Nonheme Oxoiron(IV) Complexes of Tris(2-pyridylmethyl)amine with cis-Monoanionic Ligands
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- 作者：Jan-Uwe Rohde ; Audria Stubna ; Emile L. Bominaar ; Eckard Mü ; nck ; Wonwoo Nam ; Lawrence Que ; Jr.
- 刊名：Inorganic Chemistry
- 出版年：2006
- 出版时间：August 7, 2006
- 年：2006
- 卷：45
- 期：16
- 页码：6435 - 6445
- 全文大小：219K
- 年卷期：v.45,no.16(August 7, 2006)
- ISSN：1520-510X
文摘
Treatment of [FeIV(O)(TPA)(NCMe)](CF3SO3)2 [TPA, N,N,N-tris(2-pyridylmethyl)amine] with 3 equiv of NR4X (X =CF3CO2, Cl, or Br) in MeCN at -40 
C affords a series of metastable [FeIV(O)(TPA)(X)]+ complexes. Somecharacteristic features of the S = 1 oxoiron(IV) unit are quite insensitive to the ligand substitution in the equatorialplane, namely, the Fe-O distances (1.65-1.66 Å), the energy (~7114.5 eV) and intensity [25(2) units] of the1s-to-3d transition in the X-ray absorption spectra, and the Mössbauer isomer shifts (0.01-0.06 mm·s-1) andquadrupole splittings (0.92-0.95 mm·s-1). The coordination of the anionic X ligand, however, is evidenced by redshifts of the characteristic near-IR ligand-field bands (720-800 nm) and spectroscopic observation of the boundanion by 19F NMR for X = CF3CO2 and by EXAFS analysis for X = Cl (rFe-Cl = 2.29 Å) and Br (rFe-Br = 2.43Å). Density functional theory calculations yield Mössbauer parameters and bond lengths in good agreement withthe experimental data and produce excited-state energies that follow the trend observed in the ligand-field bands.Despite mitigating the high effective charge of the iron(IV) center, the substitution of the MeCN ligand with monoanionicligands X- decreases the thermal stability of [FeIV(O)(TPA)]2+ complexes. These anion-substituted complexes modelthe cis-X-FeIV=O units proposed in the mechanisms of oxygen-activating nonheme iron enzymes.
C affords a series of metastable [FeIV(O)(TPA)(X)]+ complexes. Somecharacteristic features of the S = 1 oxoiron(IV) unit are quite insensitive to the ligand substitution in the equatorialplane, namely, the Fe-O distances (1.65-1.66 Å), the energy (~7114.5 eV) and intensity [25(2) units] of the1s-to-3d transition in the X-ray absorption spectra, and the Mössbauer isomer shifts (0.01-0.06 mm·s-1) andquadrupole splittings (0.92-0.95 mm·s-1). The coordination of the anionic X ligand, however, is evidenced by redshifts of the characteristic near-IR ligand-field bands (720-800 nm) and spectroscopic observation of the boundanion by 19F NMR for X = CF3CO2 and by EXAFS analysis for X = Cl (rFe-Cl = 2.29 Å) and Br (rFe-Br = 2.43Å). Density functional theory calculations yield Mössbauer parameters and bond lengths in good agreement withthe experimental data and produce excited-state energies that follow the trend observed in the ligand-field bands.Despite mitigating the high effective charge of the iron(IV) center, the substitution of the MeCN ligand with monoanionicligands X- decreases the thermal stability of [FeIV(O)(TPA)]2+ complexes. These anion-substituted complexes modelthe cis-X-FeIV=O units proposed in the mechanisms of oxygen-activating nonheme iron enzymes.