Stepwise trifluoromethylation of C90(45) fullerene: a theoretical study

The trifluoromethylation of C90(45) fullerene was systematically studied using a stepwise CF3 addition approach. The thermodynamically stable C90(45)(CF3)2n isomers with 2n=2−20 were predicted for the first time at the B3LYP-D3BJ/6-311G* level of theory, in agreement with the experimentally characterised C90(45)(CF3)16/18. It was found that the stable isomers are predominantly formed by 1,4-additions of CF3 groups, and local structural characteristics strongly influence the stability of trifluoromethylated fullerene (TMF) isomers. The para additions to hexagons with strong local aromaticity and large strain, and the continuous para additions or isolated additions around the flatter hexagons with strong antiaromaticity lead to stable TMF isomers. For 2n>12, local aromatic fragments such as isolated C=C bonds and isolated hexagons are also formed to stabilise TMF isomers. Possible trifluoromethylation pathways of C90(45) were proposed based on the relative Gibbs free energies, indicating that the most stable C90(45)(CF3)2n isomers including the experimentally identified C90(45)(CF3)16/18 can be formed via direct CF3 additions. In addition, the hardness, electron affinity, and LUMO energy of stable C90(45)(CF3)2n isomers were also calculated.