Iron(III) complexes of multidentate pyridinyl ligands: synthesis, characterization and catalysis of the direct hydroxylation of benzene.
Iron(III) complexes of multidentate pyridinyl ligands: synthesis, characterization and catalysis of the direct hydroxylation of benzene.
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DOI：
10.1039/c4dt02032d
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发表时间：
2014-09
影响因子：
4
通讯作者：
Beibei Xu;W. Zhong;Zhenhong Wei;Hailong Wang;Jian Liu;Li Wu;Yonggang Feng;Xiaoming Liu
中科院分区：
文献类型：
--
作者：
Beibei Xu;W. Zhong;Zhenhong Wei;Hailong Wang;Jian Liu;Li Wu;Yonggang Feng;Xiaoming Liu
合成了三个以二（吡啶-2-亚甲基）胺（L ′）为配体的多齿配体L ′-L ′。在甲醇中，这些配体与FeCl 3·6 H2 O反应，以较好的产率生成了铁的配合物Fe-Fe（Fe：[FeL Cl 3]; Fe：[FeL Cl 3]; Fe：[FeL Cl 3]）。这些配合物已被充分表征。用X-射线单晶衍射分析确定了配合物Fe_（1-x）-Fe_（2-x）的结构。电化学研究表明，配合物Fe（Ⅲ）在溶液中部分转化为Fe（Ⅲ）（[FeL <$Cl 2] PF 6），其三个氯化物中的一个被三唑基取代。以AgPF_6为Cl（-）提取剂脱氯合成了Fe_（2+），其组成经元素分析和X射线单晶衍射分析得到进一步证实。在水和乙腈的混合介质中，四种配合物均催化过氧化氢氧化苯直接羟基化为苯酚。配合物的反应活性与其还原电位密切相关。电位越负，催化剂的反应性越强（高转化率）。这些配合物不仅催化苯的氧化，而且还催化产物苯酚的进一步氧化。在氧化过程中，当然涉及自由基机制，但也可能存在替代途径。
Three multidentate ligands, L₁-L₃, derived from bis(pyridin-2-ylmethyl)amine (L₁) were synthesized. Reaction of these ligands with FeCl3·6H2O in methanol led to the formation of the iron complexes Fe₁-Fe₃ (Fe₁: [FeL₁Cl3]; Fe₂: [FeL₂Cl3]; Fe₃: [FeL₃Cl3]) in good yields. These complexes have been fully characterized. The structures of complexes Fe₁-Fe₃ have been determined using X-ray single crystal diffraction analysis. Electrochemical investigation revealed that complex Fe₃ partially converts to Fe₄ ([FeL₃Cl2]PF6) by the replacement of one of its three chlorides with its pendant triazolyl group in solution. Fe₄ was also synthesized by dechlorination using AgPF6 as the Cl(-) abstractor and its composition was further confirmed by both elemental analysis and X-ray single crystal diffraction analysis. All four complexes catalyze the direct hydroxylation of benzene to phenol with hydrogen peroxide as an oxidant in a mixed medium of water and acetonitrile. The reactivity of the complexes correlates well with their reduction potentials. The more negative the potential, the more reactive (high conversion rate) the catalysts. These complexes catalyze not only the oxidation of benzene, but also the further oxidation of the product, phenol. In the oxidation, a radical mechanism is certainly involved but an alternative pathway may also exist.