Synthesis of end-functionalized polyacetylenes that contain polar groups by employing well-defined palladium catalysts

Article abstract of DOI:10.1002/chem.201202256

A series of [(dppf)PdBr(R)]-type complexes (dppf=1,1'- bis(diphenylphosphino)ferrocene; R=p-cyanophenyl (1 a), o-hydroxymethylphenyl (1 b), and triphenylvinyl (1 c)), in combination with silver trifluoromethanesulfonate (AgOTf), were demonstrated to be ac

Full text of DOI:10.1002/chem.201202256

FULL PAPER
DOI: 10.1002/chem.201202256
Synthesis of End-Functionalized Polyacetylenes that Contain Polar Groups
by Employing Well-Defined Palladium Catalysts
Jesus Rodriguez Castanon,[a] Keiko Kuwata,[b] Masashi Shiotsuki,*[c] and Fumio Sanda*[a]
Abstract: A series of [(dppf)PdBr(R)]-
type complexes (dppf=1,1’-bis(diphe-
nylphosphino)ferrocene; R=p-cyano-
phenyl (1a), o-hydroxymethylphenyl
(1b), and triphenylvinyl (1c)), in com-
bination with silver trifluoromethane-
sulfonate (AgOTf), were demonstrated
to be active for the polymerization of
monosubstituted polar acetylene mono-
lar weights of the polymers depended
on the combination of the Pd catalyst
and monomer that was employed.
Matrix-assisted laser-desorption/ioniza-
tion–time of flight (MALDI-TOF)
mass spectrometric analysis indicated
the formation of polymers that con-
tained the “R” and “H” groups at the
chain ends. IR spectroscopic analysis
supported the R-end-functionalization
of the polymers. NMR spectroscopy
and MS identified the presence of spe-
cies that were formed by single,
double, and triple insertion of the mon-
omers into the Pd-C6H4-p-CN bond,
thereby giving solid evidence for an in-
sertion mechanism for the present
system. Density functional theory
(DFT) calculations suggested the pref-
erence for 1,2-insertion of the mono-
mer compared to 2,1-insertion.
ꢀ
ꢀ
mers HC CCONHC4H9 (2), HC
ꢀ
CCO2C8H17
(3),
HC
Keywords: alkynes · density func-
tional calculations · end-functionali-
zation · palladium · polymerization
ꢀ
HC
CCH2OCONHC6H13
(4),
ꢀ
CCH2OCO2C6H13 (5), and HC CCH-
ACHTUNGTRENNUNG(CH3)OH (6). The yields and molecu-
Introduction
modification of the polymer architectures are achieved,
which enable the synthesis of block copolymers and star-
shaped polymers.[41]
Transition-metal catalysts polymerize various acetylene
monomers to yield substituted polyacetylenes with useful
functions, such as electro-active and photoluminescent prop-
erties, as a result of their conjugated main chains, their high
gas permeability, and the helix-forming ability of their rigid
backbones.[1–5] Well-defined transition-metal catalysts that
contain tantalum,[6] molybdenum,[7–9] ruthenium,[10–14] rhodi-
um,[15–31] nickel,[32] and palladium[33–40] are especially useful
for acetylene polymerization, because they allow control
over catalytic activity by judicious ligand design, thereby en-
abling living/controlled polymerization. As a result, precise
Among these transition-metal catalysts for acetylene poly-
merization mentioned above, Rh- and Pd-based compounds
catalyze the polymerization of acetylene monomers that are
substituted with heteroatom-containing polar groups, as well
as nonpolar hydrocarbon acetylene monomers, owing to the
low oxophilicity of late transition metals. Although Rh-
based catalysts[15–31] have been widely studied and utilized to
obtain cis-stereoregular-substituted polyacetylenes, Pd-based
catalysts[32–40] have not been extensively examined for acety-
lene polymerization, presumably owing to their lower activi-
ty compared with that of Rh catalysts. Darkwa, Pollack and
co-workers have developed well-defined [(diphosphine)Pd-
ACHUTNGREN(NUG NCCH3)ACHTUGNTERN(NGUN CH3)]OTf-type catalysts and successfully polymer-
[a] J. Rodriguez Castanon, Prof. Dr. F. Sanda
Department of Polymer Chemistry
ized phenylacetylene (PA) to obtain poly(PA)s with moder-
ate molecular weights in good yields.[36] The incorporation of
a methyl group at their chain ends was confirmed by
1H NMR and 13C NMR spectroscopic analysis of the synthe-
sized poly(PA)s. This observation indicated that PA was
polymerized through a coordination/insertion mechanism.
