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Interplay of Polarity and Confinement in Asymmetric Catalysis with Chiral Rh Diene Complexes in Microemulsions
Author(s) -
Kirchhof Manuel,
Abitaev Karina,
Abouhaileh Abdulwahab,
Gugeler Katrin,
Frey Wolfgang,
Zens Anna,
Kästner Johannes,
Sottmann Thomas,
Laschat Sabine
Publication year - 2021
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.202102752
Subject(s) - microemulsion , pulmonary surfactant , cationic polymerization , chemistry , catalysis , reaction rate constant , diene , medicinal chemistry , crystallography , chemical engineering , organic chemistry , kinetics , biochemistry , physics , natural rubber , quantum mechanics , engineering
Microemulsions provide a unique opportunity to tailor the polarity and liquid confinement in asymmetric catalysis via nanoscale polar and nonpolar domains separated by a surfactant film. For chiral diene Rh complexes, the influence of counterion and surfactant film on the catalytic activity and enantioselectivity remained elusive. To explore this issue chiral norbornadiene Rh(X) complexes (X=OTf, OTs, OAc, PO 2 F 2 ) were synthesized and characterized by X‐ray crystallography and theoretical calculations. These complexes were used in Rh‐catalyzed 1,2‐additions of phenylboroxine to N‐ tosylimine in microemulsions stabilized either exclusively by n ‐octyl‐ β ‐D‐glucopyranoside (C 8 G 1 ) or a C 8 G 1 ‐film doped with anionic or cationic surfactants (AOT, SDS and DTAB). The Rh(OAc) complex showed the largest dependence on the composition of the microemulsion, yielding up to 59 % (90 %ee) for the surfactant film doped with 5 wt% of AOT as compared to 52 % (58 %ee) for neat C 8 G 1 at constant surfactant concentration. Larger domains, determined by SAXS analysis, enabled further increase in yield and selectivity while the reaction rate almost remained constant according to kinetic studies.