A zirconocene-coupling route to substituted poly(p- phenylenedienylene)s: Band Gap tuning via conformational control

Article abstract of DOI:10.1021/ja9743811

A series of substituted poly(p-phenylenediyne)s (1a-f) was synthesized by the palladium-catalyzed cross-coupling condensation of terminal dialkynylalkanes with substituted diiodobenzenes. Polymerizations were conducted with 1,4-diiodo-5-hexoxy-2-methoxybe

Full text of DOI:10.1021/ja9743811

4354
J. Am. Chem. Soc. 1998, 120, 4354-4365
A Zirconocene-Coupling Route to Substituted
Poly(p-phenylenedienylene)s: Band Gap Tuning via Conformational
Control
Brett L. Lucht, Shane S. H. Mao, and T. Don Tilley*
Contribution from the Department of Chemistry, UniVersity of California, Berkeley,
Berkeley, California 94720-1460
ReceiVed December 29, 1997
Abstract: A series of substituted poly(p-phenylenediyne)s (1a-f) was synthesized by the palladium-catalyzed
cross-coupling condensation of terminal dialkynylalkanes with substituted diiodobenzenes. Polymerizations
were conducted with 1,4-diiodo-5-hexoxy-2-methoxybenzene or 1,4-diiodo-5-hexyl-2-methylbenzene and with
1,6-hexadiyne, 1,7-heptadiyne, or 1,8-octadiyne. Thus, six different poly(p-phenylenediyne)s (1a-f, [ArCtC-
(CH2)nCtC]m; Ar ) 5-hexoxy-2-methoxyphenylene or 5-hexyl-2-methylphenylene, and n ) 2, 3, or 4) were
obtained. Intramolecular zirconocene couplings of 1a-f afforded zirconacyclopentadiene-containing polymers
2a-f. These metal-containing polymers were then cleanly hydrolyzed to the substituted poly(p-phenylene-
dieneylene)s (3a-f, [ArCHdC(CH2)nCdCH]m; Ar ) 5-hexoxy-2-methoxyphenylene or 5-hexyl-2-methylphen-
ylene, and n ) 2, 3, or 4). Variation of the polymer structure allows for manipulation of the absorption and
emission maxima over the ranges of 316-524 nm and 437-619 nm, respectively. The optical properties of
model compounds 9a-f, (ArHCdC(CH2)nCdCHAr; Ar ) phenyl or 2,5-dimethoxy-4-methylphenyl, and n
) 2, 3, or 4) are very similar to those for polymers 3a-f. The structures of 9c (Ar ) 2,5-dimethoxy-4-
methylphenyl, n ) 2) and 9d (Ar ) phenyl, n ) 4) were determined by single-crystal X-ray crystallography.
Molecules of 9c are almost completely planar, while molecules of 9d are twisted and have poor π-orbital
overlap. The conformation of the diene unit in polymers 3a-f and the model compounds 9a-f are largely
responsible for the observed variations in optical properties. Finer tuning of the optical properties for poly-
(p-phenylenedienylene)s may be achieved via synthesis of copolymers from mixtures of 1,6-heptadiyne and
1,7-octadiyne. The optical properties of the resulting copolymers represent weighted averages for the
corresponding homopolymers. Investigation of the photophysical properties of polymers retaining some of
the diyne units suggest that defects play a major role in defining the emissive properties of the
poly(p-phenylenedienylene)s described here.
Introduction
gap and redox potentials.1i,2-4 The tuning of band gaps for
conjugated polymers has primarily been achieved via manipula-
tion of the polymer’s conjugation lengths,1i,2-4 for example, via
introduction of backbone substituents which result in confor-
mational disruption of more delocalized structures,2 or by
breaking the conjugation length at regular intervals with a spacer
In recent years there has been considerable interest in the
synthesis and properties of conjugated polymers, which combine
the processibility and mechanical properties of polymers with
the optoelectronic properties of inorganic semiconductors.1 They
have attracted interest in materials science for many potential
applications, including rechargeable battery electrodes, electro-
chromic devices, chemical and optical sensors, light emitting
diodes (LEDs), and nonlinear optical materials.1 The develop-
ment of specific functions for charge-transporting polymers
relies on manipulation of the polymer’s electronic properties
via chemical modifications. For example, the synthesis of light-
emitting polymers which produce a specific color is a chal-
lenging endeavor which requires tuning of the polymer’s band
(2) (a) Berggren, M.; Inganas, O.; Gustafsson, G.; Rasmusson, J.;
Anderson, M. R.; Hjertberg, T.; Wennerstrom, O. Nature 1991, 372, 444.
(b) Andersson, M. R.; Berggren, M.; Inganas, O.; Gustafsson, G.; Gustafs-
son-Carlberg, J. C.; Selse, D.; Hjertberg, T.; Wennerstrom, O. Macromol-
ecules 1995, 28, 7525. (c) McCullough, R. D.; Jayaraman, M. J. Chem.
Soc., Chem. Commun. 1995, 135. (d) Gill, R. E.; Malliaras, G. G.;
Wilderman, J.; Hadziioannou, G. AdV. Mater. 1994, 6, 132. Zhang, C.;
Hoger, S.; Pakbaz, K.; Wudl, F.; Heeger, A. J. J. Electron. Mater. 1993,
22, 413. (e) Grem, G.; Leising, G. Synth. Met. 1993, 57, 4105. (f) McCoy,
R. K.; Karasz, F. E.; Sarker, A.; Lahti, P. Chem. Mater. 1991, 3, 941.
(3) (a) Malliaras, G. G.; Herrema, J. K.; Wilderman, J.; Wieringa, R.
H.; Gill, R. E.; Lampoura, S. S.; Hadziioannou, G. AdV. Mater. 1993, 5,
721. (b) Kang, B. S.; Seo, M.; Jun, Y. S.; Lee, C. K.; Shin, S. C. J. Chem.
Soc., Chem. Commun. 1996, 1167. (c) Pei, Q.; Yang Y. AdV. Mater. 1995,
7, 559. (d) Hay, M.; Klavetter, F. L. J. Am. Chem. Soc. 1995, 117, 7112.
(e) Burn, P. L.; Holmes, A. B.; Kraft, A.; Bradley, D. D. C.; Brown, A. R.;
Friend, R. H. Nature 1992, 356, 47.
(1) (a) Feast, W. J.; Friend, R. H. J. Mater. Sci. 1990, 25, 3796. (b)
MacDiarmid, A. G.; Epstein, A. J. Faraday Discuss. Chem. Soc. 1989, 317.
(c) Patil, A. O.; Heeger, A. J.; Wudl, F. Chem. ReV. 1988, 88, 183. (d)
Handbook of Conducting Polymers; Skotheim, T. A., Ed.; Marcel Dekker:
New York, 1986. (e) Conjugated Polymers: The NoVel Science of
Technology of Highly Conducting and Nonlinear Optically ActiVe Materials;
Bredas, J. L., Silbey, R., Ed.; Kluwer Academic Publishers: Dordecht, 1991.
(f) Gibson, H. W. Polymer 1984, 25, 3. (g) Tour, J. M. Chem. ReV. 1996,
96, 537. (h) Bradley, D. D. C. Synth. Met. 1993, 54, 410. (i) Roncali, J.
Chem. ReV. 1997, 97, 173.
(4) (a) Zhang, C.; von Seggern, H.; Pakbas, K.; Kraabel, B.; Schmidt,
H.-W.; Heeger, A. J. Synth. Met. 1994, 62, 35. (b) Faraggi, E. Z.; Chayet,
H.; Cohen, G.; Neumann, R.; Avny, Y.; Davidov, D. AdV. Mater. 1995, 7,
742. (c) Fu, Y.; Cheng, H.; Elsenbaumer, R. L. Chem. Mater. 1997, 9,
1720.
S0002-7863(97)04381-3 CCC: $15.00 © 1998 American Chemical Society
Published on Web 04/23/1998

