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Chiral Oxazoline‐NHC Ligands with and without CR 2 Bridges: A Comparative Study in Rhodium Hydrosilylation Catalysis
Author(s) -
Schneider Nathanaëlle,
Kruck Matthias,
BelleminLaponnaz Stéphane,
Wadepohl Hubert,
Gade Lutz H.
Publication year - 2009
Publication title -
european journal of inorganic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.667
H-Index - 136
eISSN - 1099-0682
pISSN - 1434-1948
DOI - 10.1002/ejic.200801107
Subject(s) - chemistry , rhodium , oxazoline , deprotonation , hydrosilylation , acetophenone , denticity , catalysis , cationic polymerization , medicinal chemistry , ligand (biochemistry) , halide , polymer chemistry , organic chemistry , crystal structure , ion , biochemistry , receptor
A series of bidentate oxazoline‐NHC ligands has been synthesized in which the two heterocycles are connected by a CH 2 linker. The corresponding rhodium(I) complexes were prepared by direct deprotonation of the imidazolium halide salts followed by the addition of a solution of [Rh(nbd)Cl] 2 at low temperature. The cationic square planar rhodium complexes were generated by halide abstraction via addition of an excess of KPF 6 in a CH 2 Cl 2 /water solvent system. Alternatively, the deprotonation of the imidazolium hexafluorophosphates and reaction with [Rh(nbd)Cl] 2 directly gave the complex cations. These as well as oxazoline‐NHC systems, in which the two heterocycles are directly connected or through a CMe 2 bridge, were investigated in the rhodium‐catalyzed hydrosilylation of acetophenone. The comparison of the three ligand families showed that the catalysts obtained by direct coupling of oxazolines and N‐heterocyclic carbenes, generating highly rigid chelate ligands, remain the most efficient systems giving the secondary alcohols in high enantioselectivity.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)