Electron-Poor Iridium Pincer Complexes as Dehydrogenation Catalysts: Investigations into Deactivation through Formation of N₂, CO, and Hydride Complexes

A range of derivatives of an iridium pincer complex with a bis-trifluoromethyl-substituted ligand have been studied to determine how their properties differ from those of similar systems. The emphasis is on derivatives valuable for catalytic acceptorless dehydrogenation, including intermediates and deactivation products. The studies highlight small but important differences in the electron richness of the metal, as indicated by CO-stretching frequencies and hydride structures, as well as their impact on the equilibria between dihydride and tetrahydride species. T₁¹J_HD NMR studies and computational results highlight the effect of the electron-withdrawing groups on tetrahydride structures, indicating shortened H-H distances. Further, the equilibria of di- and tetrahydride species have been deduced using 2D-EXSY NMR spectroscopy, showing faster hydrogen elimination in the complex with electron-withdrawing groups incorporated into the ligand.