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 a… Show more
“…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).…”
mentioning
confidence: 86%
“…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.…”
mentioning
confidence: 99%
“…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.…”
mentioning
confidence: 99%
“…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.…”
The design, synthesis and evaluation of catalytic triads composed of a central C60 fullerene with an amine base on one side and polarizability enhancers on the other side are reported. According to an enolate addition benchmark reaction, fullerene–fullerene–amine triads display the highest selectivity in anion–π catalysis observed so far, whereas NDI–fullerene–amine triads are not much better than fullerene–amine controls (NDI=naphthalenediimide). These large differences in activity are in conflict with the small differences in intrinsic π acidity, that is, LUMO energy levels and π holes on the central fullerene. However, they are in agreement with the high polarizability of fullerene–fullerene–amine triads. Activation and deactivation of the fullerene‐centered triads by intercalators and computational data on anion binding further indicate that for functional relevance, intrinsic π acidity is less important than induced π acidity, that is, the size of the oriented macrodipole of polarizable π systems that emerges only in response to the interaction with anions and anionic transition states. The resulting transformation is thus self‐induced, the anionic intermediates and transition states create their own anion–π catalyst.
“…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).…”
mentioning
confidence: 86%
“…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.…”
mentioning
confidence: 99%
“…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.…”
mentioning
confidence: 99%
“…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.…”
The design, synthesis and evaluation of catalytic triads composed of a central C60 fullerene with an amine base on one side and polarizability enhancers on the other side are reported. According to an enolate addition benchmark reaction, fullerene–fullerene–amine triads display the highest selectivity in anion–π catalysis observed so far, whereas NDI–fullerene–amine triads are not much better than fullerene–amine controls (NDI=naphthalenediimide). These large differences in activity are in conflict with the small differences in intrinsic π acidity, that is, LUMO energy levels and π holes on the central fullerene. However, they are in agreement with the high polarizability of fullerene–fullerene–amine triads. Activation and deactivation of the fullerene‐centered triads by intercalators and computational data on anion binding further indicate that for functional relevance, intrinsic π acidity is less important than induced π acidity, that is, the size of the oriented macrodipole of polarizable π systems that emerges only in response to the interaction with anions and anionic transition states. The resulting transformation is thus self‐induced, the anionic intermediates and transition states create their own anion–π catalyst.
“…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.…”
Room-temperature phosphorescence (RTP) was realized for the first time in a polyoxometalate-based charge-transfer (CT) hybrid material bearing polyoxometalates (POMs) as electron-donors (D) and rigid naphthalene diimides (NDIs) as electron-acceptors (A), meanwhile, this hybrid material displayed photochromism as well. The significant D-A anion-π interaction induced an additional through-space charge-transfer pathway. The resulting suitable D-A CT states can efficiently bridge the relatively large energy gap between the NDI-localized π-π* and π-π* states and thus trigger the ligand-localized phosphorescence ( π-π*).
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