124,664 research outputs found
Reactivity and Syn-anti Isomerization of (eta3-geranyl)palladium Complexes and (eta3-neryl)palladium Complexes - Evidence For Electronic Control of the Regiochemistry of Nucleophilic-addition
No full textLigand-induced Selective Stabilization of the Anti Isomer In (eta-3-allyl)palladium Complexes - An Attempt To Control the E-z Stereochemistry In Palladium-promoted Allylic Substitutions
No full textConvenient Synthesis of Cationic (eta-3-allyl)palladium Complexes - Preparative and Stereochemical Aspects
No full textThe oxidative addition of allylic trifluoroacetates to Pd(dba)2 (dba = dibenzylideneacetone) gives (eta-3-allyl)palladium trifluoroacetates in excellent yields. The stereochemistry of the reaction is solvent dependent; i.e., predominant trans addition is observed in a THF/MeCN mixture, whereas cis addition dominates in pure THF. By addition of a neutral ligand the trifluoroacetates can be converted to cationic complexes either directly (giving trifluoroacetate salts) or by in situ ion exchange with tetrafluoroboric acid (giving tetrafluoroborate salts). The syn-anti stereochemistry of the cationic eta-3-allyl complexes can be largely controlled by the use of the hindered ligand 2,9-dimethyl-1,10-phenanthroline under the appropriate preparative conditions. Cationic complexes with phenanthroline ligands can also be prepared in good yields by acid-assisted oxidative addition of allylic acetates and alcohols to Pd(dba)2
The Mechanism of Nucleophilic-addition To Eta-3-allylpalladium Complexes - the Influence of Ligands On Rates and Regiochemistry
No full textLigand Effects and Nucleophilic-addition To (eta-3-allyl)palladium Complexes - A C-13 Nuclear-magnetic-resonance Study
No full textLigand Control of the Regiochemistry In the Addition of Nucleophiles To Eta-3-allyl Systems
No full textGoing Beyond Counting First Authors in Author Co-citation Analysis
No full textThe 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
Stereocontrol and Regiocontrol In Palladium-catalyzed Allylic Alkylation Using 1,10-phenanthrolines As Ligands
No full textA series of 2,9-disubstituted-1,10-phenanthroline type ligands have been used in palladium-catalyzed displacement of allylic acetates. It was found that intermediate syn- and anti-(eta3-butenyl)palladium complexes reacted with different rates and regiochemistries. Depending on the ligands, this could be used for regiocontrol as well as stereocontrol. With the parent 1,10-phenanthroline, syn complexes were formed quickly as intermediates from both (E) and (Z) allylic acetates, leading to nearly exclusive formation of (E) products. In contrast, complete retention of alkene stereochemistry was observed with 2,9-dimethyl-1,10-phenanthroline which also gave a catalyst with a considerably higher activity than catalysts based on triphenylphosphine
Dispelling the Myths Behind First-author Citation Counts
No full textWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
Selective Stabilization of the Antiisomer of (eta-3-allyl)palladium and (eta-3-allyl)platinum Complexes
No full textA number of 2,9-disubstituted 1,10-phenanthrolines are synthesized. These are used as ligands in different cationic (eta3-allyl)palladium and -platinum complexes. It was found that while a syn configuration was by far the most stable one with the parent 1,10-phenanthroline, 2,9-substituents such as methyl, chloro, cyano, and propynyl induced a preference for the anti configuration. Since terminal nucleophilic addition to anti-eta3-allyl complexes will yield (Z)-alkenes, this observation opens up a potentially selective route to (Z)-alkenes. Using molecular mechanics calculations these effects may be rationalized
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