Anion-π interactions, the anionic counterparts to well-known cation-π interactions, have emerged as a novel and powerful tool in organic synthesis. These noncovalent forces enable the stabilization of anionic intermediates and transition states (TS) on π-acidic surfaces, laying the foundation for innovative catalytic strategies. This work explores their potential not only as a stabilizing interaction but as a dynamic catalytic tool that can be actively tuned using external stimuli.
Central to this approach is the concept of induced π-acidity—whereby a π-system becomes polarized in response to an approaching anionic TS. Multiwalled carbon nanotubes (MWCNTs), with their exceptional polarizability and extended π-networks, serve as ideal scaffolds for this purpose. Aromatic and alkyl-substituted epoxides undergo efficient cyclization in MWCNT suspensions, with reaction rates increasing proportionally to nanotube loading, confirming the catalytic role of induced anion-π interactions. Enhanced performance with pyrene-tagged epoxides underscores the importance of electronic communication between substrate and catalyst.
To further control reactivity, an oriented external electric field (OEEF) was applied to modulate MWCNT polarization. Using a microfluidic device with MWCNT-coated electrodes, we demonstrate reversible electric-field-driven catalysis: switching the field direction enabled or inhibited the conversion of pyrene epoxide to its product. This dynamic control of catalysis introduces the concept of electricity as a “smart reagent.”
To study the selectivity of epoxide cyclization under OEFF, a series of methylated epoxides were synthesized. These were designed to bias the reaction pathway toward either cation-π or anion-π catalysis, depending on field polarity and substrate structure. Results revealed that reaction mechanisms could be steered toward Baldwin or anti-Baldwin pathways by simply changing the field direction, unlocking new control over chemoselectivity under bulk conditions. Subtle changes in molecular design, such as the position of aromatic tags, further fine-tuned this selectivity.
Beyond external control, we investigated the intriguing autocatalytic behavior of epoxide cyclizations under anion-π catalysis. Two bulky epoxides displayed sigmoidal kinetics, with acceleration linked to product concentration. Attempts at asymmetric induction through chiral product co-catalysts were unsuccessful, pointing to a mechanism not reliant on close-range interactions. Experimental data and computational modeling supported a novel TS involving water-mediated long-range activation from product to substrate—an unprecedented mode of remote control in catalysis.
Together, these findings position anion-π interactions as a tunable, field-responsive platform for catalysis. The dual compatibility with both cation-π and anion-π mechanisms, electric-field-directed reactivity, and discovery of water-mediated autocatalysis point toward a new paradigm: catalysis that is not only selective and efficient, but also remotely programmable. This work opens exciting opportunities for scalable, smart catalysis in synthetic chemistry and beyond.
