Polyaddition and polycondensation reactions of (2-furyl)carbenoid as step-growth polymerization strategies: Synthesis of furylcyclopropane- and furfurylidene-containing polymers

Article abstract of DOI:10.1002/anie.200352949

Polymers from carbenoid intermediates: A new approach to the synthesis of cyclopropane-and alkene-containing polymers that contain both a carbenoid donor and acceptor is described. The polymers can be effectively obtained from enyne ketones via carbenoid

Full text of DOI:10.1002/anie.200352949

Angewandte
Chemie
Step-Growth Polymerization
Polyaddition and Polycondensation Reactions of
(2-Furyl)carbenoid as Step-Growth
Polymerization Strategies: Synthesis of
Furylcyclopropane- and Furfurylidene-Containing
Polymers**
Koji Miki, Yosuke Washitake, Kouichi Ohe,* and
Sakae Uemura*
Polymerizations catalyzed by a transition-metal–carbene
complex, such as ring-opening-metathesis polymerization
(ROMP, Figure 1a)[1] and acyclic-diene-metathesis polymer-
[*] Prof. Dr. K. Ohe
Department of Energy and Hydrocarbon Chemistry
Graduate Schoolof Engineering, Kyoto University
Nishikyo-ku, Kyoto 615-8510 (Japan)
Fax: (+81)75-383-2499
E-mail: ohe@scl.kyoto-u.ac.jp
K. Miki, Y. Washitake, Prof. Dr. S. Uemura
Department of Energy and Hydrocarbon Chemistry
Graduate Schoolof Engineering, Kyoto University
Sakyo-ku, Kyoto 606-8501 (Japan)
Fax: (+81)75-753-5687
E-mail: uemura@scl.kyoto-u.ac.jp
[**] We would like to thank Professor Yoshiki Chujo, Dr. Kensuke Naka,
and Mr. Tomokazu Umeyama for their assistance with the gel
permeation chromatographic and fluorescence spectroscopic
analysis, as well as their helpful discussions. This work was
supported by a Grant-in-Aid from a 21st Century COE program of a
United Approach to New Materials Science from the Ministry of
Education, Culture, Sports, Science, and Technology, Japan. Finan-
cialsupport by Scientific Research from the Japan Society for the
Promotion of Science is gratefully acknowledged.
Supporting information for this article is available on the WWW
under http://www.angewandte.org or from the author.
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DOI: 10.1002/anie.200352949
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furyl)cyclopropane-containing polymer 3b as
a yellow
powder (Scheme 2). The yield was 85% after purification
by gel permeation chromatography (GPC) with CHCl3 as the
eluent. Meta- and para-substituted enyne ketones 1c and 1d
Figure 1. Schematic representation of transition-metal-catalyzed
metathesis polymerization.
ization (ADMET, Figure 1b),[2] have generated great excite-
ment in recent years because of their wide applicability to the
synthesis of various alkene-containing polymers. The mech-
anisms of these chain-growth and step-growth metathesis
reactions of these polymerizations require the involvement of
a carbenoid species in the catalytic cycle. Herein, we report on
transition-metal-catalyzed polyaddition (Figure 2a) and poly-
Scheme 2. A rhodium-catalyzed polyaddition reaction.
also gave the corresponding polymers 3c and 3d in yields of
78 and 92%, respectively. The molecular weights of polymers
3b–d were determined by GPC with CHCl3 employed as the
eluent and a calibration curve of polystyrene standards
¯
(Table 1). The number-average molecular weight (Mn) of
Table 1: Properties of 3a and polymers 3b–3d.[a]
[c]
[c]
[c]
Figure 2. Schematic representation of transition-metal-catalyzed poly-
additions and polycondensations using carbenoid intermediates.
¯
¯
¯
¯
1
3
Yield [%][b] Mn [Da]
Mw [Da]
Mw/Mn
lmax (UV) [nm][d]
1a 3a
–
–
–
–
316
317
323
327
1b 3b 85
1c 3c 78
1d 3d 92
6400
6300
6900
6800
6800
7600
1.1:1
1.1:1
1.1:1
condensation reactions (Figure 2b) as new step-growth poly-
merization strategies that do not involve metathesis catalysts.
