Pd-catalyzed polymerization of dienes that involves chain-walking isomerization of the growing polymer end: Synthesis of polymers composed of polymethylene and five-membered-ring units

Article abstract of DOI:10.1002/anie.200701630

(Chemical Equation Presented) Walk the line: Cyclopolymerization of 1,6-dienes with vinyl and vinylene groups catalyzed by Pd^II-diimine complexes causes chain walking of the growing polymer. This isomerization leads to polymers with trans-1,2-disubstituted cyclopentane groups located regularly along the linear polymer chain (see scheme). The polymerization is applicable for dienes with various functional groups.

Full text of DOI:10.1002/anie.200701630

Angewandte
Chemie
DOI: 10.1002/anie.200701630
Controlled Polymer-Chain Growth
Pd-Catalyzed Polymerization of Dienes that Involves Chain-Walking
Isomerization of the Growing Polymer End: Synthesis of Polymers
Composed of Polymethylene and Five-Membered-Ring Units**
Takeshi Okada, Sehoon Park, Daisuke Takeuchi, and Kohtaro Osakada*
Co-polymerization reactions of ethylene with cyclic olefins,
such as norbornene and cyclopentene as well as with 1,5- or
1,6-dienes that undergo cyclization during the polymer
growth, produce hydrocarbon polymers with five- or six-
membered cyclic units that are located randomly.[1] These
reactions that use a co-monomer with a functional group and
are catalyzed by late-transition-metal complexes provide a
steady route to functionalized polyethylenes. The reaction
using ethyl 5-norbornene-2-carboxylate catalyzed by a Ni
complex affords polyethylene with the CO2Et groups located
randomly,[2] whereas an alternating co-polymerization of
ethylene with 2-(4-methoxyphenyl)-1-methylenecyclopro-
pane catalyzed by a cobalt complex yields a polymer with
C6H4OMe groups.[3] Recently, we have succeeded in the
random co-polymerization of ethylene with isopropylidene
diallylmalonate, and obtained a polymer with five-membered
cyclic units with ester groups.[4] Although the above random
co-polymerization could regulate the averaged densities of
the functional group along the polymer chain by changing the
molar ratio of the two monomers used, it is not suited for the
precise design of the polymer structure. Herein, we report
prepared from 1a and sodium tetrakis(3,5-bis(trifluorome-
thyl)phenyl)borate) (NaBArF4) initiates the cyclopolymeri-
zation of isopropylidene allyl(crotyl)malonate (I-1) at room
temperature to produce the polymer -(CH2-C5H6(C5H6O4)-
CH2CH2)m- (poly-I-1), as shown in Equation (1) and Table 1
(entry 1). Figure 2a shows the 13C{1H} NMR spectrum of the
polymer. Signals of the CH and CH2 carbon atoms in the five-
membered ring appear at d = 46.9 and 45.8 ppm, respectively,
=
that 1,6-dienes with both terminal and internal C C bonds
undergo
a
Pd-complex-promoted cyclopolymerization
accompanied by the chain walking of the growing polymer,[5,6]
and afford polymers with (CH2)n spacers of the desired length
between the functionalized five-membered rings.
The four Pd complexes 1a–1d were used as the precursors
of the catalysts used in this study (Figure 1). A catalyst
Figure 1. Four Pd-catalyst precursors.
[*] T. Okada, S. Park, Dr. D. Takeuchi, Prof. Dr. K. Osakada
Chemical Resources Laboratory
Tokyo Institute of Technology
4259 Nagatsuta, Yokohama, 226-8503 (Japan)
Fax: (+81)45-924-5224
E-mail: kosakada@res.titech.ac.jp
[**] This work was supported by a Grant-in-Aid for Young Scientist
18750094 for Scientific Research from the Ministry of Education,
Science, Sports, and Culture, Japan.
Figure 2. 13C{1H} NMR spectra (CDCl3 at 258C)of: a)poly- I-1 (entry 1,
Table 1); b) poly- I-2 (entry 2); c) poly- I-4 (entry 4); and d) poly- I-10
(entry 7).
Supporting information for this article is available on the WWW
under http://www.angewandte.org or from the author.
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Communications
Table 1: Polymerization of 1,6-dienes by Pd complexes.[a]
Monomer[b]
Cat.
t [h]
Conv. [%][c]
Mn
Mw/Mn
[d]
[d]
Entry
1
2
3
4
5
6
7
8
I-1
I-2
I-3
I-4
I-5
I-6
I-10
I-2
II-1
III-1
IV-1
V-1
1a
1a
1a
1a
1a
1a
1a
1b
1c
1a
1d
1c
24
24
24
48
48
48
48
48
24
48
24
40
quant.
quant.
quant.
