Disentanglement of Donation and Back-Donation Effects on Experimental Observables: A Case Study of Gold-Ethyne Complexes
Disentanglement of Donation and Back-Donation Effects on Experimental Observables: A Case Study of Gold-Ethyne Complexes
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DOI：
10.1002/anie.201305505
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发表时间：
2013-10-25
影响因子：
16.6
通讯作者：
Tarantelli, Francesco
中科院分区：
文献类型：
--
作者：
Bistoni, Giovanni;Belpassi, Leonardo;Tarantelli, Francesco
杜瓦-查特-唐克森(Dcd)模型[1-3]是60多年前提出的，用来描述乙烯与金属原子的η-2配位。它给出了不饱和衬底(S)和过渡金属(M)之间的键的形式上的简单图像，其中涉及从衬底向金属的空dπ轨道赠送σ电子(S！M)和从金属的填充dπ轨道到具有适当对称性的空衬底轨道的回馈(M！s)。在不饱和有机体系中，这些空轨道通常具有π*反键特征，它们的布居倾向于削弱C±C键，但如果空轨道具有成键特征，则也可能观察到相反的效果，正如最近观察到的那样。[4-6]DCD模型在化学家中非常受欢迎，因为它代表了分析配体和金属碎片的电子性质的标准框架，特别是考虑到合理化和控制催化化学反应中底物的活化。它似乎也适合于对碳键的概括性描述。[7]尽管DCD模型被如此广泛地接受，但对捐赠和回馈捐款对碳键的相对重要性的评估往往是模棱两可和有争议的。[8-13]DCD模型的组成部分是量子力学定义不好的[14]，虽然结论通常是从间接的实验线索得出的，但它们可能是不可靠的，因为在观察到的性质和DCD键成分之间还没有建立起严格的定量关系，无论是理论上的还是经验上的。事实上，即使只是证明捐赠和回馈捐赠的相对程度完全可以从实验中提取出来，也是一项非常可取的壮举。在这里，我们证明了通过测量简单的实验观测，DCD分量可以有效地解缠，并在原理上定量地揭示出来。作为一个典型的案例研究，我们考虑了金和乙炔之间的键。
The Dewar–Chatt–Duncanson (DCD) model [1–3] was introduced more than 60 years ago to describe the η2 coordination of ethene to a coinage-metal atom. It gives a formally simple picture of the bond between an unsaturated substrate (S) and a transition metal (M), which involves the donation of π electrons from the substrate to empty dσ orbitals of the metal (S! M) and the back donation from filled dπ orbitals of the metal to empty substrate orbitals of the proper symmetry (M! S). In unsaturated organic systems, these empty orbitals have typically a π* anti-bonding character and their population tends to weaken the CÀC bond, but a reverse effect may also be observed if the empty orbitals have a bonding character, as recently observed.[4–6] The DCD model enjoys enormous popularity among chemists, as it represents the standard framework in which to analyze the electronic properties of ligands and metal fragments, especially with a view of rationalizing and controlling the activation of substrates in catalyzed chemical reactions. It appears also appropriate for the captodative description of the carbon bond.[7]Despite the fact that the DCD model is so well accepted, the assessment of the relative importance of the donation and back-donation contributions to the bond is often ambiguous and controversial.[8–13] The components of the DCD model are quantum-mechanically not well defined [14] and, while conclusions are commonly drawn from indirect experimental clues, they may be unreliable because no rigorous quantitative relationship, of either theoretical or empirical nature, has ever been established between observed properties and the DCD bond components. In fact, even just proving that the relative extent of donation and back donation can at all be extracted from experiments would be a highly desirable feat. Herein, we demonstrate that the DCD components can be effectively disentangled, and in principle quantitatively revealed, by measuring simple experimental observables. As a prototype case study we consider the bond between gold and ethyne.