Binuclear cobalt complexes of Schiff-base calixpyrroles and their roles in the catalytic reduction of dioxygen.
Binuclear cobalt complexes of Schiff-base calixpyrroles and their roles in the catalytic reduction of dioxygen.
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希夫碱杯吡咯的双核钴配合物及其在双氧催化还原中的作用。
DOI：
10.1021/ic9001175
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发表时间：
2009
影响因子：
4.6
通讯作者：
Volpe M
中科院分区：
文献类型：
--
作者：
Volpe M
本文报道了一系列八齿席夫碱杯吡咯配体L的双核钴配合物的合成与表征。钴（II）配合物[Co2（L）]是通过氨基转移法制备的，并且发现在固态和溶液中采用楔形的Pac-man几何形状。将该化合物暴露于分子氧导致形成过氧[Co2（O2）（L）]和超氧[Co2（O2）（L）]+络合物的90：10混合物，其中发现过氧配体以Pauling模式结合在固态的吡啶和乙腈加合物的双核裂缝中。双氧化合物也可以在有氧条件下在碱的存在下由Co（OAc）2和H4 L直接制备。使用循环伏安法和旋转环盘电化学研究了这种化合物的混合物催化的双氧还原，并在酸化的二茂铁溶液中使用紫外-维斯分光光度法，虽然没有看到过氧化物的形成，但反应速率很慢，并且有有限的周转。催化剂材料的失活被认为是由于形成稳定的羟基桥接的双核络合物（例如，[Co2（OH）（L）]+，其实例在结构上表征）和催化静止点（超氧阳离子）的组合，所述催化静止点通过独立于主要过氧产物的途径形成。碰撞诱导解离质谱实验表明，虽然[Co2（O2）（L）]H+离子很容易失去一个O原子，但产生的Co-O（H）-Co核心仍然抵抗进一步的碎裂。此外，DFT计算表明，双氧复合物中的O−O键距并不能很好地指示O2单元的还原程度，并提供了约的还原电位。对于二氯甲烷溶液中的[Co2（O2）（L）]+/0电对，相对于正常氢电极为+0.40 V。
The syntheses and characterization of a series of binuclear cobalt complexes of the octadentate Schiff-base calixpyrrole ligand L are described. The cobalt(II) complex [Co2(L)] was prepared by a transamination method and was found to adopt a wedged, Pac-man geometry in the solid state and in solution. Exposure of this compound to dioxygen resulted in the formation of a 90:10 mixture of the peroxo [Co2(O2)(L)] and superoxo [Co2(O2)(L)]+complexes in which the peroxo ligand was found to bind in a Pauling mode in the binuclear cleft in pyridine and acetonitrile adducts in the solid state. The dioxygen compounds can also be prepared directly from Co(OAc)2and H4L under aerobic conditions in the presence of a base. The reduction of dioxygen catalyzed by this mixture of compounds was investigated using cyclic voltammetry and rotating ring disk electrochemistry and, in acidified ferrocene solutions, using UV−vis spectrophotometry, and although no formation of peroxide was seen, reaction rates were slow and had limited turnover. The deactivation of the catalyst material is thought to be due to a combination of the formation of stable hydroxy-bridged binuclear complexes, for example, [Co2(OH)(L)]+, an example of which was characterized structurally, and the catalytic resting point, the superoxo cation, is formed by a pathway independent of the major peroxo product. Collision-induced dissociation mass spectrometry experiments showed that, while [Co2(O2)(L)]H+ions readily lose a single O atom, the resulting Co−O(H)−Co core remains resistant to further fragmentation. Furthermore, DFT calculations show that the O−O bond distance in the dioxygen complexes is not a good indicator of the degree of reduction of the O2unit and provide a reduction potential of ca. +0.40 V versus the normal hydrogen electrode for the [Co2(O2)(L)]+/0couple in dichloromethane solution.