A Zr-Coupling Route to Substituted Poly(p-phenylenedienylene)s
J. Am. Chem. Soc., Vol. 120, No. 18, 1998 4355
Scheme 1
group.3 One of the largest ranges for optical tunability, 305-
595 nm for absorption λmax values, was achieved by varying
substituents on polythiophenes.2a In addition, the role of
polymer defects on the optoelectronic properties of conjugated
polymers is very important.5 However, many of the conjugated
polymers of interest are insoluble, making the characterization
or detection of defects by spectroscopic means difficult.6
phospholes, and aromatic groups).8e,9,10 Due to their irregular
and crossconjugated structures, these polymers possess relatively
wide band gaps and display emission bands varying from 398
to 470 nm and quantum yields for emission ranging from zero
to ca. 30%.
In this paper, we describe the use of regioselective zir-
conocene-couplings in the preparation of fully conjugated
polymers. This approach takes advantage of regioselective, ring-
closing diyne couplings which employ flexible diyne spacer
groups (eq 1).7a High isolated yields (70-90%) have been
We have been exploring an organometallic approach to the
synthesis of conjugated polymers, based on the zirconocene-
coupling of diynes.7,8 This approach allows for chemical
modification of the polymers’ electronic properties, based on
the “modular” exchange of groups in the polymer backbone.
Initial attempts to produce π-conjugated polymers from 4,4′-
di(alkynyl) biphenyl derivatives resulted in primarily cross-
conjugated structures and nonregioselective couplings (Scheme
1).8e Nonetheless, it was shown that the polymer properties
could be varied via conversions of zirconacyclopentadiene
backbone units to a variety of functionalities (dienes, thiophenes,
reported for diynes with n ) 2, 3, and 4. The method reported
here for the synthesis of conjugated poly(p-phenylenedienylene)s
is outlined in eq 2.11 First, poly(arylenediyne)s were prepared
using palladium-catalyzed cross coupling,12 according to meth-
odology that has previously been employed in the synthesis of
conjugated poly(p-phenyleneethynylene)s from aryldiynes and
dihaloaryls.13 The poly(arylenediyne)s were then transformed
(5) (a) Wagaman, M. W.; Grubbs, R. H. Macromolecules 1997, 30, 3978.
(b) Burn, P. L.; Holmes, A. B.; Kraft, A.; Bradley, D. D. C.; Brown, A. R.;
Friend, R. H. J. Chem. Soc., Chem. Commun. 1992, 32. (c) Burn, P. L.;
Holmes, A. B.; Kraft, A.; Bradley, D. D. C.; Brown, A. R.; Friend, R. H.
Nature 1992, 356, 47. (d) Braun, D.; Staring, E. G. J.; Demandt, R. C. J.
E.; Rikken, G. L. J.; Kessener, Y. A. R. R.; Venhuizen, A. H. J. Synth.
Met. 1994, 66, 75. (e) Morgan, J.; Rumbles, G.; Crystall, B.; Smith, T. A.;
Bloor, D. Chem. Phys. Lett. 1992, 196, 455.
(9) Fagan, P. J.; Nugent, W. A.; Calabrese, J. C. J. Am. Chem. Soc. 1994,
116, 1880.
(6) (a) Lahti, P. M.; Modarelli, D. A.; Denton, F. R.; Lenz, R. W.; Karasz,
F. E. J. Am. Chem. Soc. 1988, 110, 7258. (b) Conticello, V. P.; Gin, D. L.;
Grubbs, R. H. J. Am. Chem. Soc. 1992, 114, 9708. (c) Gin, D. L.; Conticello,
V. P.; Grubbs, R. H. J. Am. Chem. Soc. 1992, 114, 3167. (d) Burroughs, J.
H.; Bradley, D. D. C.; Brown, A. R.; Marks, R. N.; Mackay, K.; Friend, R.
H.; Burns, P. L.; Holmes, A. B. Nature 1990, 347, 539. (e) Louwet, F.;
Vanderzande, D.; Gelan, J.; Mullins, J. Macromolecules 1995, 28, 1330.
(f) Gagnon, D. R.; Capistran, J. D.; Karasz, F. E.; Lenz, R. W. Polym.
Bull. 1984, 12, 293. (g) Antoun, S.; Karasz, F. E.; Lenz, R. W. J. Polym.
Sci., Part A 1988, 26, 1089.
(7) (a) Nugent, W. A.; Thorn, D. L.; Harlow, R. L. J. Am. Chem. Soc.
1987, 109, 2788. (b) Negishi, E.; Cederbaum, F. E.; Takahashi, T.
Tetrahedron Lett. 1986, 27, 2829. (c) Negishi, E.; Takahashi, T. Acc. Chem.
Res. 1994, 27, 124. (d) Broene, R. D.; Buchwald, S. L. Science 1993, 261,
1696.
(8) (a) Mao, S. S. H.; Tilley, T. D. J. Am. Chem. Soc. 1995, 117, 5365.
(b) Mao, S. S. H.; Tilley, T. D. J. Am. Chem. Soc. 1995, 117, 7031. (c)
Mao, S. S. H.; Tilley, T. D. Macromolecules 1996, 29, 6362. (d) Mao, S.
S. H.; Tilley, T. D. J. Organomet. Chem. 1996, 521, 425. (e) Mao, S. S.
H.; Tilley, T. D. Macromolecules 1997, 30, 5566. (f) Tilley, T. D.; Mao,
S. S. H. Modular Chemistry; Michl, J., Ed.; Kluwer Academic Publishers:
Dordrecht, 1997, 623. (g) Mao, S. S. H.; Liu, F. Q.; Tilley, T. D. J. Am.
Chem. Soc. 1998, 120, 1193.
(10) (a) Takahashi, T.; Kortora, M.; Xi, Z. F. J. Chem. Soc., Chem.
Commun. 1995, 361. (b) Takahashi, T.; Hara, R.; Nishihara, Y.; Kotora,
M. J. Am. Chem. Soc. 1996, 118, 5154. (c) Takahashi, T.; Kasai, K.; Xi, Z.
F.; Denisov, V. Chem. Lett. 1995, 5, 347.
(11) (a) Meyers, F.; Heeger, A. J.; Bredas, J. L. J. Chem. Phys. 1992,
97, 2750. (b) Sonoda, Y.; Suzuki, Y.; Van Keuren, E.; Matsuda, H.
Macromolecules 1996, 29, 288.
(12) (a) Heck, R. F.; Nolley, J. P. J. Org. Chem. 1972, 37, 2320. (b)
Mizoroki, T.; Mori, K.; Ozaki, A. Bull. Chem. Soc. Jpn. 1971, 44, 581. (c)
Mizoroki, T.; Mori, K.; Ozaki, A. Bull. Chem. Soc. Jpn. 1973, 46, 1505.
(d) Deick, H. A.; Heck, R. F. J. Am. Chem. Soc. 1974, 96, 1133. (e) de
Meijere, A.; Meyer, F. E. Angew. Chem., Int. Ed. Engl. 1994, 33, 2379. (f)
Tsuji, J. Palladium Reagents and Catalysts - InnoVations in Organic
Synthesis, John Wiley and Sons: New York, 1995. (g) Rossi, R.; Carpita,
A.; Bellina, F. Org. Prep. Proced. Int. 1995, 27, 129. (h) Heck, R. F. Acc.
Chem. Res. 1979, 12, 146.
(13) (a) Trumbo, D. L.; Marvel, C. S. J. Polym. Sci.: Part A: Polym.
Chem. 1987, 25, 839. (b) Sanechika, K.; Yamamoto, T.; Yamamoto, A.
Bull. Chem. Soc. Jpn. 1987, 57, 752. (c) Moroni, M.; Moigne; J. L.; Luzzati,
S. Macromolecules 1994, 27, 562. (d) McCarthy, T. F.; Witteler, H.; Pakula,
T.; Wegner, G. Macromolecules 1995, 28, 8350. (e) Bao, Z.; Chen, Y.;
Cai, R.; Yu, L. Macromolecules 1993, 26, 5281. (f) Swager, T. M.; Gil, C.
G.; Wrighton, M. S. J. Phys. Chem. 1995, 99, 4886.

4356 J. Am. Chem. Soc., Vol. 120, No. 18, 1998
Lucht et al.
Scheme 2
via intramolecular zirconocene coupling and hydrolysis to poly-
(arylenedieneylene)s (eq 2). Variation of substituents on the
arene ring and diene allows for tuning of the optical absorption
and emission energies for the polymers. Also, copolymeriza-
tions with combinations of different diynes result in polymers
with optical properties that are the weighted average for the
two homopolymers.
5-hexoxy-1,4-diiodobenzene (4).14 While condensations of 1,7-
octadiyne with 4 yield polymers with superior solubility
properties, the molecular weight and solubility of the polymers
proved difficult to reproduce due to the stringent need for a 1:1
stoichiometry for the two bifunctional monomers.15 This
problem was circumvented with use of 2,5-dimethoxy-4-
methyliodobenzene (5) as an end-capping agent. The addition
of low concentrations (5-20%) of 5 to polymerizations of 1,7-
octadiyne and 4 resulted in the synthesis of polymers with
reproducible molecular weights and solubilities.16
The polycondensations of 1,7-octadiyne, 1,6-heptadiyne, and
1,5-hexadiyne with 4 and 0.1 equiv of 5 were carried out with
Pd(PPh3)4/CuI catalyst in a mixture of THF and diisopropyl-
amine. The reaction time was typically 12-16 h at room
temperature although shorter reaction times can be used when
the reaction temperature is raised to 50 °C. The polymers
remained soluble during the reaction and were isolated as pale
yellow-brown solids by precipitation from methanol. Polymers
1a-c were purified by washing chloroform solutions with dilute
NH4OH and water, followed by reprecipitation from methanol.
The latter procedure results in a substantially reduced yield (by
almost 50%); however, it was found that transformations of
1a-c to 3a-c could be carried out with the crude polymers.
The molecular weights of polymers 1a-c, as determined by
gel permeation chromatography (GPC; polystyrene standards;
Mn ) 4500-5500; PDI ) 1.7-5.5), are similar to the theoretical
values expected for condensation polymerizations with addition
of 10% of an end cap (n ) 20, Mn ) 6000)15 and are consistent
with the number average molecular weights determined by end-
group analysis (4700-5400; 1H NMR spectroscopy). Nonethe-
less, it is difficult from the spectroscopic data to conclude that
While the method outlined in eq 2 may lead to a variety of
interesting polymers, this strategy will inherently lead to polymer
defects for nonquantitative transformations involving the poly-
mer backbone. For the reactions described here, these conver-
sions are nearly quantitative, as judged by spectroscopic
characterization of the polymers and comparisons with related
reactions of small molecules.7,8 However, incomplete conver-
sions present possibilities for the synthesis of additional
polymers with interesting “hybrid” properties, and conjugated
polymers with breaks in the conjugation lengths (defects) have
been found to exhibit both increased quantum yields and higher
solubilities.5a
Results and Discussion
Synthesis and Characterization of Polymers. The general
procedure employed for synthesis of poly(p-phenylenedien-
ylene)s is outlined in Scheme 2. An initial attempt to employ
this method, using 1,4-diiodobenzene and 1,7-octadiyne, resulted
in formation of an insoluble polymer. For this synthetic scheme,
polymers 1 must have reasonably high solubilities in THF at
-78 °C to allow for complete conversion to polymers of type
2. Soluble polymers of type 1 were obtained by employing
asymmetrically substituted arene monomers such as 2-methoxy-
(14) (a) Rodriguez-Parada, J. M.; Duran, R.; Wegner, G. Macromolecules
1989, 22, 2507. (b) Duran, R.; Ballauff, M.; Wenzel, M.; Wegner, G.
Macromolecules 1988, 21, 2897. (c) Wenzel, M.; Ballauff, M.; Wegner,
G. Makromol. Chem. 1987, 188, 2865. (d) Gettinger, C. L.; Heeger, A. J.;
Drake, J. M.; Pine, D. J. J. Chem. Phys 1994, 101, 1673.
(15) Billmeyer, F. W. Textbook of Polymer Science; John Wiley and
Sons: New York, 1984.
(16) (a) Swager, T. M.; Gil, C. G.; Wrighton, M. S. J. Phys. Chem. 1995,
99, 4886. (b) Weder, C.; Wrighton, M. S. Macromolecules 1996, 29, 5157.

