Electric-Field-Assisted Anion−π Catalysis

Abstract

This report focuses on the remote control of anion-π catalysis by electric fields. We have synthesized and immobilized anion-π catalysts to explore the addition reaction of malonic acid half thioesters to enolate acceptors on conductive indium tin oxide surfaces. Exposed to increasing electric fields, anion-π catalysts show an increase in activity and an inversion of selectivity. These changes originate from a more than 100-fold rate enhancement of the disfavored enolate addition reaction that coincides with an increase in selectivity of transition-state recognition by up to -14.8 kJ mol. The addition of nitrate with strong π affinity nullified (IC = 2.2 mM) the responsiveness of anion-π catalysts to electric fields. These results support that the polarization of the π-acidic naphthalenediimide surface in anion-π catalysts with electric fields increases the recognition of anionic intermediates and transition states on this polarized π surface, that is, the existence and relevance of electric-field-assisted anion-π catalysis.

Remote Control of Anion–π Catalysis on Fullerene‐Centered Catalytic Triads

“…This activity is outstanding not only in the context of this work, it is a new record for anion–π interactions in organocatalysis (excluding anion–π enzymes) 3, 4, 5, 7. The activity found for triad 1 exceeded expectations from the lowering LUMO levels of fullerenes from 6 to 2 and 1 clearly (Figures 3 e,f) and disagreed with predictions based on π holes on the central fullerene (Figures 3 e,g).…”

“…Their comparable relevance is generally recognized only if the interactions are too strong and continue into either nucleophilic and electrophilic aromatic substitutions or the generation of radical anions and cations, respectively. Whereas the exact nature of anion–π interactions is still under debate, intrinsic π acidity, that is, low‐lying LUMO energies, π holes (areas with positive molecular electrostatic potential (MEP), Figures 1 a,b), positive quadrupole moments perpendicular to the aromatic plane or in‐plane dipoles from electron‐withdrawing substituents, have received much attention, resulting in much interest in small, compact π surfaces such as, for instance, in hexafluorobenzene or naphthalenediimides (NDIs) 1, 3, 4, 5. Despite much encouragement from pioneering theoretical studies,6 induced anion–π interactions have been largely ignored in practice.…”

“…Despite much encouragement from pioneering theoretical studies,6 induced anion–π interactions have been largely ignored in practice. However, very recent results from anion–π catalysis, that is, the stabilization of anionic transition states on aromatic surfaces,3 revealed that activities increase in response to electric fields,4 with increasing length of π‐stacked foldamers,5 and on fullerenes 7. The discovery of anion–π catalysis on fullerenes was of particular interest because this most popular carbon allotrope8 has received little attention with regard to both anion–π interactions9 and catalysis 10.…”

“…The addition of malonic acid half thioester (MAHT) 17 to nitroolefin 18 was selected to probe anion–π catalysis with triads 1 – 5 (Figure 3 a) 3, 4, 5. This transformation has emerged as the benchmark reaction.…”

Anion–π Interaction‐Induced Room‐Temperature Phosphorescence of a Polyoxometalate‐Based Charge‐Transfer Hybrid Material

“…However, to the best of our knowledge,R TP has never been achieved with polyoxometalate-based hybrid materials so far,w hich commonlye xhibit novel or enhanced properties, such as gas storage, heterogeneous catalysis, and chemical separations. [8] However,i ti se xtremely rare to utilize unorthodox anion-p interactions, which have versatile uses in anion/molecule recognition, [9] ion/electron transport, [10] and anion-p catalysis, [11] to construct photoluminescent materials. In these molecular systems( co-crystals, mixed crystals,e tc.…”