St Claire Tamara N., Balch Alan L.
Department of Chemistry, University of California, Davis, California 95616.
Inorg Chem. 1999 Feb 22;38(4):684-691. doi: 10.1021/ic981178d.
The effects of using hydrazine rather than ascorbic acid on the coupled oxidation of (OEP)Fe(II)(py)(2) (OEP is the dianion of octaethylporphyrin, py is pyridine) have been investigated with the goal of directly detecting reactive intermediates during the process of heme degradation by dioxygen. The reaction products, [(OEOP)Fe(II)(py)(2)]Cl and (OEB)Fe(III)(py)(2) (OEOP is the monoanion of octaethyl-5-oxaporphyrin and OEB is the trianion of octaethylbilindione), and their yields are similar to those of the standard coupled oxidation process. The reaction has been monitored in situ in pyridine/dichloromethane mixtures by (1)H NMR spectroscopy. The recently isolated and crystallographically characterized complex, (OEPO)Fe(py)(2) (OEOP is the trianion of octaethyloxaphlorin), has been identified as a key intermediate. Addition of dioxygen to (OEP)Fe(II)(py)(2) in pyridine with hydrazine present also produces two new transient species: (OEPO)Fe(py)(N(2)D(4)) and (OEPO)Fe(N(2)D(4))(2). These complexes have also be produced independently by low-temperature titration of hydrazine into a solution of {(OEPO)Fe}(2). Thus, hydrazine acts as an axial ligand during the early stages of the coupled oxidation process. However, the two hydrazine-containing complexes eventually are converted into (OEPO)Fe(py)(2) before [(OEOP)Fe(II)(py)(2)]Cl and (OEB)Fe(III)(py)(2) are formed. The observations reported here suggest that the coupled oxidation process can be divided into two stages. The first stage involves the meso C-H bond and results in introduction of oxygen at that site with the formation of the three intermediates: (OEPO)Fe(N(2)H(4))(2), (OEPO)Fe(N(2)H(2))(py), and (OEPO)Fe(py)(2). The second stage of the coupled oxidation process involves C-C bond breaking and the conversion of the hydroxylated heme, (OEPO)Fe(py)(2), into the final products, (OEOP)Fe(II)(py)(2) and (OEB)Fe(III)(py)(2).
为了在二氧导致血红素降解的过程中直接检测反应中间体，研究了使用肼而非抗坏血酸对（OEP）Fe（II）（py）₂（OEP是八乙基卟啉二价阴离子，py是吡啶）的偶联氧化的影响。反应产物[（OEOP）Fe（II）（py）₂]Cl和（OEB）Fe（III）（py）₂（OEOP是八乙基-5-氧杂卟啉一价阴离子，OEB是八乙基双二氢卟吩三价阴离子）及其产率与标准偶联氧化过程的产物相似。通过¹H NMR光谱对吡啶/二氯甲烷混合物中的反应进行了原位监测。最近分离并通过晶体学表征的配合物（OEPO）Fe（py）₂（OEOP是八乙基氧杂卟吩三价阴离子）已被确定为关键中间体。在存在肼的情况下，向吡啶中的（OEP）Fe（II）（py）₂中加入二氧还产生了两个新的瞬态物种：（OEPO）Fe（py）（N₂D₄）和（OEPO）Fe（N₂D₄）₂。这些配合物也可通过将肼低温滴定到{（OEPO）Fe}₂溶液中独立制备。因此，在偶联氧化过程的早期阶段，肼充当轴向配体。然而，在形成[（OEOP）Fe（II）（py）₂]Cl和（OEB）Fe（III）（py）₂之前，这两种含肼的配合物最终会转化为（OEPO）Fe（py）₂。此处报道的观察结果表明，偶联氧化过程可分为两个阶段。第一阶段涉及中位C-H键，导致在该位点引入氧，形成三种中间体：（OEPO）Fe（N₂H₄）₂、（OEPO）Fe（N₂H₂）（py）和（OEPO）Fe（py）₂。偶联氧化过程的第二阶段涉及C-C键断裂以及羟基化血红素（OEPO）Fe（py）₂转化为最终产物[（OEOP）Fe（II）（py）₂]⁺和（OEB）Fe（III）（py）₂。
