Abstract
A combined ESI‐MS/NMR mechanistic study on the palladium‐catalysed cross‐coupling reaction between aryldiazonium salts and aryltrifluoroborates with bis(μ‐acetato)bis(4,4′‐difluoroazobenzene‐C^2^,N)dipalladium(II) (4) as the precatalyst is reported. The reaction follows a Pd^0^/Pd^II^ cycle after reduction of 4 to a molecular Pd^0^ species (I), which according to the combined ESI‐MS and ^19^F NMR studies, bears an arylated azobenzene ligand. Oxidative addition by the diazonium salt generates the arylpalladium(II) intermediate (II), which was also detected in solution. The catalytic cycle is completed with a transmetallation between II and theorganoborate, which is followed by fast reductive elimination of the cross‐coupling product to restore the molecular Pd^0^ species I. A concurrent activation path was also observed which consists of the formation of (4,4′‐difluoroazobenzene‐C^2^,N)dipalladium(II) tetrafluoroborate (7) by the reaction of 4 with the diazonium salt and subsequent reduction by the aryltrifluoroborate to give I. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)