Chiang Ming-Hsi, Liu Yu-Chiao, Yang Shu-Ting, Lee Gene-Hsiang
Institute of Chemistry, Academia Sinica, Nankang, Taipei 115, Taiwan.
Inorg Chem. 2009 Aug 17;48(16):7604-12. doi: 10.1021/ic900564q.
Iron azadithiolate phosphine-substituted complex and its protonated species featuring the NH proton and/or bridging Fe hydride, Fe(2)(mu-S(CH(2))(2)N(n)Pr(H)(m)(CH(2))(2)S)(mu-H)(n)(CO)(4)(PMe(3))(2)((2m+2n)+) (1, m = n = 0; 1-2H(N), m = 1, n = 0; 1-2H(N)2H(Fe), m = n = 1), are prepared to mimic the active site of Fe-only hydrogenase. X-ray crystallographic analyses of these three complexes reveal that two diiron subunits are linked by two azadiethylenethiolate bridges to construct a dimer-of-dimer structure. (31)P NMR spectroscopy confirms two trimethylphosphine ligands within the diiron moiety are arranged in the apical/basal configuration, which is consistent with the solid-state structural characterization. Deprotonation of the NH proton in 1-2H(N) and 1-2H(N)2H(Fe) occurs in the presence of triethanolamine (TEOA), which generates 1 and 1-2H(Fe), respectively. Deprotonation of the Fe hydride is accomplished by addition of bistriphenylphosphineimminium chloride ([PPN]Cl). It is observed that the Fe hydride species, 1-2H(Fe), is a kinetic product which converts to its thermodynamically stable tautomer, 1-2H(N), in solution, as evidenced by IR and NMR spectroscopy. The pK(a) values of the aza nitrogen and the diiron sites are estimated to be 8.9-15.9 and <8.9, respectively. 1-2H(N)2H(Fe) has been observed to evolve H(2) electrocatalytically at a mild potential (-1.42 V vs Fc/Fc(+)) in CH(3)CN solution. Catalysis of 1-2H(N)2H(Fe) is found to be as efficient as that of the related diiron azadithiolate complexes. In the absence of a proton source, 1-2H(N)2H(Fe) undergoes four irreversible reduction processes at -1.26, -1.42, -1.82, and -2.43 V, which are attributed to the reduction events from 1-2H(N)2H(Fe), 1-2H(Fe), 1-2H(N), and 1, respectively, according to bulk electrolysis and voltammetry in combination of titration experiments with acids.
铁氮杂二硫醇膦取代配合物及其具有NH质子和/或桥联铁氢化物的质子化物种，即Fe(2)(μ-S(CH(2))(2)N(n)Pr(H)(m)(CH(2))(2)S)(μ-H)(n)(CO)(4)(PMe(3))(2)((2m + 2n)+) (1, m = n = 0; 1 - 2H(N), m = 1, n = 0; 1 - 2H(N)2H(Fe), m = n = 1)，被制备用于模拟仅含Fe的氢化酶的活性位点。对这三种配合物的X射线晶体学分析表明，两个二铁亚基通过两个氮杂二乙硫醇盐桥相连，构建了一个二聚体的二聚体结构。(31)P NMR光谱证实二铁部分内的两个三甲基膦配体以顶端/基部构型排列，这与固态结构表征一致。在三乙醇胺(TEOA)存在下，1 - 2H(N)和1 - 2H(N)2H(Fe)中的NH质子发生去质子化，分别生成1和1 - 2H(Fe)。通过加入双三苯基膦亚胺氯化物([PPN]Cl)实现铁氢化物的去质子化。观察到铁氢化物物种1 - 2H(Fe)是一种动力学产物，在溶液中会转化为其热力学稳定的互变异构体1 - 2H(N)，红外光谱和核磁共振光谱证明了这一点。氮杂氮和二铁位点的pK(a)值估计分别为8.9 - 15.9和<8.9。已观察到1 - 2H(N)2H(Fe)在CH(3)CN溶液中在温和电位(-1.42 V vs Fc/Fc(+))下电催化释放H(2)。发现1 - 2H(N)2H(Fe)的催化效率与相关的二铁氮杂二硫醇配合物相同。在没有质子源的情况下，1 - 2H(N)2H(Fe)在-1.26、-1.42、-1.82和-2.43 V处经历四个不可逆还原过程，根据大量电解和伏安法结合酸滴定实验，这些过程分别归因于从1 - 2H(N)2H(Fe)、1 - 2H(Fe)、1 - 2H(N)和1的还原事件。
