Acyclic diene metathesis polymerization of divinylarenes and divinylferrocenes with grubbs-type olefin metathesis catalysts

Article abstract of DOI:10.1021/om701277p

1,4-Di(2-ethylhexyl)2,5-divinylbenzene, 1,4-di(2-ethylhexyloxy)-2,5- divinylbenzene, and 9,9-di(2-emylhexyl)-2,7-divinylfluorene were synthesized from the respective dialdehydes and ADMET polymerized using Grubbs II or Grubbs-Hoveyda-Grela-type olefin metathesis catalysts. The continuous removal of ethene under a dynamic vacuum of 20 mbar at elevated temperatures in high boiling solvents (1,2-dichlorobenzene) resulted in the formation of long-chain poly[2,5-di(2-ethylhexyl)-p-phenylenevinylene] (M_n > 100 kDa, P_n = 330, M_w/M_n = 3.1) and poly[9,9-di(2- ethylhexyl)fluorenyl-2,7-vinylene] (M_n > 70 kDa, P_n = 178). The PPV forms a free-standing film after evaporation of a toluene solution. 1,3-(Diisopropenyl)ferrocene could not be polymerized in this manner; ferrocene-containing polymers were obtained with 1,1′-di(4-vinylphenyl)-3, 3′,4,4′-tetramethylferrocene.

Full text of DOI:10.1021/om701277p

Organometallics 2008, 27, 1479–1485
1479
Acyclic Diene Metathesis Polymerization of Divinylarenes and
Divinylferrocenes with Grubbs-Type Olefin Metathesis Catalysts
Holger Weychardt and Herbert Plenio*
Anorganische Chemie im Zintl-Institute, Darmstadt UniVersity of Technology, Petersenstr. 18,
D-64287 Darmstadt, Germany
ReceiVed December 21, 2007
1,4-Di(2-ethylhexyl)2,5-divinylbenzene, 1,4-di(2-ethylhexyloxy)-2,5-divinylbenzene, and 9,9-di(2-
ethylhexyl)-2,7-divinylfluorene were synthesized from the respective dialdehydes and ADMET polymerized
using Grubbs II or Grubbs-Hoveyda-Grela-type olefin metathesis catalysts. The continuous removal of
ethene under a dynamic vacuum of 20 mbar at elevated temperatures in high boiling solvents (1,2-
dichlorobenzene) resulted in the formation of long-chain poly[2,5-di(2-ethylhexyl)-p-phenylenevinylene]
(Mn > 100 kDa, Pn ) 330, Mw/Mn ) 3.1) and poly[9,9-di(2-ethylhexyl)fluorenyl-2,7-vinylene] (Mn > 70
kDa, Pn ) 178). The PPV forms a free-standing film after evaporation of a toluene solution.
1,3-(Diisopropenyl)ferrocene could not be polymerized in this manner; ferrocene-containing polymers
were obtained with 1,1′-di(4-vinylphenyl)-3,3′,4,4′-tetramethylferrocene.
The ADMET (acyclic diene metathesis) polymeriation16,17
has rarely been used to synthesize conjugated polymers18 or
PPV-type polymers.19 Advantages of the ADMET approach are
the absence of problematic end groups, the typical trans-
configuration of the metathetically generated double bonds, and
the absence of branching within the polymer structure. Pioneer-
ing work from Thorn-Csányi utilized Schrock-type olefin
metathesis catalyst for the PPV synthesis from the respective
substituted divinylbenzenes. However, only short-chain oligo-
meric PPV were formed.20–22 Nomura et al. tested Grubbs-type
catalysts to obtain extended chain PPV,23 but this approach
critically relies on the removal of ethene by repeatedly cooling
the reaction mixture to -30 °C every 60 min, followed by
evacuation and reheating to the ADMET reaction temperature.
Such heat-cool-vacuum cycles were repeated during 5–24 h
to effect the PPV synthesis using Grubbs II or Grubbs-Hoveyda
catalysts. On the other hand, Harper et al. reported on the
formation of PPV oligomers when using Grubbs II catalyst.24
Introduction
Organic polymers such as poly(p-phenylenevinylenes) (PPVs)
are important materials with an excellent perspective toward
applications in organic light emitting diodes (OLED) and organic
photoconductors.1,2 Numerous polymerization procedures, such
as, for example, the Wessling,3 Gilch,4 Wittig and Wittig–
Horner,5,6 Heck,7–9 Suzuki,10,11 Stille,12 and ROMP reactions,13
have been applied in the synthesis of such polymers, and none
of them is entirely free from problems such as the incomplete
elimination of precursor functional groups. The Heck coupling
suffers from undesired 1,1-coupling reactions and an ill-defined
stereochemistry at the double-bond 1,2-cis/trans mixtures.14
Problems in controlling chain architecture and molecular mass
result in chain defects and large polydispersities in Gilch reaction
derived PPVs.4 Those problems are critical in device applica-
tions,15 and further advances in polymerization methodology
are required.
The significant progress in olefin metathesis catalyst develop-
ment in the last few years25–34 prompted us to study ADMET
* To whom correspondence should be addressed. E-mail: plenio@
tu-darmstadt.de.
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10.1021/om701277p CCC: $40.75
2008 American Chemical Society
Publication on Web 03/08/2008

1480 Organometallics, Vol. 27, No. 7, 2008
Weychardt and Plenio
Scheme 1. Synthesis of the Monomers 1-3a
+ -
a
Reagents and conditions: (a) n-BuLi, DMF, Et2O, -78 °C then aq HCl; (b) (Ph3PCH3) I , nBuLi, THF, rt.
polymerization of various divinylarenes, including ferrocene-
Table 1. ADMET Polymerization of
1,4-Di(2-ethylhexyl)-2,5-divinylbenzenea
containing monomers.35 The organometallic building block
could serve as a redox-switch to reversibly alter the optical and
conductivity properties for sensor devices.36 We wish to report
here on the synthesis of the respective high molecular weight
polymers via ADMET utilizing Grubbs-type olefin metathesis
catalysts.
