Switchable mesomorphic materials based on the ferrocene - Ferrocenium redox system: Electron-transfer-generated columnar liquid-crystalline phases

Article abstract of DOI:10.1021/om9905308

Oxidation of the non-mesomorphic ferrocene derivative 1 with silver toluene-4-sulfonate gave the ferrocenium derivative 2, which showed a monotropic columnar phase. The latter two-dimensional phase is composed of ribbons, in which derivative 2 is organized into bilayers, and has a centered rectangular symmetry with a = 318.3 ? and c = 94.9 ?. The M?ssbauer spectra of the ferrocene derivative 1 yields hyperfine parameters that are typical of these derivatives and are, as expected, virtually independent of temperature. In a similar fashion, the hyperfine parameters of the ferrocenium derivative 2 are typical of these derivatives, but in this case at both 78 and 4.2 K slow paramagnetic relaxation of the magnetic moment associated with the rather well isolated paramagnetic ferrocenium ion is observed. The temperature-dependent magnetic susceptibilities of 2 are in agreement with those expected for weakly interacting ferrocenium cores. No magnetic-field-induced orientation was observed upon cooling the sample from the isotropic phase down to the columnar phase. Ferrocene and ferrocenium are valuable units for the design of liquid-crystalline switches.

Full text of DOI:10.1021/om9905308

Organometallics 1999, 18, 5553-5559
5553
Sw itch a ble Mesom or p h ic Ma ter ia ls Ba sed on th e
F er r ocen e-F er r ocen iu m Red ox System :
Electr on -Tr a n sfer -Gen er a ted Colu m n a r
Liqu id -Cr ysta llin e P h a ses
Robert Deschenaux,* Martin Schweissguth, and Maria-Teresa Vilches
Institut de Chimie, Universite´ de Neuchaˆtel, Avenue de Bellevaux 51,
2000 Neuchaˆtel, Switzerland
Anne-Marie Levelut*
Laboratoire de Physique des Solides, Universite´ Paris-Sud, Baˆtiment 510,
91405 Orsay Cedex, France
Dimitri Hautot and Gary J . Long*
Department of Chemistry, University of MissourisRolla, Rolla, Missouri 65409-0010
Dominique Luneau*
Laboratoire de Chimie de Coordination, Service de Chimie Inorganique et Biologique,
De´partement de Recherche Fondamentale sur la Matie`re Condense´e, Commissariat a` l'Energie
Atomique, 17 Rue des Martyrs, 38054 Grenoble Cedex, France
Received J uly 12, 1999
Oxidation of the non-mesomorphic ferrocene derivative 1 with silver toluene-4-sulfonate
gave the ferrocenium derivative 2, which showed a monotropic columnar phase. The latter
two-dimensional phase is composed of ribbons, in which derivative 2 is organized into
bilayers, and has a centered rectangular symmetry with a ) 318.3 Å and c ) 94.9 Å. The
Mo¨ssbauer spectra of the ferrocene derivative 1 yields hyperfine parameters that are typical
of these derivatives and are, as expected, virtually independent of temperature. In a similar
fashion, the hyperfine parameters of the ferrocenium derivative 2 are typical of these
derivatives, but in this case at both 78 and 4.2 K slow paramagnetic relaxation of the
magnetic moment associated with the rather well isolated paramagnetic ferrocenium ion is
observed. The temperature-dependent magnetic susceptibilities of 2 are in agreement with
those expected for weakly interacting ferrocenium cores. No magnetic-field-induced orienta-
tion was observed upon cooling the sample from the isotropic phase down to the columnar
phase. Ferrocene and ferrocenium are valuable units for the design of liquid-crystalline
switches.
In tr od u ction
ferrocene:3 (1) polycatenar ferrocene derivatives gave
columnar liquid-crystalline phases,4 (2) functionaliza-
tion of ferrocene with flexible chains led to mesomor-
phism near room temperature,5 and (3) 1,3-disubstitut-
ed ferrocene derivatives had a greater tendency to form
liquid-crystalline phases than their 1,1′-isomeric ana-
logues.6 Therefore, we anticipated that the system
described in Chart 1 reflected only one particular
switching mode and that modification of the organic
entity connected to the ferrocene nucleus would lead to
different situations: other possibilities are the switching
Recently, we reported the first evidence that the
ferrocene-ferrocenium redox system can be used to
prepare switchable liquid crystals (Chart 1):1 although
the ferrocene derivative I was non-mesomorphic, its
oxidized form II gave rise to a monotropic smectic A
phase. A peralkylated ferrocene was selected as the
redox-active center in order to utilize the ease of the
oxidation process of this unit in comparison with less
alkylated ferrocenes.2
The mesomorphic properties of ferrocene-containing
thermotropic liquid crystals depend on the nature,
number, and position of the substituents located on the
(3) Deschenaux, R.; Goodby, J . W. In Ferrocenes: Homogeneous
Catalysis, Organic Synthesis, Materials Science; Togni, A., Hayashi,
T., Eds.; VCH: Weinheim, Germany, 1995; Chapter 9.
