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π‐π Catalysis Made Asymmetric—Enantiomerization Catalysis Mediated by the Chiral π‐System of a Perylene Bisimide Cyclophane

The rate of [5]helicene enantiomerization has been enhanced by a factor of about 700 by using a chiral perylene bisimide (PBI) cyclophane host at room temperature. Computational models suggest the reaction barrier is lowered through a stabilization of the nonplanar transition-state structure of [5]helicene within the cyclophane through π-π catalysis, supported by a ground-state destabilization of the heterochiral host–guest complex.


Enzymes actuate catalysis through a combination of transition state stabilization and ground state destabilization, inducing enantioselectivity through chiral binding sites. Here, we present a supramolecular model system which employs these basic principles to catalyze the enantiomerization of [5]helicene. Catalysis is hereby mediated not through a network of functional groups but through π-π catalysis exerted from the curved aromatic framework of a chiral perylene bisimide (PBI) cyclophane offering a binding pocket that is intricately complementary with the enantiomerization transition structure. Although transition state stabilization originates simply from dispersion and electrostatic interactions, enantiomerization kinetics are accelerated by a factor of ca. 700 at 295 K. Comparison with the meso-congener of the catalytically active cyclophane shows that upon configurational inversion in only one PBI moiety the catalytic effect is lost, highlighting the importance of precise transition structure recognition in supramolecular enzyme mimics.

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