A Zr-Coupling Route to Substituted Poly(p-phenylenedienylene)s
J. Am. Chem. Soc., Vol. 120, No. 18, 1998 4357
Table 1. Optical Properties of Poly(phenylenedieneylene)s
λ
max (nm)
λ
max (nm)
λmax (nm)
a
polymer absorption excitation emission
color
ꢀmax
3a
3b
3c
3d
3e
3f
368
472
524
316
414
438
368
390
420
314
365
375
489
546
619
437
495
556
yellow
red
purple
colorless 19 000
orange
red
6 900
7 900
20 000
9 500
14 000
a ꢀmax ) the molar absorptivity per repeat unit of the polymer.
quantitative end-capping has occurred. Polymers 1a-c are
completely soluble in THF, toluene, and chloroform. The 13C
NMR spectra for these polymers contain four resonances for
the alkynyl groups, representing environments involving both
o-OMe and o-OHex substituents. The IR spectra of 1a-c
contain weak alkyne stretches at 2232-2235 cm-1, which are
consistent with unsymmetrically substituted carbon-carbon
triple bonds. Palladium-catalyzed cross coupling can result in
the formation of alkyne-alkyne coupling products in addition
to the desired products, but such couplings are minimized by
using palladium(0) catalysts such as Pd(PPh3)4.12g We observed
no evidence for alkyne-alkyne coupling by 1H NMR spectros-
copy.
Figure 1. Absorption spectra for polymers 3a (‚‚‚), 3b (- - -), 3c (s).
resonances between 6.0 and 8.0 ppm attributed to the vinyl and
aryl protons. However, 3f has several other small resonances
in this region, which may represent defects in the polymer
arising from incomplete conversion of diyne to diene units. The
IR spectra for all polymers 3a-f contain no evidence for alkynyl
absorbances, indicating relatively efficient conversion of alkyne
to alkene functionalities.
The resulting molecular weights for 1a-f and 3a-f are highly
dependent on the amount of added capping group. Syntheses
of 3b with higher (0.2 equiv) or lower (0.05 equiv) amounts of
5 resulted in molecular weights (GPC) which were consistent
with the theoretical values (0.05 equiv: Mn/Mw ) 12 000/
50 000; 0.1 equiv: 5300/19 000; 0.2 equiv: 2400/9600). The
lower-molecular-weight polymers were found to be substantially
more soluble, while the optical properties (vide infra) did not
vary significantly with molecular weight.
Optical Properties of Polymers. The photophysical proper-
ties of polymers 3a-f in dilute deoxygenated THF solutions
were investigated. Absorption data are summarized in Table
1, and Figure 1 presents absorption spectra for polymers 3a-c.
The absorption spectra have a strong dependence on both the
size of the polymer-fused ring and on the nature of substituents
on the aryl ring. A red-shift in the absorption maximum as the
ring size decreases (4 > 5 > 6) in both the alkoxy- (3c > 3b
> 3a) and alkyl- (3f > 3e > 3d) substituted polymers indicates
an increase in π-delocalization along the polymer backbone.
These changes in electronic properties undoubtedly reflect
variations in the average conjugation lengths, as determined by
dihedral angles along the chain. Electron donation from alkoxy
substituents on polymers 3a-c results in an auxochromic red
shift of 52-76 nm relative to the alkyl-substituted polymers
3d-f.17
Emission and excitation spectra were acquired on dilute
deoxygenated THF solutions of polymers 3a-f with optical
absorption maxima between 0.07 and 0.13. Emission spectra
for polymers 3a-f are independent of the excitation wavelength
but highly dependent on the structure of the polymer (Table 1).
The photoluminescence quantum yields, determined relative to
a quinine bisulfate standard, are fairly low (<0.01) for all
polymers 3a-f.18 The low quantum yields are somewhat
surprising, but increasing the rigidity of conjugated polymers
is known to result in a decrease in photoluminesence ef-
ficiency.19 Excitation spectra for polymers 3a (Figure 2) and
In a similar manner, treatment of 1,4-diiodo-2-methyl-5-
hexylbenzene (6) with 1,7-octadiyne, 1,6-heptadiyne, or 1,5-
hexadiyne in the presence of Pd(PPh3)4/CuI produced the soluble
polymers 1d-f. The degree of polymerization was controlled
by addition of 0.1 equiv of 2-iodotoluene (7). Polymer
molecular weights determined by GPC (Mn ) 4200-5500; PDI
) 2.1-2.5) are consistent with both the theoretical prediction
(n ) 20; 5400) and values determined by end-group analysis
(4800-5200). Four well-resolved alkynyl resonances, and
broad resonances for the main-chain methylene carbons, are
observed in the 13C NMR spectrum, consistent with unsym-
metrically substituted aryl rings. The IR spectra contain weak
alkyne absorbances at 2226-2229 cm-1
.
Solutions of 1a-f in THF were added dropwise over 5 min
to a fresh solution of “zirconocene”, generated by the addition
of n-BuLi to Cp2ZrCl2 in THF at -78 °C.7b Warming to room
temperature afforded deeply colored solutions of the zirconium-
containing polymers (2a: red; 2b: green; 2c: blue; 2d: yellow-
orange; 2e: red; 2f: violet). These conversions are highly
sensitive to the amount of added n-BuLi, such that significant
deviations from the ideal stoichiometry of 1.95 equiv per equiv
of Cp2ZrCl2 led to impure materials. Also, 2a-f decompose
to black inhomogeneous mixtures when stirred in solution at
room temperature for > 8 h. Therefore these polymers were
not isolated or characterized in solution but were converted
directly to the corresponding polymers 3a-f by addition of
excess 6 M HCl.
Polymers 3a-f exhibit colors that are highly dependent on
the number of methylene units in the polymer-fused rings (Table
1) and are soluble in toluene, chloroform, and THF. The
molecular weights of 3a-f, as determined by GPC (Mn
)
5400-6300; PDI ) 3-6), are consistent with expected theoreti-
cal values (n ) 20, 6000). End-group analyses were generally
not possible since the broad polymer resonances obscured peaks
for the end groups. Subtle, apparent differences in the molecular
weights of polymers 1a-f vs 3a-f, as determined by GPC,
presumably reflect changes in the polymer structures and not
the overall degree of polymerization. The 13C aromatic and
vinyl resonances are extremely broad and difficult to distinguish,
while the alkoxy side chain and aliphatic ring resonances are
sharp and well resolved. Polymers 3a-e exhibit three major
(17) (a) Gill, R. E.; Meetsma, A.; Hadziioannou, G. AdV. Mater. 1996,
8, 212. (b) Reynolds, J. R.; Child, A. D.; Ruiz, J. P.; Hong, S. Y.; Marynick,
D. S. Macromolecules 1993, 26, 2095.
(18) Handbook of Organic Photochemistry; Scaiano, J. C., Ed.; CRC
Press: Boca Raton, FL, 1989; Vol. 1, Chapter 8, p 231.
(19) Zhang, Q. T.; Tour, J. M. J. Am. Chem. Soc. 1997, 119, 9624.

4358 J. Am. Chem. Soc., Vol. 120, No. 18, 1998
Lucht et al.
Figure 2. Absorption (s), emission (‚‚‚), and excitation (- - -) spectra
of 3a. The sharp peak in the emission spectrum results from Raman
scattering.
Figure 4. Absorption spectra for compounds 9a (‚‚‚), 9b (- - -), 9c
(s).
derivatives containing an exocyclic cyclohexadiene group have
been conducted.22 The data suggest that 1,2-dimethylenecy-
clobutane has a planar conformation while 1,2-dimethylenecy-
clohexane has a chair conformation with torsion angles of
approximately 55-60° for the diene system. In polymers 3a-
f, steric interactions between the fused ring and aryl substituents
may also play an important role in determining conjugation
between the aryl and diene π-systems.
The 1,4-diphenylbutadiene compounds 9a-f were synthesized
via the three-step procedure shown in eq 3. Diynes 8a-f were
obtained in high yield as crystalline solids or oils by palladium-
catalyzed cross-couplings. Intramolecular zirconocene cou-
plings of 8a-f in THF afforded deep red solutions of the
zirconacyclopentadienes, which were hydrolyzed with concen-
trated HCl to give the diene products 9a-f as crystalline
products from 1:1 pentane/OEt2. The chemical structures of
9a-f were confirmed by 1H and 13C NMR, IR, and high-
resolution mass spectroscopy. In general, spectroscopic proper-
ties for these compounds are very similar to those for the
corresponding polymers 3a-f.
Figure 3. Absorption (s), emission (- - -), and excitation (‚‚‚) spectra
of 3b. The sharp peaks in the emission and excitation spectra result
from Raman scattering.
3d reproduce the corresponding absorption spectra; however,
excitation spectra for polymers 3b (Figure 3), 3c, 3e, and 3f do
not. The excitation spectra indicate that emissions from
polymers 3b, 3c, 3e, and 3f result from excitation into the high
energy shoulder of the absorption band. We do not fully
understand the observed differences in absorption and excitation
spectra, but we believe that they are caused by the presence of
defects in some of the polymers (vide infra). Emission from
short oligomers was ruled out by photophysical investigations
of fractionated polymers. However, we cannot at this time
exclude the possibility that emission results from discrete, short-
conjugation sequences within the polymer backbone.20 Also,
since the excitation spectra do not fully reproduce the absorption
spectra for 3b, 3c, 3e, and 3f, values for the photoluminescence
quantum yields of these polymers are not very readily inter-
preted.
Synthesis and Characterization of Model Compounds. To
investigate the origin of the diverse colors and optical properties
for polymers 3a-f, appropriate model compounds were syn-
thesized. The red-shifts for the polymers’ absorptions and
emissions (3c > 3b > 3a) vary inversely with the size of the
fused ring and is therefore in agreement with the conformational
properties of 1,2-dimethylenecycloalkanes which have been
studied by computational methods, photoelectron spectroscopy,
microwave spectroscopy, and NMR spectroscopy.21 In addition,
several X-ray crystallographic determinations of vitamin D
Optical Properties of Model Compounds. We investigated
the photophysical properties of 9a-f in dilute, deoxygenated
chloroform solutions. A strong bathochromic shift of the
absorption maxima for both the substituted (9a-c, Figure 4)
and unsubstituted (9d-f) 1,4-diaryldienes is associated with a
decrease in the size of the backbone-fused ring (Table 2). In
(21) (a) Hofmann, H.; Cimiragilia, R. J. Org. Chem. 1990, 55, 2151.
(b) Hemmersbach, P.; Klessinger, M.; Bruckmann, P. J. Am. Chem. Soc.
1978, 100, 6344. (c) Avairah, T. K.; Cook, R. L.; Malloy, T. B. J. Mol.
Spectrosc. 1975, 54, 231. (d) Asmus, P.; Klessinger, M. Tetrahedron 1974,
30, 2477. (e) Pfeffer, H. U.; Klessinger, M. Org. Magn. Reson. 1977, 9,
121.
(22) (a) Hodgkin, D. C.; Rimmer, B. M.; Dunitz, J. D.; Trueblood, K.
N. J. Chem. Soc. 1963, 4945. (b) Knobler, C.; Romers, C.; Braun, P. B.;
Hornstra, J. Acta Crystallogr., Sect. B 1972, 28, 2097. (c) Trinh-Toan;
DeLuca, H. F.; Dahl, L. F. J. Org. Chem. 1976, 41, 3476. (d) Trinh-Toan;
Ryan, R. C.; Simon, G. L.; Calabrese, J. C.; Dahl, L. F.; De Luca, H. F. J.
Chem. Soc., Perkin Trans. 1977, 2, 393. (e) Hull, S. E.; Leban, I.; Main,
P.; White, P. S.; Woolfson, M. M. Acta Crystallogr., Sect. B 1976, 32,
2374.
(20) (a) Morgan, J.; Rumbles, G.; Crystall, B.; Smith, T. A.; Bloor, D.
Chem Phys. Lett. 1992, 196, 455. (b) Brown, A. J.; Rumbles, G.; Philips,
D.; Bloor, D. Chem. Phys. Lett. 1988, 151, 247.

