Selective Functionalization on [60]Fullerene Governed by Tether Length

Abstract

In order to accomplish the selective synthesis of [60]fullerene bisadducts, the reactions of [60]fullerene with compounds in which two α,α‘-dibromo-o-xylene moieties were connected by an oligomethylene chain (n = 2−5) were investigated. By this method, only two isomers (cis-2- and cis-3-isomers) were selectively obtained when n = 2 and 3, while another isomer (e-isomer) was obtained when n = 5. When n = 4, a complex mixture of bisadducts was formed and has not been separated so far. cis-2-Bisadducts have been, for the first time, selectively obtained in the fullerene chemistry. The structures of bisadducts were determined on the basis of 1H, 13C NMR, IR, UV−vis, and mass spectroscopies. According to the NMR experiments, the symmetries of cis-2-, cis-3-, and e-isomers were concluded to be Cs, C2, and C1, respectively. Chiral cis-3- and e-bisadducts were successfully resolved into the respective enantiomers on a chiral HPLC column, although cis-2-bisadducts only gave a single peak. The UV−vis spectra of cis-2-, cis-3-, and e-bisadducts were remarkably different from one another. Specifically, the e-bisadducts showed a characteristic absorption peak around 420 nm. The cleavage of the oligomethylene chain produced the corresponding [60]fullerene derivatives possessing two phenol moieties. These compounds are applicable to further functionalization.