(4) Deschenaux, R.; Monnet, F.; Serrano, E.; Turpin, F.; Levelut,
A.-M. Helv. Chim. Acta 1998, 81, 2072.
(5) Deschenaux, R.; Turpin, F.; Guillon, D. Macromolecules 1997,
30, 3759.
(1) Deschenaux, R.; Schweissguth, M.; Levelut, A.-M. Chem. Com-
mun. 1996, 1275.
(2) Zanello, P. In Ferrocenes: Homogeneous Catalysis, Organic
Synthesis, Materials Science; Togni, A., Hayashi, T., Eds.; VCH:
Weinheim, Germany, 1995; Chapter 7.
(6) Deschenaux, R.; Marendaz, J .-L. J . Chem. Soc., Chem. Commun.
1991, 909.
10.1021/om9905308 CCC: $18.00 © 1999 American Chemical Society
Publication on Web 12/02/1999

5554 Organometallics, Vol. 18, No. 26, 1999
Deschenaux et al.
Ch a r t 1
Ch a r t 2
Ta ble 1. P h a se Tr a n sition s of Com p ou n d s 1 a n d 2
from a mesomorphic ferrocene to a non-mesomorphic
ferrocenium (the reverse sequence from that presented
in Chart 1) or between mesomorphic ferrocene and
ferrocenium derivatives, each of them giving rise to
different liquid-crystalline phases.
The ultimate objective of our research is the design
of ferrocene-based switchable liquid crystals with tailor-
made properties. To reach this goal, an understanding
of the structural factors (number of aromatic rings in
the rigid rod, length of the terminal alkyl chain, length
of the spacer between the ferrocene and the rigid
segment, nature of the counterion) which govern the
mesomorphism is essential and requires the design and
study of further structures.
We report, herein, the synthesis, liquid-crystalline,
Mo¨ssbauer spectral, and magnetic properties of com-
pounds 1 and 2 (Chart 2) which form a new mesogenic
redox-active couple. In comparison with I and II, a
longer alkyl chain was used to functionalize the prome-
sogenic organic rod (18 carbon atoms instead of 10). The
purpose of this change was to explore the possibility of
obtaining other liquid-crystalline phases than that
observed for II. In 1 and 2, the three aromatic rings
are connected differently than in I and II. This modi-
fication was applied only for synthetic purposes, such
as ease of purification of the intermediates, and was not
expected to influence markedly the thermal and meso-
morphic properties of the resulting compounds.
compound
phase transitiona
T, K
∆H, kJ /mol
1
2
Cr f I
Cr f I
(I f Colrect
407b
396b
374d
55
81
e
c
)
a
Cr ) crystalline state, I ) isotropic liquid, Colrect ) rectangular
columnar phase. b Onset transition determined by DSC during the
first heating run. c Monotropic transition. Determined by polar-
d
ized optical microscopy. e Not detected; see main text for details.
phonium bromide under Wittig reaction conditions gave
4. Esterification of 4 with 4-benzyloxy-4′-hydroxybiphen-
yl8 yielded 5. Reduction of the carbon-carbon double
bond and removal of the benzyl protected group was
accomplished under hydrogenation reaction conditions
and gave 6, which, when condensed with 4-octadecyl-
oxybenzoic acid,9 led to the expected ferrocene derivative
1. Oxidation of 1 with silver toluene-4-sulfonate yielded
the ferrocenium species 2.
Liqu id -Cr ysta llin e P r op er ties. The thermal and
liquid-crystalline behavior of 1 and 2 were examined by
polarized optical microscopy (POM), differential scan-
ning calorimetry (DSC), and X-ray diffraction (XRD).
The thermal and liquid-crystalline results are listed in
Table 1.
No liquid-crystalline properties were observed for 1.
The unique event that was detected is the melting of
the sample into an isotropic melt.