A Zr-Coupling Route to Substituted Poly(p-phenylenedienylene)s
J. Am. Chem. Soc., Vol. 120, No. 18, 1998 4359
Table 2. Optical Properties of 1,4-Diphenyldienes
λ
max (nm)
absorption
λ
max (nm)
emission
b
compd
Φa
ꢀmax
9a
9b
9c
9d
9e
9f
326
368
372, 388, 408
294
334
448
455
429, 456, 484
379
410
0.011
0.032
0.29
0.003
0.004
0.007
13 000
21 000
40 000
29 000
33 000
45 000
328, 346, 364
383, 407, 430
b
a Φ ) photoluminesence quantum yield. ꢀmax ) the molar absorp-
tivity.
Figure 6. X-ray crystallographic structures of model compounds 9c
(A) and 9d (B).
Figure 5. Absorption (s), emission (- - -), and excitation (‚‚‚) spectra
of 9c.
Structural Analyses of 9c and 9d. The molecular structures
of 9c and 9d (Figure 6) were determined to establish relation-
ships between structural conformations and the corresponding
electronic properties. Most of the metrical parameters for these
compounds are unexceptional, and the most significant confor-
mational differences may be described in terms of dihedral
angles. For 9c, the C(5)-C(6)-C(7)-C(8) and C(7)-C(8)-
C(11)-C(12) dihedral angles of 1.3° and 2.6°, respectively,
describe an essentially planar (and highly conjugated) molecule.
The angle between the two least-squares planes of the aryl rings
is only 3.0°. The related dihedral angles for 9d, C(6)-C(5)-
C(4)-C(3) and C(4)-C(3)-C(3*)-C(4*), are 30.9° and 42.4°,
respectively, resulting in much less π-orbital overlap and
electron delocalization for this compound.
Random Copolymers. The above results describe the tuning
of electronic properties for conjugated polymers via variations
in two structural parameters: the conformation of a diene unit
and the nature of the aromatic ring substitutions. In principle,
a finer tuning of electronic properties may be achieved by
combining different monomer types in various ratios into
random copolymers. By preparing copolymers incorporating
both five- and six-membered fused rings, we have achieved
smooth variations in electronic properties for the resulting
polymers. To prepare random copolymers with optical proper-
ties that are the weighted average of two homopolymers, two
primary requirements need to be satisfied. The conjugation must
be extended over more than one repeat unit of the polymer,
and the rates of polymerization for the different monomers must
be very similar. The polymers described here meet both of these
requirements. First, polymers 3a-f have significant conjugation
lengths, as indicated by the red shift in the absorption maxima
of the polymers with respect to those for the model compounds
9a-f. Also, the polymerization rates for 1,7-octadiyne, 1,6-
heptadiyne, and 1,5-hexadiyne are very similar. This allows
for a random distribution of monomer units, since no kinetic
preference exists for homopolymerizations.
addition, alkoxy substitution results in an auxochomic red shift
of 30-40 nm for all model compounds. Therefore, trends in
the absorption characteristics of the model compounds 9a-f
are very similar to those observed for polymers 3a-f, except
for two primary differences. The first is that cyclobutanes 9c
and 9f exhibit fine structure in their absorption spectra, as
observed for trans-1,4-diphenylbutadiene.23 The second dif-
ference is the bathochromic shift for the absorption maxima
for polymers 3a-f relative to the respective molecular species,
which corresponds to greater conjugation lengths for the
polymers. Additionally, polymers 3b, 3c, 3e, and 3f are
substantially more red shifted (74-106 nm) than polymers 3a
and 3d (22-42 nm) with respect to their model compounds.
This is consistent with the assumption that π-orbital overlap is
more efficient in polymers with smaller fused rings.
Emission and excitation spectra were acquired on dilute
chloroform solutions of 9a-f with optical absorbances of 0.07-
0.13. The emission spectra of 9a-f are independent of
excitation wavelength and exhibit shifts in energies that parallel
the absorption spectra (Table 2), with the emission energies
shifting to longer wavelengths as the fused ring size decreases.
Emission spectra are Stokes-shifted by 55-122 nm relative to
the corresponding absorption spectra, and the magnitude of this
shift varies directly with the size of the fused ring (6 > 5 > 4).
Model compounds 9a, 9b, 9d, 9e, and 9f have low photolumi-
nescence quantum yields (<0.03), but 9c exhibits a quantum
yield of 0.29. This is at least partially consistent with a
combination of the expected effects of increased rigidity and
alkoxy-substitution,24 but the origins of these differences are
currently not fully understood. Excitation spectra of 9a, 9b,
9c (Figure 5), and 9d-f reproduce the absorption spectra,
confirming that emission correlates with the absorption band.
(23) Pinckard, J. H.; Wille, B.; Zechmeister, L. J. Am. Chem. Soc. 1948,
70, 1938.
(24) Guilbault, G. G. Practical Fluorescence; Marcel Dekker: New York,
1973.
The synthesis of random copolymers employs a procedure

4360 J. Am. Chem. Soc., Vol. 120, No. 18, 1998
Lucht et al.
Scheme 3
1a-e to 3a-e also appear to be quantitative by 1H NMR
spectroscopy. Furthermore, the lack of alkyne IR absorbances
in polymers 3a-f suggests that the alkyne-to-alkene conversion
is at least 95% complete. The only polymer that exhibits
evidence for polymer defects by 1H NMR spectroscopy (in the
aromatic region) is 3f. Several small resonances in the spectrum
for 3f may represent defects that arise from incomplete
conversion of diyne to diene units.
Polymers 3a-e have absorption spectra that are fairly
symmetric with only a single maximum, while 3f has two
absorption maximasa primary one at 438 nm and a second,
lower intensity band at higher energy (380 nm) which is very
similar to the excitation maximum (375 nm) for this polymer.
We therefore propose that the absorption feature at 380 nm and
the excitation maximum for 3f both result from defects in the
polymer.
Table 3. Optical Properties of Copolymers
λ
max (nm)
λ
max (nm)
absorbance
polymer % n % m absorption emission band width (nm)a
3a
100
75
50
25
0
0
25
50
75
100
368
378
418
448
472
489
497
514
533
546
110
150
140
120
140
11a
11b
11c
3b
a The full width at half-maximum intensity of the absorption
spectrum.
analogous to that used for the homopolymers, as shown in
Scheme 3. Treatment of 4 with various ratios of 1,7-octadiyne
and 1,6-heptadiyne in the presence of Pd(PPh3)4/CuI provided
polymers 10a-c. Intramolecular zirconocene coupling of 10a-
c, followed by hydrolysis with HCl, resulted in formation of
the random copolymers 11a-c. The polymer resulting from a
50:50 mixture of 1,7-octadiyne and 1,6-heptadiyne (11b)
exhibits an absorption maximum at 418 nm and an emission
maximum at 514 nm. Both of these values are very close to
the average absorption and emission maxima for the corre-
sponding homopolymers 3a and 3b. Significantly, the band-
widths of the copolymers are very similar to those for the
homopolymers, indicating the presence of uniquely defined
chromophores (Table 3). Polymerizations with other diyne
ratios yielded copolymers 11a and 11c, with absorption and
emission maxima that are close to the weighted average for the
two homopolymers (Table 3). As shown in Figure 7, there is
a linear correlation between the 1,7-octadiyne/1,6-heptadiyne
ratio and the absorption maxima. Based on these results, we
anticipate that it should be straightforward to prepare poly-
(phenylenedienylene)s with absorption and emission maxima
which take on any value in the 316-524 and 437-619 nm
ranges, respectively.
While NMR and IR data suggest that polymers 3a-e are
defect-free, the excitation spectra of polymers 3b, 3c, 3e, and
3f suggest that polymer defects (resulting from incomplete
conversion of diyne units) may be responsible for the observed
emissions. Treatment of 1b with less than 1.0 equiv of
zirconocene (0.5 equiv) under previously described conditions
results in formation of the “highly defective” copolymer 12 (eq
4). Polymer 12 exhibits an alkyne stretch at 2230 cm-1 in the
infrared spectrum, with approximately half of the intensity of
the alkyne stretch for 1b. Additionally, the absorption spectrum
of 12 is intermediate between those for 1b and 3b (Figure 8).
Role of Polymer Defects. The preparation of conjugated
polymers via a multistep process involving the chemical
conversion of one polymer structure to another is potentially
susceptible to less than quantitative conversions and incorpora-
tion of defects into the backbone. Conversions of 8a-f to 9a-f
are quantitative by NMR spectroscopy. The conversions of

A Zr-Coupling Route to Substituted Poly(p-phenylenedienylene)s
J. Am. Chem. Soc., Vol. 120, No. 18, 1998 4361
polymer; however, aryl substituent effects are also important.
This conformational control of the polymer backbone via the
incorporation of exocyclic dienes represents a new approach
for tuning the optical properties of conjugated polymers. In
addition to the formation of polymers with a single type of
exocyclic diene, random copolymers with both five- and six-
membered fused rings allow for further fine-tuning of the
polymer band gap. This suggests that the optical absorption
and emission maxima can be tuned to any wavelength within
the ranges of 316-524 nm and 437-619 nm, respectively.
Further investigation of the photophysical properties of poly-
(p-phenylenedienylene)s suggests that polymer emissions may
be associated with imperfections in the polymers that result from
incomplete conversion of the alkyne groups. This further
supports the view that polymer defects can play a vital role in
determining the optoelectric properties of conjugated polymers.
We anticipate that polymerization reactions of the type described
here will be useful for the synthesis of a variety of new
conjugated polymers, since both the palladium- and zirconocene-
coupling steps are compatible with many arenes and hetero-
arenes. Future reports will describe the use of solubilizing
diynes for the preparation of poly(arylenedienylene)s.25
Figure 7. Plot of the absorption maxima vs mole fraction of m for
random copolymers see Scheme 3.
Experimental Section
General Procedures. All procedures were carried out in a nitrogen-
filled Vacuum Atmospheres drybox or in Schlenk-type glassware
interfaced to a vacuum line. Reagents used in this study were purchased
from commercial sources and purified, dried, and deoxygenated as
necessary. Dry, oxygen-free solvents were employed throughout. All
solvents were distilled from sodium/benzophenone ketyl. Benzene-d6
was purified by vacuum distillation from Na/K alloy. Elemental
analyses were performed by the UCB Microanalytical Laboratory. IR
spectra were recorded on a Mattson Infinity FT-IR spectrometer. NMR
spectra were recorded on a Bruker AMX (300 MHz) or a Bruker AMX
(400 MHz) NMR spectrometer. Molecular weights of the polymers
were determined by gel permeation chromatography (GPC; Waters
Company; Detector: Differential Refractometer R401; Waters 501
HPLC pump; Waters 745 Data Module) with THF as eluting solvent
and polystyrene standards.
Emission spectra were collected by using an Instruments SA/Jobin
Yvon-Spex Fluoromax photon-counting fluorimeter equipped with a
Xe arc lamp excitation source and a Hamamatsu R928P photomultiplier
tube operating at -900 Vdc. Data were collected on thoroughly
deoxygenated solutions (THF for polymers, CHCl3 for model com-
pounds) having an optical density of 0.07-0.13 (1.0 cm path length)
at the excitation wavelength. Background measurements on the solvent
blanks revealed no signals other than the expected Raman lines of the
neat solvent. The excitation energy for photoluminescence spectra was
10 nm lower than the absorption maximum, and excitation spectra were
acquired at the emission maximum. All quantum yield measurements
were carried out at a single excitation wavelength (350 nm). Spectra
were corrected using a NIST standard of spectral irradiance (Optronic
Laboratories, Inc., OL220M tungsten quartz lamp). All subsequent
manipulations were carried out with the corrected spectra.
Figure 8. Absorption spectra of 1b (- - -), 3b (‚‚‚), and 12 (s).
The emission spectrum of 12 has maxima at 364, 371, 469,
and 489 nm. The two shorter wavelength emissions (364 and
371 nm) correspond to emissions from segments which are
similar to 1b (the emission spectrum of 1b has two maxima at
360 and 368 nm). The longer wavelength emissions (469 and
489 nm) are consistent with segments which have been
converted to dienes. The excitation spectra of both 1b and 12
accurately reproduce the absorption spectra. However, the
excitation spectrum of 12 resembles that for 3b, with both
featuring excitation maxima at 390 nm. This suggests that
emission from 3b results primarily from polymer defects. Also,
since emission and excitation spectra for polymers 3b, 3c, 3e,
and 3f are dependent upon the size of the fused ring, the emitting
chromophores in each case are associated with both alkyne and
diene fragments. Given the apparent influence of defects on
determining emmision properties, it may seem somewhat
surprising that the emission energies vary considerably from
one diene polymer to another (see Table 1). This implies that
the excitons decay from defects with somewhat different
structures, which could occur if the emitting (defect) chro-
mophores include at least an alkyne-arene-diene unit. The
fluorescence quantum yields for polymers 1b and 12 are 0.035
and 0.021, respectively, almost an order of magnitude larger
than the quantum yield observed for 3b. Note that defects in
conjugated polymers are known to result in higher fluorescence
quantum yields due to inhibition of the migration of excitons
to quenching sites.5
Relative quantum yield (Φ) values are reported relative to a 1.0 N
H2SO4 solution of quinine bisulfate (Φ ) 0.546)16 and calculated
according to the equation
2
Iu As ηu
Φu ) Φs
(A )(I )(η )
u
s
s
Conclusions
where Φu is the radiative quantum yield of the sample, Φs is the
radiative quantum yield of the standard, Iu and Is are the integrated
emission intensities of the sample and standard, respectively, Au and
As are the absorbances of the sample and standard, respectively, at the
excitation wavelength (350 nm), and ηu and ηs are the indexes of
The results presented here demonstrate that poly(p-phen-
ylenedienylene)s are readily accessible via zirconocene-coupling
routes, which provide means for fine control over polymer
electronic properties. The optical tunability operates primarily
via conformational properties of exocyclic diene units in the
(25) Lucht, B. L.; Tilley, T. D. unpublished results.

