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Molecular Self-Organization of Amphotropic Cyanobiphenyl Mesogens.

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X[nm]
-
Fig. 2. UVjVIS spectra of 5 (solid line) and 3 (dotted line).
Figure 2 shows the UVjVIS spectra of the radialene 5 and
the diphosphinidenecyclobutene 3, indicating that the absorption spectrum of 5 shows a red shift compared to that of
3. The absorption peaks due to x-x* transition for both 3
and 5 appeared at 243-244 nm with almost equal intensities,
in contrast the absorption band at 298 nm due to the conjugated double bonds associated with phosphorus atom(s) for
3 is shifted by about 30 nm to a longer wavelength at 327 nm
with a slightly increased intensity for 5. Moreover, a featureless band above 400 nm appeared in the spectrum of 5, indicating a very extended conjugated n-electron system. Similar
bands also occur in the carbon analogues of 5,[12.1 3 ] suggesting that the diphospha[4]radialene 5 contains a new x-electron system,['41which in terms of its electro-, photo-, and
coordination chemistry is of interest.
Exper imen t a1 Procedure
2: Underargon at room temperature, 3-phenyl-l-propyne(0.92 g, 7.9 mmo1)in
T H F (5 mL) was added to one equivalent ofethylmagnesium bromide in T H F
(12 mL), and stirred for 3 h. To this solution was added 2,4,6-tri-tertbutylphenyl(ch1oro)phosphane (ArPHCI) (7.2 mmol)[15] in T H F (10 mL) at
O"C, and the mixture was stirred for 20 min. After workup (including chromatography on silica gel) and recrystallization from acetonitrile, 2 (1.3 g,
3.3 mmol) was obtained in 46% yield (based on the starting material ArPH,
(2.0 g. 7.2 mmol) used for the preparation of ArPHCI).
3: Under argon and in the dark, 2 (1.3 g, 3.3 mmol) in T H F (15 mL) was
allowed to react with one equivalent of phenyllithium (1.05 M, cyclohexane/
ether solution) at - 78 ' T , and then stirred for 30 min at room temperature. The
solution was cooled to -78°C and 1,2-dibromoethane (0.28 mL, 3.2 mmol)
was added. the mixture was then gradually allowed to warm up to room temperature and stirred for 1 h. The chromatographic workup on silica gel gave 3
(0.31 g. 0.40 mmol) in 24% yield.
5 : The cyclobutene 3 (52.8 mg, 0.0674 mmol) in CCI, (2.5 mL) was brominated
with NBS (24.7 mg, 0.139 mmol) under reflux for 25 min. After the succinimide
had been filtered off, the filtrate was concentrated to give a yellow solid. This
solid contained about 60% [16] bromobenzylcyclobutene 4 (a 1 : 1 mixture of dl
and m t w form 6("P) = 175.8 and 175.7). The dibromide 4 thus obtained was
dissolved i n T H F (5mL) and was allowed to react with butyllithium
(0.135 mmol, 1.63 M, hexane) for 15 min at - 78 "C and 30 min a! room temperature in THF to give an orange solution. The solution was concentrated, and
the resulting solid was washed with acetonitrile. Chromatographic workup
(silica gel. hexane) gave 11.1 mg of 5 as an orange solid in 21 YOyield (based on
3). Similar results were obtained when zinc powder (4 equiv) was used to eliminate the bromine (in diglyme at 50°C for 13 h) (5,21 % yield).
P. Folling, B. Josten, M. Siray, V. Winkhaus, F. Knoch, Angew. Chem.
1984, 96, 621; Angen. Chem. I n t . Ed. Engl. 1984,23,619.
[31 M. Yoshifuji, I.Shima, N. Inamoto, K. Hirotsu, T, Higuchi, J. Am. Chem.
Sue. 1981, 103,4587; ibid. 1982, 104,6167.
[4] M. Yoshifuji. K. Toyota, I. Matsuda, T. Niitsu. N. Inamoto, K. Hirotsu,
T. Higuchi, Tetrahedron 1988, 44. 1363.
[5] R. Appel, V. Winkhaus, F. Knoch, Chem. Ber. 1987, 120,243.
[6] G.Mirkl, P. Kreitmeier, H. Noth, K. Polborn, Angew. Chem. 1990, 102,
958; Angen. Chem. In!. Ed. Engl. 1990,29,927.
[7] M. Yoshifuji, K. Toyota, M. Murayama, H. Yoshimura, A. Okamoto. K.
Hirotsu, S . Nagase, Chem. Lerl. 1990, 2195.
