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Conjugated Liquid Crystalline Polymers.

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can be exchanged with D,O. Thus, two insertions of two
adamantylidenes into two different 0 - H bonds of fl-CD
have taken place. The absolute amount of OH insertion
products 4 B-CD and 5 . 8-CD detected by FAB mass spectrometry (Scheme 1 ) is not yet known. Since these compounds could not be found by CP/MAS I3C N M R spectroscopy. they must have been formed each in less than 5 YO
yield.
Adamantylidene is believed to be a ground-state singlet
carbene. and the generation of the triplet state fails even in
the presence of photosensitizers.'t51 The question of whether
adamantylidene entrapped in ,6-CD is also a singlet cannot
be answered a t this time. Laser flash photolysis studies may
solve this problem, as well as answer questions concerned
with the detailed differences in the reactive behavior of a
"free" adamantanylidem and a (partially) entrapped one.
[XI FAB mass spectra were obtained by bombarding the samples in a glycerol
o r trieihanolainine matrix with approximately 33 keV bcam of Cs' ions,
and the desorhed ions were analyzed with the first stage of ii VG analytical
ZAB-T four-sector mass spectrometer. Exact mass measurements were
within <3.8 ppm of theoretical values. Collisional activation of the i n / :
1267.4 ion and mass analysis of products with the second stage produces
~ Hmass
~ ~ .
evidence for rupture of the C D ring hut not for loss O ~ C ~ , The
Enxrnol.
spectrometer was briefly described by M. L. Gross M~th~ds
1990,193,131.
[9] The calculations were performed with the SYBYL 6.0 version from Tripos
Associates, Inc., o n an 4D/35 IRlS workstation from Silicon GraphicsJnc.
The "dock molecules" program was used to obtain the total energy o f t h e
complex with consideration of different possible conformations of I within
{KD.
[lo] For the aziiie formation at least three mechanisins have to be discussed.
two of them require the intermediacy of a carhene (see ref. [ j b ] rol. 1. p.
111).
[I 11 In addition, variable amounts of adamantanone were formed.
[l2] S. D. Isaev, V. P. Sherstyuk. 0.
F. Ko~lov.V. Skripkin. I Yanku. 7iw.
Eksp. Kliin?. 1991. 27, 211.
1131 R. Kupfer, planned Ph.D. dissertation. State University of New York at
Binghamton.
[I41 This sample which contained "empty" and "filled" p-CD molecules (ratio:
CB.2:l. determined by N M R spectroscopy) was treated with D,O in order
to exchange the number of active hydrogen atoms. The ( M - H)-ion of
/ K D shifts from in/: 1133.4 to 1153.4. indicating that all 21 active hydrogen atoms of [i-CD had been replaced with deuterium atoms. and that an
(,"I
- D ) - ion had been desorbed. The exchange was not complete: there
were still some isomers with 20.19.18. and 17 deuterium atoms, but i t was
the most exchange that could be accomplished. For 4 . /I-CD, 20 active
hydrogen atoms could be exchanged as indicated by a shift from rn/z
1267.4 for ( M - H)- to i?i/z 3286.5 for ( M D).. One aclive hydrogen
atom was lost owing to carhene insertion into an 0 - H bond.
[IS] S. Morgan, J. E. Jackson. M. S. PlatL, J. A m . Clinn. Snc. 1991.113, 2782.
1161 a ) D. J. Martella. M. Jones. Jr.. P. von R. Schleyer. W. F. Maier. J Am.
Chrm Soc. 1979. 101. 7634: b) D. Lcnoir. J. Firl. Li~higrAiiri. ChPiii. 1974,
1467.
[17] J. Michl. G. J. Radziszewski. J. W. Downing. K. B. Wiberg. F H. Walker,
R. D. Miller. P. KOvd~ib.M. Jawdosiuk. V. BonaCit-Koutecky, Pure Appl.
Chrin. 1983.55,31 5.