4362 J. Am. Chem. Soc., Vol. 120, No. 18, 1998
Lucht et al.
refraction of the sample and the standard solutions. Multiple measure-
ments on each sample indicated a precision of ca. 10% for our reported
values of Φ.
H, CH), 7.20 (s, 1 H, CH). 13C {1H} NMR (100 MHz, CDCl3): δ
14.15 (CH3), 19.20 (CH2), 20.03 (CH2), 22.64 (CH3), 27.98 (CH2), 29.19
(CH2), 30.61 (CH2), 31.76 (CH2), 34.03 (CH2), 79.76, 79.96 (CtC),
93.81, 94.45 (CtC), 122.51, 122.93, 131.87, 132.90, 136.88, 141.76
(C6H2). Mn/Mw ) 4600/12 000 by GPC. IR (film, KBr, cm-1) 3020,
2927, 2857, 2226 (CtC), 1492, 1456, 1437, 1327, 896, 734.
Polymer 1a. A 100 mL Schlenk flask was charged with 4 (1.0 g,
2.2 mmol), 5 (0.06 g, 0.2 mmol), Pd(PPh3)4 (0.13 g, 0.11 mmol), CuI
(0.04 g, 0.21 mmol), i-Pr2NH (7.0 mL), and THF (15.0 mL). To this
solution under N2 was added 1,7-octadiyne (0.24 g, 2.3 mmol) in 0.5
mL of THF. The resulting solution was allowed to stir at room
temperature for 16 h. During this period, a substantial amount of white
precipitate formed. The reaction mixture was then added slowly to
rapidly stirring methanol (300 mL) to precipitate the crude polymer
1a in near quantitative yield. The polymer was further purified by
washing a chloroform (50 mL) solution with dilute NH4OH and then
H2O, evaporating the chloroform solution to dryness by rotoevaporation,
redissolving the polymer in THF, and finally precipitating the polymer
by adding the THF solution to rapidly stirring methanol (300 mL).
This yields 1a (44%, 0.30 g) as a light yellow-brown gummy solid. 1H
NMR (400 MHz, CDCl3): δ 0.88 (br, 3 H, CH3), 1.31 (br, 4 H, CH2),
1.45 (br, 2 H, CH2), 1.74 (br, 2 H, CH2), 1.81 (br, 4 H, CH2), 2.53 (br,
4 H, CH2), 3.80 (br, 3 H, OCH3), 3.92 (t, J ) 6.6 Hz, 2 H), CH2O,
6.81 (s, 1 H, CH), 6.84 (s, 1 H, CH). 13C {1H} NMR (100 MHz,
CDCl3): δ 14.03 (CH3), 19.40 (multiple resonances, CH2), 22.63 (CH2),
25.66 (CH2), 27.8 (multiple resonances, CH2), 29.26 (CH2), 31.55 (CH2),
56.32 (OCH3), 65.59 (OCH2), 77.2 (multiple resonances, CtC), 95.11
(multiple resonances, CtC), 113.13, 113.92, 115.38, 117.59, 153.54,
153.80 (C6H2). Mn/Mw ) 5400/30 000 by GPC. IR (film, KBr, cm-1):
2940, 2861, 2232 (CtC), 1501, 1464, 1403, 1273, 1204, 1039, 862.
Polymer 1e. This compound was prepared by a procedure identical
to that for 1d, using 1,6-heptadiyne (0.23 g, 2.5 mmol) instead of 1,7-
octadiyne and (0.09 g, 0.4 mmol) of 2-iodotoluene (7) to yield a lower
molecular weight polymer with better solubility. This yields 1e (42%,
0.28 g) as a light yellow-brown gummy solid. 1H NMR (400 MHz,
CDCl3): δ 0.87 (br, 3 H, CH3), 1.30 (br, 6 H, CH2), 1.59 (br, 2 H,
CH2), 1.92 (br, 2 H, CH2), 2.34 (s, 3 H, CH3), 2.65 (br, 2 H, CH2),
2.67 (br, 4 H, CH2), 7.18 (s, 1 H, CH), 7.19 (s, 1 H, CH). 13C {1H}
NMR (100 MHz, CDCl3): δ 14.12 (CH3), 18.89 (CH2), 20.01 (CH2),
22.61 (CH3), 28.17 (CH2), 29.19 (CH2), 30.63 (CH2), 31.76 (CH2), 34.03
(CH2), 80.02, 80.19 (CtC), 93.16, 93.89 (CtC), 122.46, 122.94,
131.91, 132.89, 136.90, 141.84 (C6H2). Mn/Mw ) 2000/3000 by GPC.
IR (film, KBr, cm-1) 2952, 2927, 2857, 2227 (CtC stretch), 1492,
1456, 1436, 1028, 892, 693.
Polymer 1f. This compound was prepared by a procedure identical
to that for 1d, using 1,5-hexadiyne (0.20 g, 2.5 mmol) instead of 1,7-
octadiyne and 2-iodotoluene (0.09 g, 0.4 mmol), to yield a lower
molecular weight polymer with better solubility. This yields 1f (40%,
0.25 g) as a light yellow-brown gummy solid. 1H NMR (400 MHz,
CDCl3): δ 0.88 (t, J ) 5.1 Hz, 3 H, CH3), 1.28 (br, 6 H, CH2), 1.56
(br, 2 H, CH2), 2.33 (s, 3 H, CH3), 2.68 (t, J ) 6.0, 2 H, CH2), 2.78 (s,
4 H, CH2), 7.20 (s, 1 H, CH2), 7.24 (s, 1 H, CH2). 13C {1H} NMR
(100 MHz, CDCl3): δ 14.08 (CH3), 19.91 (CH2), 20.11 (CH2), 22.56
(CH3), 28.89 (CH2), 30.44 (CH2), 31.65 (CH2), 33.82 (CH2), 80.32,
80.53 (CtC), 92.48, 93.06 (CtC), 122.32, 122.78, 131.92, 132.79,
137.04, 141.92 (C6H2). Mn/Mw ) 2300/3500 by GPC. IR (film, KBr,
cm-1) 3020, 2953, 2925, 2856, 2230 (CtC stretch), 1492, 1456, 1437,
1337, 1254, 895.
Polymer 1b. This compound was prepared by a procedure identical
that for 1a, using 1,6-heptadiyne (2.1 g, 2.3 mmol) instead of 1,7-
octadiyne. This yields 1b (41%, 0.28 g) as a light yellow-brown
gummy solid. 1H NMR (400 MHz, CDCl3): δ 0.88 (t, J ) 7.0 Hz,
3H, CH3), 1.32 (br, 4H, CH2), 1.47 (br, 2H, CH2), 1.79 (mult, 2 H,
CH2), 1.94 (mult, 2 H, CH2), 2.65 (br, 4 H, CH2), 3.81 (s, 3 H, OCH3),
3.94 (t, J ) 3.94, 2 H, CH2O) 6.85 (s, 1 H, CH), 6.87 (s, 1 H, CH). 13
C
{1H} NMR (100 MHz, CDCl3): δ 13.86 (CH3), 18.93 (multiple
resonances, CH2), 22.48 (CH2), 25.55 (CH2), 27.88 (CH2), 29.13 (CH2),
31.41 (CH2), 56.15 (CH3O), 69.42 (CH2O), 77.20 (CtC), 94.47 (CtC),
112.9, 113.7, 115.2, 117.4, 128.4, 153.4, 163.6 (C6H2). Mn/Mw ) 5300/
19 000 by GPC. IR (film, KBr, cm-1) 2948, 2903, 2867, 2835, 2232
(CtC stretch), 1502, 1465, 1403, 1273, 1229, 1038, 862.
Polymer 3a. A 100 mL Schlenk flask was charged with Cp2ZrCl2
(1.0 g, 3.4 mmol) and 30 mL of dry THF. The resulting solution was
cooled to -78 °C in a dry ice acetone bath, and n-BuLi (4.0 mL, 1.6
M, 6.4 mmol) was added dropwise over 5 min. The solution was
allowed to stir for 15 min at -78 °C, and then crude 1a (0.72 g, 2.3
mmol of diyne units) in 10 mL of dry THF was slowly added via
cannulae over 5 min. The reaction mixture was allowed to stir under
N2, while the bath slowly warmed to room temperature (3-4 h) and
then was allowed to stir for an additional 1 h at room temperature.
The conversion is very sensitive to a modest excess of n-BuLi, and
the product (2a) will decompose if stirred at room temperature for >
8 h. 2a was not isolated but was converted directly to 3a by addition
of HCl (15 mL, 6 M). The reaction mixture was then added slowly to
rapidly stirring methanol (400 mL) to precipitate crude polymer 3a.
The polymer was purified by washing with methanol and then pentane.
This yields 3a (88%, 0.65 g) as a bright yellow solid. 1H NMR (400
MHz, CDCl3): δ 0.87 (br, 3 H, CH3), 1.32 (br, 4 H, CH2), 1.45 (br, 2
H, CH2), 1.68 (br, 4 H, ring CH2), 1.76 (br, 2 H, CH2), 2.65 (br, 4 H,
ring CH2), 3.81 (br, 3 H, OCH3), 3.95 (br, 2 H, OCH2), 6.72 (s, 2 H,
CH), 6.81 (s, 2 H, CH). 13C {1H} NMR (100 MHz, CDCl3): δ 14.05
(CH3), 22.62 (CH3), 25.78, 26.43, 29.42, 30.57, 31.61, (all CH2), 56.23
(OCH3), 69.79 (OCH2), 113.36, 115.96, 119.49, 125.85, 127.01, 143.75,
150.47, 151.32 (aromatic and alkene). Mn/Mw ) 6200/23 000 by GPC.
Anal. Calcd for C438H582O44: C, 80.28; H, 8.97. Found: C, 79.92;
H, 9.03. IR (film, KBr, cm-1) 2930, 2857, 1493, 1463, 1404, 1205,
1037, 880.
Polymer 1c. This compound was prepared by a procedure identical
to that for 1a, using 1,5-hexadiyne (0.19 g, 2.4 mmol) instead of 1,7-
octadiyne and (0.11 g, 0.4 mmol) of 5 to yield a lower molecular weight
polymer with better solubility. This yields 1c (42%, 0.29 g) as a light
yellow-brown gummy solid. 1H NMR (400 MHz, CDCl3): δ 0.90 (br,
3 H, CH3), 1.31 (br, 4 H, CH2), 1.45 (br, 2 H, CH2), 1.75 (br, 2 H,
CH2), 2.80 (br, 4 H, ring CH2), 3.78 (s, 3 H, CH3O), 3.90 (t, J ) 6.51,
2 H, CH2O), 6.85 (s, 1 H, CH), 6.88 (s, 1 H, CH). 13C {1H} NMR
(100 MHz, CDCl3): δ 14.04 (CH3), 20.19 (CH2), 22.62 (CH2), 25.64
(CH2), 29.21 (CH2), 31.54 (CH2), 56.36 (CH3O), 69.72 (CH2O), 77.73
(CtC), 93.77 (CtC), 113.07, 113.89, 115.62, 117.98, 153.59, 153.79
(C6H2). Mn/Mw ) 2600/4600 by GPC. IR (film, KBr, cm-1) 2936,
2861, 2235 (CtC stretch), 1501, 1464, 1403, 1273, 1203, 1039, 863.
Polymer 1d. A 100 mL Schlenk flask was charged with 6 (1.0 g,
2.3 mmol), 2-iodotoluene (7, 0.4 g, 0.2 mmol), Pd(PPh3)4 (0.13 g, 0.11
mmol), CuI (0.04 g, 0.21 mmol), i-Pr2NH (7.0 mL), and THF (15.0
mL). To this solution under N2 was added 1,7-octadiyne (0.25 g, 2.4
mmol) in 0.5 mL of THF. The resulting solution was allowed to stir
at room temperature for 16 h. During this period, a substantial amount
of white precipitate formed. The reaction mixture was then added
slowly to rapidly stirring methanol (300 mL) to precipitate the crude
polymer 1d in near-quantitative yield. The polymer was further purified
by washing a chloroform (50 mL) solution with dilute NH4OH and
then H2O, evaporating the chloroform solution to dryness by roto-
evaporation, redissolving the polymer in THF, and finally precipitating
the polymer by adding the THF solution to rapidly stirring methanol
(300 mL). This yields 1d (48%, 0.32 g) as a light yellow-brown gummy
solid. 1H NMR (400 MHz, CDCl3): δ 0.88 (br, 3 H, CH3), 1.31 (br,
6 H, CH2), 1.60 (br, 2 H, CH2), 1.82 (br, 4 H, CH2), 2.34 (s, 3 H,
CH3), 2.53 (br, 4 H, CH2), 2.68 (t, J ) 5.4 Hz, 2 H, CH2), 7.18 (s, 1
Polymer 3b. This compound was prepared by a procedure identical
to that for 3a, using 1b (0.68 g, 2.3 mmol of diyne units) instead of
1a. This yields 3b (92%, 0.63 g) as a red solid. 1H NMR (400 MHz,
CDCl3): δ 0.91 (br, 3 H, CH3), 1.37 (br, 4 H, CH2), 1.53 (br, 2 H,
CH2), 1.85 (br, 2 H, ring CH2), 1.87 (br, 2 H, CH2), 2.81 (br, 4 H, ring
CH2), 3.88 (s, 3 H, OCH3), 4.01 (br, 2 H, OCH2), 7.04 (s, 2 H, CH),
7.33 (s, 1 H, CH), 7.37 (s, 1 H, CH). 13C {1H} NMR (100 MHz,
CDCl3): δ 14.12 (CH3), 22.73 (CH3), 25.07 (CH2), 25.95 (CH2), 29.50
(CH2), 31.71 (CH2), 32.18 (CH2), 56.15 (OCH3), 69.68 (OCH2), 111.59,
113.81, 114.03, 126.71, 127.02, 144.41, 150.84, 151.33 (aromatic and

