Villegas-Escobar Nery, Toro-Labbé Alejandro, Schaefer Henry F
Centro Integrativo de Biología y Química Aplicada (CIBQA), Universidad Bernardo O'Higgins, General Gana 1702, Santiago, 8370854, Chile.
Laboratorio de Química Teórica Computacional (QTC), Facultad de Química, Pontificia Universidad Católica de Chile, Avenida Vicuña Mackenna 4860, Santiago, Chile.
Chemistry. 2021 Dec 9;27(69):17369-17378. doi: 10.1002/chem.202103082. Epub 2021 Oct 22.
Aluminyl anions are low-valent, anionic, and carbenoid aluminum species commonly found stabilized with potassium cations from the reaction of Al-halogen precursors and alkali compounds. These systems are very reactive toward the activation of σ-bonds and in reactions with electrophiles. Various research groups have detected that the potassium atoms play a stabilization role via electrostatic and cation interactions with nearby (aromatic)-carbocyclic rings from both the ligand and from the reaction with unsaturated substrates. Since stabilizing K⋯H bonds are witnessed in the activation of this class of molecules, we aim to unveil the role of these metals in the activation of the smaller and less polarizable H molecule, together with a comprehensive characterization of the reaction mechanism. In this work, the activation of H utilizing a NON-xanthene-Al dimer, [K{Al(NON)}] (D) and monomeric, [Al(NON)] (M) complexes are studied using density functional theory and high-level coupled-cluster theory to reveal the potential role of K atoms during the activation of this gas. Furthermore, we aim to reveal whether D is more reactive than M (or vice versa), or if complicity between the two monomer units exits within the D complex toward the activation of H . The results suggest that activation energies using the dimeric and monomeric complexes were found to be very close (around 33 kcal mol ). However, a partition of activation energies unveiled that the nature of the energy barriers for the monomeric and dimeric complexes are inherently different. The former is dominated by a more substantial distortion of the reactants (and increased interaction energies between them). Interestingly, during the oxidative addition, the distortion of the Al complex is minimal, while H distorts the most, usually over 0.77 . Overall, it is found here that electrostatic and induction energies between the complexes and H are the main stabilizing components up to the respective transition states. The results suggest that the K atoms act as stabilizers of the dimeric structure, and their cooperative role on the reaction mechanism may be negligible, acting as mere spectators in the activation of H . Cooperation between the two monomers in D is lacking, and therefore the subsequent activation of H is wholly disengaged.
铝酰阴离子是低价、阴离子型且类卡宾的铝物种，通常由铝卤前驱体与碱化合物反应生成的钾阳离子来稳定。这些体系对σ键的活化以及与亲电试剂的反应具有很高的活性。多个研究小组已经检测到，钾原子通过与配体中附近的（芳族）碳环以及与不饱和底物反应形成的碳环之间的静电和阳离子相互作用发挥稳定作用。由于在这类分子的活化过程中观察到了稳定的K⋯H键，我们旨在揭示这些金属在较小且极化率较低的H分子活化中的作用，同时全面表征反应机理。在这项工作中，利用密度泛函理论和高水平耦合簇理论研究了使用非呫吨铝二聚体[K{Al(NON)}]（D）和单体[Al(NON)]（M）配合物对H的活化，以揭示钾原子在该气体活化过程中的潜在作用。此外，我们旨在揭示D是否比M更具反应活性（反之亦然），或者D配合物中的两个单体单元之间是否存在协同作用来活化H。结果表明，使用二聚体和单体配合物的活化能非常接近（约33 kcal mol）。然而，活化能的分配表明，单体和二聚体配合物的能垒性质本质上是不同的。前者主要由反应物的更大程度变形（以及它们之间增加的相互作用能）主导。有趣的是，在氧化加成过程中，铝配合物的变形最小，而H的变形最大，通常超过0.77 。总体而言，在此发现配合物与H之间的静电和诱导能是直至各自过渡态的主要稳定成分。结果表明，钾原子充当二聚体结构的稳定剂，它们在反应机理上的协同作用可能可以忽略不计，在H的活化过程中仅仅充当旁观者。D中两个单体之间缺乏协同作用，因此随后对H 的活化完全不相关。
