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Anion-π catalysis, that is the stabilization of anionic transition states on π-acidic aromatic surfaces, has so far been developed with naphthalenediimides (NDIs). This report introduces perylenediimides (PDIs) to anion-π catalysis. The quadrupole moment of PDIs (+23.2 B) is found to exceed that of NDIs and reach new records with acceptors in the core (+70.9 B), and their larger surface provides space to better accommodate chemical transformations. Unlike NDIs, the activity of PDI catalysts for enolate and enamine addition is determined by the twist of their π surface rather than their reducibility. These results, further strengthened by nitrate inhibition and circular dichroism spectroscopy, support an understanding of anion-π interactions centered around quadrupole moments, i.e., electrostatic contributions, rather than redox potentials and charge transfer. The large PDI surfaces provide access to the highest enantioselectivities observed so far in anion-π catalysis (96 % ee). [ABSTRACT FROM AUTHOR]

Of central importance in chemistry and biology, enolate chemistry is an attractive topic to elaborate on possible contributions of anion-π interactions to catalysis. To demonstrate the existence of such contributions, experimental evidence for the stabilization of not only anions but also anionic intermediates and transition states on π-acidic aromatic surfaces is decisive. To tackle this challenge for enolate chemistry with maximal precision and minimal uncertainty, malonate dilactones are covalently positioned on the π-acidic surface of naphthalenediimides (NDIs). Their presence is directly visible in the upfield shifts of the α-protons in the 1H NMR spectra. The reactivity of these protons on π-acidic surfaces is measured by hydrogen-deuterium (H-D) exchange for 11 different examples, excluding controls. The velocity of H-D exchange increases with π acidity (NDI core substituents: SO2R>SOR>H>OR>OR/NR2>SR>NR2). The H-D exchange kinetics vary with the structure of the enolate (malonates>methylmalonates, dilactones>dithiolactones). Moreover, they depend on the distance to the π surface (bridge length: 11-13 atoms). Most importantly, H-D exchange depends strongly on the chirality of the π surface (chiral sulfoxides as core substituents; the crystal structure of the enantiopure ( R, R, P)-macrocycle is reported). For maximal π acidity, transition-state stabilizations up to −18.8 kJ mol−1 are obtained for H-D exchange. The Brønsted acidity of the enols increases strongly with π acidity of the aromatic surface, the lowest measured p Ka=10.9 calculates to a Δp Ka=−5.5. Corresponding to the deprotonation of arginine residues in neutral water, considered as 'impossible' in biology, the found enolate-π interactions are very important. The strong dependence of enolate stabilization on the unprecedented seven-component π-acidity gradient over almost 1 eV demonstrates quantitatively that such important anion-π activities can be expected only from strong enough π acids. [ABSTRACT FROM AUTHOR]

The crystal structure of a malonate dilactone, placed on the π‐acidic surface of a naphthalenediimide with chiral sulfoxide acceptors in the core, is depicted on the cover. Such macrodilactones are essential to directly follow enolate–π interactions by NMR spectroscopy, also during deuterium exchange. This least interfering method is used to extract all there is to learn about the stabilization of enolate intermediates and transition states on π‐acidic aromatic surfaces. More information can be found in the Full Paper by S. Matile et al. on page 2648 ff. [ABSTRACT FROM AUTHOR]