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Metallomesogens with a Cholesteric Mesophase.

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[l] Recent reviews: a) L. E. Orgel, Nulure 1992.358,203-209; b) A. Eschenmoser. E. Loewenthal. Chrm. Soc. Rev. 1992, 1-16; c) S. Hoffmann,
Angrw. Chem. 1992, 104, 1032- 1035: Angen. Chem. lnt. Ed. Engl. 1992,
31,1013- 1016; d ) M. Famulok, J. S. Nowick, J. Rebek, Acra Chem. Scund.
1992. 46, 315- 324; e) G. von Kiedrowski, J. Helbing. B. Wlotzka, S. Jordan. M. Matzen, T. Achilles, D. Sievers, A. Terfort, B. C. Kahrs, Nuchr.
Chcm. Tech. Lub. 1992. 40. 578-588.
[2] Sequence notations principally concern oligodeoxynucleotide derivatives ;
the prefix d for deoxy is omitted here. Abbreviations: M e = 5'-0-methyl,
M T M = S-0-methylthiomethyl. q 3 = 5'-azido-5'-deoxy. H2N = 5'-amino-5'deoxy. Ho = 5'-hydroxy, p = 3-phosphate. p = 3'-(2-chlorophenyl)phosphate, pPT1:= 3'-(2-phenylthioethyI)phosphate, pn = 3'-5'-phosphoamidate (the sequences, when not otherwise specified, are always in the
5' + 3' direction); HPLC = high-performance liquid chromatography,
RPC' = reversed-phase column.
(31 G . von Kiedrowski, Angrn.. Chem. 1986, 98, 932-934; Angew. Chem. 1121.
Ed. Engl. 1986. 25, 932- 935.
[4] a ) For the theory of the square root law and parabolic growth see: G . von
Kiedrowski. Bioorg. Chern. Front. 1993, 3, 113- 146. b) Interestlngly,
parabolic growth is also described in connection with the propagation of
computer viruses: J. 0. Kephart. S. R. White Proc 1991 IEEE Computer
Symp. R e x Securucj undPrivucy, IEEE Computer Society, Washington, 1991, 343-359.
[S] G. von Kiedrowski, B. Wlotzka, J. Helbing, M. Matzen, S. Jordan, Angeic..
Clr~wi.1991. 103, 456-459. 1066; Angew. Chem. In/. Ed. Engl. 1991, 30.
423-426. 892.
[61 Further self-replicating systems with self-complementary templates from
t u o starting materials: a ) W. S. Zielinski, L. E. Orgel, Nururr 1987, 327,
346- 347: b) G . von Kiedrowski, B. Wlotzka. J. Helbing. A n g e n . Chem.
1989. lo/, 1259-1261; Angew. Chem. Int. Ed. Engl. 1989,2X. 1235-1237;
c) T. T]ivikua, P. Ballester. J. Rebek, Jr., J. Am. C h e w Soc. 1990, 112.
1749 - 1250; d) J. S. Nowick, Q. Feng. T. Tjivikua. P. Ballester. J. Rebek,
Jr ibid. 1991. 113,8831-8839; e) I - I . Hong, Q. Feng. V. Rotello, J. Rebek.
S&nw 1992. ,755. 848-850; f) Q , Feng, T. K. Park, J. Rebek, [hid. 1992,
2.36. 1 1 79 1180; g) A. Terfort, G . von Kiedrowski. Angnr. Ciiem. 1992,
1114. 626 -628: Angeic.. Chrm. In!. Ed. Engl. 1992, 31, 654-656. Related
examples: h) W. S. Zielinski, L. E. Orgel, J. Mol. E w l . 1989. 29. 281 -283,
i) K . E. Ng, L. E. Orgel, ibid. 1989, 29. 101 - 107; j) J. T. Goodwin, D. G.
Lynn.J Am. Chem. Soc. 1992. 114.9197-9198; k) F. Persico, J. D. Wuest,
J. 0 r g . Chem. 1993, 5X. 95.
[7] Other systems: Self-replicating micelles: a) P. A. Bachmann. P. Walde,
P L. Luisi. J. Lang, J. Am. Chrm. Soc. 1990. 112. 8200-8201; b ) P . A.
