Molecular mechanics of bridged ferrocene derivatives: Conformational energy surfaces of [3]‐, [4]‐ and [4 5 ] ferrocenophanes

A molecular mechanical model is presented which allows computational interpretation of stereodynamics in ferrocenophanes by using a simple form of bending potential for angles involving the central iron atom and extended to carbon atoms of different cyclopentadienyl rings. Potential energy surfaces of [3] ‐, [4] ‐ and [4 5 ] ferrocenophanes were studied in detail. For [3] ferrocenophane, the calculated energy barrier of the bridge reversal process agrees well with the experimental value. The previous interpretation of a rigid bridge in [4] ferrocenophane is questioned on the basis of the calculated low barriers. The predominance of experimentally indistinguishable enantiomeric pairs may be responsible for the misinterpretation. [4 5 ] Ferrocenophane is estimated to interconvert into D 5 ‐symmetric global energy minima over barriers of 13–15 kcal mol −1 through one‐by‐one flipping of five tetramethylene bridges.