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[7] a) R. Kersting. U . Lemmer, R. F. Mahrt. K. Leo, H. Kurz, H. Baessler, E. 0. Goebel, P h j s . Rev. Lett. 1993. 70, 3820. b) C . Heller, I . H. Campell, D. L. Smith, private communication.

[K] K. S. Woo. 0. Lhort, S. C. Graham, D. 0. C. Bradley, R. H. Friend. C. Quattrocchi. J. L. Bredas. R. Schenk, K. Mullen, Synrh. M e f . 1993.59, 13.

[9] J. Hcinzc, I. Mortenson. K. Miillen. R. Schenk, J. Chrm. Soc. 1987, 701. [I 01 K. Meerholz, H. Gregorius, K. Mullen. J. Heinie. Adv. Muter. 1994,6,671. [ l l ] M. Fahhnann. 0. Lhost. F. Meyers, J. L. Bredas, S. C. Graham, R . H.

Friend. P. L. Burn, A. B. Holnies. K. Kaeriyama. Y Sonoda. M. Logd- hind. S. Strafstroin. W. R . Salaneck, Sj,rilh. Mrf. 1993, 55-57. 263.

[12] J. L. Bredas, R. R. Chancc. R. H. Baughman, R. Silbcy, J. Chem. Phj>s. 1982, 76, 3673.

[I31 A. W. Adainson in A 2wthook of Phy.sicu( Chemistry, Academic Press, New York. 2nd cd. 1979. pp. 669-673.

[I41 M. J. S. Dewar. W. Thiel. J ilm. Chcm. Soc. 1977, 99. 4899. [I51 M. J. S. Dewar. W. Thiel. J. .4m. Chern. Soc. 1977, 99, 4907. 1161 M. J. S. Dewar. E. G. Zoebisch, E. F. Healy, J. J. P. Stewart, J. An?. Chem.

[I71 .I. J. P. Stewart. J Cunip. Chem. 1989, 10. 209. [I81 J. J. P. Stewart, J Comp. Chfwi. 1989, 10, 221 [I91 S. C. Graham. D. I). C. Bradley. R . H. Friend. C. Spangler, Sj'nrh. M ~ I .

Soc. 1985. 107. 3902.

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[21] J. L. Lcng, S. Jeglinski, X. Wci, R. E. Benner, Z. V. Vardeny, F. Guo, S.

[22] M . Chandross. S. Mammdar. S . Jeglinski, X. Wei, Z. V. Vardeuy, E. W.

[23] M. Helbig. H. -H. Hijrhuld. Makromol. C/irm. 1993, 194, 1607. [24] A. Schmidt, M. 1.. Anderson. N. R. Arinstrong, J. Appl. Phys. 1995. in

[25] R . Schcnk, H. Gregorius. K. Meerholz. J. Heinze, K. Miillen, J . Am. Chml.

[26] H. Liith. Swffut.e\ and Ifiierfcrcrs ofSolids, Springer. Berlin 1993, pp. 470.

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Soc. 1991, 113, 2634.

Synthesis of Novel Polymers Containing Cyclo- butadiene Thiophene and Alkyne Units : Polymeric Organometallic Mesogens""

By Maukus Altmann, Volker Enkelnqann, Giinther Lieser, and Uwe H . F: Bum*

Organometallic polymersi1 - 31 hold a great future poten- tial for the design of electroresponsive,i21 NLO active[41 and liquid crystalline materials,i31 even though only a few (com- pared to organic polymers) polymeric organometallic sys- tems have been synthesized to date and even fewer have been scrutinized according to their physical and material science properties. The most prominent examples of organometallic polymers include Hagiharas' liquid crystalline platinum or palladium-alkyne copolymers (which also show interesting nonlinear optical properties) and Dembeks' Cr(CO),-substi- tuted a r a m i d e ~ ' ~ ~ ] (first prepared by Jin et al.[3h1) which both show lyotropic nematic liquid crystalline behavior.13]

We, on the other hand, are interested in the chemistry and materials science of ethynyl-substituted cyclobutadiene com- plexes and their use as building blocks in the synthesis of

["I Dr. U. H F. Bun/, M . Altmann. Dr. V. Enkclmann, Dr. G. Liescr Max-Planck-lnstitut f i r Polymerforschung Ackerniannweg 10, D-55021 Mainz (FRG)

[**I This work has been supported by the DFG. Stiftung Volkswagenwerk, and the Fonds der Chemischcn Industrie. UHFB is a D F G scholar (1994- 1996) and thanks Prof. K. Mullen and A. Runz for generous support.

polymers and star-shaped arrays utilizing Stille or Heck-type couplings.[51 Specifically, we are interested in the synthesis of liquid crystalline rigid-rod polymers containing [ 1,3-(di- ethynyl)cyclobutadiene]cyclopentadienylcobalt moietiesL6] and the engineering of their phase properties in dependence of their side groups.

