Lehnert Nicolai, Fujisawa Kiyoshi, Solomon Edward I
Department of Chemistry, Stanford University, Stanford, California 94305-5080, USA.
Inorg Chem. 2003 Jan 27;42(2):469-81. doi: 10.1021/ic020496g.
The spectroscopic properties and electronic structure of the four-coordinate high-spin [FeIII(L3)(OOtBu)]+ complex (1; L3 = hydrotris(3-tert-butyl-5-isopropyl-1-pyrazolyl)borate; tBu = tert-butyl) are investigated and compared to the six-coordinated high-spin [Fe(6-Me3TPA)(OHx)(OOtBu)]x+ system (TPA = tris(2-pyridylmethyl)amine, x = 1 or 2) studied earlier [Lehnert, N.; Ho, R. Y. N.; Que, L., Jr.; Solomon, E. I. J. Am. Chem. Soc. 2001, 123, 12802-12816]. Complex 1 is characterized by Raman features at 889 and 830 cm-1 which are assigned to the O-O stretch (mixed with the symmetric C-C stretch) and a band at 625 cm-1 that corresponds to nu(Fe-O). The UV-vis spectrum shows a charge-transfer (CT) transition at 510 nm from the alkylperoxo pi v* (v = vertical to C-O-O plane) to a d orbital of Fe(III). A second CT is identified from MCD at 370 nm that is assigned to a transition from pi h* (h = horizontal to C-O-O plane) to an Fe(III) d orbital. For the TPA complex the pi v* CT is at 560 nm while the pi h* CT is to higher energy than 250 nm. These spectroscopic differences between four- and six-coordinate Fe(III)-OOR complexes are interpreted on the basis of their different ligand fields. In addition, the electronic structure of Fe-OOPtn complexes with the biologically relevant pterinperoxo ligand are investigated. Substitution of the tert-butyl group in 1 by pterin leads to the corresponding Fe(III)-OOPtn species (2), which shows a stronger electron donation from the peroxide to Fe(III) than 1. This is related to the lower ionization potential of pterin. Reduction of 2 by one electron leads to the Fe(II)-OOPtn complex (3), which is relevant as a model for potential intermediates in pterin-dependent hydroxylases. However, in the four-coordinate ligand field of 3, the additional electron is located in a nonbonding d orbital of iron. Hence, the pterinperoxo ligand is not activated for heterolytic cleavage of the O-O bond in this system. This is also evident from the calculated reaction energies that are endothermic by at least 20 kcal/mol.
研究了四配位高自旋[FeIII(L3)(OOtBu)]+配合物(1;L3 = 氢三(3 - 叔丁基 - 5 - 异丙基 - 1 - 吡唑基)硼酸酯;tBu = 叔丁基)的光谱性质和电子结构，并与先前研究的六配位高自旋[Fe(6 - Me3TPA)(OHx)(OOtBu)]x+体系(TPA = 三(2 - 吡啶甲基)胺，x = 1或2)[Lehnert, N.; Ho, R. Y. N.; Que, L., Jr.; Solomon, E. I. J. Am. Chem. Soc. 2001, 123, 12802 - 12816]进行了比较。配合物1的特征拉曼峰位于889和830 cm-1处，归属为O - O伸缩振动(与对称C - C伸缩振动混合)，625 cm-1处的峰对应于ν(Fe - O)。紫外可见光谱显示在510 nm处有一个电荷转移(CT)跃迁，从烷基过氧π v*(v = 垂直于C - O - O平面)到Fe(III)的d轨道。通过磁圆二色光谱(MCD)在370 nm处鉴定出第二个CT跃迁，归属为从π h*(h = 平行于C - O - O平面)到Fe(III) d轨道的跃迁。对于TPA配合物，π v* CT跃迁在560 nm处，而π h* CT跃迁在高于250 nm的更高能量处。基于四配位和六配位Fe(III) - OOR配合物不同的配体场对这些光谱差异进行了解释。此外，还研究了与生物相关的蝶呤过氧配体的Fe - OOPtn配合物的电子结构。用蝶呤取代1中的叔丁基得到相应的Fe(III) - OOPtn物种(2)，它显示出比1更强的过氧化物向Fe(III)的电子给予作用。这与蝶呤较低的电离势有关。2经单电子还原得到Fe(II) - OOPtn配合物(3)，它作为蝶呤依赖性羟化酶中潜在中间体的模型具有相关性。然而，在3的四配位配体场中，额外的电子位于铁的非键d轨道中。因此，在该体系中蝶呤过氧配体未被激活用于O - O键的异裂。这也从计算得到的至少吸热20 kcal/mol的反应能量中明显体现出来。
