We report the coordination chemistry of indole based tripodal tetraphosphine ligands to iron(II), cobalt(II) and nickel(II). These complexes are formed by simple synthetic protocols and were characterized by a combination of spectroscopic techniques and single‐crystal X‐ray analysis. The molecular structures as determined by X‐ray diffraction show that the geometry of the nickel and cobalt complexes are distorted trigonal bipyramidal. The monocationic iron(II) complexes also have distorted trigonal bipyramidal geometries, but the dicationic analogue has an octahedral geometry. Two‐electron reduction of the cobalt(+II) and the nickel(+II) complexes in the presence of N2 did not lead to the coordination of N2. In contrast, two‐electron reduction of the iron(+II) complexes did lead to coordination of dinitrogen to the iron center. The Fe0N2 L1H complex has a trigonal bipyramidal geometry, and the N–N bond length of the coordinated dinitrogen ligand is longer than that of free dinitrogen, indicating that coordination to this iron(0) complex results in activation of the N≡N bond.

中文翻译：

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3-甲基吲哚基三足四膦配体与铁(+II)、钴(+II)和镍(+II)的配位及其后续双电子还原研究

我们报道了基于吲哚的三足四膦配体与铁(II)、钴(II)和镍(II)的配位化学。这些复合物是通过简单的合成方案形成的，并通过光谱技术和单晶 X 射线分析的结合来表征。X射线衍射测定的分子结构表明镍钴配合物的几何形状是扭曲的三角双锥体。单阳离子铁(II)配合物也具有扭曲的三角双锥几何形状，但双阳离子类似物具有八面体几何形状。在 N2 存在下，钴（+II）和镍（+II）配合物的双电子还原不会导致 N2 的配位。相反，铁(+II)络合物的双电子还原确实导致二氮与铁中心的配位。Fe0N2 L1H配合物具有三角双锥几何形状，并且配位二氮配体的N-N键长度比游离二氮长，表明与该铁(0)配合物的配位导致N−N键的激活。