Optically active [(eta 6 -arene)Cr(CO) 3]-based diphosphines : synthesis and application in asymmetric homogeneous hydrogenation

Chiral diphosphines have become an important class of ligands for asymmetric catalysis. It is the success itself of enantioselective catalysis that has enhanced the demand for new chiral ligands for essentially two reasons. The first one is that no class of ligands can be considered universal anymore, as it is linked to a finite however broad scope of substrates and reactions. The second reason is the proprietary protection of established ligands. Based on these considerations, the range of chelating diphosphines based on [(h6-benzene)Cr(CO)3] complexes which has recently become accessible through the implementation of a stereocontrolled synthetic strategy has been extended. These ligands, which are endowed with central and planar chirality, offer a range of possibilities for their steric, electronic and conformational properties to be modulated. The new ligands have been prepared starting from [(h6-arene)Cr(CO)3] complexes derived from commercially available optically active benzylamines bearing a para-substituent other than hydrogen, in order to asses the influence of such a substituent on the electronic properties of the final diphosphines. The synthetic challenges posed by such a substituent are reviewed. Diphosphines supported by a more rigid scaffold have been prepared as well starting from optically pure (S)-N,N-dimethylaminoindane. By proper choice of reaction conditions, complexation of this amine to the Cr(CO)3 moiety turns out to be highly diastereoselective. The efficiency of the new ligands has been tested in the rhodium promoted asymmetric homogeneous hydrogenation of (Z)-N-acetylaminocinnamic acid methylester and dimethyl itaconate. All the new diphosphines provide rhodium catalyst precursors which promote complete conversion of the substrates. Catalytic performances are dependent on the electron richness and steric demands of the phosphorous substituents and enantioselectivities between 87 and 91% ee are obtained with the more electron rich ligands. No dramatic changes in chiral induction are observed by changing the substituent on the Cr-coordinated arene: likely, the electron-withdrawing nature of the Cr(CO)3 group levels out any contribution these substituents bring about on the electron dowry of the [(h6-arene)Cr(CO)3] moiety as a whole. Nor does the presence of a more rigid scaffold significantly change the catalytic performances of diphosphines derived from [(h6-N,N-dimethyl-1-aminoindane)Cr(CO)3].

Grantor dc:publisher

Publikationsserver der RWTH Aachen University

Year dc:date

2004

Author dc:creator

• Alberico, Elisabetta

Contributors dc:contributor

• Salzer, Albrecht

• info:eu-repo/classification/ddc/540
• Chromkomplexe Tricarbonylverbindungen
• Aromaten
• Diphosphine
• Asymmetrische Synthese
• Katalytische Hydrierung
• Asymmetrische Reaktion
• Rhodiumkomplexe
• Phosphine
• Chemie
• Chromium
• Diphosphines
• Catalysis
• Hydrogenation

Statement dc:rights

• info:eu-repo/semantics/openAccess

Language dc:language

eng

Identifier

https://publications.rwth-aachen.de/search?p=id:%22RWTH-CONV-208160%22

OAI identifier oai:identifier

oai:publications.rwth-aachen.de:59345