solvent
T (°C)
Mn (103)
Mw/Mn
Pn
3,4-dichlorotoluenec
3,4-dichlorotoluenec
3,4-dichlorotoluenec
3,4-dichlorotoluenec
1,2,4-trichlorobenzenec
1,2,4-trichlorobenzenec
1,2,4-trichlorobenzenec
1,2,4-trichlorobenzenec
4-chloroanisolc
45
55
65
75
45
55
65
75
45
55
45
55
65
75
45
55
65
75
24.9
47.4
56.7
67.8
26.8
44.6
55.5
74.2
7.3
16.3
33.7
42.2
63.9
66.5
53.8
54.7
77.9
107.3
2.4
2.8
3.2
3.3
2.4
2.6
3.0
3.0
3.4
6.6
3.2
3.3
3.4
3.6
2.8
2.8
3.0
3.1
76
145
174
207
81
136
169
227
22
Results and Discussion
In order to improve the efficiency of the ADMET polymer-
ization, the continuous removal of ethene from the reaction flask
appears to be a more convenient strategy compared to a
discontinuous heat-cool-vacuum sequence. This approach
requires high boiling solvents and catalysts, which need to be
stable for long periods of time at elevated temperatures. Various
Grubbs-type catalysts are fairly robust and were tested in
combination with solvents such as 3,4-dichlorotoluene (bp 210
°C), 1,2,4-trichlorobenzene (bp 213 °C), 1,2-dichlorobenzene
(bp 180 °C), and 4-chloroanisol (bp 202 °C).
4-chloroanisolc
50
1,2,4-trichlorobenzeneb
1,2,4-trichlorobenzeneb
1,2,4-trichlorobenzeneb
1,2,4-trichlorobenzeneb
1,2-dichlorobenzeneb,d
1,2-dichlorobenzeneb,d
1,2-dichlorobenzeneb,d
1,2-dichlorobenzeneb,d
104
129
196
204
165
167
240
330
a Conditions: 1 mol% catalyst, initial monomer concentration 0.2 M,
reaction time 3 d. b Catalyst 1. c Catalyst 2. d Slow evaporation of sol-
vent. Optimized reaction conditions but with very slow evaporation of
solvent (p ) 20 mbar).
Monomer Synthesis. The three divinyl monomers 1,23 2, and
3 were synthesized by converting the respective dibromides into
the dialdehydes4,23,37,38 and then into the desired divinyls using
(Ph3PCH3)+I- (Scheme 1). The advantage of this synthetic route
is the facile separation of the desired products (dialdehyde and
divinyl species) from monoaldehyde impurities, which may
result from the incomplete conversion of the dibromide (Scheme
1, a) or the incomplete Wittig reaction to the divinyl monomers
(Scheme 1, b). The strong polarity change of the reactants in
each conversion step (Scheme 1) facilitates the chromatographic
separation of the respective monofunctional species. 1,4-Bis[(2-
ethylhexyl)oxy]-2,5-divinylbenzene has previously been syn-
thesized via Stille coupling of the respective diiodide with
Sn(vinyl)4.37 However, this approach inevitably produces small
amounts of monovinylated products, which are difficult to
remove from the divinylbenzene product. However, in order to
enable the efficient polymerization of the monomers to a high
molecular weight PPV, high-purity starting materials are
mandatory.
Scheme 2. Catalysts Used for ADMET Polymerization
PPV via ADMET Polymerization. We tested several
solvent/catalyst combinations for the ADMET polymerization
of the divinyl monomer 1 (Table 1). In order to drive olefin
metathesis to completion the continuous removal of ethene
appears to be very helpful; this is best done by performing the
reaction under mild vacuum. Consequently, high boiling solvents
are required. The four solvents, 1,2-dichlorobenzene, 3,4-
dichlorotoluene, 1,2,4-trichlorobenzene, and 4-chloroanisol, and
the Grubbs I and the Grubbs-Hoveyda-Grela complex39
(Scheme 2) were tested in the ADMET polymerization of 9,9-
di(2-ethylhexyl)fluorenyl-2,7-vinylene (Scheme 3). Reactions
were carried out under a dynamic vacuum of 20 mbar pressure.
(31) Romero, P. E.; Piers, W. E. J. Am. Chem. Soc. 2005, 127, 5032.
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Macromol. Symp. 2006, 245–246, 22.
The course of the condensation reaction can be followed by
monitoring the fluorescence of the reaction mixture, which
(36) Fery-Forgues, S.; Delavaux-Nicot, B. J. Photochem. Photobiol. A
2000, 132, 137.
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N. W.; Kim, C. Y. J. Poly. Sci. A 2004, 42, 557.
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Chem. 2003, 1, 1157.
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G.; Grela, K. J. Am. Chem. Soc. 2004, 126, 9318.

Acyclic Diene Metathesis Polymerization of DiVinylarenes
Organometallics, Vol. 27, No. 7, 2008 1481
Scheme 3. Synthesis of the ADMET Polymers
Figure 1. GPC trace of poly-1.
as can be seen in Table 1, in the long run both catalysts produce
roughly the same polymers. Given the identity of the active
species this is hardly surprising.
Initially, we tried to avoid the evaporation of the solvents by
applying a -15 °C cooled reflux condenser on top of the
reaction flask. However, we later realized that the very slow
evaporation of the solvent during a few days poses no problem.
On the contrary, the use of the comparatively volatile solvent
(1,2-dichlorobenzene, bp 180 °C) led to the formation of very
high molecular weight polymers, even though a viscous solution
was already formed during the first day, while on the third day
a yellow gumlike solid remained in the flask. This material was
dissolved in CH2Cl2, and following the normal workup, very
high molecular weight polymers were isolated. The polymer
produced at 75 °C using catalyst 2 has a Mn in excess of 100000
corresponding to a 330-mer.