Inspired by this work, we synthesized [(dppf)Pd-
Graduate School of Engineering, Kyoto University
Katsura Campus, Nishikyo-ku, Kyoto, 615-8510 (Japan)
Fax : (+81)75-383-2592
E-mail: sanda.fumio.5n@kyoto-u.ac.jp
[b] Dr. K. Kuwata
Department of Synthetic Chemistry and
Biological Chemistry
AHCTUNGRTEG(NNUN NCCH3)(R)]OTf-type catalysts for the polymerization of
Graduate School of Engineering, Kyoto University
Katsura Campus, Nishikyo-ku, Kyoto, 615-8510 (Japan)
PA.[38] We have shown that R groups are introduced at the
chain ends of poly(PA), and we have synthesized block co-
polymers by utilizing end-functionalized poly(PA)s as mac-
roinitiators. Thus far, only a couple of examples of Pd cata-
lysts have been reported for the polymerization of non-PA-
type acetylene monomers that contain polar groups,[33–35] in
spite of the encouraging results of PA polymerization with
[c] Prof. Dr. M. Shiotsuki
Molecular Engineering Institute
Kinki University
Kayanomori, Iizuka, Fukuoka 820-8555 (Japan)
E-mail: mshiotsuki@moleng.fuk.kindai.ac.jp
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.201202256.
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Table 1. Polymerization of monosubstituted acetylenes 2–6 by
[(dppf)PdBr(R)] (1a–1c)/AgOTf.[a]
[d]
Sample[b]
Monomer Cat. Yield[c] [%] Mw
PDI[d]
2.37
poly(2)-1a
poly(2)-1b
poly(2)-1c
poly(3)-1a
poly(3)-1a[f]
poly(3)-1b
poly(3)-1c
poly(4)-1a
poly(4)-1b
poly(4)-1c
poly(5)-1a
poly(6)-1a
poly(6)-1b
poly(6)-1c
2
2
2
3
3
3
3
4
4
4
5
6
6
6
1a
1b
1c
1a
1a
1b
1c
1a
1b
1c
1a
1a
1b
1c
84
90
93
21
21
29
25
28
42
8
2300
2000 (63%)[e] 1.26
2000 (56%)[e] 1.28
5800
13000
7400
1.45
2.89
1.41
1.28
6600
7900 (80%)[g] 2.01
4900 (82%)[g] 1.61
8700 (78%)[g] 1.65
[h]
–
3700 (81%)[i]
10600
15000
2.20
5.52
6.60
8.60
55
47
22
27300
[a] [Pd]=10 mm, [AgOTf]=12 mm, [monomer]0 =0.5 m in CH3CN/
CH2Cl2 (1:3 v/v), 308C, 24 h. [b] Defined by the combination of catalyst
that are used and the polymer that is obtained. [c] Poly(2): n-hexane-in-
soluble part; poly(3) and poly(4): MeOH-insoluble part; poly(6): Et2O-
insoluble part. [d] Estimated by SEC (PS standards). Eluent: THF for
poly(2) and poly(3), CHCl3 for poly(4) and poly(5), and N,N-dimethyl-
formamide (DMF) for poly(6). [e] Peak-area ratio, as determined by
SEC. The other part corresponded to low-molecular-weight oligomers.
[f] [monomer]0/[Pd]=100. [g] Peak-area ratio, as determined by SEC. A
broad high-molecular-weight signal was also observed (area ratio: about
15%). [h] Not determined because the polymer was not obtained as n-
hexane-, MeOH-, or Et2O-insoluble parts but was isolated by preparative
HPLC. [i] Data for the residual mass after removal of the solvent from
the reaction mixture.
Scheme 1. Polymerization of monosubstituted polar acetylene monomers
2–6 by well-defined Pd catalysts 1a–1c/AgOTf.
well-characterized Pd catalysts[36–38,40] and the many exam-
ples of Rh-catalyzed polymerization of non-PA monomers.
Herein, we report the polymerization of monosubstituted
acetylenes (2–6, Scheme 1) that contain polar groups with
well-defined [(dppf)PdBr(R)]-type complexes (1a–1c,
Scheme 1). Moreover, we report the mechanistic aspects of
this polymerization reaction, based on NMR and IR spec-
troscopic analysis, MS analysis, as well as DFT calculations.
