Structural and chemical properties of half-sandwich rhodium complexes supported by the bis(2-pyridyl)methane ligand
Structural and chemical properties of half-sandwich rhodium complexes supported by the bis(2-pyridyl)methane ligand
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双(2-吡啶基)甲烷配体负载的半夹心铑配合物的结构和化学性质
DOI：
10.1039/c9dt01821b
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发表时间：
2019
影响因子：
4
通讯作者：
Blakemore, James D.
中科院分区：
文献类型：
--
作者：
Lionetti, Davide;Day, Victor W.;Blakemore, James D.
[Cp双齿螯合配体负载的[Rh]配合物（Cp* =五甲基环戊二烯基）是一类用于氧化还原化学和催化研究的有用化合物。在这里，我们表明双（2-吡啶基）甲烷配体（也称为二吡啶基甲烷或dpma）可以支持形式上+III和+II铑氧化态的[Cp*Rh]配合物。具体地说，两个新的铑配合物（[Cp*Rh（dpma）（L）]n+，L = Cl−，CH 3CN）已被分离和结构表征，并已与带有相关的二甲基二吡啶基甲烷（Me 2dpma）配体的[Cp*Rh]配合物的性质进行了比较。配合物[Cp*Rh（dpma）（NCCH 3）]2+显示准可逆的铑（III/II）的还原循环伏安法;相关的电子顺磁共振（EPR）光谱研究证实获得不寻常的铑（II）的氧化态。然而，如电化学研究和化学还原实验中所观察到的，进一步还原到形式上的铑（I）氧化态之后是dpma的去质子化。这种反应性可以理解为由于dpma配体中存在双苄基质子而发生，因为使用类似的Me 2dpma能够在不涉及配体去质子化的情况下还原成铑（I）。这些研究结果突出了配体骨架取代模式在影响高度还原的络合物的稳定性方面的重要作用，高度还原的络合物是用于研究催化中的电子和质子管理的一类关键金属物种。
[Cp*Rh] complexes (Cp* = pentamethylcyclopentadienyl) supported by bidentate chelating ligands are a useful class of compounds for studies of redox chemistry and catalysis. Here, we show that the bis(2-pyridyl)methane ligand, also known as dipyridylmethane or dpma, can support [Cp*Rh] complexes in the formally +III and +II rhodium oxidation states. Specifically, two new rhodium complexes ([Cp*Rh(dpma)(L)]n+, L = Cl−, CH3CN) have been isolated and structurally characterized, and the properties of the complexes have been compared with those of [Cp*Rh] complexes bearing the related dimethyldipyridylmethane (Me2dpma) ligand. Complex [Cp*Rh(dpma)(NCCH3)]2+ displays a quasireversible rhodium(III/II) reduction by cyclic voltammetry; related electron paramagnetic resonance (EPR) spectroscopic studies confirm access to the unusual rhodium(II) oxidation state. Further reduction to the formally rhodium(I) oxidation state, however, is followed by deprotonation of dpma, as observed in electrochemical studies and chemical reduction experiments. This reactivity can be understood to occur as a consequence of the presence of doubly benzylic protons in the dpma ligand, since use of the analogous Me2dpma enables reduction to rhodium(I) without involvement of ligand deprotonation. These findings highlight the important role of the ligand backbone substitution pattern in influencing the stability of highly-reduced complexes, a key class of metal species for study of electron and proton management in catalysis.