Crystal structure of 1,3-benzene-bis(1-ferrocenyl-3-hydroxyprop-2-en-1-one), (C5H5)Fe(C22H16O4)Fe(C5H5)

Abstract

Source of materialAcetylferrocene was obtained from the reaction of ferrocene and acetic anhydride as described previously [1]. A solution of sodium ethoxide (5.036 g, 74 mmol), acetylferrocene (16.877 g, 74 mmol) and dimethyl isophthalate (7.157 g, 37 mmol) in 60 ml THF was refluxed under nitrogen for 3 h. The yellow solid was filtered, washed with THF, then dissolved in hot water and finally acidified with aqueous acetic acid to afford the title compound (8.032 g, yield 37 %) as dark red solid. Recrystallization from dichloromethane and hexane gave crystals suitable for X-ray analysis (m.p. 184.5-185.7°C). DiscussionEnaminones have been studied not only as ligands in coordination chemistry [2], but also as chiral auxiliaries in organic synthesis [3]. In continuation of investigation of the chemistry of organometallic enaminones, the title compound, as an intermediate, has been synthesized via the Claisen condensation of acetylferrocene and dimethyl isophthalate [4,5]. 1 H NMR spectroscopy shows that the compound exists in the enol, and not in the keto form in solution. Interestingly, IR spectroscopy displays only the enol form in the solid state, this fact has been fully confirmed by the crystal structure (figure, top). As also noted for the related structure of (Z)-1-ferrocenyl-3-hydroxy-3-(2-pyridyl)-prop-2-en-1-one [6], the O=CC=CO fragments are planar. The bond lengths indicate electron delocalization [7]. Two O=CC=CO planes are twisted with respect to the benzene ring (C6 C10) and the substituted cyclopentadienyl ring (C23 C27) by 26.0(3)°, 7.2(3)°and 22.9(3)°, 9.3 (3)°, respectively. The two cyclopentadienyl rings in the ferrocenyl group are almost parallel (dihedral angles are 2.1(4)°for the first ferrocenyl group and 2.9(4)°for the second one) and adopt a different conformation, viz. eclipsed for the first ferrocenyl group and staggered for the second. Furthermore, two ferrocenyl groups are cis with respect to the benzene ring. The C13C14 and C18C20 bonds of 1.481(7) Å and 1.484(7) Å, respectively, which are typical of a single C sp2Csp2 bond, suggest that the benzene ring is not involved in the conjugation of the O=CC=CO groups. In addition to the intramolecular hydrogen bonds (OH···O=C), intermolecular hydrogen bond (CH···O=C) is also present in the crystal structure of the title compound ( figure, bottom).