Synthesis and Regiochemistry of [60]Fullerenyl 2-Methylmalonate Bisadducts and their Facile Electron-Accepting Properties

A simple one-pot reaction using in situ chemically generated Na-naphthalenide as an electron reductant in the preferential generation of C602− is described. Trapping of C602− intermediate with 2 molar equiv of sterically hindered 2-bromo-2-methylmalonate ester afforded two singly bonded fullerenyl bisadducts C60[-CMe(CO2Et)2]2 in 35% and 7% yield, respectively. The regiochemistry of these two products was determined to be 1,4- and 1,16-bisadducts, respectively, by NMR, UV−vis−NIR, LCMS, and X-ray single crystal structural analysis. The minor 1,16-bisadduct 2 exhibits long wavelength absorption bands in the near-IR region and prominent electron-accepting characteristics as compared with those of the major 1,4-bisadduct and pristine C60. As revealed by DFT calculation, we propose that the origin of these unusual characters of 2 arises from the moiety of [18π]-trannulene, in close resemblance to that of the highly symmetrical emerald green 1,16,29,38,43,60-hexaadduct of C60, EF-6MCn. Accordingly, we anticipate a fast progressive formation of plausible 1,16-bisadduct-like intermediate moieties on a C60 cage as the precursor structure leading to the formation of EF-6MCn, by taking the corresponding regiochemistry and electronic properties into account.