Benzyne Adds Across a Closed 5−6 Ring Fusion in C70: Evidence for Bond Delocalization in Fullerenes
journal contributionposted on 1998-02-26, 00:00 authored by Mark S. Meier, Guan-Wu Wang, Robert C. Haddon, Carolyn Pratt Brock, Michael A. Lloyd, John P. Selegue
Addition of benzyne to C70 results in four isomeric monoadducts (compounds 1a−d) in a 42:35:13:10 ratio as determined by 1H NMR. These compounds were separated by repeated passes through HPLC columns. The major isomer (1a) resulted from addition to the highly pyramidalized C1−C2 bond as shown by 13C NMR and UV/vis spectroscopy. The structure of the C1−C2 adduct (1a) was confirmed by X-ray crystallography. The second isomer (1b) was assigned as an adduct to the C5−C6 bond on the basis of 13C NMR and UV/vis spectroscopy. Compound 1c exhibited a 13C spectrum consistent with an adduct to the C7 and C8 positions. The presence of sp3 13C NMR resonances proved that the C7−C8 bond is still intact, making this the first identification of direct addition to a 5−6 ring fusion in a fullerene, and the first example of an adduct to a 5−6 ring fusion where the ring fusion bond remains intact. The fourth isomer (1d) displayed spectral data consistent with a compound with C1 symmetry and is assigned as an adduct to the C7−C21 bond.