No abstract

Trimerization of acetylferrocene and of (acetylcyclopentadienyl)tricarbonyl-manganese proceeds efficiently in the presence of ethanol and tetrachlorosilane. The resulting 1,3,5-trisubstituted benzenes have been characterized by X-ray crystallography and compared with the structure of (1,3,5-triphenylbenzene)tris(tricarbonylchromium). The efficacy of EtOH–SiCl4 as a combined reagent for the trimerization of polycyclic ketones is also discussed. Finally, the synthesis and structure of [CpMn(CO)2]2(µ-C=CHPr), derived from the reaction of cymantrene with butyllithium and phenylacetyl chloride at room temperature, is described.Key words: ketone, condensation, cyclization, organometallics, arenes.

Protonation of 3-ferrocenyl-2,4,5-triphenylcyclopentadienone with trifluoroacetic acid results in the formation of the first hydroxyfulvalene complex. The dramatic deshielding and decoalescence of the 1H and 13C NMR signals in the ferrocenyl region offer evidence for the participation of the metal in the stabilization of the positive charge, which results in restricted rotation of the ferrocenyl group. As determined by NMR spectroscopy, the maximum barrier to rotation in the neutral species is ca. 9 kcal mol-1, whereas the minimum barrier in the cation considerably exceeds 13 kcal mol-1. The difference in rotational barriers for the neutral and protonated species is rationalized by using DFT calculations.