A Quantitative Look on Ferrocene Distortion Paths

Ferrocenes symmetry is commonly described as either eclipsed (D₅h) or staggered (D₅d). Continuous symmetry analysis of the core structure of over 7,000 substituted ferrocenes extracted from the Cambridge Crystallographic Database (CSD) provides a quantitative way to describe the geometrical variations that take place during an eclipsed-staggered twist conformational change. In addition, a bending distortion path is explored described by the loss of C₅ rotation symmetry. Gas phase DFT calculations provide a theoretical background to describe these distortion paths and define symmetry profiles for conformer interconversion processes and the interplay between them. Calculations of the continuous chirality measure (CCM) presented below show that ferrocene is almost always chiral to some degree and that the eclipsed conformation is far more abundant than the staggered conformation (Figure 1: Black - DFT results, purple - experimental results). Handedness in terms of the M/P helicity convention is discussed.