Paper
Dalton Transactions
6
(a) S. Harder, in Early Maingroup Metals in Catalysis:
Concepts and Reactions, Wiley-VCH, Weinheim, Germany,
2019; (b) S. Harder, Chem. Rev., 2010, 110, 3852;
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2001, 40, 4261; (d) M. H. Chisholm, J. Gallucci and
K. Phomphrai, Chem. Commun., 2003, 48; (e) F. Buch,
J. Brettar and S. Harder, Angew. Chem., Int. Ed., 2006, 118,
2807; (f) M. R. Crimmin, A. G. M. Barrett, M. S. Hill,
P. B. Hitchcock and P. A. Procopiou, Organometallics, 2008,
27, 497; (g) S. Ziemann, S. Krieck, H. Görls and
M. Westerhausen, Organometallics, 2018, 37, 924;
(h) H. Bauer, M. Alonso, C. Fischer, B. Rösch, H. Elsen and
S. Harder, Angew. Chem., Int. Ed., 2018, 57, 15177;
(i) M. He, M. T. Gamer and P. W. Roesky, Organometallics,
2016, 35, 2638.
Conclusion
R
A series of novel chiral Ae catalysts ( 1-Ae), based on the axially
chiral ligand (R)-BINAM, were synthesized in good to excellent
yields. All compounds were fully characterized using NMR
spectroscopy, elemental analysis and X-ray diffraction. Facile
ligand exchange reactions by the Schlenk equilibrium were not
observed, even not when heated to 100 °C for several days. Full
conversion in catalytic IAH of unactivated aminoalkenes was
achieved at room temperature as fast as
5 minutes.
Enantioselectivities up to 57% ee have been determined,
which to the best of our knowledge marks the highest enantio-
selectivity in Ca catalyzed IAH. Double protonation of the dia-
nionic BINAM ligand during catalysis was identified as the
main catalyst degradation process. Improving catalyst stability
by enhanced chelation resulted in complete catalyst inactivity.
Although progress was achieved, these investigations clearly
demonstrate that enantioselective IAH catalysis with more
reactive heavier Ae metal catalysts remains a challenge.
7 M. S. Hill, D. J. Liptrot and C. Weetman, Chem. Soc. Rev.,
2016, 45, 972.
8 (a) Y. Yamashita, T. Tsubogo and S. Kobayashi, Early
Maingroup Metals in Catalysis: Concepts and Reactions, ed. S.
Harder, Wiley-VCH, Weinheim, Germany, 2019, pp.
311–345; (b) T. Poisson, Y. Yamashita and S. Kobayashi,
Conflicts of interest
J. Am. Chem. Soc., 2010, 132, 7890; (c) S. Kobayashi and
Y. Yamashita, Acc. Chem. Res., 2011, 44, 58; (d) T. Tsubogo,
Y. Yamashita and S. Kobayashi, Angew. Chem., Int. Ed.,
There are no conflicts to declare.
2
009, 48, 9117.
S. Neal, A. Ellern and A. Sadow, J. Organomet. Chem., 2011,
96, 228.
0 P. Horrillo-Martinez and K. Hultzsch, Tetrahedron Lett.,
009, 50, 2054.
1 X. Zhang, T. Emge and K. Hultzsch, Angew. Chem., Int. Ed.,
012, 51, 394.
9
Acknowledgements
6
1
1
1
We thank Antigone Roth for elemental analysis and SH thanks
the Deutsche Forschungsgemeinschaft for funding of this
project (HA 3218/8-1).
2
2
2 B. Schmid, S. Frieß, A. Herrera, A. Linden, F. Heinemann,
H. Locke, S. Harder and R. Dorta, Dalton Trans., 2016, 45,
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3184 | Dalton Trans., 2021, 50, 3178–3185
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