(7) Kreindlin, A. Z.; Fadeeva, S. S.; Rybinskaya, M. I. Izv. Akad.
Nauk SSSR, Ser. Khim. 1984, 403.
Resu lts a n d Discu ssion
(8) (a) Shedouda, I. G.; Shi, Y.; Neubert, M. E. Mol. Cryst. Liq. Cryst.
1994, 257, 209. (b) Bruce, J . M.; Chaudhry, A. J . Chem. Soc., Perkin
Trans. 1 1974, 295.
(9) Deschenaux, R.; Marendaz, J .-L., Santiago, J . Helv. Chim. Acta
1993, 76, 865.
Syn th esis. The preparation of 1 and 2 is described
in Scheme 1. Treatment of nonamethylferrocene car-
boxaldehyde7 (3) with (4-carboxybutyl)triphenylphos-

Switchable Mesomorphic Materials
Organometallics, Vol. 18, No. 26, 1999 5555
Sch em e 1a
F igu r e 1. Texture of the rectangular columnar phase
displayed by 1 upon cooling slowly the sample from the
isotropic liquid to 374 K.
F igu r e 2. Schematic representation of the columnar
rectangular liquid-crystalline phase.
Ta ble 2. Obser ved a n d Ca lcu la ted d Sp a cin gs (Å)
of th e Liqu id -Cr ysta llin e P h a se of Com p ou n d 2a
h
k
l
dobs
dcalc
2
1
4
3
6
5
0
0
0
0
0
0
0
0
0
1
0
1
0
1
2
158.5
90.2
79.2
70.7
159.1
91.2
79.6
70.8
53.1
52.7
47.5
a
Key: (a) (4-carboxybutyl)triphenylphosphonium bromide,
tBuOK, THF, 84%; (b) 4-benzyloxy-4′-hydroxybiphenyl, N,N′-
dicyclohexylcarbodiimide (DCC), 4-pyrrolidinopyridine, CH2Cl2,
77%; (c) H2, Pd/C, CH2Cl2, 78%; (d) 4-octadecyloxybenzoic acid,
N,N′-dicyclohexylcarbodiimide (DCC), 4-pyrrolidinopyridine,
CH2Cl2, 69%; (e) silver toluene-4-sulfonate, CH2Cl2/acetone,
78%. All the reactions were carried out at room temperature.
47.6
18.4
5
0
5
18.2
a
The lattice is centered rectangular (a ) 318.3 Å and c ) 94.9
Å). Between the 002 and the last observed Bragg reflection there
are several unobserved reflections.
a modification of the texture at 364 K. This transforma-
tion could not be identified by POM.
The columnar nature of the liquid-crystalline phase
was established by XRD. The structure of the phase is
shown in Figure 2, and the XRD data are collected in
Table 2.
The unit cell of this two-dimensional phase has a
centered rectangular symmetry of dimensions 318.3 Å
× 94.9 Å. By Corey-Pauling-Koltun (CPK) space-filling
molecular models, an approximate molecular length of
51 Å was obtained for 1 in the fully extended conforma-
tion. Therefore, there are two molecules within the
thickness of the ribbons, an organization that corre-
Upon heating, compound 2 melted into an isotropic
fluid, and the formation of a columnar liquid-crystalline
phase was observed at 374 K by POM when the sample
was cooled from the isotropic melt. The mesophase was
identified from its optical texture, which is typical for
columnar liquid-crystalline phases (Figure 1). As a
consequence of a very small enthalpy change, no exo-
thermic peak was detected by DSC at 374 K. Such an
observation has already been reported for columnar-to-
isotropic fluid phase transition.10 Further cooling led to
(10) Kang, S. H.; Kim, M.; Lee, H.-K.; Kang, Y.-S.; Zin, W.-C.; Kim,
K. Chem. Commun. 1999, 93.

5556 Organometallics, Vol. 18, No. 26, 1999
Deschenaux et al.
sponds to a bilayer. The total length of two aligned
molecules (2 × 51 ) 102 Å) is larger than the thickness
of the ribbon (94.9 Å). The discrepancy between both
values (i.e., 102 and 94.9 Å) indicates that the molecules
are slightly interdigitated and/or not in a fully elongated
conformation. The ribbons are disposed in staggered
rows. Constraint of curvatures due to the difference of
molecular areas between the ferrocene unit and the
paraffinic chain is probably responsible for the forma-
tion of columns.11
XRD measurements were also recorded at 363 K. At
this temperature, the diffraction pattern revealed the
formation of a crystalline structure. Therefore, the
modification observed by POM at 364 K reflected
solidification of the sample.
