Formation of a 14‐Electron Intermediate in Iridium Catalysis through Reductive Elimination: Dissociation Is Rate Determining

Oxidative addition and reductive elimination are fundamental processes in organometallic chemistry and are important in catalytic transformations involving C–H bonds. Herein, the article reports on the dynamics of benzene reductive elimination from iridium complexes bearing bisphosphinite ( POCOP ) and phosphine (PCP) based pincer ligands. The reductive elimination forms an important 14‐electron catalytic intermediate that has eluded detection. Using NMR spectroscopy, including dynamic 31 P NMR and 1D/2D exchange spectroscopy experiments, it is demonstrated that in POCOP‐Ir(Ph)H complexes reductive coupling and benzene dissociation are experimentally separable steps, with reductive coupling being fast and dissociation slow. In contrast, PCP‐Ir(Ph)H exhibits slower reductive coupling and more facile dissociation. Rate constants and activation parameters for both processes are determined and trapping experiments with external olefins further quantifies dissociation kinetics. The data show that comparatively electron‐poor POCOP complexes facilitate reductive coupling but inhibit ligand dissociation compared to electron‐rich PCP analogs. These findings highlight mechanistic nuances in exchange processes, including differences in resting states for dehydrogenation, and demonstrate the importance of directly identifying the step being measured in dynamic NMR studies.