A PNNH Pincer Ligand Allows Access to Monovalent Iron.
A PNNH Pincer Ligand Allows Access to Monovalent Iron.
复制标题
PNNH 钳配体允许接触单价铁。
作者：
A. Polezhaev;Cameron J Liss;J. Telser;Chun;K. G. Caulton
不对称臂的钳形PNNH（膦-吡啶基-吡唑）配体与FeCl 2反应产生五配位单体[（PNNH）FeCl 2]，其NH质子通过形成氢键捕获THF。用Li[N（SiMe 3）2 ]去质子化该NH官能团没有得到四配位[（PNN）FeCl]，而是保留了LiCl以产生[（PNNLi）FeCl 2]，其中锂在吡唑基β-氮和铁上的氯化物之一之间桥接。该化合物在CO作用下发生单电子还原，失去LiCl，形成四方锥结构的单价铁[（PNN）Fe（CO）2 ]，其特征在于通过IR，Mössbauer和EPR光谱，X射线衍射和DFT计算。循环伏安法研究表明[（PNN）Fe（CO）2 ]存在一个可逆的还原波，还原产物用KC 8合成。产物K[（PNN）Fe（CO）2 ]含有饱和的五配位Fe 0;（PNN）Fe亚基是阴离子，K+阳离子簇靠近两个CO配体的吡唑基侧。钾亲电体通过与相邻单元的CO的氧原子相互作用来完成其配位层，从而产生聚合物链。[（PNN）Fe（CO）2 ]与HBpin（4，4，5，5-四甲基-1，3，2-二氧杂硼杂环戊烷）的反应导致金属中心的还原（通过释放H2）和吡唑β-氮原子的硼基化。这种氧化还原活性的H-B键在金属-配体组装体上的加成是金属-配体协同性的一个不寻常的例子，并建立了一个支持三种不同氧化态铁的配体。
Reaction of the unsymmetrically armed pincer PNNH (phosphine-pyridyl-pyrazole) ligand with FeCl2 yielded the five-coordinate monomer [(PNNH)FeCl2 ], the NH proton of which captures THF through the formation of a hydrogen bond. Deprotonation of this NH functionality with Li[N(SiMe3 )2 ] did not give the four-coordinate [(PNN)FeCl], but instead retained LiCl to yield [(PNNLi)FeCl2 ], in which the lithium bridges between the pyrazolate β-nitrogen and one of the chlorides on iron. One-electron reduction of this compound under CO occurred with the loss of LiCl to form the square-pyramidal monovalent iron in [(PNN)Fe(CO)2 ], which was characterized by IR, Mössbauer, and EPR spectroscopy, X-ray diffraction, and DFT calculations. Cyclic voltammetry studies of [(PNN)Fe(CO)2 ] showed a reversible reduction wave and the reduction product was synthesized by using KC8 . The product K[(PNN)Fe(CO)2 ] contains saturated, five-coordinate Fe0 ; the (PNN)Fe subunit is anionic and the K+ cations cluster close to the pyrazolate side of the two CO ligands. Potassium electrophile complete its coordination sphere through interactions with the oxygen atom of a CO of a neighboring unit, thereby creating a polymeric chain. The reaction of [(PNN)Fe(CO)2 ] with HBpin (4,4,5,5-tetramethyl-1,3,2-dioxaborolane) resulted in the reduction of the metal center (by release of H2 ) and borylation of the pyrazole β-nitrogen atom. This redox-active addition of the H-B bond across the metal-ligand assembly is an unusual example of metal-ligand cooperativity and establishes a ligand that supports iron in three different oxidation states.
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