Bachmann. P. L. Luisi, J. Lang. Nature 1992, 357, 57-59. En route to
self-replicating ribozyines: c) J. A. Doudna, J. W. Szostak, h i d . 1989, 339,
519; d ) J. A. Doudna. J. Couture, J. W. Szostak, Science 1991, 251,16053610. e) For self-replicating algorithms. see articles in Arr[/icrd LiJe. The
Procrc~ding.\N/ un Interdisciplinury Workshop on the Synthesis und Simulu1ioii o/ Lri'mg Systems Held September, 1987 in Los Atumos, New Mexico
(Ed.: C. G. Langton). Addison-Wesley, Redwood City, USA, 1989;
f ) J. A. Reggia, S. L. Armentrout, H.-H. Chou, Y Peng, Science 1993,259.
1282- 1287.
[8] a ) J. Helbing. Dissertation, Gottingen, 1990; b) T. Achilles. G. von
Kiedrowski. unpublished; c) synthesis method employed: V. A. Efimov,
0. G. Chakhmakhcheva, Y. A. Ovchinnikov, Nuclic Acids Res. 1985, 13,
3651 3670.
[9] The following standard conditions were chosen for all described reactions:
T = 20 'C; 0.2 M EDC; 0.1 M MeIm/pH 7 2; reactant concentrations:
2 mM.
[lo] Nucleosil ' 3 8 . 4 x 250 mm; A : 0.1 M sodium hydrogen carbonate, B: acetonitrile/water 30:70 (v/v); flow rate 1 m L m i n - ' ; gradient (B): 1 8 % 28%in5min,28%-42%in2min,42%-50%in4min,50%-75%in
2.5 min, and 0.5 min 75%; detection at 1. = 254 nm.
11 11 As trace products in the conversion of (A B C), all possible oligomerization products of the type B,, AB,,, B,C. and AB,C are assumed ( n > 11,
because each amino reactant (B,,, B,C) can in principle be condensed with
each 3'-terminal phosphate reactant (AB,. B,) to give the corresponding
3'S-phosphoamidate. However, with the exception of ABC, higher condensation products could not be reliably identified in the HPLC profile.
[12] The elution behavior of the nucleotide reactants on C1X is determined
mainly by the terminal groups. Compounds with polar termini, for example B and BB. elute immedialely and hence cannot be separated.
[13] AC'. A B and A B were prepared by solid-phase synthesis (phosphoamiditc method). The formation ofphosphodiesters between 3-phosphates and
the terminal hydroxy groups of these templates is negligible under the
reaction conditions; the templates can be regarded as inert.
[14] B. Wlotzka, Dissertation. Gottingen, 1992.
[15] a ) S. M . Freier, A. Sinclair, T. Neilson, D. H. Turner, J. Mol. Biol. 1985,
1x5. 645 -648, b) K. H. Breslauer. R. Frank. H. Bliicker, L. A. Marky.
Proc. Null. Acud. Sci. USA 1986. 83, 3746- 3749.
[16] E Smthmiry. 1. Gladkih, J. Thror. Bid. 1989. 138. 55-58.
Metallomesogens with a Cholesteric Mesophase**
By Maria J. Baena, Julio Buey, Pablo Espinet,*
Heinz-S. Kitzerow, and Gerd Heppke
Metallomesogens, liquid crystals containing coordinated
metal atoms, have seen a rapid development in the last few
years."] In a very short period metallomesogens displaying
almost every mesophase previously found in organic mesogens--calamitic (nematic and smectic phases), discotic, polymeric, and amphiphilic phases-have been reported. Rather
surprisingly, chiral metallomesogens are scarce; only one
material displaying a chiral smectic C mesophase (and hence
ferroelectric) had been reportedf21until very recently, when
two paramagnetic chiral smectic C metallomesogens were
described.[31There is no representative of the chiral nematic
(cholesteric, Ch) mesophase. We report here the first metallomesogens displaying cholesteric behavior, which have been
obtained within the now-large family of metallomesogens
derived from ortho-palladated imines and azines.I2.41
Imine 1 reacts with Pd(OAcf, in acetic acid (50"C,
overnight) to give complex 2a (X = OAc) which shows
no mesogenic behavior (crystalline/217"C/isotropic)
(Scheme I).['] Treatment of 2a in CH,Cl, with HCI (Pd/
+ +
Angew Chcm I n / . Ed. Engl.
