Understanding the unique reactivity patterns of nickel/JoSPOphos manifold in the nickel-catalyzed enantioselective C–H cyclization of imidazoles
| Autor: | Rositha Kuniyil, Lutz Ackermann, Antonis M. Messinis, Jian-Biao Liu, Xin Wang, Xiao-Jun Liu, De-Zhan Chen |
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| Rok vydání: | 2021 |
| Předmět: |
chemistry.chemical_classification
010405 organic chemistry Alkene Migratory insertion Enantioselective synthesis chemistry.chemical_element General Chemistry 010402 general chemistry 01 natural sciences Oxidative addition Combinatorial chemistry Reductive elimination 0104 chemical sciences Catalysis Chemistry Nickel chemistry Reactivity (chemistry) |
| Zdroj: | Chemical Science |
| ISSN: | 2041-6539 2041-6520 |
| Popis: | The 3d transition metal-catalyzed enantioselective C–H functionalization provides a sustainable strategy for the construction of chiral molecules. A better understanding of the catalytic nature of the reactions and the factors controlling the enantioselectivity is important for rational design of more efficient systems. Herein, the mechanisms of Ni-catalyzed enantioselective C–H cyclization of imidazoles are investigated by density functional theory (DFT) calculations. Both the π-allyl nickel(ii)-promoted σ-complex-assisted metathesis (σ-CAM) and the nickel(0)-catalyzed oxidative addition (OA) mechanisms are disfavored. In addition to the typically proposed ligand-to-ligand hydrogen transfer (LLHT) mechanism, the reaction can also proceed via an unconventional σ-CAM mechanism that involves hydrogen transfer from the JoSPOphos ligand to the alkene through P–H oxidative addition/migratory insertion, C(sp2)–H activation via σ-CAM, and C–C reductive elimination. Importantly, computational results based on this new mechanism can indeed reproduce the experimentally observed enantioselectivities. Further, the catalytic activity of the π-allyl nickel(ii) complex can be rationalized by the regeneration of the active nickel(0) catalyst via a stepwise hydrogen transfer, which was confirmed by experimental studies. The calculations reveal several significant roles of the secondary phosphine oxide (SPO) unit in JoSPOphos during the reaction. The improved mechanistic understanding will enable design of novel enantioselective C–H transformations. Several unique reactivity patterns of the Ni/JoSPOphos manifold, including facile hydrogen transfer via the two-step oxidative addition/migratory insertion and C(sp2)–H activation via an unconventional σ-CAM mechanism, were disclosed in this work. |
| Databáze: | OpenAIRE |
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