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  • 1
    Electronic Resource
    Electronic Resource
    Kinetic Investigations of the Hydrogenation of Diolefin Ligands in Catalyst Precursors for the Asymmetric Reduction of Prochiral Olefins, II[1] (1996)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 129 (1996), S. 85-89 
    Details
    ISSN: 0009-2940
    Keywords: Rhodium complexes, chiral ; Hydrogenation ; Bisolefins ; Thermodynamic stability ; Kinetic control ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Asymmetric hydrogenations of prochiral olefines by means of chiral rhodium(I) complexes of the type [Rh(L)(PP*)]A (L = COD, [(Z,Z)-cycloocta-1,5-diene], or NBD (norborna-2;5-diene), PP* = chiral bisphosphane forming seven-membered chelate rings, A = anion like BF4-) are often associated with induction periods caused by partial blocking of the catalyst. NBD complexes are hydrogenated faster than the corresponding COD complexes. Catalytic hydrogenation of COD/NBD mixtures and the determination of the ratio of the Michaelis constants showed that the steady-state concentration of the COD complex under hydrogen is higher than that of the NBD complex. However, under argon the NBD complex predominates owing to its higher thermodynamic stability compared with that of the COD complex as determined by 31P-NMR spectoscopy. This complete reversion of the ther-modynamically determined ratios of COD to NBD complex concentration under hydrogenation conditions was proven by means of UV/Vis spectroscopy.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19961290117
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Catalytic and Structural Features of Hydroxy and Methoxy Groups as Hemilabile Coordinating Ligands in Chiral (Diphosphane)rhodium(I) Hydrogenation Catalysts (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 1291-1295 
    Details
    ISSN: 1434-1948
    Keywords: Asymmetric catalysis ; Hydrogenations ; Hemilabile ligand ; Hydroxy phosphane ; Methoxy phosphane ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The influence of two threo-arranged methoxy or hydroxy groups as hemilabile ligands in seven-membered (diphosphane)RhI chelates upon the asymmetric hydrogenation is studied. In comparison to the parent complex based on 1,4-bis(diphenylphosphanyl)butane (DPPB) a lowering of the reaction rate is caused by the hemilabile ligands. The catalyst bearing the hydroxy groups gives significantly higher enantioselectivities than the corresponding methoxy complex (by ca. 35 % ee). X-ray structural analysis reveals that the oxygen atom of the hydroxy group is by 0.9 Å closer to the metal center than that of the methyl ether. 31P-NMR studies give evidence that the dihydroxy diphosphane ligand binds at low temperature exclusively in the η3-coordination mode, whereas for the dimethoxy complex also an η2-coordinated isomer can be found. These differences in complexation could be responsible for the superior enantioselectivities achieved with this and other hydroxy catalysts.
    Type of Medium: Electronic Resource
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    Paper (German National Licenses)
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