1,721,157 research outputs found
Novel Olefin Metathesis Ruthenium Catalysts Bearing Backbone- Substituted Unsymmetrical NHC Ligands
No full textStable Ru-based catalysts containing unsym-
metrical N-heterocyclic carbene (NHC) ligands with phenyl
substituents on the backbone in syn and anti stereochemical
relationships have been easily prepared and fully characterized.
Preliminary investigation revealed that, depending on the
backbone configuration, the new Ru complexes displayed
different catalytic behaviors in representative olefin metathesis
reactions
Influence of syn and anti substitution on the backbone of NHC-ruthenium catalysts in olefin metathesis
No full textHeteroscorpionate-based Zn2+, Co2+ and Cu2+ Complexes: Synthesis, Characterization and Hydrogen Sulfide Sensing
No full textIron and Manganese Pyridoxal-Based Complexes as Fluorescent Probes for Nitrite and Nitrate Anions in Aqueous Solution
No full textWater-soluble iron and manganese pyridoxal-based complexes pyr2enFeCl (1) and pyr2enMnCl (2) (pyr2en = N,N′- ethylenebis(pyridoxylideneiminato) have been synthesized and characterized. Proof-of-principle results that the title complexes can be efficiently used as fluorescent probes for nitrite and nitrate detection are provided. The fluorescent complex pyr2enFeCl (1) selectively recognizes nitrate anions by fluorescent enhancement in an aqueous solution displaying high binding affinities. ESI-MS experiments clearly show the binding of these anions via the substitution of the chloride anion at the metal center. The pyridoxal-based manganese complexes of NO2− and NO3− have been isolated, and their structures have been established by singlecrystal XRD. Density functional theory (DFT) calculations show that the substitution of the chloride anion at the metal center by the nitrite or nitrate anion is favored by the gain in the energies of hydration
Synthesis and characterization of palladacyclopentadiene complexes with N-heterocyclic carbene ligands
Full text linkNew palladacyclopentadiene compounds containing different chelate NHC-thioether and NHC-pyridine\ud
ligands have been prepared by transfer of the functionalized carbenes from the respective silver complexes\ud
to the polymeric precursors [PdC-COOR)4]n (R = Me, t-Bu). Their dynamic behaviour in solution\ud
was discussed and the solid-structure of 2c was determined by X-ray crystallography.\ud
The treatment of [Pd(C-COOCH3)4]n with two equivalents of the carbene silver complexes led to the\ud
(NHC)2Pd(C4-COOCH3)4 derivatives (3cei), a new class of compounds with only PdeC bonds. A serious\ud
limitation to this synthetic procedure is an excessive steric crowding around the metal centre.\ud
The complexes 3 are present in solution as a mixture of two atropoisomers, due to restricted rotation\ud
around the CarbeneePd bond. The kinetics of equilibration between the two configurational isomers was\ud
studied for complex 3c, which was also structurally defined by X-ray crystallography (anti isomer).\ud
Finally a synthetic protocol was set up for the synthesis of mixed NHC-Phosphine and NHC-Isocyanide\ud
palladacyclopentadiene complexes. In this procedure the order of addition of the reactants is of great\ud
importanc
Iron complexes of bis(oxazoline) ligand as novel catalysts for efficient Atom Transfer Radical Polymerization of styrene.
No full textFe(box)Cl2 and Fe(box)Cl3 (box = 1,1’-bis(4,4-dimethyl-1,3-oxazolin-2-yl)ethane) are efficient catalysts in atom transfer radical polymerization (ATRP) of styrene. The complex Fe(box)Cl2 exhibited good monomer conversion (55-60 mol-% in 24 h, 120 °C) and produced polymers with average molecular weight distribution (Mw/Mn) in the range 1.4-1.5. The polymerization of styrene was more efficiently controlled by Fe(box)Cl3 under reverse ATRP protocol using the 1,1,2,2-tetraphenyl-1,2-ethanediol (TPED) initiator: polydispersity values of 1.1, typical of a living catalyst, were reached at high monomer conversion (>70%)
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Enantioselective reactions of 2-bromopropanamides with primary secondary or tertiary amines. Synthesis of some alaninamides.
No full textEnantiomeric 2-bromopropanamides react with primary, secondary, or tertiary aliphatic amines in toluene at room temperature, yielding the corresponding secondary or tertiary amino, or quaternary ammonium amide. If the reacting amines are good nucleophiles, either product is obtainable in high yield and e.e., by running the reaction either in the presence or absence of Ag2O. With a less nucleophilic amine, Ag2O or Ag+ promotes the formation either of an optically active amine derivative, or a high diastereomeric excess of a dimeric derivative, whose structure was ascertained by X-ray analysis. © 1991
Oxidative addition of organic halides on palladium(0) complexes stabilized by dimethylfumarate and quinoline-based N–P or N–S spectator ligands
Full text linkWe have studied the oxidative addition of some organic halides on palladium(0) dimethylfumarate\ud
complexes bearing heteroditopic (N–P or N–S) quinoline-based spectator ligands from the experimental\ud
and theoretical point of view. We have measured the half-life of some oxidative addition reactions carried\ud
out in two different solvents (CD2Cl2 and CD3CN). The reactions were studied under mild conditions by\ud
NMR and the reactivities of different oxidants towards the complexes under study were compared.\ud
The rates of reaction were influenced by the nature of the spectator ligands and the solvent. The\ud
thioquinoline derivatives display a higher reactivity than that of the phosphoquinoline complexes and\ud
in general the reaction rates are higher in CD3CN than in CD2Cl2, although such a behavior is not always\ud
observed. We propose a plausible mechanism for the oxidative reaction in different solvents based on the\ud
experimental results and an adequate computational approach. Finally, the solid state structures of two\ud
reaction products were resolved and reported
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