Capture of reactive monophosphine-ligated palladium(0) intermediates by mass spectrometry.

A long-sought-after reactive monophosphine-ligated palladium(0) intermediate, Pd(0)L (L = phosphine ligand), was detected for the first time from the activation of the Buchwald precatalyst with base. The detection was enabled using desorption electrospray ionization mass spectrometry (DESI-MS) in combination with online reaction monitoring. The subsequent oxidative addition of Pd(0)L with aryl halide and C-N coupling with amine via reductive elimination was also probed using DESI-MS.