Protic N-heterocyclic Carbene versus Pyrazole: Rigorous Comparison of Proton- and Electron-Donating Abilities in a Pincer-Type Framework
Protic N-heterocyclic Carbene versus Pyrazole: Rigorous Comparison of Proton- and Electron-Donating Abilities in a Pincer-Type Framework
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质子 N-杂环卡宾与吡唑：钳型框架中质子和电子供给能力的严格比较
DOI：
10.1002/chem.201602552
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发表时间：
2016
期刊：
影响因子：
--
通讯作者：
and Shigeki Kuwata
中科院分区：
文献类型：
--
作者：
Tatsuro Toda;Akihiro Yoshinari;Takao Ikariya;and Shigeki Kuwata
质子响应配体的酸度的评估，如质子N-杂环卡宾（NHC）轴承NH-翼尖提供了一个关键，了解酶和人工催化中的金属配体合作。在这里，我们设计了一个CNN钳型钌配合物2，在对称骨架中含有质子NHC和等电子吡唑单元，以比较它们的酸性和给电子能力。该合成是通过2-（咪唑-1-基）-6-（吡唑-3-基）吡啶与[RuCl 2（PPh 3）3]的直接C-H金属化来实现的。15 N-标记实验证实2的去质子化首先发生在吡唑侧，清楚地表明质子吡唑比NHC基团更酸性。电化学测量以及衍生为羰基络合物证明质子NHC比质子化和去质子化形式的吡唑更具供电子性。
Evaluation of the acidity of proton‐responsive ligands such as protic N‐heterocyclic carbenes (NHCs) bearing an NH‐wingtip provides a key to understanding the metal–ligand cooperation in enzymatic and artificial catalysis. Here, we design a CNN pincer‐type ruthenium complex2bearing protic NHC and isoelectronic pyrazole units in a symmetrical skeleton, to compare their acidities and electron‐donating abilities. The synthesis is achieved by direct C−H metalation of 2‐(imidazol‐1‐yl)‐6‐(pyrazol‐3‐yl)pyridine with [RuCl2(PPh3)3].15N‐Labeling experiments confirm that deprotonation of2occurs first at the pyrazole side, indicating clearly that the protic pyrazole is more acidic than the NHC group. The electrochemical measurements as well as derivatization to carbonyl complexes demonstrate that the protic NHC is more electron‐donating than pyrazole in both protonated and deprotonated forms.