Search results for "Bene"
showing 10 items of 2408 documents
PCP-bridged chalcogen-centred anions: coordination chemistry and carbon-based reactivity.
2012
Since the discovery of the stabilising influence of thiophosphinoyl groups in methanediides by Le Floch et al. (Angew. Chem. Int. Ed., 2004, 43, 6382), numerous transition metal, lanthanide and actinide complexes of bis(thiophosphinoyl) carbene ligands have been investigated with an emphasis on the electronic structure and reactivity of the metal–carbon bonds. This Perspective begins by discussing main group (s- and p-block) complexes of this ligand and draws attention to differences compared to their d and f-block analogues. Investigations targeting the heavy chalcogen analogues of the Le Floch ligand have revealed an unusual carbon-based reactivity that led to the discovery of novel multi…
A new pyridine-bis-N-heterocyclic carbene ligand and its coordination to Rh: Synthesis and characterization
2005
Abstract The new bis(imidazolylidene) tripodal ligand precursor (2-pyridine)bis(3-methylimidazolium-1-yl)methane diiodide, [H2PYBIMMe]I2, has been obtained by a simple method. The molecular structure of this new ligand precursor has been determined by means of X-ray diffraction. The coordination of this ligand to Rh, provides a Rh(III) complex with very low solubility in most solvents, which we attributed to the polymeric nature of the species. Solution of this polymer in DMSO provided a biscarbene Rh(III) complex in which the pyridine fragment remained unbound.
1,3-Dimethylimidazolium-2-carboxylate: the unexpected synthesis of an ionic liquid precursor and carbene-CO2 adductElectronic supplementary informati…
2002
1,3-Dimethylimidazolium-2-carboxylate is formed in good yield, rather than the anticipated organic salt, 1,3-dimethylimidazolium methyl carbonate, as the reaction product resulting from both N-alkylation and C-carboxylation of 1-methylimidazole with dimethyl carbonate; the crystal structure of the zwitterion exhibits π-stacked rings and two-dimensional sheets constructed by hydrogen-bonds from imidazolium-ring hydrogens to the carboxylate group.
Poly(2-oxazoline)s Functionalized with Palladium Carbene Complexes: Soluble, Amphiphilic Polymer Supports for C−C Coupling Reactions in Water
2004
This paper describes the synthesis and characterization of a new class of amphiphilic, water-soluble diblock copolymers based on 2-oxazoline derivatives with pendent N-heterocyclic carbene/palladium catalysts in the hydrophobic block. The synthetic strategy involves a four-step synthesis of three functionalized monomers, each composed of a bis(imidazoline-2-ylidene)palladium(II) diiodide derivative that is covalently linked to a 2-oxazoline monomer via a flexible alkyl spacer (alkyl = butyl, hexyl, octyl). The structure of the monomers was analyzed by 1H and 13C NMR spectroscopy, MALDI-TOF, and elemental analysis. Three diblock copolymers P1−P3 with the monomers being part of the hydrophobi…
Biological activity of resveratrol, a stilbenic compound from grapevines, against Botrytis cinerea, the causal agent for gray mold
1997
The biological activity of resveratrol, a stilbenic compound synthesized by grapevines in response to various stresses, was reevaluated against Botrytis cinerea using a novel in vitro system that enabled direct observation of the fungus with an inverted microscope. We determined that 90 μg resveratrol/ml reduced germination of B. cinerea conidia by ca. 50%. Moreover, resveratrol was shown to significantly reduce mycelial growth of B. cinerea at concentrations ranging from 60 to 140 μg/ml. Exposure to resveratrol at concentrations ranging from 60 to 140 μg/ml resulted in cytological changes in B. cinerea, such as production of secondary or tertiary germ tubes by conidia, cytoplasmic granulat…
Degradation of stilbene-type phytoalexins in relation to the pathogenicity of Botrytis cinerea to grapevines
1996
The ability of eight isolates of Botrytis cinerea to degrade the stilbene phytoalexins, resveratrol and pterostilbene, was compared with their pathogenicity to grapevines. All strains which degraded resveratrol and pterostilbene were highly or moderately pathogenic to in vitro cultures of grapevines (Vitis rupestris) after inoculation with agar disks containing mycelium, while those which were unable to degrade phytoalexins were non-pathogenic. In all cases, the hydroxystilbene-degrading activity was related to the presence of laccase activity in the culture filtrates, as shown by using syringaldazine as substrate. The role of laccase-mediated degradation of phytoalexins in relation to path…
Stilbene Content of MatureVitis viniferaBerries in Response to UV-C Elicitation
2001
A method using HPLC analysis has been used to compare the level of resveratrol and its derivatives, piceid, pterostilbene and epsilon-viniferin, in grapevine berries of three Vitis vinifera varieties. The concentration of these compounds has been evaluated in healthy and Botrytis cinerea infected grape clusters, both in natural vineyard conditions and in response to UV elicitation.
The Significance of Stilbene-Type Phytoalexin Degradation by Culture Filtrates of Botrytis Cinerea in the Vine-Botrytis Interaction
1993
Phytoalexins, antimicrobial compounds, synthesized by a plant in response to infection or a variety of stresses are known to be the most efficient way by which grapevines withstand an attack by Botrytis cinerea Pers., the causal organism for grey mould. In that plant, such responses include the production of a simple stilbene, resveratrol, and the biosynthetically related compounds, viniferins and pterostilbene. If stilbene-type phytoalexins represent a contributory factor in the resistance of grapevines to B.cinerea, the capacity of the pathogen to metabolize antifungal compounds released by the host could also play a significant role in the outcome of the interaction between grapevines an…
An ELF analysis of the C–C bond formation step in the N-heterocyclic carbene-catalyzed hydroacylation of unactivated C–C double bonds
2012
The changes in electron-density along the C–C bond-formation step in the N-heterocyclic carbene-catalyzed hydroacylation of unactivated double bonds has been studied by an electron localization function (ELF) analysis at the B3LYP/6-31G** level in order to characterize the reaction mechanism. Analysis of DFT reactivity indices and the natural bond orbital and ELF analysis at the most relevant points of the intrinsic reaction coordinate indicate that the reaction path takes place through a two-stage one-step mechanism with non-polar character. In the first stage a hydrogen atom is transferred from the hydroxyl group of Breslow intermediate 12 to the terminal olefinic carbon atom, to yield a …
Anionic Monosubstituted Cyclopentadienylsamarium Derivatives: Catalysts for a Stereospecific Isoprene Polymerization
1998
New alkyl and allyl complexes 1–3 {1: [Cp′2Sm(C3H5)]n, Cp′ = Me3CC5H4; 2: [Me4C2(C5H4)2]Sm(C3H5)2Li(dme),dme = (CH3OCH2CH2OCH3); 3: Cp′2SmMe2Li(dioxane)} were synthesized from (Cp′2SmCl)2and from the magnesium derivative [Me4C2(C5H4)2]SmCl · MgCl2(THF)4 (4). The ansa anionic complex 2 exhibited good activity for the stereospecific 1,4-trans polymerization of isoprene, whereas the neutral derivative 1 was inactive. In the same way, the anionic complex [Cp′2SmMe2]Li(dioxane) (3) was found to be an ethylene polymerization catalyst of very short lifetime. The lack of reactivity of 1 is related to the associated structure of this coordinatively unsaturated complex: this fact was established by t…