Gas-Phase Study of the Formation and Dissociation of Fe(CO)4H2: Kinetics and Bond Dissociation Energies

Time-resolved IR spectroscopy has been used to study the oxidative addition of H 2 to Fe(CO) 4 and its reverse reaction, the reductive elimination of H 2 from Fe(CO) 4 H 2, in the gas phase. The rate constant for oxidative addition of H 2 shows little temperature dependence, indicating that if there is an activation barrier for this process it is small (<4 kcal mol - 1 ). The activation barrier for the reductive elimination of H 2 is 20.5 ± 2.1 kcal mol - 1 . From these measurements, the average of the dissociation energies for the two Fe−H bonds in Fe(CO) 4 H 2 is calculated to be 62 ± 2 kcal mol - 1 . Kinetic measurements employing D 2 indicate small kinetic isotope effects for both the oxidative addition and reductive elimination reactions.