Detection of Reaction Intermediates in Suzuki-Miyaura by Electrospray Ionization Ion Mobility Mass Spectrometry

Mass spectrometry is one of the most extensive scientific analysis techniques, which plays an important role in analysis and research of biology, pharmaceutical, chemical industry, new materials and so on. At present, the research method of organic reaction mechanism is mainly through the detection of hypothetical organic reaction intermediates, combined with density functional calculation. Therefore, it is of great significance for mass spectrometer with high sensitivity to analyze and detect the intermediates in organic reactions. In this study, C-C coupling reaction in Suzuki-Miyaura reaction was studied. 3-Bromopyridine, 3-bromoquinoline and 3-bromo-5-phenylpyridine were used to react with phenylboronic acid, 2-methylphenylboric acid and 3,5-dimethylphenylboric acid, respectively, and Pd(PPh3)4 was used as catalyst to carry out one-pot reaction in toluene solvent. During the reaction, the samples were taken at regular intervals, and the intermediates generated after the oxidative addition and transmetalation processes in the Suzuki-Miyaura coupling reaction were detected using electrospray ionization-ion mobility time-of-flight mass spectrometry (ESI-TIMS-TOF MS). The results showed that:1) For the intermediates formed in the oxidative addition process, arylboric acids are not involved in the formation of arylboric acids, the mass-charge ratios observed in the reactions with different arylboric acids are the same. While, the intermediates formed after transfer metallization are different with the two substances involved in the coupling reaction. 2) The isotopic peaks of the detected intermediates are consistent with the predicted spectra. 3) The ion mobility of the detected groups can be detected by TIMS-TOF to distinguish the isomers, and the fragmented small groups can be observed by MS/MS analysis of the detected intermediates. The data of mass-charge ratio, ion mobility and MS/MS obtained by TIMS-TOF are helpful to study organic reaction mechanism, and also can provide a reference for the reaction mechanism catalyzed by metal Pd.