Synthesis and physical properties of ferrocene derivatives (XXV) liquid crystallinity of 1,3-disubstituted ferrocene derivatives

Article abstract of DOI:10.1080/15421406.2011.581526

Liquid crystallinity of 1,3-disubstituted ferrocene derivatives was studied by DSC and polarizing microscope. The name of the derivatives is 1,3-bis[-[4-(4-methoxyphenoxycarbonyl)phenoxy]alkyloxycarbonyl]ferrocene. Nine members from n = 2 to 10 were synthesized (n is carbon number of alkyl chain in the sample). All samples except n = 2 and 4 exhibited monotropic nematic liquid crystalline phase. In addition, smectic X (not yet completely identified) was also observed in n = 8 and 10. Liquid crystalline phase transition phenomena were discussed from a viewpoint of molecular shape. Copyright Taylor & Francis Group, LLC.

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Synthesis and Physical Properties of
Ferrocene Derivatives (XXV) Liquid
Crystallinity of 1,3-Disubstituted
Ferrocene Derivatives
Naotake Nakamura a & Shinya Kagawa a
a Department of Applied Chemistry, College of Life Sciences ,
Ritsumeikan University , 1-1-1, Nojihigashi, Kusatsu, Shiga 525-8577,
Japan
Published online: 07 Oct 2011.
To cite this article: Naotake Nakamura & Shinya Kagawa (2011) Synthesis and Physical Properties of
Ferrocene Derivatives (XXV) Liquid Crystallinity of 1,3-Disubstituted Ferrocene Derivatives, Molecular
Crystals and Liquid Crystals, 549:1, 150-159, DOI: 10.1080/15421406.2011.581526
To link to this article: http://dx.doi.org/10.1080/15421406.2011.581526
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Mol. Cryst. Liq. Cryst., Vol. 549: pp. 150–159, 2011
Copyright © Taylor & Francis Group, LLC
ISSN: 1542-1406 print/1563-5287 online
DOI: 10.1080/15421406.2011.581526
Synthesis and Physical Properties of Ferrocene
Derivatives (XXV)
Liquid Crystallinity of 1,3-Disubstituted
Ferrocene Derivatives
NAOTAKE NAKAMURA∗ AND SHINYA KAGAWA
Department of Applied Chemistry, College of Life Sciences, Ritsumeikan
University, 1-1-1, Nojihigashi, Kusatsu, Shiga 525-8577, Japan
Liquid crystallinity of 1,3-disubstituted ferrocene derivatives was studied by DSC
and polarizing microscope. The name of the derivatives is 1,3-bis[ω-[4-(4-
methoxyphenoxycarbonyl)phenoxy]alkyloxycarbonyl]ferrocene. Nine members from
n = 2 to 10 were synthesized (n is carbon number of alkyl chain in the sample).
All samples except n = 2 and 4 exhibited monotropic nematic liquid crystalline phase.
In addition, smectic X (not yet completely identified) was also observed in n = 8 and
10. Liquid crystalline phase transition phenomena were discussed from a viewpoint of
molecular shape.
1. Introduction
The iron is one of the transitional metals, and ferrocene contains one iron atom in its
molecule. If liquid crystals containing ferrocene are synthesized, they are expected to show
many interesting physical properties such as electric, magnetic, and so on, in addition to
liquid crystallinity. It is possible to introduce not only one substituent including a mesogenic
group but also two or three ones into ferrocenyl moiety, because ferrocene molecule has two
cyclopentadienyl rings which easily undergo a substituted reaction like benzene. Therefore,
widely different kind of ferrocene derivatives, for example, monosubstituted ferrocene
derivatives, 1,1ꢀ-disubstituted ones and 1,3-disubstituted ones, have been studied by many
researchers and many papers have been published up to now [1].
Liquid crystalline monosubstituted ferrocene derivatives were firstly reported by
J. Malthe´te and J. Billard in 1976 [2], and J. Bhatt and coworkers reported liquid crys-
talline 1,1ꢀ- disubstituted ones in 1988 [3].
R. Deschenaux and J.-L. Marendaz reported 1,3-disubstituted ferrocene-containing
liquid crystals, as an initial study in 1991 [4]. They synthesized 1,3-bis[ω-4-(4-n-
alkoxyphenylcarbonyloxy)phenoxycarbonyl]ferrocene. Here, the number of carbon atom
in alkoxyl terminal group was abbreviated as cn. They prepared 16 members, of which
cn is from 1 to 18, except cn = 15 and 17. All members exhibited enantiotropic liquid
crystallinity, more specifically, nematic phase was observed in the members from cn = 1
to 16. Smectic C phase appeared only above cn = 12 in addition to nematic one. Here, the
smectic C phase in cn = 12 were observed in cooling process only, and cn = 18 exhibited
∗Corresponding author. E-mail: nakamura@sk.ritsumei.ac.jp
150