Scheme 4. Synthesis of a 1,3-(Diisopropenyl)ferrocenea
1
PPV Polymer Properties. In the vinylic region of the H
NMR spectra of poly-1, poly-2, and poly-3, only a single signal
at 7.27 ppm is visible. Peaks at 6.65 ppm, corresponding to the
cis-vinyl-H,40 are not observed. In our ADMET polymers, the
R-methylene protons display only one signal, which is indicative
of a highly ordered structure. It was reported that poly[2,5-
diheptyl-p-phenylenevinylene] synthesized via the Wessling
route displays two signals for the inequivalent R-methylene
protons at 2.77 and 2.43 ppm.41 The second signal was assigned
to a less ordered structure. Obviously, the ADMET polymers
reported here are all-trans and defect-free within the sensitivity
of the NMR experiment.
A high degree of polymerization and the resulting morphology
changes are required to enable the efficient formation of polymer
films, which is of decisive importance for OLED applications.
The morphology of the PPV poly-1 changes drastically upon
chain elongation; with Pn ) 22 a yellow powder is formed,
while simple evaporation of a toluene solution of the long chain
poly-1 with Pn ) 227 or Pn ) 330 (Figure 1) gave a
mechanically stable, yellow foil (Figure 2).
ADMET Polymerization of 1,4-Di(2-ethylhexyloxy)-2,5-
divinylbenzene. Next we applied the optimized ADMET
conditions to 4-di(2-ethylhexyloxy)-2,5-divinylbenzene 2 to
produce poly-2. However, in the polymerization reaction this
monomer performed poorly. Table 2 summarizes the data; even
at elevated temperatures the degree of polymerization is modest.
The likely reason for this failure is that o-vinyl ethers are able
to act as bidentate ligands to Ru forming inhibited Grubbs-
Hoveyda type species with chelating monomers, such as 2.
a
Reagents and conditions: (a) THF, -78 °C; (b) optimized ADMET
conditions.
initially is pink and then changes to blue and green and finally
yellow, indicative of the growing polymer chain. During the
reaction, the viscosity of the reaction mixture changes, turning
oily on the second day and highly viscous on the third day, so
stirring became difficult. This is due to partial loss of solvent
as well as to the formation of polymers. After the reaction,
dilution with toluene, quenching of the catalyst with ethylvinyl-
ether and filtration of the solution into acetone led to the
precipitation of the yellow polymer, which was finally filtered
off and dried. Following this procedure, a number of polym-
erization experiments using different catalysts and solvents were
performed and the resulting polymers analyzed by GPC
(Table 1).
Both catalysts produce high molecular weight polymers with
dispersities of close to 3 in 3,4-dichlorotoluene, 1,2,4-trichloro-
benzene, and 1,2-dichlorobenzene. This is slightly higher than
the theoretical Mw/Mn of 2 expected for this polycondensation
reaction.16 The ADMET results in the various solvents do not
differ drastically; the only exception is 4-chloroanisol in which
much shorter chain length (Pn ) 50) and very high polydis-
persities were produced. The reason for this is unclear, but it
has been reported that Grubbs-type olefin metathesis catalysts
in ethereal solvents (Et2O, THF) are less efficient. Catalyst 2
(Scheme 3) initiates more quickly (rapid ethene evolution) but,
(40) Rehahn, M.; Schlüter, A. D. Macromol. Chem. Rap. Commun. 1990,
11, 375.
(41) Sonoda, Y.; Kaeriyama, K. Bull. Chem. Soc. Jpn. 1992, 65, 85.

1482 Organometallics, Vol. 27, No. 7, 2008
Weychardt and Plenio
Figure 3. UV/vis spectra of poly-1, -2, and -3 (10-5 M in THF).
Figure 2. Free-standing film of poly-1 (Pn ) 330) under UV
illumination.
Table 2. ADMET Polymerization of
1,4-Di(2-ethylhexyloxy)-2,5-divinylbenzene 2a
T (°C)
Mn (103)
Mw/Mn
Pn
55
65
75
1.4
1.7
3.9
1.2
2.5
2.6
4
5
11
a Conditions: 1 mol % of catalyst, initial monomer concentration 0.2
M, reaction time 3 d, solvent 1,2,4-trichlorobenzene, catalyst 2.
Table 3. ADMET Polymerization of
9,9-Di(2-ethylhexyl)-2,7-divinylfluorene 3a
initial monomer
concentration (M)
T (°C)
Mn (103)
Mw/Mn
Pn
0.20
0.10
0.05
0.05
45
45
45
55
17.4
25.8
34.5
73.5
1.9
2.3
2.7
2.7
42
62
84
Figure 4. Emission spectra of poly-1, -2, and -3 (excitation
wavelength 250 nm (poly-1, -3), 330 nm (poly-2); 10-5 M, in
THF).
178
a Conditions:
1,2,4-trichlorobenzene, catalyst 2.
1
mol
%
of catalyst, reaction time
3
d, solvent
ꢀ (L · mol-1 · cm-1), and λmax emission (nm)) poly-1 (423,
25300, 492), poly-2 (496, 24500, 554), and poly-3 (454, 71600,
464).
ADMET Polymerization of 9,9-Di(2-ethylhexyl)fluorenyl-
2,7-vinylene. The synthesis of poly[9,9-di(2-ethylhexyl)fluo-
renyl-2,7-vinylene] 3 was carried out according to the optimized
procedure for poly[2,5-di(2-ethylhexyl)-p-phenylenevinylene].
The polymerization of 3 at 0.2 M initial concentration led
to the precipitation of a yellow-green powder after a single day.
The amount of insoluble material further increased during the
next 48 h. Filtration of the polymer and analysis by GPC
analysis showed this to be of relatively low molecular weight
(Table 3). Obviously, solubility problems of the growing
polymer chain led to the formation of short chains. Conse-
quently, the experiments were repeated using lower initial
monomer concentrations of 0.1 and 0.05 M, respectively, which
resulted in much longer polymer chains.
The reason for the limited solubility of the fluorene-based
polymer could be that in contrast to poly-1 the solubilizing
groups are attached on one side of the molecule only, facilitating
the association of the flat aromatic fluorene backbone. In
contrast, in poly-1 the growing chain is encapsulated by the
two alkyl chains on both sides of the monomer. This interpreta-
tion is supported by the appearance of the poly-3 which forms
a brittle solid, quite unlike the flexible poly-1.
