Metal-ring interactions in group 2 ansa-metallocenes: assessed with the local vibrational mode theory.

Abstract

Ansa-metallocenes, a vital class of organometallic compounds, have attracted significant attention due to their diverse structural motifs and their pivotal roles in catalysis and materials science. We investigated 37 distinct group 2 ansa-metallocenes at the B3LYP-D3/def2-TZVP level of theory. Utilizing local mode force constants derived from our local vibrational mode theory, including a special force constant directly targeting the metal-ring interaction, we could unveil latent structural differences between solvated and non-solvated metallocenophanes and the influence of the solvent on complex stability and structure. We could quantify the intrinsic strength of the metal-cyclopentadienyl (M-Cp) bonds and the influence of the bridging motifs on the stiffness of the Cp-M-Cp angles, another determinant of complex stability. LMA was complemented by the analysis of electronic density, utilizing the quantum theory of atoms in molecules (QTAIM), which confirmed both the impact of solvent coordination on the strength of the M-Cp bond(s) and the influence of the bridging motif on the Cp-M-Cp angles. The specific effect of the ansa-motif on the M-Cp interaction was further elucidated by a comparison with linear/bent metallocene structures. In summary, our results identify the local mode analysis as an efficient tool for unraveling the intricate molecular properties of ansa-metallocenes and their unique structural features.