Cooperative Au/Ag Dual-Catalyzed Cross-Dehydrogenative Biaryl Coupling: Reaction Development and Mechanistic Insight

• Published in: Journal of the American Chemical Society Vol. 141; no. 7; pp. 3187 - 3197
• Main Authors: Li, Weipeng, Yuan, Dandan, Wang, Guoqiang, Zhao, Yue, Xie, Jin, Li, Shuhua, Zhu, Chengjian
• Format: Journal Article
• Language: English
• Published: WASHINGTON American Chemical Society 20.02.2019; Amer Chemical Soc
• Subjects: Chemistry; Chemistry, Multidisciplinary; Physical Sciences; Science & Technology; GOLD CATALYSIS; VISIBLE-LIGHT PHOTOREDOX; SILVER; ARYLATION; ARENES; COMPLEXES; ARYL; C-H ACTIVATION; REDUCTIVE ELIMINATION; SELECTIVITY
• ISSN: 0002-7863; 1520-5126
• DOI: 10.1021/jacs.8b12929

An operationally simple and highly selective Au/Ag bimetallic-catalyzed cross-dehydrogenative biaryl coupling between pyrazoles and fluoroarenes has been developed. With this reaction, a wide range of biheteroaryl products can be obtained in moderate to good yields with excellent functional group compatibility. The exact role of silver salts, previously overlooked in most gold-catalyzed transformations, has been carefully investigated in this biaryl coupling. Insightful experimental and theoretical studies indicate that silver acetate is the actual catalyst for C–H activation of electron-poor arenes, rather than the previously reported gold­(I)-catalyzed process. An unprecedented Au/Ag dual catalysis is proposed, in which silver­(I) is responsible for the activation of electron-poor fluoroarenes via a concerted metalation–deprotonation pathway, and gold­(III) is responsible for the activation of electron-rich pyrazoles via an electrophilic aromatic substitution process. Kinetic studies reveal that ArFnAu­(III)-mediated C–H activation of pyrazoles is most likely the rate-limiting step.