1993. 32, N o . 8
* CHCl
Scheme 1. Za: X
OAc; Zb: X
HCI = 1 /I) affords 2 b (X = CI) (crystalline/l76 "C/
SJ247 "C/isotropic) which, on treatment with ( R ) K0,CCHClMe in CH,Cl,/acetone (1 /I), yields complex
3 (crystalline/l52 "C/S,/l86 "C/isotropic/203 "C/Sa/224 "C/
isotropic). All the complexes gave satisfactory C,H,N-analyses. The mesogenic behavior of the planar complex 2 b and
the nonmesogenic behavior of the folded compound 2a are
to be expected from our previous result^,[^.^' but the meso['I
Prof. Dr. P. Espinet, Dr. M. J. Baena, J. Buey
Departamento de Quimica Inorginica
Facultad de Ciencias
Universidad de Valladolid. E-47 005 Valladolid (Spain)
Telefax: Int. code (83)423-013
Dr. H.-S. Kitzerow. Prof. Dr. G . Heppke.
Technische Universitit Berlin -ER 11Strasse des 17. Juni 135, D-10623 Berlin ( F R G )
This work was supported by the Comision Interministerial de Ciencia y
Tecnologia (Project MAT90-0325), the Consejeria de Cultura de la Junta
de Castilla y Leon. Iberdrola, (stipend for M. J. B.), and the Deutsche
Forschungsgemeinschaft (SFB 335).
VCH VeriugsgeselBrhufi mhH. 0-69451 Weinheim, 1993
O57O-O833j93jOSO~-l20l3 IO.OO+ .25:0
genic behavior of the folded complex 3 is unexpected and
one ( p < 0). Similar inversions of the helical pitch have been
remarkable. We had expected that the 2-chloropropionato
previously reported in organic systems.[' ' - 14] The induced
ligand, which is bulkier than the acetato ligand, would dischirality can be described by the helical twisting power
turb the molecular packing and hinder mesogenic behavior
k = p- ' c- ',which is independent on the concentration c of
more; however, the dipole moment introduced with the C-CI
the chiral compound for most substances. From the temperbond apparently increases the strength of the intermolecular
ature dependence of this quantity (Fig. 2) the inversion teminteractions enough to compensate for the unfavorable steric
peratures 7; = 89.8 "C for compound 4a and 7: = 100.4 "C
effect, and 3 is indeed mesomorphic. The compound is also
(extrapolated) for compound 4c are obtained.
remarkable for its double-melting
Treatment of 3 with mercaptans HSC,H,,+, (Pd/HSR =
2/1) produces the mixed-bridge compounds 4 (4a: n = 6;
4b: n = l o ; 4c: n =IS). The complexes gave satisfactory
C,H,N-analyses; molecular weight determinations in CHCI,
and 'H NMR spectra are also consistent with a bridged dinuclear compound. We discuss only the data obtained for
4a; the results for 4b and 4c are similar. The easily observable signals for H, (6 =7.83, s) and H, (6 =7.49 d,
J = 2.34 Hz) indicate a unique cis arrangement of the two
imine moieties in the complex.['] In contrast, the chloro- and Ilpc
carboxylato-bridged complexes 2 and 3, respectively, have
trans structures. To the best of our knowledge bridged
dimers with ortho-palladated ligands either have trans structures (and hence have no net dipole moment) or are mixtures
' ' 40I ' 601 ' 80I ' 100I ' 120
of trans and cis isomers, in which the latter is typically the
very minor component. The carboxylato/thiolato bridges of
T ["C]
the compounds described here seem to force a cis arrangement. This is particularly interesting in view of possible apFig. 2. Temperature dependence of the helical twisting power for 4 a and 4c
( p = cholesteric helical pitch, c = concentration of the chiral compound in
plications of these compounds as frequency doublers in nonwt Yo).
