4-Ferrocenylphenol

The title compound, [Fe(C5H5)(C11H9O)], is of interest as a precursor to the synthesis of cheap ferrocene-based liquid crystals. The –OH substituent only results in weak C—H⋯O weak interactions between one of cyclopentadienyl (Cp) ring H atoms and the O atom of a neighbouring molecule with a distance of 3.308 (3) Å between the donor and acceptor atoms. The interplanar angle between the Cp and benzene rings is 13.0 (4)°. There are also weak O—H⋯π and C—H⋯π interactions involving the unsubstituted Cp and the benzene ring, respectively.

The title compound, [Fe(C 5 H 5 )(C 11 H 9 O)], is of interest as a precursor to the synthesis of cheap ferrocene-based liquid crystals. The -OH substituent only results in weak C-HÁ Á ÁO weak interactions between one of cyclopentadienyl (Cp) ring H atoms and the O atom of a neighbouring molecule with a distance of 3.308 (3) Å between the donor and acceptor atoms. The interplanar angle between the Cp and benzene rings is 13.0 (4) . There are also weak O-HÁ Á Á and C-HÁ Á Á interactions involving the unsubstituted Cp and the benzene ring, respectively.

Comment
The synthesis of arylferrocenes especially compounds prepared by the reaction of para-substituted anilines via diazonium reactions to yield phenylferrocenes has evoked the interest of material scientists (Togni & Hayashi, 1995). For example, arylferrocenes have been established as precursors in the synthesis of ferrocenomesogens especially those with ferrocenyl moiety incorporated as a terminal group (Imrie et al., 2002). These class of compounds are most readily prepared by crosscoupling reactions, e.g. of iodoferrocene (Imrie et al., 2003) with arylboronic (Tsukazaki et al., 1996) and organotin compounds (Lin et al., 1995). Alternative cross-coupling reagents include aryl halides with tin (Guillaneux & Kagan, 1995), zinc (Foxman & Rosenblum, 1993) and ferrocenylboronic acids (Knapp & Rehahn, 1993). In this paper we report the synthesis of 4-hydroxyphenylferrocene using 4-aminophenol which was obtained via diazonium reaction.
The title compound (I) (Fig. 1) is a precursor prepared as part of a study to develop starting materials from cheaper sources for the development of new ionic liquid and liquid crystal materials (Nyamori & Bala, 2008a;2008b). Due to the -OH subtituent on the benzyl ring it was thought that the property of (I) will be dominated by intra-or intermolecular hydrogen bonding, but analysis revealed no classical hydrogen bonds. Hence, the high melting point of 162 o C may be attributed to a concerted contribution from all molecular contacts within the crystal of (I) ( Table 1: Cg(1) is the centroid of the unsubstituted Cp and Cg(3) the centroid of the benzene ring).
In the crystal of (I), the two cp rings are marginally tilted towards each other with a tilt angle between the planes of the two rings of 0.41 (5)°, while the interplanar angle between the cp and the phenyl ring is 13.0 (4)°.

Experimental
In an excess of 2M hydrochloric acid at 5 °C was dissolved 4-aminophenol (12.00 g, 0.11 mol) followed by slow addition of sodium nitrite (8.00 g, 0.11 mol) in cold water (20 cm 3 ) also at 5 °C. The solution was left to stir at this temperature for 30 min and the resultant solution was filtered. The filtrate was immediately added to a cold thoroughly stirred solution of ferrocene (18.00 g, 0.10 mol) in diethyl ether (500 cm 3 ). Stirring was continued at 5 °C for 8 h. The ether layer was then separated, washed with water (3 x 100 cm 3 ) and dried over anhydrous sodium sulfate. The solution was concentrated and the residue was passed through a column of alumina. Dichloromethane: hexane (1:1) eluted unreacted ferrocene. Further elution of the column with diethyl ether yielded 4-ferrocenylphenol (5.22 g, 32%) as yellow crystals recrystallized from hexane, mp 162 o C.

Refinement
All H atoms attached to C atoms were fixed geometrically and treated as riding with C-H = 0.95 Å and U iso (H) = 1.2U eq (C).
Hydrogen atom attached to oxygen was freely refined. Fig. 1. Molecular structure of the title complex with the atom labelling scheme. Ellipsoids are drawn at the 50% probability level.