Isolation of a Mixed Valence Diiron Hydride: Evidence for a Spectator Hydride in Hydrogen Evolution Catalysis
Isolation of a Mixed Valence Diiron Hydride: Evidence for a Spectator Hydride in Hydrogen Evolution Catalysis
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DOI：
10.1021/ja312458f
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发表时间：
2013-03-06
影响因子：
15
通讯作者：
Stein, Matthias
中科院分区：
文献类型：
--
作者：
Wang, Wenguang;Nilges, Mark J.;Stein, Matthias
采用十甲基钴二烯酸还原不同的氢化物[H1](+)，得到混合价二铁氢化物配合物（mu H）Fe-2(pdt)(CO)(2)(dppv)(2) ([H1](0)，其中pdt =1,3-丙二硫酸酯，dppv =顺式-1,2- c2h2 （PPh2)(2)）。晶体学分析表明[H1](0)保留了其前体的立体化学性质，其中一个dppv配体横跨两个基位，另一个横跨顶端和基位。Fe-Fe键从2.66埃延长到2.80埃，但Fe-P键的变化很小。虽然在前驱体中Fe-H距离难以区分，但在[H1](0)中相差0.2埃。x波段电子顺磁共振（EPR）谱显示了两种立体异构体的存在，其中一种具有晶体特征，另一种对称（sym）异构体的贡献约为10%，其中两种dppv配体都位于顶基位置。dppv配体的不对称（不对称）排列反映在A（P-31）的值上，其范围从31 MHz的基础磷化氢到284 MHz的顶端磷化氢。利用密度泛函理论计算对[H1](0)的电子结构进行合理化，并对包括H-1和P-31超精细耦合在内的EPR参数进行光谱模拟和赋值。[HI](0)和[D1](0)的EPR谱表明，单占据分子轨道主要定位于与H键较长的Fe中心，即Fe- ii -H中心点中心点中心点Fe- i。对于unsym-和sym[H1](0)，与氢化物的耦合分别为A(H-1) = 55和74 MHz。用H+处理[H1](0)得到相当于H-2和[H1]（+）的0.5。D+还原得到D-2，使氢化物配体保持完整。这些实验表明，该配合物中的桥接氢化物配体是析氢反应的旁观者。
The mixed-valence diiron hydrido complex (mu H)Fe-2(pdt)(CO)(2)(dppv)(2) ([H1](0), where pdt =1,3-propanedithiolate and dppv = cis-1,2-C2H2(PPh2)(2)), was generated by reduction of the differous hydride [H1](+) using decamethylcobaltocene. Crystallographic analysis shows that [H1](0) retains the stereochemistry of its precursor, where one dppv ligand spans two basal sites and the other spans apical and basal positions. The Fe-Fe bond elongates to 2.80 from 2.66 angstrom, but the Fe-P bonds only change subtly. Although the Fe-H distances are indistinguishable in the precursor, they differ by 0.2 angstrom in [H1](0). The X-band electron paramagnetic resonance (EPR) spectrum reveals the presence of two stereoisomers, the one characterized crystallographically and a contribution of about 10% from a second symmetrical (sym) isomer wherein both dppv ligands occupy apical-basal sites. The unsymmetrical (unsym) arrangement of the dppv ligands is reflected in the values of A(P-31), which range from 31 MHz for the basal phosphines to 284 MHz for the apical phosphine. Density functional theory calculations were employed to rationalize the electronic structure of [H1](0) and to facilitate spectral simulation and assignment of EPR parameters including H-1 and P-31 hyperfine couplings. The EPR spectra of [HI](0) and [D1](0) demonstrate that the singly occupied molecular orbital is primarily localized on the Fe center with the longer bond to H, that is, Fe-II-H center dot center dot center dot Fe-I. The coupling to the hydride is A(H-1) = 55 and 74 MHz for unsym- amd sym[H1](0), respectively. Treatment of [H1](0) with H+ gives 0.5 equiv of H-2 and [H1](+). Reduction of D+ affords D-2, leaving the hydride ligand intact. These experiments demonstrate that the bridging hydride ligand in this complex is a spectator in the hydrogen evolution reaction.