Academic literature on the topic 'Oxoiron(IV)porphyrin cation-radical'

博士
國立中興大學
化學系所
103
In the first study of my thesis, we study the electronic structures and orbital interactions between iron d orbitals and porphyrin HOMOs for two kinds of iron porphyrins with respect to planar structure and saddled deformation by means of paramagnetic NMR and DFT (Density Functional Theory) calculation. In 2003, Prof. Ru-Jen Cheng had first demonstrated the orbital interaction between metal dz2 and porphyrin a2u orbital in planar high-spin iron(III) porphyrins, and this dz2-a2u interaction is determined by the symmetry of iron porphyrins, to which many iron d and porphyrin frontier orbitals are similar. The concept of “symmetry switch” are thus raised and it can be examined by combining DFT calculations with paramagnetic NMR spectroscopy, which had been known a significant tool for paramagnetic iron porphyrins. For the analysis of Fe(OETPP)ClO4, the interaction between iron dx2-y2 and porphyrin a2u become symmetric allowed due to descending symmetry to C2v. Although dz2-a2u interaction still exists, the strength of dx2-y2-a2u interaction is greatly superior to dz2-a2u interaction. This critical change of orbital interaction leads to dramatic NMR property changes in between planar and saddled five-coordinate intermediate-spin iron(III) porphyrin complexes. In the second topic, we further discuss the electronic structure composed of iron(III) porphyrin cation radical with exchange interaction between high-spin iron ion (S = 5/2) and porphyrin radical (S = 1/2). In the early literatures, the ferromagnetic (S = 3) and antiferromagnetic (S = 2) coupling interaction had been attributed to different orbital interaction between iron d orbital and porphyrin a2u orbital with different symmetry for planar porphyrins, Fe(TPP‧)(ClO4)2 and [Fe(TPP‧)Cl]SbCl6. The main evidence is based on their opposite pattern with respect to 1H NMR chemical shifts of phenyl-H signals, indicating considerable spin density with alternative directions localized at meso-carbon, which is the primary atom in a2u HOMO orbital. However, as for antiferromagnetic case, it is originally reharded as direct spin flip from ferromagnetic coupling, in which none or very weak spacial overlap occurs between iron dx2-y2 and a2u orbital. Attempt to elucidate the detailed bonding interaction, a highly saddle-deformed OETPP was employed in this study. With comparing the X-ray structures of Fe(OETPP)Cl and its one-electron oxidized product, [Fe(OETPP‧)Cl]SbCl6, they exhibit similar structural characteristics in their iron cores. Bonding analyses from DFT calculations suggest that the overlap between iron dx2-y2 and a2u orbital not only essentially exist in Fe(OETPP)Cl, but also in [Fe(OETPP‧)Cl]SbCl6, in which this orbital overlap behaves as a strong bond formation. This result indicates that the one-electron oxidation occur at metal-porphyrin hybrid molecular orbital rather than only at a2u. However, the spin localized property in 1H NMR spectrum shall result from spin polarization of a paired electrons at the bonding orbital composed of iron dx2-y2 and porphyrin a2u orbitals by the rest unpaired electrons resided in d orbitals (dxy, dxz,yz, and dz2), respectively. For the third topic, we focus on research of Compound I (Cpd I), which denoted to iron(IV)-oxo protein-bounded porphyrin radical cation, the key intermediate of cytochrome P450 or peroxidase. Planar Fe(TMP)Cl and saddled Fe(OETp-XPP)Cl (X = H, CH3) were employed to discuss the structural effect of porphyrin ring in the formations of Cpd I models. When 1.5 equiv. of mCPBA is used, planar Fe(TMP)Cl was directly removed two electrons to form [FeIV=O(TMP‧)]+ at -80 oC, however, by contrast, one-electron oxidized intermediate of Fe(OETPP)Cl was only detected by NMR and UV-vis in the same reaction condition. Until warming the reaction to room temperature, a Cpd I-like signal was obtained. According to its alternative 1H NMR chemical shifts of phenyl-H signals and EPR data (g = 4, S = 3/2), the new species could be [FeIV=O(OETPP‧)]+ with antiferromagnetic interaction composed of the high-spin iron(IV) center (S = 2) and porphyrin a2u radical (S = 1/2). This state different from planar [FeIV=O(TMP‧)]+, indicating the ring deformation indeed induces the change of electronic state of Cpd I. This result may further alter its catalytic activity. The catalytic study of the saddled Cpd I model are still in progresses in our laboratory.