Transmetallation in the Suzuki-Miyaura Reaction

A detailed study of the transmetaUation in the Suzuki-Miyaura reaction by the group of Amatore and Jutand shows that hydroxide [261] and fluoride anions [262] form the key trans-[ArPdX(L)2] complexes that react with the boronic acid in a rate-determining transmetaUation. In addition, the anions promote the reductive elimination. Conversely, the anions disfavor the reaction by formation of nonreactive anionic [Ar B(OH)3 X ] (7t=l-3). Countercations M (Na , K , and Cs+) of anionic bases in the palladium-catalyzed Suzuki-Miyaura reactions decelerate the transmetaUation step in the following decreasing reactivity order nBu4NOH KOH CsOH NaOH this is due to the complexation of the hydroxy ligand in [ArPd(OH)(PPh3)2] by M+[263]. 

Several intermediates in the Suzuki-Miyaura coupUng of bromopyridines with arylboronic adds have been identified by in situ analysis of the reaction by electrospray ionization mass spectrometry (ESI-MS) [268]. Interestingly, monitoring the coupling by ESI-MS demonstrates that, at the end of the reaction, there is an accumulation of binuclear Pd(0)-Pd(II) halide clusters, which are stiU catalytically active [269]. 

The transmetallation in the y-selective Suzuki-Miyaura coupling between potassium allyltrifluoroborates with haloarenes is rate-determining and was shown 

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