The fragility of the sample at elevated temperature
and under X-ray irradiation was revealed by XRD,
which indicated that the columns degraded into lamel-
lae (i.e., the columnar phase transformed into a fluid
lamellar phase); the layer periodicity decreased by about
10% (from 94.9 Å to ca. 85 Å) within 1 h.
The results obtained for 1 and 2 can be rationalized
on the basis of structural considerations. The non-
mesomorphic character of 1 is the consequence of the
presence of the bulky alkylated ferrocene unit, a unit
that decreases the intermolecular interactions3 respon-
sible for generating mesomorphism. This interpretation
is supported by results we recently obtained: an in-
crease in the length of the promesogenic rod (four
aromatic rings instead of three) led to materials showing
enantiotropic liquid-crystalline behavior.12 The meso-
morphic character of 2 proves that ionic interactions
play an important role in inducing mesomorphism.
Finally, the monotropic nature of the liquid-crystalline
phase exhibited by 2 also results from the presence of
the bulky alkylated ferrocene which reduces the inter-
molecular interactions as for 1.
Mo1ssba u er Sp ectr oscop y. The Mo¨ssbauer spectra
can be divided into two groups: the unoxidized species
and the oxidized material. The first group of spectra all
exhibit a simple quadrupole doublet, as is shown in
Figure 3 for 1. These spectra have been fit with the same
linewidth for each component of the doublet, but in some
cases, the relative areas of the two components differed
by a few percent, presumably as a result of texture. The
resulting spectra and the spectral hyperfine parameters,
which are given in Table 3, are typical of those ob-
served13 for Cp2Fe and its derivatives. However, it
should be noted that the isomer shifts, δ, of (Me5Cp)2Fe
are slightly lower than those of Cp2Fe. The lower values
correspond to a higher s-electron density at the iron
nucleus in (Me5Cp)2Fe as a consequence of the ad-
ditional stability associated with its stronger bonding
as compared to Cp2Fe. In contrast, the observed isomer
shifts for (Me5Cp)2Fe and its derivative 1 are, as
expected, essentially identical within experimental er-
ror, and the presence of the mesogenic framework has
little influence upon the bonding at the iron site.
F igu r e 3. Mo¨ssbauer effect spectra of 1.
Ta ble 3. Mo1ssba u er Sp ectr a l P a r a m eter s of Cp 2F e,
(Me5Cp )2F e, a n d 1
∆EQ,
Meff,
compound T, K δ, mm/sa mm/s Γ, mm/s g/mol ΘD, K
Cp2Fe
295 0.447
85 0.533
2.40
2.40
0.23
0.26
101b
104b
129
94b
88b
71
(Me5Cp)2Fe 295 0.428(4) 2.48(2) 0.23(1)
85 0.503
295 0.434
78 0.504
2.48
2.44
2.46
0.25
0.24
0.24
1
a
The isomer shifts are reported relative to room temperature
b
R-iron foil. Obtained from ref 15.
However, the mesogenic framework does make small,
but probably real, differences in the local site symmetry
at the iron, as is reflected in the small differences in
the quadrupole splittings, ∆EQ.
By studying the temperature dependence of the
Mo¨ssbauer spectral isomer shifts and absorption areas,
it is possible to determine14 the effective recoil mass,
M
eff, and the effective Mo¨ssbauer temperature, ΘD, of
an iron-containing compound. The effective recoil mass
is a measure of the covalency of the iron bonding,
whereas the effective Mo¨ssbauer temperature is equiva-
lent to the Debye temperature of an element. These
measurements have been carried out earlier15 for Cp2-
Fe and (Me5Cp)2Fe, and the resulting values are given
in Table 3. The equivalent values for 1 are also given
in Table 3, although in this case the results are based
on only two data points and thus are more uncertain.
The observed values do seem to indicate a higher
covalency and a smaller Mo¨ssbauer temperature for 1
as compared to Cp2Fe and (Me5Cp)2Fe.
The Mo¨ssbauer spectra of the oxidized compound 2
(Figure 4) are quite different from those of the unoxi-
dized species. At 295 K, only one line is observed, and
as expected, the large quadrupole splitting of the (Me5-
Cp)2Fe derivatives has collapsed to virtually zero. If the
295 K spectra is measured over a reduced velocity range,
(11) (a) Hendrikx, Y.; Levelut, A.-M. Mol. Cryst. Liq. Cryst. 1988,
165, 233. (b) Sigaud, G.; Hardouin, F.; Achard, M. F.; Levelut, A.-M.