Synthesis and Physical Properties of Ferrocene Derivatives (XXV)
151
enantiotropic smectic C phase only. The molecular and crystal structure analyses were
carried out by X-ray diffraction method, and “T” shaped molecular structure was found
out [5].
We have been studied liquid crystallinity of monosubstituted ferrocene derivatives
since 1993 [6–8] and 1,1ꢀ-disubstituted ones since 1994 [9,10].
Many reports on structural study of the monosubstituted ferrocene derivatives [11–19]
and 1,1ꢀ-disubstituted ones [20–24] were presented by N.Nakamura and his coworkers.
Recently, a new paper on the relationship between liquid crystallinity and the structural
data among all the monosubstituted homologues, and a structural comparison between the
monosubstituted ferrocene derivatives and the 1,1ꢀ-disubstituted ones were made [25].
In this work, 1,3-disubstituted ferrocene derivatives were newly designed, synthesized
and investigated on its liquid crystallinity. The structural feature of the samples studied here
is that the substituents including mesogenic groups are the same as those of monosubstituted
[8] and 1,1ꢀ-disubstituted ferrocene derivatives [9,10], previously studied in our laboratory.
2. Experimental
Nine members of 1,3-bis[ω-[4-(4ꢀ-methoxyphenoxycarbonyl)phenoxy]alkyloxycarbonyl]-
ferrocene (abbreviated here after 1,3-bMAF-n, n is carbon number of alkyl chain in the
sample. n = 2-10) have been synthesized. General chemical structure of 1,3-bMAF-n
is shown in Figure 1. A flexible alkyl chain exists between the mesogenic group and
the ferrocenyl moiety. It is considered that the flexible alkyl chain plays an important
role to compensate the bulky effect of the ferrocenyl moiety, because the existence of the
ferrocenyl moiety may hinder to make a linear molecular shape, which is rod-like one.
As is well known, the linear molecular shape is desirable to show liquid crystallinity.
The synthetic route is shown in Figure 2. Purifications of all intermediate products and
objective compounds were repeated many times and judged to be pure by TLC which
showed only one spot. The compounds obtained here are identified as objective compounds
using 1H-NMR(JEOL ECS-400).
As an example, the reaction condition and yield of 1,3-bMAF-5 are described below,
because 1,3-bMAF-5 is one of the liquid crystalline derivatives of 1,3-bMAF-n.
1) Starting material, commercially available acetylferrocene, was reduced by LiAlH4
with AlCl3 under room temperature. Ethylferrocene was obtained. Yield was 82.0%.
2) Ethylferrocene was converted to 1-acetyl-3-ethylferrocene using acetic anhydride
under room temperature. Reaction mixture was treated by open column chromatog-
raphy for separation and purification. Yield was 88.1%.
3) Ethyl group of 1-acetyl-3-ethylferrocene was oxidized to acetyl group by MnO2
under 60◦C, and obtained 1,3-diacetylferrocene. Yield is 1.9%.
4) 1,3-ferrocenyl dicarboxylic acid was obtained from 1,3-diacetylferrocene using
NaOBr after stirring 1 hr on ice bath and 3 hr stirring under room temperature.
Yield was 72.0%.
Figure 1. General chemical structure of 1,3-bMAF-n.

