Nature of Fe-CH2 bonds in ferrocenylmethyl and ferrocenylenedimethyl cations

Quantum-chemical calculations of ferrocenylmethyl ([C5H5FeC5H4CH2](+)) and ferrocenylenedimethyl ([C5H5FeC5H3(CH2)(2)](2+)) cations with full geometry optimization were carried out using the Hartree-Fock (HF) approximation, density functional theory (DFT), and at the second-order Moller-Plesset (MP2) level of perturbation theory in the 6-311G* basis set. The methods with inclusion of electron correlation in explicit form indicate that the CH2 groups deviate from the cyclopentadienyl ring planes toward the Fe atom due to formation of the Fe-CH2 bonds. According to Hartree-Fock calculations, ligands in these ions are virtually planar. The metallonium character of the ions studied was demonstrated based on the results of analysis of the electron density distribution and frontier orbitals.