Apically linked iron(ii) α-dioximate and α-oximehydrazonate bis-clathrochelates: synthesis, structure and electrocatalytic properties
作者:Irina G. Belaya、Semen V. Svidlov、Alexander V. Dolganov、Genrikh E. Zelinskii、Tamara V. Potapova、Anna V. Vologzhanina、Oleg A. Varzatskii、Yurii N. Bubnov、Yan Z. Voloshin
DOI:10.1039/c3dt50881a
日期:——
Iron(II) α-oximehydrazonate and α-dioximate bis-clathrochelates with apical hydrocarbon linkers were obtained by template condensation on an iron(II) ion followed by H+-catalyzed macrobicyclization of the bis-semiclathrochelate precursor with formaldehyde and triethyl orthoformate, and by transmetallation of the triethylantimony-containing clathrochelate precursor with diboron-containing bifunctional Lewis acids, respectively. The geometry of the para-phenylenediboron-capped iron(II) bis-clathrochelate studied by single-crystal X-ray diffraction is intermediate between a trigonal prism and a trigonal antiprism with a distortion angle of 20.4°; the rigidity of its C6H4 linker results in the presence of the expected three-fold pseudo-rotational Bâ¯Feâ¯Bâ¯Bâ¯Feâ¯B axis and a staggered conformation of the cyclohexane-containing chelate moieties. The cyclic voltammograms (CVs) for the oximehydrazonate bis-clathrochelates contain single one-electron (for each metallocentre, and therefore, two electrons per molecule) quasi-reversible reduction waves assigned to the redox-processes of Fe2+/+, and no interaction is observed between the two encapsulated iron(I)-containing metallocenters; six strong electron-withdrawing ethoxy substituents in the 1,3,5-triazacyclohexane capping fragments substantially affect the potential of this reduction. The corresponding waves for the dioximate complexes are irreversible: due to the structural rigidity of the caging tris-dioximate ligands, their reduced dianionic forms are unstable on the CV time scale. The CV for the hexaethoxy bis-clathrochelate complex contains one two-electron reversible oxidation wave assigned to the metal-centered oxidation of Fe2+/3+, whereas those for its dioximate analogs are quasi-reversible. The relative lability of the ligand cavity in binuclear oximehydrazonates causes a stabilization of both the oxidized and the reduced forms; the reduced iron(I)-containing species are highly electrocatalytically active in the hydrogen-producing 2H+/H2 reaction. Their higher activity as compared with that for dioximate bis-clathrochelates was explained by the higher availability of the catalytically active metallocentres for H+ ions.
通过铁(II)离子上的模板缩合,然后用甲醛和原甲酸三乙酯催化双羰基螯合物前体的 H+ 大双环化反应,得到了带有顶端碳氢化合物连接体的δ-肟肼酸铁(II)和δ-二氧杂环双羰基螯合物、以及用含二硼的双官能路易斯酸对含三乙基锑的螯合物前体进行反金属化。用单晶 X 射线衍射法研究的对位亚苯基二硼封端的双螯合铁(II)的几何形状介于三棱柱和三反棱柱之间,畸变角为 20.4°;其 C6H4 连接体的刚性导致了预期的三重假旋转 Bâ¯Feâ¯Bâ¯Bâ¯Feâ¯B 轴的存在以及含环己烷螯合物分子的交错构象。肟肼酸双螯合物的循环伏安图(CVs)包含单个单电子(每个金属中心,因此每个分子有两个电子)准可逆还原波,归因于 Fe2+/+ 的氧化还原过程,并且在两个封装的含铁(I)金属中心之间没有观察到相互作用;1,3,5-三氮杂环己烷封端片段中的六个强夺电子乙氧基取代基极大地影响了这种还原的电位。二氧杂环化合物的相应波形是不可逆的:由于笼状三-二氧杂环配体的结构刚性,它们的还原二离子形式在 CV 时间尺度上是不稳定的。六乙氧基双氯代螯合物的 CV 包含一个双电子可逆氧化波,该氧化波归因于 Fe2+/3+ 的金属中心氧化,而其二氧类似物的 CV 则是准可逆的。双核肟肼酸盐中配体空腔的相对易变性使氧化型和还原型都趋于稳定;含铁(I)的还原型在产氢的 2H+/H2 反应中具有很高的电催化活性。与二氧杂环双螯合物相比,它们的活性更高,这是因为催化活性金属中心对 H+ 离子的可用性更高。