The electronic structure perturbations caused by cyclopentadienyl substitutions in the series of complexes (η5-C5H5)2Ru, (η5-C5Me5)(η5-C 5H5)Ru, (η5-C5Me5)2Ru, (η5-C5Me5)(η5-C 5-Cl5)Ru, and (η5-C5Me5)(η5-C 5F5)Ru are measured by gas-phase photoelectron spectroscopy. The shifts of the valence metal- and cyclopentadienyl-based ionizations give an indication of the overall electronic effects of methyl and halogen substitutions on the cyclopentadienyl rings. The halogen substituent interaction is an admixture of inductive σ-electron-withdrawing and filled-filled π-electron-overlap effects, which act in opposite directions. The π-overlap interaction is relatively weak in the case of chlorine substitution for hydrogen, and the combined σand π interactions give rise to an overall withdrawal of electron density from the metal center and increase in the metal d-based ionization energies. Fluorine substituents on cyclopentadienyl make the ring only slightly more electron withdrawing than η5-C5Cl5, despite the much greater electronegativity of fluorine compared to chlorine. The electron withdrawing ability of η5-C5F5 is tempered by the greater filled-filled interaction of the fluorine pπ orbitale with the cyclopentadienyl pπ orbitals, which lessens the stabilization of these orbitals and the withdrawal of electron density from the metal. It is interesting that in each case the metal d-based ionizations are stabilized more than the cyclopentadienyl π-based ionizations with halogen substitution for hydrogen, such that these ionizations begin to merge in the lowest ionization energy band.
ASJC Scopus subject areas
- Physical and Theoretical Chemistry
- Organic Chemistry
- Inorganic Chemistry