An Update on Phosphine-Imidazolin-2-Imine Iridium(I) Catalysts for Hydrogen Isotope Exchange

The reaction of the bidentate P,N ligand [2-(1,3,4,5-tetramethylimidazolin-2-imino)phenyl]di-tert-butylphosphine (1) with [Ir(COD)Cl](2) (COD=1,5-cyclooctadiene) followed by addition of sodium tetrakis[3,5-bis(trifluoromethyl)phenyl]borate, NaBArF24, or lithium tetrakis(nonafluoro-tert-butoxy)aluminate, Li[Al{OC(CF3)(3)}(4)], afforded the complexes [(1)Ir(COD)][BArF24] (2 a) and [(1)Ir(COD)][Al{OC(CF3)(3)}(4)] (2 b). Exposure of 2 b to one atmosphere of dihydrogen gas afforded the diiridium tetrahydride [(1)(2)Ir2H4][Al{OC(CF3)(3)}(4)](2) (3 b). The molecular structures of 2 a, 2 b, and 3 b were determined by single-crystal X-ray diffraction analyses. In the latter complex, the positions of the hydrogen atoms in the Ir2H4 core could be refined freely, which had previously proved impossible for the corresponding complex 3 a containing the BArF24 anion. Since 2 a is an established catalyst for ortho-directed hydrogen isotope exchange (HIE), the performance of 2 a and 2 b in deuterium labelling reactions was compared for various substrates, including phenylacetic acid derivates and nitrogen-containing aromatic compounds.