[8] K. Toyota, K.Tashiro, M. Yoshifuji, Chem. Letr. 1991, 2079.
[9] K . Toyota, K. Fdshiro, M. Yoshifuji, S. Nagase, Bull. Chrm. Sue. Jpn.
1992,65, 2297.
[lo] Crystal data of 5 : recrystallized from a mixture of toluene and
dichloromethane. C,,H,,P,, M , = 781.09. Monoclinic, space group P2,/c,
u =15.03(1),
b =15.405(5), c = 21.288(3) A; fi = 93.93(3)"; V =
4918(3) A'. Z = 4, @cr,.a =1.055 gem-', p = 1.16cm-'; 9383 reflections
with 28 s 50.0 were recorded on a four-circle diffractometer (Mo,, radiation, graphite monochromator). Of these. 4047 with i > 3u(I) were
judged as observed. The structure was solved with MULTAN88 [17]. The
non-hydrogen atoms were refined anisotropically. Hydrogen atoms were
included, hut their positions were not refined. R = 0.069, R, = 0.045. Further details of the crystal structure investigation are avaibabk on request
from the Director of the Cambridge Crystallographic Data Centre,
12 Union Road, GB-Cambridge CB2 lEZ, (UK), on quoting the full journal citation.
[ l l ] M. Yoshifuji, N. Inamoto, K.Hirotsu, T. Higuchi, J. Chem. SOC.Chem.
Commun. 1985, 1109.
[12] M. Iyoda, H. Otani, M . Oda, Y Kai, Y Baba, N. Kasai, J. Am. Chem. Soc.
1986, f08,5371.
[13] F. Toda, K . Kumada, N. Ishiguro, K. Akagi, BuN. Chem Soc. Jpn. 1970,
43, 3535; K. Tanaka, F. Toda, Tetrahedron Lett. 1980,21,2713.
[14] H. Hopf, G.Maas, Angew. Chem. 1992,104,953; Angew. Chem. Int. Ed.
Engl. 1992, 31,931.
[15] M. Yoshifuji, S . Sasaki, N. Inamoto, Tetrahedron Lett. 1989, 30,839.
[16] In addition the yellow solid contained Z,6-bis(2,4,6-tri-tert-butylphenyl)3.4-bis(cc-bromobenzyl)-1,6-diphospha-l,2.4.S-hexatetraene(about 40 %)
which was also a 1 :1 mixture of the dland me30 forms (6 (-"P) = 49.7 and
47.9). Attempted purification has not yet been successful because of the
instability of4. Therefore the subsequent reaction was carried out without
purification.
[17] T. Debaerdemaeker, G.Germain, P. Main, L. S. Refaat, C. Tate. M. M.
Woolfson, Computer Programsfor the Automatic Solution uJCr.vstul Structuresfrom X-Ray Dflracriun Data. University of York, 1988.
Moiecular Self-organization of Amphotropic
Cyanobiphenyl Mesogens**
By Detlev Joachimi, Carsten Tschierske,* Henning Miiller,
Joachirn Heinz Wendorff, Ludo(f Schneider,
and R a y Kleppinger
Hydrogen bonds are directed interactions whose energies
lie between those of covalent bonds and nonspecific, intermolecular interactions. Intermolecular hydrogen bonds are,
therefore, very important in the formation of macrostructures in biological systems. Molecular self-organization
through hydrogen bonds also plays an important role in
materials science. This is expressed, amongst other properties, in the formation ofliquid crystalline phases which represent a state of matter characterized by order and mobility at
the molecular level. The amphiphilic carbohydrate derivd[*I
Received: March 27,1993 IZ 5948 IE]
German version: Angew. Chem. 1993, 10s. 1256
111 M.Yoshifuji, K. Toyota. K. Shibayama, N. Inamoto, Tetrulzedroe Lett.
1984.25, 1809; M. Yoshifuji. H. Yoshimura, K. Toyota, Chem. Lett. 1990,
827.
121 M. Yoshifuji. K. Toyota, N. Inamoto, J. Chem. SOC.Chem. Commun. 1984,
689, M.Yoshifuji, S . Sasaki, N. Inamoto. ibrd. 1989, 1732; H. H.Karsch,
F. H. Kohler, H.-U. Reisacher, Tetrahedron Lert. 1984,25,3687; R.Appel.
Angeu,. Chem. Inr. Ed. EngI. 1993, 32, No.
