Research Progress of Suzuki-Miyaura Cross-Coupling Reaction Mechanism

During the past several decades, Suzuki-Miyaura cross-coupling reaction has emerged and flourished as one of the most remarkable and practical methods to construct C-C bond. The substrates, organoboronic compounds, are usually more stable, less toxic and easier to obtain compared with other metal or metalloid alternatives. Suzuki-Miyaura cross-coupling reaction possesses extraordinary merits of demonstrated efficiency, broad functional group compatibility and mild reaction conditions. It has been the premier method to construct C-C bond for organic synthetic chemists and has been widely applied in the industrial syntheses. The rapid development of Suzuki-Miyaura cross-coupling reaction is accompanied with the progress of mechanism studies. It is well accepted that the catalytic cycle of Suzuki-Miyaura cross-coupling reaction contains three main steps: oxidative addition of organic halides to Pd catalysts, transmetalation between oxidative addition intermediates and organoboronic compounds, and reductive elimination from transmetalation intermediates to form C-C bond along with regenerating Pd catalysts. However, these three main steps can be influenced by diverse reaction conditions, and different reaction pathways may occur within each single step. Furthermore, beyond the oxidative addition and transmetalation intermediates, other transient but crucial intermediates may exist. To figure out these issues and discover more insights into SuzukiMiyaura cross-coupling reaction, numerous researchers have designed and conducted systematic investigations. Herein, the recent progress of mechanism studies is summarized and discussed. The steps of oxidative addition, transmetalation and reductive elimination are discussed in detail. Moreover, a brief introduction of transition-metal-free and base-free Suzuki-Miyaura cross-coupling reactions which show more possibilities of the reaction mechanism is given. Besides summary of precedent research works, our opinions about future development of the mechanism studies are also given. Although breakthroughs have been made in the mechanism studies, further investigations are needed to bring comprehensive knowledge of this reaction and help us further optimize the reaction conditions.