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Bolaamphiphilic Polyols a Novel Class of Amphotropic Liquid Crystals.

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for an X-ray structure analysis were obtained by dissolving the white solid in a
mixture ofethanolldiethyl ether and cooling the solution to - 30 "C for ca. 24 h.
Received: November 23, 1990 [Z 4292 IE]
German version: Angew. Chem. 103 (1991) 439
T ( C H Z I n TOH
oH
CAS Registry numbers:
1, 132513-41-8; 2, 132513-42-9; 4, 24508-00-7; Pt(cod),,
(H,C=CHSiMe,),O, 2627-95-4; maleic anhydride, 108-31-6.
12130-66-4;
[l] For reviews, see C. S. Cundy, B. M. Kingston, M. F. Lappert. Adv.
Organornet Chem. If (1973) 330; I. L. Speier, ibid. 17 (1979) 407; F. 0.
Stark, J. R. Falkender, A. P. Wright in G. Wilkinson, F, G. A. Stone, E. W.
Abel (Eds.): Comprehensive Organometallic Chemistry, Vol. 2, Pergamon,
Oxford, 1982, p. 305.
[2] (a) D. N. Willing, US-A 3419 593 (1968); (b) B. D. Karstedt. US-A
3175452 (1973).
[3] G. Chandra, P. B. Hitchcock, M. F. Lappert, P. Y. Lo, Orgunomerallics 6
(1987) 191.
[4] Complex 1 in [D,]toluene (or + 10% toluene for '95Pt-NMR spectrum)
solution wascharacterized by 195Pt('H},29Si('H}, "C{'H/, 'H, and2D
'H-'H COSY NMR spectroscopy [this enabled a correlation to be made
of the coupling between the adjacent protons on each of the vinyl groups;
there are three distinct vinyl groups coordinated to each Pt center, *.J('H195Pt)ca. 55 Hz] [ll]. The '3C('H)-NMR data showed (DEPT) the presence of three methine (6 = 58.1, 56.4,57.3) and three methylene (6 = 57.0,
57.2, 56.4) vinylic carbon atoms, each with coupling constants 'J(13CI9'Pt) of ca. 110 Hz. The assignment of the bridginglchelating vinylic
protons was established by a sequence of decoupling and NOE experiments"'].
[5] Crystal data of 1: C,,H,,O,Pt,Si,,
M = 949.4, monoclinic, space group
C2/c, a = 29.810(5), b = 10.180(3), c = 12.527(2)A,
= 107.64",
V = 3622.8 A'. Z = 4, pcOlrd
= 1.74 gcm-3. The crystal data were collected on a CAD-4 diffractometer [p(MoK.) = 80.1 cm-']. A total of 3330
unique reflections was measured for 2 < 0 < 25" and + h + k _+ I, and
1775 reflections with lF21 > 1.5 u(F2)were used in the refinement where
u(F2)= {u2(r)+ 0.04(02}''2/L,. The structure was solved by routine
heavy atom methods and refined by full matrix least squares. Hydrogen
atoms were at fixed calculated positions with a common B,, of 6.0 A*. The
final residuals were R = 0.046, R = 0.070. Further details of the crystal
structure investigation are available on request from the Director of the
Cambridge Crystallographic Data Centre, University Chemical Laboratory, Lensfield Road, Cambridge CB2 IEW on quoting the full journal citation.
[6] I. A. K. Howard, Acra Crystallogr. Sect. B(38) (1982) 2896.
[7] I. A. K. Howard, S. A. Mason, J. L. Spencer, Proc. Roy. SOC.London A
386 (1983) 145.
[8] M. Green, J. A. K. Howard, I. L. Spencer. F. G. A. Stone, J Chem. Sot.
Dalton Trans. 1977, 271.
191 The '95Pt{'H}-NMR spectrum of complex 2 showed a sharp singlet at
d = - 5987 rel. to external KJPtCI,] (recorded in 10% [D,]toluene/
toluene, 303 K, 17.2 MHz). The coordinated maleic anhydride protons
were observed as a singlet at 5 = 4.98. [ZJ(1H-'95Pt)= 63 Hz] (recorded in
[DJacetone, 303 K, 360.1 MHz).