J . Physique 1981, 42, 107.
(12) Deschenaux, R.; Schweissguth, M.; Vilches, M.-T. Unpublished
results.
(13) Parish, R. V. In The Organic Chemistry of Iron; Koerner von
Gustorf, E. A., Grevels, F., Fischler, I., Eds.; Academic Press: New
York, 1978; Vol. 1, p 192.
(14) Earnst, R. D.; Wilson, D. R.; Herber, R. H. J . Am. Chem. Soc.
1984, 106, 1646.
(15) Long, G. J . Unpublished results.

Switchable Mesomorphic Materials
Organometallics, Vol. 18, No. 26, 1999 5557
F igu r e 5. Temperature dependence of the product of the
magnetic susceptibility with temperature for 2.
susceptibility with temperature, øT, for compound 2 is
shown in Figure 5. The variation of øT is almost
independent of temperature with an average value of
0.80 cm3 K mol-1. This large deviation from the spin-
only value of 0.375 cm3 K mol-1 is in agreement with
literature data reported for various ferrocenium salts17,18
and is attributed to spin-orbit coupling combined with
2
a low-symmetry crystal field distortion on the E2g
-
(a1g e2g3) ground state of the ferrocenium ion.17 The
slight decrease in øT observed at low temperature (0.71
cm3 K mol-1 at 6 K) suggests weak intermolecular
antiferromagnetic interactions between the ferrocenium
centers in agreement with Mo¨ssbauer spectra studies
(see above). Indeed, because of the steric hindrance of
the mesogenic fragment, the ferrocenium magnetic
centers are not expected to interact strongly. No sig-
nificant changes were noticed during the melting pro-
cess. The observed slight decrease in the 390-410 K
temperature range is mainly due to a decentering of the
sample associated with a volume contraction in the
sample holder, a contraction that is almost compensated
for upon re-centering the sample at the end of the
heating process (at 410 K).
Possible correlations between the magnetic and me-
somorphic properties, a through magnetic-field-induced
orientation of the magnetic centers that have the
required anisotropy,19 have also been investigated. No
significant change has been observed in the magnetic
susceptibility when the sample was cooled from the
isotropic fluid (410 K) into the columnar liquid-crystal-
line phase: superimposable heating and cooling curves
were obtained (not shown). This may be due to the low
anisotropy of the ferrocenium associated with the effect
of the bulky organic substituents, substituents that do
not permit strong intermolecular interactions, but do
favor disorientation.
2
F igu r e 4. Mo¨ssbauer effect spectra of 2.
Ta ble 4. Mo1ssba u er Sp ectr a l P a r a m eter s of
Com p ou n d 2
T, K
Heff , kOe
δ, mm/sa
∆EQ, mm/s
Γ, mm/s
295
78
4.2
a
0
13
208
0.38
0.47
0.53
0.26
0.36
The isomer shifts are reported relative to room temperature
R-iron foil.
the observed spectra do show some structure which may
result from either a quadrupole interaction at the iron
site or a distribution of site environments. If fit with a
quadrupole doublet, the 295 K spectral parameters
given in Table 4 are obtained, parameters that are all
very similar to those obtained13 for a variety of [Cp2-
Fe]+-containing compounds.
At 78 and 4.2 K, the spectra of 2 are broadened as is
shown in Figure 4. The broadening results from slow
paramagnetic relaxation on the Mo¨ssbauer time scale
of the unpaired electrons present in these paramagnetic
compounds.16 The resulting average effective paramag-
netic hyperfine fields have been estimated by fitting the
spectra either with a magnetic sextet or with a sextet
and a singlet or doublet. Thus, the resulting average
effective paramagnetic hyperfine fields, which are given
in Table 4, are only a first approximation. Future work
will include the fitting of these spectra as a function of
temperature with a paramagnetic relaxation model.
Ma gn etic Su scep tibility Mea su r em en ts. The tem-
perature dependence of the product of the magnetic
(17) (a) Sohn, Y. S.; Hendrickson, D. N.; Gray, H. B. J . Am. Chem.
Soc. 1970, 92, 3233. (b) Hendrickson, D. N.; Sohn, Y. S.; Gray, H. B.
