Complexation of unsaturated carbon-carbon bonds in π-conjugated polymers with transition metals

Article abstract of DOI:10.1021/ja003727w

The present paper explores the possibility of preparing π-conjugated organometallic polymer hybrid systems based on a poly(p-phenylene ethynylene) (PPE) derivative, in which the ethynylene moieties of the polymer are coordinated to platinum(II) centers. The use of the bifunctional [Pt-(μ-Cl)Cl(PhCH=CH₂)]₂ (2) allows, under appropriate conditions, the formation of three-dimensionally cross-linked, conjugated PPE-platinum(II) networks. The synthesis of [Pt-(μ-Cl)Cl(PhC≡CPh)]₂, as a model compound, and a series of model reactions of 2 with diphenylacetylene (3) have enabled an NMR study which has revealed a number of equilibria, and suggests a mixed Pt-styrene-acetylene complex as a key structure. As expected, the coordination of Pt markedly influences the photophysical characteristics of the PPE. The photoluminescence is efficiently quenched, and the absorption maximum in the visible regime experiences a hypsochromic shift upon complexation with 2.

Full text of DOI:10.1021/ja003727w

VOLUME 123, NUMBER 17
MAY 2, 2001
© Copyright 2001 by the
American Chemical Society
Complexation of Unsaturated Carbon-Carbon Bonds in π-Conjugated
Polymers with Transition Metals
Christian Huber,† Felix Bangerter,† Walter R. Caseri,† and Christoph Weder*,‡
Contribution from the Department of Materials, Institute of Polymers, ETH Zu¨rich, UniVersita¨tsstrasse 41,
UNO C15, 8092 Zu¨rich, Switzerland, and Department of Macromolecular Science and Engineering,
Case Western ReserVe UniVersity, 2100 Adelbert Road, CleVeland, Ohio 44106-7202
ReceiVed October 19, 2000
Abstract: The present paper explores the possibility of preparing π-conjugated organometallic polymer hybrid
systems based on a poly(p-phenylene ethynylene) (PPE) derivative, in which the ethynylene moieties of the
polymer are coordinated to platinum(II) centers. The use of the “bifunctional” [Pt-(µ-Cl)Cl(PhCHdCH2)]2
(2) allows, under appropriate conditions, the formation of three-dimensionally cross-linked, conjugated PPE-
platinum(II) networks. The synthesis of [Pt-(µ-Cl)Cl(PhCtCPh)]2, as a model compound, and a series of
model reactions of 2 with diphenylacetylene (3) have enabled an NMR study which has revealed a number of
equilibria, and suggests a mixed Pt-styrene-acetylene complex as a key structure. As expected, the coordination
of Pt markedly influences the photophysical characteristics of the PPE. The photoluminescence is efficiently
quenched, and the absorption maximum in the visible regime experiences a hypsochromic shift upon
complexation with 2.
Introduction
methods of conjugated polymer materials with unique, field-
responsive properties. Among a variety of tools that allow the
manipulation of the electronic properties of conjugated macro-
molecules, the introduction of transition metals into conjugated
polymers has recently received considerable attention.5,6 The
latter is promoted by the opportunity to tailor both components
of these hybrid systems and the possibility to exploit a diversity
of effects, including charge-transfer-, redox-, and energy transfer
processes. Of particular attractivity to us is thesto our best
knowledge previously never exploitedspossibility to complex
conjugated polymers with bifunctional metal centers that allow
the formation of three-dimensionally cross-linked conjugated
structures. Such conjugated networks may overcome the notori-
In the past two decades, π-conjugated polymers have attracted
significant interest, since these materials may combine the
processability and outstanding mechanical properties of poly-
mers with the exceptional, readily tailored electronic and optical
properties of functional organic molecules.1 Especially the
discoveries of electrically (semi)conducting,2 nonlinear optical
(NLO),3 and photo- and electroluminescent (PL, EL)4 polymers
have promoted the development of synthesis and processing
† ETH Zu¨rich.
‡ Case Western Reserve University.
(1) Friend, R. H. In Conjugated Polymers and Related Materials, The
Interconnection of Chemical and Electronic Structure; Proceedings of the
81st Nobel Symposium; Salaneck, W. R., Lundstro¨m, I., Ranby, B., Eds.;
Oxford University Press: New York, 1993; p 285.
(2) Handbook of Conducting Polymers, 2nd ed.; Skotheim, T. J.,
Elsenbaumer, R. L., Reynolds, J. R., Eds.; Dekker: New York, 1998.
(3) Bre´das, J. L.; Adant, C.; Tackx, P.; Persoons, A. Chem. ReV. 1994,
94, 243.
(4) Kraft, A.; Grimsdale, A. C.; Holmes, A. B. Angew. Chem., Int. Ed.
Engl. 1998, 37, 403.
(5) Manners, I. Angew. Chem., Int. Ed. Engl. 1996, 35, 1602.
(6) (a)Rehahn, M. Acta Polym. 1998, 49, 201. (b) Rehahn, M.; Schott,
A.; Knapp, R. Macromolecules 1996, 29, 478.
10.1021/ja003727w CCC: $20.00 © 2001 American Chemical Society
Published on Web 03/28/2001

3858 J. Am. Chem. Soc., Vol. 123, No. 17, 2001
Huber et al.
