Resonance raman spectra of nitridoiron(V) porphyrin intermediates produced by laser photolysis
Resonance raman spectra of nitridoiron(V) porphyrin intermediates produced by laser photolysis
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激光光解产生的硝基铁(V)卟啉中间体的共振拉曼光谱
DOI：
10.1021/ja00187a010
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发表时间：
1989
影响因子：
15
通讯作者：
K. Nakamoto
中科院分区：
文献类型：
--
作者：
W. Wagner;K. Nakamoto
在~ 30 K下，用激光辐照叠氮铁（V）卟啉薄膜制备了相应的氮铁卟啉NFeOEP（OEP，octagethylporphinato anion）、NFeTPP（TPP，tetraphenylporphinato anion）和NFeTMP（TMP，tetramesitylporphinato anion）.通过在共振拉曼（RR）光谱中对于OEP和TPP络合物在876 cm-1处以及对于TMP络合物在873 cm-1处的n（Fe= N）（r，伸缩振动）的出现来检测氮化物络合物的形成。这些分配证实了所观察到的频率偏移，由于56 Fe/54 Fe和14 N/15 N同位素取代。OEP和TPP络合物的结构敏感谱带频率表明氮络合物的Fe（V）态，排除了形成r-阳离子自由基的可能性。虽然自旋态不能通过振动光谱确定，但相对较小的Fe= N伸缩力常数（5.07 mdyn/A）有利于高自旋（d^）1（diz）1（d>，z）1构型，这是在等电子氧锰（IV）卟啉中发现的。在OEP复合物的情况下，RR光谱提供了反应方案的证据，其中NFevOEP首先通过N3 FemOEP复合物由于低功率照射的激光光解形成（406.7-514.5-nm范围内1-60 mW），随后通过局部加热转化为µ-氮化物二聚体（FeOEP）2N，这发生在向样品施加高激光功率（在413.1nm处为220 mW）时。该二聚体在438 CHT 1处表现出对称的Fe-N-Fe伸缩带，其在56 Fe/54 Fe和14 N/15 N取代后显示出预期的位移。高频区结构敏感带的位置也证实了µ-nitrido二聚体的形成。上述反应类似于氧铁卟啉在低温下的自氧化过程，在室温下生成铁基卟啉作为中间体，最终产物为μ-二聚体。
Nitridoiron (V) porphyrins, NFeOEP (OEP, octaethylporphinato anion), NFeTPP (TPP, tetraphenylporphinato anion), and NFeTMP (TMP, tetramesitylporphinatoanion), were produced by laser irradiation of thin films of the corresponding azido complexes at~ 30 K. Formation of the nitrido complexes was detected by the appearance of the n (Fe= N)(r, stretching vibration) at 876 cm" 1 for the OEPand TPP complexes and at 873 cm" 1 for the TMP complex in resonance Raman (RR) spectra. These assignments were confirmed by observed frequency shifts due to 56Fe/54Fe and 14N/15N isotopic substitutions. Frequencies of structure-sensitive bands known for OEPand TPP complexes suggest the Fe (V) state for the nitrido complex and rule out the possibility of rr-cation-radical formation. Although the spin state cannot be determineddefinitively by vibrational spectroscopy, the relatively small Fe= N stretching force constant (5.07 mdyn/A) favors the high-spin (d^) 1 (diz) 1 (d>, z) 1 configuration that was found for isoelectronic oxomanganese (IV) porphyrins. In the case of the OEP complex, RR spectroscopy provides evidence for a reaction scheme inwhich NFevOEP is first formedby laser photolysis of the N3FemOEP complex due to low-power irradiation (1-60 mW in the 406.7-514.5-nm range) and subsequently converted to the µ-nitrido dimer (FeOEP) 2N by local heating, which occurred when high laser power (220 mW at 413.1 nm) was applied to the sample. This dimer exhibits the symmetric Fe-N-Fe stretching band at 438 cm" 1, which shows expected shifts upon 56Fe/54Fe and l4N/15N substitutions. Formationof the µ-nitrido dimer is also confirmed by the positions of the structure-sensitive bands in the high-frequency region. The above reaction scheme resembles theautoxidation process of oxyiron porphyrins at low temperature which yields ferrylporphyrins as the intermediate and the µ- dimer as the final productat room temperature.