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Naotake Nakamura and Shinya Kagawa
Figure 2. Synthetic route of 1,3-bMAF-n.
5) Halogen exchange reaction from Br to I was carried out. That is, commercially
available 5-bromopentane-1-ol was refluxed 3hr with NaI under 65◦C, and 5-
iodopentane-1-ol was obtained. Yield was 88.9%.
6) 4ꢀ-Methoxyphenyl-4-hydroxybenzoate was etherified with 5-iodopentane-1-ol by
stirring 24hr under 50◦C. Reaction mixture was treated by open column chromatog-
raphy. Yield was 41.5%.
7) 1,3-Ferrocenyl dicarboxylic acid was esterified with the compound obtained above
by stirring 24 hr under room temperature, in order to obtain objective compound.
Reaction mixture was treated by open column chromatography. Yield was 63.0%.
In Figure 3, 1H-NMR spectrum of 1,3-bMAF-5 is shown, as an example. All protons
were marked by A-J and α-γ , as mentioned in upper part of Figure 3. Corresponding peaks

Synthesis and Physical Properties of Ferrocene Derivatives (XXV)
153
Figure 3. 1H-NMR spectrum of 1,3-bMAF-5.
in Figure 3 were also marked by A-J and α-γ . The identification was carried out by this
way for all samples.
Obtained 1H-NMR δ-values of all samples studied here are mentioned below.
1,3-bMAF-2
δ 8.15(d, 4H, J = 8.68), 7.09(d, 4H, J = 9.16), 7.01(d, 4H, J = 8.72), 6.91(d, 4H, J =
9.16), 5.48(s, 1H,), 5.02(d, 2H, J = 0.92), 4.62(t, 4H, J = 3.87), 4.36(t, 4H, J = 4.58),
4.20(s, 5H), 3.81(s, 6H,)
1,3-bMAF-3
δ 8.13(d, 4H, J = 9.16), 7.09(d, 4H, J = 9.16), 6.98(d, 4H, J = 8.48), 6.91(d, 4H, J =
9.16), 5.42(s, 1H), 4.98(d, 2H, J = 1.36), 4.44(t, 4H, J = 6.40), 4.21(t, 4H, J = 5.96),
4.16(s, 5H), 3.80(s, 6H), 2.25(d, 4H, J = 6.29),
1,3-bMAF-4
δ 8.12(d, 4H, J = 8.68), 7.10(d, 4H, J = 9.16), 6.96(d, 4H, J = 8.68), 6.91(d, 4H, J =
9.16), 5.43(s, 1H), 4.98(d, 2H, J = 0.92), 4.32(t, 4H, J = 5.96), 4.24(s, 5H), 4.12(t,
4H, J = 5.72), 3.80(s, 6H), 1.96(br, 8H,)
1,3-bMAF-5
δ 8.12(d, 4H, J = 8.68), 7.10(d, 4H, J = 9.16), 6.96(d, 4H, J = 8.68), 6.91(d, 4H, J =
9.16), 5.43(s, 1H), 4.98(d, 2H, J = 0.92), 4.32(t, 4H, J = 5.96), 4.24(s, 5H), 4.12(t, 4H,