47
20
27
35
67
34
38
7900
13600
12200
10400
10100
11500
6900
1.68
1.75
1.91
1.97
2.31
1.90
1.71
1.36
1.25
1.60
2.23
1.21
1900
9
18900
10600
5500
10
11
12[e]
80
quant.
19000
Scheme 1. Plausible mechanism for the polymerization of I-n. P=poly-
mer chain, L=solvent.
[a] Reaction conditions: Pd complex=0.01 mmol, NaBARF=
0.012 mmol, [monomer]/[Pd]=70, solvent=CH2Cl2 (0.5 mL), at RT.
[b] Roman numeral refers to lower framework; Arabic numeral refers to
1
number of CH2 groups in upper chain (n). [c] Determined by H NMR
spectroscopy. [d] Determined by GC using CHCl3 (entries 1–8, 10–12)or
DMF (entry 9)as an eluent. [e] Reaction at À208C.
The Pd-catalyzed polymerization of 2-butene was reported to
proceed by insertion and chain-straightening reactions to
yield a polymer with a regulated structure.[9]
which indicates that the rings have an exclusive trans-1,2-
disubstituted structure.[4,7]
Table 1 shows a summary of the results of the polymer-
ization of the dienes that contain a longer alkyl group,
(CH2)nH (n = 2–6, 10), at one of the vinyl carbon atoms. The
polymerization of I-2 and I-3 proceeded smoothly to give a
polymer with molecular weights (Mn) of 13600 and 12200,
respectively (Table 1, entries 2 and 3). The polymerization of
I-4, I-5, I-6, and I-10 for 48 h produces the corresponding
polymers in 20–47% yield (Table 1, entries 4–7), thus sug-
gesting lower reactivities of the above dienes than I-1, I-2, and
I-3. The 13C NMR spectra of poly-I-2, poly-I-4, and poly-I-10
are shown in Figure 2b–d. The signals from olefinic carbon
atoms (d = 115–140 ppm) and methyl carbon atoms attached
to a polymer chain (d = 11–20 ppm) are not observed. The
1H NMR spectra of the polymers poly-I-1 to poly-I-10,
however, exhibit two small signals at d = 5.2–5.4 ppm and
d = 5.5–5.7 ppm.[7] These signals may be assigned to the
internal olefinic end group, and the relative intensities of the
signals of the polymer-chain hydrogen atoms are consistent
with the degree of polymerization estimated by GPC. The
13C{1H} NMR spectra of poly-I-1 and poly-I-2 exhibit two
peaks for CH2 (f1, f2) carbon atoms at almost equal intensities,
which correspond to the racemo and meso diads of the
neighboring five-membered rings. The use of 1b with a C2-
symmetric structure[4] increases the amount of racemo diad
(isotactic) to 60% (Table 1, entry 8).
1,6-Octadienes with a barbituric acid group II-1 and a
sulfonamide group III-1 at the respective 3-positions undergo
polymerization catalyzed by 1c or 1a to afford a polymer with
highly polar groups (Table 1, entries 9 and 10). A diene with a
fluorenylidene group IV-1 also polymerizes to form a polymer
without polar substituents (Table 1, entry 11). The diene 5-
allyl-5-crotyl-2,2-dimethyl-1,3-dioxane (V-1) undergoes living
polymerization in the presence of 1c/NaBArF4 (Table 1,
entry 12). Figure 3 shows linear plots of Mn values of the
polymer against the conversion of the monomer. The re-
addition of V-1 after the first-stage polymerization (Mn =
10800, Mw/Mn = 1.20) brings about second-stage polymeri-
zation to afford a polymer with an increased molecular weight
(Mn = 22400, Mw/Mn = 1.24).[10]
Scheme 1 shows the polymer growth mechanism proposed
on the basis of the polymerization of olefins catalyzed by
Brookhart-type Ni and Pd complexes.[6] The insertion of the
=
vinyl (-CH CH2) group of the monomer into the Pd–polymer
bond, followed by the intramolecular insertion of the vinylene
=
(-CH CH-) group, yields a five-membered ring, similar to the
cycloisomerization and cyclopolymerization of diallylmalo-
nates.[4,8] The secondary alkyl–Pd intermediate A that is
formed is isomerized into B with the primary alkyl ligand by
chain walking.[6] The coordination/insertion reaction of
another monomer molecule occurs after the isomerization.
Figure 3. Relationship between the molecular weight of poly-V-1 and
the conversion of V-1.
