Sulfur Oxygenates of Biomimetics of the Diiron Subsite of the [FeFe]-Hydrogenase Active Site: Properties and Oxygen Damage Repair Possibilities

This study explores the site specificity (sulfur vs the Fe−Fe bond) of oxygenation of diiron (FeIFeI and FeIIFeII) organometallics that model the 2-iron subsite in the active site of [FeFe]-hydrogenase: (μ-pdt)[Fe(CO)2L][Fe(CO)2L′] (L = L′ = CO (1); L = PPh3, L′ = CO (2); L = L′ = PMe3 (4)) and (μ-pdt)(μ-H)[Fe(CO)2PMe3]2 (5). DFT computations find that the Fe−Fe bond in the FeIFeI diiron models is thermodynamically favored to produce the μ-oxo or oxidative addition product, FeII−O−FeII; nevertheless, the sulfur-based HOMO−1 accounts for the experimentally observed mono- and bis-O-atom adducts at sulfur, i.e., (μ-pst)[Fe(CO)2L][Fe(CO)2L′] (pst = −S(CH2)3S(O)−, 1,3-propanesulfenatothiolate; L = L′ = CO (1-O); L = PPh3, L′ = CO (2-O); L = L′ = PMe3 (4-O)) and (μ-pds)[Fe(CO)2L][Fe(CO)2L′] (pds = −(O)S(CH2)3S(O)−, 1,3-propanedisulfenato; L = PPh3, L′ = CO (2-O2)). The FeII(μ-H)FeII diiron model (5), for which the HOMO is largely of sulfur character, exclusively yields S-oxygenation. The depressing effect of such bridging ligand modification on the dynamic NMR properties arising from rotation of the Fe(CO)3 correlates with higher barriers to the CO/PMe3 exchange of (μ-pst)[Fe(CO)3]2 as compared to (μ-pdt)[Fe(CO)3]2. Five molecular structures are confirmed by X-ray diffraction: 1-O, 2-O, 2-O2, 4-O, and 6. Deoxygenation with reclamation of the μ-pdt parent complex occurs in a proton/electron-coupled process. The possible biological relevance of oxygenation and deoxygenation studies is discussed.

本研究针对模拟[FeFe]-氢化酶活性中心二铁亚基的二铁（FeIFeI与FeIIFeII）有机金属配合物的氧合反应位点选择性（硫位点vs Fe-Fe键位点）展开探究，所研究的配合物包括(μ-pdt)[Fe(CO)₂L][Fe(CO)₂L′]（其中L=L′=CO记为1；L=三苯基膦(PPh3)，L′=CO记为2；L=L′=三甲基膦(PMe3)记为4）以及(μ-pdt)(μ-H)[Fe(CO)₂PMe3]₂（记为5）。密度泛函理论（DFT）计算结果表明，FeIFeI型二铁模型中的Fe-Fe键在热力学上更倾向于生成μ-氧桥或氧化加成产物FeII-O-FeII；然而，基于硫原子的最高占据分子轨道-1（HOMO-1）可解释实验中观测到的硫位点单氧与双氧加合产物，即(μ-pst)[Fe(CO)₂L][Fe(CO)₂L′]（其中pst为−S(CH2)3S(O)−，即1,3-丙烷亚磺酰硫醇盐；L=L′=CO记为1-O；L=PPh3，L′=CO记为2-O；L=L′=PMe3记为4-O）与(μ-pds)[Fe(CO)₂L][Fe(CO)₂L′]（其中pds为−(O)S(CH2)3S(O)−，即1,3-丙烷二亚磺酰基；L=PPh3，L′=CO记为2-O2）。而HOMO主要具有硫原子特征的FeII(μ-H)FeII型二铁模型（5）则仅发生硫位氧合反应。此类桥联配体修饰对Fe(CO)3旋转引发的动态核磁共振（NMR）性质产生的抑制效应，与(μ-pst)[Fe(CO)3]₂相较于(μ-pdt)[Fe(CO)3]₂更高的CO/PMe3交换能垒具有相关性。通过X射线衍射（X-ray diffraction）确认了5个分子的晶体结构：1-O、2-O、2-O₂、4-O与6。通过质子/电子耦合过程可实现脱氧反应并回收μ-pdt母体配合物。本研究最后讨论了氧合与脱氧反应研究潜在的生物学意义。