(area ratios: 78–82%), broad peaks were observed at
higher-molecular-weight regions for both poly(4) and
poly(5). Monomer 6, which contained a hydroxy group, also
polymerized to afford poly(6) with Mw values of 10600–
27300 in 22–55% yield. To the best of our knowledge, this is
the first example of the polymerization of a hydroxy-group-
containing acetylene with Pd catalysts under ambient condi-
tions.[42] The large polydispersity index (PDI) values of
poly(6) may be due to interactions between the hydroxy
groups and the active Pd centers during the polymerization
process, thereby leading to termination reactions. A model
reaction supported this assumption, that is, when 1cOTf was
left in C6D6 (0.5 mL) with 50 equivalents of MeOH at 558C
for 24 h, triphenylethylene was formed in 50% yield, as con-
Results and Discussion
Polymerization: The reactions of well-defined Pd complexes
1a–1c with AgOTf yield [(dppf)PdACTHNUTRGNEUNG(NCCH3)(R)]OTf (R=
C6H4-p-CN (1aOTf), R=C6H4-o-CH2OH (1bOTf), and R=
C(Ph)=CPh2 (1cOTf)), which catalyze the polymerization of
phenylacetylene.[36,38] Herein, the polymerization of mono-
mers 2–6, which contain polar groups (e.g., amide, ester, car-
bamate, carbonate, and hydroxy groups) was carried out
under the conditions given in Scheme 1. As shown in
Table 1, the yields and molecular weights of the polymers
largely depended on the monomers and the catalysts. Poly-
mers poly(2), which featured weight-average molecular
weights in the range Mw =2000–2300, were obtained in 84–
93% yield. Despite having an analogous structure to mono-
mer 2, monomer 3 gave its corresponding polymers, poly(3),
in poor yield (21–29%), although its Mw values (5800–7400)
was higher than those of poly(2). Under the same condi-
tions, monomer 4 afforded powdery polymers, poly(4), that
were insoluble in MeOH and featured Mw values from 4900
to 8700, whilst monomer 5 gave no solid, but rather a liquid
polymer, poly(5), in spite of sharing a similar structure to
poly(4). Poly(5), with Mw =3700, was isolated by evaporat-
ing the solvent from the polymerization mixture. In addition
to the main size-exclusion chromatography (SEC) peaks
1
firmed by H NMR and13C NMR spectroscopy (see the Sup-
porting Information, Figure S1) and by MS (electron ioniza-
tion (EI)). The other products of the reaction could not be
identified. Judging from this result, we considered that ter-
mination step occurred by the reactions of the hydroxy
ꢁ
groups of compound 6 and/or poly(6) with Pd C=C species,
which should be formed from either insertion of the mono-
mer between the Pd and R groups or its subsequent inser-
tion products (see below).[38,43] In fact when 50 equivalents
of compound 6 were stepwise added to 1aOTf (1 equivalent
every 5 min, a total of 50 steps), a polymer with Mw =5600
and PDI=3.14 was obtained in 32% yield. This result indi-
cates that the termination reaction occurs less when the
local monomer concentration is decreased (see the Support-
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Synthesis of End-Functionalized Polyacetylenes
FULL PAPER
ing Information, Table S1). The Mw of poly(3)-1a increased
from 5800 to 13000 as the [monomer]0/[Pd] ratio was in-
creased from 50 to 100. A similar behavior was expected for
the other monomers, but the [monomer]0/[Pd] value was
kept at 50 for the sake of easier polymer-structure analysis.
Polymer characterization: First, the structures of the poly-
mers were examined by 1H NMR and IR spectroscopy.
Poly(2) exhibited very broad signals at d=6.0–8.3 ppm,
which were assigned to the vinylene protons of the main
chain (see the Supporting Information, Figure S2). It was
difficult to determine the cis content from the integration
ratio owing to the broadness of the peaks. Because highly
cis-stereoregular polyacetylenes commonly exhibit relatively
sharp resonances for the vinylene protons, it seems that the
cis-content of poly(2) is lower than that of the polymers that
were obtained by polymerization with Rh catalysts.[44–47] This
conclusion was also supported by the presence of IR absorp-
tion peaks at n˜ =1276 (s) and 901 cmꢁ1 (w), which were as-
signed to a trans structure, as well as a peak at n˜ =742 cmꢁ1
(m) that was assigned to a cis structure (see the Supporting
Information, Figure S3).[48] Poly(3)–poly(6) showed trends in
Figure 2. MALDI-TOF mass spectrum of poly(3)-1a; inset shows the par-
tial amplification of a selected region the spectrum.
1
their H NMR and IR spectra that were similar to those of
poly(2).[49]
The end-functionalization of the polymers that were syn-
thesized by 1aOTf with C6H4-p-CN groups could be ob-
served by IR spectroscopy, as shown in Figure 1 for the
poly(6) series that were obtained from initiators 1a–1c as
ꢀ
representative examples. A C N stretching peak is observed
Figure 3. Comparison between the MALDI-TOF mass spectra of the
poly(3) series, which were obtained by polymerization reactions that
were initiated with compounds 1a, 1b, and 1c.
