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

• Published in: Journal of the American Chemical Society Vol. 142; no. 5; pp. 2134 - 2139
• Main Authors: Spicer, Rebecca L, Stergiou, Athanasios D, Young, Tom A, Duarte, Fernanda, Symes, Mark D, Lusby, Paul J
• Format: Journal Article
• Language: English
• Published: WASHINGTON American Chemical Society 05.02.2020; Amer Chemical Soc
• Subjects: catalytic activity; Chemistry; Chemistry, Multidisciplinary; cycloaddition reactions; electron transfer; encapsulation; oxidants; Physical Sciences; protonation; quinones; redox potential; Science & Technology; stoichiometry; voltammetry; ACCELERATION; COMPLEX; TURNOVER; CAGE; DIELS-ALDER REACTIONS; CYCLOADDITIONS; STRATEGY; SUPRAMOLECULAR CATALYSIS; VALENCE
• ISSN: 0002-7863; 1520-5126; 1520-5126
• DOI: 10.1021/jacs.9b11273

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.