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Dense Integration of Stable Aromatic Radicals within the Two-Dimensional Interlayer Space of Clay Minerals via Clay-Catalyzed Deamination of Arylammoniums

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journal contribution
posted on 05.10.2020, 20:32 by Fuminao Kishimoto, Kyohei Hisano, Toru Wakihara, Tatsuya Okubo
Here, we have successfully demonstrated the dense integration of aryl radical cations within two-dimensional interlayer nanospace of abundant magnesium aluminosilicate clay minerals via spontaneous intercalation of the arylammoniums into the clays and a subsequent “clay-catalyzed deamination (CCD)” of the intercalated arylammoniums for aryl radical formation. Quantitative radical measurement reveals that every 1-anthrylammonium molecule intercalated into a Saponite clay converts to one 1-dihydrated anthracene radical cation via the CCD process. The current method realizes extremely dense integration of the anthracene radical cation in the interlayer space of magnesium aluminosilicate (∼190 μmol per 1 g of sample), which is nearly 100 times denser than the reported values of aromatic radical storage in aluminosilicate zeolites. We can also demonstrate the integration of pyrene radical cations and naphthalene radical cations with various substituent groups within the interlayer space of Saponite via the CCD, confirming that the CCD process enables to achieve the integration of arbitrary aryl radical cations. Since the interlayer radicals are protected by the precise layered structure of clay minerals, the radicals exhibit extremely high stability, e.g., the radicals did not degrade in ambient conditions for over 6 months. More surprisingly, around 90% radicals remained under harsh conditions (high temperature (80 °C) and UV light irradiation). Note that even with such high stability, in situ delamination of the layered clay minerals in solvent systems allows the aryl radical cations to be used in chemical reactions. It can be expected that such the ambivalence of the aryl radical species in nanocavities (high stability and on-demand reactivity) will exploit new reaction pathways where the radical species play a role of crucial intermediates, e.g., heterogeneous catalysis and radical polymerizations.