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首页> 外文期刊>Chemistry: A European journal >pi-face donor properties of N-heterocyclic carbenes in Grubbs II complexes
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pi-face donor properties of N-heterocyclic carbenes in Grubbs II complexes

机译：Grubbs II配合物中N-杂环卡宾的pi-face供体性质

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摘要

The electron-donating properties of eighteen N-heterocyclic carbenes (N,N'-bis(2,6-dimethylphenyl)imidazol)-2-ylidene and the respective dihydro ligands) with 4,4'-R substituted aryl rings (4,4'-R = NEt2, OMe, Me, H, SMe, F, Cl, Br, I) in the respective Grubbs II complexes were studied using electrochemical techniques. The nature of the 4-R substituent has a strong influence on the Ru-II/III redox potentials ranging between Delta E-1/2 = + 0.196 and + 0.532 V Three unsymmetrical Grubbs II complexes with 4-R = 4-R' were also synthesized. Dynamic NMR spectroscopy revealed the restricted rotation around the (NHC)C-Ru bond (Delta G = 89 kJ mol(-1) at 333 K) resulting in two atropisomers, respectively, with an isomer ratio close to unity. Each of the isomers, that is the two orientations of the 4-R/4-R' substituted mesityl ring with respect to the R=CHPh unit, gives rise to different redox potentials (4-R = NEt2, 4-R' = Br: Delta E-1/2 = + 0.232 and + 0.451 V). In the oxidized Grubbs II complex (4-R = NEt2, H) and in the cathodic isomer the electron rich aryl ring is located above the Ru=CHPh unit. This orientational effect provides clear evidence for strong pi-pi through-space interactions in the Ru-III complexes, assuming that the alternative through-bond transfer of electron density is equally efficient in both isomers.
机译：18个带有4,4'-R取代的芳基环的N-杂环卡宾（N，N'-双（2,6-二甲基苯基）咪唑）-2-亚基和各自的二氢配体）的供电子特性使用电化学技术研究了各自的Grubbs II配合物中的4'-R = NEt2，OMe，Me，H，SMe，F，Cl，Br，I）。 4-R取代基的性质对Ru-II / III氧化还原电势有很大影响，其范围介于Delta E-1 / 2 = + 0.196和+ 0.532 V之间。三个具有4-R = 4-R'的不对称Grubbs II配合物也被合成。动态NMR光谱显示绕（NHC）C-Ru键旋转受限（在333 K下Delta G = 89 kJ mol（-1））分别导致两种阻转异构体，其异构体比率接近于1。每种异构体，即4-R / 4-R'取代的均基环相对于R = CHPh单元的两个方向，都会产生不同的氧化还原电势（4-R = NEt2，4-R'= Br：ΔE-1 / 2 = + 0.232和+ 0.451 V）。在氧化的Grubbs II配合物（4-R = NEt2，H）中和在阴极异构体中，富电子芳基环位于Ru = CHPh单元上方。假定电子密度的替代性通过键的转移在两种异构体中同样有效，这种取向效应为Ru-III络合物中强烈的pi-pi贯穿空间相互作用提供了清晰的证据。

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