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

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journal contribution
posted on 22.01.2020, 20:21 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.