1,720,979 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 textStereocontrol 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
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
Molybdenum-catalyzed allylic substitution. Influence of 1,10-phenanthroline ligands on reactivity and selectivity
No full textSome new allylmolybdenum complexes containing 1,10-phenanthroline or 2,9-dimethyl-1,10-phenanthroline as Ligand have been synthesized and shown to have different geometries by NMR and X-ray diffraction analysis. The geometries of the complexes were elucidated by NMR techniques and confirmed by X-ray diffraction analysis. The catalytic activity and the influence on regio- and stereocontrol in the alkylation of allylic acetates have been investigated. The 2,9-dimethyl-1,10-phenanthroline complex was found to be a very efficient catalyst for selective conversion of (Z)-allyl acetates into (Z)-products
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