Structure and fluxional behavior of (η⁴-butadiene)Fe(CO)<inf>2</inf>L (L = CO, PH<inf>3</inf>, PMe<inf>3</inf>) complexes. A density functional study

The structure and fluxional behavior of (η4-butadiene)Fe(CO)2L (L = CO, PH3, PMe3) complexes have been studied using density functional methods. For (butadiene)Fe(CO)3, the geometry obtained is in excellent agreement with the gas-phase experimental data. The calculation of the harmonic vibrational frequencies has permitted the reassignment of several frequencies observed in the IR and Raman spectra. The computed Fe-butadiene binding energy is in all cases about 52 kcal mol-1, in excellent agreement with the experimental data corresponding to the (butadiene)Fe(CO)3 complex. The nature of the bonding has been analyzed in terms of steric and electronic interactions. The butadiene-Fe rotational barriers have been computed, and the origin of the barrier has been discussed.