Modeling [Fe-Fe] hydrogenase: evidence for bridging carbonyl and distal iron coordination vacancy in an electrocatalytically competent proton reduction by an iron thiolate assembly that operates through Fe(0)-Fe(II) levels
Modeling [Fe-Fe] hydrogenase: evidence for bridging carbonyl and distal iron coordination vacancy in an electrocatalytically competent proton reduction by an iron thiolate assembly that operates through Fe(0)-Fe(II) levels
复制标题
DOI：
10.1021/ja071331f
复制
发表时间：
2007-09-12
影响因子：
15
通讯作者：
Best, Stephen P.
中科院分区：
文献类型：
--
作者：
Cheah, Mun Hon;Tard, Cedric;Best, Stephen P.
在ν(CO)区域对Fe - 4{Me(CH₂S)₃}₂(CO)₈（4Fe6S）进行的红外光谱电化学研究表明，中性和阴离子形式的所有CO基团都末端结合在Fe原子上；然而，对于二价阴离子，至少有一个CO基团的配位模式发生了转变。密度泛函理论计算紧密地重现了现有的结构和ν(CO)光谱。4Fe6S²⁻的计算结构与[Fe - Fe]氢化酶H簇的双铁亚位点非常相似，具有一个桥连的CO基团以及在由两个桥连硫醇盐连接的成对二硫醇盐桥连(FeFe11)-Fe - 0亚基的外层Fe原子上的一个开放配位位点。基于4Fe6S²⁻的全末端CO异构体进行的几何优化没有得到稳定结构，但揭示了一个二阶鞍点，其能量比CO桥连形式高约11.53 kcal/mol。对4Fe6S电催化质子还原的光谱电化学研究表明，从初级还原过程（相对于Ag/AgCl，E₁/₂′ = -0.71 V）的缓慢转换涉及4Fe6S⁻的限速质子化，随后还原为H:4Fe6S⁻。在足以生成4Fe6S²⁻的电位下可实现快速电催化质子还原，其中从4Fe6S的(FeFe11)-Fe - 11核心消除氢气的速率比从Fe₂(μ - S(CH₂)₃S)(CO)₆的(FeFe1)-Fe - 1核心快约500倍。与之前所有已确定的模型化合物相比，从4Fe6S获得的电催化速率显著提高，这似乎与其和H - 簇之间独特的共同特征有关，即转换涉及双铁单元相同的形式氧化还原态((FeFe11)-Fe - 1和(FeFe11)-Fe - 0)，(FeFe11)-Fe - 0单元外层Fe原子上存在一个开放位点，以及与第二个单电子氧化还原单元的硫醇盐桥连。
IR spectroelectrochemistry of Fe-4{Me(CH2S)(3)}(2)(CO)(8) (4Fe6S) in the v(CO) region shows that the neutral and anion forms have all their CO groups terminally bound to the Fe atoms; however, for the dianion there is a switch of the coordination mode of at least one of the CO groups. The available structural and v(CO) spectra are closely reproduced by density-functional theory calculations. The calculated structure of 4Fe6S(2)- closely mirrors that of the diiron subsite of the [Fe-Fe] hydrogenase H cluster with a bridging CO group and an open coordination site on the outer Fe atom of pairs of dithiolate-bridged (FeFe11)-Fe-0 subunits connected by two bridging thiolates. Geometry optimization based on the all-terminal CO isomer of 4Fe6S(2)does not give a stable structure but reveals a second-order saddle point ca. 11.53 kcal mol(-1) higher in energy than the CO-bridged form. Spectroelectrochemical studies of electrocatalytic proton reduction by 4Fe6S show that slow turnover from the primary reduction process (E-1/2' = -0.71 V vs Ag/AgCl) involves rate-limiting protonation of 4Fe6S(-) followed by reduction to H:4Fe6S-. Rapid electrocatalytic proton reduction is obtained at potentials sufficient to access 4Fe6S2-, where the rate of dihydrogen elimination from the (FeFe11)-Fe-11 core of 4Fe6S is ca. 500 times faster than that from the (FeFe1)-Fe-1 core of Fe-2(mu-S(CH2)(3)S)(CO)(6). The dramatically increased rate of electrocatalysis obtained from 4Fe6S over all previously identified model compounds appears to be related to the features uniquely common between it and the H-cluster, namely, that turnover involves the same formal redox states of the diiron unit ((FeFe11)-Fe-1 and (FeFe11)-Fe-0), the presence of an open site on the outer Fe atom of the (FeFe11)-Fe-0 unit, and the thiolate-bridge to a second one-electron redox unit.