Real-time monitoring of a cobalt-mediated one-pot transition metal-catalyzed multicomponent reaction

[Display omitted] •Cobalt(II)-promoted hydrodehalogenation was not previously reported for this MCR.•Hydrodehalogenation is an undesired transformation in this MCR.•Hydrodehalogenation were detected thanks to the use of charge-tagged aryl halides.•Cobalt(II) complexes suppress the signals of mechanistically important species.•PSI-ESI-MS can also be used in mechanistic studies of heterogeneous catalysis. In this paper, pressurized sample infusion electrospray ionization mass spectrometry (PSI-ESI-MS) and FTIR spectroscopy were used to investigate the mechanism of a like-Barbier cobalt-mediated one-pot transition metal-catalyzed multicomponent reaction (MCR). The use of charge-tagged aryl halides allowed for the detection of cobalt(II)-promoted hydrodehalogenation products. Although these products were also detected in the off-line ESI-MS monitoring, the ability of PSI-ESI-MS to track real-time changes in the reaction mixture composition proved cobalt(II) was responsible for the undesired transformation. The occurrence of cobalt(II)-promoted hydrodehalogenation as a side reaction in this MCR had not been considered in previous mechanistic proposals and represents an important mechanistic consideration.