A theoretical study of the reaction H₂ + Fe(CO)₄ ⇌ H₂Fe(CO)₄

Density functional theory (DFT) methods, with three different gradient-corrected functionals (BP86, BLYP, and B3LYP), have been used to calculate molecular geometries and energies along the pathway for oxidative addition of H₂ to Fe(CO)₄ leading to H₂Fe(CO)₄. The geometry of H₂Fe(CO)₄, optimized using each of the different functionals, is in good agreement with experimental results. The enthalpies for reductive elimination of H₂ from H₂Fe(CO)₄, referenced to both the first excited singlet and the triplet ground state of Fe(CO)₄, have been calculated using the BP86, BLYP, and B3LYP functionals and are compared to the experimental result of 21 ± 2 kcal mol^-1. The mechanism for the oxidative addition of H₂ to Fe(CO)₄ is discussed and compared with experimental observations. The geometry of a dihydrogen intermediate, (η²-H₂)Fe(CO)₄, and the transition state between (η²-H₂)Fe(CO)₄ and H₂Fe(CO)₄, along the reaction path, has also been optimized.