Instead the intermediate is a metal carbenoid generated from
a carbenoid trigger embedded in the monomer. This method
uses a new class of monomer that contains both a carbenoid
donor and acceptor and yields alternating copolymers con-
taining cyclopropanes or alkenes.
We previously reported the formation of (2-furyl)carbe-
noid 2 from enyne ketone 1a with Group 6 transition-metal
complexes,[3] and its application to the catalytic cyclopropa-
nation of various alkenes leading to (2-furyl)cyclopropanes
(Scheme 1).[4] Our studies focused on catalytic reactions
[a] Reaction conditions: A mixture of 1 (0.20 mmol) and [{Rh(OAc)2}2]
(0.0050 mmol) in CH2Cl2 (2 mL) was stirred at room temperature under
nitrogen for 1 min. [b] The yield of the isolated product after purification
by gelpermeation chromatography (CHCl 3). [c] Determination by gel
permeation chromatographic analysis (CHCl3) with
standard. [d] The absorption spectra were recorded in dilute CHCl3
solutions at room temperature.
a polystyrene
3b–d was 6300–6900 Da, which corresponds to a degree of
polymerization of 27–29, with a Mw/Mn ratio of 1.1:1. The
¯
¯
¯
¯
molecular weights (Mn and Mw) of 3d obtained without any
purification were lowered to 6100 and 6800 Da, respectively,
because of the contamination of low-molecular-weight
oligomers. Some properties of the model compound 3a and
polymers 3b–3d are listed in Table 1. The UV/Vis spectra of
dilute solutions of 3a–3d in CHCl3 at room temperature
exhibited absorption maxima near 320 nm. Although there
are no clear differences in the absorption maxima between 3a
and polymers 3b–3d, alternating copolymers with regularly
embedded cyclopropane units should attract a great deal of
interest in polymer chemistry.
Scheme 1. Catalytic cyclopropanation using an in situ generated
(2-furyl)carbenoid.
=
Since introducing a C C bond rather than a cyclopropane
involving (2-furyl)carbenoids, which led us to discover new
carbene-transfer polymerizations of enyne ketones that had
suitable functionalities to act as carbenoid acceptors.
We examined the synthesis of polymers containing furyl
and cyclopropane groups using a catalytic cyclopropanation
reaction. When an enyne ketone 1b with a vinyl group at the
ortho position of the phenyl ring was treated in CH2Cl2 in the
presence of a catalytic amount of [{Rh(OAc)2}2] at room
temperature, the reaction immediately afforded the (2-
ring in polymers 3b–3d was anticipated to extend the
p conjugation, we investigated the synthesis of a furfuryli-
dene-containing polymer 4 by using a carbene-transfer
reaction (Figure 2b). The synthesis of furfurylidene-contain-
ing compound 4a was attempted as a model compound. The
reaction of 1a with 1.2 equivalents of benzaldehyde and
1.2 equivalents of triphenylphosphane in ClCH2CH2Cl in the
presence of 2.5 mol% of [{Rh(OAc)2}2] at 708C for 1 h
afforded 2-benzylidenefuran 4a in a yield of 77% (cis:trans =
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10:90; Scheme 3). Compound 4a was not obtained in the
absence of triphenylphosphane.[5] Therefore, the formation of
4a can be rationalized by the generation of the (2-furyl)-
phosphorus ylide 5 from the (2-furyl)carbenoid 2 and reaction
In conclusion, we have developed a polymerization of
enyne ketones to give furylcyclopropane-containing polymers
3 and furfurylidene-containing polymers 4 by the in situ
generation of (2-furyl)carbene complexes with a [Rh(OAc)2]2
catalyst. The two systems could be widely applicable to
polymer synthesis and may find some applications in other
polymerizations using catalytic 2-furfurylidene-transfer reac-
tions.
Experimental Section
Typical procedure: 3b: [{Rh(OAc)2}2] (2.2 mg, 0.0050 mmol) was
added at room temperature under nitrogen to a solution of 1b (47 mg,
0.20 mmol) in CH2Cl2 (2 mL). After stirring the mixture for 1 min, the
rhodium catalyst was removed by centrifugal separation. The solvent
was removed under reduced pressure to afford the cyclopropane-
containing polymer 3b as a yellow powder (40 mg, 0.17 mmol, 85%
Scheme 3. A rhodium-catalyzed Wittig-type condensation of 1a.
