Characterization of the polymerization catalyst [(2,5-norbornadiene) Rh{C(Ph)=CPh2}(PPh3)] and identification of the end structures of poly(phenylacetylenes) obtained by polymerization using this catalyst

Article abstract of DOI:10.1021/om300642b

The structures of [(2,5-norbornadiene)Rh{C(Ph)=CPh₂}(PPh ₃)] (1) and its reaction product with CH₃CO₂H were elucidated by ¹H, ¹³C, and ³¹P NMR spectroscopy, mass spectrometry, an

Full text of DOI:10.1021/om300642b

Article
pubs.acs.org/Organometallics
Characterization of the Polymerization Catalyst [(2,5-
norbornadiene)Rh{C(Ph)CPh2}(PPh3)] and Identification of the End
Structures of Poly(phenylacetylenes) Obtained by Polymerization
Using This Catalyst
Shohei Kumazawa,† Jesus Rodriguez Castanon,† Naoya Onishi,† Keiko Kuwata,‡ Masashi Shiotsuki,*,§
and Fumio Sanda*,†
‡
†Department of Polymer Chemistry and Department of Synthetic Chemistry and Biological Chemistry, Graduate School of
Engineering, Kyoto University, Katsura Campus, Nishikyo-ku, Kyoto 615-8510, Japan
§Molecular Engineering Institute, Kinki University, Kayanomori, Iizuka, Fukuoka 820-8555, Japan
S
* Supporting Information
ABSTRACT: The structures of [(2,5-norbornadiene)Rh{C-
(Ph)CPh2}(PPh3)] (1) and its reaction product with
CH3CO2H were elucidated by 1H, 13C, and 31P NMR
spectroscopy, mass spectrometry, and single-crystal X-ray
analysis. The presence of two conformational isomers of 1 was
verified by NMR spectroscopy, which was well-supported by
DFT calculations. Phenylacetylene was polymerized using 1 as a
catalyst with [M]0/[Rh] = 10 and quenched with CH3CO2H and
CH3CO2D. The incorporation of H and D at the polymer ends
1
was confirmed by MALDI-TOF mass spectrometry and H and
1H−13C HSQC NMR spectroscopy. The polymerization degree was calculated to be 11 by 1H NMR spectroscopy, which agreed
well with the theoretical value.
of PA derivatives by two- and three-component Rh catalyst
systems such as [(nbd)Rh(CCPh)(PPh3)2]/DMAP (DMAP
= 4-(dimethylamino)pyridine) and [(nbd)Rh(μ-OMe)]2/
PPh3/DMAP.3 Farnetti and co-workers proposed another Rh-
based living polymerization catalyst system based on [(nbd)-
Rh(μ-OMe)]2/1,4-bis(diphenylphosphino)butane.4 Misumi
and Masuda accomplished the living polymerization of PA
derivatives using [(nbd)RhCl]2/PPh3/[LiC(Ph)CPh2],5
which showed quantitative initiation efficiency. Here, [(nbd)-
RhCl(PPh3)] was formed by the reaction of [(nbd)RhCl]2 and
PPh3, followed by its transformation into the active species
[(nbd)Rh{C(Ph)CPh2}(PPh3)]. The reaction is initiated by
the insertion of a triple bond of the monomer between the Rh
center and a vinylic carbon atom, and successive monomer
insertions give the polymer. An analogous complex, [(nbd)-
Rh{C(Ph)CPh2}{P(4-F-C6H4)3}], was isolated and proved
to mediate the living polymerization of PA.6 This complex also
catalyzes the pseudoliving polymerization of N-propargyla-
mides.7 Poly(N-propargylamides) adopt a helical conformation
stabilized by intramolecular hydrogen bonding as well as steric
repulsion between the side chains.8 Interestingly, the helical
structure can transform into a random conformation,
accompanied by a color change and a decrease in stiffness
INTRODUCTION
■
Substituted polyacetylenes have attracted considerable atten-
tion, owing to their optoelectronic properties stemming from
the π-conjugated backbone. The introduction of functional
groups at the side chains provides polyacetylenes with useful
structural features such as a helical conformation and liquid
crystallinity, and they have been applied in molecular
recognition, stimuli-responsive materials, catalytic studies, and
gas permeability.1 Substituted polyacetylenes are commonly
synthesized by polymerization of the corresponding acetylene
monomers using transition-metal catalysts. Polymerization of
substituted acetylenes based on early-transition-metal catalysts,
including Nb, Ta, Mo, and W, occurs via a metathesis
mechanism, while late-transition-metal catalysts, such as those
composed of Rh, Pd, and Ir, display a coordination−insertion
mechanism. Rh-based catalysts are especially useful for the
synthesis of cis-stereoregular substituted polyacetylenes because
they are highly tolerant toward polar groups. Since the first
report on the [(nbd)RhCl]2 (nbd = 2,5-norbornadiene)/Et3N-
catalyzed polymerization of phenylacetylene (PA) derivatives
by Tabata and co-workers,2 various efforts have been aimed at
developing well-defined Rh catalysts to improve control over
polymerization and catalytic activity. Some Rh catalysts enable
the living polymerization of PA derivatives, leading to the
synthesis of end-functionalized polymers and block copolymers.