The good solvation of poly[2,5-di(2-ethylhexyl)-p-phenyl-
enevinylene] and its orientational freedom in solution leads to
broad and unstructured absorption spectra.42 On comparing the
spectrum of poly-1 with that of poly[2,5-di(2-ethylhexyl)-p-
phenylenevinylene] reported by Nomura et al., the absorption
maximum in the latter polymer lies at 412 nm.23 The batho-
chromic shift of 11 nm in poly-1 should be related to the
different chain length and provides evidence for extended
conjugation chain lengths.
The broad absorption spectrum of poly[2,5-di(2-ethylhexyl-
oxy)-p-phenylenevinylene] has different absorption maxima due
to the electron-donating character of the alkoxy groups. In the
spectrum of poly[2-methoxy-5-(2-ethylexyloxy)-p-phenyl-
enevinylene] (λmax) 501 nm),43 the absorption maximum is
shifted by 5 nm to longer wavelength with respect to poly-2.
This is caused by the much lower average number of repeating
units (Pn ) 11 in poly-2), indicating that the maximum of
effective conjugation chain length has not been reached.44 The
spectrum of poly[9,9-di(2-ethylhexyl)fluorenyl-2,7-vinylene]
poly-3 is more structured, displaying two relatively narrow
Optical Properties of the Polymers. Poly-1, -2, and -3
display different colors, which are due to πfπ* transitions in
the conjugated π-electron system. The absorption and emission
spectra of the respective polymers in solution (10-5 M in THF)
were determined (Figures 3 and 4). The spectroscopic data of
the respective polymers are as follows: (λmax absorption (nm),
(42) Gettinger, C. L.; Heeger, A. J.; Drake, J. M.; Pine, D. J. J. Chem.
Phys. 1994, 101, 1673.
(43) Wu, X.; Shi, G.; Chen, F.; Han, S.; Peng, J. J. Polym. Sci.: Part A
2004, 42, 3049.
(44) Peeters, E.; Ramos, A. M.; Meskers, S. C. J.; Janssen, R. A. J.
J. Chem. Phys. 2000, 112, 9445.

Acyclic Diene Metathesis Polymerization of DiVinylarenes
Organometallics, Vol. 27, No. 7, 2008 1483
Scheme 5. Synthesis of a Divinyl-Substituted Ferrocenea
bands at 427 and 454 nm. This is indicative of a more
aggregated structure of poly-3,42 likely caused by π-stacking
of the fluorene units and separation of the 2-ethylhexyl groups.
The emission spectra of poly[2,5-di(2-ethylhexyl)-p-phenyle-
nevinylene] (λmax) 492, 524 nm) exhibit two bands, and since
those are not the mirror image of the absorption spectrum it
follows that the emission comes from individual segments of
the polymer.45
The emission spectrum of poly[2,5-di(2-ethylhexyloxy)-p-
phenylenevinylene] (λmax) 554 nm) experiences a bathochromic
shift but is otherwise similar to that of poly-1. A comparison
with the emission spectrum of poly[2-methoxy-5-(2-ethylexyl-
oxy)-p-phenylenvinylene (λmax) 582 nm) again reveals that the
convergence of the conjugation length has not been reached.
The emission of poly[9,9-di(2-ethylhexyl)fluorenyl-2,7-vinyl-
ene] (λmax) 464, 494 nm) is much better resolved than those
of the other polymers reported here, and the same arguments
regarding the polymer microstructure apply.
a
Reagent and conditions: (a) nBuLi, TMEDA, N-formylpiperidine;
(b) (Ph3PCH3)+I-, nBuLi, THF, rt.
Scheme 6. ADMET Copolymerization (3 d, 55 °C, Catalyst 2
(1 mol %), Initial Monomer Concentration 0.5 M)
Attempted Synthesis of a Ferrocenylene-Vinylene Poly-
mer. In an attempt to produce PPV-related ferrocene polymers,
we synthesized a ferrocene with two terminal olefins. The five
methyl groups were intended to serve as solubilizing units;
related ROMP generated ferrocene polymers were reported to
be soluble only in the presence of such moieties.46–48 The 1,3-
substitutent pattern was chosen, since it allows a more efficient
transfer of electronic information along the chain than 1,1′-
substituted ferrocenes.49–51 3-(1-Methylethenyl)-6,6-dimethyl-
fulvene 4 was synthesized using a modified synthesis based on
Fenton’s work,52 and a different procedure was recently
published by Erker.53 The reaction of the 1,3-(diisopropenyl)-
cyclopentadienide with Cp*Fe(tmeda)Cl54 gave the 1,3-(diiso-
propenyl)ferrocene 6 in 78% yield.
The optimized ADMET procedure with catalysts 1 and 2 was
tried for the synthesis of the respective polymer. Unfortunately,
we were not able to obtain the desired ferrocene polymer, even
when 5 mol % of catalyst and elevated temperatures (75 °C)
were used. Only starting material was isolated following
chromatographic workup of the reaction mixture.
ADMET Copolymerization of Fluorene and Ferrocene
Divinyls. In order to obtain ferrocene-containing polymers, a
different organometallic building block was required (Scheme
5). 1-(4-Bromophenyl)-3,4-dimethylcyclopentadienide was re-
acted with FeCl2 · (THF)1.5 to yield 1,1′-di(4-bromophenyl)-
3,3′,4,4′-tetramethylferrocene 7 in 46% yield; the four methyl
groups are required as solubilizing groups. The dilithiation of
ferrocene 7 and the reaction with N-formylpiperazine gave the
dialdehyde 8 in 76% yield, which upon reaction with the Wittig
reagent resulted in the formation of the divinyl 9 in 95%. The
four methyl substituents are useful as solubilizing groups.
The copolymerization of 4 equiv of divinylfluorene 3 and 1
equiv of divinylferrocene 9 was successful using our optimized
ADMET protocol (Scheme 6); the resulting polymer has Mn )
25100, Mw/Mn ) 1.6, and Pn ) 60. The ratio of the two
monomers in the resulting polymer closely resembles the
monomer composition, indicative of similar polymerization
efficiency.
