Syntheses of Ferrocene Derivatives with Potentially Mesogenic Functional Substituents W. Edward Lindsell* and Lin Xinxin Department of Chemistry, Heriot-Watt University, Riccarton, Edinburgh EH14 4AS, UK Ferrocenyl imines, Fe{5-C5H4CH=NC6H4OCnH2n + 1-4)}(5-C5H5) and Fe{5-C5H3-1-(CO2Et)-3-(CH=NC6H4O- CnH2n + 1-4)}(5-C5H5) (n = 5^9) produced fromformylferrocene and1-(ethoxycarbonyl)-3-(formyl)ferrocene, respectively, and some diaryl esters of ferrocenedicarboxlic acids have been synthesised and characterised by analysis and spectroscopy. There is considerable interest in metal-containing liquid crystalline materials1 and a number of mesogenic com- pounds containing the ferrocene moiety has been made in recent years, including monofunctionalised, 1,3- and 1,1'- difuntionalised and trifunctionalised systems.3 We are inter- ested in developing mesogenic ferrocene entities with suit- able substituents for inclusion as side-chains in polymers.In this paper we report syntheses and characterisation of some precursor compounds.Various 1,3-ferrocene diesters with enantiotropic meso- phases have previously been prepared from ferrocene-1,3- dicarboxylic acid (1a), but the only reported route to the precursor diacid involves a lengthy set of sequential reac- tions from ethylferrocene.3,15 We have used a simpler, more versatile route to 1,3-disubstituted ferrocenes from (Z5- cyclopentadienyl)(Z6-p-xylene)iron(II) hexa�uorophosphate, easily prepared from unsubstituted ferrocene, and 2-(ethoxy- carbonyl)-6-(dimethylamino)pentafulvene, see Scheme 1.16 The initial product, following work-up by hydrolysis, is 1-(ethoxycarbonyl)-3-(formyl)ferrocene (2) and this can be used directly to form other 1,3-substituted derivatives by reactions at the aldehydic and/or ester functions.Alternatively, 2 is readily oxidised by silver(I) to ferrocene- 1,3-dicarboxylic acid (1a) from which 1,3-diesters and re- lated ferrocenes are preparable.Using 2 as a precursor, the new derivatives 10±14 were prepared. Also, for synthetic and spectroscopic comparisons, the imines 5±9 were obtained from formyl ferrocene. Moreover, we produced diester derivatives from 1a, includ- ing the previous uncharacterised species 3 and 4, and the re- lated 1,1'-isomers 15 and 16 from ferrocene-1,1'-dicarboxylic acid. The new compounds were characterised by analytical measurements and by IR, 1H and, in some cases, 13C NMR spectra. NMR resonances were assigned and include typical signals for the aromatic, imine and ester nuclei; e.g.[Fe{Z5- 1,3-C5H3(CO2Et)(CH=NC6H4OC5H11-4)}(Z5-C5H5)] (10) dH (CDCl3) 0.9 (br, 3 H, CH3), 1.4 (complex, 7 H, CH2 and CH3), 1.8 (m, 2 H, CH2), 3.95 (0t, 2 H, OCH2), 4.98, 5.07 and 5.40 (br, 3 H, H-2, -4, -5 of C5H3), 6.9 and 7.1 (AA'BB' m, 4, H, C6H4), 8.30 (s, 1 H, CH=N); dC (13C{1H}; CDCl3) 14.0 and 14.5 (CH3), 22.4, 28.2 and 29.0 (CH2), 60.4 and 68.3 (OCH2), 70.9 (C5H5), 70.7, 71.1 and 72.5 (CH, C-2, -4, -5 of C5H3), 74.0 (quat.-C, CCO2Et of C5H4), 83.8 (quat.-C, CCH=N of C5H4), 115.1 and 121.7 (arom.-CH), 145.2 (quat.arom.-C), 157.3 (CH=N), 157.6 (quat. arom.-C), 170.6 (CO). Visual observations of the thermal properties of the isolated compounds, using a hot-stage microscope, do not indicate well de®ned thermotropic mesogenic properties for most of the products, but attachment of an array of these entities as side chains to a functionalised polymer backbone by linking to the second substituent of a di-substituted ferrocene may generate liquid crystalline polymers.J. Chem. Research (S), 1998, 62±63 J. Chem. Research (M), 1998, 0423±0433 Fe CH 5–9 n = 5–9, respectively N OCnH2 n + 1 Fe X 15 X = CO2 CN 16 X = CO2 CO2 1b X = CO2H OMe X Fe+ PF6 – + NMe2 CO2Et Fe HO2C CO2H 1a Fe+ EtO2C CHO 2 Fe EtO2C HC 10–14 n = 5–9, respectively N OCnH2 n + 1 Fe ArO2C CO2Ar i,ii iii v vi iv 3 Ar = CN 4 Ar = OMe CO2 Scheme1 Reagents: i, h, ii,NaOHag^EtOH; iii, Ag2O^NaOH; iv, H2NC6H4OCnH2n + 1-4; v, (COCl)2; vi,HOAr *To receive any correspondence (e-mail: W.E.Lindsell@hw.ac.uk). 62 J. CHEM. RESEARCH (S), 1998L. X. thanks the Chinese Government for support. We also thank Professor J. M. G. Cowie, Heriot-Watt University, for helpful discussions. Techniques used: IR, 1H and 13C NMR, thermal polarising optical microscopy Tables: 1 (yields, melting points and analytical data for ferrocene derivatives) References: 23 Received, 13th August 1997; Accepted, 7th October 1997 Paper E/7/05941H References cited in this synopsis 1 E.g., see: S. A. Hudson and P. M. Maitlis, Chem. Rev., 1993, 93, 861; A.-M. Giroud-Goquin and P. M. Maitlis, Angew. Chem., Int. Ed. Engl., 1991, 30, 375; D. W. Bruce, J. Chem. Soc., Dalton Trans., 1993, 2983. 3 E.g., see: R. Deschenaux and J. W. Goodby, Ferrocenes, 1995, ed. A. Togni and T. Hayashi, VCH, Weinheim, ch. 9 and refer- ences cited therein. 15 (a) A. N. Nesmeyanov, E. V. Leonova, N. S. Kochetkova, A. I. Malkova and A. G. Makarovskaya, J. Organomet. Chem., 1975, 96, 275; (b) M. Hisatome, O. Tachikawa, M. Sasho and K. Yamakawa, J. Organomet. Chem., 1981, 217, C17; A. Kashara, T. Izumi, Y. Yoshida and I. Shimizu, Bull. Chem. Soc. Jpn., 1982, 55, 1901. 16 P. Bickert, B. Hildebrandt and K. Hafner, Organometallics, 1984, 3, 653. J. CHEM. RESEARCH (S), 1998