Ion-Pair Breakers and Anionic Brønsted Acids for Helmholtz-Layer Catalysis with External Electric Fields in...

Area of Science:

• Organic Chemistry
• Physical Chemistry
• Materials Science

Background:

• Catalysis using externally applied electric fields (AEFs) is theoretically promising but challenging for organic synthesis.
• Previous work introduced catalytic Helmholtz layers in microfluidic capacitors to generate effective electric fields (EEFs) for catalysis.

Purpose of the Study:

• To identify fundamental principles for constructing catalytic Helmholtz layers.
• Focus on optimizing ion-pair separation and integrating functional motifs for enhanced catalytic activity and selectivity.

Main Methods:

• Utilized epoxide-opening polyether cascade cyclizations in apolar solvents as benchmark reactions.
• Investigated the nonlinear relationship between applied voltage (V) and reaction yield (Y) for tight ion pairs.
• Introduced anion-binding ion-pair breakers, such as Schreiner thioureas, to facilitate ion-pair separation.

Main Results:

• Nonlinear yield-voltage curves indicate the formation of catalytic Helmholtz layers above a critical voltage.
• Effective electric fields (EEFs) stabilize transition states, with catalysis assisted by EF-acidified anionic Brønsted acids.
• Ion-pair breakers successfully lowered critical voltage, increased maximal yields, and influenced reaction selectivity.

Conclusions:

• The study provides a mechanistic framework for voltage-gated electric-field catalysis (EFC).
• Demonstrated the potential of functionalized Helmholtz layers for practical, high-voltage organic synthesis.
• Highlights the importance of ion-pair separation and functional motif integration for EFC efficiency.