The mixed fluorene-ferrocene poly-4 has a significantly better
solubility than the polyfluorene poly-3. While the poor solubility
of poly-3 was attributed to the efficient packing of the fluorene
units, the incorporation of a significant amount of flexible
ferrocene units into the polymer seems to disfavor the close
association of the arenes.
It is interesting to note that the incorporation of ferrocene
into the polymer chain leads to a drastic decrease of the
fluorescence intensity of poly-4 compared to poly-3 (Figure 5).
Several explanations are feasible: (a) ferrocene is known to act
as an efficient quencher, (b) the absorption maximum of
ferrocene lies at 440 nm, which is close to the emission
maximum of poly-4, and (c) the effective conjugation length
in poly-4 can be expected to be much shorter due to the less
efficient conjugation across the 1,1′-substituted ferrocene unit.
(45) Weder, C.; Wrighton, M. S. Macromolecules 1996, 29, 5157.
(46) Stanton, C. E.; Lee, T. R.; Grubbs, R. H.; Lewis, N. S.; Pudelski,
J. K.; Callstrom, M. R.; Erickson, M. S.; McLaughlin, M. L. Macromol-
ecules 1995, 28, 8713.
(47) Heo, R. W.; Park, J.-S.; Goodson, J. T.; Claudio, G. C.; Takenaga,
M.; Albright, T. A.; Lee, T. R. Tetrahedron 2004, 60, 7225.
(48) Heo, R. W.; Park, J.-S.; Lee, T. R. Macromolecules 2005, 38, 2564.
(49) Plenio, H.; Hermann, J.; Leukel, J. Eur. J. Inorg. Chem. 1998, 2063.
(50) Plenio, H.; Hermann, J.; Sehring, A. Chem. Eur. J. 2000, 6, 1820.
(51) Baumert, M.; Fröhlich, J.; Stieger, M.; Frey, H.; Mülhaupt, R.;
Plenio, H. Macromol. Rap. Commun. 1999, 20, 203.
(52) Fenton, D. M.; Hurwitz, M. J. J. Org. Chem. 1963, 28, 1646.
(53) Paradies, J.; Fröhlich, R.; Kehr, G.; Erker, G. Organometallics 2006,
25, 3920.
Summary and Conclusions
We have developed a reaction protocol which allows the efficient
ADMET polymerization of 1,4-bis(2-ethylhexyl)-2,5-divinylben-
zene 1 and 9,9-di(2-ethylhexyl)fluorenyl-2,7-vinylene 3 in high
boiling solvents with continuous removal of ethene under 20 mbar
dynamic vacuum using equally efficient Grubbs II and Grubbs-
Hoveyda-Grela-type catalysts. The highly fluorescent, all-trans-
(54) Jonas, K.; Klusmann, P.; Goddard, R. Z. Naturforsch. B 1995, 50,
394.

1484 Organometallics, Vol. 27, No. 7, 2008
Weychardt and Plenio
CHO), 7.71 (s, 2 H, aryl-H), 2.98 (d, 4 H, aryl-CH2-), 1.57–1.21 (m,
18 H, alkyl-H), 0.95–0.88 (m, 12 H, -CH3). 13C NMR (CDCl3): δ
191.6, 142.5, 136.9, 133.5, 42.1, 35.9, 32.2, 28.7, 25.5, 22.9, 13.0,
10.7.
1,4-Di(2-ethylhexyl)-2,5-divinylbenzene (1). To a suspension
of (Ph3PCH3)+I- (8.60 g, 21.25 mmol) in THF (250 mL) at 0 °C
was added n-BuLi (8.5 mL, 21.25 mmol, 2.5 M), followed after
10 min by a solution of the 2,5-di(2-ethylhexyl)benzene-1,4-
dicarbaldehyde (2.54 g, 7.10 mmol) in THF (70 mL). The reaction
mixture was allowed to room temperature and stirring continued
for 1 d. The reaction mixture was added to water (250 mL) and
stirred for 10 min and then the product extracted with diethyl ether
(3 × 100 mL). The combined organic solutions were dried over
MgSO4 and filtered and the volatiles evaporated. The residue was
purified by chromatography (silica, n-pentane). Yield: 1.73 g, 4.89
1
mmol, 69%. H NMR (CDCl3): δ 7.21 (s, 2 H, aryl-H), 6.95 (dd,
Figure 5. Emission spectra of poly-3 and -4 (excitation wavelength
2 H, vinyl-H), 5.60 (dd, 2 H, vinyl-H), 5.22 (dd, 2 H, vinyl-H),
2.55 (d, 4 H, aryl-CH2), 1.56–1.23 (m, 18 H, alkyl-H), 0.96–0.84
(m, 12 H, -CH3). 13C NMR (CDCl3): δ 136.8, 135.7, 134.8, 127.7,
114.4, 40.3, 37.3, 32.4, 28.7, 25.6, 23.1, 14.1, 10.8.
250 nm, 10-5 M, in THF).
configured, defect-free PPV-type poly-1 with Pn ) 330 and Mn >
100 kDa obtained in this manner forms a free-standing film upon
evaporation of a toluene solution. The UV/vis spectra are indicative
of extended conjugation chain length. The ADMET polymerization
of monomer 3 suffers from the diminished solubility of the resulting
polymer, nonetheless Pn ) 177 with Mn ) 75 kDa is possible,
when working in dilute solutions. We were not at all able to
ADMET polymerize 1,3-isopropenylferrocene using the optimized
ADMET protocol. The incorporation of ferrocene in a poly-
vinylene-type polymer is possible only when using 1,1′-di(4-
vinylphenyl)-3,3′, 4,4′-tetramethylferrocene as the monomer. The
key to high molecular weights obtained by us is the use of high
purity monomers and the slow but continuous removal of solvent
and ethene from the reaction mixture.
9,9-Di(2-ethylhexyl)fluorenyl-2,7-dicarbaldehyde. A solution
of 9,9-di(2-ethylhexyl)fluorenyl-2,7-dibromide (16.62 g, 30.3 mmol)
was cooled to -78 °C and n-BuLi (28 mL, 70.0 mmol, 2.5 M) added.
