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) approximate to SD(Fe) approximate to 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 AlBr(4)(-) > AlCl(4)(-) > BCl(4)(-) > PF(6)(-) > AsF(6)(-) > SbF(6)(-) > BF(4)(-) > Tf(2)N(-) > AlF(4)(-) > HSO(4)(-) > CF(3)SO(3)(-) > CF(3)CO(2)(-) > Cl(-). However, the long distance between the IL part and the :atalytic 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.