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Zwitterionic Iridium Complexes with P,N‐Ligands as Catalysts for the Asymmetric Hydrogenation of Alkenes
Author(s) -
Franzke Axel,
Pfaltz Andreas
Publication year - 2011
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.201003314
Subject(s) - cationic polymerization , iridium , chemistry , oxazoline , catalysis , asymmetric hydrogenation , substituent , enantioselective synthesis , covalent bond , bimetallic strip , hydroamination , medicinal chemistry , counterion , polymer chemistry , metal , organic chemistry , combinatorial chemistry , ion
Several zwitterionic iridium complexes based on chiral P,N‐ligands with imidazoline or oxazoline donors and anionic tetraarylborate or aryltrifluoroborate substituents have been synthesized. The corresponding cationic analogues have also been prepared, to evaluate the effect of the covalent linkage between the anion and the cationic metal complex in catalytic reactions. The respective pairs of structurally analogous precatalysts have been compared for their efficacies in the asymmetric hydrogenation of unfunctionalized olefins. In most cases, the anionic derivatization has virtually no influence on the asymmetric induction of the iridium complex. This is in accordance with X‐ray structural studies, which have shown that the chiral environment of the cationic metal center is not affected by the anionic substituent. Depending on the nature of the counterion employed, the zwitterionic catalysts proved to be significantly more reactive than their cationic counterparts in nonpolar solvents.