Variable-temperature H-1 NMR studies and ab initio (B3LYP) calculations have revealed hydride site exchange in [Ir(H)(2)(H-2)((PBu2Ph)-Ph-t)(2)][BAr4'] [Ar' = C6H3(CF3)(2)-3,5] as well as fluxional and HD formation processes in [Ir(H)(2)(H-2)(2)((PBu2Ph)-Ph-t)(2)][BAr4'] that occur via independent mechanisms.