Host-Guest-Induced Electron Transfer Triggers Radical-Cation Catalysis

Area of Science:

• Supramolecular Chemistry
• Catalysis
• Organic Synthesis

Background:

• Encapsulation is a known method to modify substrate reactivity in catalysis.
• Quinones are typically stoichiometric oxidants and can be challenging to handle due to reactivity.

Purpose of the Study:

• To explore an alternative catalytic strategy using a supramolecular capsule to activate quinones.
• To enable bulk-phase radical-cation cycloadditions using catalytic amounts of quinones.

Main Methods:

• Utilized a simple palladium (Pd₂L₄) capsule for host-guest complexation.
• Employed solution electron-transfer experiments and cyclic voltammetry to study redox potentials.
• Investigated the protection of reduced quinone species within the capsule.

Main Results:

• The Pd₂L₄ capsule catalytically activated otherwise inactive quinones.
• The capsule shifted the quinone redox potential anodically by 1 V.
• The capsule protected the reduced semiquinone from protonation, enabling catalytic turnover.

Conclusions:

• A Pd₂L₄ capsule can transform quinones into catalytic single-electron acceptors.
• This host-guest-induced electron hole release offers a new strategy for catalysis.
• The approach may be applicable to other reactive species in non-encapsulated catalysis.