Inorg. Chem. 1971, 10, 1559. (c) Maki, A. H.; Berry, T. E. J . Am. Chem.
Soc. 1965, 87, 4437. (d) Robbins, J . L.; Edelstein, N.; Spencer, B.;
Smart, J . C. J . Am. Chem. Soc. 1982, 104, 1882.
(18) Broderick, W. E.; Thompson, J . A.; Godfrey, M. R.; Sabat, M.;
Hoffman, B. M. J . Am. Chem. Soc. 1989, 111, 7656.
(19) (a) Galyametdinov, Yu.; Athanassopoulou, M. A.; Griesar, K.;
Kharitonova, O.; Soto-Bustamante, E. A.; Tinchurina, L.; Ovchinnikov,
I.; Haase, W. Chem. Mater. 1996, 8, 922. (b) Bikchantaev, I.; Ga-
lyametdinov, Yu.; Prosvirin, A.; Griesar, K.; Soto-Bustamante, E. A.;
Haase, W. Liq. Cryst. 1995, 18, 231.
(16) Hoy, G. R. In Mo¨ssbauer Spectroscopy Applied to Inorganic
Chemistry; Long, G., Ed.; Plenum Press: New York, 1984; Vol. 1, p
195.

5558 Organometallics, Vol. 18, No. 26, 1999
Deschenaux et al.
should be similar. The absolute spectral absorption areas are
reproducible to (0.5%, and as a consequence, the effective
recoil masses are valid to ca. (10 g/mol and the effective
Mo¨ssbauer temperatures are valid to ca. (5 K.
Ma gn etic Mea su r em en ts. The temperature dependence
of the magnetic susceptibility was measured using a SHE
superconducting SQUID magnetometer in a field of 0.5 T. The
sample was first heated from 6 to 410 K (isotropic melt) and
then cooled into the columnar phase. The data were corrected
for the magnetization of the aluminum sample holder, and the
magnetic susceptibility was corrected for the diamagnetism
of the constituent atoms using Pascal constants.
Con clu sion s
The above results, in conjuction with those we have
already reported for I and II,1 prove that the ferrocene-
ferrocenium couple is a valuable system for preparing
redox-active liquid-crystalline switches: first, the nature
of the liquid-crystalline phases can be tuned (1 and 2,
switching mode between isotropic and columnar phases;
I and II, switching mode between isotropic and smectic
phases1) by means of synthesis at the organometallic
level, and second, the Mo¨ssbauer and magnetic char-
acteristics observed for 1 and 2 are similar to those of
the parent ferrocene and ferrocenium species. This
result is of fundamental importance because it shows
that grafting of a mesogenic group onto ferrocene or
ferrocenium ion does not alter the remarkable features
of these entities. The design of switchable anisotropic
materials that combine the unique properties of fer-
rocene and ferrocenium with liquid-crystalline features,
such as their fluidity and organization, has become
feasible.
Abbr evia tion s. N,N′-Dicyclohexylcarbodiimide ) DCC;
column chromatography ) CC.
Syn th esis. Com p ou n d 4. To a suspension of (4-carboxy-
butyl)triphenylphosphonium bromide (8.91 g, 20.10 mmol) in
THF (35 mL) (under N2) was added dropwise a solution of
potassium tert-butoxide (5.63 g, 50.17 mmol) in THF (30 mL).
The mixture was stirred for 20 min, and a solution of
nonamethylferrocene carboxaldehyde (3) (3.42 g, 10.05 mmol)
in THF (30 mL) was added dropwise. The mixture was stirred
for 3 h and concentrated to dryness. To the solid residue was
added diethyl ether and a 5 N NaOH aqueous solution (3 is
soluble in diethyl ether; 4 is soluble in the alkaline solution).
The layers were separated, and the aqueous phase was
acidified with a 2 N HCl aqueous solution to acidic pH. Then,
AcOEt was added. The organic layer was recovered, dried
(MgSO4), and evaporated to dryness. Purification of the solid
residue by CC (hexane/acetone, 2:1) gave pure 4 (3.57 g, 84%).
Exp er im en ta l Section
Ma ter ia ls. THF (sodium, benzophenone, under N2) and
CH2Cl2 (P2O5, under N2) were distilled prior to use. (4-
Carboxybutyl)triphenylphosphonium bromide (Fluka, 99%), t-
BuOK (Fluka, 99%), N,N′-dicyclohexylcarbodiimide (Fluka,
99%), silver toluene-4-sulfonate (Fluka, 96%), 4-pyrrolidino-
pyridine (Aldrich, 98%), and acetone (Fluka, puriss p.a.) were
used as received. Nonamethylferrocene carboxaldehyde (3),7
4-benzyloxy-4′-hydroxybiphenyl,8 and 4-octadecyloxybenzoic
acid9 were prepared following literature procedures. All the
reactions were carried out at room temperature.