While the homopolymer of 1 is crystalline, a copolymer of 1 with 2,5-(dihexy1)benzene exhibits thermotropic behav- ior.[61 In this communication we wish to report the synthesis of a new class of organometallic polymers containing thio- phene and the unusual phase behavior of a copolymer of 1 with 3-hexylthiophene forming a smectic lyotropic liquid crystalline phase.

Diethynyl 1, which has been prepared 1979 by Vollhardt['] is available on a multigram scale and was used as a monomer. The synthesis of 3a-e is achieved by a typical Heck coupling of 1 with 2a-e in piperidiner8I as solvent and base, using CuI and PdCI,(PPh,), as catalysts. The typical reaction time is 18 h (see Scheme 1). The polymers 3 are isolated as ochre-yellow and air stable powders in yields between 77 -84 O%.

SiMe3 I

1

Scheme 1

2

n

3

Both NMR-spectra and IR-spectra of 3a-e confirm the absence of terminal alkyne functionalities. While the NMR- spectra of the parent 3a and of 3d and 3e are simple due to their high symmetry, in the case of 3b and 3c the spectra are complicated due the fact that the mono-substituted thio- phenes can be incorporated into the polymer in three differ- ent ways (Scheme 2). If only the cases A and B would occur, a doubling of the observed signals is expected. For the situa- tion C another set of seven signals (1"-7") should be ob- served.

In the I3C-NMR spectrum of 3b a split of the signals into two sets of roughly equal intensities indicates that A and B are predominant. A third set tentatively assigned to C is almost hidden under noise. The reason for the much lower abundance of C might be due to the fact that 1 first reacts

Communications ADVANCED MATERIALS

A B

C

Scheme 2.

with the sterically least crowded side of 2b so that mostly A is formed. In later stages of the reaction B forms by reaction of two A fragments with 1.

The molecular weights (GPC, Table 1) of 3a-e show typ- ical P, values between 15 and 40 depending on the sub- stituent pattern of the utilized thiophene monomer. We were able to corroborate these results by elemental analysis, find- ing values of iodine in the range between 3 and 5 %, allowing us to estimate P, independently. This holds under the condi- tion that all end groups are iodine-carrying thiophenyl units and that dehalogenation processes can be ignored.

Table 1. Substituent key for 2 and 3, yields of 3 and GPC (polystyrene standard in chloroform) results of 3.

2,3 R’ R yield(3) M, (Id) M, (103) Pna Db

a H H 78% 8.10 12.0 18 1.44

b Hexyl H 82 % 14.0 30.0 27 2.14

c Dodecyl H 79 % 5.18 11.35 15 2.19

d Hexyl Hcxyl 81 % 9.60 29.0 15 2.99

e Dodecyl Dodecyl XI % 13.38 35.21 42 2.64

[a] P.: Degree of polymerization; [b] D = M,/M, , polydispersity

All of the obtained polymers show lyotropic nematic phases upon slow concentration of their solutions in chlori- nated solvents. The liquid crystalline phases were evidenced by observation of the typical schlieren texture which did not disappear upon complete removal of solvent. A frozen liquid crystalline phase is formed thus, in which the orientational long range order and the singularities of the parent phase are retained. An exception is observed in the phase behavior of 3b. Upon concentration it forms a fan-like texture (Fig. 1) typically observed in low molecular weight smectic com- pounds, but not in nematic phases.[g] Slow evaporation of a solution of 3a,c,d,e in dichloromethane yielded almost X-ray amorphous samples showing only a reflection at d = 10 8, corresponding to the intrachain Co- Co distance.

Fig. 1. Fan-type texture of a lyotropic sample of 3b under crossed polarizers. This picture has been taken in the frozen lyotropic state. The solvent used was chloroform.

Slow evaporation of dichloromethane of an anisotropic solution of 3b afforded a material which was crystalline due to X-ray powder diffractometry. Additionally, electron mi- croscopy and diffraction were performed upon dried thin films of 3b which had been used for polarization microscopy. In both cases the same set of reflections was observed. Select- ed area electron diffraction made it possible to examine ori- ented domains. The following reflections were observed : 10.08, (m), 8.1 8, (om), 6.1, 5.5, 4.6, 3.5, 2.68, (e) ( m = meridional, om = off meridional, e = equatorial) indicating the presence of a three dimensionally ordered phase.

