title: Diels-Alder reaction on free C₆₈ fullerene and endohedral Sc₃N@C₆₈ fullerene violating the isolated pentagon rule: importance of pentagon adjacency.
abstract: The reaction mechanism and regioselectivity of the Diels-Alder reactions of C68 and Sc3N@C68, which violate the isolated pentagon rule, were studied with density functional theory calculations. For C68, the [5,5] bond is the most favored thermodynamically, whereas the cycloaddition on the [5,6] bond has the lowest activation energy. Upon encapsulation of the metallic cluster, the exohedral reactivity of Sc3N@C68 is reduced remarkably owing to charge transfer from the cluster to the fullerene cage. The [5,5] bond becomes the most reactive site thermodynamically and kinetically. The bonds around the pentagon adjacency show the highest chemical reactivity, which demonstrates the importance of pentagon adjacency. Furthermore, the viability of Diels-Alder cycloadditions of several dienes and Sc3N@C68 was examined theoretically. o-Quinodimethane is predicted to react with Sc3N@C68 easily, which implies the possibility of using Diels-Alder cycloaddition to functionalize Sc3N@C68.
authors.affiliation: Institute for Chemical Physics & Department of Chemistry, Xi'an Jiaotong University, Xi'an 710049 (China), Fax: (+86) 29-8266-8559.
authors.forename: Tao
authors.initials: T
authors.lastname: Yang
authors.forename: Xiang
authors.initials: X
authors.lastname: Zhao
authors.forename: Shigeru
authors.initials: S
authors.lastname: Nagase
authors.forename: Takeshi
authors.initials: T
authors.lastname: Akasaka
keywords: cycloaddition; density functional calculations; fullerenes; reaction mechanisms; regioselectivity