linear optics, where a net dipole moment is required.[*]
All three compounds 4 a 4 c show a cholesteric mesophase
in a certain range of temperatures (4a: crystalline/l40 "C/
cholesteric/l57 "C/isotropic; 4b: crystalline/l09.5 "C/S,/
The relationship between the unusual temperature depen115.2 "C/cholesteric/l37.6 "C/isotropic; 4c: crystalline/92 "C/
dence of the pitch of the cholesteric helix and the chemical
S,/128.3 "C/cholesteric/l31.7 "C/isotropic). In order to
structure of the new mesogens calls to mind earlier investigacharacterize their chirality in mesophase condition~,[~]
tions on mesogenic esters of (S)-l,2-propanediol and (R,R)measured the pitch of the cholesteric phase induced by 4a
2,3-butanediol which also show a helix inversion,'''] Like
and 4c in mixtures of the respective chiral metallomesogen
compounds 4 a 4 c , the structure of these esters is characterand RO-TN 404 (a commercial, wide-range nematic solvent
ized by two large mesogenic groups that are connected to
from Hoffmann-La Roche, containing cyano-substituted
each other. It was proposed that the inversion effect is due to
biphenyls and pyrimidine derivatives), by applying the
presence of two conformers, which induce cholesteric
Grandjean-Can0 method. [ '1
structures with opposing helical screw senses, and which are
The cholesteric mixtures show a temperature dependence
in temperature-dependent thermodynamic equilibrium. The
of the pitchp which is characterized by a divergence o f p and
presented here seem to confirm that molecules
an inversion of the helical screw sense with changing tempercontaining two mesogenic wings tend to favor helix inverature (Fig. 1). At low temperatures we found a right-handed
sion. However, it should be noted that twist inversion has
cholesteric helix ( p > 0), at high temperatures a left-handed
also been observed in compounds exhibiting a different type
of structure.['3. l41
Received: November 27, 1992,
Revised version: February 11,1993 [Z 5707 IE]
German version: Angew. Chem. 1993, 105, 1238
# I
# I
'I I
T ["C]
Fig. 1. Temperature dependence of the cholesteric pitch p for a mixture of
21.2 wt% of 4 a and 78.8 wt% of the commmercial nematic solvent ROTN 404.
Verlagsgesellschafi mhH. 0-69451 Weinhem, 1993
[l] Reviews: A. M. Giroud-Godquin, P. M. Maitlis, Angew. Chem. 1991,103.
370; Angew. Chem. Int. Ed. Engl. 1991.30, 375; P. Espinet. M. A. Esteruelas, L. A. Oro, J. L. Serrano, E. Sola, Coord. Chem. Rev. 1992, 117, 215;
Inorganic Materials (Eds.: D. Bruce, D. OHare), Wiley, New York, 1992.
121 P. Espinet, J. Etxebarria, M. Marcos, J. Perez, A. Remon, J. L. Serrano,
Angew. Chem. 1989,101,1076; Angew. Chem. Int. Ed. Engl. 1989,28,1065.
I31 M. Marcos, J. L. Serrano, T. Sierra, M. J. Gimenez, Angew. Chem. 1992,
104, 1523; Angew. Chem. Inl. Ed. Engl. 1992, 31, 1471.
[4] J. Barbera, P. Espinet. E. Lalinde, M. Marcos, J. L. Serrano, Liq. Cryst.
1987, 2, 833; P. Espinet, E. Lalinde, M. Marcos, J. Perez, J. L. Serrano,
Organomerallics 1990, 9, 555; P. Espinet, J. Perez, M. Marcos, M. B. Ros,
J. L. Serrano, J. Barbera, A. M. Levelut, &id. 1990,9,2028; M. B. Ros, N.
Ruiz, J. L. Serrano, P. Espinet, Liq. Crysr. 1991, 9, 77; M. J. Baena, P.
