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

Abstract

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 (SDO), charge (QO), or isotropic fermi contact couplings (IFCCO) of the O atom in the Fe═O part and (2) decreasing the spin density carried by the Fe atom (SDFe) or the HOMO–LUMO gap between a catalyst and reactant (LUMOC–HOMOR). The order of the correlation between the structure parameters and the reactivity is SDo > Qo > IFCCO ≈ SDFe ≈ LUMOC–HOMOR. 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.