Dynamic Ion Speciation During Hydrolysis of Aryltrifluoroborates

Organotrifluoroborates serve as a coupling partner during transmetallation in the Suzuki-Miyaura reaction but require hydrolysis prior to the coupling reaction. Their anionic nature allows study of their hydrolysis by electrospray ionization mass spectrometry (ESI-MS) by real-time monitoring, complemented by pH analysis. Induction periods varied according to the borates employed, and a dynamic series of equilibria for numerous ions was observed during hydrolysis. We found that the induction periods and reaction rates were sensitive to the R group of the borates, the shape of reaction vessel, and stir rate, and that after complete decay of all of the aryltrifluoroborate ion the solution contained a variety of partially hydrolyzed species.