Scharf Lennart T, Rodstein Ilja, Schmidt Michelle, Scherpf Thorsten, Gessner Viktoria H
Chair of Inorganic Chemistry II, Faculty of Chemistry and Biochemistry, Ruhr University Bochum, Universitätsstrasse 150, 44780 Bochum, Germany.
ACS Catal. 2020 Jan 17;10(2):999-1009. doi: 10.1021/acscatal.9b04666. Epub 2019 Dec 11.
Comprehensive mechanistic insights into the activity of different catalysts based on different ligands are important for further ligand design and catalyst improvement. Herein, we report a combined computational and experimental study on the mechanism and catalytic activity of the ylide-substituted phosphine CyP-C(Me)PCy (keYPhos, ) in C-N coupling reactions including a comparison with the established and often-applied phosphines JohnPhos () and P(Bu) (). Density functional theory (DFT) calculations together with the possible isolation of several intermediates within the catalytic cycle demonstrate that readily forms low-coordinated palladium complexes [such as ], which easily undergo oxidative addition and subsequent amine coordination as well as reductive elimination. Due to the possible opening and closing of the P-C-P angle in , the steric bulk can be adjusted to the metal environment so that retains its conformation throughout the whole catalytic cycle, thus leading to fast catalysis at room temperature. Comparative studies of the three ligands with Pddba as a Pd source show that only efficiently allows for the coupling of aryl chlorides at room temperature. DFT studies suggest that this is mainly due to the reluctance/inability of and to form the catalytically active species under these reaction conditions. In contrast, the YPhos ligand readily forms the prereactive complex and undergoes the first oxidative addition reaction. These observations are confirmed by kinetic studies, which indicate a short induction period for the formation of the catalytically active species of , followed by fast catalysis. This behavior of is due to its unique electronic and steric properties, which support low activation barriers and fast catalyst generation.
深入了解基于不同配体的不同催化剂的活性机制，对于进一步的配体设计和催化剂改进至关重要。在此，我们报告了一项关于叶立德取代膦CyP-C(Me)PCy（keYPhos）在C-N偶联反应中的机理和催化活性的计算与实验相结合的研究，包括与已确立且常用的膦JohnPhos和P(Bu)进行比较。密度泛函理论（DFT）计算以及催化循环中几种中间体的可能分离表明，keYPhos很容易形成低配位钯配合物（如 ），这些配合物易于进行氧化加成、随后的胺配位以及还原消除。由于keYPhos中P-C-P角可能的开合，其空间位阻可以根据金属环境进行调整，使得keYPhos在整个催化循环中保持其构象，从而在室温下实现快速催化。以Pddba作为钯源对这三种配体进行的比较研究表明，只有keYPhos能在室温下有效地实现芳基氯的偶联。DFT研究表明，这主要是由于JohnPhos和P(Bu)在这些反应条件下难以/无法形成催化活性物种。相比之下，YPhos配体很容易形成预反应配合物并进行首次氧化加成反应。动力学研究证实了这些观察结果，该研究表明keYPhos形成催化活性物种的诱导期较短，随后是快速催化。keYPhos的这种行为归因于其独特的电子和空间性质，这些性质有助于降低活化能垒并快速生成催化剂。
