Dipp=2,6‐PrCH) is reported as a highly efficient precatalyst for the hydroboration of aldimines and ketamines with pinacolborane (see scheme).
    Keywords: Homogeneous Catalysis ; Hydroboration ; Imines ; Magnesium ; Main Group Elements
    ISSN: 0947-6539
    E-ISSN: 1521-3765
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  • 4
    Language: English
    In: Chemistry – A European Journal, 13 July 2015, Vol.21(29), pp.10548-10557
    Description: A wide variety of functionalised imidazolidine‐2‐ones and ‐thiones, 2‐imino‐imidazolidines and thiazolidine‐2‐thiones have been synthesised under very mild reaction conditions by using simple and cost‐effective alkaline earth bis(amide) precatalysts, [Ae{N(SiMe)}(THF)] (Ae=Mg, Ca, Sr). The reactions ensue with 100 % atom efficiency as one‐pot cascades from simple, commercially available terminal alkyne and heterocumulene reagents. The reactions take place through the initial assembly of propargylamidines, which are utilised in subsequent cyclisation reactions through addition of the isocyanate, isothiocyanate and, in one case, carbon disulfide reagents. This reactivity is deduced to take place through a well‐defined sequence of heterocumulene hydroacetylenation and alkyne hydroamidation steps, which are all mediated at the alkaline earth centre. The rate and regioselectivity of the cyclisation reactions are, thus, found to be heavily dependent upon the identity of the catalytic alkaline earth centre employed. Similarly, the selectivity of the reactions was observed to be profoundly affected by stereoelectronic variations in the individual substrates, albeit by a similar Group 2‐centred reaction mechanism in all cases studied. ‐2‐ones and ‐thiones, 2‐imino‐imidazolidines and thiazolidine‐2‐thiones may be synthesised by using simple alkaline earth bis(amide) precatalysts with 100 % atom efficiency in one‐pot cascades from commercially available terminal alkyne and heterocumulene reagents (see scheme).
    Keywords: Alkaline Earths Metals ; Cascade Reactions ; Cycloaddition ; Synthetic Methods
    ISSN: 0947-6539
    E-ISSN: 1521-3765
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  • 5
    Language: English
    In: Organometallics, 01/13/2014, Vol.33(1), pp.206-216
    Description: Reaction of a sterically encumbered bis(imino)acenapthene (dipp-BIAN) with either potassium alkyl or the heavier alkaline-earth dialkyl [Ae{CH(SiMe3)2}2(THF)2] (Ae = Mg, Ca, Sr) reagents results in dearomatization of the aromatic ligand. The heteroleptic alkaline-earth alkyl species show enhanced stability toward Schlenk-type redistribution but undergo solution exchange when the bis(trimethylsilyl)methyl substituent is replaced by an anionic ligand of lower overall steric demands. In contrast, analogous reactions performed with [Ba{CH(SiMe3)2}2(THF)2] evidenced facile solution redistribution and resulted in an unusual C–C coupling reaction which is suggested to result from a sterically induced reductive process. An assessment of the Mg, Ca, and Sr alkyl compounds as precatalysts for the intramolecular hydroamination of aminoalkenes evidenced enhanced reactivity, which is ascribed to the greater solution stability of the catalytically active species. Most notably the calcium species may even be applied to ...
    Keywords: Chemistry;
    ISSN: 0276-7333
    E-ISSN: 1520-6041
    Source: American Chemical Society (via CrossRef)
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  • 6
    Language: English
    In: Organometallics, 02/09/2015, Vol.34(3), pp.653-662
    Description: A stable three-coordinate dimethylberyllium species coordinated by the 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene (IMes) ligand is readily converted to the corresponding methylhydrido derivative through metathetical reaction with phenylsilane. Attempts to synthesize the corresponding molecular dihydrides are, however, unsuccessful and result in ring opening of an IMes ligand through hydride transfer to the donor carbon atom and the consequent formation of a heterocyclic beryllium organoamide. In agreement with previous calculations, we suggest that this process occurs via a Schlenk-type equilibration process and formation of a four-coordinate bis-NHC beryllium dihydride. These species are not observed, however, as the steric pressure exerted by coordination of the two sterically demanding IMes ligands is sufficient to induce hydride transfer. The latter deduction is supported by the observation that a similar ring-opened product, but derived from methyl and hydride transfer, is available through the...
    Keywords: Chemistry;
    ISSN: 0276-7333
    E-ISSN: 1520-6041
    Source: American Chemical Society (via CrossRef)
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  • 7
    Language: English
    In: Chemical communications (Cambridge, England), 14 May 2012, Vol.48(38), pp.4567-9
    Description: The heteroleptic magnesium alkyl complex [CH{C(Me)NAr}(2)Mg(n)Bu] (Ar = 2,6-(i)Pr(2)C(6)H(3)) is reported as a highly efficient pre-catalyst for the hydroboration of aldehydes and ketones with pinacolborane.
    Keywords: Chemistry;
    ISSN: 13597345
    E-ISSN: 1364-548X
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  • 8
    Language: English
    In: Organometallics, 11/14/2011, Vol.30(21), pp.5556-5559
    ISSN: 0276-7333
    E-ISSN: 1520-6041
    Source: American Chemical Society (via CrossRef)
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  • 9
    Language: English
    In: Angewandte Chemie International Edition, 26 June 2015, Vol.54(27), pp.7882-7885
    Description: Sequential reactions between a 2,6‐diisopropylphenyl‐substituted β‐diketiminato magnesium ‐butyl derivative and P allow the highly discriminating synthesis of unusual [BuP] and [BuP] cluster dianions. : The controlled, sequential activation of white phosphorus (P) can be mediated by organomagnesium compounds with appropriate supporting ligands. The activation leads to the highly discriminating synthesis of unusual [BuP] and [BuP] cluster dianions.
    Keywords: Cluster Compounds ; Magnesium ; P 4 Activation ; Phosphorus ; Structure Elucidation
    ISSN: 1433-7851
    E-ISSN: 1521-3773
    Source: John Wiley & Sons, Inc.
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  • 10
    Language: English
    In: Angewandte Chemie International Edition, 27 February 2012, Vol.51(9), pp.2098-2100
    Description: Interaction of a well‐defined adduct of MeBeH and an N‐heterocyclic carbene (NHC) with PhSiH results in complete rupture of the heterocycle, and activation of the NHC through effective BeH insertion into a CN bond of the heterocycle (see scheme; Ar=2,6‐diisopropylphenyl, IPr=1,3‐bis(2,6‐diisopropylphenyl)imidazol‐2‐ylidene).
    Keywords: Alkaline‐Earth Metals ; Beryllium ; Cn Activation ; Hydrides ; N‐Heterocyclic Carbenes
    ISSN: 1433-7851
    E-ISSN: 1521-3773
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