The conjugated polymer employed in the present work is
MEH-OPPE (7),18 a highly soluble poly(2,5-dialkoxy-p-
phenylene ethynylene) derivative which is representative for a
family of conjugated polymers with well-documented PL,19
EL,20 and NLO properties,21 and offers two ethynylene moieties
per repeat unit as potential ligand sites (Scheme 3). On the other
hand, platinum(II) is well-known to form stable complexes with
unsaturated organic ligands.22 Its square-planar ligand sphere
offers the advantage of a restricted number of isomers (when
compared to octahedrically coordinated metal centers), and
ligand exchange reactions can readily be followed in situ by
nuclear magnetic resonance methods, due to the nuclear spin
Figure 1. Schematic representation of the π-conjugated organometallic
polymers proposed.
1
of /2 of 195Pt. Concomitantly, we have elected to exemplary
ous problems that are usually associated with interchain charge
transfer through hopping processes7 and may be expected to
exhibit improved transport characteristics. The latter, in turn,
are anticipated to vastly rectify a number of electromagnetic
properties and eventually may lead to, for example, increased
electrical conductivity and improved nonlinear optical response.
Conventional concepts for the design of π-conjugated orga-
nometallic polymers include the formulation of simple blends
of metal complexes and a conjugated polymer,8 as well as the
incorporation of metal centers into polymers through coordi-
native bonds.6,9-11 In the latter case, the metal atoms may be
coordinated to,9,11 or integrated in, the polymer backbone6 or
alternatively can be attached via conjugated or nonconjugated
spacer units in the form of side groups.10 Among a plethora of
functional groups which may serve as ligands for transition
metals, we here focus on the utilization of unsaturated (acyclic)
carbon-carbon bonds as potential binding sites. These moieties
allow the formation of a wide variety of metal complexes that
access a broad spectrum of interesting electronic characteris-
tics12,13 and have also previously been used for the synthesis of
organometallic polymer systems; the polymeric silyl acetylene-
cobalt-carbonyl complexes introduced by Corriu and co-
workers provide a prominent example for the latter.14 However,
the concept of directly employing ethynylene or vinylene
moieties for the controlled formation of metal-complexed
macromoleculessto our best knowledgeshas never been adapted
for π-conjugated polymers.15 This is surprising in view of the
availability of unsaturated bonds in conjugated polymers,4 in
particular in poly(p-phenylene vinylene) (PPV),16 poly(p-
phenylene ethynylene) (PPE),17 and their derivatives, which
represent role models of conjugated polymers. Thus, we have
embarked on the exploration of the possibility to synthesize and
process cross-linked, π-conjugated, organometallic polymer
hybrid systems, and here present our initial study on the
synthesis and characterization of novel poly(p-phenylene ethy-
nylene) platinum(II) complexes (Figure 1).
employ the dinuclear [Pt-(µ-Cl)Cl(PhCHdCH2)]2 (2)22 (Scheme
1) in the present study, assuming that the lattersafter ligand
exchangescan readily form complexes with the MEH-OPPE’s
ethynylene moieties. Of particular attractivity, of course, is the
“bifunctional” nature of 2, which we anticipatedsand demon-
stratesto allow, under appropriate conditions, the formation of
three-dimensionally cross-linked, conjugated structures.
Results and Discussion
The dinuclear sym-trans-[Pt-(µ-Cl)Cl(PhCHdCH2)]2 com-
plex 2 was synthesized from cis-dichlorobis(styrene)platinum-
(II) (1a) (Scheme 1) according to a previously published
procedure.22 We should point out also that 1a might react with
the PPE in desirable fashion; however, in contrast to 2 it exhibits
only a limited solubility in suitable solvents for the polymer
(e.g., CHCl3, toluene). To explore the behavior of sym-trans-
[Pt-(µ-Cl)Cl(PhCHdCH2)]2 in ligand-exchange reactions with
molecules containing ethynylene moieties, we first conducted
a number of model reactions. First, 2 was treated with an excess
of diphenylacetylene in dichloromethane solution, and the
reaction product was isolated by precipitation with pentane
(Scheme 1). The chemical composition of the product, as
determined by organic elemental analysis, is consistent with the
dinuclear [Pt-(µ-Cl)Cl(PhCtCPh)]2 complex 3. Consistently,
the styrene ligands were quantitatively replaced by dipheny-
lacetylene, as is evident from 1H NMR spectroscopy. Free
styrene could, indeed, be observed in the supernatant solution
after precipitation of 3, when the reaction was repeated using
deuterated solvents. The 1H NMR spectrum of 3 shows a number
of well-resolved signals above 8 ppm, which are absent in the
case of both educts, and are, also in their magnitude, consistent
with the complexation of the diphenylacetylene. The 195Pt NMR
spectrum reveals two different platinum signals which we
explain with the coexistence of different isomers, for example,
the sym-cis and sym-trans isomer of the dinuclear complex (for
simplicity, all complexes occurring in different isomers are
represented in their sym-trans form in Schemes 1-3). The
signals associated with 3 are clearly broader than those of 2,
suggesting that dynamic processes are more pronounced in the
former, even at a temperature of 203 K. We should note that 3
was found to slowly decompose in dichloromethane solution,
as unequivocally demonstrated by NMR spectra taken after 16
h at room temperature. The 195Pt NMR spectrum of 3 remains
essentially unchanged upon addition of an excess (7 equiv) of
(7) Sirringhaus, H.; Brown, P. J.; Friend, R. H.; Nielsen, M. M.;
Bechgaard, K.; Langeveld-Voss, B. M. W.; Spiering, A. J. H.; Janssen, R.
