A cyclic diaminocarbene with a pyramidalized nitrogen atom: a stable N-heterocyclic carbene with enhanced electrophilicity.
A cyclic diaminocarbene with a pyramidalized nitrogen atom: a stable N-heterocyclic carbene with enhanced electrophilicity.
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DOI：
10.1002/anie.201202137
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发表时间：
2012-06-18
影响因子：
16.6
通讯作者：
Bertrand, Guy
中科院分区：
文献类型：
--
作者：
Martin, David;Lassauque, Nicolas;Donnadieu, Bruno;Bertrand, Guy
自从它们被发现以来，[1，2]有成千上万的论文涉及稳定卡宾的制备和使用。其中，[3-6] N-杂环卡宾（NHC）A是研究最多的。[7-12]尽管NHC具有广泛的应用，但它们仍然具有低模块性，这将它们限制在窄范围的强σ-供体配体和亲核试剂中。近年来，人们已经成功地开发了几种策略来调节它们的σ-给体性质，这主要与卡宾取代基的σ-效应有关。[8]然而，NHC的π-受体性质的调节更具挑战性，因为高能LUMO由两个氨基基团对卡宾空轨道的强π-捐赠决定。[13]如图1所示，用供σ烷基（B）取代供π电子和吸σ氨基取代基导致亲电性和亲核性增加。[14羰基可以被引入主链中以与碳烯中心竞争氮π贡献。所谓的二氨基卡宾C是非常亲电的，但以牺牲它们的亲核性为代价。[16-19]在这里，我们报告了环状二氨基卡宾的合成和单晶X射线衍射研究，其保留了经典NHC的亲核性，但显示出增强的亲电性。我们推断，为了获得保留经典NHC A的亲核性的卡宾，应该使用不带有吸电子取代基的氨基。为了同时增强亲电性，这些氨基取代基之一应被限制将其孤对电子贡献给卡宾中心。为了支持我们的假设，我们进行了从头计算，预测母体NHC A的一个氮的异构化，如Apyr所示，显著降低了LUMO的能量，而没有降低HOMO能量（图1）。
Since their discovery,[1, 2] thousands of papers have dealt with the preparation and use of stable carbenes. Arguably, among them,[3–6] the N-heterocyclic carbenes (NHCs) A have been the most studied.[7–12] Despite their widespread applications, NHCs still suffer from low modularity, which confines them to a narrow range of strong σ-donor ligands and nucleophiles. In recent years, several strategies have successfully been developed for tuning their σ-donor properties, which are mainly linked to the σ-effect of the carbene substituents.[8] However, the modulation of the π-acceptor properties of NHCs is more challenging since the high-energy LUMO is ruled by the strong π-donation of the two amino groups to the carbene vacant orbital.[13] As shown in Figure 1, the replacement of a π-electron donating and σ-withdrawing amino substituent by a σ-donating alkyl group (B) leads to an increase of electrophilicity but also nucleophilicity.[14, 15] Carbonyls can be introduced in the backbone in order to compete with the carbene center for the nitrogen πdonation. The so-called diamidocarbenes C are very electrophilic, but at the expense of their nucleophilicity.[16–19] Here we report the synthesis and single crystal X-ray diffraction study of a cyclic diaminocarbene, which retains the nucleophilicity of classical NHCs, but displays enhanced electrophilicity.We reasoned that for obtaining a carbene that retains the nucleophilicity of classical NHCs A, amino groups not bearing electron withdrawing substituents should be used. To concomitantly enhance the electrophilicity, one of these amino substituents should be restricted from donating its lone pair to the carbene center. To support our hypothesis, we performed ab initio calculations, which predicted that the pyramidalization of one nitrogen of the parent NHC A, as shown in Apyr, significantly decreases the energy of the LUMO, without lowering the HOMO energy (Figure 1).
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影响因子：
2.8
作者：
Hudnall, Todd W.;Tennyson, Andrew G.;Bielawski, Christopher W.
通讯作者：
Bielawski, Christopher W.
影响因子：
46.2
作者：
BUCHANAN, GL
通讯作者：
BUCHANAN, GL
影响因子：
15
作者：
Goedecke, Catharina;Leibold, Michael;Frenking, Gernot
通讯作者：
Frenking, Gernot
影响因子：
4.9
作者：
Higgins, Eleanor M.;Sherwood, Jennifer A.;O'Donoghue, AnnMarie C.
通讯作者：
O'Donoghue, AnnMarie C.
影响因子：
4.9
作者：
Alder, RW;Blake, ME;Quayle, MJ
通讯作者：
Quayle, MJ