Nature of the Bonding in Metal-Silane σ-Complexes
Nature of the Bonding in Metal-Silane σ-Complexes
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DOI：
10.1021/ic8019777
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发表时间：
2009-02-16
影响因子：
4.6
通讯作者：
Scherer, Wolfgang
中科院分区：
文献类型：
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作者：
McGrady, G. Sean;Sirsch, Peter;Scherer, Wolfgang
金属硅烷西格玛键相互作用的性质已经通过一系列实验和计算技术在几个关键系统中进行了研究。通过单晶中子衍射测定了[Cp'Mn(CO)(2)(eta(2)-HSiHPh2)] 1 的结构，Si原子处的几何形状近似于三角双锥体；显着键距和角度为 Mn-H(1) 1.575(14)、Si-H(1) 1.806(14)、Si-H(2) 1.501(13) 埃和 H(1)-Si-H(2) 148.5(8) 度。该配合物与 [Cp'Mn(CO)(2)(eta(2)-HSiFPh2)] 2 类似，其结构和键合特性最近已通过基于高分辨率 X 射线和中子衍射数据的电荷密度研究确定。这些西格玛键配合物中硅原子的几何形状与其他含有超配位硅的系统中的几何形状进行了比较。溶液中 1 和 2 的 Mn-H 距离已使用 NMR T-1 弛豫测量进行了估计，每种情况下的值为 1.56(3) 埃，与中子衍射推导出的距离非常一致。采用密度泛函理论计算来探索 1 和 2 中 Mn-H-Si 单元以及相关体系 [Cp'Mn(CO)(2)(eta(2) -HSiCl3)] 3 中的成键。这些研究支持这样的观点，即硅烷配体向过渡金属中心的氧化加成可以描述为一个不对称过程，其中 Mn-H 键在早期形成，同时 Mn-Si 键的建立和 Mn-Si 键的活化。 eta(2) 配位的 Si-H 部分受 Mn -> sigma*(X-Si-H) 回馈程度控制，该程度随着金属配位 Si-H 键反式 X 取代基吸电子特性的增加而增加。这种离域分子轨道 (MO) 方法得到了实验和理论电荷密度相结合的研究的补充和支持：源函数 S(r,Omega) 提供了每个原子对特定参考点 r 处的密度贡献的相对重要性的度量，清楚地表明 Mn(eta(2)-SiH) 部分的所有三个原子对 Mn-Si 键临界点处的密度的贡献程度非常相似，与 MO 模型非常一致。因此，我们提出了一个一致且统一的概念，该概念解释了这些硅烷σ键配合物中Si-H的活化程度。
The nature of metal silane sigma-bond interaction has been investigated in several key systems by a range of experimental and computational techniques. The structure of [Cp'Mn(CO)(2)(eta(2)-HSiHPh2)] 1 has been determined by single crystal neutron diffraction, and the geometry at the Si atom is shown to approximate a trigonal bipyramid; salient bond distances and angles are Mn-H(1) 1.575(14), Si-H(1) 1.806(14), Si-H(2) 1.501(13) angstrom, and H(1)-Si-H(2) 148.5(8)degrees. This complex is similar to [Cp'Mn(CO)(2)(eta(2)-HSiFPh2)] 2, whose structure and bonding characteristics have recently been determined by charge density studies based on high-resolution X-ray and neutron diffraction data. The geometry at the Si atom in these sigma-bond complexes is compared with that in other systems containing hypercoordinate silicon. The Mn-H distances for 1 and 2 in solution have been estimated using NMR T-1 relaxation measurements, giving a value of 1.56(3) angstrom in each case, in excellent agreement with the distances deduced from neutron diffraction. Density functional theory calculations have been employed to explore the bonding in the Mn-H-Si unit in 1 and 2 and in the related system [Cp'Mn(CO)(2)(eta(2) -HSiCl3)] 3. These studies support the idea that the oxidative addition of a silane ligand to a transition metal center may be described as an asymmetric process in which the Mn-H bond is formed at an early stage, while both the establishment of the Mn-Si bond and also the activation of the eta(2)-coordinated Si-H moiety are controlled by the extent of Mn -> sigma*(X-Si-H) back-donation, which increases with increasing electron-withdrawing character of the X substituent trans to the metal-coordinated Si-H bond. This delocalized molecular orbital (MO) approach is complemented and supported by combined experimental and theoretical charge density studies: the source function S(r,Omega), which provides a measure of the relative importance of each atom's contribution to the density at a specific reference point r, clearly shows that all three atoms of the Mn(eta(2)-SiH) moiety contribute to a very similar extent to the density at the Mn-Si bond critical point, in pleasing agreement with the MO model. Hence, we advance a consistent and unifying concept which accounts for the degree of Si-H activation in these silane sigma-bond complexes.