The solution was warmed to room temperature and stirring continued
for another 2 h. After cooling again to -78 °C, a solution of DMF
(5.6 mL, 5.26 g, 72 mmol) in diethyl ether (15 mL) was added
dropwise. The reaction mixture was allowed to room temperature and
stirring continued for 18 h. The reaction mixture was dumped on ice-
cooled 2 N HCl (100 mL), the organic layer separated, and the aqueous
phase extracted with diethyl ether (3 × 150 mL). The combined
ethereal solutions were dried over MgSO4, filtered, and evaporated.
The residue was purified by chromatography (silica, cyclohexane/ethyl
acetate) 10:1). Yield: (6.58 g, 14.7 mmol, 49%). 1H NMR (CDCl3):
δ 10.10 (s, 2 H, aryl-CHO), 7.94 (m, 6 H, aryl-H), 2.09 (d, 4 H, aryl-
CH2), 0.85–0.41 (m, 30 H, alkyl-H). 13C NMR (CDCl3): δ 191.9,
152.6, 145.7, 135.9, 129.9, 124.8, 121.3, 55.3, 44.3, 34.7, 33.6, 27.9,
26.9, 22.6, 13.9, 10.2.
Experimental Section
NMR spectroscopy: Bruker AM-200 (1H 200 MHz), Bruker AC-
300 (1H 300 MHz, 31P 121 MHz, 13C 75 MHz), and Bruker Advance
500 (1H 500 MHz, 13C 125 MHz) and were referenced vs TMS (1H,
13C) and 85% aq H3PO4 (31P). UV/vis spectra: 10 mm quartz glass
cuvettes on a Specord S10 (Firma Analytik Jena) using a tungsten-
halogen and a D2 source. Photoluminescence: 10 mm quartz glass
cuvettes, Cary eclipse fluorescence photometer (Varian), pulsed Xe-
lamp. GPC measurements: in THF with toluene internal standard at
303 K, 1.0 mL/min flow, Waters 486 UV detection (254 nm), Waters
RI 410 refractometer; columns, PSS (SDV 1000000, SDV 100000
and SDV 1000) (PSS ) polystyrene standard calibration). Starting
materials were commercially available or synthesized according to
literature procedures: 3,4-dimethylcyclopentadiene55 and 1-(4-bro-
mophenyl)-3,4-dimethylcyclopentadiene.56
1,4-Di(2-ethylhexyloxy)-2,5-divinylbenzene (2). To a suspen-
sion of (Ph3PCH3)+I- (7.15 g, 17.7 mmol) in THF (100 mL) at 0
°C was added n-BuLi (7.1 mL, 17.7 mmol, 2.5 M), followed after
10 min by a solution of the dialdehyde (2.28 g, 5.9 mmol) in THF
(60 mL). The reaction mixture was allowed to room temperature
and stirring continued for 1 d. The reaction mixture was added to
water (300 mL) and stirred for 10 min and then the product
extracted with diethyl ether (3 × 100 mL). The combined organic
solutions were dried over MgSO4 and filtered and the volatiles
evaporated. The residue was purified by chromatography (silica,
1
n-pentane). Yield: 1.59 g, 4.1 mmol, 70%. H NMR (CDCl3): δ
7.05 (dd, 2 H, vinyl-H), 6.99 (s, 2 H, aryl-H), 5.72 (dd, 2 H, vinyl-
H), 5.24 (dd, 2 H, vinyl-H), 3.85 (d, 4 H, O-CH2), 1.76–1.31 (m,
18 H, alkyl-H), 0.96–0.88 (m, 12 H, -CH3). 13C NMR (CDCl3):
δ 150.7, 131.6, 127.1, 113.8, 110.1, 71.5, 39.7, 30.7, 29.2, 24.1,
23.1, 14.1, 11.2.
2,5-Di(2-ethylhexyl)benzene-1,4-dicarbaldehyde. A solution of
the 2,5-di(2-ethylhexyl)benzene-1,4-dibromide (4.60 g, 10.0 mmol) in
diethyl ether (125 mL) was cooled to -78 °C and t-BuLi (15.0 mL,
22.0 mmol, 1.5 M) added dropwise. The reaction mixture was stirred
(1 h) at this temperature and then DMF (1.93 mL, 1.83 g, 25.0 mmol)
added, followed after 30 min by more t-BuLi (30.00 mL, 44.0 mmol,
1.5 M) and 1 h later by the next batch of DMF (3.86 mL, 3.60 g, 50.0
mmol). The reaction mixture was allowed to room temperature during
12 h and then poured into ice-cooled 2 N HCl (150 mL). The organic
layer was separated and the aqueous phase extracted with diethylether
(3 × 50 mL). The combined ethereal solutions were dried over MgSO4
and filtered, and the volatiles were evaporated. The residue was purified
by chromatography (silica, cyclohexane/ethyl acetate ) 40:1). Yield:
9,9-Di(2-ethylhexyl)-2,7-divinylfluorene (3). To a suspension of
(Ph3PCH3)+I- (17.83 g, 44.2 mmol) in THF (250 mL) at 0 °C was
added n-BuLi (17.68 mL, 44.2 mmol, 2.5 M), followed after 10 min
by a solution of the 9,9-di(2-ethylhexyl)fluorenyl-2,7-dicarbaldehyde
(6.58 g, 14.7 mmol) in THF (120 mL). The reaction mixture was
allowed to warm to room temperature and stirring continued for 1 d.
The reaction mixture was added to water (300 mL) and stirred for 10
min and then the product extracted with diethyl ether (3 × 150 mL).
The combined organic solutions were dried over MgSO4 and filtered
and the volatiles evaporated. The residue was purified by chromatog-
1
1.97 g, 5.5 mmol, 55%. H NMR (CDCl3): δ 10.38 (s, 2 H, aryl-
1
raphy (silica, n-pentane). Yield: 5.60 g, 12.6 mmol, 86%. H NMR
(CDCl3): δ 7.51 (d, 2 H, aryl-H), 7.29 (m, 4 H, aryl-H), 6.70 (dd, 2
H, vinyl-H), 5.68 (dd, 2 H, vinyl-H), 5.13 (dd, 2 H, vinyl-H), 1.90 (d,
4 H, aryl-CH2), 0.83–0.40 (m, 30 H, alkyl-H). 13C NMR (CDCl3): δ
(55) Plenio, H.; Diodone, R. J. Org. Chem. 1993, 58, 6650.
