Gas-phase studies of copper catalyzed aerobic cross coupling of thiol esters and arylboronic acids

Electrospray ionization/mass spectrometry (ESI-MS) is used to monitor a Cu-catalyzed aerobic cross-coupling reaction between thiol esters and arylboronic acids. The ESI spectra show the formation of Cu-complexes with the starting thiol ester 1 and the coupling product. The formation of an ionic complex at m/z 305 is observed, most likely occurring upon the elimination of a mixed anhydride from [(1)CuOAc](+). An online monitoring of the reaction using ESI-MS was carried out allowing calculation of rate constants and thermodynamic parameters (H-double dagger, S-double dagger, and G(double dagger)) for the title reaction.