Iron Phosphine Catalyzed Cross-Coupling of Tetraorganoborates and Related Group 13 Nucleophiles with Alkyl Halides
Iron Phosphine Catalyzed Cross-Coupling of Tetraorganoborates and Related Group 13 Nucleophiles with Alkyl Halides
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DOI：
10.1021/om500518r
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发表时间：
2014-10-27
期刊：
影响因子：
2.8
通讯作者：
Taylor, Joseph
中科院分区：
文献类型：
--
作者：
Bedford, Robin B.;Brenner, Peter B.;Taylor, Joseph
铁膦络合物被证明是烷基、苄基和烯丙基卤化物与芳基三有机硼酸盐以及相关的铝、镓、铟和铊基亲核试剂交叉偶联的良好预催化剂。机理研究表明，虽然 Fe(I) 可以在催化相关的时间尺度上获得，但较低的平均氧化态的形成速度不够快，不足以与催化相关。 EPR 光谱研究揭示了在一系列 13 族亲核试剂的代表性催化反应和相关过程中存在双（二膦）铁（I）配合物。通过穆斯堡尔光谱和单晶 X 射线结构分析研究了孤立的例子，同时通过色散校正的 B3LYP DFT 计算探测了电子结构。对具有大二膦配体的铁系统的 EPR 研究揭示了 S = 1/2 物质的存在，这与具有不等膦供体环境的单（二膦）铁（I）物质的形成一致。对模型配合物的 DFT 分析使我们能够排除 T 形 Fe(I) 结构，因为预计它是高自旋的。
Iron phosphine complexes prove to be good precatalysts for the cross-coupling of alkyl, benzyl, and allyl halides with not only aryl triorganoborate salts but also related aluminum-, gallium-, indium-, and thallium-based nucleophiles. Mechanistic studies revealed that while Fe(I) can be accessed on catalytically relevant time scales, lower average oxidation states are not formed fast enough to be relevant to catalysis. EPR spectroscopic studies reveal the presence of bis(diphosphine)iron(I) complexes in representative catalytic reactions and related processes with a range of group 13 nucleophiles. Isolated examples were studied by Mossbauer spectroscopy and single-crystal X-ray structural analysis, while the electronic structure was probed by dispersion-corrected B3LYP DFT calculations. An EPR study on an iron system with a bulky diphosphine ligand revealed the presence of an S = 1/2 species consistent with the formation of a mono(diphosphine)iron(I) species with inequivalent phosphine donor environments. DFT analysis of model complexes allowed us to rule out a T-shaped Fe(I) structure, as this is predicted to be high spin.