THEORETICAL-STUDY OF IRON LIGAND-BINDING - MECHANISM OF FERROCENE FORMATION FROM IRON PLUS CYCLOPENTADIENE

The mechanism of ferrocene formation from atomic iron and cyclopentadiene has been studied by ab initio methods. A reasonable qualitative interpretation can be obtained after empirical corrections are made for deficiencies in the calculation. The first correction compensates for the energy difference between ground-state iron (4s23d6) and a configuration appropriate for binding the cyclopentadienyl (Cp) groups. The second correction compensates for the underestimation of the Cp binding energy to iron. The initial step of the mechanism is the insertion of Fe into a CH bond of cyclopentadiene. The resulting high-spin complex binds another molecule of cyclopentadiene and undergoes conversion to a low-spin complex. Elimination of H-2 from the final complex is predicted to be facile.