Structure and nature of the metal-ligand interactions in mimed iron(II) phosphametallocenes

Quantum mechanical calculations at the density functional level (DFT) were carried out in order to analyze the structure and nature of the metal-ligand interactions in mixed iron(II) metallocenes of the type Fe(Cp)(L), where L stands for the ligands [C5H5](-), [C4H4P](-), [1,3-P2C3H3](-), and [1,2,4-P3C2H2](-). The nature of the metal-ligand interactions is analyzed by means of the charge decomposition analysis (CDA), in which the extent of donation, backdonation, and repulsive polarization of the electron density, in the region of the bond, is discussed in light of the varying number of heteroatoms at the rings. The aromaticity of the free ligands and the energies involved in the ligand displacement reactions for the process [Fe(CP)(2)] + L- --> [Fe(Cp)(L)] + Cp- were also computed and are discussed. Our results reveal that changing a CH group of the cyclopentadienyl ligand to phosphorus has the effect of changing drastically the electronic structure of the resulting metallocene and, thus, the reactivity of these compounds.