| Summary: | 碩士 === 國立中興大學 === 化學系所 === 106 === In this study, paramagnetic NMR spectroscopy, X-ray diffraction, magnetic susceptibility and DFT calculation are employed to elucidate the strong bonding interaction between iron(III) dx2-y2 and porphyrin a2u orbitals of [Fe(OMTPP∙)Cl]SbCl6 and [Fe(OETPP∙)Cl]SbCl6. Their crystal structures clearly indicate that their saddle deformations are increased compared to those prior to oxidations. Their 1H NMR data present the S = 2 states for such one-electron oxidation states, and demonstrate that their structures in solutions remain strong saddle deformations. In light of 1H NMR spectroscopy of [Fe(TPP∙)Cl]SbCl6 resembling to the above cases, we postulate that the ring structure of [Fe(TPP∙)Cl]+ may possess strongly saddle to have great bonding interaction between iron(III) dx2-y2 and porphyrin a2u orbitals. In the DFT calculations, the degrees of phenyl ring rotation and saddled deformation will also affect their NMR spectra.
In another topic, we observe O-O bond homolytic cleavage of (OETPP)FeIIIO(H)OtBu formed in the reaction of Fe(OETPP)ClO4 with TBHP and its activation parameters (ΔH≠ = 47(2) kJ mol-1, ΔS≠ = 83(9)J mol-1K-1) is measured by low-temperature UV-vis spectral data. The corresponding one-electron oxidation product is identified as [Fe(OETPP∙)OH]+, which is an isoelectronic structure as oxoiron(IV) porphyrin, by UV-vis, NMR spectroscopy and ESI-MS spectrometry. According to the experiments of NMR and ESI-MS, we also find that ·OtBu radical will convert Fe(OETPP)ClO4 to [Fe(OETPP∙)OtBu]+. Furthermore, these related iron(III) porphyrin radical cations can be carried out one more electron oxidation to isoporphyrins, an isoelectronic structure as Compound I. These iron(III) saddled isoporphyrins are shown to be reactive for highly selective chlorination of cyclohexene.
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