Electronegativity Versus Lone Pair Shape:  A Comparative Study of Phosphaferrocenes and Azaferrocenes

The electron localization function (ELF), calculated at the DFT/B3LYP level of theory, has been used to analyze various phosphaferrocenes and azaferrocenes. The analysis of the bonding situation and electronic structure in the complexes reveals the importance of the shape of the heteroelement lone pair. Thus, the electron-withdrawing capability of the heteroatom-substituted ring is not only a consequence of electronegativity but also a result of the extension of the lone pair. Our data allow a model of the electrophilic reactivity of these complexes to be proposed.