合成及鑑定含有共軛系統之鐵硫化合物以模擬氫化酵素之活化中心

Synthesis and Characterization of Biomimetic Diiron Dithiolate Complexes Containing Conjugated Systems Related to the Active Site of [FeFe]-Hydrogenase

李建璋(Chien-Chang Lee)

指導教授 ： 劉陵崗

共同指導教授 ： 江明錫(Ming-Hsi Chiang)

國立臺灣大學/理學院/化學研究所/碩士(2015年)

https://doi.org/10.6342/NTU.2015.10260

摘要

本論文主要是藉由化學合成的方法來模擬鐵-鐵氫化酵素，並合成出一系列含有不同bridgehead之鐵硫化合物 [(μ-(R-NMI)S2)Fe2(CO)6] (R = Ph (1)，p-BrPh (2)，p-iPrPh (3)，BZI (4，benzimidazole))；配位基 [(R-NMI)S2] (NMI = naphthalene monoimide)是一個redox-active ligand，用於仿照在生物體中的 [Fe4S4] ferredoxin-like cluster。在本研究中，以X-ray單晶繞射解出分子結構，藉由電化學分析化合物1-4的氧化還原特性，在此發現化合物1-3的電化學行為是類似，而後以紅外線光譜儀偵測化合物3及4的還原反應，並配合DFT理論計算作佐證，結果指出化合物3及4的第一個還原電位皆主要為發生在NMI配位基之還原。而後再以還原劑還原化合物3形成32-，藉以探討化合物3的第二個還原行為，同樣地以DFT理論計算作輔助，結果指出化合物32-的兩個電子分佈在 NMI配位基以及雙鐵雙硫中心上，而隨著時間增長，還原態32-的其中一個鐵硫鍵會斷裂，其中一個C≡O會旋轉至雙鐵中心以橋接方式鍵結，形成 [(μ,κ2-(p-iPrPh-NMI)S2)(μ-CO)Fe2(CO)5]2- (3’2-)，由DFT理論計算結果來看，3’2-的兩個電子主要是在雙鐵雙硫中心，表示隨時間增長，32-會發生電子轉移現象，電子由NMI配位基傳遞至雙鐵雙硫中心。將化合物3’2-進行酸化反應形成3’H-，由2H{1H}-NMR光譜分析，3’H-的質子化應是在終端的硫上，當化合物3’H-再進行一次酸化反應後會回到化合物3，推測應是生成氫氣而脫離，並藉此推測出化合物3的催化機制。

關鍵字

鐵鐵氫化酵素

並列摘要

Diiron dithiolate complexes containing conjugated systems, [(μ-(R-NMI)S2)Fe2 (CO)6] (R = Ph (1), p-BrPh (2), p-iPrPh (3), BZI (4, benzimidazole), NMI = naphthalene monoimide) were synthesized and characterized by IR, NMR spectroscopy, X-ray single crystallography and cyclic voltammetry. We used the extensive conjugated ligands that are redox-active to mimic the function of the [Fe4S4] ferredoxin-like cluster in the active site of [FeFe]-hydrogenase. When 3 and 4 were reduced by one equivlenat of cobaltocene, the spectroscopic and density functional theory results indicated that the electron is mainly localized at the NMI ligand. In the doubly reduced species 32-, two electrons are delocalized between the NMI unit and the [Fe2S2] core. Since 32- is unstable in solution, 32- was converted to a Fe-S bond-ruptured species, [(μ,κ2-(p-iPrPh-NMI)S2)(μ-CO)Fe2(CO)5]2- (32-) in 2 hr at 200 K. In 3’2-, the two added electrons are mainly resided at the [Fe2S2] core, confirmed by DFT calculations. Compared withe the NPA (natural population analysis) of 32- and 3’2-, the results showed that the electronic structure of 32- rearranges to a more stable structure 3’2-. We measured the catalytic rate constant (kcat) of the hydrogen production of complexes 1-4 by cyclic voltammetry. The protonated intermediate species were obtained from the reaction of complexes 3 and 4 with TFA. The results showed that the ketone oxygen or imidazole nitrogen on the NMI unit could form hydrogen bonded or protonated species, respectively, confirmed by DFT calculations. In summary, the electron density within the NMI unit in 32- migrates to the [Fe2S2] core when 32- is converted to 3’2-. Our results showed that the NMI ligand is an appropriate ligand to mimic the [Fe4S4] ferredoxin-like cluster in the active site of [FeFe]-hydrogenase.

並列關鍵字

[FeFe]-Hydrogenase ； NMI ； redox-active ； NPA

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