Tech n iqu es. Column chromatography used silica gel 60
(0.060-0.200 mm, SDS). Melting points (uncorrected) were
determined on a Bu¨chi 530 instrument. Transition tempera-
tures (onset point) and enthalpies were determined with a
Mettler DSC 30 differential scanning calorimeter connected
to a Mettler TA 4000 processor, under N2, at a rate of 10 °C/
min; Mettler TA72.2/0.5 Graphware was used for treatment
of the data. Optical studies were made using a Zeiss-Axioscop
polarizing microscope equipped with a Linkam-THMS-600
variable-temperature stage, under N2. 1H and 13C NMR spectra
were recorded on a Varian Gemini 200 spectrometer or a
Bruker AMX 400 with the solvent as an internal standard.
Elemental analyses were done by Mikroelementaranalytisches
Laboratorium ETH-Zurich.
1
Mp ) 120 °C. H NMR (200 MHz, acetone-d6): δ 6.05 (d, 1 H,
CHd), 5.8-5.6 (m, 1 H, CHd), 2.38 (t, 2 H, CH2CO2), 2.19 (m,
2 H, CdCCH2), 1.79 (m, 2 H, CH2CH2CO2), 1.74 (s, 6 H, CH3),
1.65 (s, 6 H, CH3), 1.59 (s, 15 H, CH3). Anal. Calcd for C25H36O2-
Fe (424.41): C, 70.75; H, 8.55. Found: C, 70.53; H, 8.54.
Com p ou n d 5. To a mixture of 4 (3.57 g, 8.41 mmol),
4-benzyloxy-4′-hydroxybiphenyl (2.79 g, 10.10 mmol), DCC
(2.08 g, 10.08 mmol), and CH2Cl2 (140 mL) was added
4-pyrrolidinopyridine (0.26 g, 1.75 mmol). The mixture was
stirred for 3 h and evaporated to dryness. Purification of the
solid residue by CC (CH2Cl2/Et3N, 100:1) gave pure 5 (4.42 g,
1
77%). Mp ) 132 °C. H NMR (200 MHz, acetone-d6): δ 7.65-
7.33 (m, 9 H, aromatic protons), 7.17 (d, 2 H, aromatic protons),
7.11 (d, 2 H, aromatic protons), 6.11 (d, 1 H, CHd), 5.8-5.7
(m, 1 H, CHd), 5.19 (s, 2 H, CH2Ph), 2.69 (t, 2 H, CH2CO2),
2.29 (m, 2 H, CdCCH2), 1.90 (m, 2 H, CH2CH2CO2), 1.76 (s, 6
H, CH3), 1.66 (s, 6 H, CH3), 1.60 (s, 15 H, CH3). Anal. Calcd
for C44H50O3Fe (682.73): C, 77.41; H, 7.38. Found: C, 77.44;
H, 7.36.
Com p ou n d 6. A mixture of 5 (2.26 g, 3.31 mmol), Pd-
(10%)/C (0.22 g), and CH2Cl2 (80 mL) was stirred under 4 bar
of H2 for 18 h. The mixture was filtered and the solvent
evaporated to dryness. Purification of the solid residue by CC
(first with CH2Cl2/Et3N, 100:1, to recover unreacted 5, and then
with acetone) and crystallization (EtOH) gave pure 6 (1.53 g,
78%). Mp ) 181 °C. 1H NMR (200 MHz, acetone-d6): δ 7.60
(d, 2 H, aromatic protons), 7.50 (d, 2 H, aromatic protons), 7.12
(d, 2 H, aromatic protons), 6.93 (d, 2 H, aromatic protons), 2.58
(t, 2 H, CH2CO2), 2.21 (t, 2 H, CpCH2), 1.8-1.6 [3 × s (27 H,
CH3) and 1 m (CH2CH2CO2)], 1.5-1.2 (m, 6 H, CH2). Anal.
Calcd for C37H46O3Fe (594.62): C, 74.74; H, 7.80. Found: C,
74.33; H, 7.88.