Noyori and co-workers have reported the living polymerization
Received: July 10, 2012
Published: September 24, 2012
© 2012 American Chemical Society
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spectrometer. The injector temperature and GC/MS interface
temperature were set at 230 and 260 °C, respectively, and helium
was used as a carrier gas (1 mL/min). Chromatographic separation
was achieved using a GL Sciences GC capillary column (30 m length
InertCap 5MS/Sil, 0.25 mm i.d., 0.25 μm film thickness). The column
temperature was maintained at 70 °C for 2 min, raised to 320 at 20
°C/min, and then kept at 320 °C for 30 min. The operation was
carried out at a mass resolution of 1000 (for low-resolution
measurements) and 5000 (for high-resolution measurements), while
the electron ionization energy was 70 eV with an ion-source
temperature of 260 °C.
Materials. Unless otherwise stated, reagents and solvents were
purchased and used without purification. The polymerization catalyst
[(nbd)Rh{C(Ph)CPh2}(PPh3)] (1) was synthesized by reaction of
[(nbd)RhCl]2 and [MgBr{C(Ph)CPh2}] with PPh3 following a
literature method.5,6,21,22 PA (Aldrich) was distilled over CaH2 under
reduced pressure before use. Toluene used for the polymerization was
distilled over CaH2 immediately before use.
Polymerization. A typical procedure was as follows: a solution of
1 (71 mg, 0.10 mmol) and PPh3 (262 mg, 1.0 mmol) in toluene (1.89
mL) was fed under argon into a glass tube equipped with a three-way
stopcock. PA (0.11 mL, 1.0 mmol) was added to the solution, and the
resulting mixture was stirred at 30 °C for 1 h. CH3CO2H (0.57 mL, 10
mmol) was added, and the resulting mixture was stirred at room
temperature for 10 min to quench the reaction. The solution was
poured into methanol (50 mL) to precipitate the polymer. The yellow
precipitate was filtered and dried under vacuum at room temperature
for several hours. The polymer was purified by preparative HPLC (for
details see Instrumentation). The polymer sample was finally freeze-
dried from a benzene solution to remove the solvent.
