Sergeieva Tetiana, Demirer T Ilgin, Wuttke Axel, Mata Ricardo A, Schäfer André, Linker Gerrit-Jan, Andrada Diego M
Department of Chemistry, Saarland University, Campus Saarbrücken, 66123 Saarbrücken, Germany.
Institute for Physical Chemistry, Georg-August-University Göttingen, Tammannstrasse 6, D-37077 Göttingen, Germany.
Phys Chem Chem Phys. 2023 Aug 2;25(30):20657-20667. doi: 10.1039/d2cp05020j.
Metallocenes are well-established compounds in organometallic chemistry, and can exhibit either a coplanar structure or a bent structure according to the nature of the metal center (E) and the cyclopentadienyl ligands (Cp). Herein, we re-examine the chemical bonding to underline the origins of the geometry and stability observed experimentally. To this end, we have analysed a series of group 2 metallocenes [Ae(CR)] (Ae = Be-Ba and R = H, Me, F, Cl, Br, and I) with a combination of computational methods, namely energy decomposition analysis (EDA), polarizability model (PM), and dispersion interaction densities (DIDs). Although the metal-ligand bonding nature is mainly an electrostatic interaction (65-78%), the covalent character is not negligible (33-22%). Notably, the heavier the metal center, the stronger the d-orbital interaction with a 50% contribution to the total covalent interaction. The dispersion interaction between the Cp ligands counts only for 1% of the interaction. Despite that orbital contributions become stronger for heavier metals, they never represent the energy main term. Instead, given the electrostatic nature of the metallocene bonds, we propose a model based on polarizability, which faithfully predicts the bending angle. Although dispersion interactions have a fair contribution to strengthen the bending angle, the polarizability plays a major role.
茂金属是有机金属化学中已被充分确立的化合物，根据金属中心（E）和环戊二烯基配体（Cp）的性质，其可以呈现共面结构或弯曲结构。在此，我们重新审视化学键，以强调实验观察到的几何形状和稳定性的起源。为此，我们结合能量分解分析（EDA）、极化率模型（PM）和色散相互作用密度（DIDs）等计算方法，分析了一系列第2族茂金属[Ae(CR)]（Ae = Be - Ba，R = H、Me、F、Cl、Br和I）。尽管金属 - 配体键合性质主要是静电相互作用（65 - 78%），但共价特征也不可忽略（33 - 22%）。值得注意的是，金属中心越重，d轨道相互作用越强，对总共价相互作用的贡献为50%。Cp配体之间的色散相互作用仅占相互作用的1%。尽管对于较重的金属，轨道贡献变得更强，但它们从未代表能量的主要项。相反，鉴于茂金属键的静电性质，我们提出了一个基于极化率的模型，该模型能准确预测弯曲角度。尽管色散相互作用对增强弯曲角度有相当大的贡献，但极化率起主要作用。