Figure 1. IR spectra of poly(6)-1a, poly(6)-1b, and poly(6)-1c.
observed for poly(3)-1a, as shown in Figure 2. Both sets of
peaks feature an interval between their corresponding peaks
of 183.21, which is consistent with the calculated m/z value
of a monomer unit (182.13). Noticeable differences between
the absolute values exist between the intense peak series of
poly(3)-1a, poly(3)-1b, and poly(3)-1c. These differences
agree with those that arise from identical polymer chains
that contain different chain ends. For instance, the differ-
ence between the signals of poly(3)-1a and poly(3)-1c is
152.77, which matches reasonably well with the calculated
m/z difference (153.09) between the C(Ph)=CPh2 and C6H4-
p-CN chain-end functional groups. Another chain end can
be assigned to the H atom from the calculated isotope pat-
terns for the observed signals (Figure 4). The structure of
at n˜ =2228 cmꢁ1 in the IR spectrum of poly(6)-1a, whereas
no such peak is observed in the same region in the spectra
of poly(6)-1b and poly(6)-1c. It is difficult to confirm the in-
troduction of the R groups into these latter two polymers by
IR spectroscopy, owing to the lack of such clear absorption
peaks.
The structures of poly(5)-1a and the poly(3) series were
also examined by MALDI-TOF mass spectrometry by em-
ploying 2,5-dihydroxybenzoic acid (DHB) as a matrix and
sodium trifluoroacetate (NaTFA) as a cationizer (see Figure
S9 (the Supporting Information) for poly(5)-1a and Figure 2
and Figure 3, for poly(3) series). Two series of peaks were
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M. Shiotsuki, F. Sanda et al.
Figure 4. Selected isotope patterns in the MALDI-TOF mass spectra (en-
larged view of the data shown in Figure 3) and their corresponding calcu-
lated patterns for a) poly(3)-1a, b) poly(3)-1b, and c) poly(3)-1c.
Figure 5. 1H NMR and 31P NMR spectra of a) 1aOTf, b) 1aOTf+1 equiv
of 5, and c) 1aOTf+3 equiv of 5 measured in CD3CN/CD2Cl2 (1:3 v/v),
[1aOTf]0 =34 mm, RT (s: solvent).
poly(5)-1a is also thought to correspond to a main chain
with H and C6H4-p-CN chain ends, according to MALDI-
TOF mass spectrometry (see the Supporting Information,
Figure S9).
Stoichiometric reactions: Stoichiometric reactions between a
catalyst and 1–3 equivalents of the monomers were carried
out to obtain further information on the end-functionaliza-
tion process. We examined the initial insertion of compound
ꢁ
5 into the Pd C bond of catalyst 1aOTf, which was formed
in situ from compound 1a and AgOTf, by NMR spectrosco-
1
py. Figure 5 shows the H NMR and 31P NMR spectra of a
sample solution of catalyst 1aOTf in CD3CN/CD2Cl2 upon
the stepwise addition of one, two, and three equivalents of
compound 5 in an NMR sample tube. After the addition of
1
one equivalent of compound 5, the H NMR signals for the
vinylene proton appeared at d=6.32 ppm (dd, J=14.0 and
10.0 Hz). These peaks for the vinylene protons accounted
for the 1,2-insertion products, based upon the DFT calcula-
tions (see below).[50] These signals intensified upon addition
of the second and third portions of compound 5 (Figure 5,
top). In the 31P NMR spectra, the pair of doublets for cata-
lyst 1aOTf at d=30.79 and 11.61 ppm (2J
ACHTNUTRGNE(NUG P,P)=27.5 Hz)
became progressively less intense, with an accompanying ap-
Scheme 2. Insertion of substituted acetylenes between the Pd and R
groups of [(dppf)PdACHTNUGTRENUNG(NCCH3)(R)]OTf.
pearance of a new pair of doublets at d=31.34 and
11.98 ppm (2J
G
showed peaks that corresponded to single-, double-, triple-,
dition of 1–3 equivalents of compound 5. This new pair of
signals was assigned to the species that were formed by the
single insertion of compound 5 (Scheme 2). This monomer
insertion was supported by the MS (ESI) data, which
quadruple-, and quintuple-insertion products of compound 5
ꢁ
into the Pd C bond of 1aOTf (Figure 6). Similar results
were obtained when monomer 4 was used instead of com-
pound 5 (see the Supporting Information, Figures S12–S14).
