Sulfonated Diiron Complexes as Water-Soluble Models of the [Fe–Fe]-Hydrogenase Enzyme Active Site

A series of diiron complexes developed as fundamental models of the two-iron subsite in the [FeFe]-hydrogenase enzyme active site show water-solubility by virtue of a sulfonate group incorporated into the −SCH2NRCH2S- dithiolate unit that bridges two FeI(CO)2L moieties. The sulfanilic acid group imparts even greater water solubility in the presence of β-cyclodextrin, β-CyD, for which NMR studies suggest aryl-sulfonate inclusion into the cyclodextrin cavity as earlier demonstrated in the X-ray crystal structure of 1Na·2 β-CyD clathrate, where 1Na = Na+(μ-SCH2N(C6H4SO3–)CH2S-)[Fe(CO)3]2, (Singleton et al., J. Am. Chem. Soc. 2010, 132, 8870). Electrochemical analysis of the complexes for potential as electrocatalysts for proton reduction to H2 finds the presence of β-CyD to diminish response, possibly reflecting inhibition of structural rearrangements required of the diiron unit for a facile catalytic cycle. Advantages of the aryl sulfonate approach include entry into a variety of water-soluble derivatives from the well-known (μ-SRS)[Fe(CO)3]2 parent biomimetic, that are stable in O2-free aqueous solutions.

一系列作为[FeFe]-氢化酶([FeFe]-hydrogenase)活性位点中二铁亚基基础模型开发的二铁配合物，通过在桥连两个FeI(CO)2L基团的−SCH2NRCH2S-二硫醇盐配体中引入磺酸基，获得水溶性。对氨基苯磺酸基团在β-环糊精(β-cyclodextrin, β-CyD)存在下可赋予配合物更高的水溶性；核磁共振(NMR)研究表明，芳基磺酸盐包合进入环糊精空腔，这一点此前已在1Na·2β-CyD包合物的X射线晶体结构中得到证实，其中1Na = Na+(μ-SCH2N(C6H4SO3–)CH2S-)[Fe(CO)3]2（Singleton等，《美国化学会志》，2010年，132卷，8870页）。对该系列配合物作为质子还原生成氢气(H2)的电催化剂潜力开展电化学分析后发现，β-CyD的存在会降低其电化学响应，这可能反映出二铁单元完成高效催化循环所需的结构重排受到了抑制。芳基磺酸盐修饰策略的优势在于，可从经典的(μ-SRS)[Fe(CO)3]2母本仿生配合物出发，制备一系列水溶性衍生物，这类衍生物在无氧水溶液中具有良好的稳定性。