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

The study of a novel EMF, U@C (s)(4)-C-82, reveals the remarkable chemical propertiesofactinide endohedral metallofullerenes (EMFs). The addition sites forboth nucleophilic (BH) and electrophilic (carbene) reactions of U@C (s)(4)-C-82 are unexpectedly locatedon adjacent carbon atoms far away from the metal, representing a rareexample of chemical reactivity control by means of the actinide-cageinteraction. Actinide endohedral metallofullerenes (EMFs) are a fullerenefamilythat possess unique actinide-carbon cage host-guestmolecular and electronic structures. In this work, a novel actinideEMF, U@C (s)(4)-C-82, was successfullysynthesized and characterized, and its chemical reactivity was investigated.Crystallographic analysis shows that U@C (s)(4)-C-82, a new isomer of U@C-82, has a C (s)(4)-C-82 cage, which has never beendiscovered in the form of empty or endohedral fullerenes. Its uniquechemical reactivities were further revealed through the Bingel-Hirschreaction and carbene addition reaction studies. The Bingel-Hirschreaction of U@C (s)(4)-C-82 showsexceptionally high selectivity and product yield, yielding only onemajor addition adduct. Moreover, the addition sites for both reactionsare unexpectedly located on adjacent carbon atoms far away from theactinide metal, despite the nucleophilic (Bingel-Hirsch) andelectrophilic (carbene addition) nature of either reactant. Densityfunctional theory (DFT) calculations suggest that this chemical behavior,unprecedented for EMFs, is directed by the unusually strong interactionbetween U and the sumanene motif of the carbon cage in U@C (s)(4)-C-82, which makes the energy increase whenit is disrupted. This work reveals remarkable chemical propertiesof actinide EMFs originating from their unique electronic structuresand highlights the key role of actinide-cage interactions inthe determination of their chemical behaviors.