Computation. All calculations were performed with the Gaussian
09 program23 running on the supercomputer system of the Academic
Center for Computing and Media Studies of Kyoto University. The
density functional theory (DFT)24 method with Becke’s three-
parameter hybrid functional25 and the LYP correlation functional
(B3LYP)26 were utilized in conjunction with the LANL2DZ basis set
to fully optimize geometries.27
upon a rise in temperature and/or the addition of a polar
solvent, and it is expected that sophisticated stimuli-responsive
materials can be developed on the basis of substituted
polyacetylenes of controlled stereoregularity and molecular
weight. We have recently demonstrated that Rh catalysts
containing a strongly π-acidic diene, tetrafluorobenzobarrelene
(tfb), show an extremely high catalytic activity in comparison to
their nbd counterparts. Examples of these Rh catalysts with tfb
ligands include [(tfb)Rh{C(Ph)CPh2}(PPh3)]/PPh3,9
[(tfb)Rh+(η6-Ph)B−Ph3],10 and [(tfb)Rh+(PPh3)2](B−Ph4)].11
The mechanistic aspects of polymerization, especially those
of initiation and propagation, together with cis stereoselectivity
have been studied extensively using various experimental
techniques such as NMR spectroscopy combined with isotope
labeling12 and DFT calculations.13 In contrast, the termination
mechanism of Rh-catalyzed acetylene polymerization has so far
only been elucidated to a minor extent, presumably due to the
difficulties arising from the spectroscopic analysis of polymer
termini. Matrix-assisted laser desorption/ionization time of
flight (MALDI-TOF) mass spectrometric analysis of polymers
can identify the structure of the polymer termini, allowing a
detailed investigation of the polymerization mechanism and the
effect of the termini on the polymer properties.14−20 To the
best of our knowledge, there has been no report regarding the
mass spectrometric analysis of the terminal structures of
substituted polyacetylenes obtained by Rh-catalyzed polymer-
ization. Regarding the utility of the properties of substituted
polyacetylenes, the elucidation of the terminal structures may
give rise to the development of end-functionalized substituted
polyacetylenes, leading to an even broader utilization of Rh-
based polymers. In the present study, we analyze the terminal
structure of poly(PA), obtained by living polymerization with a
well-defined Rh catalyst, using mass spectrometry together with
NMR spectroscopy and DFT calculations, and provide a
discussion of the termination mechanism.
RESULTS AND DISCUSSION
■
EXPERIMENTAL SECTION
Analysis of the Product of Rh Catalyst 1 and
CH3CO2H. Rh catalysts are mostly used for the polymerization
of monosubstituted acetylene monomers because of their high
functional group tolerance and the cis stereoregularity of the
resulting polymers, which are useful for application in
functional materials.1k However, it remains unclear what
happens to the formed polymers after isolation by means of
pouring the polymerization mixtures into poor solvents such as
methanol. It has been reported that acetic acid (CH3CO2H)
quenches the Rh-catalyzed polymerization of monosubstituted
acetylenes.3 In the course of this study, we first analyzed by 31P,
13C, and 1H NMR spectroscopy and GC-MS a mixture of 1 and
CH3CO2H, which served as a model for the reaction between
the growing polymer chain and CH3CO2H.
■
Instrumentation. X-ray crystal structure data were collected on a
Rigaku RAXIS RAPID imaging plate area detector with graphite-
monochromated Mo Kα radiation (λ = 0.710 75 Å). Crystals of
suitable size were mounted on a nylon loop and then transferred to a
goniostat for characterization and data collection. The structure was
solved by direct methods and expanded using Fourier techniques. All
calculations were performed using the crystallographic software
package of Rigaku Corp. and Rigaku/MSC CrystalStructure version
1
1
3.7. H (400 or 700 MHz), 13C (100 MHz), H−13C heteronuclear
single quantum coherence (HSQC), and 31P NMR spectra (162
MHz) were recorded on JEOL EX-400, AL-400, and Bruker DRX-700
spectrometers. Polymers were isolated by preparative high-perform-
ance liquid chromatography (HPLC) on JAIGEL-1H and JAIGEL-2H.