In Figure 2 an electron micrograph of a thin film of 3b is shown. It was verified by electron diffraction that the chains are oriented parallel to the substrate. In analogy to the mor- phology of many polymers we interpret the quasi-regular systems of stripes in Figure 2 as lamellae seen edge-on. The thickness of the lamellae (ca. 30nm) corresponds to the length of a macromolecule. It is assumed that the polymer chains are oriented perpendicular to the lamellae surface so

Fig, 2. TEM of a dried shadowed sample of 3b showing the formation of lamellae.

A h , . M a w . 1995, 7, No. 8 0 VCIf Verlagsgesrllschuft mhH, 0-69469 Weinheim, 1995 0935-9648!9510808-0727 $5.00+ .25/0 727

ADVANCED MATERIALS

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that the end groups are preferentially located in the inter- lamellar region. The results of the diffraction experiments indicate that the polymer chains are in register, i.e. adjacent chains are arranged such that the cyclobutadiene residues are correlated with respect to each other. In this model rotation- al disorder is possible. The term smectic describes in this context the correlation between monomer units rather than between discrete polymer chains.

Similar results have been found previously with a number of different worm-like polymers substituted by flexible side chains (polydiacetylenes. substituted poly-p-phenylenes and phthalocyaninatopolysiloxanes) in frozen lyotropic phases."" The high order of crystallized 3b is in agreement with the assumption of the transient formation of a smectic lyotropic phase. In order to characterize this smectic lyo- tropic phase a diluted sample of 3b was slowly concentrated by evaporation of trichlorobenzene solutions and different stages of this process were monitored by X-ray diffraction.

In the diluted solution no sharp reflections are seen. After most of the solvent had evaporated, sharp peaks of all equa- torial reflections appear. In the area where in the crystallized sample non-equatorial reflections are located, a broad re- gion of scattered intensity is observed. This is in accordance with the scattering behavior of a smectic phase, where the equatorial reflections are retained, and the meridional and the off-meridional reflections transform into streaks which in the diffraction pattern of a non-oriented sample show up as broad features which we observe.

From the above experimental results we conclude, that the crystallization of 3b proceeds through the transient phase of a lyotropic smectic state, hitherto not observed in polymeric organometallic systems

Experimental The following is a typical polymerization procedure leading to polymer 3b.

The syiithcsis of the polymers 3a,c-e is completely analogous. An amount of 341 mg (0.926mmol) 1. 40.2 nig PdCI2(PPh,),. 8.8mg CuI (5 mol%) and 389 mg (0.926 mniol) 2b are stirred i n 40 mL of degassed and argon-fluqhed piperidine for 18 h at 21 'C. To remove ammonium salts the solution is filtered, the piperidine is removed under reduced pressure, the residue dissolved in chloroform and slowly precipitated into methanol. The precipitate is isolated by centrifugation. redissolved into chloroform and added to - 300 m L pentane where It forms a clear solution. Upon standing at - 30 'C for 48 h a precipitate of 3b develops and is isolated as ochre-yellow powder in 82%, which forms transparent films when cast quickly from chloroform onto a glass slide.

3a: IR (KBr): ,s[cni-'] = 3104 (C=C-H), 2955,2897 (C-H), 2182 (C=C) , 1445,1247,848; 'H-NMR (CD,CI,): 6 = 0.32 (s, 18 H. TMS-H), 4.98 (s, 5 H, Cp-H). 6.94 (s. 2H, thiophene-H): "C-NMR (CD,CI,): 6 = ~ 0.35 (q, TMS- C ) , 64.98. 76.37 (2 s, cyclobntadiene-C), 81.79 (d, Cp-C). 83.89, 93.93 (2 s, alkync-C). 125.31 (s. thiophene-C), 131.00 (d. thiophene-C).

3b: IR (KBr). v [cm-'] = 3105 (CEC-H), 2955, 2928, 2899 (C-H), 2182 (C=C), 1458, 1246. 847; 'H-NMR (CD,CI,): 6 = 0.13 (br.s, ISH, TMS-H), 0.91 (br.s. 3H, hexyl-CH,). 1.33 (hr.s, 6H. hexyl-H), 1.57 (br.s, 2H, hexyl-Hj, 2.57 (hr.s, 2H, hexyl-H). 4.98 (hr.s, 5H, Cp-H), 6.83 (br.s, thiophene-H); "C- NMR (CDIC1,): d = -- 0.24 (q. TMS-C), 14.25 (q. methyl-C). 23.04, 29.46, 30.07, 30.68, 32.09, (5 t. hexyl-C). 65.32. 65.08, 76.10, 77.08 (4 s, cyclobutadi- ene-Cj, 81.86(d, Cp-C). 83 60, X4.2X, 93.53, 95.78 (s, alkyne-C), 120.60, 123.70 (s, thiophene-C). 132 09 (d. thiophene-C), 147.03 (s, thiophene-C).