154
Naotake Nakamura and Shinya Kagawa
J = 5.72), 3.80(s, 6H), 1.86(quin, 4H, J = 6.63), 1.77(quin, 4H, J = 6.75), 1.64(quin,
4H, J = 6.75)
1,3-bMAF-6
δ 8.11(d, 4H, J = 8.68), 7.09(d, 4H, J = 8.72), 6.94(d, 4H, J = 8.68), 6.91(d, 4H, J = 9.16),
5.42(s, 1H), 4.97(d, 2H, J = 0.68), 4.24(t, 4H, J = 7.56), 4.22(s, 5H), 4.05(t, 4H, J =
6.18), 3.80(s, 6H), 1.86(quin, 4H, J = 6.63), 1.77(quin, 4H, J = 6.75), 1.54(br, 8H)
1,3-bMAF-7
δ 8.11(d, 4H, J = 8.24), 7.09(d, 4H, J = 8.72), 6.94(m, 8H), 5.42(s, 1H), 4.97(s, 2H), 4.22(t,
4H, J = 6.86) 4.22(s, 5H, J = 6.86), 4.03(t, 4H, J = 6.40), 3.81(s, 6H), 1.83(quin, 4H,
J = 6.87), 1.74(quin, 4H, J = 6.98), 1.47(br, 12H)
1,3-bMAF-8
δ 8.11(d, 4H, J = 9.16), 7.09(d, 4H, J = 9.16), 6.92(m, 8H), 5.42(s, 1H) 4.97(d, 2H, J =
1.40), 4.22(t, 4H, J = 7.56), 4.22(s, 5H, J = 7.56) 4.02(t, 4H, J = 7.93), 3.80(s, 6H),
1.82(quin, 4H, J = 7.10), 1.73(quin, 4H, J = 6.87), 1.41(br, 16H)
1,3-bMAF-9
δ 8.11(d, 4H, J = 9.16), 7.09(d, 4H, J = 9.16), 6.92(m, 8H), 5.42(s, 1H), 4.96(d, 2H, J =
1.36), 4.22(t, 4H, J = 4.41), 4.22(s, 5H, J = 4.41),4.01(t, 4H, J = 6.64), 3.80(s, 6H),
1.80(quin, 4H, J = 6.98), 1.72(quin, 4H, J = 6.87), 1.37(br, 20H)
1,3-bMAF-10
δ 8.11(d, 4H, J = 9.16), 7.09(d, 4H, J = 9.16), 6.92(m, 8H), 5.42(s, 1H), 4.96(d, 2H, J =
1.36), 4.22(t, 4H, J = 4.41), 4.22(s, 5H, J = 4.41),4.01(t, 4H, J = 6.64), 3.80(s, 6H),
1.80(quin, 4H, J = 6.98), 1.72(quin, 4H, J = 6.87), 1.32(br, 24H)
Phase transition phenomena were studied by polarizing microscope (Nikon XTP-11)
equipped with temperature controller system (Mettler FP800 and Mettler FP82HT Hot
Stage), and DSC (Perkin Elmer Pyris 1) of which temperature and calorie are calibrated
using 99.9999% indium. Scanning rate of these apparatuses is 5◦C/min.
3. Results and Discussion
As an example, DSC chart of 1,3-bMAF-2 is shown in Figure 4. On the first heating
process, peak A corresponding to melting point of unstable solid crystal was observed, and
recrystallization underwent continuously showing peak B. Peak C was the melting point
Figure 4. DSC chart of 1,3-bMAF-2 (5.0◦C/min).