Number- and weight-average molecular weights (Mn and Mw) were
determined by size exclusion chromatography (SEC) on a JASCO PU-
980/RI-930 chromatograph, using a KF-805 (Shodex) × 3 column
with a molecular weight limit of 4 × 106 calibrated with polystyrene
standards, using THF as the eluent (column temperature 40 °C, flow
rate 1 mL/min). MALDI-TOF mass spectra were recorded on a
Bruker Daltonics Ultraflex III TOF/TOF equipped with a 355 nm
YAG laser in reflectron mode and using an acceleration voltage of 25
kV. Samples for MALDI-TOF mass spectrometry were prepared from
a CH2Cl2 solution by mixing the sample (10 mg/mL) in a volume
ratio of 1:100:1 with the matrix trans-2-[3-(4-tert-butylphenyl)-2-
methyl-2-propenylidene]malononitrile (20 mg/mL) and AgOCOCF3
(2 mg/mL), respectively. All mass differences were calculated by
comparing mass values of two base peaks (the peak of most populated
isotopomers). GC-mass spectra were recorded on an Agilent
Technologies GC HP-6890 coupled with a JEOL JMS-700 mass
The synthesis of complex 1 and its analogous complex was
reported previously in the literature,21 although no spectro-
scopic data for 1 were given.28 We therefore characterized the
1
structure of 1 by H, 13C, and 31P NMR spectroscopy along
with a single-crystal X-ray analysis of 1. In the 31P NMR
spectrum of 1 (measured in CD2Cl2) two sets of doublets were
observed in a ratio of 1.00:2.72 at 26.7 and 26.2 ppm having
coupling constants of JRh−P = 183 and 185 Hz (Figure 1). In
order to obtain information on the presence of conformational
isomers, we measured the variable-temperature (VT) 31P NMR
spectra of 1 in toluene-d8. Two sets of doublets were observed
in a ratio of 1:2.15 at 26.9 and 26.3 ppm having coupling
constants JRh−P = 183 and 187 Hz at room temperature. The
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Figure 2. ORTEP drawing of the molecular structure of 1 (50%
probability ellipsoids).
Figure 3. Relationship between the dihedral angle (ϕ) values of P−
Rh−CC and energies of 1 calculated by the B3LYP/LANL2DZ
method.
Figure 1. 1H (400 MHz), 13C (100 MHz), and 31P NMR spectra (162
MHz) of 1 measured in CD2Cl2 ([1] = 2.55 × 10−2 M) at room
temperature. An asterisk indicates the solvent.
presence of two rotational isomers was indeed well supported
by the existence of two conformers with ϕ = 90 and 270° and
very close energy minima (energy difference 0.009 kJ/mol).33
The rotational barrier between them was calculated to be 75.5
kJ/mol, which was in good agreement with that (73.2 kJ/mol)
estimated by the VT NMR measurement mentioned above. X-
ray crystallographic analysis (Figure 2) revealed that the ϕ
value of the conformer is 80.5° in the solid state, which agrees
with that of the most stable conformer predicted by DFT
calculations. The crystallographic geometries coincide with the
calculated geometries, which supports the accuracy of the DFT
method in predicting the conformation.
ratio of the two signal sets depended on the solvent. The
coalescence temperature was 89 °C in toluene-d8.29 Thus, the
two signal sets are assigned to two conformational isomers that
exist within the time scale of the NMR experiment. The
rotational barrier between the two isomers was estimated to be
73.2 kJ/mol.30 The H and 13C NMR spectra support the
1
presence of the conformational isomers indicated by the 31P
NMR spectroscopic measurement.
The solid-state structure of 1 was determined by single
crystal X-ray analysis (Figure 2).31 The Rh atom exists in a
distorted-square-planar coordination geometry, i.e., the α-
carbon of −C(Ph)CPh2 is located in a plane formed by
the Rh atom and the centers of the two norbornadiene double
bonds, while the phosphorus atom of PPh3 lies 31.5° aside the
plane, presumably because of steric repulsion between the
bulky PPh3 and −C(Ph)CPh2 groups.
1
Figure 4 shows the H, 13C, and 31P NMR spectra of a
mixture of catalyst 1 and 100 equiv of CH3CO2H in CD2Cl2.
One doublet was observed at 28.8 ppm with JRh−P = 174 Hz,
whereas no singlet was observed at −5.6 ppm assignable to
PPh3, indicating that no PPh3 was liberated from Rh.34 The
formation of triphenylethylene (m/z 256)35 was, however,
1
DFT calculations were performed to obtain more detailed
information on the conformation of complex 1. Figure 3 shows
the energy map of the conformers of 1 optimized by the
B3LYP/LANL2DZ method. The dihedral angle ϕ of the P−
Rh−CC atoms was varied by 15° increments.32 The
confirmed by GC-mass spectrometry and H and 13C NMR
spectroscopy by comparison with an authentic sample. From
these results, it is tentatively concluded that the −C(Ph)
CPh2 group of 1 was replaced with −OAc by the addition of
CH3CO2H, while PPh3 remained coordinated to Rh to form
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Scheme 1. Reaction of 1 with CH3CO2H
Figure 5. Possible conformers of [(nbd)Rh(OCOCH3)(PPh3)] before
(S2, S3A, S3B) and after (S2opt, S3A opt, S3B opt) full geometry
optimization by the DFT method (B3LYP/LANL2DZ). Legend: Rh,
green; P, orange; O, red; C, gray; H, white.