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Synthesis of End-Functionalized Polyacetylenes
FULL PAPER
The next step is the insertion of a monomer between the
Pd center and the R group via a metallacyclobutane transi-
tion state (TSIa). The monomer donates p-electrons from
ꢁ
the triple bond to the Pd center to form a Pd C bond. Si-
multaneously, the R group leaves the Pd atom and moves
ꢁ
closer to the monomer to form an R C bond. The formation
of 1,2-inserted product IIIa is endothermic (X=NH,
+13.5 kJmolꢁ1; X=O, +19.4 kJmolꢁ1), whilst that of IIIa–
CH3CN is exothermic (X=NH, ꢁ23.4 kJmolꢁ1
; X=O,
ꢁ22.3 kJmolꢁ1) relative to structure I. It is likely that the
CH3CN moiety coordinates to the Pd center to stabilize the
ꢁ
intermediate. The extension of conjugation from the Pd R
ꢁ
group of structure I to the Pd CH=C(R)CH2OCOXC6H13
group of structure IIIa–CH3CN should also be effective in
enhancing the stability of the structure. Once products IIIa
and/or IIIa–CH3CN are formed, the carbonyl group of the
monomer unit cannot coordinate to Pd owing to geometry
restrictions, that is, intermediate IIIa’ does not exist owing
to the large strain.
The second monomer-insertion process starts with the co-
ordination of another monomer to one square-planar site of
the Pd center, thereby resulting in the formation of IVa. In
a fashion that is similar to the first monomer-insertion proc-
ess, IVa is thought to turn into IVa’, owing to stabilization
from the chelation of the carbonyl group.[52] The second
monomer is inserted via a four-membered transition state
(TSIIa), in a similar manner to TSIa. We assumed that the
activation energy for TSIIa is lower than that of TSIa, judg-
ing from the largely exothermic DG values on going from
Figure 6. a) ESI mass spectrum of a mixture of 1aOTf and 3 equiv of 5.
b,c): Isotope patterns in the ESI mass spectra and their corresponding
calculated patterns for the single- and double-insertion products, respec-
tively.
IVa’
to
Va
(X=NH,
ꢁ126.7 kJmolꢁ1
;
X=O,
These results demonstrate the end-functionalization of these
polymers by the Pd catalysts.
ꢁ125.8 kJmolꢁ1) compared to those on going from IIa’ to
IIIa (X=NH, ꢁ22.5 kJmolꢁ1; X=O: ꢁ31.6 kJmolꢁ1) and/or
those on going from IIa’ to IIIa–CH3CN (X=NH,
ꢁ59.4 kJmolꢁ1; X=O, ꢁ73.3 kJmolꢁ1). Further extension of
the conjugation seems to be effective for stabilizing Va,
even in the absence of CH3CN.
DFT calculations: These aforementioned results are consis-
tent with a mechanism that involves insertion of the acety-
[43,51]
ꢁ
lenes into a Pd C bond.
DFT calculations were carried
out to obtain detailed information on the polymerization
mechanism. Monomers 4 and 5 were employed as represen-
tative examples and [(dppf)Pd(C6H4-p-CN)Br] was used as
the representative Pd complex to catalyze the polymeriza-
tion reactions. Scheme 3, top shows the reaction pathway for
1,2-insertion of the first and second monomers into cationic
PdII species I, which is formed from the reaction of a
square-planar PdII complex that is coordinated to dppf, p-cy-
anophenyl (R), and Br groups with AgOTf in CH3CN/
CH2Cl2. The first step is the replacement of the CH3CN
moiety in I with a monomer to form intermediate IIa, which
is coordinated by the triple bond of the monomer. After the
optimization of the geometry of IIa, which has a distance
between the Pd and carbonyl-oxygen atoms of longer than
6 ꢁ, this species was automatically converted into IIa’ with
Scheme 3, bottom shows the reaction pathway for 2,1-in-
sertion of the first and second monomers into structure I.
Upon optimizing the geometry, intermediate IIb does not
ꢁ
automatically convert into its analogue, IIb’ (Pd O distance:
X=NH, 3.18 ꢁ; X=O, 3.38 ꢁ), which is chelated by the
triple bond and the carbonyl group; this chelation is differ-
ent to that in the IIa!IIa’ transformation during the 1,2-in-
sertion (see above). Although the DG values of IIb’ are
smaller than those of IIb, a direct path from IIb to TSIb
may exist. It seems that 2,1-insertion is unfavorable com-
pared to 1,2-insertion judging from the DG values of IIb,
which are larger than those of IIa’, as predicted from the
larger steric repulsion between the bulky dppf and
CH2OCOXC6H13 moieties. Interestingly, the 2,1-insertion
product IIIb is automatically converted into IIIb’, which is
ꢁ
ꢁ
Pd O distances of 3.42 ꢁ (X=NH) and 3.55 ꢁ (X=O).
chelated by C=O in a square-planar geometry (Pd O dis-
This result suggests that intermediate IIa easily turns into
IIa’, which is stabilized by chelation with the carbonyl group
of the monomer that is oriented perpendicular to a square-
planar surface that consists of Pd, dppf, C6H4-p-CN (R), and
the triple bond of the monomer.
tance: X=NH, 2.16 ꢁ; X=O, 2.18 ꢁ). The formation of
IIIb’ is largely exothermic (X=NH, ꢁ51.8 kJmolꢁ1; X=O,
ꢁ29.9 kJmolꢁ1) relative to structure I, whilst the formation
of IVb is largely endothermic (X=NH, +50.7 kJmolꢁ1; X=
O, +54.8 kJmolꢁ1). Once IIIb’ is formed, the second mono-
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M. Shiotsuki, F. Sanda et al.