A. J.; Meijer, E. W.; Herwig, P.; de Leeuw, D. M. Nature 1999, 401, 685.
(8) McGehee, M. D.; Bergstedt, T.; Zhang, C.; Saab, A. P.; O’Regan,
M. B.; Bazan, G. C.; Srdanov, V.; Heeger, A. J. AdV. Mater. 1999, 11,
1349.
(9) Ley, K. D.; Whittle, E.; Bartberger, M. D.; Schanze, K. S. J. Am.
Chem. Soc. 1997, 119, 3423.
(10) Wong, C. T.; Chan, W. K. AdV. Mater. 1999, 11, 455.
(11) Wright, M. E. Macromolecules 1989, 22, 3256.
(12) Bevilacqua, J. M.; Eisenberg, R. Inorg. Chem. 1994, 33, 2913.
(13) Savoie, C.; Reber, C. Can. J. Chem. 1996, 74, 28.
(14) Corriu, R. J.-P.; Douglas, W. E.; Yang, Z.-X.; Polymer 1993, 34,
3535.
(18) Dellsperger, S.; Do¨tz, D.; Smith, P.; Weder, C. Macromol. Chem.
Phys. 2000, 201, 192.
(15) Note, however, that speculations about the formation of a cross-
linked polymer network involving (η6-arene)Cr(CO)2(ethynyl) bridges have
been reported before, in context with the thermal decomposition of
conjugated polymers comprising η6-arene moieties.11
(16) Scherf, U. Top. Curr. Chem. 1999, 201, 163.
(19) Weder, Ch.; Wrighton, M. S. Macromolecules 1996, 29, 5157.
(20) Montali, A.; Weder, Ch.; Smith, P. Synth. Met. 1997, 97, 123.
(21) He, G. S.; Weder, Ch.; Smith, P.; Prasad, P. N. IEEE J. Quantum
Electron. 1998, 34, 2279.
(22) Albinati, A.; Caseri, W. R.; Pregosin, P. S. Organometallics 1987,
6, 788.
(17) Bunz, U. Chem. ReV. 2000, 100, 1605.

Conjugated PPE-Platinum(II) Networks
J. Am. Chem. Soc., Vol. 123, No. 17, 2001 3859
Scheme 1. Synthesis of the Dinuclear Platinum(II) Complex [Pt-(µ-Cl)Cl(PhCHdCH2)]2 (2) and Model Compound
[Pt-(µ-Cl)Cl(PhCtCPh)]2 (3)a
a
Note that for simplicity, all complexes occurring in different isomers are represented in their sym-trans form.
Scheme 2. Suggested Equilibria (Summarized) for the Reaction of (a) [Pt-(µ-Cl)Cl(PhCHdCH2)]2 (2) and Diphenylacetylene
(DPA), (b) [Pt-(µ-Cl)Cl(PhCtCPh)]2 (3), and [Pt-(µ-Cl)Cl(PhCHdCH2)]2 (2), and (c) [Pt-(µ-Cl)Cl(PhCtCPh)]2 (3) and
Styrene
diphenylacetylene, suggesting that dichlorobis(diphenylacety-
lene)platinum(II) (4) is not formed in appreciable concentration
under the conditions applied (reaction at room temperature for
1 h).
that styrene is a substantially stronger ligand than dipheny-
lacetylene for the complexes investigated here. The 195Pt NMR
spectra of these solutions are void of the characteristic signals
of 3 but feature a new signal at -2600 ppm, the relative intensity
of which also increased as a function of reaction time and
diphenylacetylene concentration. At first glance, the four signals
associated with 2 (between -2300 and -2420 ppm) are still
present, but their relative intensities change significantly, and
the signals broaden considerably. The signal at -2600 ppm
coincides with the chemical shift of trans-dichlorobis(styrene)-
platinum(II) (1b).23 The facts that diphenylacetylene coordinates
to Pt, that no free styrene is observed, and that 1b seems to be
formed suggest an equilibrium reaction according to Scheme
(23) Caseri, W.; Pregosin, P. S. Organometallics 1988, 7, 1373.
Interestingly, the formation of 3 could not be observed in
situ, when sym-trans-[Pt-(µ-Cl)Cl(PhCHdCH2)]2 (2) and
diphenylacetylene were combined in dichloromethane under
similar conditions as applied for the above-discussed isolation
1
of 3 (Scheme 2a). The H NMR spectra of solutions of 2 and
diphenylacetylene show a weak signal above 8 ppm, which was
found to increase as a function of time (over several hours) and
diphenylacetylene concentration and is consistent with the
formation of a diphenylacetylene-Pt complex. Importantly, no
free styrene could be observed in the 1H NMR spectra, indicating

3860 J. Am. Chem. Soc., Vol. 123, No. 17, 2001
Huber et al.