Figure 4. 1H (400 MHz), 13C (100 MHz), and 31P NMR spectra (162
MHz) of a mixture of 1 and 100 equiv of CH3CO2H measured in
CD2Cl2 ([1]0 = 2.55 × 10−2 M). A single asterisk indicates the solvent,
and double asterisks indicate CH3CO2H. No change was observed
between spectra of the samples recorded immediately after mixing of
the reagents and spectra that were acquired 1 day later.
Scheme 2. Polymerization of PA Using 1 as a Catalyst
complex 2 or 3 (Scheme 1). Unfortunately, no concrete
1
evidence for the formation of 2/3 was obtained from the H
and 13C NMR spectra.
Although [(nbd)Rh(OCOR)(PPh3)] (R = CH3, CF3)36,37
has been synthesized previously by reaction of [(nbd)Rh-
(OCOR)]2 and PPh3, the detailed stereoconfiguration has not
yet been elucidated. In the present study, DFT (B3LYP/
LANL2DZ) calculations were carried out to gain insight into
the species formed by the addition of CH3CO2H to 1. Figure 5
shows the three starting geometries S2, S3A, and S3B. Here, S2
is a square-planar conformer tetracoordinated by nbd,
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a
Table 1. Polymerization of PA
Chart 1. PA 23-mers Obtained by the Polymerizations
Quenched with CH3CO2H and CH3CO2D
polymer
b
c
d
d
acid
yield (%)
Mn
Mw/Mn
CH3CO2H
CH3CO2D
53
53
1700
1900
1.10
1.10
a
Conditions: [M]0 = 0.50 M in toluene, [M]0:[Rh] = 10, [PPh3]:[Rh]
b
c
= 10, 30 °C, 1 h. [acid]:[Rh] = 100. Isolated by precipitation in
MeOH, followed by preparative HPLC separation, where only the
d
fraction corresponding to the peak top was collected. Estimated by
SEC (polystyrene standards, THF).
OCOCH3, and PPh3, S3A is a square-pyramidal conformer
pentacoordinated by nbd, chelating acetate, and PPh3, where
PPh3 is oriented nearly perpendicular to the square-planar
surface, and S3B is a second square-pyramidal conformer, in
which one oxygen atom of OCOCH3 is oriented nearly
perpendicular to the square-planar surface. After full geometry
optimization, S2 gave a square-planar conformer S2opt (E = −3
441 548.5 kJ/mol), whereas both S3A and S3B yielded the
square-planar conformers S3A opt (E = −3 441 548.5 kJ/mol)
and S3B opt (E = −3 441 535.7 kJ/mol). The unfavorable
conformation of S2 can be understood from the relatively small
chelate angle of O−Rh−O (64°) in comparison to those of
ene−Rh−ene (73°) and O−Rh−P (89°). Interestingly,
conformations S2opt and S3A opt were completely identical,
even though their starting geometries (S2 and S3A) differed
significantly. Considering that S3A opt and S3B opt are super-
imposable via rotation of the Rh−O and Rh−P bonds and S2opt
(=S3A opt) is 12.8 kJ/mol more stable than S3B opt, S3B opt is
regarded as one conformation of local minimum conformers,
whose population is much smaller than that of S2opt (=S3A opt).
Consequently, it seems likely that Rh complex 2 is formed by
reaction of 1 with CH3CO2H as illustrated in Scheme 1,
accompanied by the formation of triphenylethylene.38
Polymer Synthesis. Poly(PA) was synthesized by the
polymerization of PA using 1 as an initiator in the presence of
PPh3 as a cocatalyst, which stabilizes the active species leading
to living polymerization (Scheme 2).5 To obtain a low-
molecular-weight polymer the monomer to initiator ratio was
10:1, which makes the analysis of the chain end relatively
straightforward. Directly after the beginning of the polymer-
ization the color of the polymerization mixture changed from
pale yellow to orange, gradually becoming deep orange, which
indicated the presence of the conjugated acetylene backbone.
