Derivatization of fullerene dimer C120 by the Bingel reaction and a 3He NMR study of 3He@C120 monoadducts

Cyclopropanation with diethyl bromomalonate and base (the Bingel reaction) was conducted on fullerene dimer C-120 to give a mixture of "monoadducts" (45% yield) and "bisadducts" (less than or equal to 37% yield), while 18% of the C-120 remained unchanged. The "monoadducts" were separated into five positional isomers, i.e., e(face), e(edge), trans-4, trans-3, and trans-2, by preparative HPLC. Assignments were made based on H-1 (and C-13) NMR and confirmed by theoretical calculations of the addends' H-1 NMR chen-deal shifts. The relative yields of these isomers were in fair agreement with those observed for the Bingel bisaddition of C-60. The Bingel reaction was also carried out on the dimer C-120 encapsulating He-3 in one of the C-60 cages. Each positional isomer of the "monoadduct" exhibited a pair of He-3 NMR signals corresponding to an isomer with functionalization on the He-3-containing cage and the other isomer with functionalization on the empty cage. Using the He-3 NMR spectroscopy, a pair of signals for the trans-1 isomer, which eluded detection by H-1 NMR, were observed, in addition to pairs of signals for e(face), e(edge), trans-4, trans-3, and trans-2 isomers. The He-3 NMR signals for isomers with functionalization on the He-3-containing cage were spread out over a 1.82-ppm range reflecting the direct effects of the addition pattern on the C-60 Surface. In contrast, the isomers with functionalization on the empty cage exhibited He-3 NMR signals that appeared over a 0.14-ppm range, which was shown to be primarily due to changes in the diamagnetism of the functionalized cage based on theoretical calculations of He-3 NMR chemical shifts for the model system in which the C-60 cage encapsulating He-3 was removed.