Scheme 3. Suggested Equilibria for the Reaction of [Pt-(µ-Cl)Cl(PhCHdCH2)]2 (2) and MEH-OPPE (7)
2a under formation of 5. While the signal related to 1b clearly
molecular 2/diphenylacetylene model system. The 195Pt NMR
spectra of these solutions feature a signal at -2607 ppm which
is attributed to 1b, the relative intensity of which increased as
a function of PPE concentration. In addition, the four signals
associated with 2 (between -2300 and -2420 ppm) broaden
considerably if the PPE is added, as was previously observed
for the low-molecular-weight model system. Thus, based on the
striking analogy to the model system, we surmise that the
complexation of MEH-OPPE (7) with 2 (Scheme 3) under the
presently employed conditions leads to the formation of mixed
complexes 8.
appears in the 195Pt NMR spectra, characteristic signals for a
1
new Pt-diphenylacetylene complex are only detected in H
NMR spectra but in 195Pt NMR spectra appear to broadly
overlap with the signals of 2.
To obtain further proof for this interpretation, we have also
investigated the ligand-exchange reaction between 2 and 3
(Scheme 2b). As expected, the formation of 1b is not observed
in this case, while the signals of 3 are still present, and again,
the relative intensities and width of the signals in the region
between -2300 and -2420 ppm change as above, suggesting
again the formation of 5. In another experiment, we have finally
investigated the addition of styrene to 3 (Scheme 2c). In
agreement with the above observations on the relative com-
plexing strength of styrene and diphenylacetylene, 195Pt and 1H
NMR spectra show that the addition of about 2 equiv of styrene
to 3 leads to the disappearance of 3, and the observed signals
are consistent with the formation of 2, 5, and 1b (cf. Scheme
2c); if, however, an excess of styrene was added, only 1b could
be detected. We should note that in none of the systems
described above was evidence for the presence of the mono-
nuclear complex dichloro(diphenylacetylene)(styrene)platinum-
(II) obtained, but we can also not entirely exclude its presence.
The above model reactions imply that the bis(diphenylacety-
lene) complex 3 is only obtained under kinetically controlled
conditions. Therefore, 2 should be an extremely suitable
candidate for the preparation of three-dimensionally cross-linked,
conjugated polymer-Pt complexes as outlined in Figure 1 and
Scheme 3. The results suggest that in dilute solutions containing
2 and MEH-OPPE, styrene is only partially replaced, cross-
linking is essentially prevented, and thus, the reaction products
should remain dissolved. This is, of course, of vital importance
for the processability of such systems (cf. below).
The photophysical characteristics of these Pt-PPE hybrids
were investigated by steady-state photoluminescence and UV-
vis absorption measurements. The absorption and emission
spectra obtained for deoxygenated trichloromethane solutions
are shown in Figure 2; note that the 2:7 ratios were in the same
range as those used for the in situ NMR experiments (2:7 molar
ratios between 0 and 5), but due to the high extinction coefficient
of 7, the absolute concentrations had to be chosen about 50 000
times lower for the optical experiments. Figure 2a clearly shows
that the addition of 2 induces a dramatic reduction in PL
intensity, while the shape of the emission spectrum remains
essentially unchanged. As expected, the PL quenching was
observed to correlate with the concentration of 2, and the
emission was virtually entirely suppressed in the case of a 2:7
ratio of 5. This behavior is fully consistent with the formation
of complexes 8 according to Scheme 3, with exciton migration
along the polymer main chains to the complexation sites, which
seem to represent low-energy states and provide pathways for
nonemissive relaxation processes. Figure 2b shows that the
absorption spectra are also affected by addition of 2; however,
the effect is less pronounced at low concentrations of 2. The
observed hypsochromic shift of the absorption band and the
reduction of the extinction coefficient reflect that the electronic
properties of the backbone itself also are affected through the
complexation, and one could speculate that the effective
conjugation length is reduced. To rule out that the observed PL
quenching originates from Fo¨rster-type energy transfer between
noncomplexed species, we have conducted comparative experi-
ments with platinum complexes which feature strongly bound
ligands that are not expected to be replaced by the acetylenic
moieties. Gratifyingly, the photophysical characteristics of
In analogy to the above model experiments, we have studied
the in situ complexation of MEH-OPPE (7) and 2 (Scheme
3), in trichloromethane/dichloromethane mixtures employing 7:2
weight-ratios between 0 and 3.25, corresponding to molar ratios
between 0 and 4.7 (calculations are always based on the
molecular weight of the PPE’s repeat unit). Gratifyingly, all
mixtures remained completely soluble, and as a matter of fact,
1H NMR and 195Pt NMR data reflect a similar behavior for the
complexation of 7 and 2 as discussed above for the low-

Conjugated PPE-Platinum(II) Networks
J. Am. Chem. Soc., Vol. 123, No. 17, 2001 3861
Figure 2. Photoluminescence (a) and UV-vis absorption spectra (b)
of solutions of MEH-OPPE (7) (5‚10-7 g‚mL-1) and [Pt-(µ-Cl)Cl-
(PhCHdCH2)]2 (2) in CHCl3. The figures show the influence of the
concentration of 2, which is given in molar equivalents with respect to
the MEH-OPPE’s repeat unit.