(56) Jüngling, S.; Mülhaupt, R.; Plenio, H. J. Organomet. Chem. 1993,
460, 191.

Acyclic Diene Metathesis Polymerization of DiVinylarenes
Organometallics, Vol. 27, No. 7, 2008 1485
151.1, 140.9, 137.5, 135.9, 125.4, 121.6, 119.6, 112.8, 54.7, 44.4, 34.6,
33.7, 28.1, 27.1, 22.7, 14.0, 10.3.
CHO), 7.58 (d, 4 H, aryl-H), 7.18 (d, 4 H, aryl-H), 4.18 (s, 4 H, Cp-
H), 1.63 (s, 12 H, Cp-CH3). 13C NMR (CDCl3): δ 191.6, 145.8, 133.5,
129.9, 125.2, 86.2, 80.7, 69.7, 11.4.
2-Isopropenyl-6,6-dimethylfulvene (4). Na (3.45 g, 150 mmol)
was dissolved in cold (0 °C) methanol (100 mL). To the alcoholate
solution was added cyclopentadiene (12.4 mL, 9.91 g, 150 mmol)
dropwise at this temperature and stirring continued for 1 h. Next,
acetone (11.0 mL, 8.71 g, 150 mmol) was added and the reaction
mixture allowed to warm to room temperature overnight. Finally, the
solution was heated under reflux for 1 h. A second batch of NaOMe
(2.97 g, 55 mmol) in methanol (50 mL) was added, followed by
acetone (4.04 mL, 3.19 g, 55 mmol). The sequential addition of
NaOMe and acetone was repeated three times and the reaction mixture
then refluxed overnight. After cooling to room temperature, the reaction
mixture was poured on ice/water (300 mL) and the cold mixture
extracted with diethyl ether (4 × 100 mL). The combined organic
solutions were dried over MgSO4 and filtered and the volatiles
evaporated at 0 °C. The remaining liquid was purified by vacuum
distillation; the crude product (bp 50 °C/1 mbar) was then purified by
chromatography (silica, n-pentane/NEt3 ) 50: 1). Yield: 11.09 g, 76
1,1′-Di(4-vinylphenyl)-3,3′,4,4′-tetramethylferrocene (9). To
a suspension of (Ph3PCH3)+I (650 mg, 1.62 mmol) in THF (15 mL)
at 0 °C was added n-BuLi (0.65 mL, 1.62 mmol, 2.5 M), followed
after 10 min by a solution of the ferrocenedialdehyde 8 (243 mg, 0.54
mmol) in THF (15 mL). The reaction mixture was allowed to room
temperature and stirring continued for 1 d. Finally, the volatiles were
removed on vacuo, and the residue was purified by chromatography
(silica, cyclohexane/THF ) 10:1). Yield: (227 mg, 0.51 mmol, 95%).
1H NMR (CDCl3): δ 7.25 (d, 4 H, aryl-H), 7.15 (d, 4 H, aryl-H), 6.67
(dd, 2 H, vinyl-H), 5.71 (dd, 2 H, vinyl-H), 5.20 (dd, 2 H, vinyl-H),
4.16 (s, 4 H, Cp-H), 1.64 (s, 12 H, Cp-CH3). 13C NMR (CDCl3): δ
137.9, 136.9, 134.4, 126.1, 125.2, 112.3, 86.1, 80.2, 69.3, 11.5.
General ADMET Polymerization Procedure. Polymeriza-
tion of 1,4-Di(2-ethylhexyl)2,5-divinylbenzene. To the divinyl
monomer (106 mg, 0.300 mmol) in a Schlenk tube under Ar
atmosphere was added olefin metathesis catalyst stock solution (1.5
mL, 1 mol %, 2 mg, 0.003 mmol in 1,2-dichlorobenzene). The
mixture was stirred; vacuum (20 mbar) was applied and the mixture
heated to the respective reaction temperature for 3 d. After the
mixture was cooled to room temperature, toluene (5 mL) was added
to dissolve the polymer, followed by ethyl vinyl ether (0.2 mL) to
quench the catalyst. The mixture was stirred for 1 h and filtered
over a short silica plug into acetone (150 mL). The precipitated
polymer was filtered and thoroughly washed with acetone (50 mL).
Yield: >90%. All other polymers were synthesized according to
this procedure.
1
mmol, 51%. H NMR (C6D6): δ 6.95 (d, 1 H, Cp-H), 6.67 (d, 1 H,
Cp-H), 6.55 (s, 1 H, Cp-H), 6.52 (s, 1 H, isopropenyl-CH2), 5.12 (s,
1 H, isopropenyl-CH2), 2.13 (s, 3 H, isopropenyl-CH3), 1.89 (s, 6 H,
isopropylidene-CH3). 13C NMR (C6D6): δ 146.9, 146.0, 143.9, 139.8,
129.7, 122.8, 116.5, 112.5, 22.8, 21.2.
1,3-Diisopropenyl-1′,2′,3′,4′,5′-pentamethylferrocene (6). Cp*-
Fe(TMEDA)Cl (950 mg, 2.77 mmol) was suspended in THF (20
mL) and cooled to -78 °C, and a solution of freshly prepared
K+(1,3-diisopropenylcyclopentadienide) (580 mg, 3.00 mmol, in
situ prepared from 1.1. equiv of KO-t-Bu and 1.0 equiv of 4 in
THF at 0 °C) in THF (30 mL) was added. The suspension was
slowly (overnight) allowed to warm to room temperature. Next,
the volatiles were removed in vacuo, and the remaining solid was
extracted with n-pentane (3 × 30 mL). The pentane extracts were
filtered, the solvent was evaporated, and the crude product was
purified by chromatography (silica, n-pentane/NEt3 ) 50:1). Yield:
725 mg, 2.16 mmol, 78%. 1H NMR (CDCl3): δ 4.94 (d, 2 H,
isopropenyl-CH2), 3.87 (s, 1 H, Cp-H), 3.84 (s, 2 H, Cp-H), 1.85
(s, 6 H, isopropenyl-CH3), 1.63 (s, 15 H, Cp-CH3). 13C NMR
(CDCl3): δ 139.9, 108.0, 87.1, 79.8, 70.1, 65.6, 21.5, 9.6.