[18] This could also mean that adamantene 6 is not formed from the carhene 2
but from the diazirine 1 or the rearranged linear diazo precursor (see J. E.
Jackson. M. S. Platz in Advancer in Curbent, C/rriiii.srr>.,vol I (Ed.: U . H.
Brinker), JAI. Greenwich, CT, in press.
~
If the carbene 2 . 8-CD cannot easily encounter another
reaction partner, it could rearrange to the highly strained
adamantene 6, which is known to dimerize[l6I immediately,
although it has been shown to exist in a matrix at low temperature." 1' This reaction, however, does not appear to take
place if adamantylidene 2 is entrapped in B-CD.""
In conclusion, our results strongly suggest that we have
established the first intra- and intermolecular carbene insertions within any constrained molecular reaction vessel.
Erperinientol Procedure
I . /i-CD: A solution of 1 (0.49 g, 3 mmol) in diethyl ether ( I 2 mL) was added
to a solution of 8-CD hydrate (3.4 g, 3 mmol) in water (150 mL). After the
mixture had been stirred for one day. the precipitate was filtered off. washed
9evera1 tiines with water and ether. and then dried in the desiccator. Yield: 2.9 g
(2.4 mmol. 81 I!'")
Received: March 17. 1993
Revised: April 30. 1993 [ Z 5933 IE]
German version: Angeir. Cbern. 1993,f 0 5 . 1427
Plio/ol.henii.\/r~in Orgunired und Constrained Mediu (Ed. : V Ramamurrhy), VCH, Weinheim. 1991
a ) W Kirmse. Curhenr C/im?r.s/rj.,Academic Press. New York. L971:
b) Crirbmr,s. w/.s. I - 3 (Eds.: M. Jones. Jr., R. A. Moss), Wiley, New York.
1973. 1975. 1978: c) W. M.Jones. U. H. Brinker in Pericjclic R~uc/ioiis
(Eds.: A. P. Marchand. R. E. Lehr), Academic Press, New York, 1977:
d ) Mclhodm Org. Chein. (Houhcii-W q l ) 4111ed. IYS2-. vol. E19, 1989.
a ) M. Komiyama. H. Hirai. Bull. Clieni. Soc. Jpn. 1981.54.2053;b) J Ant.
C h o ~ iSoc.
.
1983.f O 5 . 2 0 1 8 ; ~ C.
) J. Ahelt. J. M. Pleier. J. Org. C A m . 1988,
53. 2 159.
Siiicc 1 sublimes easily. it should he kept in the freezer.
~n,
Berlin, 1967;
a ) E. Schmi tz, D r ~ i r i n pmi[ z w i H ~ ~ r m t o m rSpringer,
h) C / i ~ ~ i i i i . o/
\ / r Diuzirines.
~
i'ols. 1, ff (Ed.: M. T. H. Liu), CRC Press. Boca
Raton. FL. USA. 1987.
S. D. Isaev. A. G. Yurchenko, F. N. Stepanov, G. G. Kolyada. S. S.
Novikov. N. F. Karpenko. Zh. Urg. Khiin. 1973. Y, 724.
In I 8 - C D the signals at 6 = 27- 28 and 37 appear as doublets: when
rcsolution enhancements were applied !hey became two distinct signals.
For a physical mixture, these signals remained singlets. Cross polarization
dynamics, as measured by the contact time and the proton rotating-frame
reliixation time T,,(H). differed between 1 p-CD and the physical mixtui-e. indicating a single proton-spin reservoir for the complex and two
distinct proton-spin reservoirs which are separated in space for the physical niixture (see 1. R. Garbow, B. J. Gaede, J. Agric. Food Cheii?. 1992,40.
