Regioselective Mono- and Dialkylation of [6,6]-open C60(CF2): Synthetic and Kinetic Aspects

Alkylation of homofullerene [6,6]-C-60(CF2)(2-) dianion with the set of alkyl halides, RX, was established to demonstrate an effect of RX nature on the conversion, product composition, and regioselectivity. The respective C-60(CF2)RH, C-60(CF2)R-2 and C-60(CF2)R'R'' compounds were obtained in the reaction with sterically unhindered RX, isolated by HPLC and unequivocally characterized. The kinetic studies evidenced S(N)2 mechanism for both alkylation steps, yielding mono- and dialkylated C-60(CF2), respectively, and indicated the negative charge localization at the bridgehead carbon atoms as well as a steric hindrance of the CF2 moiety likely to be a key factors for the S(N)2 reaction mechanism and observed regioselectivity. The significant difference in the rate constants of the first and the second steps is attributed to the different activation barriers predicted by DFT calculations which makes possible to develop synthetic methods for the regioselective preparation of monoalkylated C-60(CF2)RH and heterodialkylated C-60(CF2)R'R'' derivatives.