10.1002/anie.201801048
Angewandte Chemie International Edition
COMMUNICATION
spectra of the [Rh(1S)2(cod)]BARF complex (Figure 4 a). While
in DCM and DCE a strong CD signal was observed, the
absorption in MeOH and THF is much weaker. The formation of
defined tropos isomers in the pyridone/ hydroxypyridine
backbone, as detected by the amplitude of the CD signal
between 290 nm and 330 nm, loosely correlates with the
enantioselectivity in the asymmetric hydrogenation of methyl
acetamidoacrylate (see Figure 4, b).
Acknowledgements
We gratefully acknowledge financial support from the DFG. We
thank Dr. Manfred Keller, Felix Bauer, Dr. Steffen Lüdeke, Dr.
Harald Scherer and Dr. Daniel Kratzert, for invaluable
assistance with NMR- and CD-spectroscopy and X-Ray
crystallography. DFT-calculations were performed on the
JUSTUS cluster supported through bwHPC and the DFG (grant
number: INST 40/467-1 FUGG).
Keywords: self-assembly • supramolecular catalysis •
asymmetric hydrogenation • axial-chirality • ligand design
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Figure 4. a. Solvent-dependence of the CD spectra of [Rh(1S)2(cod)]BARF at
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T
p
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R2
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[bar]
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1
2
3
H
H
CO2Me
CO2Et
-10
-10
0
10
10
20
20 h
20 h
48 h
93
87
70
90 (S)
91 (S)
79 (S)
Me
CO2Me
[Rh]:L:substrate
Conversion and ee determined by chiral GC.
= 1:2.2:20 (5 mol% Rh), o-DCB, c(substrate)=0.020M.
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In summary, we demonstrated the induction of axial chirality
in a dimeric, supramolecular ligand system connected via
hydrogen bonds. Through NMR studies and circular dichroism
measurements, we were able to show the formation of defined
tropos isomers in transition metal complexes of the
supramolecular ligand at low temperatures. We evaluated this
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reaction, the asymmetric hydrogenation of α-dehydrogenated
amino acids, resulting in high enantioselectivity. These results
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