gave, after purification by column chromatography (silicagel, CH2Clz/AcOEt/AcOH 8:2:0.1). the monopmtected intermediate k (51% m.p. = 146-148°C).
Ts&e&on
oo404039193 56.00 + .oo PergmcmPrcssLtd
l_ems. Vol. 34. No. 20. pp. 3293-3296.1993
Printed in Great Britain
Unsymmetrically 1,PDisubstituted Ferrocene-containing Thermotropic Liquid Crystals. Robert Deschenaux,*
Mafalda Rama, and Julio Santiago.
Universit6 de Neuchgtel, Institut de Chimie, Av. de Bellevaux 51,200O Neuchkel, Switxcrland.
Abetrack The synthesis and mesomo@ic proper& of-the first family
l,l’disubstituted f~ntaining
liiid
ofunsymmeaically
crystals ate repor&
MetaIlocene-containing liquid crystals have recently been shown to be a yaluable class of metallomesogens. Indeed, wet, and others2, described the first l,l’-disubstituted fermcene-containing liquid crystals which exhibited broad nematic and/or smectic A mesophases. Extension of our investigations to other metallocenes led to the first 1.1’~disubstituted ruthenocene-containing liquid crystals3. These latter compounds, and their fenucene analoguest. showed similar mesogenic properties. Remarkable mesomorphic hehaviour arose from fermcene substituted in the 1.3~poaition$ as large enantiotropic nematic and/or smectic C phases were observed in each case. Themmtmpic liquid crystals exhibiting smectic C phases ate of interest for the development of electm-optical devicess. All disubstitutedtbennotmpic nx%allocenederivatives studied thus far ate symmenically detivatized. Therefore,
WG
thought that a non-symmetrical structure would be of intenst to investigate further the
structure-mesogenicproperties relationship. We describe herein the synthesis and mtsanorphic behaviour of compounds la-f, which constitute the first family of unsymmetrically disubstituted Ataining new compounds, i.e. la-f, 2e,d and 4a-c, were confii
liquid crystals. The suuctmes of all by *H-Nh%Rspectroscopy and elemental
analyses.
Fe
1 8:~ll,b:n-12,c:n-13 d: *14,.: n-15,1: /kl6
3294
Fetrocene-1 ,l’-dicarboxylic acid, 2a, was converted into the diacid chloride, 2b, following a literature pmcedume. Tmatment of 2b with benxylalcohol in CH2Cl2, at MUX, in the presence of Etfl gave, after purification by column chromatography (silicagel, CH2Clz/AcOEt/AcOH 8:2:0.1). the monopmtected intermediate k (51% m.p. = 146-148°C). Themonoact‘d2cwastransformedintotheacid chloride 2d (97%. m.p. = 68-69V) by maction with oxaIylchloride (CH2Cl2, EtsN, refhtx). Esterification of 2d with 4-(decyloxy)phenyl m.p.=107-109°C).
4-hydroxyhenxoate l, 3, (CH2Cl2, EtsN, reflux) led to 4a (5696,
Removal of the henxyl protecting group under standard reaction conditions
@tOH/CH&!l2, H@d-C) gave 4b (83%. m.p. = 174177°C). which was subsequently transformed into the acid chloride 4c (%%, m.p. = 108-l 1l’C). applying the procedure used for the pmparation of 2d. Finally, condensation of 4c with dhydtoxyphenyl 4-(alkyloxy)henxoatel, 5, (n = 1l-16) (CH2Cl2, Et3N, reflux) gave the targeted molecules la-f (6570%). as orange solids7.
2 r:X-Y-OH b: X=Y=Cl c: X-o&t, Y-OR d: X-ORn,Y-Cl
4 r:x-oell b:X-OH c: X-cl
AtM?Wbn:Bn=beruyl
The thermal properdes of la-f were investigated by a combination of diierential calorimetry @SC) and polarixed optical microsqy.
scanning
The transition temperaturtsand enthalpy changes are
mported in the Table. All complexes presented smcctDgenic proper&. Ferrocene derivative la exhibited
3295
only an enantiotropic smectic A phase. Compound lb gave an cnmiotmpic
mcctic A phase, and a
monotropicsma?ticCone.F~~increaseofthealLvlchainlmgtkledu,ewrtioaopic~cCand smectic A phases and to htuad anisotropic domains. as shown by ld (17°C). lc (19%) and lf (21*(Z). However, the smectic C range increased CpC for Id, 13oC for le and 16T for 19, and, inversely, the smectic A one attenuated(10°C far Id, 6T for le and 5°C for If). Table. Phase-transitiontemperahues and enthalpy changes of the fumcene derivatives la-f.
Compound
n
Transitiona
la
11
C-SA
144
SA-I
149
9.6
lb
12
C-SA
143
42.0
(SA-SC)cp SA-I
(138) 150
C-SC
140
9.9 c
SC&d
144
c
SA-I
151
10.5
C-SC
35.9
sC-sAd
135 142
lc
Id
le
lf
13
14
15
16
Tpc
,W’/wmok *
41.0
SA-I
152
11.0
C-SC
132
37.7
S&Ad !&-I
145 151
11.0
C-SC
132
38.7
s&Ad
148
SA-1
153
11.6
The mults reported above demonstrate that intmduction of a dissymmtry
thermal Propemes. Fitly, l.l’-positionst,
in amparison
had two effects on the
with the femxme derivatives symmetricaIly substituted in the
a depression of the melting point was observed. Secondly, femcene-containing
liquid
crystals which exhibited smectic C and smectic A phases were obtained for the first time. In coaclusioo, fine tuning of the mesomrphic
pmperties for l,l’disubstituted
femmne-cuntainiag
liquid crystals has
become feasible.
Acknowledgments: We thank the Swiss National Science Foundation for financial support.
References and Notes
1. Deschenaux R., Mare&z
J.-L. and Santiago J., Helv. Chim. Acta 1993,76,865.
2. Reddy K.P. and Brown T.L., fiq. Cryst., 1992,12, 369. 3. Deschenaux R. and Santiago J., J. Mater. Chem., 1993.3.219. 4. Deschenaux R. and Mmmdaz J.-L., J. Chem. SOL, Chem. Commun., 1991,909, Deschenaux R., Kosztics I, Marendaz J.-L. and Stoeckli-Evans It, submitted. 5. Clark N.A. and Lagenvall S.T., Appl. Phys. Lerr.. 1980,36,899, Schadt M.. Displays, 1992.13, 11. 6. Knobloch F.W. and Rauscher W.H., J. Polym. Sci., 1%1,54, 651. 7. Elemental analyticaldata of femKxne derivatives la-f. la: anal. cslc. for Cs&O#e
(993.04): C 71.36, H 6.90, found: C 71.31, H 6.93.
lb:anal. cak.for C&,,H,OO1@e(1007.07): C 71.56, H 7.01; found: C 71.45, H 7.12. lc:anal. talc. for C,jtHTzOt@e (1021.09): C 71.75, H 7.11; found: C 71.75, H 7.19. Id: anal. C&J. for %2H74Ot@
(1035.12): C 71.94, H 7.21; found: C 71.88, H 7.17.
le: ml. talc. for Ctj3H7601#e (1049.15): C 72.13, H 7.30, found: C 71.72, H 7.35. If: anal. talc. for CuH78Otfle
(1063.18): C 72.30, H 7.39; found: C 72.26, H 7.43.
(Received in France 24 February 1993; accepted 19 March 1993)