Figure 3. Photoluminescence (a) and UV-vis absorption spectra (b)
of spin-cast films of MEH-OPPE (7) and [Pt-(µ-Cl)Cl(PhCHdCH2)]2
(2). The figures show the influence of the concentration of 2, which is
given in molar equivalents with respect to the MEH-OPPE’s repeat
unit.
solutions of the PPE 7 were found to remain unchanged upon
addition of bis(2,5-pentanedionato)platinum(II) or 1,5-cyclooc-
tadienedimethylplatinum(II) (molar ratio of Pt-complex:7 of 1).
Pt/MEH-OPPE films of good optical quality were prepared
by spin coating of trichloromethane solutions comprising 2 and
7 at molar ratios between 0 and 1 (see Experimental Section
for details). Important for the preparation of these films is the
fact that Pt/MEH-OPPE solutions of homogeneous appearance
could be prepared at polymer concentrations useful for this
processing method (10 mg‚mL-1) if MEH-OPPE of a number-
average molecular weight of about 8100 g‚mol-1 was employed.
Interestingly, once the films had been prepared, they were found
to be insoluble in trichloromethane and toluene, indicating that
indeed cross-linking complexes (i.e., 9, z > 0) as shown in
Scheme 3 were formed. In agreement, the Pt-containing films
could readily be released from the substrate and exhibited
mechanical properties that allowed them to be easily handled
in free-standing form, very much in contrast to untreated MEH-
OPPE films which, due to the PPE’s low molecular weight,
were extremely brittle. The insolubility of these films in the
solvent of their origin could simply be a kinetic phenomenon,
but may also be an indication that styrene has evaporated during
processing and, therefore, has been withdrawn from the equi-
librium. The fact that the addition of styrene to the solvent was
found to readily dissolve the films and restored the photolumi-
nescence of the released PPE strongly supports the latter
prospect and shows that the Pt-PPE complexation is indeed
reversible. In view of the extreme sensitivity of the PPE’s PL
characteristics toward complexation with Pt(II) (Figure 2a) and
the expected hypsochromic shift of the PL emission band upon
chain-scission, the observed restoration of the PPE’s PL seems
to suggest that the PPE has been essentially re-converted to its
original form. IR spectra of films containing 2 and 7 at molar
ratios of 0.1 and 1, respectively, show besides the characteristic
signals of 7 also appreciable signals due to coordinated styrene,
which besides 9 indicate the presence of 2 or mixed styrene
acetylene complexes (e.g. 8).
The absorption and emission spectra of the Pt/MEH-OPPE
films produced are shown in Figure 3. The observed changes
in their photophysical characteristics as a function of the amount
of 2 added are qualitatively similar to those of the solutions.
However, Figure 3a demonstrates that already the presence of
minute amounts of 2 leads to an essentially complete quenching
of the PL emission. Of course, this behavior reflects again a
pronounced shift of the equilibrium outlined in Scheme 3 in
the solid state and indicates substantial coordination of the Pt
already at low concentrations of 2. Also in the case of films,
we have conducted comparative experiments using PPE (7) and
bis(2,5-pentanedionato)platinum(II) (molar ratio of 1). The PL
spectrum of the latter, Pt-containing film perfectly matches the
one of the neat PPE, indicating that even in this dense, highly
Pt-loaded system, the electronic interactions between the PPE
and the Pt complex are negligible and that coordination between
Pt and PPE moieties is indeed required to substantially influence
the optical characteristics of the conjugated polymer system.
Conclusions
In summary, we have shown with the example of poly(p-
phenylene ethynylene) that the ethynylene moieties comprised
in π-conjugated polymers can readily coordinate to platinum-
(II) in exchange with weakly bound ligands. The “bifunctional”
[Pt-(µ-Cl)Cl(PhCHdCH2)]2 employed in the present study,
under appropriate conditions, allows the formation of three-
dimensionally cross-linked, conjugated PPE-Pt networks.
Importantly, in dilute solutions, the equilibrium of the presently
investigated PPE-Pt systems dictates non-crosslinked structures,
and the system remains homogeneous and therewith processable.

3862 J. Am. Chem. Soc., Vol. 123, No. 17, 2001
Huber et al.
br, 2 H, CdCH2), 4.82 (m, 2 H, CdCH2); 195Pt NMR (64 MHz, CD2-
Cl2, 203 K) δ -2306, -2320, -2331, -2414, -2600 (weak). After 1
h: 1H NMR (300 MHz, CD2Cl2, 203 K) δ 8.10 (m br, ∼0.2 H,
coordinated diphenylacetylene), 7.55 (m, ∼14 H, ar), 7.40 (m, ∼16 H,
ar), 6.50 (m, 2 H, CdCH), 5.15 (m br, 2 H, CdCH2), 4.82 (m, 2 H,
CdCH2); 195Pt NMR (64 MHz, CD2Cl2, 203 K) δ -2306, -2320,
-2331, -2414, -2600 (weak). After 18 h: 1H NMR (300 MHz, CD2-
Cl2, 203 K) δ 8.10 (m br, ∼0.2 H, coordinated diphenylacetylene),
7.55 (m, ∼14 H, ar), 7.40 (m, ∼16 H, ar), 6.50 (m, 2 H, CdCH), 5.15
(m br, 2 H, CdCH2), 4.82 (m, 2 H, CdCH2); 195Pt NMR (64 MHz,
CD2Cl2, 203 K) δ -2306, -2320, -2331, -2413, -2600.