Synthesis and Physical Properties of Ferrocene Derivatives (XXV)
155
Figure 5. DSC chart of 1,3-bMAF-5 (5.0◦C/min).
of stable solid. On the first cooling and second heating processes, glass transition points
were observed at D and E. As it is difficult to see the glass transition points in this Figure,
enlarged glass transition point E was illustrated in the Figure. That is, no liquid crystalline
phase transition points observed on the cooling and the heating processes. As an another
example, DSC chart and texture of 1,3-bMAF-5 are shown in Figures 5 and 6, respectively.
On the first heating process, peak A was observed at 121◦C as melting point, where the
temperature was measured by onset one. Peaks B and C were observed at 77 and 61 ◦C on
the first cooling process as phase transition point from isotropic liquid to liquid crystalline
phase and that from the liquid crystalline phase to solid crystal, respectively. This phase
observed above was identified as liquid crystalline nematic phase from the typical texture
shown in Figure 6, because its Schlieren texture strongly suggested nematic phase. On the
second heating process, only one peak D was observed. This point was judged to be the
melting point from the polarizing microscopic observation.
Phase transition phenomena observed here were summarized in Figure 7. Allmembers
except 1,3-bMAF-2 and 4 showed monotropic liquid crystalline phase. A few hystereses of
the transition points were observed. The phenomena were sometimes seen on monotropic
phase transition. In addition, phase transition temperatures measured by DSC were depend-
ing on the scanning rate. These liquid crystalline phases were identified as nematic phase
by the texture observation using the polarizing microscope as mentioned above. Another
liquid crystalline phase was observed at lower temperature side in 1,3-bMAF-8 and 10. This
lower temperature phase was identified as smectic one from the typical texture observed
by the polarizing microscope. As is well known, widely different kind of smectic phases
have been authorized. As this smectic phase is not yet completely identified in this work,
the phase observed here is named as SmX in Figure 7, temporarily.
Figure 8 exhibits the relation between carbon number of alkyl chain (n) and the
transition temperature from isotropic liquid to liquid crystalline phase observed on the first
cooling process.
Even-odd effect is clearly observed in Figure 8. This effect is considered as follows.
Molecular models of 1,3-bMAF-3 and 4 designed by Chem 3D Ultra program as exam-
ples of odd member and even one are presented in Figures 9 and 10, respectively. Simplified
molecular models are also shown in Figures 11 and 12, respectively. It is easily understood
that 1,3-bMAF-3 is rod like while 1,3-bMAF-4 is curved. Namely, molecular shape of the
odd members is regarded as the rod like, which is desirable to appear liquid crystalline
phase. It becomes more desirable with increasing carbon number in the alkyl chain, because

156
Naotake Nakamura and Shinya Kagawa
Figure 6. Optical texture of 1,3-bMAF-5 taken at 74◦C under the polarizing microscope (×400).
Figure 7. Phase transition temperature of liquid crystalline 1,3-bMAF-n.

Synthesis and Physical Properties of Ferrocene Derivatives (XXV)
157
Figure 8. Transition temperature of 1,3-bMAF-n on cooling process against the carbon number of
alkyl chain (n).
Figure 9. Molecular structure of 1,3-bMAF-3 drawn by Chem 3D Ultra.
Figure 10. Molecular structure of 1,3-bMAF-4 drawn by Chem 3D Ultra.
Figure 11. Simplified molecular models for the odd members.

158
Naotake Nakamura and Shinya Kagawa
Figure 12. Simplified molecular models for the even members.
Figure 13. Transition temperature of 1,3-bMAF-n against the carbon number of alkyl chain (n),
(even number).
the aspect ratio increases with increasing alkyl chain length. On the other hand, the transition
temperature from isotropic liquid to liquid crystalline phase of even members is rather low
compared with that of odd ones. It is considered that the molecular shape of even members
is curved a little as is shown in the Figures 10 and 12. The curved effect might be com-
pensated a little with increasing carbon number of the alkyl chain, but this compensational
effect is not large enough to turn over the transition temperature of odd members.
Temperature dependence of the transition temperatures of even members is shown in
Figure 13. The transition temperature from isotropic liquid to liquid crystalline phase (T1)
descends gradually with decreasing carbon number of alkyl chain. On the other hand, glass
transition point (T2) also gradually descends with increasing carbon number (n). As a result,
these two lines cross each other at around n = 4. Therefore, T1 of 1,3-bMAF-2 may appear
too low from T2. In fact, 1,3-bMAF-2 didn’t show the liquid crystalline phase. Similarly,
1,3-bMAF-4alsodidn’t showtheliquidcrystallinephasebythesamereason. Itisconsidered
that this is one of the reason why 1,3-bMAF-2 and 4 show no liquid crystalline phase.
Acknowledgement
A High-Tech Research Center Project for Private Universities matching fund subsidy from
MEXT (Ministry of Education, Culture, Sports, Science and Technology), 2006-2010 is
gratefully acknowledged for partial financial support of the present work.

Synthesis and Physical Properties of Ferrocene Derivatives (XXV)
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