U@C_s(4)-C₈₂: A Different Cage Isomer with Reactivity Controlled by U-Sumanene Interaction

Abstract

Actinide endohedral metallofullerenes (EMFs) are a fullerene family that possess unique actinide–carbon cage host–guest molecular and electronic structures. In this work, a novel actinide EMF, U@C s(4)-C82, was successfully synthesized and characterized, and its chemical reactivity was investigated. Crystallographic analysis shows that U@C s(4)-C82, a new isomer of U@C82, has a C s(4)-C82 cage, which has never been discovered in the form of empty or endohedral fullerenes. Its unique chemical reactivities were further revealed through the Bingel–Hirsch reaction and carbene addition reaction studies. The Bingel–Hirsch reaction of U@C s(4)-C82 shows exceptionally high selectivity and product yield, yielding only one major addition adduct. Moreover, the addition sites for both reactions are unexpectedly located on adjacent carbon atoms far away from the actinide metal, despite the nucleophilic (Bingel–Hirsch) and electrophilic (carbene addition) nature of either reactant. Density functional theory (DFT) calculations suggest that this chemical behavior, unprecedented for EMFs, is directed by the unusually strong interaction between U and the sumanene motif of the carbon cage in U@C s(4)-C82, which makes the energy increase when it is disrupted. This work reveals remarkable chemical properties of actinide EMFs originating from their unique electronic structures and highlights the key role of actinide–cage interactions in the determination of their chemical behaviors.

The smallest endohedral borafullerene: structural isomerization, electronic properties, aromaticity and reactivity of U@C27B

“…S11†). Notably, our calculations reveal that U@C 27 B features much stronger metal–cage covalency than all 13 monometallic U@C 2 n (2 n = 74–86) characterized by X-ray diffraction thus far 9–14 due to its smallest cage size and large U-cage orbital overlaps (Fig. 8b and S12†).…”

“…Actinide-based EMFs thus exhibit novel electronic structures, intriguing bonding patterns and strong metal–cage coordination interactions rather different from other types of EMFs. 6 Significantly, a series of U-based mono-EMFs, 9–14 di-EMFs 15 and clusterfullerenes 16–23 have been successfully synthesized and characterized as single crystals in recent years. The studies on actinide-based EMFs greatly update the knowledge of cluster science, chemical bonding and coordination chemistry.…”

Th@C2(14)-C86 and Th@C3(18)-C86: two missing C86 isomers stabilized by the encapsulation of thorium

“…10–12 Thus, previous studies suggest that the ionic model often used to predict the most stable structures of EMFs is likely not applicable to some actinide mono-EMFs. In addition, some previously unknown fullerene cage isomers were obtained in the form of actinide mono-EMFs, such as M@ C 1 (17 418)-C 76 , 12,13 M@ C 1 (28 324)-C 80 , 12 U@ C s (4)-C 82 , 14 and U@ D 2 (21)-C 84 . 15…”