ACTHNUTRGNEUNG
Scheme 3. Reaction pathways for 1,2- and 2,1-insertions of CHCH2OCOXC6H13 (X=NH, O) into [(dppf)PdII(NCCH3)(C6H4-p-CN)]+; dppf and C6H4-p-
CN are shown as an arc and R, respectively. The values below the compound numbers represent their relative G values [kJmolꢁ1], based on I. The coun-
teranion (TfO) is omitted for clarity.
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Synthesis of End-Functionalized Polyacetylenes
FULL PAPER
DFT calculations: All of the calculations were performed with the
GAUSSIAN 09 program[53] on the supercomputer system at Academic
Center for Computing and Media Studies, Kyoto University. The inte-
grated molecular orbital and molecular mechanics method
(ONIOM)[54,55] was used, in which density functional theory (DFT)[56,57]
with B3LYP/LANL2DZ and the semiempirical method with the PM6
Hamiltonian were employed for a higher layer (Pd, dppf moiety except
for the phenyl groups, and CHCCH2OCONH or CHCCH2OCOO) and a
lower layer (rest of the groups), respectively.
mer may no longer be able to coordinate to Pd at the
square-planar site, thereby resulting in a dead end of the
polymerization process. The second monomer-inserted inter-
mediate, Vb, which can be formed from IVb via TSIIb, au-
tomatically turns into Vb’ after optimization of the geome-
try, in a similar manner to that of IIIb!IIIb’.
Materials: Unless otherwise stated, the reagents and solvents were used
as received from commercial suppliers (Aldrich and Wako).
[(dppf)PdBr(C6H4-p-CN)] (1a),[38] [(dppf)PdBr(C6H4-o-CH2OH)] (1b),[38]
Conclusion
{(dppf)PdBr[C(Ph)=CPh2]} (1c),[38] N-butyl-2-propiolamide (2)[58]
, and
We have demonstrated the polymerization of polar-substi-
tuted acetylene monomers 2–6 catalyzed by well-defined Pd
complexes 1a–1c in combination with AgOTf, thereby
octyl propiolate (3)[46, 59] were synthesized according to literature proce-
dures. 3-Butyn-2-ol (6) (Aldrich) was distilled prior to use. Solvents for
polymerization were purified by using standard procedures before use.
forming [(dppf)PdACHTUNGTRENNUNG(NCCH3)(R)]OTf as an active catalytic
Synthesis of propargyl-N-hexylcarbamate (4): Compound 4 was synthe-
sized according to a modified literature procedure.[60] A solution of prop-
argyl alcohol (1.6 g, 29 mmol) and pyridine (2.9 g, 37 mmol) in CH2Cl2
(40 mL) was added dropwise to a solution of p-nitrophenyl chloroformate
(10.0 g, 50 mmol) in CH2Cl2 (60 mL) at ꢁ508C and the resulting mixture
was stirred at ꢁ508C for 14 h. Then, the mixture was washed successively
with aqueous solutions of NaHCO3 and NaCl. The organic phase was
separated, dried over anhydrous MgSO4, filtered, and concentrated on a
rotary evaporator. The residue was dissolved in DMF (100 mL) and pyri-
dine (5.0 g, 63 mmol) was added to the solution. Hexylamine (3.1 g,
30 mmol) was added dropwise to the solution at 08C and the mixture
was allowed to warm to RT. After additional stirring overnight, water
(160 mL) was added to the reaction mixture and the solution was extract-
ed with Et2O. The organic phase was washed with 1 m NaOH (aq) until
the aqueous phase became colorless. The organic phase was dried over
MgSO4, filtered, and then concentrated on a rotary evaporator. The resi-
due was purified by column chromatography on silica gel (n-hexane/
EtOAc, 30:1 v/v) and then by distillation under reduced pressure to
afford propargyl-N-hexylcarbamate as a colorless oil. Yield: 2.6 g (47%);
1H NMR (CDCl3, 258C, TMS): d=0.88 (t, J=7.2 Hz, 3H; CH3), 1.24–
1.34 (m, 6H; CH2CH2CH2CH3), 1.43–1.49 (m, 2H; NHCH2CH2), 2.04 (s,
species. The R groups of catalysts 1a–1c were introduced at
the chain ends of poly(2)–poly(6), as confirmed by IR spec-
troscopy and MALDI-TOF mass spectrometry. This incor-
poration was also confirmed by 1H NMR and 31P NMR
spectroscopic analysis of stoichiometric reactions between
the catalyst and the monomers. MS (ESI) analysis confirmed
the production of compounds that were formed by single-
quintuple insertions of monomers 4 and 5 between the Pd
and R atoms of 1aOTf. The isotope patterns agreed well
with those that were calculated for the single- and double-
insertion products. DFT calculations suggested that 1,2-in-
sertion was preferable to 2,1-insertion, most likely owing to
steric repulsion between the bulky dppf ligand and an in-
coming monomer. Currently, we are investigating new Pd
catalysts for acetylene polymerization, with the goal of im-
proving the catalytic activity and cis-stereoregularity of the
resulting polymers, especially compared to the capabilities
of Rh catalysts.