Espinet, M. B. Ros, J. L. Serrano, Angew. Chem. 1991, 103. 716; Angew.
Chem. Inr. Ed. Engl. 1991, 30, 711.
[S] The phases observed were characterized with a polarizing microscope; the
abbreviation S, that appears later in the text refers to a smectic A phase
characterized by an untilted, liquid-crystalline layer structure.
0570-0833i93j0808-1202 S 10.00+.25jO
Angew. Chem Int. Ed. Engl. 1993, 32. No. 8
[6] Other examples ofcompounds with double-melting behavior: K. Ohta. M.
Yokohama, S . Kusabayashi, H. Mikawa, J Chem. Sor. Chem. Commun.
1980,392; K. Ohta. H. Muroki, K. 1. Hatdda, 1. Yamamoto, K. Matsuzaki. Mol. Cryst. Liy. Cryst. 1985, 130, 249; K. Ohta, H. Muroki. K. I.
Hatada. A. Takagi. H. Ema, I. Yamamoto, K. Matsuzaki, ibid. 1986, 140,
163; K. Ohta. H. Ema. H. Muroki, I. Yamamoto. K. Matsuzaki, &id.
1987. 147, 61.
[7] The nonequivalence of the two halves of the dimer caused by the chiral
center becomes apparent only at - 20 "C in the 'H NMR spectrum: at this
temperature the t w o nonequivalent Haatoms give rise to two very close but
distinct singlets.
Modified complexes of type 4 have been measured. and frequency doubling was observed: J. Zyss, I. Ledoux, J. Martin, J. Buey, P. Espinet,
[a];" of the complexes ( c =1, CH,CI,): 4a, -8.8; 4b, -8.0; 4c, -7.7.
R. Cano. Bull. Soc. Fr. Mineral. Cristallogr. 1967, 90. 333. Cholesteric
mixtures containing about 20 wt% of the chiral additive were placed hetween a flat glass slide and a spherical lens. Both surfaces were rubbed to
provide a uniform planar anchoring. The disclination rings in the sample,
which correspond to steps ofp/2. were observed using a polarizing microscope. The pitch p was calculated from the diameters of these rings.
H. Finkelmann, H. Stegemeyer, Z. Naturforsch. A 1973, 28, 799.
G. Heppke. D. Lotzsch. F. Oestreicher, 2. Naturforsch. A 1987, 42, 279.
L. Komitov, S. T. Lagerwall, B. Stebler. G . Anderson, K . Flatiscler, Ferroelimrics 1991. 114, 167.
A. J. Slaney, I. Nishiyama, P. Styring, J. W. Goodhy, J. Mater. Chem. 1992,
2. 805.
and SmA phases at noticeably lower temperatures. Thus the
monomeric complexes may be taken repeatedly to the
isotropic state without signs of decomposition.[41
Taking these two observations into account, we aimed to
synthesize ferroelectric metallomesogens with low transition
temperatures, which would allow potential applications as
both liquid crystals and in nonlinear optics.16' Our first approach was the introduction of chirality in the alkyl chains
of the above-mentioned acac complexes,[41but this did not
lead to the desired SmC* phases. However, analogues 3 a
(n = 10) and 3 b ( n = 14) with modified 8-diketonate ligands
formed a ferroelectric SmC* liquid crystalline phase at lower
temperatures, showed thermal stability under working conditions, and displayed switching times a thousand times
shorter than that of the first ferroelectric metallomesogen
The synthesis of compounds 3 from 1 (Scheme 1) proceeded via the dinuclear complexes 2. The reaction of 2a, bC5]
with thallium(1) P-diketonate['I in CH,Cl, provided the
mononuclear complexes 3a and 3b, respectively. Both complexes gave correct elemental analyses, and 'H NMR and IR
spectra in full agreement with the structure proposed.