1,1′-Di(4-bromophenyl)-3,3′,4,4′-tetramethylferrocene (7). 1-Bro-
mophenyl-3,4-dimethylcyclopentadiene (4.98 g, 20.0 mmol) was
dissolved in diethyl ether and then cooled to -20 °C followed by
LDA (40 mL, 22.0 mmol, 0.55 M/THF) addition. After being stirred
for 1 h at this temperature, the solution was slowly added to a
suspension of FeCl2 · (THF)1.5 (2.23 g, 9.5 mmol) in THF (50 mL).
The reaction mixture was allowed to warm to room temperature
overnight. The volatiles were removed in vacuo, and the residue
was extracted with toluene (5 × 200 mL). The toluene solution
was filtered, the solvent evaporated, and the crude product purified
by sublimation (190 °C, 0.05 mbar). Yield: (5.10 g, 9.2 mmol, 46%).
1H NMR (CDCl3): δ 7.26 (d, 4 H, aryl-H), 7.02 (d, 4 H, aryl-H),
4.08 (s, 4 H, Cp-H), 1.71 (s, 12 H, Cp-CH3). 13C NMR (CDCl3):
δ 137.1, 131.3, 126.6, 118.7, 84.7, 81.4, 68.8, 11.5.
Poly[2,5-di(2-ethylhexyl)-p-phenylenevinylene] (poly-1). 1H
NMR (CDCl3): δ 7.41 (br, 2 H, aryl-H), 7.27 (br, 2 H, vinyl-H),
2.70 (br, 4 H, aryl-CH2), 1.61 (br, 2 H, -CH-alkyl), 1.30 (br, 16
H, alkyl-H), 0.90 (br, 12 H, -CH3). 13C NMR (CDCl3): δ 137.4,
135.4, 127.9, 126.8, 40.3, 37.9, 32.6, 28.9, 25.7, 23.1, 14.1, 11.0.
Poly[2,5-di(2-ethylhexyloxy)-p-phenylenevinylene] (poly-2). 1H
NMR (CDCl3): δ 7.46 (br, 2 H, vinyl-H), 7.14 (br, 2 H, aryl-H), 3.89
(br, 4 H, aryl-CH2), 1.76 (br, 2 H, -CH-alkyl), 1.61–1.20 (m, 16 H,
alkyl-H), 0.90 (m, 12 H, -CH3). 13C NMR (CDCl3): δ 150.1, 130.5,
121.5, 109.4, 70.7, 38.8, 29.7, 28.2, 23.3, 22.1, 13.1, 10.4.
1
Poly[9,9-di(2-ethylhexyl)fluorenyl-2,7-vinylene] (poly-3). H
NMR (CDCl3): δ 7.60 (br, 2 H, aryl-H), 7.49 (br, 4 H, aryl-H),
7.18 (br, 2 H, vinyl-H), 2.10 (br, 4 H, aryl-CH2), 0.84–0.50 (m, 30
H, alkyl-H). 13C NMR (CDCl3): δ 151.3, 140.7, 136.1, 128.5, 125.8,
121.8, 119.8, 54.7, 44.6, 34.7, 33.7, 28.1, 27.1, 22.7, 14.0, 10.3.
Ferrocenyl-fluorenyl-vinylene Copolymer (poly-4). Four equiva-
lents of the fluorene monomer (177.0 mg, 0.400 mmol) and 1 equiv
of the ferrocene monomer (44.5 mg, 0.100 mmol) were polymerized
according to the standard procedure. Yield: polymer (190.0 mg,
1
0.457 mmol, 92%). H NMR (CDCl3): δ 7.67 (br, 4 H, aryl-H),
7.52 (br, 8 H, aryl-H), 7.42 (br, 4 H, aryl-H), 7.19 (br, 4 H, vinyl-
H), 4.18 (br, 2 H, Cp-H), 2.16 (br, 8 H, aryl-CH2), 1.51 (br, 6 H,
Cp-CH3), 0.86–0.50 (m, 60 H, alkyl-H). 13C NMR (CDCl3): δ
151.3, 140.7, 136.0, 128.5, 126.4, 125.7, 125.5, 121.8, 119.8, 84.8,
69.2, 54.7, 44.7, 34.7, 33.7, 28.1, 27.1, 22.7, 14.1, 11.6, 10.3.
1,1′-Di(4-formylphenyl), 3,3′,4,4′-tetramethylferrocene (8). To
a solution of the ferrocene 7 (1.00 g, 1.81 mmol) in diethyl ether (50
mL) at 0 °C was first added TMEDA (0.54 mL, 0.42 g, 3.62 mmol)
followed by n-BuLi (1.45 mL, 3.62 mmol, 2.5 M). The reaction
mixture was allowed to room temperature and stirred at this temperature
for 1 d. Next, N-formylpiperidine (0.42 mL, 0.43 g, 3.80 mmol) was
added and stirring continued for another 12 h. Finally, the reaction
mixture was added dropwise into ice-cooled 2 N HCl (50 mL) and
the layers separated. The aqueous phase was extracted with CH2Cl2
(3 × 100 mL), the combined organic solutions were dried over MgSO4
andfiltered, and the volatiles were evaporated. The residue was purified
by chromatography (silica, cyclohexane/ethylacetate ) 2:1). Yield:
Acknowledgment. Support by the TU Darmstadt and the
Fonds der Chemischen Industrie is acknowledged. We thank
Prof. Dr. M. Rehahn, DKI (Deutsches Kunststoffinstitut), and
Prof. Reggelin for GPC measurements.
Supporting Information Available: 1H and 13C NMR spectra
of the new compounds described in the manuscript. This material
is available free of charge via the Internet at http://pubs.acs.org.
1
0.62 g, 1.38 mmol, 76%. H NMR (CDCl3): δ 9.85 (s, 2 H, aryl-
OM701277P