Synthesis and physical properties of ferrocene derivatives (XXII): Monosubstituted ferrocene derivatives containing biphenyl group in the mesogenic one

Article abstract of DOI:10.1080/15421400903400811

The monosubstituted ferrocene derivatives containing biphenyl group in mesogenic one, -[4-(4-methoxybiphenoxy carbonyl) phenoxycarbonyl] alkyl 4-ferrocenylbenzoate, have been synthesized by changing the carbon atoms number of the flexible spacer. The anal

Full text of DOI:10.1080/15421400903400811

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Synthesis and Physical Properties
of Ferrocene Derivatives (XXII):
Monosubstituted Ferrocene Derivatives
Containing Biphenyl Group in the
Mesogenic One
a
Naotake Nakamura a , Masaru Ishimizu a , Masako Nishikawa∗ &
a
Naomi Dogen∗∗
a Department of Applied Chemistry, College of Science and
Engineering, Ritsumeikan University, Kusatsu, Shiga, Japan
Version of record first published: 22 Feb 2010
To cite this article: Naotake Nakamura, Masaru Ishimizu, Masako Nishikawa∗ & Naomi Dogen∗∗
(2010): Synthesis and Physical Properties of Ferrocene Derivatives (XXII): Monosubstituted Ferrocene
Derivatives Containing Biphenyl Group in the Mesogenic One, Molecular Crystals and Liquid Crystals,
516:1, 114-121
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Mol. Cryst. Liq. Cryst., Vol. 516: pp. 114–121, 2010
Copyright # Taylor & Francis Group, LLC
ISSN: 1542-1406 print=1563-5287 online
DOI: 10.1080/15421400903400811
Synthesis and Physical Properties of Ferrocene
Derivatives (XXII): Monosubstituted
Ferrocene Derivatives Containing Biphenyl
Group in the Mesogenic One
NAOTAKE NAKAMURA, MASARU ISHIMIZU,
MASAKO NISHIKAWAꢀ, AND NAOMI DOGENꢀꢀ
Department of Applied Chemistry, College of Science and Engineering,
Ritsumeikan University, Kusatsu, Shiga, Japan
The monosubstituted ferrocene derivatives containing biphenyl group in mesogenic one,
x-[4-(4-methoxybiphenoxy carbonyl) phenoxycarbonyl] alkyl 4-ferrocenylbenzoate,
have been synthesized by changing the carbon atoms number of the flexible spacer.
The analogous compounds in which phenyl group was contained instead of biphenyl
one have been prepared and reported previously. Their phase transition behavior has
been studied by a differential scanning calorimeter and a polarizing microscope. The
effect of an existence of the biphenyl group on their phase transition behavior
and a comparison of the phase transition phenomena with that of x-[4-(4-
methoxyphenoxy carbonyl) phenoxycarbonyl] alkyl 4-ferrocenylbenzoate will be
discussed.
Keywords Crystal structure; ferrocene; liquid crystal; metallomesogen;
monosubstituted ferrocene derivative
1. Introduction
If a transition metal is introduced into an organic compound containing mesogenic
group, it may be expected that the molecule show not only liquid crystallinity but
also interesting physical properties. To introduce the transition metal into the
ꢀPresent address: Molex Japan Co., Ltd., 1-5-4, Fukami-Higashi, Yamato, Kanagawa
242-8585, Japan.
ꢀꢀPresent address: Showa Inc Manufacturing Co., Ltd., 1063, Kohji, Konan, Koka, Shiga
520-3306, Japan.
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. We are grateful
to Associat Prof. T. Hanasaki and Dr. K. Uno, Ritsumeikan University, Japan, for useful
discussion.
Address correspondence to Naotake Nakamura, Department of Applied Chemistry,
College of Science and Engineering, Ritsumeikan University, 1-1-1, Nojihigashi, Kusatsu,
Shiga 525-8577, Japan. E-mail: nakamura@se.ritsumei.ac.jp
114