ꢀ
ꢀ
1H; HC C), 3.11–3.16 (m, 2H; NHCH2), 4.68 (s, 2H; CCH2O),
4.72 ppm (br s, 1H; NH); 13C NMR (CDCl3, 258C, TMS): d=13.9, 22.5,
26.3, 29.8, 31.4, 41.2, 52.3, 74.4, 78.4, 155.4 ppm; HRMS (ESI): m/z calcd
for C10H17NO2H: 184.1332 [M+H]+; found: 184.1331; elemental analysis
calcd (%) for C10H17NO2: C 65.54, H 9.35, N 7.64; found: C 65.29, H 9.43,
N 7.47.
Experimental Section
Synthesis of hexyl propargyl carbonate (5): Compound was synthesized
by using hexanol in place of hexylamine in a manner similar to that for
the synthesis of propargyl-N-hexylcarbamate. Yield: 23% (colorless oil);
1H NMR (CDCl3, 258C, TMS): d=0.89 (t, J=6.8 Hz, 3H; CH2CH3),
1.28–1.37 (m, 6H; CH2CH2CH2CH3), 1.64–1.71 (m, 2H; OCH2CH2), 2.52
Measurements: 1H NMR (400 MHz) and 13C NMR spectra (100 MHz)
were recorded on JEOL EX-400 or AL-400 spectrometers. Chemical
shifts were referenced to CHDCl2 (d=5.32 ppm), CHCl3 (d=7.26 ppm),
or C6HD5 (d=7.16 ppm) as an internal standard. 31P NMR spectra
(162 MHz) were recorded on JEOL ECX-400 or EX-400 spectrometers
ꢀ
(t, J=2.4 Hz, 1H; HC C), 4.17 (t, J=6.8 Hz, 2H; OCH2), 4.73 ppm (d,
with PACHTUNGTRENNUNG(OMe)3 as an external standard (d=140 ppm). IR spectra were
J=2.4 Hz, 2H; CCH2O); 13C NMR (CDCl3, 258C, TMS): d=13.9, 22.5,
ꢀ
measured on a JASCO FT/IR-4100 spectrophotometer by using the KBr
method. Elemental analysis was performed at the Microanalytical Center
of Kyoto University. MS (MALDI-TOF) was performed on a Bruker
Daltonics ultraflexIII TOF/TOF that was equipped with a 355 nm YAG
laser in reflectron mode at an accelerating voltage of 25 kV. Samples for
MALDI-TOF mass spectrometry were purified by column chromatogra-
phy on silica gel (CH2Cl2/THF, 1:1 v/v), to remove any residual Pd prior
to the measurements, and prepared by mixing solutions of the polymer
(10 mgmLꢁ1), DHB (20 mgmLꢁ1), and NaTFA (2 mgmLꢁ1) in CH2Cl2 in
a ratio of 1:10:1. All of the mass differences discussed below were calcu-
lated by comparing the mass values of two base peaks of the most-abun-
dant isotopomers. The weight-averaged molecular weight (Mw) and the
25.3, 28.5, 31.3, 55.1, 68.8, 75.5, 77.1, 154.6 ppm; HRMS (ESI): m/z calcd
for C10H16O3H: 185.1172 [M+H]+; found: 185.1171; elemental analysis
calcd (%) for C10H16O3: C 65.19, H 8.75; found: C 65.26, H 8.82.
Polymerization: All of the polymerization reactions were performed
under an Ar atmosphere. A representative example is as follows: A solu-
tion of CH3CN/CH2Cl2 (1 mL, 1:1 v/v) was added to a mixture of Pd
complex 1a (18 mg, 2.0ꢂ10ꢁ2 mmol) and AgOTf (6.2 mg, 2.4ꢂ
10ꢁ2 mmol) to form a cationic Pd derivative. After stirring the mixture at
RT for 5 min, the white precipitate (AgBr) was removed by filtration.
