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

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journal contribution
posted on 22.01.2020 by Rebecca L. Spicer, Athanasios D. Stergiou, Tom A. Young, Fernanda Duarte, Mark D. Symes, Paul J. Lusby
Modifying the reactivity of substrates by encapsulation is a fundamental principle of capsule catalysis. Here we show an alternative strategy, wherein catalytic activation of otherwise inactive quinone “co-factors” by a simple Pd2L4 capsule promotes a range of bulk-phase, radical-cation cycloadditions. Solution electron-transfer experiments and cyclic voltammetry show that the cage anodically shifts the redox potential of the encapsulated quinone by a significant 1 V. Moreover, the capsule also protects the reduced semiquinone from protonation, thus transforming the role of quinones from stoichiometric oxidants into catalytic single-electron acceptors. We envisage that the host–guest-induced release of an “electron hole” will translate to various forms of non-encapsulated catalysis that involve other difficult-to-handle, highly reactive species.