Iron and manganese (III) porphyrin covalently bound to poly(acryloyl chloride) as biomimetic heterogeneous catalysts for alkene epoxidation by NaIO4: advantage of iron (III) porphyrin and significance of nitrogen donor axial ligands

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Poly(acrylic acid) (PAA) was converted to poly(acryloyl chloride) (PAC) by thionyl chloride and the prepared PAC was used as support for iron tetrakis(4-benzylamine)porphyrin (Fe(TBaminP)OAc). The Fe-porphyrin was covalently bound to the PAC to produce Fe(TBaminP)OAc@PAC as reusable heterogeneous catalysts for alkene epoxidation with sodium periodate (NaIO4). The newly synthesized Fe catalyst was characterized by FT-IR, EDX, SEM and TEM techniques. A similar procedure was followed for synthesis and characterization of Mn(TBaminP)OAc@PAC using Mn(TBaminP)OAc and PAC. The Fe and Mn content of the catalysts were measured by atomic absorption spectroscopy (AAS). We have found that among Mn(TBaminP)OAc, Fe(TBaminP)OAc (heterogeneous catalysts), Mn(TBaminP)OAc@PAC and Fe(TBaminP)OAc@PAC (homogenous catalysts) the later is the best catalyst for alkene epoxidation by NaIO4 in CH3CN/H2O. The epoxidation reactions are sensitive to the nature and concentration of nitrogen donor axial ligands (i.e., imidazole) and the activity of the catalysts and the epoxidation yields increased with using such ligands in the reaction mixture. The Fe(TBaminP)OAc@PAC was found to be a stable catalyst and can be recycled for at least four times without considerable loss of catalytic activity.