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A highly tunable family of chiral bisphospholanes for rh-catalyzed enantioselective hydrogenation reactions
Authors:Holz Jens  Zayas Odalys  Jiao Haijun  Baumann Wolfgang  Spannenberg Anke  Monsees Axel  Riermeier Thomas H  Almena Juan  Kadyrov Renat  Börner Armin
Institution:Leibniz-Institut für Katalyse e.V. an der Universit?t Rostock, A.-Einstein-Str. 29a, 18059 Rostock, Germany. jens.holz@ifok-rostock.de
Abstract:A set of 16 new and closely related bisphospholane ligands have been prepared by using a highly flexible and convergent approach. Each synthesis can be performed on an industrially relevant scale. The bisphosphines differ in the nature of the bridge connecting both phospholane units. Bridges are formed by three-, four-, five- and six-membered heterocyclic or alicyclic rings. Bisphospholanes and their Rh-precatalysts have been investigated by using results of theoretical calculations (DFT) and analytic measurements ((31)P and (103)Rh NMR spectroscopy, X-ray structure analysis). The studies showed that catalysts based on ligands with maleic anhydride or maleimide bridges give constantly superior enantioselectivities in methanol as the solvent. This may account for optimised steric and electronic effects. However, by changing the solvent catalysts with other backbones can give rise to excellent results. This gives proof that simple correlations between steric and electronic properties and results in the enantioselective hydrogenation frequently claimed in literature are not general.
Keywords:asymmetric catalysis  density functional calculations  hydrogenation  phosphane ligands  rhodium
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