Com p ou n d 1. A solution of 6 (180 mg, 0.303 mmol),
4-octadecyloxybenzoic acid (118 mg, 0.302 mol), DCC (62 mg,
0.300 mmol), and 4-pyrrolidinopyridine (catalytic amount) in
CH2Cl2 (20 mL) was stirred for 6 h under N2, filtered, and
evaporated to dryness. Purification of the solid residue by CC
(CH2Cl2/Et3N, 98:2) and crystallization (acetone) gave pure 1
(202 mg, 69%). 1H NMR (200 MHz, CDCl3): δ 8.17 (d, 2 H,
aromatic protons), 7.60 (d, 2 H, aromatic protons), 7.59 (d, 2
H, aromatic protons), 7.28 (d, 2 H, aromatic protons), 7.15 (d,
2 H, aromatic protons), 6.99 (d, 2 H, aromatic protons), 4.06
X-r a y Diffr a ction Stu d ies. Compound 2 was introduced
into a Lindemann glass tube of about 0.7 mm in diameter. As
the sample decomposed in the temperature range of the liquid-
crystalline phase, the exposure times were limited by using
Synchrotron radiation (D43 at LURE, Orsay, France) and an
imaging plate detector. The wavelength was 1.45 Å and the
sample-to-detector distance 390 mm; an evacuated tube was
placed between the sample and the detector in order to reduce
the scattering background.
Mo1ssba u er Sp ectr oscop y. The Mo¨ssbauer spectra were
obtained between 4.2 and 295 K on a constant-acceleration
spectrometer that used a room-temperature rhodium matrix
cobalt-57 source and was calibrated at room temperature with
R-iron foil. The absorber thicknesses ranged from 75 to 100
mg/cm2, and the resulting spectra have been fit with
a
quadrupole doublet or, in some cases, with an added sextet.
Four spectral measurements at 295 K on three different
spectrometers with two separate preparations of (Me5Cp)2Fe
indicate that its isomer shift, quadrupole splitting, and
linewidth are reproducible to (0.004, (0.02, and (0.01 mm/
s, respectively. The accuracy for the remaining compounds

Switchable Mesomorphic Materials
Organometallics, Vol. 18, No. 26, 1999 5559
(t, 2 H, OCH2), 2.58 (t, 2 H, CH2CO2), 2.06 (t, 2 H, CpCH2),
1.9-1.2 [3 × s (27 H, CH3) and 1 × m (38 H, CH2)], 0.89 (t, 3
H, CH3). 13C NMR (100 MHz, CDCl3): δ 172.20, 164.85, 163.50,
150.49, 150.11, 138.01, 137.89, 132.22, 128.02, 122.07, 121.83,
121.35, 114.22, 82.67, 78.77, 78.60, 78.08, 68.23, 34.24, 31.88,
30.57, 29.66, 29.55, 29.52, 29.32, 29.18, 29.04, 25.93, 25.04,
24.91, 22.64, 14.08, 9.42, 9.39. Anal. Calcd for C62H86O5Fe
(967.21): C, 76.99; H, 8.96. Found: C, 77.11; H, 9.07.
Com p ou n d 2. To a solution of 1 (120 mg, 0.124 mmol) in
CH2Cl2/acetone (10 mL, 1:1) was added dropwise a solution of
silver toluene-4-sulfonate (35 mg, 0.125 mmol) in acetone (10
mL). The mixture was stirred for 5 min, filtered over Celite,
and evaporated to dryness. Purification of the solid residue
by CC (first with CH2Cl2/MeOH, 98:2, to recover unreacted 1,
and then with a gradient of CH2Cl2/MeOH, 98:2 f 90:10) and
crystallization (acetone/AcOEt) gave pure 2 (110 mg, 78%).
Anal. Calcd for C69H93O8SFe (1138.40): C, 72.80; H, 8.23; S,
2.82. Found: C, 72.76; H, 8.27; S, 2.89.
Ack n ow led gm en t. R.D. acknowledges the Swiss
National Science Foundation for financial support.
G.J .L. thanks Drs. O. A. Pringle and P. C. Ezekwenna
and Mr. R. Rossow for experimental help in obtaining
the Mo¨ssbauer spectra; this research was supported in
part by the U.S. National Science Foundation through
a Division of Materials Research Grant No. 95-21739.
D.L. acknowledges the Commissariat a` l’Energie Atom-
ique (CEA), the C.N.R.S., and the TMR research net-
work 3MD (ERBFMRXCT980181) from the European
Community for financial support.
OM9905308