Conjugated, Liquid Crystalline Polymers**
By Luping Yu,* Zhenan Bao, and Rubing Cui
Liquid crystalline (LC) polymers are of great interest in
fundamental science and the development of advanced materials.[" Three main types of LC polymers have been extensively studied: 1 ) side-chain LC polymers, 2) main-chain LC
polymers with flexible spacers, and 3) rigid main-chain LC
polymers. The study of type 3 LC polymers stemmed from
the discovery that poly(p-phenyleneterephthalamide) forms
an LC solution from which high-modulus fibers may be
spun.[2.31 These polymers are particularly important because
of their exceptional strength and high-temperature properties induced by the LC ordering. However, since these materials are not very soluble, fabrication is extremely difficult.
To overcome these problems, in recent years there has been
considerable efforts to prepare LC polymers with a rigid
['I
'
156).
Prof. L. Yu, Z. N. Bao
Department of Chemistry, The University of Chicago
5735 S. Ellis Avenue, Chicago. IL 60637 (USA)
TelePax: Int. code (312) 702-0805
Dr. R. Cai
The Sherwin-Williams Co, Chicago IL
This work was supported by the Office of Naval Research (grants N0001493-1-0092), the Camille & Henry Dreyfus Foundation (New Faculty
Award), and The Petroleum Research Fund, administered by the American Chemical Society.
+
I**]
main chain and flexible side chains, for example, polyamides
and polyesters with alkyl side chains.'4]
In the past decades, conjugated polymers have attracted
much attention due to their electrical properties, for example
conductivity, and optical properties;['however, structural studies of these materials have been
Their
potential as liquid crystalline materials has not yet been explored largely because traditional conjugated polymers are
intractable and infusible.[5
Nevertheless, conjugated
polymers obviously have a stiff chain which could act as the
mesogenic unit and lead to properties known for type 3 LC
polymers. In these compounds electrical. optical, and liquid
crystalline properties are interrelated. For example, the conductivity and the third-order nonlinear optical (NLO) susceptibility strongly depend upon the orientation of conjugated polymer chains.[61After a conjugated polymer is aligned
by mechanical stretching, the conductivity parallel to the
stretching directions is much greater than in the perpendicular direction, and the anisotropy of physical properties is
enhanced.
These considerations have led to the synthesis of soluble
and fusible conjugated polymers.[61Recently, we found that
the Stille reaction is very versatile for the synthesis of conjugated polymers.[g1We prepared poly( 1,4-phenylene-2,5-thiophene) with different alkyi side chains utilizing this reaction
(Scheme 1). Our latest studies show that these polymers form
OCnH2n+ 1
X
G
X
OC"H2"+1
~~
t
+(y&
H2,+ ,CnO
5
described in detail elsewhere.[', 'I The spectroscopic studies
(NMR, FT-IR, UVjVIS) and elemental analyses support the
structures we proposed.
Thermogravimetric analyses (TGA) show that all of these
polymers remain stable up to 400 "C under nitrogen. Thermograms obtained from differential scanning calorimetry
(DSC; DuPont 90 calorimeter) were recorded at heating
rates of 10 "Cmin-' under a nitrogen flow. Polymers A, B,
and C show glass transition temperatures (second-order
transition) at 100, 90, and 75 "C, respectively. All of these
thermograms display at least two transitions as the temperature is increased from 50 to 300 "C (Fig. l), corresponding to
the melting of the side chains (T',,*) and the backbones ( Tm2).
Two more transitions above the sharp melting transition for
polymer A can also be noted. The higher temperature transition corresponds to the transition (T,) from the liquid crystalline to the isotropic phase and was confirmed by the optical microscopy. The other transition cannot be assigned,
although the difference between the phases in these two temperature regions is apparent in the X-ray diffractogram
(Fig. 2). Similar behavior observed in aromatic polyesters"
\
/
* C ? L +1
26 ["I
A-H
-
Scheme 1. Synthesis of poly(1,4-phenylene-2.5-thiophene) A-H. A: n = 4, B.
n=5,C:n=6.D:n=l,E:n=8.F:n=9,G:n=l2.H:n=16.[Pd(PPh,),CIJ was used as catalyst when X = I, [Pd(PPh,)&LiCI when
X = CF,SO,.
