Reactions of nitrogen oxides with the five-coordinate FeIII(porphyrin) nitrito intermediate Fe(Por)(ONO) in sublimed solids
Reactions of nitrogen oxides with the five-coordinate FeIII(porphyrin) nitrito intermediate Fe(Por)(ONO) in sublimed solids
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DOI：
10.1021/ja067245h
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发表时间：
2007-03-28
影响因子：
15
通讯作者：
Ford, Peter C.
中科院分区：
文献类型：
--
作者：
Kurtikyan, Tigran S.;Hovhannisyan, Astghik A.;Ford, Peter C.
描述了几种氮氧化物与血红素/NxOy 系统的铁卟啉模型反应的详细实验研究。 FTIR、光学光谱和同位素标记实验表明，少量的 NO2 与升华的铁 (II) 络合物 Fe(Por) 薄层（Por = 内消旋四苯基卟啉二价阴离子，TPP 或内消旋四对甲苯卟啉二价阴离子，TTP）发生反应，导致形成 5 配位亚硝基络合物 Fe(Por)(eta(1)-ONO) (1)，它们相当稳定，但在真空下分解非常缓慢，主要产生相应的亚硝酰配合物 Fe(Por)(NO)。 1 与新的 NO2 增量进一步反应，形成硝基配合物 Fe(Por)(eta(2)-O2NO) (2)。 NO 与 1 在低温下的相互作用涉及配体加成，得到亚硝基-亚硝酰基复合物 Fe(Por)(eta(1)-ONO)(NO) (3；然而，这些化合物在升温时异构化为硝基-亚硝基类似物 Fe(Por)(eta(1)-NO2)(NO) (4)。标记氮氧化物的实验论证了分子内异构化（“翻转”）机制，而不是涉及解离的机制6 配位物种 3 和 4 中的 Fe(III) 中心是低自旋的，而 1 似乎是高自旋的，尽管对卟啉模型 Fe(P)(亚硝酸盐) 的 DFT 计算表明双硝基物种以及四重态和六重态亚硝基络合物的能量都相对接近，硝基亚硝基络合物 4 在 NO 气氛下是稳定的，但在强环境下会分解。泵送得到亚硝酰亚铁配合物 Fe(Por)(NO) 和亚硝基铁配合物 Fe(Por)(eta(1)-ONO) 的混合物，表明 NO 和 NO2 的竞争性解离。因此，4 中 NO 的损失伴随着硝基 -> 亚硝基异构化，这与 1 是铁卟啉的 5 配位 NO2 配合物中更稳定的情况一致。
Detailed experimental studies are described for reactions of several nitrogen oxides with iron porphyrin models for heme/NxOy systems. It is shown by FTIR and optical spectroscopy and by isotope labeling experiments that reaction of small increments of NO2 with sublimed thin layers of the iron(II) complex Fe(Por) (Por = meso-tetraphenylporphyrinato dianion, TPP, or meso-tetra-p-tolylporphyrinato dianion, TTP) leads to formation of the 5-coordinate nitrito complexes Fe(Por)(eta(1)-ONO) (1), which are fairly stable but very slowly decompose under vacuum giving mostly the corresponding nitrosyl complexes Fe(Por)(NO). Further reaction of 1 with new NO2 increments leads to formation of the nitrato complex Fe(Por)(eta(2)-O2NO) (2). The interaction of NO with 1 at low temperature involves ligand addition to give the nitrito-nitrosyl complexes Fe(Por)(eta(1)-ONO)(NO) (3; however, these isomerize to the nitro-nitrosyl analogs Fe(Por)(eta(1)-NO2)(NO) (4) upon warming. Experiments with labeled nitrogen oxides argue for an intramolecular isomerization ("flipping") mechanism rather than one involving dissociation and rebinding of NO2. The Fe(III) centers in the 6-coordinate species 3 and 4 are low spin in contrast to 1, which appears to be high-spin, although DFT computations of the porphinato models Fe(P)(nitrite) suggest that the doublet nitro species and the quartet and sextet nitrito complexes are all relatively close in energy. The nitro-nitrosyl complex 4 is stable under an NO atmosphere but decomposes under intense pumping to give a mixture of the ferrous nitrosyl complex Fe(Por)(NO) and the ferric nitrito complex Fe(Por)(eta(1)-ONO) indicating the competitive dissociation of NO and NO2. Hence, loss of NO from 4 is accompanied with nitro -> nitrito isomerization consistent with 1 being the more stable of the 5-coordinate NO2 complexes of iron porphyrins.