Dossmann Héloïse, Gatineau David, Clavier Hervé, Memboeuf Antony, Lesage Denis, Gimbert Yves
Sorbonne Université, CNRS, Institut Parisien de Chimie Moléculaire, IPCM, Paris 75005, France.
Aix Marseille Univ, CNRS, Centrale Marseille, iSm2, Marseille, France.
J Phys Chem A. 2020 Oct 22;124(42):8753-8765. doi: 10.1021/acs.jpca.0c06746. Epub 2020 Oct 12.
In organometallic chemistry, especially in the catalysis area, accessing the finest tuning of a catalytic reaction pathway requires a detailed knowledge of the steric and electronic influences of the ligands bound to the metal center. Usually, the M-L bond between a ligand and metal is depicted by the Dewar-Chatt-Duncanson model involving two opposite interactions, σ-donor and π-acceptor effects of the ligand. The experimental evaluation of these effects is essential and complementary to in-depth theoretical approaches that are able to provide a detailed description of the M-L bond. In this work, we present a study of LMo(CO) complexes with L being various tertiary phosphine ligands by means of mass-selected high-resolution photoelectron spectroscopy (PES) performed with synchrotron radiation, DFT, and energy decomposition analyses (EDA) combined with the natural orbitals for chemical valence (NOCV) analysis. These methods enable a separated access of the σ-donor and π-acceptor effects of ligands by probing either the electronic configuration of the complex (PES) or the interaction of the ligand with the metal (EDA). Three series of PR ligands with various electronic influences are investigated: the strong donating alkyl substituents (PMe, PEt, and PPr), the intermediate PPhMe ( = 0-3) set, and the PPhPyrl set ( = 0-3 with Pyrl being the strong electron withdrawing pyrrolyl group CHN). For each complex, their adiabatic and vertical ionization energies (IEs) could be determined with a 0.03 eV precision. Experiment and theory show an excellent agreement, either for the IE determination or electronic effect analysis. The ability to interpret the spectra is shown to depend on the character of the ligand. "Innocent" ligands provide the spectra that are the most straightforward to analyze, whereas the "non-innocent" ligands (which are ionized prior to the metal center) render the analysis more difficult due to an increased number of molecular orbitals in the energy range considered. A very good linear correlation is finally found between the measured adiabatic ionization energies and the interaction energy term obtained by EDA for each of these two types of ligands, which opens interesting perspective for the prediction of ligand characters.
在有机金属化学中，尤其是在催化领域，要实现催化反应路径的精确调控，需要详细了解与金属中心相连的配体的空间和电子影响。通常，配体与金属之间的M-L键由Dewar-Chatt-Duncanson模型描述，该模型涉及两种相反的相互作用，即配体的σ-供体和π-受体效应。这些效应的实验评估至关重要，并且是能够详细描述M-L键的深入理论方法的补充。在这项工作中，我们通过使用同步辐射进行的质量选择高分辨率光电子能谱（PES）、密度泛函理论（DFT）以及结合化学价自然轨道（NOCV）分析的能量分解分析（EDA），对L为各种叔膦配体的LMo(CO)配合物进行了研究。这些方法能够通过探测配合物的电子构型（PES）或配体与金属的相互作用（EDA），分别获取配体的σ-供体和π-受体效应。研究了具有不同电子影响的三类PR配体：强给电子烷基取代基（PMe、PEt和PPr）、中间的PPhMe（= 0 - 3）组以及PPhPyrl组（= 0 - 3，其中Pyrl是强吸电子吡咯基CHN）。对于每个配合物，其绝热和垂直电离能（IEs）能够以0.03 eV的精度测定。实验和理论在IE测定或电子效应分析方面都显示出了极好的一致性。结果表明，解释光谱的能力取决于配体的性质。“无害”配体提供的光谱最易于分析，而“非无害”配体（在金属中心之前被电离）由于在所考虑的能量范围内分子轨道数量增加，使得分析更加困难。最终发现，对于这两类配体中的每一类，测量的绝热电离能与通过EDA获得的相互作用能项之间都存在非常好的线性相关性，这为预测配体性质开辟了有趣的前景。
