title: Regioselective benzyl radical addition to an open-shell cluster metallofullerene. Crystallographic studies of cocrystallized Sc3C2@Ih-C80 and its singly bonded derivative.
abstract: The endohedral fullerene once erroneously identified as Sc3@C82 was recently shown to be Sc3C2@Ih-C80, the first example of an open-shell cluster metallofullerene. We herein report that benzyl bromide (1) reacts with Sc3C2@ Ih-C80 via a regioselective radical addition that affords only one isomer of the adduct Sc3C2@Ih-C80(CH2C6H5) (2) in high yield. An X-ray crystallographic study of 2 demonstrated that the benzyl moiety is singly bonded to the fullerene cage, which eliminates the paramagnetism of the endohedral in agreement with the ESR results. Interestingly, X-ray results further reveal that the 3-fold disordered Sc3C2 cluster adopts two different configurations inside the cage. These configurations represent the so-called "planar" form and the computationally predicted, but not crystallographically characterized, "trifoliate" form. It is noteworthy that this is the first crystallographic observation of the "trifoliate" form for the Sc3C2 cluster. In contrast, crystallographic investigation of a Sc3C2@Ih-C80/Ni(OEP) cocrystal, in which the endohedral persists in an open-shell structure with paramagnetism, indicates that only the former form occurs in pristine Sc3C2@ Ih-C80. These results demonstrate that the cluster configuration in EMFs is highly sensitive to the electronic structure, which is tunable by exohedral modification. In addition, the electrochemical behavior of Sc3C2@Ih-C80 has been markedly changed by the radical addition, but the absorption spectra of the pristine and the derivative are both featureless. These results suggest that the unpaired electron of Sc3C2@Ih-C80 is buried in the Sc3C2 cluster and does not affect the electronic configuration of the cage.
authors.affiliation: State Key Laboratory of Materials Processing and Die & Mold Technology, School of Materials Science and Engineering, Huazhong University of Science and Technology (HUST) , Wuhan, 430074, China.
authors.forename: Hongyun
authors.initials: H
authors.lastname: Fang
authors.forename: Hailin
authors.initials: H
authors.lastname: Cong
authors.forename: Mitsuaki
authors.initials: M
authors.lastname: Suzuki
authors.forename: Lipiao
authors.initials: L
authors.lastname: Bao
authors.forename: Bing
authors.initials: B
authors.lastname: Yu
authors.forename: Yunpeng
authors.initials: Y
authors.lastname: Xie
authors.forename: Naomi
authors.initials: N
authors.lastname: Mizorogi
authors.forename: Marilyn M
authors.initials: MM
authors.lastname: Olmstead
authors.forename: Alan L
authors.initials: AL
authors.lastname: Balch
authors.forename: Shigeru
authors.initials: S
authors.lastname: Nagase
authors.forename: Takeshi
authors.initials: T
authors.lastname: Akasaka
authors.forename: Xing
authors.initials: X
authors.lastname: Lu
mesh_terms: D001593:Benzyl Compounds / Q000737:chemistry*; D018360:Crystallography, X-Ray; D037741:Fullerenes / Q000737:chemistry*; D008958:Models, Molecular; D015394:Molecular Structure; D009942:Organometallic Compounds / Q000138:chemical synthesis* / Q000737:chemistry; D012538:Scandium / Q000737:chemistry*; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization
chemical_list: D001593:Benzyl Compounds; D037741:Fullerenes; D009942:Organometallic Compounds; C038682:benzyl bromide; D012538:Scandium