Structural characterization of cis-2,6-(E,E)-bis(ferrocenylidene)-N-methyl-4-piperidone and DFT evaluation of alternative polymorphic modifications via ferrocene rotation

The molecular structure of cis-2,6-(E,E)-bis(ferrocenylidene)-N-methyl-4-piperidone (1) has been determined by X-ray crystallography. Compound 1 crystallizes in the monoclinic chiral space group P2(1), a = 6.0055(17) Å, b = 12.802(4) Å, c = 14.465(4) Å, β = 95.438(4)°, V = 1107.1(5) Å3, Z = 2, and Dcalc = 1.516 Mg/m3; R = 0.0335, Rw = 0.0682 for 4230 reflections with I > 2σ(I). The substituents at the vinyl group of each chalcone moiety exhibit a trans (entgegen) disposition, and the two ferrocene moieties adopt a syn orientation and are located on the side of the piperidone ring opposite of the nitrogen lone electron pair. Molecules of 1 pack in chains along the a axis and exhibit weak intermolecular C-H⋯O hydrogen bonds involving the ferrocene and carbonyl moieties of adjacent molecules. The energy difference between the ferrocene rotational isomers in 1 has been evaluated by DFT, and the lowest energy structure is represented by the solid-state structure. The barriers for the rotational isomerization of the ferrocene groups have been evaluated and are discussed in the context of polymorphic modifications available to 1.

The molecular structure of cis-2,6-(E,E)-bis(ferrocenylidene)-N-methyl-4-piperidone (1) has been determined by X-ray crystallography, and a trans disposition of the substituents at the exocyclic alkenyl groups belonging to the bis(chalcone) moiety and a cis orientation for the two ferrocene moieties confirmed. The DFT-computed energy difference between the solid-state structure and the rotational isomers involving the ferrocene moieties is small and favors the solid-state structure.Figure optionsDownload as PowerPoint slideHighlights
► Rotational isomerization and polymorphism in a bis(ferrocene) derivative.
► DFT evaluation of rotational isomers.
► Functionalization of N-methyl-4-piperidone with ferrocenecarboxaldehyde.