π-Complexed polyfluoroarenes: a reactivity, bonding and spectroscopic study of (η6-C6F6)Cr(η6-C6H6) and related molecules

Abstract

The syntheses, structures and reactivity of fluorinated di-arene chromium sandwich complexes (chromarenes) are reviewed, and their bonding characteristics probed by an analysis of their spectroscopic properties. In particular, density functional theory, together with a detailed vibrational study of (C₆F₆)Cr(C₆H₆), has been used to study a system containing the very rare hexahapto-coordinated hexafluorobenzene ligand. The structural, reactivity and spectroscopic data yield a consistent picture whereby electron density is transferred from the chromium to both rings, but to a much greater extent to the fluorinated ligand. The result is a marked decrease in the stretching and bending vibrational modes of the fluorinated ring, and also dramatic changes in the ¹⁹F NMR chemical shifts and coupling constants. This contrasts with the situation in the organic mixed arene system C₆F₆/C₆H₆ where intermolecular interactions are rather minimal.