Structure–Reactivity Relationships of Metalloporphyrin Modified by Ionic Liquid and Its Analogue

The influence of ionic liquid (IL) modification on the reactivity of metalloporphyrins was carefully investigated to design a recoverable and highly effective metalloporphyrin catalyst. On the basis of the research, which included a total of 34 different catalysts, the following modification methods make metalloporphyrins more powerful: (1) increasing the spin density (SD_O), charge (Q_O), or isotropic fermi contact couplings (IFCC_O) of the O atom in the FeO part and (2) decreasing the spin density carried by the Fe atom (SD_Fe) or the HOMO–LUMO gap between a catalyst and reactant (LUMO_C–HOMO_R). The order of the correlation between the structure parameters and the reactivity is SD_o > Q_o > IFCC_O ≈ SD_Fe ≈ LUMO_C–HOMO_R. Compared with changing the cation of metalloporphyrins, changing the anion is a more effective way to increase the reactivity. The order is AlBr₄^– > AlCl₄^– > BCl₄^– > PF₆^– > AsF₆^– > SbF₆^– > BF₄^– > Tf₂N^– > AlF₄^– > HSO₄^– > CF₃SO₃^– > CF₃CO₂^– > Cl^–. However, the long distance between the IL part and the catalytic active center or electron-donating substituent on the N atom weaken the influence induced by the IL modification. These structure–reactivity relationships could be used in designing a catalyst.