Department of General Chemistry (ALGC), Vrije Universiteit Brussel (VUB), Pleinlaan 2, 1050 Brussels (Belgium).
Chemphyschem. 2013 Oct 7;14(14):3233-47. doi: 10.1002/cphc.201300596. Epub 2013 Aug 15.
The reactivity of dicoordinated Sn(0) compounds, stannylones, is probed using density functional theory (DFT)-based reactivity indices and compared with the reactivity of dicoordinated Sn(II) compounds, stannylenes. For the former compounds, the influence of different types of electron-donating ligands, such as cyclic and acyclic carbenes, stannylenes and phosphines, on the reactivity of the central Sn atom is analyzed in detail. Sn(0) compounds are found to be relatively soft systems with a high nucleophilicity, and the plots of the Fukui function f(-) for an electrophilic attack consistently predict the highest reactivity on the Sn atom. Next, complexes of dicoordinated Sn compounds with different Lewis acids of variable hardness are computed. In a first part, the double-base character of stannylones is demonstrated in interactions with the hardest Lewis acid H(+). Both the first and second proton affinities (PAs) are high and are well correlated with the atomic charge on the Sn atom, probing its local hardness. These observations are also in line with electrostatic potential plots that demonstrate that the tin atom in Sn(0) compounds bears a higher negative charge in comparison to Sn(II) compounds. Stannylones and stannylenes can be distinguished from each other by the partial charges at Sn and by various reactivity indices. It also becomes clear that there is a smooth transition between the two classes of compounds. We furthermore demonstrate both from DFT-based reactivity indices and from energy decomposition analysis, combined with natural orbitals for chemical valence (EDA-NOCV), that the monocomplexed stannylones are still nucleophilic and as reactive towards a second Lewis acid as towards the first one. The dominating interaction is a strong σ-type interaction from the Sn atom towards the Lewis acid. The interaction energy is higher for complexes with the cation Ag(+) than with the non-charged electrophiles BH(3), BF(3), and AlCl(3).
使用基于密度泛函理论（DFT）的反应性指标探测二配位 Sn(0) 化合物（锡酮）的反应性，并将其与二配位 Sn(II) 化合物（锡烯）的反应性进行比较。对于前一种化合物，详细分析了不同类型的给电子配体（如环状和非环状卡宾、锡烯和膦）对中心 Sn 原子反应性的影响。Sn(0) 化合物被发现是相对柔软的体系，具有高亲核性，亲电攻击的福井函数 f(-) 图一致预测 Sn 原子的最高反应性。接下来，计算了不同路易斯酸硬度的二配位 Sn 化合物配合物。在第一部分中，锡酮的双基特征在与最强路易斯酸 H(+) 的相互作用中得到证明。第一和第二质子亲和力 (PA) 都很高，并且与 Sn 原子上的原子电荷很好相关，探测其局部硬度。这些观察结果也与静电势图一致，表明与 Sn(II) 化合物相比，Sn(0) 化合物中的锡原子带有更高的负电荷。锡酮和锡烯可以通过 Sn 上的部分电荷和各种反应性指标来区分。还清楚的是，这两类化合物之间存在平稳过渡。我们还通过基于 DFT 的反应性指标以及通过能量分解分析，结合化学价自然轨道（EDA-NOCV），证明单配位的锡酮仍然具有亲核性，并且对第二个路易斯酸的反应性与对第一个路易斯酸的反应性一样高。主要的相互作用是 Sn 原子向路易斯酸的强 σ 型相互作用。与非带电亲电试剂 BH(3)、BF(3) 和 AlCl(3) 相比，具有阳离子 Ag(+) 的配合物的相互作用能更高。