Improved Properties of Ferroelectric Liquid
Crystals from Palladium fl-Diketone Complexes**
By Maria Jesus Baena, Pablo Espinet,* Maria Blanca Ros,
Jose Luis Serrano," and Amaya Ezcurra
Ferroelectric liquid crystals (FLCs)"] are one of the main
interests in research on liquid crystals. Although many organic mesogens are known for FLCs, there are few examples
of analogous metal complexes['. 3l and most of them have
high transition temperatures that affect their thermal stability. The first FLC metallomesogen reported,['] a dimeric
ortho-palladated azine complex (a mixture of isomers), displayed some undesirable drawbacks : high transition temperatures (K 102°C SmC* 119°C SmA 149°C I) leading to
thermal instability in the mesophases and a very long switching time (nearly one second). We then discovered that altering the highly symmetrical molecular shape of these dimers
results in lower melting
Whereas dimeric compounds [{(C-N)PdCl),] (C-N = ortho-palladated imine with
long alkyl chains) form SmA and SmC phases at high temp e r a t u r e ~monomeric
complexes [ (C-N)Pd(acac)] form N
[*] Dr. P. Espinet, M. J. Baena
Quimica Inorganica, Facultad de Ciencias
Universidad de Valladolid
E-47005 Valladolid (Spain)
Telefax: Int. code + (83)423-013
Dr. J. L. Serrano, Dr. M. 8 . Ros
Quimica Organica, Facultad de Ciencias-I.C.M.A.
Universidad de Zaragoza-C.S.I.C.
E-50009 Zaragoza (Spain)
Telefax: Int. code + (76)567920
Dr. A. Ezcurra
Fisica Aplicada 11, Facultad de Ciencias
Universidad del Pais Vasco, Aptdo. 644
E-48080 Bilbdo (Spain)
This work was financed by the Comision lnterministerial de Ciencia y
Tecnologia (Projects MAT90-0325, MAT90-0813, and MAT91-0962C0201) and the Consejeria de Cultura de la Junta de Castilla y Leon. M. J. B.
thanks Iberduero for a fellowship. We thank Dr. J. Barhera for the X-ray
measurements and M. M. Zurbano for supplying the 8-diketone. Abbreviations: C = crystalline, SmC' = chiral smectic C phase,
SmA = smectic A phase, I = isotropic, N = nematic, FLC = ferroelectric
liquid crystal.
Angen.. Chem. Int. Ed. Engl. 1993, 32, No. 8
l a (n : 10)
l b ( n : 14)
Pa (n : 10)
2b (n : 14)
3a (n : 10)
3b (n : 14)
Scheme 1. a) Pd,(AcO),/AcOH; b) HCIIMeOH; c) TI [p-H,,C,,OC,H,CO),.
The thermotropic behavior of the 8-diketonate derivatives
was studied by optical microscopy and differential scanning
calorimetry (DSC) at 10 Kmin-' (Table 1). Smectic A and
chiral smectic C phases were assigned on the basis of their
optical textures and confirmed by X-ray diffraction studies.
The chiral smectic C phase showed a characteristic focalconic texture, and no dechiralization lines were observed.
The ferroelectric properties of these two 8-diketonate complexes-spontaneous polarizations (P,), switching times (T~),
viscosities (y,), and tilt angles (+are
summarized in
Table 1.['I Figure 1 shows the dependence of P, and 0 of the
ferroelectric palladium complexes on temperature.
These metallomesogens have moderate P, values with
maxima at 29 and 22 nCcm-' for 3 a and 3 b respectively,
and maximum optical tilt angles very close to the optimum
tilt angle in FLCs of 22.5". It is noteworthy that the tilt
angles could not be calculated from the X-ray diffraction
measurements, as no significant differences between the layer thickness at the SmA and SmC* phases were detected.['']
The switching times of the new ferroelectric palladium
complexes 3a, b are on the order of milliseconds. Although
this is noticeably slower than the switching times of typical
organic FLCs (microseconds), these new complexes switch
three orders of magnitude faster than the first palladium
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cholesterol, mesophases, metallomesogens
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