Ferrocene Derivatives
115
organic molecule, it is convenient to use metallocene such as ferrocene, The ferrocene
easily causes substitution reaction as well as benzene.
Liquid crystalline ferrocene derivative had firstly observed in monosubstituted
one [1]. After that, many different kinds of monosubstituted derivatives and disub-
stituted ones have been synthesized from a viewpoint of liquid crystals. Many papers
on liquid crystalline ferrocene derivatives are reviewed recently [2].
Disubstituted ferrocene derivatives can be classified into three types, 1, 2-, 1, 3-,
and 1, 10-disubstituted ones according to the position of the substituents. The liquid
crystalline monosubstituted ferrocene derivatives are further classified into two types
in accordance with their molecular structure as shown in Figure 1.
Type 1, the mesogenic group is directly introduced into a cyclopentadienyl ring
of the ferrocene, and the mesogenic group has a flexible alkyl chain as a terminal
group (Fig. 1a).
Type 2, methylene chain as a flexible spacer is located between the ferrocenyl
moiety and the mesogenic one (Fig. 1b).
Type 1 exhibited enentiotropic liquid crystalline phase, while Type 2 showed
monotropic one. Many reports have been published on the type 1 [2].
A series of monosubstituted ferrocene derivatives, x-[4-(4-methoxyphenoxy car-
bonyl) phenoxycarbonyl] alkyl 4-ferrocenylbenzoate (abbreviated hereafter as
MPAF-n, n ¼ 1ꢁ11, where n is the number of carbon atoms in the flexible methylene
unit) which belongs in type 2 (Fig. 1(b)) were prepared in our laboratory [3,4]. The
general chemical structure of MPAF-n is shown in Figure 2(a). Five members, these
are MPAF-4, 6, 8, 9, 10, and 11, exhibited monotropic nematic and smectic liquid
crystalline phases [3,4].
In the present study, we synthesized the type 2 compounds (Fig. 2(b)), which
contain the biphenyl group in the mesogenic one instead of phenyl group in
MPAF-n. The reason why is that the compounds synthesized here are expected to
exhibit enantiotropic liquid crystalline phase, because a promotion ability of an
appearance of liquid crystallinity of the biphenyl group is stronger than that of
the phenyl group. Name of the newly designed compounds is x-[4-(4-
methoxybiphenoxy carbonyl) phenoxycarbonyl] alkyl 4-ferrocenylbenzoate
(abbreviated hereafter as MBPAF-n, where n is the number of carbon atoms in
Figure 1. General structures of liquid crystalline mono-substituted ferrocene derivative.

116
N. Nakamura et al.
Figure 2. General structures of (a) MPAF-n and (b) MBPAF-n.
the flexible methylene unit), and the general chemical structure of MBPAF-n is
shown in Figure 2(b). Using these compounds, studies on the phase transition
phenomena were made.
2. Experimentals
Figure 3 shows a synthetic route of MBPAF-6 as an example. After purification, the
compounds were identified by 1H-NMR (JEOL, ALPHA-400 (400 MHz)) spec-
1
trometer using CDCl3 and DMSO as a solvent. We mentioned H-NMR data of
MBPAF-n synthesized in this study below.
MBPAF-6
1H-NMR data of MBPAF-6 in d(ppm): 0.88(t, 2H), 1.26(quin, 2H), 1.83(quin,
4H), 2.64(t, 2H), 3.86(s, 3H), 4.08(s, 4H), 4.35(t, 2H), 4.40(t, 4H), 4.72(t, 2H),
6.99(d, 2H), 7.25(d, 2H), 7.27(d, 2H), 7.51(d, 2H), 7.54(d, 2H), 7.60(d, 2H),
7.97(d, 2H), 8.26(d, 2H).
MBPAF-7
1H-NMR data of MBPAF-7 in d(ppm): 1.49(quin, 6H), 1.80(quin, 4H), 2.62(t,
2H), 3.86(s, 3H), 4.08(s, 4H), 4.27(t, 2H), 4.40(t, 4H), 4.72(t, 2H), 6.99(d, 2H),
7.25(d, 2H), 7.27(d, 2H), 7.51(d, 2H), 7.54(d, 2H), 7.60(d, 2H), 7.97(d, 2H),
8.26(d, 2H).
MBPAF-8
1H-NMR data of MBPAF-8 in d(ppm): 1.25(t, 2H), 1.48(quin, 8H), 1.79(quin,
2H), 2.61(t, 2H), 3.86(s, 3H), 4.08(s, 4H), 4.33(t, 2H), 4.40(t, 4H), 4.72(t, 2H),
6.99(d, 2H), 7.25(d, 2H), 7.27(d, 2H), 7.51(d, 2H), 7.54(d, 2H), 7.60(d, 2H),
7.97(d, 2H), 8.26(d, 2H).
MBPAF-9
1H-NMR data of MBPAF-9 in d(ppm): 1.45(quin, 10H), 1.48(quin, 8H),
1.79(quin, 4H), 2.60(t, 2H), 3.86(s, 3H), 4.08(s, 4H), 4.32(t, 2H), 4.40(t, 4H),
4.72(t, 2H), 6.99(d, 2H), 7.25(d, 2H), 7.27(d, 2H), 7.51(d, 2H), 7.54(d, 2H), 7.60(d,
2H), 7.97(d, 2H), 8.26(d, 2H).

