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, PO2F2) 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 (C8G1) or a C8G1‐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 C8G1 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.
The influence of anionic and cationic co‐surfactants in nonionic microemulsions on the performance of chiral Rh‐norbornadiene complexes with different counterions in the 1,2‐addition of phenylboronic acids to N‐tosylimines is described. Catalytic studies revealed the unique role of the counterion and the type of co‐surfactant. NMR experiments and the calculated intrinsic binding orbitals suggest that the anion exchange with co‐surfactant accelerates the formation of the catalytically active Rh‐OH complex, thus increasing the yield and affecting the enantioselectivity. For more information, see the Full Paper by M. Kirchhof, K. Abitaev and co‐workers on page 16853 ff.
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