[lo] M.T. Chicote, M. Green, J. L. Spencer, F, G . A. Stone, J. Vicente, J
Organornet. Chem. 137 (1977) C8.
[ll] N. J. W. Warhurst, D. Phil. thesis, University of Sussex 1990.
Bolaamphiphilic Polyols, a Novel Class of
Amphotropic Liquid Crystals
By Frank Hentrich, Carsten Tschierske,* and Horst Zaschke
Amphiphilic molecules can aggregate to supramolecular
systems. An important form of this molecular self-organization is the formation of liquid crystalline phases.['] Thus,
amphiphilic n-alkane-1,2-diols 1, with a chain length of
n 2 5, exhibit monotropic mesophases which are stabilizable
by addition of water.[21These compounds are structurally
related with liquid crystalline carbohydrate derivativesr3]
and can be regarded as the simplest members of this large
[*] Dr. C. Tschierske, Dipl.-Chem. F. Hentrich, Prof. Dr. H. Zaschke
Sektion Chemie, WB Organische Chemie der Universitat Halle-Wittenberg
Weinbergweg 16, 0-4050 Halle (FRG)
440
2o-d
HO
0 VCH Verlagsgesellschaft mbH, W-6940 Weinheim, 1991
'5(CHylg<OOHH
HO
Scheme 1. n
=
3
HO-ICHzII<oH
OH
6
18 (21 [4]), 12 (4b), 9 (2b, 4 a), 5 (2c). 4 (2d).
class of amphiphilic mesogens. As recently reported, liquid
crystalline phases are drastically stabilized by the coupling of
two amphiphilic diols 1 (n = 9) via their hydrophobic molecular terminals to give the biamphiphilic (bolaamphiphilic)
tetrol 2a.r4I
We have now synthesized further bolaamphiphilic polyols
with substantially shorter polymethylene chains and structurally different hydrophilic head groups,t51in order to generalize this structural principle.r6] The liquid crystalline
properties of the new substances 2-7 determined by polarization microscopic and differential scanning calorimetric
(DSC) investigations are listed in Table 1. Surprisingly, even
compound 2c, with the very short pentamethylene spacer
between ethane-1,2-diol groups, still has thermotropic liquid
crystalline properties, although its hypothetical molecular
halves (compound 1 with n = 2 and 3) do not display
mesophases. Therefore, bolaamphiphilic polyols should not
only be considered as simple, dimeric amphiphilic diols, but
The
as an independent class of amphotropic me~ogens.['~]
general validity of this structural concept is further supported
by the variety of hydrophilic groups. Only in the case of compound 2 d and the symmetrical propane-l,3-diol derivatives
were no mesophases detectable. The isotropic melts of compounds 4 are only very slightly supercoolable, and possible
metastable mesophases are not recognizable. All other compounds show only a slight tendency to crystallize (often only
after several days), so that their monotropic mesophases are
easily observable. As a comparison of compounds 2a-2d
shows, the clearing points increase drastically with increasing length of the polymethylene chain. Compound 2 b and
the bolaamphiphilic trio1 5 are liquid crystalline above the
melting point. The unsymmetrical tetrol 3 has the greatest
mesophase diversity. On cooling the isotropic melts the appearance of a birefringence is observed under the polarizing
microscope at 84°C with a fan-like texture typical for lamellar a-phases, which can be oriented homeotropically very
easily by shearing. This points to a layer structure, whereby
the individual molecules in the layers do not exhibit longrange order. The hydroxy groups should, like those of amphiphilic diols, be coupled via a dynamic network of cooperative hydrogen bridges to give tile-shaped aggregates, which
are both separated as well as bound by the conformationally
mobile (molten) polymethylene chains (L, phase). On further
cooling to 75°C the texture changes and the viscosity increases considerably. Probably the transition to a more highly ordered mesophase with rigid parallel polymethylene
chains (Lp) occurs at this point.t7. Both phase transformations have unusually high phase-transition enthalpies. At
43"C, a further phase transition of small enthalpy takes
+
0570-0833/91/0404-0440$3.50 .2SjO
Angew. Chem. Int. Ed. Engl. 30 (1991j No. 4
place, which, however, cannot be observed in more detail as
a result of the onsetting crystallization.