3c: IR (KBr) I' [cm '1 = 3105 (C=C-H), 2955, 2927. 2859 (C H). 2187 ( C K ) , 1451,1247.848: 'H-NMR (CD,CI,): 6 = 0.33 (s, 18 H, TMS-H), 0.89 (br.s, 3 H, dodecyl-CH,). 1.28 (br.7. 1 8 H. dodecyl-H), 1.55 (hr.s, 2H. dodecyl- H). 2.54 (br.s, 211. dodecyl-H), 4 97 (hr.s, 5H, Cp-H), 6.84 (br.s, lH, thiophene- H); I3C-NMK (CD,CI,): 6 = ~ 0.37 (q. TMS-C). 14.27 (q, dodecyl-CH,),

23.08, 29.54. 29.75, 29.83. 29.90. 30.04, 30.32. 30.74. 32.56 (9 t, dodecyl-CHz), 65.26,64.99,76.17, 76.09 (4s,cyclobutddiene-C). 81.71 (d. Cp-C), 84.27,83.59. 95.61, 93.48 (4 s, alkyne-C), 120.58. 123.68 (2 s. thiophene-C). 132.07 (d, thio- pheiie-C). 147.03 (s, thiophene-C).

3d: TR (KBr): 18 [cm-'1 = 3106 ( C z C - H). 2955, 2930, 2857 (C-H), 2185 (C=C) , 1469, 1246, 848: 'H-NMR (CDzC1,): 6 = 0 33 (hr.s, IXH, TMS-H), 0.90 (br.s, 6H, hexyl-CH,). 1 34 (br.s, 12H, hexyl-H). 1.56 (hr.7, 4H, hexyl-H). 2.53 (br.s. 4H, hexyl-H), 4.97 (br.s, 5H, Cp-H); "CC-NMR (CD,CI,): 6 = ~ 0.21 (q,TMS-C), 13.91 (q. hexyl-CH,), 22.73,28.79.7_9.50.30.44,31.83. (5 t. hexyl-C), 65.10, 75.57 (2 s, cyclohutadiene-C), 81.29 (d. Cp-C), 83.88. 95.07 ( 2 s. alkyne-C), 119.73 (s. thiophene-C), 145.42 (s, thiophene-C)

3r: IR (KBr): v[cm- '1 = 3106 ( C d - H). 2955, 2925. 2853 (C-H), 2187

'J(H,H) = 6.0 Hz. 6H. dodecyl-CH,). 1.28 (br.s, 36H, dodecyl-Hj. 1.53 (hr.s. 4H. dodecyl-H), 2.56 (br.s, 4H. dodecyl-H). 4.97 (s, SH, Cp-H); "C-NMR (CD,Cl,): 6 = ~ 0.20 (q. TMS-C). 14.29 (q, dodecyl-CH,). 23.3 1.29.21,29.78. 30.10, 30.24. 30.88, 32.35 (7 1. dodecyl-C). 65.51, 75.94 (2 s. cyclohutadiene-C). 81.66 (d, Cp-C). 84.31. 95.44 (2 s, alkyne-C), 320.09. (s. rhiophene-C). 145.80 (s, thiophene-C).

For the detection oflyotropic liquid crystalline phases a drop of a saturated solution of 3a-e in chloroform was spread onto a microscopy slide and held for 48 h in a small vessel in a saturated chloroform atmosphere while the solvent evaporated slowly. The samples (with an open upper surface) were inspected under a polarization microscope to reveal the presence of a schlieren or a fan-like texture.

(C=C) , 1466, 1247, 847; 'H-NMR (CD,CI,): 6 = 0.34 (s. TMS-H). 0.90 (t.

Received: February 22, 1995 Final version: April 12, 1995

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728 VCH ~ , r l L i g \ g [ ~ \ e l l ~ ~ h ~ ~ f nzhH 0-69469 Wemhefm I995 09754648 9510808-0728 $ 5 00+ 25 0 Adb Moter 1995, 7, No 8