Fig. 2. Results of a temperature-dependent X-ray diffraction experiment with
synchronized radiation. Each experiment lasted 8 h. The Pt line was used for
calibration. the X-ray soiirce was Ni-filtered Cu,, radiation.
nematic phases when they are heated above their melting
points, proving that conjugated polymers may also be liquid
crystals. This paper reports our results on the LC properties
of polymers A-H; the syntheses and physical properties are
has been ascribed to the smectic-to-nematic phase transition.
However, polymer A did not show any typical smectic patterns under the optical microscope.
Since we could not detect the nematic-to-isotropic phase
transition of other polymers having alkyl side chains with
more than eight carbon atoms by DSC measurements, polarizing microscopy was performed (Nikon HFX-IIA microscope equipped with a Linkam (TMS-90) hot stage). All of
the polymers exhibit a birefringent fluid melt above their
melting temperatures and a characteristic shear opalescence,
indicating a nematic phase. Figure 3 shows the textures of
the mesophases of polymers A and E. Typical schlieren textures can be seen, further demonstrating the presence of a
nematic phase. Both DSC studies and observations from
polarizing optical microscopy indicate that the melting and
the clearing transition temperatures are affected by the
lengths of the side chains. In Figure 4 the transition temperatures of polymers A-H are plotted against the number of
carbon atoms n in the alkyl side chain. As n increases, the
melting (T,) and clearing temperatures (T,) of the polymers
decrease steadily. Depending upon the length of the side
chain, the liquid crystal range is between 56 and 20 "C.
The X-ray diffraction studies indicate that the polymers
precipitated as crystailine materials. The X-ray diffraction
results for polymer A with a synchronized diffractometer are
shown in Figure 2. Two strong diffraction maxima at 26
values of 10 and 23.5" can be noted. As temperature was
increased, the spacings at 8.51 and 3.79 A increased due to
AH
I
I
50
.
v-
A
n=4
. . . . . . . . . . .
100 150 200 250 300 350
T["C]
Fig. 1. DSC thermogrdms of polymers A, C, D. and G; heating rate
10 "Cmin-', nitrogen atmosphere. The polymers were annealed before the
DSC scan: polymer A, 145 C for 12 h ; polymer C . 100°C for 12 h; polymer D.
115'C for 16 h ; polymer G . 65°C for 12 h.
1346
$3
VCH Yerlrgsge.~ellrchu/rn h H . 0-69451 Weinham, 1993
OS70-0833193/0909-1346 S 10.00
+ .25/0
A n p i . Chem. Inl. Ed. Engl. 1993, 32, N o . 9
ity of polymers can be controlled by the length of the side
chains. We also can easily change the structure of the conjugated main chain. For example, the 2,5-linkage of thiophene
results in a main chain with a bent structure, and the chain
packing should thus be different from that of polymers with
linear structures such as 2,5-phenylene and 1,4-naphthaIene.
(Although polyphenylene has been synthesized before, to
our knowledge no liquid crystal property study was reported.) Our findings should serve as a basis for further investigations of LC behavior in conjugated polymers.
Received: March 15, 1993 [Z 5926 IE]
German version. Angeu. Glum. 1993. 105. 1392
Fig 3 The textures of the mesophases of polymers A (top) and E (bottom)
under crossed polarirers at 220 ' C and 159 'C, respectively, ( x 100). The arrows indicate the recognizable singularities S = _+ 1/2.
thermal expansion. As the temperature increased above the
melting temperature, these two diffraction peaks became
very diffuse (barely visible), which is typical for a nematic
phase.
h
300
I\.
100
2
4
D
6
Structure and Electrochemical Behavior of the
Paramagnetic Anion [Ir14(CO)2,]-,Possessing a
Trigonal Bipyramidal Arrangement of Metal
Atoms**
By Roberto Della Pergola, Luigi Garlaschelli,*
Mario Manassero, Norbert0 Masciocchi,*
and Piero Zanello*
'
K
[I] Liquid Crystalline Polymers, ACS Svmp. Ser. 1990, 435.