The liquid crystalline phases of bolaamphiphilic polyols
can be modified by addition of water, whereby the
mesophases of compounds with long polymethylene spacers
(e.g. 2a and 6) are stabilized and those with shorter poly-
Table 1. Phase transition temperatures [a] T [ T ] of the bolaamphiphilic poly01s 2-7 [b]. The values in brackets refer to the enthalpies A H kJmol-' [c].
Cpd.
n [d]
Water-free samples
2 a [el
2b
18
9
k 87 L, 142 La 145 i
k 110 L, 115 i
(42.4) (17.2)
k 77 L, 36 i
(37.8) (7.2)
k 83 i
k 95 (L,, 43 L, 75 L. 84) i
(58.9) (0.9) (6.2) (7.0)
k 103 i
k 135 i
k 48 (Lo, 45) L, 70.5 i
(18.2) (0.9) (11.1)
k 89.5 (L, 61.5 L, 62) i
(59.9) (13.2) [i]
k 69 (L,, 35 L, 48) i
(53.2) (2.6) (18.3)
2c
5
2d
3
4
9
4a
4b
5 [gl
9
12
9
6 [h]
11
7
9
Water-saturated samples
L. 166 i
L. 59 i
-
L,41.5 i
- Ifl
- [fl
L. 56 i
L,77 i
L. 21 i
Received: October 31, 1990 [Z 4262 IE]
German version: Angew. Chem. f 0 3 (1991) 429
[a] Abbreviations: c = crystalline (the compounds have different melting temperatures and exhibit further solid-solid transitions depending on their previous history. In each case, the highest melting temperatures are quoted); L,,
L, = lamellar mesophases; i = isotropic phase; [b] correct C, H analyses, 'HNMR and I3C-NMR spectra have been recorded; [c] see [lo]; [d] length of the
polymethylene chain between the head groups; [el see [4]; [fl crystallizes out; [g]
see [ll]; [h] see [12]; [i] peaks not separated.
methylene chains are destabilized (Table 1). The mesophase
destabilization is more pronounced the greater the ratio between hydrophilic and hydrophobic structural units (hydrophilic -hydrophobic balance). This can be interpreted as
resulting from the effect of two counteracting influences : the
incorporation of water molecules in the region of the head
groups leads to a strengthening of the hydrogen bonding
IT1
115
100 -
70.5
65
50
38
26
no
mesophase
7
Fig. 1. Influence of polar substituents X on the clearing temperatures T,, ["C]
of amphiphilic diols and the stepwise transition of amphiphilic diols to bolaamphiphilic polyols. [a] See [2a]. [b] see [9].
Angew. Chem. Int. Ed. Engl. 30 (1991) No. 4
between the hydrophilic groups and stabilizes the mesophases. The hydration of the head groups, however, also
forces the polymethylene chains apart. The resulting free
space between the molecules can, only in the case of sufficiently long polymethylene chains, be filled through their
additional motions. As a result, one observes in the case of
water-saturated samples, the appearance of the L, phase,
and, in the case of short-chain compounds, a destabilization
or complete suppression of liquid crystalline phases. Figure
1 illustrates the stepwise transition from the amphiphilic diol
to the bolaamphiphilic polyol. On introduction of increasingly polar terminal substituents into the hydrophobic moiety of the molecule of amphiphilic d i o l ~ , [the
~ ] distinct orientation of the molecules in the double layers is lost, since these
polar groups can be incorporated into the network of the
intermolecular hydrogen bridges in ever increasing amount
with increasing ability to participate in hydrogen bonding. If
these terminal substituents function only as proton acceptors, then they break the hydrogen bridge network and thereby destabilize the associates. However, if this terminal group
is both proton acceptor as well as proton donor, then it can
be incorporated concurrently in the hydrogen-bridge network of the head groups and additionally stabilize the mesophase.
0 VCH
[l] H. Kelker, R. Hatz: Handbook of Liquid Crystals, Verlag Chemie, Weinheim 1980.