8
0 VCH
[**I
Dr. habil. C. Tschierske, Dr. D. Joachimi, H. Miiller
Institut fur Organische Chemie der Universitit Halle-Wittenberg
Weinhergweg 16, PSF 8, D-06120 Halle (FRG)
Telefax: Int. code + (345)649065
Prof. Dr. J. H. Wendorff, L. Schneider, R. Kleppinger
Institut f u r Physikalische Chemie der Universitit Marhurg (FRG)
This work was supported by the Deutsche Forschungsgemeinschaft and
the Fonds der Chemischen Industrie. We thank Merck for the donation of
chemicals. The names of the compounds in this publication do not conform to IUPAC nomenclature since cyanohiphenyl is an accepted term in
the field of liquid crystals (Editorial note).
Verlagsgesrll.rchafr mbH. 0-69451 Weinhem, 1993
0570-0833~93j0808-ll65$10.00+ .25/0
1165
tives and polyhydroxyl amphiphiles which form lamellar or
columnar macrostructures are an important class of compounds whose mesogenicity depends on the ability to form
hydrogen bonds.['] Amphiphilic n-alkane-I ,2-diols, for example 1, may be regarded as the simplest compounds of this
type.['] In certain temperature ranges these compounds show
lamellar mesophases in which the molecules are arranged in
layers, and the hydroxyl groups are linked through a dynamic network of cooperative hydrogen bonds. The liquid crystalline phases of these compounds can be modified and stabilized by the inclusion of rigid calamitic structural elements
(Fig. l).13*41
Comparison of compounds 3 and 4 shows that
T ["CI-
50
I
125
156
3
4
I
Fig. 1. The influence ofcalamitic structural elements of different lengths on the
liquid crystalline properties of amphiphilic diols, and the comparison of the
amphiphilic diol3 [4] with a nonamphiphilic mesogen 4 [5]. The lower bars for
compounds 1.2, and 3 represent the lyotroplc mesophase behavior of samples
saturated with water. For an explanation of the abbreviations see Table 1 [a].
the introduction of a 1,Zdiol unit to the end of an n-alkyl
side chain of the nonamphiphilic phenyl benzoate 4 causes
the change from a nematic mesophase to a smectic phase.
4-Alkoxy-4-cyanobiphenyls are also known to be calamitic
liquid
We have attempted to combine the two
types of mesogenic molecular structures-the amphiphilic
diols and the calamitic cyanobiphenyl mesogens-and have
examined how this affects the ability for molecular self-organization.
The phase transition temperatures of the 4'-[w,(o - 1)-dihydroxyalkoxy]-4-~yanobiphenyls
5 which we have synthesized are collected in Table 1, and compared with the
analogous 4-alkoxy-4-cyanobiphenyls 6. It can be seen that
the stability of liquid crystalline phases is raised considerably
by the introduction of the 1,2-diol unit. But in spite of the
diol group no induction of a smectic phase is observed. On
the contrary, while compound 6 c shows a smectic A phase
stable up to 67 "C, the 1,2-diol derivative 5 d can be supercooled to 55 "C without any sign of a phase transition. The
appearance of a smectic A phase is first observed with compound 5e. Its stability increases with further chain extension
(5f) and finally completely displaces the nematic phase. Xray scattering measurements on the nematic phase of 5c
shows two diffuse halos. The halo observed in the wide angle
range at 20 = 20" corresponds to a mean distance of
1166
8
VCH Verlugsgesellsrhuft m h H , 0.69451 Wernheim, 1993
C
W
O
R
OH
5: R = (CH,),-CH-CH,OH
I
6 : R = (CH,),-CH,-CH,
Table 1. Comparison of the phase transitions [a] and assoclated temperatures
T YC] of 4-[w,(w l)-dihydroxy]-4-cyanobiphenyls 5 [b] and 4-aIkoxy-4cyanobiphenyls 6 [5].
~
n
Compd. Phase, T
1
2
5a
5b
4
5c
6
5d
8
5e
9
5f
150
100
96
N
cr116
cr115
cr86
cr97
cr57
cr82
cr
cr98
cr
crlll
N'
N
S,
N
S,
N
S,
S,
S,
S,
Compd. Phase, T
129is [c]
133is
166is [d,e]
125is
133is[d, 4
119is
128is Id, el
llON 110.5is
122is [d, el
127is
6a
cr78 (N77.5) is
6b
cr57 N75.5is
6c
cr54SA67N80is
6d
cr59.5SA87.5is
[a] Determined on a hot table by usmg a polarization microsope; abbreviations: cr = crystalline; N = nematic mesophase; N* = cholesteric mesophase;
S, = smectic A phase; S , = smectic C phase; is = isotropic liquid; L,, L, =
lamellar mesophases; the values in parentheses characterize monotropic
(metastable) mesophases. [b] Correct C,H analyses, 'HNMR and I3C NMR
spectra available. [c] ( S )enantiomer, see 161. [d] Phase transition temperatures
of the water-saturated samples. [el Determined by observations of contact
preparations in sealed glass capillaries with a polarization microscope.
