Kinetic and mechanistic examination of NBu4[IrH2(CO)2I2] and NBu4[RhH2(CO)2I2] via para-hydrogen enhanced NMR spectroscopy

para-Hydrogen enhanced NMR signals are used to show that NBu4[M(CO)(2)I-2] (M = Rh, Ir) add hydrogen to form NBu4{all-cis-[M(H)(2)(CO)(2)I-2]} which for M = Ir undergoes H-2 elimination in a step where Delta H double dagger 106 +/- 10 kJ mol(-1) and Delta S double dagger 60 +/- 6 J K-1 mol(-1) while showing a rich substitution chemistry with PPh3 that leads to both charged and neutral products via square pyramidal Ir(H)(2)(CO)(2)I.