A Zr-Coupling Route to Substituted Poly(p-phenylenedienylene)s
J. Am. Chem. Soc., Vol. 120, No. 18, 1998 4363
alkene). Mn/Mw ) 6400/22 000 by GPC. Anal. Calcd for C418H542O44:
C13H18O2I2: C, 33.93; H, 3.95. Found: C, 33.87; H, 3.92. IR (KBr,
cm-1) 2963, 2936, 2859, 1485, 1462, 1434, 1350, 1214, 1055, 1020,
996, 941, 850, 774.
C, 80.05; H, 8.73. Found: C, 76.67; H, 8.45. IR (film, KBr, cm-1
2951, 2930, 2866, 1492, 1462, 1409, 1203, 1037, 881.
)
Polymer 3c. This compound was prepared by a procedure identical
to that for 3a, using 1c (0.68 g, 2.4 mmol of diyne units) instead of 1a.
This yields 3c (88%, 0.60 g) as a purple solid. 1H NMR (400 MHz,
CDCl3): δ 0.91 (br, 3 H, CH3), 1.30 (br, 4 H, CH2), 1.52 (br, 2 H,
CH2), 1.84 (br, 2 H, CH2), 3.16 (br, 4 H, ring CH2), 3.85 (s, 3 H, OCH3),
3.98 (br, 2 H, OCH2), 6.97 (s, 2 H, CH), 7.08 (s, 1 H, CH), 7.10 (s, 1
H, CH). 13C {1H} NMR (100 MHz, CDCl3): δ 14.04 (CH3), 22.61
(CH3), 25.86 (CH2), 29.39 (CH2), 30.72 (CH2), 31.65 (CH2), 56.19
(OCH3), 69.61 (OCH2), 109.68, 111.56, 111.72, 125.81, 126.45, 143.65,
150.65, 151.06 (aromatic and alkene). Mn/Mw ) 3200/7700 by GPC.
Anal. Calcd for C208H262O24: C, 79.39; H, 8.41. Found: C, 79.52;
H, 8.69. IR (film, KBr, cm-1) 2952, 2932, 2861, 1495, 1464, 1413,
1285, 1206, 1040, 873, 802.
Polymer 3d. This compound was prepared by a procedure identical
to that for 3a, using 1d (0.64 g, 2.3 mmol of diyne units) instead of
1a. This yields 3d (90%, 0.58 g) as a colorless solid. 1H NMR (400
MHz, CDCl3): δ 0.89 (br, 3 H, CH3), 1.33 (br, 6 H, CH2), 1.58 (br, 2
H, CH2), 1.65 (br, 4 H, ring CH2), 2.31 (s, 3 H, CH3), 2.50 (br, 4 H,
ring CH2), 2.62 (br, 2 H, CH2), 6.56 (br, 1 H, CH), 6.61 (br, 1 H, CH),
7.04 (br, 2 H, CH). 13C {1H} NMR (100 MHz, CDCl3): δ 14.11 (CH3),
19.73 (CH2), 22.68 (CH3), 26.81 (CH2), 29.27 (CH2), 30.50 (CH2), 30.92
(CH2), 31.79 (CH2), 33.26 (CH2), 122.10, 130.32, 131.29, 133.75,
134.94, 135.58, 138.59, 142.61 (aromatic and alkene). Mn/Mw ) 4300/
2,5-Dimethoxy-4-methyliodobenzene (5). This compound was
prepared from 1,4-dimethoxy-3-methylbenzene, via a modified literature
procedure.16 A 1000 mL flask was charged with 12.0 g of 1,4-
dimethoxy-3-methylbenzene (79 mmol), 13.0 g of I2 (50 mmol), 1.8 g
of HIO3 (8.5 mmol), 300 mL of CH3COOH, 80 mL of H2O, and 20
mL of H2SO4. The reaction mixture was heated at 70 °C for 12 h and
treated as described above. Recrystallization from methanol gave 19.9
g of 5 as white crystals (91% yield). 1H NMR (400 MHz, CDCl3): δ
2.19 (s, 3H, CH3), 3.77 (s, 3H, OCH3), 3.83 (s, 3H, OCH3), 6.68 (s,
1H, C6H2), 7.17 (s, 1H, C6H2). 13C {1H} NMR (100 MHz, CDCl3): δ
16.5 (CH3), 56.1 (OCH3), 57.0 (OCH3), 81.4, 114.0, 121.0, 127.9, 152.2,
152.5 (aromatic). Anal. Calcd for C9H11O2I: C, 38.87; H, 3.99.
Found: C, 38.97; H, 3.94. IR (KBr, cm-1) 3003, 2959, 2919, 2840,
1494, 1467, 1440, 1368, 1280, 1212, 1047, 1030, 853, 778, 707.
1,4-Diiodo-2-methyl-5-hexylbenzene (6). This compound was
prepared from 1-hexyl-4-methylbenzene, via a modified literature
procedure.26 A 1000 mL flask was charged with 50.0 g of 1-hexyl-
4-methylbenzene (283 mmol), 50.0 g of I2 (200 mmol), 10 g of HIO3
(57 mmol), 350 mL of CH3COOH, 50 mL of H2O, and 30 mL of
H2SO4. The reaction mixture was heated at 70 °C for 4 days and treated
as described above. Recrystallization from methanol gave 71.3 g of 6
as white crystals (59% yield). 1H NMR (400 MHz, CDCl3): δ 0.89
(t, 3H, J ) 6.8, CH3), 1.31 (mult, 6H, CH2), 1.53 (mult, 2H, CH2),
2.33 (s, 3H, CH3), 2.58 (t, 2H, J ) 6.5, CH2), 7.59 (s, 1H, C6H2), 7.64
(s, 1H, C6H2). 13C {1H} NMR (100 MHz, CDCl3): δ 14.09 (CH3),
22.58 (CH3), 26.87, 28.95, 30.18, 31.59, 39.79 (CH2), 100.09, 100.86,
138.82, 139.70, 140.68, 144.77 (aromatic). Anal. Calcd for C13H18I2:
C, 36.45; H, 4.25. Found: C, 36.58; H, 4.22. IR (KBr, cm-1) 2950,
2921, 2847, 1459, 1343, 1039, 878, 768.
1,8-bis-(2′,5′-dimethoxy-4′-methylphenyl)-1,7-octadiyne (8a). A
500-mL round-bottom flask was charged with 2,5-dimethoxy-4-
methyliodobenzene (5, 5.0 g, 18 mmol), Pd(PPh3)4 (0.11 g, 0.10 mmol),
CuI (0.04 g, 0.21 mmol), i-Pr2NH (50 mL), and THF (100 mL). To
the solution was added 1,7-octadiyne (0.98 g, 9.2 mmol) dropwise over
5 min. The reaction mixture was stirred at room temperature for 18 h.
During this period, a substantial amount of white precipitate formed.
Addition of pentane (200 mL) to the reaction mixture was followed
by washing with dilute HCl, H2O, saturated NaHCO3, and H2O. The
pentane was removed by rotoevaporation, and the residual oil was
dissolved in warm methanol and recrystallized at -40 °C to yield white
crystals (3.2 g, 87% yield): mp ) 117-119 °C. 1H NMR (400 MHz,
