转自：康龙化成
Ruthenium/η5‑Phenoxo-Catalyzed Amination ofPhenols with Amines
KaiChen, Yixuan Ma, Yunzhi Lin, Jia-Yue Li, and Hang Shi*
Key Laboratory of Precise Synthesis ofFunctional Molecules of Zhejiang Province, Department of Chemistry, School of Science and Research Center forIndustries of the Future, Westlake University, Hangzhou, Zhejiang Province310030, China;
Institute of Natural Sciences,Westlake Institute for Advanced Study, Hangzhou, Zhejiang Province 310024,China;
Department of Chemistry, ZhejiangUniversity, Hangzhou, Zhejiang Province 310027, China; Key Laboratory ofPrecise Synthesis of Functional Molecules of ZhejiangProvince, Department of Chemistry, School of Science and Research Center forIndustries of the Future, Westlake University, Hangzhou, ZhejiangProvince 310030, China
—J. Am. Chem. Soc., 2024,https://doi.org/10.1021/jacs.4c02089.
Recommended by Murong Xu_MC3
ABSTRACT: Ruthenium(II)complexes are known to form η6-arene complexes with benzene-containingcompounds through π-coordination, a property extensively utilized to initiatereactions not typically observed with free arenes. A prime example isnucleophilic aromatic substitution, where ruthenium-complexed aryl halidesundergo nucleophilic attack, allowing the direct synthesis of diverse aromaticcompounds by displacing halides with nucleophiles. However, this activationrelies on the electron-withdrawing effect of the Ru(II) species, as well as ishindered by the resistance of η6-arenes to arene exchange. In the previouspursuit of catalysis, the emphasis of ligand design has centered on promotingarene exchange. In this study, we extended the ruthenium activation strategy toumpolung substitution reactions of phenols. The amination proceeds through adirect condensation between phenols and amines, with a key intermediateidentified as [bis(η5-phenoxo)Ru], which is in situ generated from acommercially available ruthenium catalyst. In comparison with the well-studiedcyclopentadienyl (Cp) type ligands, we demonstrated that an η5-phenoxo motif,as a superior alternative to Cp, contributes to the amination of phenols in twocrucial ways: its less electron-donating nature enhances the withdrawing effectof the ruthenium unit, facilitating substitution on the phenol complex; itsdistinctive behavior in arene exchange allows for conducting the amination witha catalytic amount of metal. Additionally, hydrogen bonding, wherein the phenoxoserves as the acceptor, was found to be important for the substitution. Theversatility of this ruthenium-catalyzed amination was validated by performingreactions with a diverse array of phenols exhibiting various electronicproperties, in combination with a wide range of primary amines. This workexemplifies the expansion of the scope of π-coordination activation incatalysis through innovative ligand development.
Ru-CatalyzedSubstitution Reactions via Transient η6-Arenes
Catalyst Evaluation
Ru-Catalyzed Amination of Phenols
Plausible CatalyticCycle
Prof. HangShi et al havesuccessfully developed a ruthenium-catalyzed dehydrativecondensation between phenols and amines. Investigations, combining experimentalstudies and computational calculations, have provided insights into themechanistic aspects of the substitution step as well as the arene exchange. Theversatile η5-phenoxoligand wasfound to play a crucial role in promoting both the nucleophilic attachment byamines with proton donors and the ligand exchange of anilines by phenols, while Cp* wasproven ineffective. Building upon these findings, they are actively engaged inongoing research to further expand the scope of this strategy. Considering therare application of η5-phenoxo in catalytic reactions, this study isanticipated to pique interest in other domains beyond π-coordinationactivation, where Cp-based catalysts are typically employed.
