Catalysis of H2/D2 scrambling and other H/D exchange processes by [Fe]-hydrogenase model complexes
Catalysis of H2/D2 scrambling and other H/D exchange processes by [Fe]-hydrogenase model complexes
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DOI：
10.1021/ic020237r
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发表时间：
2002-07-29
影响因子：
4.6
通讯作者：
Darensbourg, MY
中科院分区：
文献类型：
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作者：
Zhao, X;Georgakaki, IP;Darensbourg, MY
[Fe]-氢化酶模型复合物 (mu-pdt)[Fe(CO)(2)(PMe3)](2) (pdt = SCH2CH2CH2S) 的质子化产生具有高场 H-1 NMR 共振的物质，分离为稳定的 {(mu-H)(mu-pdt)[Fe(CO)(2)(PMe3)](2)} [PF6](-) 盐。结构表征发现 2Fe2S 蝶形核几乎没有差异，Fe-Fe 键合中性物质和桥接氢化物物质的 (FeFe)-Fe-... 距离分别为 2.555(2) 和 2.578(1) 埃（Zhao, X.；Georgakaki, I. P.；Miller, M. L.；Yarbrough, J. C.；Darensbourg, M. Y.化学杂志，2001，123，9710）。两者都类似于在三个仅含 Fe 的氢化酶活性位点 2Fe2S 簇的结构中发现的平均 (FeFe)-Fe-... 距离：2.6 埃。一系列类似的配合物 (mu-edt)-、(mu-o-xyldt)- 和 (mu-SEt)(2)[Fe(CO)(2)(PMe3)](2) (edt = SCH2-CH2S; o-xyldt = SCH2C6H4CH2S)、(mu-pdt)[Fe(CO)(2)(PMe2Ph)](2) 及其质子化衍生物显示出中性配合物的 Fe-Fe 键长和阳离子桥联氢化物中的 (FeFe)-Fe-... 距离的均匀性。 PMe3 和 PMe2Ph 配体的位置由 (mu-SRS) 或 (mu-SR)(2) 桥中 S-C 键的方向以及随后的 R 空间位阻决定。比较了 Fe-\\(mu-H)Fe-\\ 复合物促进 H/D 交换反应的能力，已用作 H(2)ase 活性的测定。在光促进但 CO 抑制的反应中，{(mu-H)(mu-pdt)[Fe(CO)(2)(PMe3)](2)}(+) 络合物表现出与 D-2 的 H/D 交换活性，在 CH2Cl2 和丙酮中产生 {(mu-D)(mu-pdt)[Fe(CO)(2)(PMe3)](2)}(+)，但在 CH3CN 中不产生。在光存在下，Fe-\\(mu-H)Fe-\\催化剂也会促进D2O和H-2之间的H/D扰乱。开放位点的要求表明反应中的关键步骤涉及 D-2 或 H-2 与 Fell 结合，然后通过内部氢化物碱或外部水去质子化。正如该系列成员相似的催化效率所表明的，桥联硫醇盐的性质对反应影响很小。与 [Fe]H2ase 酶活性位点氧化还原水平的比较表明，至少一个 Fell 必须可用于 H2 的吸收，而质子吸收需要还原或富电子的 (FeFe\)-Fe-\ 金属-金属键合的氧化还原水平。
Protonation of the [Fe]-hydrogenase model complex (mu-pdt)[Fe(CO)(2)(PMe3)](2) (pdt = SCH2CH2CH2S) produces a species with a high field H-1 NMR resonance, isolated as the stable {(mu-H)(mu-pdt)[Fe(CO)(2)(PMe3)](2)} [PF6](-) salt. Structural characterization found little difference in the 2Fe2S butterfly cores, with (FeFe)-Fe-... distances of 2.555(2) and 2.578(1) Angstrom for the Fe-Fe bonded neutral species and the bridging hydride species, respectively (Zhao, X.; Georgakaki, I. P.; Miller, M. L.; Yarbrough, J. C.; Darensbourg, M. Y. J. Am. Chem. Soc. 2001, 123, 9710). Both are similar to the average (FeFe)-Fe-... distance found in structures of three Fe-only hydrogenase active site 2Fe2S clusters: 2.6 Angstrom. A series of similar complexes (mu-edt)-, (mu-o-xyldt)-, and (mu-SEt)(2)[Fe(CO)(2)(PMe3)](2) (edt = SCH2-CH2S; o-xyldt = SCH2C6H4CH2S), (mu-pdt)[Fe(CO)(2)(PMe2Ph)](2), and their protonated derivatives likewise show uniformity in the Fe-Fe bond lengths of the neutral complexes and (FeFe)-Fe-... distances in the cationic bridging hydrides. The positions of the PMe3 and PMe2Ph ligands are dictated by the orientation of the S-C bonds in the (mu-SRS) or (mu-SR)(2) bridges and the subsequent steric hindrance of R. The Fe-\\(mu-H)Fe-\\ complexes were compared for their ability to facilitate H/D exchange reactions, as have been used as assays of H(2)ase activity. In a reaction that is promoted by light but inhibited by CO, the {(mu-H)(mu-pdt)[Fe(CO)(2)(PMe3)](2)}(+) complex shows H/D exchange activity with D-2, producing {(mu-D)(mu-pdt)[Fe(CO)(2)(PMe3)](2)}(+) in CH2Cl2 and in acetone, but not in CH3CN. In the presence of light, H/D scrambling between D2O and H-2 is also promoted by the Fe-\\(mu-H)Fe-\\ catalyst. The requirement of an open site suggests that the key step in the reactions involves D-2 or H-2 binding to Fell followed by deprotonation by the internal hydride base, or by external water. As indicated by similar catalytic efficiencies of members of the series, the nature of the bridging thiolates has little influence on the reactions. Comparison to [Fe]H2ase enzyme active site redox levels suggests that at least one Fell must be available for H2 uptake while a reduced or an electron-rich (FeFe\)-Fe-\ metal-metal bonded redox level is required for proton uptake.