Magnetic circular dichroism and computational study of mononuclear and dinuclear iron(IV) complexes

被引:27
作者
Ye, Shengfa [1 ]
Xue, Genqiang [2 ]
Krivokapic, Itana [1 ]
Petrenko, Taras [1 ]
Bill, Eckhard [1 ]
Que, Lawrence, Jr. [2 ]
Neese, Frank [1 ]
机构
[1] Max Planck Inst Chem Energiekonvers, D-45470 Mulheim, Germany
[2] Univ Minnesota, Ctr Met Biocatalysis, Dept Chem, Minneapolis, MN 55455 USA
基金
美国国家卫生研究院;
关键词
C-H BOND; DENSITY-FUNCTIONAL THEORY; MATRIX RENORMALIZATION-GROUP; GAUSSIAN-BASIS SETS; ELECTRONIC-STRUCTURE; METHANE MONOOXYGENASE; DIOXYGEN ACTIVATION; TRANSITION-METAL; DIAMOND CORE; ACTIVE-SITE;
D O I
10.1039/c4sc03268c
中图分类号
O6 [化学];
学科分类号
0703 ;
摘要
High-valent iron(IV)-oxo species are key intermediates in the catalytic cycles of a range of O-2-activating iron enzymes. This work presents a detailed study of the electronic structures of mononuclear ([Fe-IV(O)(L)(NCMe)](2+), 1, L = tris(3,5-dimethyl-4-methoxylpyridyl-2-methyl)amine) and dinuclear ([(L) Fe-IV(O)(mu-O) Fe-IV(OH)(L)](3+), 2) iron(IV) complexes using absorption (ABS), magnetic circular dichroism (MCD) spectroscopy and wave-function-based quantum chemical calculations. For complex 1, the experimental MCD spectra at 2-10 K are dominated by a broad positive band between 12 000 and 18 000 cm(-1). As the temperature increases up to similar to 20 K, this feature is gradually replaced by a derivative-shaped signal. The computed MCD spectra are in excellent agreement with experiment, which reproduce not only the excitation energies and the MCD signs of key transitions but also their temperature-dependent intensity variations. To further corroborate the assignments suggested by the calculations, the individual MCD sign for each transition is independently determined from the corresponding electron donating and accepting orbitals. Thus, unambiguous assignments can be made for the observed transitions in 1. The ABS/MCD data of complex 2 exhibit ten features that are assigned as ligand-field transitions or oxo- or hydroxo-to-metal charge transfer bands, based on MCD/ABS intensity ratios, calculated excitation energies, polarizations, and MCD signs. In comparison with complex 1, the electronic structure of the Fe-IV=O site is not significantly perturbed by the binding to another iron(IV) center. This may explain the experimental finding that complexes 1 and 2 have similar reactivities toward C-H bond activation and O-atom transfer.
引用
收藏
页码:2909 / 2921
页数:13
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