Department of Chemistry and Center for Environmentally Beneficial Catalysis, University of Kansas, Lawrence, Kansas 66045, USA.
J Am Chem Soc. 2010 Mar 3;132(8):2821-31. doi: 10.1021/ja910235g.
A set of four Mn(II)(L(7)py(2)(R)) complexes, supported by the tetradentate 1,4-bis(2-pyridylmethyl)-1,4-diazepane ligand and derivatives with pyridine substituents in the 5 (R = Br) and 6 positions (R = Me and MeO), are reported. X-ray crystal structures of these complexes all show the L(7)py(2)(R) ligands bound to give a trans complex. Treatment of these Mn(II) precursors with either H(2)O(2)/Et(3)N or KO(2) in MeCN at -40 degrees C results in the formation of peroxomanganese complexes Mn(III)(O(2))(L(7)py(2)(R)) differing only in the identity of the pyridine ring substituent. The electronic structures of two of these complexes, Mn(III)(O(2))(L(7)py(2)(H)) and Mn(III)(O(2))(L(7)py(2)(Me)), were examined in detail using electronic absorption, low-temperature magnetic circular dichroism (MCD) and variable-temperature variable-field (VTVH) MCD spectroscopies to determine ground-state zero-field splitting (ZFS) parameters and electronic transition energies, intensities, and polarizations. DFT and TD-DFT computations were used to validate the structures of Mn(III)(O(2))(L(7)py(2)(H)) and Mn(III)(O(2))(L(7)py(2)(Me)), further corroborating their assignment as peroxomanganese(III) species. While these complexes exhibit similar ZFS parameters, their low-temperature MCD spectra reveal significant shifts in electronic transition energies that are correlated to differences in Mn-O(2) interactions among these complexes. Taken together, these results indicate that, while the Mn(III)(O(2))(L(7)py(2)(H)) complex exhibits symmetric Mn-O(peroxo) bond lengths, consistent with a side-on bound peroxo ligand, the peroxo ligand of the Mn(III)(O(2))(L(7)py(2)(Me)) complex is bound in a more end-on fashion, with asymmetric Mn-O(peroxo) distances. This difference in binding mode is rationalized in terms of the greater electron-donating abilities of the methyl-appended pyridines and suggests a simple way to modulate Mn(III)-O(2) bonding through ligand perturbations.
报道了一组四个Mn(II)(L(7)py(2)(R))配合物，这些配合物由四齿配体 1,4-双(2-吡啶基甲基)-1,4-二氮杂环庚烷和在 5 位（R = Br）和 6 位（R = Me 和 MeO）具有吡啶取代基的衍生物支持。这些配合物的 X 射线晶体结构均显示 L(7)py(2)(R)配体呈反式结合。在-40℃下，用 H(2)O(2)/Et(3)N 或 KO(2)处理这些 Mn(II)前体，可形成过氧锰配合物Mn(III)(O(2))(L(7)py(2)(R))，不同之处仅在于吡啶环取代基的不同。这两种配合物Mn(III)(O(2))(L(7)py(2)(H))和Mn(III)(O(2))(L(7)py(2)(Me))的电子结构使用电子吸收、低温磁圆二色性（MCD）和变温变场（VTVH）MCD 光谱法进行了详细研究，以确定基态零场分裂（ZFS）参数和电子跃迁能量、强度和偏振。DFT 和 TD-DFT 计算用于验证Mn(III)(O(2))(L(7)py(2)(H))和Mn(III)(O(2))(L(7)py(2)(Me))的结构，进一步证实了它们作为过氧锰(III)物种的归属。尽管这些配合物表现出相似的 ZFS 参数，但它们的低温 MCD 光谱揭示了电子跃迁能量的显著位移，这与这些配合物中 Mn-O(2)相互作用的差异有关。总之，这些结果表明，尽管Mn(III)(O(2))(L(7)py(2)(H))配合物表现出对称的 Mn-O(过氧)键长，与侧接绑定的过氧配体一致，但Mn(III)(O(2))(L(7)py(2)(Me))配合物的过氧配体以更端接的方式结合，具有不对称的 Mn-O(过氧)距离。这种结合模式的差异可以根据附加吡啶的供电子能力来解释，并提出了一种通过配体扰动调节 Mn(III)-O(2)键合的简单方法。