After 1 h, the polymerization mixture was divided into two
Figure 6. (left) MALDI-TOF mass spectra of poly(PA)s quenched with CH3CO2H and CH3CO2D. (right) Expanded spectra between m/z 2480
and 2750.
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Figure 7. Isotope patterns of the observed (top) and calculated (bottom) MALDI-TOF mass spectra for poly(PA) quenched with CH3CO2H and
CH3CO2D.
Scheme 3. Polymerization Pathway of PA using 1 as an
Initiator
difference between the quenchers on the isolation of the
polymers.39
The structures of the polymers were examined by MALDI-
TOF mass spectrometry (Figure 6). The peaks feature an
interval of 102 amu, which is consistent with the calculated m/z
(102.05) of a monomer unit. Since no other peaks are observed
outside of this series, it can be concluded that the polymers
consist of a homogeneous combination of repeating units,
initiator groups, and end groups. The isotope patterns of the
two samples agreed well with those calculated for polymers
bearing H and D termini, respectively (Chart 1, Figure 7). In
both cases, −C(Ph)CPh2 is considered as the initiating end
group. Furthermore, the m/z difference between the polymers
is 1.011, which is consistent with the calculated value of 1.006.
Scheme 3 illustrates the polymerization pathways of
monomer coordination−insertion and termination with
CH3CO2H. First, the triple bond of a PA monomer coordinates
to the Rh center, accompanied by the simultaneous dissociation
of PPh3 from Rh. Next, the PA inserts between the Rh and
vinylic carbon atom. During this step, 2,1-insertion is more
likely than 1,2-insertion because the π orbital of the benzene
ring of PA significantly interacts with the d orbital of Rh during
2,1-insertion to stabilize the transition state, while no such
interaction is observed during 1,2-insertion.40 The insertion is
expected to take place in a cis manner, as commonly observed
in Rh-catalyzed acetylene polymerizations. It is likely that the
propagating end is quenched in a fashion similar to the reaction
parts and 100 equiv of CH3CO2H and CH3CO2D (vs Rh) was
added to each reaction mixture separately, followed by stirring
for 10 min to quench the polymerization. The polymers were
isolated by precipitation in methanol, followed by preparative
HPLC separation to remove lower molecular weight oligomers
and initiator residues. The collection of only a fraction around
the peak top accounted for the relatively low polymer yield
(53%) in both cases. The yields, molecular weights, and
polydispersity indexes of the polymers obtained by quenching
with either CH3CO2H or CH3CO2D were almost identical
(Table 1), indicating the absence of an effect of the acidity
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NMR Spectroscopic Analysis of the Polymers. Figure 8
shows the 1H NMR spectra in CD2Cl2 of the polymers
obtained by quenching with CH3CO2H and CH3CO2D.41
A
clear difference is the presence of a doublet signal centered at
6.10 ppm for the CH3CO2H-quenched polymer (Figure 8,
top), which can be assigned to the terminal Ha proton and is
absent in the CH3CO2D-quenched polymer (Figure 8,
bottom). The coupling constant of J = 16.7 Hz indicates a
trans geometry of Ha and Hb,42 supporting a cis-stereoregular
polymerization. For the CH3CO2H-quenched polymer the Hb
proton is observed as a doublet signal coupled to Ha, both of
which partially overlap with other signals. On the other hand,
for the CH3CO2D-quenched polymer, the Hb proton is
observed as a singlet due to the absence of Ha, where Hb
partially overlaps with other signals as well. The polymerization
degree was calculated to be 11 on the basis of the integrals
between Ha and Hc.43 This value agrees well with the
theoretical value (i.e., 10).44 The H−13C HSQC spectra of
1
the two poly(PA) samples furthermore clearly indicate the
presence and absence of an Ha signal in the polymers quenched
with CH3CO2H and CH3CO2D, respectively (Figure 9).