As expected, the coordination of Pt markedly influences the
photophysical characteristics of the PPE. After having employed
[Pt-(µ-Cl)Cl(PhCHdCH2)]2 in the present study to demonstrate
the possibility of preparing a new family of π-conjugated
organometallic polymer hybrid systems, we envision the exten-
sion of the present concepts to the use of metal complexes with
specific PL characteristics and the conduction of experiments
related to the charge-carrier transport in such cross-linked
π-conjugated polymer systems.
The above experiment was repeated with 86 mg instead of 4.5 mg
of diphenylacetylene and NMR spectra were recorded about 10 min, 1
h, and 18 h, respectively, after mixing. After 10 min: 1H NMR (300
MHz, CD2Cl2, 203 K) δ 8.10 (m br, ∼1.3 H, coordinated dipheny-
lacetylene), 8.00-7.05 (m, ∼300 H, ar), 6.50 (m, 2 H, CdCH), 5.15
(m br, 2 H, CdCH2), 4.82 (m, 2 H, CdCH2); 195Pt NMR (64 MHz,
CD2Cl2, 203 K) δ -2305, -2320, -2328, -2412, -2601. After 1 h:
1H NMR (300 MHz, CD2Cl2, 203 K) δ 8.10 (m br, ∼2 H, coordinated
diphenylacetylene), 8.00-7.05 (m, ∼300 H, ar), 6.50 (m, 2 H, Cd
CH), 5.15 (m br, 2 H, CdCH2), 4.82 (m, 2 H, CdCH2); 195Pt NMR
(64 MHz, CD2Cl2, 203 K) δ -2305, -2320, -2328, -2412, -2601.
After 18 h: Multitudes of signals indicate decomposition of the
complex.
In an NMR tube, sym-trans-[Pt-(µ-Cl)Cl(PhCHdCH2)]2 (2) (20 mg,
0.028 mmol) was dissolved in CD2Cl2 (0.75 mL), and diphenylacetylene
(172 mg, 0.97 mmol) was added. The solution was kept at room
temperature, and an excess cyclohexane-d12 was added, causing the
immediate precipitation of a solid. The latter was isolated by centrifuga-
tion and decantation of the supernatant solution, and NMR spectra of
solid and supernatant solution were immediately recorded. Supernatant
solution: 1H NMR (300 MHz, CD2Cl2, 203 K) δ 7.60-7.00 (m, excess
diphenylacetylene), 6.61 (d × d, 1 H, CdCH), 5.60 (d, 1 H, CdCH2,
J ) 17.0 Hz), 5.08 (d, 1 H, CdCH2, J ) 11.3 Hz), 1.40 (m, excess
cyclohexane-d12). Solid: 195Pt NMR (64 MHz, CD2Cl2, 203 K) δ
-1871, -1932.
Investigation of the Ligand-Exchange Reaction between sym-
trans-[Pt-(µ-Cl)Cl(PhCHdCH2)]2 (2) and [Pt-(µ-Cl)Cl(PhCt
CPh)]2 (3). In an NMR tube, sym-trans-[Pt-(µ-Cl)Cl(PhCHdCH2)]2
(2) (10 mg, 0.014 mmol) was dissolved in CD2Cl2 (0.75 mL), and [Pt-
(µ-Cl)Cl(PhCtCPh)]2 (3) (12 mg, 0.014 mmol) was added. The solution
was kept at room temperature, and NMR spectra were recorded about
10 min and 5 h, respectively, after mixing. After 10 min: 195Pt NMR
(64 MHz, CD2Cl2, 213 K) δ -1610 (weak), -1888, -1912, -2303,
-2317, -2326, -2409. After 5 h:195Pt NMR (64 MHz, CD2Cl2, 213
K) δ -1888, -1912, -2303, -2317, -2326, -2409.
Experimental Section
Materials and Methods. All reagents and solvents were of analytical
grade quality, were purchased from Aldrich Chemical Co. or Fluka,
and were used without further purification. cis-Dichlorobis(styrene)-
platinum(II) (1),22 sym-trans-[Pt-(µ-Cl)Cl(PhCHdCH2)]2 (2),22 and
MEH-OPPE (7)18 of a number-average molecular weight of 8100
g‚mol-1 were prepared as described before. H NMR and 195Pt NMR
1
spectral data were obtained in CD2Cl2 or CDCl3 or mixtures of these
solvents on a Bruker 300 MHz NMR spectrometer and are expressed
in ppm relative to tetramethylsilane (1H) and sodium hexachloroplati-
nate(IV) (195Pt), respectively. IR spectra were recorded on KBr
substrates on a Bruker IFS 66v. Elemental analyses were carried out
by the Microanalysis Laboratory of the Laboratory of Organic
Chemistry of ETH Zu¨rich. UV-vis absorption spectra were obtained
on a Perkin-Elmer Lambda 900. PL spectra were measured under
excitation at 380 nm on a SPEX Fluorolog 3 (model FL3-12).
Corrections for the spectral dispersion of the Xe-lamp, the instrument
throughput, and the detector response were applied.
