Rohde Jan-Uwe, Stubna Audria, Bominaar Emile L, Münck Eckard, Nam Wonwoo, Que Lawrence
Department of Chemistry and Center for Metals in Biocatalysis, University of Minnesota, Minneapolis, MN 55455, USA.
Inorg Chem. 2006 Aug 7;45(16):6435-45. doi: 10.1021/ic060740u.
Treatment of Fe(IV)(O)(TPA)(NCMe)2 [TPA, N,N,N-tris(2-pyridylmethyl)amine] with 3 equiv of NR4X (X = CF3CO2, Cl, or Br) in MeCN at -40 degrees C affords a series of metastable [Fe(IV)(O)(TPA)(X)]+ complexes. Some characteristic features of the S = 1 oxoiron(IV) unit are quite insensitive to the ligand substitution in the equatorial plane, namely, the Fe-O distances (1.65-1.66 A), the energy ( approximately 7114.5 eV) and intensity [25(2) units] of the 1s-to-3d transition in the X-ray absorption spectra, and the Mössbauer isomer shifts (0.01-0.06 mm.s(-1)) and quadrupole splittings (0.92-0.95 mm.s(-1)). The coordination of the anionic X ligand, however, is evidenced by red shifts of the characteristic near-IR ligand-field bands (720-800 nm) and spectroscopic observation of the bound anion by (19)F NMR for X = CF3CO2 and by EXAFS analysis for X = Cl (r(Fe-Cl) = 2.29 A) and Br (r(Fe-Br) = 2.43 A). Density functional theory calculations yield Mössbauer parameters and bond lengths in good agreement with the 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 monoanionic ligands X- decreases the thermal stability of [Fe(IV)(O)(TPA)]2+ complexes. These anion-substituted complexes model the cis-X-Fe(IV)=O units proposed in the mechanisms of oxygen-activating nonheme iron enzymes.
在-40℃下，将Fe(IV)(O)(TPA)(NCMe)2 [TPA，N,N,N-三(2-吡啶甲基)胺]与3当量的NR4X（X = CF3CO2、Cl或Br）在乙腈中反应，得到一系列亚稳的[Fe(IV)(O)(TPA)(X)]+配合物。S = 1的氧合铁(IV)单元的一些特征对赤道平面上的配体取代相当不敏感，即铁-氧距离（1.65 - 1.66 Å）、X射线吸收光谱中1s到3d跃迁的能量（约7114.5 eV）和强度[25(2)单位]，以及穆斯堡尔同质异能位移（0.01 - 0.06 mm·s(-1)）和四极分裂（0.92 - 0.95 mm·s(-1)）。然而，阴离子X配体的配位通过特征近红外配体场带（720 - 800 nm）的红移以及对于X = CF3CO2通过(19)F NMR对结合阴离子的光谱观察，以及对于X = Cl（r(Fe-Cl) = 2.29 Å）和Br（r(Fe-Br) = 2.43 Å）通过扩展X射线吸收精细结构分析得以证明。密度泛函理论计算得出的穆斯堡尔参数和键长与实验数据吻合良好，并产生与配体场带中观察到的趋势一致的激发态能量。尽管减轻了铁(IV)中心的高有效电荷，但用单阴离子配体X-取代乙腈配体降低了[Fe(IV)(O)(TPA)]2+配合物的热稳定性。这些阴离子取代的配合物模拟了氧活化非血红素铁酶机制中提出的顺式-X-Fe(IV)=O单元。
