Complexes [Cu(I)(2,4-dimethylphenoxy)2]− (A) and [Cu(II)(2,4-dimethylphenoxy)2(p-tolyl)]− (B) were observed by in situ electrospray ionization mass spectrometry (ESI-MS) analysis of the ligand free copper(I)-catalyzed C–O coupling reaction using Cs2CO3 under the catalytic reaction conditions indicating that they could be intermediates in the reaction. The radical scavenger cumene retarded the reaction. Catalytic cycles involving a free radical path are proposed based on these observations.