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Differential scanning calorimetry (DSC) measurements
on the series of poly-I and poly-V polymers shows a change of
the glass transition of these polymers that depends on the
structures. The relationship between the glass transition
temperature and the alkyl chain length are summarized in
Figure 4. Increase of the alkyl chain length of the monomer
[1]a) W. Kaminsky, A. Noll, Polym. Bull. 1993, 31, 175 – 182; b) J.
Kiesewetter, W. Kaminsky, Chem. Eur. J. 2003, 9, 1750 – 1758;
c) F. G. Sernetz, R. Mülhaupt, R. M. Waymouth, Polym. Bull.
1997, 38, 141 – 148; d) T. N. Choo, R. M. Waymouth, J. Am.
Chem. Soc. 2002, 124, 4188 – 4189; e) C. Janiak, P. G. Lassahn, J.
Mol. Catal. A 2001, 166, 193 – 209; f) M. Fujita, G. W. Coates,
Macromolecules 2002, 35, 9640 – 9647; g) N. Naga, Y. Imanishi,
Macromol. Chem. Phys. 2002, 203, 771 – 777; h) T. Hasan, T.
Ikeda, T. Shiono, Macromolecules 2004, 37, 8503 – 8509; i) W.
Wang, M. Fujiki, K. Nomura, J. Am. Chem. Soc. 2005, 127, 4582 –
4583.
[2]T. R. Younkin, E. F. Connor, J. I. Henderson, S. K. Friedrich,
R. H. Grubbs, D. A. Banslben, Science 2000, 287, 460 – 462.
[3]D. Takeuchi, K. Anada, K. Osakada, Angew. Chem. 2004, 116,
1253 – 1253; Angew. Chem. Int. Ed. 2004, 43, 1233 – 1235.
[4]S. Park, D. Takeuchi, K. Osakada, J. Am. Chem. Soc. 2006, 128,
3510 – 3511.
[5]For
a recent cyclopolymerization of dienes without polar
functional groups using Fe and Co complexes, see: D. Takeuchi,
R. Matsuura, S. Park, K. Osakada, J. Am. Chem. Soc., 2007, 129,
7002 – 7003.
[6]a) L. K. Johnson, S. Mecking, M. Brookhart, J. Am. Chem. Soc.
1996, 118, 267 – 268; b) E. F. McCord, S. J. McLain, L. T. J.
Nelson, S. D. Ittel, D. Temple, C. M. Killian, L. K. Johnson, M.
Brookhart, Macromolecules 2007, 40, 410 – 420; c) A. Berkefeld,
S. Mecking, Angew. Chem. 2006, 118, 6190 – 6193; Angew. Chem.
Int. Ed. 2006, 45, 6044 – 6046; d) J. M. Rose, A. E. Cherian, G. W.
Coates, J. Am. Chem. Soc. 2006, 128, 4186 – 4187.
Figure 4. Relationship between the alkyl chain length (n)and glass
*
transition temperature of poly-I ( )and poly- V (&).
[7]The 1H NMR spectra of poly-I-1 to poly-I-10 (olefinic hydrogen
region) are available in the Supporting Information (Figure S3).
[8]a) R. A. Widenhoefer, M. A. DeCarli, J. Am. Chem. Soc. 1998,
120, 3805 – 3806; b) N. S. Perch, P. Kisanga, R. A. Widenhoefer,
Organometallics 2000, 19, 2541 – 2545; c) N. S. Perch, R. A.
Widenhoefer, J. Am. Chem. Soc. 2004, 126, 6332 – 6346; d) R. A.
Widenhoefer, Acc. Chem. Res. 2002, 35, 905 – 913.
[9]a) M. D. Leatherman, M. Brookhart, Macromolecules 2001, 34,
2748 – 2750; b) W. Liu, M. Brookhart, Organometallics 2004, 23,
6099 – 6107; c) A. E. Cherian, E. B. Lobkovsky, G. W. Coates,
Chem. Commun. 2003, 2566 – 2567.
lowers the glass transition temperature of both of the
resulting polymers.
In summary, the polymerization of 1,6-dienes catalyzed by
Pd complexes affords polymers with trans-1,2-disubstituted
five-membered rings. This provides a route for the introduc-
tion of the cyclic units and functional groups at regular
intervals along a polymer chain.
Received: April 13, 2007
Published online: July 12, 2007
[10]For a review on living polymerization of olefins by transition-
metal complexes, see: G. J. Domski, J. M. Rose, G. W. Coates,
A. D. Bolig, M. Brookhart, Prog. Polym. Sci. 2007, 32, 30 – 92.
Keywords: cyclopolymerization · dienes · isomerization ·
palladium · polymers
.
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