Ferrocenyl-penta-(-naphthyl)benzene — Synthesis, structure, and dynamic behaviour

3-Ferrocenyl-2,4,5-tri-(β-naphthyl)cyclopentadienone undergoes a Diels–Alder reaction with di-(β-naphthyl) acetylene to yield, after elimination of carbon monoxide, ferrocenyl-penta-(β-naphthyl)benzene (4). 1 H and 13 C variable-temperature NMR studies on 4 reveal the existence of multiple diastereoisomers at low temperature. These data are interpreted in terms of slowed rotation of the naphthyl groups, and are supported by the X-ray crystal structure of 4, which exhibits disorder at three of the naphthyl sites.Key words: sterically crowded molecules, hindered rotations, crystallography, NMR.