[2] P. W. Morgan, Macromo1ecule.s 1977, 10. 1381.
[3] S. L. Kwolek, P. W. Morgan. J. R. Schaefer, L. W. Gulrich, Mucromolec.ules 1977, 10, 1390.
I41 M. Ballauff, Angew. Chem. 1989, 101, 261 ; Angrw. Chrm. I n t . Ed. Engl.
1989, 28. 253, and references therein.
[5] Handbook ofcond~rctingpo1vmer.s.Vol. 1,2(Ed.: T. A. Skotheim). Dekker,
New York, 1986.
[6] Ele~troresponsisP Molecular and Polymeric Sysrems, Vol 2 (Ed.: T. A.
Skotheim), Dekker, New York. 1991.
[7] Conjugated Conducting Po1vmer.s ( S p r q e r S w . SulidStute Sci. 1992. 102).
181 T. J. Pross. M. 1. Winokur. J. Moulton. P. Slith. A. J. Heeger, Motmrnolecu1e.s 1992, 25, 4364.
[9] Z. N.Bao, W. K. Chan, L. P. Yu, Chem. Muter. 1993, 5. 2
[lo] Z . N. Bao, L. P. Yu. Macromolecules. submitted.
1111 M. Ballauff, G. F. Schmidt, Mol. Cryst. Liq. Cryst. 1987, 147. 163.
[12] M. Ballauff, Mut.romolc.cuks 1986. 19. 1366.
8
10
12
14
16
1:B
20
n Fig. 4. Transition temperatures of polymers with different alkyl side chains.
From these results, we can see that polymers A-H have
promising LC properties. Ballauff has pointed out that the
side chains behave more o r less like bound solvent molecules,
rendering the polymer soluble and fusible.[121This model of
bound solvent molecules accounts for the change in the transition temperature as a function of the length of the side
chain.
We have shown clear evidence of a nematic LC phase for
the new conjugated polymers A-H, which were prepared by
the Stille coupling reaction. Certain properties of the polymers such as transition temperatures, solubility, and fusibilA n g m Chrm. lnr Ed. Engl. 1993, 32, No. 9
The number of well-defined and structurally characterized, high-nuclearity clusters is increasing, but slowly. Knowledge in this field is somehow hampered by experimental difficulties: most compounds are obtained in very small
amounts with reactions of low reproducibility, and the characterization is simply restricted to the crystal structure. In
other cases in which a large number of physico-chemical
measurements are available, high nuclearity clusters have
been shown to possess unusual properties which deserve
more detailed investigation.["
Within the latter group, [Ir,,(C0),,]2-~21 and [Ir12(CO)24]2-[31were obtained by oxidation of [Ir6(C0),,]*with [Cu(NCCH,),]+, through the intermediacy of the
['I
[**I
Prof. L. Garlaschelli, Dr. R. Della Pergola
Dipartimento di Chimica lnorganica e Metallorganica
via G. Venezian 21, 1-20133 Milano (Italy)
Dr. N. Masciocchi, Prof. M. Manassero
Istituto di Chimica Strutturistica Inorganica
via G. Venezian 21. 1-20133 Milano (Italy)
Prof. P. Zanello
Dipartimento di Chimica dell' Universiti
Pian dei Mantellini 44, 1-53100 Siena (Italy)
We acknowledge the financial support of the Minister0 dell'Universiti e
della Ricerca Scientifica et Tecnologica (MURST) and of Consiglio Italiano delle Ricerche (CNR). ESR spectra were recorded by Prof. Franca
Morazzoni. to whom we are indebted.
c) VCH Verlagsgesrllschuft mhH, 0-69451 Weinheim, 1993
0S70-0~33!93/0909-1347$ 10.00f ,2510
1347
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