NMR Spectra of sym-trans-[Pt-(µ-Cl)Cl(PhCHdCH2)]2 (2). For
the purpose of internal reference, NMR spectra of 2 were recorded. 1H
NMR (300 MHz, CD2Cl2, 203 K) δ 7.55-7.28 (3 × m, 10 H, ar),
6.50 (m br, 2 H, CdCH), 5.15-4.40 (m, 4 H, CdCH2); 1H NMR (300
MHz, CD2Cl2, 300 K) δ 7.75-7.50 (m, 6 H, ar), 7.49-7.30 (m, 4 H,
ar), 6.55 (m br, 2 H, CdCH), 5.13 (m br, 2 H, CdCH2), 4.78 (m, 2 H,
CdCH2); 195Pt NMR (64 MHz, CD2Cl2, 203 K) δ -2306, -2321,
-2331, -2415; 195Pt NMR (64 MHz, CD2Cl2, 300 K) δ -2306, -2321,
-2331, -2415.
Synthesis of [Pt-(µ-Cl)Cl(PhCtCPh)]2 (3). sym-trans-[Pt-(µ-Cl)-
Cl(PhCHdCH2)]2 (2) (433 mg, 0.588 mmol) was dissolved in CH2Cl2
(24 mL), the solution was filtered, and diphenylacetylene (2.47 g, 13.9
mmol) was added. The reaction mixture was stirred for 5 min at room
temperature, and pentane (220 mL) was added, causing the immediate
precipitation of the product. The suspension was allowed to stand for
30 min, and the solid was filtered off, washed with pentane (30 mL),
and dried in vacuo. Reprecipitation from dichloromethane/pentane (30/
85 mL) followed by drying in vacuo afforded 218 mg (0.246 mmol,
42%) of a brown solid. 1H NMR (300 MHz, CD2Cl2, 213 K) δ 8.47-
8.01 (m, ∼4 H, ar ortho to CtC and facing Pt), 7.98-6.89 (m, ∼16
H, other ar), 195Pt NMR (64 MHz, CD2Cl2, 213 K) δ -1610 (weak),
-1868, -1926. Anal. Calcd for C28H20Cl4Pt2: C, 37.85; H, 2.27; Cl,
15.96. Found: C, 37.38; H, 2.53; Cl, 15.12.
Investigation of the Ligand-Exchange Reaction between [Pt-
(µ-Cl)Cl(PhCtCPh)]2 (3) and Diphenylacetylene. In an NMR tube,
[Pt-(µ-Cl)Cl(PhCtCPh)]2 (3) (10 mg, 0.011 mmol) was dissolved in
CD2Cl2 (0.75 mL), and diphenylacetylene (172 mg, 0.079 mmol) was
added. The solution was kept at room temperature, and NMR spectra
were recorded about 10 min and 1 h, respectively, after mixing. After
10 min: 195Pt NMR (64 MHz, CD2Cl2, 223 K) δ -1867, -1926, -2537
(weak). After 1 h:195Pt NMR (64 MHz, CD2Cl2, 223 K) δ -1867,
-1926, -2207 (weak), -2537 (weak).
Investigation of the Ligand-Exchange Reaction between [Pt-
(µ-Cl)Cl(PhCtCPh)]2 (3) and Styrene. In an NMR tube, [Pt-(µ-
Cl)Cl(PhCtCPh)]2 (3) (7.1 mg, 0.008 mmol) was dissolved in CD2Cl2
(0.75 mL), and styrene (1.8 µL, 0.016 mmol) was added. The solution
was kept at room temperature, and NMR spectra were recorded about
1
10 min after mixing. H NMR (300 MHz, CD2Cl2, 203 K) δ 8.03 (m
br, ∼1 H, coordinated diphenylacetylene), 7.55 (m, ∼12 H, ar), 7.40
(m, ∼18 H, ar), 6.50 (m, 2 H, CdCH), 5.15-4.80 (m br, 4 H, Cd
CH2); 195Pt NMR (64 MHz, CD2Cl2, 203 K) δ -2321, 2332, -2413,
-2600.
The above experiment was repeated with 11.8 µL instead of 1.8 µL
of styrene. The solution was kept at room temperature, and NMR spectra
were recorded about 10 min after mixing. 195Pt NMR (64 MHz, CD2-
Cl2, 223 K) δ -2604.
