In situ analysis and real-time monitoring of the decomposition of the 2nd Grubbs catalyst in CH3CN by droplet spray ionization tandem mass spectrometry

Abstract

The 2^nd Grubbs catalysts are widely used in areas of organic and polymer synthesis. However, relatively little data on the decomposition of the 2^nd Grubbs catalysts are available. In this work, in situ analysis and real-time monitoring of the decomposition of the 2^nd Grubbs catalyst in CH₃CN was studied using droplet spray ionization mass spectrometry (DSI-MS). The degradation time ranged from seconds to minutes. The reactive intermediates and products were captured by the combination of DSI with an Orbitrap mass spectrometer, and were identified by tandem mass spectrometry. The decomposition of the 2^nd Grubbs catalyst occurred via the loss of the phosphine and chloride ligand, and the intermediates generated during the decomposition reaction tended to form hexacoordinate acetonitrile adducts. Moreover, CH₃CN used as spray solvent not only sped up the decomposition of the 2^nd Grubbs catalyst, but also stabilized the transient Ru-intermediates by generation of Ru–CH₃CN adducts. Finally, a possible decomposition pathway of the 2^nd Grubbs catalyst in CH₃CN was proposed. These results above are helpful for researchers to design more efficient catalysts, to optimize reaction conditions, and to choose an appropriate reaction solvent to avoid the decomposition of the Grubbs catalysts.