NONHEME IRON CENTERS IN OXYGEN ACTIVATION - CHARACTERIZATION OF AN IRON(III) HYDROPEROXIDE INTERMEDIATE
NONHEME IRON CENTERS IN OXYGEN ACTIVATION - CHARACTERIZATION OF AN IRON(III) HYDROPEROXIDE INTERMEDIATE
复制标题
DOI：
10.1002/anie.199515121
复制
发表时间：
1995-07-31
期刊：
影响因子：
--
通讯作者：
QUE, L
中科院分区：
文献类型：
--
作者：
LUBBEN, M;MEETSMA, A;QUE, L
的协调。一种与卟啉系统明显不同的情况，卟啉系统中吡咯基团在基面上。配合物1具有一个低自旋铁（r1）中心，其Fe - N键长度较短，为1.91-1.98，并且其所有质子都可以通过其H NMR谱的反磁区特征来解释，与低自旋铁（1i）配合物一致。这种低自旋铁（]!）中心的热力学稳定性可能是合成过程中初始形成的铁（rir）配合物还原的驱动力。N4Py配体稳定铁(n)态的能力得到了CH， CN中1的循环伏安法的支持，在990 mV下，与Fe /Fe偶对对应的普通氢电极（NH E）相比，N4Py配体在990 mV下发生了可逆氧化。在丙酮中，配合物I在458nm处（8:= 4000M-'cm-'）具有明显的uvm光谱（图2）。用过量（80等量）的H， O, at-8”C在丙酮中处理1，会导致出现：紫色物种的颜色= 530 nm， E= z1 1 0 0~~ 1 ' cnl)，半衰期为45分钟（图2）。Chowever At25”。由于h2o的歧化，紫色在几分钟内消失，但由于加入更多的H， O，而重新出现。用H， O对1进行UViVis滴定，结果表明，加入0.5等量H， Oz后，1的特征带完全消失，再加入H202后，2的紫色出现，说明1在形成2之前首先转化为铁（r1r）。中间体2的EPR谱g值为2.1 7。1. 我吗?， 1.98（图2附页）。表明低自旋铁-(111)种。其信号强度占铁存在的80%，并与紫色发色团的强度直接相关。我们把2的紫色归因于过氧化物到铁（iii）的电荷转移跃迁，但是。不像高自旋过氧化物铁（iii）配合物。”由于2的光不稳定性，这种分配不能用共振拉曼光谱证实。其它低自旋过氧化物铁（II1） spe-
of coordination. a situation markedly different from porphyrin systems wherc the pyrrole groups are within the basal plane. Complex 1 has a low-spin iron (r1) center as indicated by the short Fe N bond lengths of 1.91-1.98 Furthermore all its protons can bc accounted for by features in the diamagnetic region of its' H NMR spectrum, consistent with a low-spin iron (1i) complex. The thermodynamic stability of this low-spin iron (]!) ccnter IS probably the driving force for the reduction of the initially formed iron (rir) complex in the synthetic procedure. The ability 01'the N4Py ligand to stabilize the iron (n) state is supported by thc cyclic voltammetry of 1 in CH, CN which shows a reversible oxidation at 990 mV vs the normal hydrogen electrode (NH E) corresponding to the Fe"'/Fe" couple. Complex I exhibits a UVMs spectrum with a distinct band at 458 nm (8:= 4000M-'cm-') in acetone (Fig. 2). Treatment of 1 in acetone with an excess (80 equiv) of H, O, at-8" C causes the appear: uice of a purple species= 530 nm, E= Z 1 1 0 0~~'cnLl) witha half-lifeof45 min (Fig. 2). At25" Chowever. the purple color disappears within minutes due to disproportionation of H20,, but reappears by the addition of more H, O,. A UViVis titration of 1 with H, O, shows that the characteristic band for 1 completely disappears with the addition of 0.5 equiv H, Oz before the purple color of 2 appears with further addition of H202, indicating that 1 is first converted to an iron (r1r) species prior to forming 2. The intermediate 2 exhibits an EPR spectrum with g values at 2.1 7. 1. I?, and 1.98 (Fig. 2 inset). indicative of a low-spin iron-(111) species. Its hignal intensity accounts for as much as 80% of the iron preseni and correlates directly with the intensity of the purple chromophore. We ascribe the purple color of 2 to a peroxide-to-iron (iii) charge transfer transition, but. unlike for high-spin peroxoiron (iii) complexes." 0J this assignment could not be corroborated by resonance Raman spectroscopy due to the photoinstability of 2. Other low-spin peroxoiron (II1) spe-