Effect of Solvent and Ancillary Ligands on the Catalytic H/D Exchange Reactivity of Cp*IrIII(L) Complexes

The reactivity of a series of Cp*Ir-III(L) complexes that contain a diverse set of ancillary ligands, L, (L = PMe3, N-heterocyclic carbene, NHC = 1,3-dimethylimidazol-2-ylidene, aqua, 4-t-butylpyridine, and 4-(2,4,6-tris-(4-t-butylphenyl)pyridinium)pyridine tetrafluoroborate) has been, examined in catalytic H/D exchange reactions between C6H6 and a series of deuterated solvents (methanol-d(4), acetic acid-d(4), and trifluoroacetic acid-d(1)). These studies demonstrate that (1) the mechanism of catalytic H/D exchange is significantly influenced by the nature of the solvent; (2) electron-donating ligands (PMe3, NHC) promote the formation of Ir hydrides in methanol-d(4), and these are critical intermediates in catalytic H/D exchange processes, and (3) weak/poorly donating ligands (4-t-butylpyridine, 4-(2,4,6-tris-(4-t-butylphenyl)pyridinium)pyridine tetrafluoroborate and aqua) can support efficient H/D exchange catalysis in acetic acid-d(4).