[2] a) C. Tschierske, G. Brezesinski, F. Kuschel, H. Zaschke. Mol. Cryst. Liq.
Crysr. Left. Sect. 6 (1989) 139; b) H. van Doren, Disserrarion, Groningen
1989.
131 G. A. Jeffrey, Acc. Chem. Res. 19 (1986) 168; J. W. Goodby, M. A. Marcus, E. Chin, P. L. Finn, B. Pfannemiiller, Liq. Cryst. 3(1988) 1569; V. Vill.
T. Bocker, J. Thiem, F. Fischer, ibid. 6 (1989) 349; H. van Doren. R. van
der Geest, C. F. De Ruijter, R. M. Kellogg, H. Wynberg, ibid.8(1990) 109;
K. Praefcke, B. Kohne, A. Eckert, J. Hempel, Z . Narurforsch. B 45 (1990)
1084; W. V. Dahlhoff, ibid. B 42 (1987) 661; D. Baeyens-Volant, R. Fornasier, E. Szalai, C. David, Mol. Crysr. Liq. Cryst. 135 (1986) 93 and
references cited therein.
[4] C. Tschierske, H. Zaschke, J. Chem. Soc. Chem. Commun. 1990, 1013.
[5] The compounds 2b-2d, 3, 5, and 7 were obtained by Os0,-catalyzed
dihydroxylation of the corresponding olefins according to the method
described by V. van Rheenen, R. C. Kelley, D. F. Cha, Tetrahedron Lett.
1976, 1973; l,(W-l)-alkanedienes + 2b-2d; 2-hydroxymethyltridec-12en-1-01 [12] + 3; undec-10-en-1-01 5 ; 3-oxatetradec-13-en-1-01(prepared by reaction of 1-bromoundec-10-ene with ethylene glycol/NaOMe/
MeOH) -,7. The synthesis of the compounds 4 a and 4 b was achieved by
reduction of tetraethyl undecane-l,l,ll,l I-tetracarboxylate and tetraethyl
tridecane-l,1,13,13-tetracarboxylate,respectively, with LiAlH, in THE
The synthesis of compound 6 is described in Ref. [12]. The polyols were
purified by column chromatography (CHCIJMeOH 9 5 5 ) and finally recrystallized from hexane/ethyl acetate or CHCI,.
[6] Bolaamphiphilic carbohydrates and bolaamphiphilic polyols with two hydrocarbon chains; W. V. Dahlhoff, 2.Naturforsch. B43 (1988) 1367; J.-H.
Fuhrhop, D. Fritsch, Acc. Chem. Res. 19(1986) 130; A. Gulik, V. Luuati,
M. De Rosa, A. Gambacorta, J. Mol. B i d . 182 (1985) 13.
[7] Preliminary X-ray diffraction investigations by Dr. S . Diele (Universitat
Halle-Wittenberg) confirm the proposed structure of the mesophases.
[8] A birefringence also occurs in the homeotropically oriented regions; it can
be greatly increased by shearing the sample. A non-orthogonal orientation
of the polymethylene chains with respect to the layer planes can therefore
not be ruled out as yet.
191 C. Tschierske, H. Zaschke, S. Wolgast, G. Brezesinski, F, Kuschel. Mol.
Crysr. Liq. Cryst. Lett. Secf. 7 (1990) 131.
[lo] We thank Herr D. Lotsch and Prof. Dr. G . Heppke (Technische Universitlt
Berlin) for kind permission to carry out the measurements with their facilities.
[ l l ] K. Shishido, M. Kawanishi, K. Kondo, T. Morimoto, A. Saito, N. Fukue,
J. Org. Chem. 27 (1962) 4073.
[I21 N. Pietschmann, G. Brezesinski, C. Tschierske, H. Zaschke, F. Kuschel,
Liq. Cryst. 5 (1989) 1697.
[13] Amphotropic mesogens form thermotropic and, after addition of solvent,
also lyotropic, liquid crystalline phases. H. Ringsdorf, B. Schlarb, J.
Venzmer, Angew. Chem. 100 (1988) 117; Angew. Chem. Int. Ed. Engl. 27
(1988) 113.
Verlagsgesellschaft mbH, W-6940 Weinheim. 1991
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