Unsymmetrically 1,PDisubstituted Ferrocene ... - Science Direct

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gave, after purification by column chromatography (silicagel, CH2Clz/AcOEt/AcOH 8:2:0.1). the monopmtected intermediate k (51% m.p. = 146-148°C).
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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

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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

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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)