School of Materials Science & Engineering, PCFM Lab, Department of Chemistry, Sun Yat-sen University, Guangzhou, 510275, P. R. China.
College of Chemistry and Molecular Engineering, Zhengzhou University, Zhengzhou, 450001, P. R. China.
Chemistry. 2019 Oct 28;25(60):13785-13798. doi: 10.1002/chem.201903193. Epub 2019 Sep 20.
As a new type of bifunctional catalyst, the Lewis acid transition-metal (LA-TM) catalysts have been widely applied for hydrogen activation. This study presents a mechanistic framework to understand the LA-TM-catalyzed H activation through DFT studies. The mer(trans)-homolytic cleavage, the fac(cis)-homolytic cleavage, the synergetic heterolytic cleavage, and the dissociative heterolytic cleavage should be taken as general mechanisms for the field of LA-TM catalysis. Four typical LA-TM catalysts, the Z-type κ -L B-Rh complex tri(azaindolyl)borane-Rh, the X-type κ -L B-Co complex bis-phosphino-boryl (PBP)-Co, the η -BC-type κ -L B-Pd complex diphosphine-borane (DPB)-Pd, and the Z-type κ -LB-Pt complex (boryl)iminomethane (BIM)-Pt are selected as representative models to systematically illustrate their mechanistic features and explore the influencing factors on mechanistic variations. Our results indicate that the tri(azaindolyl)borane-Rh catalyst favors the synergetic heterolytic mechanism; the PBP-Co catalyst prefers the mer(trans)-homolytic mechanism; the DPB-Pd catalyst operates through the fac(cis)-homolytic mechanism, whereas the BIM-Pt catalyst tends to undergo the dissociative heterolytic mechanism. The mechanistic variations are determined by the coordination geometry, the LA-TM bonding nature, the electronic structure of the TM center, and the flexibility or steric effect of the LA ligands. The presented mechanistic framework should provide helpful guidelines for LA-TM catalyst design and reaction developments.
作为一种新型双功能催化剂，路易斯酸过渡金属（LA-TM）催化剂已广泛应用于氢活化。本研究通过 DFT 研究提出了一种理解 LA-TM 催化 H 活化的机理框架。均（反）-均裂、面（顺）-均裂、协同异裂和离解异裂应作为 LA-TM 催化的一般机制。选择四种典型的 LA-TM 催化剂，即 Z 型 κ -L B-Rh 配合物三（氮杂吲哚基）硼烷-Rh、X 型 κ -L B-Co 配合物双膦基硼（PBP）-Co、η -BC 型 κ -L B-Pd 配合物二膦基硼烷（DPB）-Pd 和 Z 型 κ -LB-Pt 配合物（硼基）亚胺甲烷（BIM）-Pt 作为代表性模型，系统阐明它们的机理特征，并探索对机理变化的影响因素。我们的结果表明，三（氮杂吲哚基）硼烷-Rh 催化剂有利于协同异裂机制；PBP-Co 催化剂倾向于均（反）裂机制；DPB-Pd 催化剂通过面（顺）裂机制起作用，而 BIM-Pt 催化剂倾向于经历离解异裂机制。机理变化取决于配位几何、LA-TM 键合性质、TM 中心的电子结构以及 LA 配体的柔韧性或空间位阻效应。所提出的机理框架应为 LA-TM 催化剂设计和反应开发提供有益的指导。