1
NMR Experiments on Pt/MEH-OPPE Solutions. H NMR and
195Pt NMR experiments were conducted at 203 K on a sample which
originally contained 20 mg of sym-trans-[Pt-(µ-Cl)Cl(PhCHdCH2)]2
(2) in a mixture of CD2Cl2 and CHCl3 (2:1 v/v) and to which 10, 20,
or 65 mg of MEH-OPPE (7) were added. 20 mg 2/0 mg 7: 1H NMR
7.61-7.33 (m, 10 H, ar styrene), 6.56 (m, 2 H, dCH styrene), 5.25-
4.75 (m, 4 H, dCH2 styrene); 195Pt NMR -2304, -2327, -2329,
-2412. 20 mg 2/10 mg 7: 1H NMR 7.61-7.34 (m, 10 H, ar styrene),
7.12-7.01 (m, 2 H, ar MEH-OPPE), 6.56 (m, 2 H, dCH styrene),
5.21-4.89 (m, 4 H, dCH2 styrene), 3.96 (m, 5 H, OCH3 and OCH2
MEH-OPPE), 1.91 (m, 1 H, CH MEH-OPPE), 1.52-1.33 (m, 8 H,
Investigation of the Ligand-Exchange Reaction between sym-
trans-[Pt-(µ-Cl)Cl(PhCHdCH2)]2 (2) and Diphenylacetylene. In an
NMR tube, sym-trans-[Pt-(µ-Cl)Cl(PhCHdCH2)]2 (2) (10 mg, 0.014
mmol) was dissolved in CD2Cl2 (0.75 mL), and diphenylacetylene (4.5
mg, 0.025 mmol) was added. The solution was kept at room temper-
ature, and NMR spectra were recorded about 10 min, 1 h, and 18 h,
respectively, after mixing. After 10 min:1H NMR (300 MHz, CD2Cl2,
203 K) δ 8.10 (m br, ∼0.2 H, coordinated diphenylacetylene), 7.55
(m, ∼14 H, ar), 7.38 (m, ∼16 H, ar), 6.50 (m, 2 H, CdCH), 5.15 (m

Conjugated PPE-Platinum(II) Networks
J. Am. Chem. Soc., Vol. 123, No. 17, 2001 3863
4 × CH2 MEH-OPPE), 0.99 (s, 3 H, CH3 MEH-OPPE), 0.91 (s, 3
H, CH3 MEH-OPPE); 195Pt NMR -2304, -2329, -2412, -2607. 20
mg 2/20 mg 7: 1H NMR 7.59-7.34 (m, 10 H, ar styrene), 7.12-7.01
(m, 2 H, ar MEH-OPPE), 6.56 (m, 2 H, dCH styrene), 5.21-4.88
(m, 4 H, dCH2 styrene), 3.96 (m, 5 H, OCH3 and OCH2 MEH-OPPE),
1.91 (m, 1 H, CH MEH-OPPE), 1.53-1.34 (m, 8 H, 4 × CH2 MEH-
OPPE), 0.99 (s, 3 H, CH3 MEH-OPPE), 0.91 (s, 3 H, CH3 MEH-
OPPE); 195Pt NMR -2304, -2328, -2412, -2607. 20 mg 2/65 mg 7:
1H NMR 7.56-7.42 (m, 10 H, ar styrene), 7.12-7.01 (m, 2 H, ar
MEH-OPPE), 6.56 (m, ∼2 H, dCH styrene), 5.21-4.88 (m, ∼4 H,
dCH2 styrene), 3.95 (m, 5 H, OCH3 and OCH2 MEH-OPPE), 1.90
(m, 1 H, CH MEH-OPPE), 1.52-1.33 (m, 8 H, 4 × CH2 MEH-
OPPE), 0.95 (m, 6 H, 2 × CH3 MEH-OPPE); 195Pt NMR -2304,
-2326, -2410, -2607.
Photophysical Experiments on Pt/MEH-OPPE Solutions. For
all UV-vis absorption and emission experiments in solution, spectro-
scopic grade CHCl3 was used, and the concentration of MEH-OPPE
was kept at 5‚10-7 g‚mL-1. The solutions were prepared by adding a
selected amount (cf. Figure 2) of [Pt-(µ-Cl)Cl(PhCHdCH2)]2 (2), bis-
(2,5-pentanedionato)platinum(II), or 1,5-cyclooctadienedimethylplati-
num(II) to an aliquot of a MEH-OPPE/CHCl3 solution and deoxy-
genating the sample by sparging with Ar for 15 min prior to use.
Film Preparation. For the preparation of Pt/MEH-OPPE films,
MEH-OPPE was first dissolved in CHCl3 at a concentration of about
8.3 × 10-3 g‚mL-1. A selected amount of [Pt-(µ-Cl)Cl(PhCHdCH2)]2
(2) or bis(2,5-pentanedionato)platinum(II) was added to the MEH-
OPPE/CHCl3 solution. Immediately after dissolution of the metal
complex, the solutions were filtered through a 0.2 µm filter (Gelman
Acrodisc PTFE) and were spin-cast (1000 rpm/15 s) onto fused silica
substrates. The polymer films were dried under vacuum at room
temperature and in the dark.
For IR spectra, films were prepared by drop casting the above
solutions on KBr-pellets and drying under vacuum at room temperature
and in the dark. Position of selected IR signals (in cm-1): Film of 2:7
molar ratio of 1: 3074 (styrene C-H st), 3054 (styrene C-H st), 3024
(styrene C-H st), 2952 (diphenylacetylene C-H st), 2873 (dipheny-
lacetylene C-H st), 2861 (diphenylacetylene C-H st), 1600 (styrene
CdC aryl st), 1202 (diphenylacetylene), 1034 (diphenylacetylene), 862
(diphenylacetylene), 780 (diphenylacetylene), 753 (styrene), 689 (sty-
rene). Film of 2:7 molar ratio of 0.1: identical peak positions, lower
relative intensity of the signals originating from styrene.
Photophysical Experiments on Pt/MEH-OPPE Films. Emission
studies on polymer films were performed in air. The samples were
positioned normal to the incident beam, and the emission was detected
at an angle of 22.5 ° from the incident beam.
Acknowledgment. We are indebted to Professor Paul Smith
of ETH Zu¨rich for many enlightening discussions and his
enthusiastic support of this work. We also cordially thank Simon
Dellsperger of ETH Zu¨rich for crucial assistance with the
synthetic experiments.
JA003727W