[f] From DSC measurements.
0.44 nm, and is assigned to the closely associated alkyl
chains. In the narrow angle region there is a broad halo
which is typical for a nematic phase. The average distance is
about 1.5 nm, which indicates that no stable dimers, such as
those known to occur with mesogenic carboxylic acids, are
found in the nematic phase. Thus no influence of hydrogen
bonding on the structural parameters can be demonstrated.
Here the hydrogen bonds function exclusively as stabilizers
of the mesophase. In Figure 2 sections of the IR spectra of
compound 5 c and 1,2-propanediol are compared. The absorption maximum for both compounds shifts to higher
wave numbers with rising temperature. This is a result of the
breaking of intermolecular hydrogen bonds between the diol
groups with rising temperature. In comparison with 1,2-
4000
3000
4000
+
3000
c[cm-']
Fig. 2. Sections of the temperature-dependent IR spectra of compound 5c
(left) and 1,2-propanediol (right) in the range 2500-4000 cm-' ;measured with
a BIORAD-FTS-40 spectrophotometer, in a heated thermal cell SPECAC P/N
21.500.
O570-0833/93/o808-lIn6$lO.OO+.ZSjO
Angen Chem. Inr. Ed. Eng/.1993, 32, No. 8
propanediol, the temperature dependence of the mesogenic
diol5c is much more evident, and an especially large shift is
observed in the region of the phase transition. This verifies
that, already, in the nematic phase, some of the hydroxyl
groups are not intermolecularly associated during the average time of the measurement. The formation of the nematic
mesophase can, therefore, be explained by disorder in the
layer structure. The cyano group could be responsible for
this, since these can form hydrogen bonds with hydroxy
groups.[71This clearly gives rise to disorder in the smectic
layer structure, and a nematic phase is thus favored. But
when the length of the alkylene spacers between the diol head
group and the cyanobiphenyl unit is further extended the
effect of the separation of the hydrophobic and hydrophilic
parts of the molecule becomes evident and leads to the formation of smectic layer structures. Similar results were also
obtained by Griffin et al. in the investigation of 4-(o-hydroxyalkoxy)-4-~yanobiphenyls
(for example 7 in Fig. 3).“’
r
[OCI-
75.5) 78
60
92 110
NC
=(Q
J-OO
-H
I
115
133
6
Fig. 3. The influence of the number of hydroxyl groups on the thermotropic
mesophase behavior of 4-cyanobiphenyl mesogens 5-7 [8],8 [lo]. and 9 [ll].
The lower bars for compounds 5 and 8 represent the lyotropic mesophase
behavior of the water saturated samples. For an explanation of the abbreviations see Table 1 [a].
With respect to mesophase stability, these compounds, since
they only have one hydroxyl group available for intermolecular association, lie between the nonamphiphilic compounds
6 and the 1,2-diol derivatives 5. Smectic mesophases could
not be detected even for long-chain compounds of this class
of substances.
Since the 4-(w,o-1 -dihydroxyalkoxy)-4-cyanobiphenyls5
are amphiphilic compounds, their mesogenic properties
should be influenced by the addition of water. The phase
transition temperatures of samples of compounds 5 b-e, saturated with water, are compared with those of the anhydrous
substances in Table 1. It is clear that the addition of water
leads not only to a considerable stabilization of the
mesophase, but also to the induction of a smectic layer structure.[’’ We interpret this as meaning that the water molecules
can be incorporated into the network of hydrogen bonds of
the diol head group, strengthening the interactions between
the groups and thus hindering the parallel movement of
single molecules.
Increasing the number of hydrogen bonds should be possible not only by the inclusion of water molecules but, in
Angeu. Chrm. In/. Ed. Engl. 1993, 32, No. 8
general, by increasing the number of available hydroxyl
groups in the vicinity of the head group. A comparison of 5b
with compounds 8[”] and 9[111in Figure 3 clearly hows that
covalent hydroxyl groups can also cause the induction of
smectic mesophases. Thus, by influencing hydrogen bonds,
it is possible to control specifically the molecular arrangement of amphiphilic molecules.