CDCl3): δ 1.83 (t, J ) 5.9, 4H, CH2), 2.20 (s, 6 H, CH3), 2.54 (t, J )
7.0, 4 H, CH2), 3.76 (s, 6 H, CH3O), 3.82 (s, 6 H, CH3O), 6.66 (s, 2 H,
C6H2), 6.83 (s, 2 H, C6H2). 13C {1H} NMR (100 MHz, CDCl3): δ
16.6 (CH2), 19.4 (CH3), 28.1 (CH2), 55.9, 56.5 (CH3O), 77.2, 93.3
(CtC), 110.2, 114.1, 115.0, 127.8, 151.3, 154.0 (C6H2). HRMS m/z
calcd 406.2144; found 406.2136. IR (Nujol, KBr, cm-1) 2954, 2924,
2855, 1502. 1210, 1042, 862.
29 000 by GPC. Anal. Calcd for C434H574
: C, 89.99; H, 10.01.
Found: C, 86.44; H, 9.31. IR (film, KBr, cm-1) 2927, 2856, 1488,
1456, 1260, 1060, 913, 815.
Polymer 3e. This compound was prepared by a procedure identical
to that for 3a, using 1e (0.64 g, 2.4 mmol of diyne units) instead of 1a.
This yields 3e (84%, 0.55 g) as a orange solid. 1H NMR (400 MHz,
CDCl3): δ 0.88 (br, 3 H, CH3), 1.32 (br, 6 H, CH2), 1.60 (br, 2 H,
CH2), 1.79 (br, 2 H, ring CH2), 2.39 (br, 3 H, CH3), 2.73 (br, 6 H, CH2
and ring CH2), 7.07 (br, 1 H, CH), 7.12 (br, 1 H, CH), 7.26 (br, 2 H,
CH). 13C {1H} NMR (100 MHz, CDCl3): δ 14.11 (CH3), 19.85 (CH2),
22.72 (CH3), 25.09 (CH2), 29.36 (CH2), 31.20 (CH2), 31.83 (CH2), 32.21
(CH2), 33.52 (CH2), 116.39, 129.41, 130.33, 133.58, 135.01, 134.40,
138.64, 144.21 (aromatic and alkene). Mn/Mw ) 2400/6300 by GPC.
Anal. Calcd for C414H534: C, 90.21; H, 9.79. Found: C, 82.25; H,
9.40. IR (film, KBr, cm-1) 2953, 2927, 2856, 1699, 1456, 1054, 904.
Polymer 3f. This compound was prepared by a procedure identical
to that for 3a, using 1f (0.60 g, 2.4 mmol of diyne units) instead of 1a.
This yields 3f (92%, 0.57 g) as a red solid. 1H NMR (400 MHz,
CDCl3): δ 0.91 (br, 3 H, CH3), 1.34 (br, 6 H, CH3), 1.63 (br, 2 H,
CH2), 2.40 (br, 3 H, CH3), 2.56 (br, 2 H, CH2), 3.15 (br, 4 H, ring
CH2), 6.85 (br, 2 H, CH), 7.21 (br, 1 H, CH), 7.28 (br, 1 H, CH). 13
C
{1H} NMR (100 MHz, CDCl3): δ 14.13 (CH3),19.53, 19.83, 19,89
(all CH3), 22.70 (CH3), 29.22 (CH2), 30.63 (CH2), 30.81 (CH2), 31.22
(CH2), 31.77 (CH2), 33.23 (CH2), 114.12, 126.89, 128.05, 129.01,
133.38, 135.12, 138.38, 144.02 (aromatic and alkene). Mn/Mw ) 4200/
9400 by GPC. Anal. Calcd for C204H254: C, 90.52; H, 9.48. Found:
C, 87.29; H, 9.55. IR (film, KBr, cm-1) 2954, 2925, 2856, 1489, 1457,
886.
1,7-Bis(2′,5′-dimethoxy-4′-methylphenyl)-1,6-heptadiyne (8b). This
compound was prepared by a procedure identical to that for 8a, using
1,6-heptadiyne (0.92, 4.4 mmol) instead of 1,7-octadiyne. The product
was isolated as a light yellow solid after recrystallization from methanol
(3.0 g, 85% yield): mp ) 98-101 °C. 1H NMR (400 MHz, CDCl3):
δ 1.85 (q, J ) 6.8, 2H, CH2), 2.27 (s, 6 H, CH3), 2.76 (t, J ) 6.4, 4 H,
CH2), 3.83 (s, 6 H, CH3O), 3.85 (s, 6 H, CH3O), 6.73 (s, 2 H, C6H2),
6.96 (s, 2 H, C6H2). 13C {1H} NMR (100 MHz, CDCl3): δ 16.6 (CH2),
19.1 (CH3), 28.2 (CH2), 55.8 (OCH3), 56.5 (OCH3), 77.4, 92.7 (CtC),
110.1, 114.0, 115.0, 127.9, 151.3, 153.9 (C6H2). HRMS m/z calcd
392.1988; found 392.1984. IR (Nujol, KBr, cm-1) 2954, 2924, 2854,
1512, 1499, 1396, 1282, 1225, 1209, 1042, 869, 843, 796.
1,6-Bis(2′,5′-dimethoxy-4′-methylphenyl)-1,5-hexadiyne (8c). This
compound was prepared by a procedure identical to that for 8a, using
1,5-hexadiyne (0.72 g, 9.2 mmol) instead of 1,7-octadiyne. The product
was isolated as a light yellow solid after recrystallization from methanol
(2.5 g, 72% yield): mp ) 131-133 °C. 1H NMR (400 MHz,
CDCl3): δ 2.20 (s, 6 H, CH3), 2.81 (s, 4 H, CH2CC), 3.73 (s, 6 H,
2-Methoxy-5-hexoxy-1,4-diiodobenzene (4). This compound was
synthesized from 1-n-hexoxy-4-methoxybenzene, via a modified lit-
erature procedure.16 A 1000 mL flask was charged with 30 g of 1-n-
hexoxy-4-methoxybenzene (144 mmol), 32 g of I2 (126 mmol), 7.2 g
of HIO3 (41 mmol), 30 mL of H2SO4, 50 mL of H2O, and 300 mL of
CH3COOH. The reaction mixture was heated at 70 °C for 12 h,
followed by neutralization with a saturated NaOH solution until pH >
6. The reaction mixture was extracted with pentane (3 × 200 mL)
and washed with saturated aqueous Na2S2O3 (2 × 250 mL) to remove
the residual I2. Removal of solvent from the combined extracts gave
a white solid, which was recrystallized from methanol to give 50.4 g
of 4 as white crystals (76% yield). 1H NMR (400 MHz, C6D6): δ
0.89 (t, 3H, J ) 6.8, CH3), 1.25 (m, 6H, CH2), 1.50 (m, 2H, CH2),
2.96 (s, 3H, OCH3), 3.30 (t, 2H, J ) 6.8), CH2O), 6.94 (s, 1H, C6H2),
7.05 (s, 1H, C6H2). 13C{1H} NMR (400 MHz, C6D6): 14.26 (CH3),
22.93, 25.96, 29.31, 31.72 (CH2), 56.29 (OCH2), 69.84 (OCH3), 85.93,
86.58, 121.58, 122.91, 153.27, 153.59 (aromatic). Anal. Calcd for
(26) Rehanhn, M.; Schlu¨ter, A. D.; Feast, W. J. Synthesis 1988, 386.

