Liu Tianbiao, Li Bin, Singleton Michael L, Hall Michael B, Darensbourg Marcetta Y
Department of Chemistry, Texas A&M University, College Station, Texas 77843, USA.
J Am Chem Soc. 2009 Jun 17;131(23):8296-307. doi: 10.1021/ja9016528.
This study explores the site specificity (sulfur vs the Fe-Fe bond) of oxygenation of diiron (Fe(I)Fe(I) and Fe(II)Fe(II)) organometallics that model the 2-iron subsite in the active site of [FeFe]-hydrogenase: (mu-pdt)[Fe(CO)(2)L][Fe(CO)(2)L'] (L = L' = CO (1); L = PPh(3), L' = CO (2); L = L' = PMe(3) (4)) and (mu-pdt)(mu-H)Fe(CO)(2)PMe(3) (5). DFT computations find that the Fe-Fe bond in the Fe(I)Fe(I) diiron models is thermodynamically favored to produce the mu-oxo or oxidative addition product, Fe(II)-O-Fe(II); nevertheless, the sulfur-based HOMO-1 accounts for the experimentally observed mono- and bis-O-atom adducts at sulfur, i.e., (mu-pst)[Fe(CO)(2)L][Fe(CO)(2)L'] (pst = -S(CH(2))(3)S(O)-, 1,3-propanesulfenatothiolate; L = L' = CO (1-O); L = PPh(3), L' = CO (2-O); L = L' = PMe(3) (4-O)) and (mu-pds)[Fe(CO)(2)L][Fe(CO)(2)L'] (pds = -(O)S(CH(2))(3)S(O)-, 1,3-propanedisulfenato; L = PPh(3), L' = CO (2-O(2))). The Fe(II)(mu-H)Fe(II) 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/PMe(3) exchange of (mu-pst)Fe(CO)(3) as compared to (mu-pdt)Fe(CO)(3). Five molecular structures are confirmed by X-ray diffraction: 1-O, 2-O, 2-O(2), 4-O, and 6. Deoxygenation with reclamation of the mu-pdt parent complex occurs in a proton/electron-coupled process. The possible biological relevance of oxygenation and deoxygenation studies is discussed.
本研究探索了模拟[FeFe]-氢化酶活性位点中二铁亚位点的二铁（Fe(I)Fe(I)和Fe(II)Fe(II)）有机金属化合物的氧化位点特异性（硫与Fe-Fe键）：(μ-pdt)[Fe(CO)₂L][Fe(CO)₂L']（L = L' = CO (1)；L = PPh₃，L' = CO (2)；L = L' = PMe₃ (4)）和(μ-pdt)(μ-H)[Fe(CO)₂PMe₃]₂ (5)。密度泛函理论计算发现，Fe(I)Fe(I)二铁模型中的Fe-Fe键在热力学上有利于生成μ-氧代或氧化加成产物Fe(II)-O-Fe(II)；然而，基于硫的HOMO-1解释了实验观察到的硫上的单原子和双原子加合物，即(μ-pst)[Fe(CO)₂L][Fe(CO)₂L']（pst = -S(CH₂)₃S(O)-，1,3-丙烷亚磺酰硫醇盐；L = L' = CO (1-O)；L = PPh₃，L' = CO (2-O)；L = L' = PMe₃ (4-O)）和(μ-pds)[Fe(CO)₂L][Fe(CO)₂L']（pds = -(O)S(CH₂)₃S(O)-，1,3-丙二亚磺酸盐；L = PPh₃，L' = CO (2-O₂)）。Fe(II)(μ-H)Fe(II)二铁模型(5)的HOMO主要具有硫的特征，只产生硫氧化。与(μ-pdt)[Fe(CO)₃]₂相比，这种桥连配体修饰对由Fe(CO)₃旋转引起的动态核磁共振性质的抑制作用与(μ-pst)[Fe(CO)₃]₂中CO/PMe₃交换的更高势垒相关。通过X射线衍射确定了五个分子结构：1-O、2-O、2-O₂、4-O和6。在质子/电子耦合过程中发生脱氧并回收μ-pdt母体配合物。讨论了氧化和脱氧研究可能的生物学相关性。
