Reaction of C602− with Organic Halides Revisited in DMF: Proton Transfer from Water to RC60− and Unexpected Formation of 1,2-Dihydro[60]fullerenes

The reactions of dianionic C(60) with organic halides, which have been studied extensively in benzonitrile (PhCN), are revisited in a different solvent medium, N,N-dimethylformamide (DMF), by using ArCH(2)Br (Ar = Ph, C(6)H(4)CH(3), C(6)H(4)Br). Interestingly, instead of the 1,4-R(2)C(60) adducts, which are the typical products when the reactions are carried out in PhCN, the 1,2-dihydro[60]fullerenes (1,2-HRC(60)) have been obtained as the major products in DMF, except for the case of o-CH(3)C(6)H(4)CH(2)Br probably due to the steric effect. The obtained 1,2-dihydro[60]fullerenes have been characterized with single-crystal diffraction, (1)H and (13)C NMR, high-resolution mass spectrometry (HRMS), and UV-vis. Further examination with deuterated reagents including PhCD(2)Br, DMF-d(7), and D(2)O has revealed that the fullerenyl hydrogen of 1,2-dihydrofullerenes originates from traces of water residue in DMF. When the reaction is re-examined in PhCN with the addition of an excessive amount of water, the yield of 1,2-dihydrofullerene increases significantly, but is still lower compared with that obtained in DMF, demonstrating a considerable solvent effect on the reactivity of C(60)(2-). A possible mechanism accounting for such a difference is proposed. The work has presented an alternative protocol for effective preparation of 1,2-dihydro[60]fullerenes, and may also provide clues toward a better understanding of the proton transfer process for anionic C(60)-mediated reducing reactions involving H(2)O.