Synthesis, Reactivity, and Electronic Structure of a Bioinspired Heterobimetallic [Ni(μ‑S2)Fe] Complex with Disulfur Monoradical character

The
first synthesis of a monoradical Ni­(μ-S2)­Fe
core in the [(Nacnac)­Ni­(μ-S2)­Fe­(dmpe)2] complex 3 could be accomplished in good yields by
PMe3 elimination from the zerovalent iron complex [(dmpe)2(PMe3)­Fe] (2; dmpe =1,2-bis­(dimethylphosphine)­ethane)
upon reaction with the supersulfido nickel­(II) complex [(Nacnac)­Ni­(S2)] (1; Nacnac = CH­{(CMe)­(2,6-iPr2C6H3N)}2). Complex 3 bears Ni­(II) and Fe­(II) centers, both of which are in a
low-spin state. A single electron is located in the HOMO and is somewhat
delocalized over the Ni­(μ-S2)Fe core, so that the
bridging disulfur subunit exhibits some “subsulfide”
S23– character. Compound 3 represents a bioinspired example of a monoradical with a Ni­(μ-S2)Fe structural motif, reminiscent of the Ni­(μ-S2)Fe core structure of the active site in [NiFe] hydrogenases.
Its oxidation with [Fe­(η5-C5H5)2]­[B­(C6H3(CF3)2)4] affords the product [(Nacnac)­Ni­(μ-S)2Fe­(dmpe)2]­[B­(C6H3(CF3)2)4] (4), and complex 3 can alternatively be prepared via a reductive route upon reaction
of [Co­(η5-C5Me5)2]­[(Nacnac)­NiS2] (6) with the Fe(0) precursor 2. All synthesized complexes were fully characterized, including
in some cases single-crystal X-ray diffraction analysis, magnetometry,
EPR, NMR, and 57Fe Mössbauer spectroscopy. DFT calculations
were used to compute the spectroscopic parameters and to establish
the electronic structure of 3 and its oxidized and reduced
forms and related complexes.

首次成功合成了一例单核素镍（μ-S2）铁核，该核素存在于[(Nacnac)­Ni­(μ-S2)­Fe­(dmpe)2]复合物3中，其合成过程通过从零价铁复合物[(dmpe)2(PMe3)­Fe]（2；dmpe =1,2-双（二甲基膦）乙烷）中消除PMe3，并与超硫代镍（II）复合物[(Nacnac)­Ni­(S2)]（1；Nacnac = CH­{(CMe)­(2,6-iPr2C6H3N)}2）反应而实现。复合物3含有镍（II）和铁（II）中心，两者均处于低自旋态。单电子位于最高占据分子轨道（HOMO）中，并在镍（μ-S2）铁核心上呈现出某种程度的离域，使得桥连二硫亚基显示出一定的“亚硫代”S23-特征。化合物3代表了一种生物启发性的单核素实例，具有镍（μ-S2）铁结构模式，与[NiFe]氢化酶活性位点的镍（μ-S2）铁核心结构相似。通过与[Fe­(η5-C5H5)2]­[B­(C6H3(CF3)2)4]的氧化反应，可得产物[(Nacnac)­Ni­(μ-S)2Fe­(dmpe)2]­[B­(C6H3(CF3)2)4]（4），且复合物3还可通过[Co­(η5-C5Me5)2]­[(Nacnac)­NiS2]（6）与铁（0）前体2的反应，通过还原途径来制备。所有合成的复合物均得到了全面表征，包括某些情况下的单晶X射线衍射分析、磁测量、EPR、NMR以及57Fe Mössbauer光谱学。DFT计算被用于计算光谱学参数，并确定3及其氧化和还原形式及相关复合物的电子结构。