Perylene Bisimide Cyclophanes as Biaryl Enantiomerization Catalysts─Explorations into π-π Catalysis and Host-Guest Chirality Transfer.

Abstract

The racemization of axially chiral biaryls is a fundamental step toward transforming kinetic resolutions into dynamic kinetic resolutions (DKRs). The high enantiomerization barriers of many biaryl compounds of synthetic relevance, however, may render DKR strategies challenging. Here, we computationally explore the potential of a para-xylene bridged perylene bisimide cyclophane to serve as a conceptually transferrable biaryl enantiomerization catalyst for fundamental biphenyl and binaphthyl scaffolds, as well as the versatile reagent 1,1'-binaphthyl-2,2'-diol and a precursor to the heterobiaryl ligand QUINAP. The calculated enantiomerization barriers of the different biaryls decrease by 19.8-73.2% upon complexation, suggesting that the cyclophane may form an effective biaryl racemization catalyst. We find that these observed barrier reductions predominantly originate from a combination of transition structure stabilization through π-π stacking interactions between the shape-complementary transition structures and catalyst, as well as ground-state destabilization of the less complementary reactants, indicating a generalizable strategy toward biaryl racemization catalysis. In exploring all enantiomerization pathways of the biaryls under consideration, we further find a systematic enantiomer- and conformer-dependent chirality transfer from biaryl to cyclophane in host-guest complexes.