Zeonjuk Lei Liu, Vankova Nina, Mavrandonakis Andreas, Heine Thomas, Röschenthaler Gerd-Volker, Eicher Johannes
School of Engineering and Science, Jacobs University Bremen, Campus Ring 1, 28759, Bremen (Germany).
Chemistry. 2013 Dec 16;19(51):17413-24. doi: 10.1002/chem.201302727. Epub 2013 Nov 8.
We report herein a comprehensive theoretical study of the thermodynamics and kinetics of molecular hydrogen activation by frustrated Lewis pairs (FLPs). A series of intermolecularly combined boranes (Lewis acids) and phosphines (Lewis bases), with experimentally established different reactivities towards H2, have been subjected to DFT and (SCS-)MP2 calculations, and analyzed in terms of their structural properties, the energetics of association of the FLPs, and the kinetics of their interactions with H2 and hydrogenation to the ion-pair products. The analysis included the following steps: 1) assessment of the ability/inability of the Lewis species to preorganize into FLPs with an optimum arrangement of the acid and base sites for preconditioning the reaction with H2 , 2) comprehension of the different thermodynamics of hydrogenation of the selected FLPs by comparing the Gibbs energies of the overall reactions, and 3) estimation of the mechanism of the activation of H2 by identifying the reaction steps and the associated kinetic barriers. The results of our studies correlate well with experimental findings and have clarified the reasons for the observed different reactivities of the investigated systems, ranging from reversible or nonreversible activation to no reaction with H2. The derived predictions could assist the future design of Lewis acid-base systems with desired properties and applicability as metal-free hydrogenation catalysts.
我们在此报告了关于受阻路易斯酸碱对（FLP）活化分子氢的热力学和动力学的全面理论研究。一系列分子间组合的硼烷（路易斯酸）和膦（路易斯碱），它们对H₂的反应活性已通过实验确定，对其进行了密度泛函理论（DFT）和（二阶微扰理论的标量相对论修正）（SCS -）MP2计算，并从它们的结构性质、FLP缔合的能量学以及它们与H₂相互作用和氢化生成离子对产物的动力学方面进行了分析。分析包括以下步骤：1）评估路易斯物种能否/是否能够预组织成FLP，使其酸和碱位点具有最佳排列以预处理与H₂的反应；2）通过比较总反应的吉布斯自由能来理解所选FLP氢化的不同热力学；3）通过确定反应步骤和相关的动力学势垒来估计H₂活化的机理。我们的研究结果与实验结果高度相关，并阐明了所研究体系中观察到的不同反应活性的原因，这些反应活性范围从可逆或不可逆活化到不与H₂反应。所得到的预测可为未来设计具有所需性质和适用性的作为无金属氢化催化剂的路易斯酸碱体系提供帮助。