1
yield); H NMR (300 MHz, CDCl3): d = 1.12–1.86 (brm, 6H), 1.86–
2.89 (brm, 6H), 6.57–7.85 ppm (brm, 4H) [the following peaks are
attributed to terminal or internal alkene functionalities in this
polymer, the values of protons being relative ratios compared with
the above intensity; d = 4.94–5.39 (m, 0.2H), 5.39–5.75 (brm, 0.2H),
6.28–6.57 ppm (m, 0.2H)]; 13C NMR (75 MHz, CDCl3): d = 11.0, 14.1,
20.3–20.7 (br), 22.0–23.0 (br), 28.9, 29.7, 30.4, 34.1, 38.7, 68.1, 113.7,
119.2–119.4 (br), 120.7, 125.1–130.9 (br), 132.4, 135.4, 136.2, 137.2,
137.3, 145.4–145.5 ppm (br), 167.8; UV/Vis (CHCl3): lmax
(e molÀ1 dm3 cmÀ1), 317 nm (3845).
of 5 with triphenylphosphane followed by a Wittig-type
condensation of the resulting ylide with benzaldehyde.[6,7]
Thus, we extended this condensation protocol to polymer
synthesis. The polycondensation reaction of enyne ketones 1e
and 1 f as monomers with a formyl group on the phenyl ring
afforded the corresponding polymers 4e and 4 f in yields of 51
¯
and 58%. The number-average molecular weights (Mn) of 4e
4e: [{Rh(OAc)2}2] (2.2 mg, 0.0050 mmol) was added at room
temperature under nitrogen to a solution of enyne ketone 1e (48 mg,
0.20 mmol) and triphenylphosphane (0.13 g, 0.50 mmol) in 1,2-
dichloroethane (2 mL). After stirring the mixture at 708C for 1 h,
the solvent was removed under reduced pressure to give crude
polymer 4e containing phosphane compounds, which could be
removed by a gel permeation chromatography with CHCl3 as the
eluent to give 4e as an orange powder (22 mg, 0.10 mmol, 51% yield);
1H NMR (300 MHz, CDCl3): d = 1.31–2.00 (brm, 4H), 2.20–2.97
(brm, 4H), 6.81–7.24 (brm, 1H), 7.20–8.25 (brm, 5H) [d 10.00 (brs,
0.3H) assigned as terminal formyl hydrogen]; 13C NMR (75 MHz,
CDCl3): d = 14.0, 21.0, 21.1, 22.3–23.2 (br), 29.7, 34.1, 115.1, 121.0–
137.9 (br), 144.9–147.0 (br), 192.3 ppm; UV/Vis (CHCl3): lmax
(e molÀ1 dm3 cmÀ1), 380 nm (17665).
and 4 f were 6000 and 6200 Da, which correspond to a degree
of polymerization of 27 and 28, respectively. The UV/Vis
spectra of model compound 4a and polymer 4e (Table 2)
exhibited absorption maxima near 380 nm, while the spectra
of 4 f (lmax = 457 nm) showed a red-shift of 85 nm relative to
4a (lmax = 372 nm) under identical conditions. This result
indicates the effective extension of the p conjugation caused
by elongation of the 5-aryl-2-furfurylidene units in 4 f. The
fluorescence emission spectra of the solutions of 4a, 4e, and
4 f in CHCl3 (2.0 ” 10À4 m) measured at room temperature
with excitation at 380 nm (4a and 4e) or 440 nm (4 f) showed
emission peaks centered at 433, 461, and 559 nm, respec-
tively.[8]
Received: September 25, 2003 [Z52949]
Table 2: Properties of 4a and polymers 4e and 4 f.[a]
Keywords: carbenoids · homogeneous catalysis · metathesis ·
.
polymerization · rhodium
[1] For recent reviews on ROMP, see: a) R. H. Grubbs, E. Khosravi,
Mater. Sci. Technol. 1999, 20, 65; b) M. R. Buchmeiser, Chem.