The solution of the catalyst was cooled to ꢁ788C and CH2Cl2 (1 mL) and
the monomer (1.0 mmol) were added successively to the solution. The re-
sulting mixture was stirred at 308C for 24 h. Finally, the reaction mixture
was concentrated and poured into n-hexane, MeOH, or Et2O (100 mL)
to precipitate the polymer.
polydispersity index (PDI) of the polymers were determined on
a
JASCO system that was equipped with Shodex columns K803, K804, and
K805 (molecular weight limitꢂ4ꢂ106, eluted with CHCl3), Shodex col-
umns KF805ꢂ3 (molecular weight limitꢂ4ꢂ106, eluted with THF), or
Shodex columns K804, K805, and J806 (molecular weight limitꢂ4ꢂ108,
eluted with a solution of 10 mm LiBr in DMF) at 408C by using polystyr-
ene standards for calibration purposes.
Stoichiometric reactions: The reactions were carried out under an Ar at-
mosphere. The general procedure for the reaction is as follows: A solu-
tion of CD3CN/CD2Cl2 (0.5 mL, 1:3 v/v) was added to a mixture of com-
pound 1a (15 mg, 1.7ꢂ10ꢁ2 mmol) and AgOTf (5.2 mg, 2.0ꢂ10ꢁ2 mmol)
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M. Shiotsuki, F. Sanda et al.
in an NMR sample tube. Then, compound 4 (3.1 mg, 1.7ꢂ10ꢁ2 mmol) or
5 (3.1 mg, 1.7ꢂ10ꢁ2 mmol) was added to the resulting mixture at ꢁ788C,
followed by vigorous shaking of the tube. Subsequent increments of the
monomer were added in a similar manner to the first addition. Every
step of the reaction was monitored by NMR spectroscopy. The ESI mass
spectra were measured without purification.
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Acknowledgements
The authors are grateful to Prof. Toshio Masuda (Fukui University of
Technology), Prof. James Darkwa (the University of Johannesburg), Prof.
Kenneth B. Wagener and Dr. Kathryn R. Williams (the University of
Florida), and Dr. Natsuhiro Sano (Nippon Chemical Industrial, NCI) for
their useful suggestions. This research was financially supported by the
NCI, the Kyoto University Global COE Program “International Center
for Integrated Research and Advanced Education in Materials Science”
from the Ministry of Education, Culture, Sports, Science and Technology-
ACHTUNGTRENNUNG(MEXT), Japan, the Collaborative Research Program for Young Scien-
tists of the ACCMS and IIMC, Kyoto University, and The Sumitomo
Foundation. J.R.C. acknowledges a scholarship from MEXT, Japan.
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[49] 1H NMR signals for the vinylene group and IR absorption peaks
that were assignable to cis and trans structures were observed as fol-
lows. Poly(3): 1H NMR (CDCl3, 258C, TMS): d=6.57.9 ppm; IR
(KBr): n˜ =921 cmꢁ1 (trans), 747 cmꢁ1 (cis). Poly(4): 1H NMR
(CDCl3, 258C, TMS): d=5.9 ppm (the cis content was estimated to
be 36% from the ratio of the integrals with the signal for the termi-
nal methyl protons in the hexyl group); IR (KBr): n˜ =1258 cmꢁ1
(trans), 725 cmꢁ1 (cis). Poly(5): 1H NMR(CDCl3, 258C, TMS): d=
5.66.8 ppm; IR (KBr): n˜ =913 cmꢁ1 (trans), 750 cmꢁ1 (cis). Poly(6):
1H NMR ([D6]DMSO, 258C, TMS): d=5.26.8 ppm; IR (KBr): n˜ =
1260 cmꢁ1, 937 cmꢁ1 (trans), 749 cmꢁ1 (cis). See references [13] and
[48] regarding the presence of cis and trans structures in substituted
polyacetylenes.
[50] Broad, weak signals also appeared at around d=5.9 and 5.7 ppm;
these peaks were assigned to the vinylene protons in the 2,1-inser-
tion products and to some other isomers.
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Received: June 26, 2012
Published online: && &&, 2012
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M. Shiotsuki, F. Sanda et al.
Polymerization
J. Rodriguez Castanon, K. Kuwata,
M. Shiotsuki,* F. Sanda* .... &&&& — &&&&
Synthesis of End-Functionalized Polya-
cetylenes that Contain Polar Groups
by Employing Well-Defined Palladium
Catalysts
Well-defined Pd complexes that con-
tained R groups were used to polymer-
ize acetylenes that were substituted
with polar groups. Analysis of the pol-
ymer structures confirmed the intro-
duction of the R groups onto one of
the polymer chain ends (see scheme).
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