CONCLUSION
■
In this article, we elucidated the structure of [(nbd)Rh{C-
(Ph)CPh2}(PPh3)] (1) by H, 13C, and 31P NMR spectros-
1
copy and single-crystal X-ray analysis. 31P NMR spectroscopic
analysis and DFT calculations revealed the presence of two
stable conformational isomers with a dihedral angle ϕ at the P−
Rh−CC atoms of 90° and 270°, one of which was confirmed
by single crystal X-ray analysis (ϕ = 80.5°). The reaction of 1
with CH3CO2H was carried out as a model reaction for
studying the CH3CO2H quenching of PA polymerization
catalyzed by 1. The formation of triphenylethylene was
observed together with the formation of Rh complex 2,
which was coordinated by nbd, CH3CO2, and PPh3, indicating
the replacement of the end group Rh moiety with a proton by
its quenching with CH3CO2H. In addition, poly(PA)s with H
and D end groups were obtained by the polymerization of PA
using 1 as a catalyst and subsequent quenching with CH3CO2H
and CH3CO2D, respectively. Their structures were reliably
Figure 8. 1H NMR spectra (700 MHz) in CD2Cl2 of poly(PA)
quenched with CH3CO2H and CH3CO2D. An asterisk indicates
CHCl3 contamination from the preparative HPLC purification. The
chemical shifts are calibrated to the CH2Cl2 signal (5.33 ppm, not
shown).38
1
confirmed by MALDI-TOF mass spectrometry and H and
1H−13C HSQC NMR spectroscopy. The cis insertion of PA
between the Rh center and C(Ph)CPh2 was confirmed by
1
determination of the H NMR coupling constant of the two
vinylene protons at the polymer ends. To our knowledge, the
present study is the first successful end group analysis of
polyacetylenes based on MALDI-TOF mass spectrometry.
ASSOCIATED CONTENT
■
S
* Supporting Information
Figures, tables, and a CIF file giving VT 31P NMR spectra of 1
measured in toluene-d8, 1H, 13C, and 31P NMR spectra of PPh3,
triphenylethylene, and mixtures with CH3CO2H measured in
CD2Cl2, GC-mass spectra of triphenylethylene, Cartesian
coordinates for 1 (ϕ (dihedral angle of P−Rh−CC) = 90,
270°), S2opt (S3A opt), and S3B opt, and crystallographic data for
1. This material is available free of charge via the Internet at
http://pubs.acs.org.
1
Figure 9. H−13C HSQC NMR spectra (700 MHz) in CD2Cl2 of
poly(PA) obtained by the polymerization quenched with CH3CO2H
(red) and CH3CO2D (blue).
illustrated in Scheme 1 and, as a result, poly(PA) with −H and
−C(Ph)CPh2 ends forms together with 2.
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AUTHOR INFORMATION
Corresponding Author
*E-mail: mshiotsuki@moleng.fuk.kindai.ac.jp (M.S.); sanda.
fumio.5n@kyoto-u.ac.jp (F.S.).
■
Notes
(17) Nagahata, R.; Sugiyama, J.; Goyal, M.; Asai, M.; Ueda, M.;
Takeuchi, K. Polym. J. 2000, 32, 854−858.
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS
■
This research was partially supported by a Grant-in-Aid for
Scientific Research from the Japan Society for Promotion of
Science (22750108), the Global COE Program, “International
Center for Integrated Research and Advanced Education in
Materials Science” from the Ministry of Education, Culture,
Sports, Science and Technology of Japan, The Ogasawara
Foundation for the Promotion of Science & Engineering, and
The Sumitomo Foundation. We are grateful to Prof. Masahiro
Shirakawa, Prof. Hidehito Tochio, and Dr. Shin Isogai for the
NMR measurements, Prof. Tetsuaki Fujihara for the X-ray
measurement, and Mr. Hiromitsu Sogawa for DFT calculations.
(19) He, J.; He, M.; Pei, J.; Ding, A.; Huang, W. Rapid Commun. Mass
Spectrom. 2001, 15, 1239−1243.
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6258.
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Organometallics 2006, 25, 1270−1278.
(22) In the present study, [MgBr{C(Ph)CPh2}] was used instead
of [LiC(Ph)CPh2] because the former gave 1 in a higher yield.
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6842
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