Received: February 23, 1993 [Z5887 IE]
German version: Angew. Chem. 1993, 105, 1205
[I] G. A. Jeffrey, L. M. Wingert, Liq. Cryst. 1992, 12, 179-202, and references therein; K. Praefcke, B. Kohne, A. Eckert, J. Hempel, Z . Naturforsch. B 1990, 45, 1084, and references therein; G. Lattermann. G.
Staufer, G. Brezesinski, Liq. Crysr. 1991, IO. 169.
[2] C. Tschierske, G. Brezesinski, F. Kuschel, H. Zaschke, Mol. Cryst. Liq.
Cryst. Lett. Sect. 1989, 6 , 139.
131 C. Tschierske, F, Hentrich, D. Joachimi. 0.Agert, H. Zaschke. Liq. Cryst.
1991,9, 571 -582.
[4] C. Tschierske, A. Lunow, D. Joachimi, E Hentrich, D. Girdziunaite, H.
Zaschke, A. Madicke. G. Brezesinski, F. Kuschel, Liq. Cryst. 1991, 9,
821 -829.
[5] D. Demus, H.Demus, H. Zaschke, F/G$sige Kristolle in Tabellen. 1st ed.
VEB Deutscher Verlag fur Grundstoffindustrie. Leipzig, 1974, p. 64; D.
Demus, H. Zaschke, F/ussige Kr-istollr in TabeNen I I , 1st ed. VEB
Deutscher Verlag fur Grundstoffindustrie, Leipzig. 1984, p. 278.
[6] Compounds Sa-6f were obtained by the etherification of 4-hydroxy-4cyanobiphenyl with the corresponding 1,2-O-isopropylidene-1,2-dihydroxyalkan-w-ols, by using the method of 0. Mitsunobu, Synthesis 1981.
1, and subsequent acid-catalyzed cleavage of the isopropylidene protective
group. For the synthesis of5a (S)-l.2-O-isopropylideneglycerol was used.
All other compounds of type 5 are racemic mixtures.
[7] A. Allerhand, P.von R. Schleyer, J Am. Chem. Sor. 1963,85, 866.
[8] A. C. Griffin, S. R. Vaidya, M o / . Crysr. Liq. C r y / . 1989, 173, 85-88.
[9] The water uptake of these compounds is limited. To determine the water
miscibility of the diols, mixtures of 5 c with increasing amounts of water
were investigated by differential scanning calorimetry (DSC). With a molar ratio of diol to water of 1 :3,the appearance of an ice peak, which is
attributed to thecrystallization of the’konbound” water, could already be
seen. At higher temperatures the water uptake should, however. beconsiderably higher.
[lo] Compound 8 was obtained by the Mitsunobu etherification of4-hydroxy4-cyanobiphenyl with 1,2-O-isopropylidene-3-(O-tetrahydropyran-2-yl)L-threitol (L. De Gaudenzi, S. Apparao, R. R. Schmidt, Tetrahedron 1990,
46, 277-290), followed by removal of the protective group.
[ l l ] The synthesis of compound 9 was achieved by treating acetobromoglucose
with the sodium salt of 4-hydroxy-4-cyanobiphenyl according to the
method of J. Conchie, G. A. Levvy in Methods in Carbohydrate Chemistry,
Vol. 20 (Eds.: R. L. Whistler, M. L. Wolfrom), Academic Press, New York,
1963, pp. 335-337.
The “Phosphonioyl(phosphoranediy1)carbene”
[ (zTr,N),P(H)CP(NzFr,),j as a Source of New
1,3-DiphosphaalIene Ylides: The First Carbodiphosphoranes with P-H Bonds**
+
By Michele Soleilhavoup, Antoine Baceiredo,
and Guy BertranP
Several types of diphosphaallenes possessing either ylidic
and/or genuine phosphorus-carbon double bonds (A,[’]
B/21 and C13])are known, and we recently the synthesis of
the titel compound 1 which can be formally regarded as D.[41
[“I Dr. G. Bertrand, M. Soleilhavoup, Dr. A. Baceiredo
Laboratoire de Chimie de Coordination du CNRS
205, route de Narbonne, F-31077Toulouse Cedex (France)
Telefax- Int. code + (61) 553 003
[**I This work was supported by the Centre National de la Recherche Scientifique. We thank Prof. R. Ahlrichs. Karlsruhe, for the preliminary communication of calculations and Dr. R. Reed for helpful discussions.
Q VCH Ver1ogsgesellschoft mbH, 0.69451 Weinbrim, 1993
0S7#-OR33~93~OSO~-ll~7
3 lO.O~+.ZS/O
1167
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