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Enantioselective Hydrogenation with Self‐Assembling Rhodium Phosphane Catalysts: Influence of Ligand Structure and Solvent
Author(s) -
Birkholz MandyNicole,
Dubrovitalia V.,
Jiao Haijun,
Michalik Dirk,
Holz Jens,
Paciello Rocco,
Breit Bernhard,
Börner Armin
Publication year - 2007
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.200601607
Subject(s) - enantioselective synthesis , chemistry , intramolecular force , ligand (biochemistry) , catalysis , hydrogen bond , rhodium , solvent , denticity , chelation , medicinal chemistry , asymmetric hydrogenation , stereochemistry , organic chemistry , crystal structure , molecule , receptor , biochemistry
Three sets of new and related chiral phospholane and phosphepine ligands have been prepared for Rh‐catalyzed enantioselective hydrogenation. The size and substitution pattern of the cyclic monophosphanes were varied. More importantly, the ligands differ in the nature of the heterocyclic group linked to the trivalent phosphorus atom: 2‐pyridone or 2‐alkoxypyridine. In the corresponding Rh complexes, the pyridone units of two monodentate P ligands can assemble by hydrogen bonding and form chelates. In contrast, synthetic precursors bearing alkoxypyridine appendages are not able to aggregate via intramolecular hydrogen bonds. The nature of self‐assembly is dependent on the nature of the P ligand and the solvent used for the hydrogenation (CH 2 Cl 2 vs. MeOH). These features affect the rate of the reaction as well as the enantioselectivity, which varied in the range of 0–99 % ee Complexation studies and DFT calculations were performed to explain these differences.