Ferrocene Derivatives
117
Figure 3. Synthetic route of MBPAF-6.
MBPAF-10
1H-NMR data of MBPAF-10 in d(ppm): 1.37(quin, 12H), 1.78(quin, 4H),
1.79(quin, 2H), 2.60(t, 2H), 3.86(s, 3H), 4.08(s, 4H), 4.30(t, 2H), 4.40(t, 4H),
4.72(t, 2H), 6.99(d, 2H), 7.25(d, 2H), 7.27(d, 2H), 7.51(d, 2H), 7.54(d, 2H), 7.60(d,
2H), 7.97(d, 2H), 8.26(d, 2H).
Thermal behavior was measured using Diamond DSC (Perkin Elmer) with heat-
ing and cooling rates of 5ꢂC=min. The textures in the liquid crystalline phases were
observed by a Nikon ECLIPSE E600 optical polarizing microscope equipped with a
heating stage (Mettler Toledo FP90).
3. Results & Dicussion
The mesogenic group in MPAF-n has two phenyl rings, on the other hand, one
phenyl group and one biphenyl one are included in MBPAF-n. Phase transition

118
N. Nakamura et al.
Table 1. Phase transition behavior of MBPAF-6ꢁ10
behavior of MBPAF-n (n ¼ 6ꢁ10) is summarized in Table 1. Only MBPAF-6
showed enantiotropic liquid crystalline phase in accordance with our expectation,
but disappointing results were obtained from all members of MBPAF-n except
MBPAF-6. In addition, phase transition temperatures measured on 1st cooling of
Figure 4. Phase transition diagram of MBPAF-n on 1st cooling.

Ferrocene Derivatives
119
Figure 5. Phase transition diagram of MPAF-n on 1st cooling [3,4].
MBPAF-n (n ¼ 6ꢁ10) and MPAF-n, (n ¼ 6ꢁ10) are illustrated in Figures 4 and 5,
respectively.
Figures show that melting and clearing temperatures of MBPAF-n are higher
than those of MPAF-n. Moreover, temperature range of liquid crystal phase in
MBPAF-n is wider than that of MPAF-n. As an example, characteristic Schlieren
texture taken at 130ꢂC in cooling of MBPAF-6 is shown in Figure 6. It suggests
the phase is nematic one. Therefore, MBPAF-n exhibited stable nematic phase.
It is considered that the fact is regarded as an existence of biphenyl group in
the mesogen.
Comparison with clearing points of MBPAF-n and MPAF-n series is summar-
ized in Figure 7. It is easily understand that clearing point of even members of
Figure 6. Optical texture of the liquid crystalline phase of MBPAF-6 taken at 130ꢂC on
cooling.

120
N. Nakamura et al.
Figure 7. Clearing point of MBPAF-n and MPAF-n [3,4] against the carbon number of meth-
ylene units on 1st cooling. No clearing points of MPAF-5 & 7 were observed [3].
MBPAF-n series is higher than those of odd members. In the odd member series, the
ferrocenyl moiety and the mesogenic group are located in the same side about
the molecular axis. On the other hand, the moiety and the group stand in the
opposite side about the axis in the even members. Therefore, even members regarded
as more linear molecular shape than that of odd ones. This means that more rigid
alignment could be possible in even members. From the point, the odd even effect
is explained in monomer and dimmer liquid crystals in general. As a result,
MBPAF-n exhibits odd even effect on the phase transition temperature.
In addition, phase transition temperatures such as clearing points and melting
one of MBPAF-n are higher than those of MPAF-n as mentioned above. This
phenomenon is ordinary one, because introduction of the biphenyl group in a
molecule leads to increase of phase transition point [5].
In the case of MBPAF-6, the length of the flexible spacer containing 6 carbon
atoms regarded as nearly equal to that of mesogenic moiety. It suggests that the stable
molecular arrangement is easily possible in this case, compared with the cases of
MBPAF-7ꢁ 10. Therefore, it is considered that MBPAF-6 exhibited enantiotropic
liquid crystalline phase. If the value of the flexible spacer decreases in MBPAF-n series,
the compounds have a liquid crystal phase in the wider temperature range. This is may
be caused by an increment in the liquid crystallinity by short flexible spacer. Therefore,
MBPAF-6 has most stable liquid crystalline phase in the homologues.
The advantage of the liquid crystalline phase of MPAF-n series is observed in
longer spacer members, such as MPAF-4, 6, 8, 9, 10, and 11 [3,4]. This fact was
explained from a point of an aspect ratio. If it increases, the possibility to appear
liquid crystalline phase also increases. In the case of MBPAF-n, lower members
become more stable. Probably, this fact is explained that an occupancy ratio of
biphenyl group to total molecular eight increases with decreasing the length of the
flexible spacer.
4. Conclusion
We synthesized monosubstituted ferrocene derivatives with type 2 which contained
biphenyl group in the mesogenic group, because the compounds were expected to

Ferrocene Derivatives
121
exhibit enantiotropic liquid crystalline phase. The name of the compounds is
MBPAF-6ꢁ9. All compounds except MBPAF-6 exhibited monotropic nematic
phase with characteristic Schlieren textures. Only, MBPAF-6 showed enantiotropic
nematic phase. The length of flexible spacer and mesogenic group of MBPAF-6
could be regarded as nearly equal each other. It may be effective to promote a close
attractive interaction between the molecules. As a result, it is considered that
MBPAF-6 exhibited enantiotropic smectic liquid crystalline phase.
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[3] Hanasaki, T., Ueda, M., & Nakamura, N. (1993). Mol. Cryst. Liq. Cryst., 237, 329–336.
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