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  • Electronic Resource  (4)
  • Allylic alkylation  (2)
  • Polymer and Materials Science  (2)
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  • Electronic Resource  (4)
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  • 1
    ISSN: 1434-1948
    Keywords: Palladium ; Phosphane ligands ; Bite angle ; Allylic alkylation ; Molecular modelling ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The natural bite angle of bidentate phosphane ligands influences the isomer distribution (syn and anti) in (1-methylallyl)(bisphosphane)Pd OTf complexes. It was found (31P- and 1H-NMR studies) that the syn/anti ratio changes from 12 (dppp) to 1.3 (sixantphos). Molecular orbital calculations [PM3(tm) level] indicate that for ligands inducing a large bite angle, the phenyl rings of the ligand embrace the allyl moiety, thus influencing the syn/anti ratio. This bite-angle effect on the syn/anti ratio is transferred to the regioselectivity in stoichiometric allylic alkylation. Ligands inducing large bite angles direct the regioselectivity towards the formation of the branched product 2. Catalytic alkylation of (E)-2-butenyl acetate showed that for ligands with a small bite angle the regioselectivity of the catalytic and stoichiometric alkylation are in good agreement. This correspondence is worse for ligands with a larger bite angle, which is rationalised in terms of the relative rates of syn/anti isomerisation and alkylation. The ligand with the largest bite angle (sixantphos) gives the most active catalytic species.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Polymers for Advanced Technologies 7 (1996), S. 625-633 
    ISSN: 1042-7147
    Keywords: Copper and rhodium complexes ; immobilization ; polydentates ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Polymer-bound tertiary amine-copper complexes and polymer-bound phosphite-rhodium complexes were studied as catalysts for oxidative coupling of phenols and hydroformylation of alkenes, respectively. The activity and stability of these catalysts could be tuned or optimized by adapting the structure of the ligands and by changing the distance between adjacent ligands along the polymer chains. The latter effect has been described in terms of strain in the intermediate chain segments in the copper complexes or enhancement of the effective local ligand concentration around the rhodium complexes.So-called immobilized homogeneous catalysts were obtained by end-grafting of both types of macromolecular catalysts on to inert and insoluble silica particles. These immobilized polymeric catalysts could easily be separated and recovered. Under proper conditions a grafted polymerbound imidazole-copper complex and a new type of polymer-bound triphenyl-phosphite-rhodium complex showed excellent stability in continuous processes.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Advanced Materials 5 (1993), S. 466-468 
    ISSN: 0935-9648
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 25-27 
    ISSN: 1434-1948
    Keywords: Bite angle ; Catalysis ; P ligands ; Palladium ; Allylic alkylation ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The effect of the natural bite angle (βn) of diphosphane ligands on catalyst selectivity and activity in the palladium-catalyzed allylic alkylation was investigated. The selectivity and rate of the reaction are mainly determined by steric hindrance induced by the diphosphane ligands. The steric hindrance at the palladium center increases as the natural bite angle of the ligand becomes larger. This results in an increasing selectivity at larger bite angles, but at very large bite angles the rate of the reaction drops. The ligand with the largest calculated bite angle, Xantphos, induced 100% selectivity but the reaction rate became low.
    Type of Medium: Electronic Resource
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