Rev. 2000, 100, 1565.
[c]
¯
¯
¯
¯
1
4
Yield
[%][b]
Mn
Mw
Mw/Mn
lmax (UV)
lmax (PL)
[Da][c] [Da][c]
[nm][d]
[nm][d,e]
[2] For recent reports on ADMET, see: a) J. C. Sworen, J. A. Smith,
K. B. Wagener, L. S. Baugh, S. P. Rucker, J. Am. Chem. Soc. 2003,
125, 2228; b) A. C. Church, J. H. Pawlow, K. B. Wagener, Macro-
molecules 2002, 35, 5746; c) S. E. Lehman, K. B. Wagener,
Macromolecules 2002, 35, 48, and references therein.
[3] K. Miki, T. Yokoi, F. Nishino, K. Ohe, S. Uemura, J. Organomet.
Chem. 2002, 645, 228.
[4] K. Miki, F. Nishino, K. Ohe, S. Uemura, J. Am. Chem. Soc. 2002,
124, 5260.
[5] The phosphane-mediated generation of (2-furyl)phosphoryl
ylides followed by a sequential Wittig-type condensation with
aldehydes has already been reported: H. Kuroda, E. Hanaki, M.
Kawakami, Tetrahedron Lett. 1999, 40, 3753; however, in the
1a 4a 77
1e 4e 51
1 f 4 f 58
–
–
–
372
380
457
433
461
559
6000
6200
6500
6900
1.1:1
1.1:1
[a] Reaction conditions: A mixture of 1 (0.20 mmol), triphenylphosphane
(0.48 mmol) and [{Rh(OAc)2}2] (0.0050 mmol) in ClCH2CH2Cl(2 mL)
was stirred at room temperature under nitrogen for 1 h. [b] The yield of
the isolated product after purification by gel permeation chromatography
(CHCl3). [c] Determination by gelpermeation chromatographic anaylsis
(CHCl3) with a polystyrene standard. [d] Absorption and emission
spectra were recorded in dilute CHCl3 solutions at room temperature.
[e] Solutions (2.0ꢀ10À4 m) were excited at 380 nm (4a and 4e) or
440 nm (4 f).
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Communications
absence of [{Rh(OAc)2}2], the reaction of 1a did not proceed
effectively to give 4a in a high yield (< 20%) even after 24 h.
[6] For recent reports on transition-metal-catalyzed olefination of
aldehydes using diazoalkanes and phosphane compounds, see:
a) G. A. Mirafzal, G. Cheng, L. K. Woo, J. Am. Chem. Soc. 2002,
124, 176; b) G. Cheng, G. A. Mirafzal, L. K. Woo, Organometal-
lics 2003, 22, 1468, and references therein; c) V. K. Aggarwal, J. R.
Fulton, C. G. Sheldon, J. de Vicente, J. Am. Chem. Soc. 2003, 125,
6034.
[7] More recently, we have reported the Doyle–Kirmse reaction with
allylic sulfides via the formation of sulfur ylides, see: Y. Kato, K.
Miki, F. Nishino, K. Ohe, S. Uemura, Org. Lett. 2003, 5, 2619.
[8] The emission spectra of polymer 4 f were dependent on concen-
tration. When the concentrations of 4 f solutions were increased
from 2.0 ” 10À6 to 2.0 ” 10À4 m, the emission at 522 nm shifted to
559 nm. The emission peak of 4 f in the solid film was also
observed at 618 nm, with a decrease in luminescence yield
probably arising from intermolecular excimer formation. For
excimer formation and luminescence in conjugated polymers, see:
a) E. Conwell, Trends Polym. Sci. 1997, 5, 218; b) H. Li, D. R.
Powell, R. K. Hayashi, R. West, Macromolecules 1998, 31, 52; c) J.
Cornil, D. A. dos Santos, X. Crispin, R. Silbey, J. L. Brꢀdas, J. Am.
Chem. Soc. 1998, 120, 1289; d) C. E. Halkyard, M. E. Rampey, L.
Kloppenburg, S. L. Studer-Martinez, U. H. F. Bunz, Macromole-
cules 1998, 31, 8655.
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