Fluorination of benzene with disubstituted N-fluoropyridinium salts in acetonitrile solution: a DFT study

In this work, fluorination activities of disubstituted N-fluoropyridinium salts on the substrate of benzene in acetonitrile solution have been investigated by density functional theory. At SMD-B3LYP/6-311G(d,p) level, geometry optimizations and frequency calculations of the reactants, transition states and products were carried out in 16 fluorination reaction channels. A high level of SMD-M06-2x/6-311++G(d,p) was used to correct the single-point energy of the stationary points based on the optimized structure. On the basis of 2-nitro-substituted N-fluoropyridinium salt, nitro, cyano, chloro, methoxy groups were substituted, respectively, at 3-,4-,5-,6-position on pyridine ring to further clarify the influence of substituents and substitution sites on fluorination activity. According to the obtained potential energy surface information and substituent effect analysis, the fluorination channel of 2,6-dinitro-substituted N-fluoropyridinium salt is the most effective because of the lowest reaction energy barrier; as a result among the 16 studied N-fluoropyridinium salts, 2,6-dinitro-substituted N-fluoropyridinium salt is the most promising fluorinating reagent.