Cooperative or Oxidative Hydrogen Addition to 2-Hydroxypyridonate Iridium Complexes: Dependence on Oxidation State

Iridium(III)–pyridone complexes are commonly found to react in a cooperative and redox-neutral manner with dihydrogen and alcohols. In this work, the reactivity preferences of Ir^I–pyridone complexes were investigated under a variety of conditions. We have found that, in contrast to Ir^III–pyridones, Ir^I–pyridone complexes display a strong preference to react non-cooperatively. With a new chelating 2-hydroxy-8-diphenylphosphinoquinoline ligand that does not dissociate after hydrogen addition, oxidative addition is still preferred. In the preparation of mono- and bidentate neutral and anionic pyridone ligands, Vaska's complex was used as a point of reference. We expect these findings to have implications for catalyst development in the field of metal–ligand cooperation.