4364 J. Am. Chem. Soc., Vol. 120, No. 18, 1998
Lucht et al.
CH3O), 3.81 (s, 6 H, CH3O), 6.66 (s, 2 H, C6H2), 6.84 (s 2H, C6H2).
13C {1H} NMR (100 MHz, CDCl3): δ 16.6 (CH2), 20.3 (CH3), 55.8,
56.6 (CH3O), 77.9, 91.9 (CtC), 110.1, 114.2, 115.2, 128.1, 151.4, 154.0
(C6H2). HRMS m/z calcd 378.1831; found 378.1828. IR (Nujol, KBr,
cm-1) 2995, 2933, 2848, 2830, 1502, 1465, 1395, 1209, 1044, 862.
1,8-Diphenyl-1,7-octadiyne (8d). A 500-mL round-bottom flask
was charged with iodobenzene (10.0 g, 49 mmol), Pd(PPh3)4 (0.11 g,
0.10 mmol), CuI (0.04 g, 0.21 mmol), i-Pr2NH (100 mL), and THF
(200 mL). To this solution was added 1,7-octadiyne (2.7 g, 25 mmol)
dropwise over 5 min. The reaction was allowed to stir at room
temperature for 18 h. During this period, a substantial amount of white
precipitate formed. Addition of pentane (200 mL) to the reaction
mixture was followed by washing with dilute HCl, H2O, saturated
NaHCO3, and H2O. The pentane was removed by rotoevaporation,
and the residual oil was dissolved in warm methanol and recrystallized
at -40 °C to yield white crystals (4.8 g, 76% yield): mp ) 31-33
°C. 1H NMR (400 MHz, CDCl3): δ 1.78 (m, 4 H, CH2), 2.49 (m, 4
H, CH2), 7.28 (m, 6 H, C6H5), 7.45 (m, 4 H, C6H5). 13C{1H} NMR
(100.7 MHz, CDCl3): δ 19.06, 27.93 (CH2), 80.98, 89.86 (CtC),
123.99, 127.59, 128.23, 131.60 (C6H5). HRMS m/z calcd 258.1409,
found 258.1412. IR (Nujol, KBr, cm-1) 3055, 2942, 2862, 2230 (CtC
stretch), 1598, 1490, 1441, 1330, 1070, 914, 756, 691.
1,7-Diphenyl-1,6-heptadiyne (8e). This compound was prepared
by a procedure identical to that for 8d, using 1,6-heptadiyne (2.3 g, 25
mmol) instead of 1,7-octadiyne. After column chromatography (silica
gel, hexane) the product was isolated as a light yellow oil (4.3 g, 72%
yield). 1H NMR (400 MHz, CDCl3): δ 1.97 (q, J ) 5.2, 2H, CH2),
2.66 (t, J ) 7.0, 4 H, CH2), 7.33 (mult, 6 H, C6H5), 7.50 (mult, 4H,
C6H5). 13C {1H} NMR (100 MHz, CDCl3): δ 18.8, 28.08 (CH2), 81.41,
89.33 (CtC), 123.95, 127.76, 128.34, 131.70 (C6H5). HRMS m/z calcd
244.1252, found 244.1245. IR (Nujol, KBr, cm-1) 2954, 2924, 2855,
2225 (CtC stretch), 1499, 1396, 1282, 1225, 1209, 1042, 918, 869,
718, 695.
1,6-Diphenyl-1,5-hexadiyne (8f). This compound was prepared by
a procedure identical to that for 8d, using 1,5-hexadiyne (2.0 g, 25
mmol) instead of 1,7-octadiyne. The product was isolated as a light
yellow solid after recrystallization from methanol (3.8 g, 67% yield):
mp ) 49-50 °C. 1H NMR (400 MHz, CDCl3): δ 2.66 (s, 4 H, CH2),
7.27 (mult, 6 H, C6H5), 7.41 (mult, 4 H, C6H5). 13C {1H} NMR (100
MHz, CDCl3): δ 19.81 (CH2), 81.57, 83.35 (CtC), 123.63, 127.78,
128.22, 131.65 (C6H5). Anal. Calcd for C18H14: C, 93.86; H 6.14;
found C, 93.43; H, 6.04. HRMS m/z calcd 230.1096, found 230.1092.
IR (Nujol, KBr, cm-1) 3055, 2911, 2840, 2450 (CtC stretch), 1488,
1441, 1275, 1071, 917, 755, 693.
(E,E)-1,2-Bis[(2′,5′-dimethoxy-4′-methylphenyl)methylene]cyclo-
hexane (9a). A 100 mL Schlenk flask was charged with Cp2ZrCl2
(0.29 g, 1.0 mmol) and 30 mL of dry THF. The solution was cooled
to -78 °C in a dry ice acetone bath, and n-BuLi (1.2 mL, 1.6 M, 1.9
mmol) was added dropwise over 5 min. The solution was allowed to
stir for 15 min at -78 °C, and then 8a (0.38 g, 0.94 mmol) in 10 mL
of dry THF was slowly added via cannulae over 5 min. The reaction
was allowed to stir under N2 while the bath slowly warmed to room
temperature (3-4 h), after which it was stirred for an additional 1 h at
room temperature. The zirconacyclopentadiene was not isolated but
was converted directly to 9a by addition of HCl (15 mL, 6 M).
Addition of Et2O (40 mL) to the reaction mixture was followed by
washing with dilute HCl, H2O, saturated NaHCO3, and H2O. The Et2O
was removed by rotoevaporation leaving a residual oil. The oil was
recrystallized from 1:1 Et2O/pentane to yield 81% of 9a (0.31 g, 0.76
mmol): mp ) 124-126 °C. 1H NMR (400 MHz, CDCl3): 1.66 (m,
4 H, CH2), 2.25 (s, 6 H, CH3), 2.62 (m, 4 H, CH2), 3.80 (s, 6 H, OCH3),
3.81 (s, 6 H, OCH3), 6.69 (s, 2 H, CH), 6.17 (s, 2 H, CH), 6.76 (s, 2
H, CH). 13C {1H} NMR (100 MHz, CDCl3): δ 16.4 (CH3), 26.4 (CH2),
30.5 (CH2), 56.1 (OCH3), 56.3 (OCH3), 113.4, 113.9, 119.5, 124.8,
126.0, 143.7, 151.0, 151.6 (C6H2 and CdC). HRMS m/z calcd
408.2301; found 408.2295. IR (Nujol, KBr, cm-1) 2928, 2856, 1501,
1398, 1302, 1209, 1045, 875.
mmol): mp ) 141-143 °C. 1H NMR (400 MHz, CDCl3): 1.83 (m,
2H, CH2), 2.25 (s, 6 H, CH3), 2.74 (m, 4 H, CH2), 3.81 (s, 6 H, OCH3),
3.83 (s, 6 H, OCH3), 6.71 (s, 2 H, CH), 6.94 (s, 2 H, CH), 7.24 (s, 2
H, CH). 13C {1H} NMR (100 MHz, CDCl3): δ 16.4 (CH3), 25.0 (CH2),
32.0 (CH2), 56.1 (OCH3), 56.3 (OCH3), 111.9, 113.8, 113.9, 125.4,
126.0, 143.6, 151.2, 151.3 (C6H2 and CdC). HRMS m/z calcd
394.2144; found 394.2146. IR (Nujol, KBr, cm-1) 2954, 2924, 2855,
1503, 1401, 1207, 1045.
(E,E)-1,2-Bis[(2′,5′-dimethoxy-4′-methylphenyl)methylene]cy-
clobutane (9c). This compound was prepared by a procedure identical
to that for 9a, using 8c (0.50 g, 1.3 mmol) instead of 8a. The oil was
recrystallized from 1:1 Et2O/pentane to yield 85% of 9c (0.42 g, 1.1
mmol): mp ) 137-141. 1H NMR (400 MHz, CDCl3): 2.24 (s, 6H,
CH3), 3.14 (s, 4 H, CH2), 3.81 (s, 6 H, OCH3), 3.84 (s, 6 H, OCH3),
6.71 (s, 2 H, CH), 6.93 (s, 2 H, CH), 7.05 (s, 2 H, CH). 13C {1H}
NMR (100 MHz, CDCl3): δ 16.4 (CH3), 30.4 (CH2), 55.9 (OCH3),
56.5 (OCH3), 109.6, 111.3, 114.4, 124.5, 126.2, 142.7, 150.9, 151.7
(C6H2 and CdC). EIMS: M+ ) 380. HRMS m/z calcd 380.1987;
found 380.1978. IR (Nujol, KBr, cm-1) 2954, 2924, 2855, 1508, 1403,
1289, 1225, 1208, 1045, 871, 850.
(E,E)-1,2-Bis(phenylmethylene)cyclohexane (9d). A 100 mL
Schlenk flask was charged with Cp2ZrCl2 (1.0 g, 3.4 mmol) and 30
mL of dry THF. The solution was cooled to -78 °C in a dry ice
acetone bath and n-BuLi (4.0 mL, 1.6 M, 6.5 mmol) was added
dropwise over 5 min. The solution was allowed to stir for 15 min at
-78 °C, and then 8d (0.83 g, 3.2 mmol) in 10 mL dry THF was slowly
added via cannulae over 5 min. The reaction was allowed to stir under
N2 while the bath slowly warmed to room temperature (3-4 h), and
stirring was continued for an additional 1 h at room temperature. The
zirconacyclopentadiene was not isolated but was converted directly to
9d by addition of HCl (15 mL, 6 M). Addition of Et2O (40 mL) to the
reaction mixture was followed by washing with dilute HCl, H2O,
saturated NaHCO3, and H2O. The Et2O was removed by rotoevapo-
ration leaving a residual oil. The oil was recrystallized from 1:1 Et2O/
pentane to yield 81% of 9d (0.68 g, 2.6 mmol): mp ) 125-127 °C.
1H NMR (400 MHz, CDCl3): 1.66 (m, 4 H, CH2), 2.65 (m, 4 H, CH2),
6.64 (s, 2 H, CH), 7.23 (m, 4 H, C6H5), 7.34 (m, 6 H, C6H5) 13C {1H}
NMR (100 MHz, CDCl3): δ 26.27 (CH2), 29.96 (CH2), 124.13, 126.34,
128.05, 129.46, 137.98, 144.47 (C6H5 and CdC). IR (Nujol, KBr,
cm-1) 3021, 2940, 2866, 1420, 921, 863, 699.
(E,E)-1,2-Bis(phenylmethylene)cyclopentane (9e). This compound
was prepared by a procedure identical to that for 9d, using 8e (0.75 g,
3.1 mmol) instead of 8d. The oil was recrystallized from 1:1 Et2O/
pentane and then sublimed to yield 84% of 9e (0.64 g, 2.6 mmol): mp
) 149-151 °C. 1H NMR (400 MHz, CDCl3): 1.85 (m, 2 H, CH2),
2.78 (m, 4 H, CH2), 6.99 (s, 2 H, CH), 7.22 (m, 2 H, C6H5), 7.36 (m,
4 H, C6H5), 7.43 (m, 4 H, C6H5). 13C {1H} NMR (100 MHz, CDCl3):
δ 25.1 (CH2), 32.0 (CH2), 119.15, 126.41, 128.30, 128.87, 138.32,
144.37 (C6H5 and CdC). HRMS m/z calcd 246.1409; found 246.1406.
Anal. Calcd for C19H18: C, 92.62; H, 7.38. Found C, 92.37; H, 7.36.
IR (Nujol, KBr, cm-1) 3052, 3025, 2953, 2924, 2855, 1485, 1446, 1175,
1077, 919, 866, 741, 695.
(E,E)-1,2-Bis(phenylmethylene)cyclobutane (9f). This compound
was prepared by a procedure identical to that for 9d, using 8f (1.5 g,
6.5 mmol) instead of 8d. The oil was recrystallized from 1:1 Et2O/
Pentane to yield 80% of 9f (1.2 g, 5.2 mmol): mp ) 125-128. 1H
NMR (400 MHz, CDCl3): 3.14 (s, 4 H, CH2), 6.34 (s, 2 H, CH), 7.19
(m, 2 H, C6H5), 7.32 (m, 8 H, C6H5). 13C {1H} NMR (100 MHz,
CDCl3): δ 30.65 (CH2), 117.50, 126.59, 127.80, 128.53, 137.42, 143.75
(C6H5 and CdC). HRMS m/z calcd 232.1252; found 232.1253. IR
(Nujol, KBr, cm-1) 3079, 3057, 3020, 2962, 2922, 1446, 908, 855,
744, 689, 512.
Acknowledgment. We thank the National Science Founda-
tion for support of this research. We thank Professor J.
McCusker, D. Wheeler, and N. Damrauer for valuable help in
obtaining the photoluminescence data. We also thank Dr. Fred
Hollander and Ryan Powers at the CHEXRAY facility at the
University of California at Berkeley for determination of the
crystal structures.
(E,E)-1,2-Bis[(2′,5′-dimethoxy-4′-methylphenyl)methylene]cyclo-
pentane (9b). This compound was prepared by a procedure identical
to that for 9a, using 8b (0.50 g, 1.3 mmol) instead of 8a. The oil was
recrystallized from 1:1 Et2O/pentane to yield 77% of 9b (0.41 g, 1.0

A Zr-Coupling Route to Substituted Poly(p-phenylenedienylene)s
J. Am. Chem. Soc., Vol. 120, No. 18, 1998 4365
Supporting Information Available: Tables of positional
and thermal parameters, bond lengths, angles, and torsional
angles and figures for the crystal structures of 9c and 9d and
absorption, excitation, and emission spectra for polymers 3c-f
(16 pages, print/PDF). See any current masthead page for
ordering information and Web access instructions.
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