Synthesis, structure, spectral and electrochemical properties, and catalytic use of cobalt(III)-Oxo cubane clusters
Synthesis, structure, spectral and electrochemical properties, and catalytic use of cobalt(III)-Oxo cubane clusters
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DOI：
10.1021/ic7011759
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发表时间：
2007-10-29
影响因子：
4.6
通讯作者：
Das, Birinchi K.
中科院分区：
文献类型：
--
作者：
Chakrabarty, Rajesh;Bora, Sanchay J.;Das, Birinchi K.
通过H_2O_2氧化Co ~（2+）、MeCO ~（2-）和吡啶或4-取代吡啶的混合物（摩尔比为1：21），在甲醇中合成了通式为Co_4 O_4（O_2CMe）（4）L ~（-4）（1）的橄榄绿钴（III）配合物，其中L = py（1a），4-M_2O（1b），4-Etpy（1c）和4-CNpy（1d）。光谱和X射线晶体学研究表明，这些配合物含有一个四聚立方烷状核[CO_4（mu（3）-O）（4）]（4+），其中四个钴原子形成一个近似的四面体，边长约为2.75埃。在晶体学确定的结构中，1a中心点NaClO 4中心点3.5H（2）O和1b中心点3 H（2）O中的每一个钴都是六配位的，即CO 4（mu（3）-O）（4）（mu-O2 CMe）（4）L-4。配合物的红外光谱在700，635和580 cm（-1）附近显示出特征谱带，这是由于中心的立方烷状核。1H-1 NMR光谱的配合物表明，溶解的物种基本上是抗磁性的，也是配合物保持其完整性在溶液中。紫外-可见光谱的绿色解决方案已被解释的配位场和电荷转移带。用循环伏安法和微分脉冲伏安法研究了配合物的电化学行为，结果表明，配合物中的[（Co-III）（4）（mu（3）-O）（4）]（4+）核发生可逆的单电子氧化，生成[（Co-III）（3）Co-IV（mu（3）-O）（4）]（5+）核，其E-1/这表明这些钴的络合物可以适合作为有机化合物氧化的催化剂。初步研究表明，镧在钴催化的纯二甲苯和对二甲苯的有氧氧化中起作用。
Olive-green cobalt(III) complexes having the general formula Co4O4(O2CMe)(4)L-4 (1) where L = py (1a), 4-Mepy (1b), 4-Etpy (1c), and 4-CNpy (1d) have been prepared by the H2O2 oxidation of a mixture of Co2+, MeCO2-, and pyridine or 4-substituted pyridines in a 1:21 molar ratio in methanol. Spectroscopic and X-ray crystallographic studies show that these complexes contain a tetrameric cubane-like core [CO4(mu(3)-O)(4)](4+) where the four cobalt atoms form an approximate tetrahedron with edge lengths of similar to 2.75 A. Each cobalt in the crystallographically determined structure Of CO4(mu(3)-O)(4)(mu-O2CMe)(4)L-4 in 1a center dot NaCIO4 center dot 3.5H(2)O and 1b center dot 3H(2)O is hexacoordinate. Infrared spectra of the complexes show characteristic bands near 700, 635, and 580 cm(-1) due to the central cubane-like core. H-1 NMR spectra of the complexes show that the dissolved species are essentially diamagnetic and also that the complexes maintain their integrity in solution. UV-vis spectra of the green solutions have been interpreted in terms of ligand-field and charge-transfer bands. The electrochemical behavior of the complexes studied by cyclic and differential pulse voltammetric techniques indicates that the [(Co-III)(4)(mu(3)-O)(4)](4+) core present in the complexes undergoes a reversible one-electron oxidation to the [(Co-III)(3)Co-IV(mu(3)-O)(4)](5+) core with an E-1/2 value below 1 V. This suggests that these complexes of cobalt may be suitable as catalysts for the oxidation of organic compounds. Preliminary investigations indicate that la has a role to play in the cobalt-catalyzed aerobic oxidation of neat ethylbenzene and p-xylene.