Korendovych Ivan V, Kryatova Olga P, Reiff William M, Rybak-Akimova Elena V
Department of Chemistry, Tufts University, Medford, Massachusetts 02155, USA.
Inorg Chem. 2007 May 14;46(10):4197-211. doi: 10.1021/ic0701209. Epub 2007 Apr 10.
Iron(II) complexes of macrocyclic pentadendate ligands 3,6,9,12,18-pentaazabicyclo[12.3.1]octadeca-1(18),14,16-triene-2,13-dione (H2pydioneN5) and 16-chloro-3,6,9,12,18-pentaazabicyclo[12.3.1]octadeca-1(18),14,16-triene-2,13-dione (H2pyCldioneN5) were synthesized and fully characterized. Complexes with one or two deprotonated amide groups of H2pydione were both isolated. In the former case the metal ion has a distorted octahedral coordination sphere; in the latter case the complex adopts a pentagonal-bipyramidal geometry. NMR experiments show that the protonation state of the ligand is preserved in a dimethyl sulfoxide (DMSO) solution. The complexes maintain a high-spin state even at low temperatures. Detailed kinetic studies of oxygenation of the iron(II) complexes showed that the deprotonation state of the complex has a profound effect on the reactivity with dioxygen. Oxygenation of the dideprotonated complex of iron(II), Fe(pydioneN5), in aprotic solvents proceeds via a path that is analogous to that of iron(II) porphyrins: via iron(III) superoxo and diiron(III) peroxo species, as evidenced by the spectral changes during the reaction, which is second-order in the concentration of the iron(II) complex, and with an inverse dependence of the reaction rate on the concentration of dioxygen. The final products of oxygenation are crystallographically characterized iron(III) mu-oxo dimers. We have also found that the presence of 1-methylimidazole stabilizes the diiron peroxo intermediate. The reaction of Fe(pydioneN5) with dioxygen in methanol is distinctly different under the same conditions. The reaction is first-order in both iron(II) complex and dioxygen, and no intermediate is spectroscopically observed. Similar behavior was observed for the monodeprotonated complex Fe(HpydioneN5)(Cl). The presence of an accessible proton either from the solvent (reactions in methanol) or from the complex itself (in Fe(HpydioneN5)(Cl)) proves sufficient to alter the oxygenation pathway in these macrocyclic systems, which is reminiscent of the properties of iron(II) porphyrin complexes. The new amidopyridine macrocycles can be considered as new members of the "expanded porphyrin analogue" family. The expansion of the cavity provides control over the spin state and availability of protons. These macrocyclic systems also allow for easy synthetic modifications, paving the way to new, versatile metal complexes.
合成并全面表征了大环五齿配体3,6,9,12,18 - 五氮杂双环[12.3.1]十八碳 - 1(18),14,16 - 三烯 - 2,13 - 二酮（H₂pydioneN₅）和16 - 氯 - 3,6,9,12,18 - 五氮杂双环[12.3.1]十八碳 - 1(18),14,16 - 三烯 - 2,13 - 二酮（H₂pyCldioneN₅）的铁（II）配合物。分离出了含有一个或两个H₂pydione去质子化酰胺基团的配合物。在前一种情况下，金属离子具有扭曲的八面体配位球；在后一种情况下，配合物采用五角双锥几何构型。核磁共振实验表明，配体的质子化状态在二甲基亚砜（DMSO）溶液中得以保留。即使在低温下，这些配合物也保持高自旋态。对铁（II）配合物氧化的详细动力学研究表明，配合物的去质子化状态对与双氧的反应活性有深远影响。在非质子溶剂中，铁（II）的双去质子化配合物Fe(pydioneN₅)的氧化通过一条类似于铁（II）卟啉的路径进行：通过铁（III）超氧和二铁（III）过氧物种，反应过程中的光谱变化证明了这一点，该反应对铁（II）配合物的浓度是二级反应，且反应速率与双氧浓度呈反比。氧化的最终产物是通过晶体学表征的铁（III）μ - 氧二聚体。我们还发现1 - 甲基咪唑的存在稳定了二铁过氧中间体。在相同条件下，Fe(pydioneN₅)与双氧在甲醇中的反应明显不同。该反应对铁（II）配合物和双氧均为一级反应，且未观察到光谱学上的中间体。对于单去质子化配合物Fe(HpydioneN₅)(Cl)也观察到了类似行为。无论是来自溶剂（甲醇中的反应）还是配合物本身（在Fe(HpydioneN₅)(Cl)中）的可接近质子的存在，都足以改变这些大环体系中的氧化途径，这让人想起铁（II）卟啉配合物的性质。新的酰胺吡啶大环可以被视为“扩展卟啉类似物”家族的新成员。空腔的扩展提供了对自旋态和质子可用性的控制。这些大环体系还便于进行合成修饰，为新型多功能金属配合物铺平了道路。
