Kinetics and Thermodynamics of the Oxidative Addition of Aryl Bromides at Palladium(I) to Form Palladium(III) Complexes

Herein, we report the systematic study of the oxidative addition or aryl bromides to a PdI center to generate stable organometallic PdIII complexes. These isolable PdIII complexes stabilized by tetradentate macrocyclic pyridinophane ligands were characterized spectroscopically, demonstrating distinct UV-Vis and EPR spectroscopic signatures that allow for reaction monitoring. The ligand scaffolds were sterically and electronically tuned using a modular synthetic approach to probe the kinetic and thermodynamic properties of the oxidative addition reaction, and a combination of UV-Vis and cryo stopped-flow spectroscopic studies reveal striking similarities to the radical oxidative addition pathway previously observed for well-defined NiI systems. In addition, these results are in strong agreement with our recent reactivity studies, which demonstrated that mononuclear PdI systems are competent catalysts in Kumada cross-coupling, and thus set the stage for an expansion of catalytic applications for odd-electron Pd systems promoting single electron processes.