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Metal-free Carbanion Salts as Initiators for the Anionic Polymerization of Acrylic and Methacrylic Acid Esters.

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L
1
5. X = CI. Br
tion) with oxalyl halide to give functionalized heteroarenes, the catalyst being re-formed.
Experimental Procedure
1 : Anhydrous Adogenm 464 (9 g; Aldrich) and oxalyl chloride (I25 mL) were
dissolved in dichloromethane (220 mL) contained in a 500-rnL Monel cylinder, and cyanogen (26 g) and HCI (3 g) were then condensed into the solution. This mixture was stirred for 3 d, the temperature being increased stepwise from 70 to 120°C. The autoclave was then opened and the precipitated
crude product, obtained as gold-yellow crystalline platelets, was separated
from soluble impurities by filtration and subsequent washing with THF.
Yield 48.5 g (60% based on (CN),). Traces of (CN), give the product a greenish-yellow color. Loss-free purification was carried out by sublimation at
3OO0C/10 ’ mbar; m.p. >270”C. Compound 1 is poorly soluble in the conventional solvents.-IR (Nujol): ?= 1745 cm-’ (v(C=O), vs).-EI-MS: m / z
326(Mc”, 24%), 162 (1/2M0”, IOO), 134([1/2Mo”-CO], 17); FI-MS: m / z
326 ( M ‘ ~”), correct isotopic pattern for C8N402C14.-’3C NMR ([D,]dimethy1 sulfoxide, 50°C): 6 = 145.9, 135.5, 131.9, 116.8.
4 : Tetrabutylarnmonium bromide ( 5 g) and oxalyl bromide (53 mL) were dissolved in dichloromethane (150 mL) contained in a 300-mL Monel cylinder,
and cyanogen (8 g) and HBr gas (8 g) were then condensed into the solution.
This mixture was stirred for 3 d, the temperature being increased stepwise
from 70 to 140°C. The autoclave was then opened and the brown reaction
solution was evaporated to dryness under vacuum. Compound 4 was sublimed at 100-130”C/10-’ mbar from the residue remaining after evaporation. Yield: ca. 45 g white crystals (73% based on cyanogen). If necessary. 4
can be purified further by recrystallization from CH2C12/hexane or by column filtration (40 g of product on 80 g of SiO, (0.060-0.200 mm), elution
with CHCI,). m.p. 150-15I0C.--IR (Nujol): V = 1348 (m).1270 (vs), 1195 (w).
1140 (s), 1035 (s), 515 (m), 468 cm-’ (m).-EI-MS: m / z 396 ( M o o , loo%),
315 ([MOO-Br], SO).-”C NMR (CDC13, 25’C): 6= 139.6.
as initiators with acrylic acid esters in the presence of catalytic amounts of Zn12 results in a group transfer polymerizationf2]with formation of polymers having M J M , values
(ratio of weight average molecular weight to the number
average molecular weight) of < 1.3. A second and in principle
. auite
. different method uses tetrabutylammonium
thiolates Bn4N@RSQas
This metal-free anionic
polymerization requires n o catalysts, but has the disadvantage that the initiators are highly nucleophilic and therefore relatively unstable, and that only oligomers with molecular weights of less than ca. 2000 can be obtained.I4] We
report here on a method which overcomes both these problems.
The initiators in this new method are the resonance-stabilized, metal-free ammonium methanides[’’ 2, 5 and 8,
which are accessible either by deprotonation of the corresponding C-H acidic precursors 1, 4 and 7, respectively,
with Bu4N00He or by reaction of the sodium salts 3, 6
and 9, respectively, with Bu,N@CIQ.
Bu,N@ OHQ
RCH(CO,R’);
1
L
No
1
CH,CH(CN),
4
Received: May 6, 1988 [ Z 2747 IE]
German version: Angew. Chem. 100 (1988) 1417
[ I ] H. W. Roesky, N. Amin, G . Remmers, A. Gieren, U. Riemann, B. Dederer, Angew. Chem. 91 (1979) 243; Angew. Chem. Int. Ed. Engl. 18 (1979)
223; D Giinther, D. Bosse, ibid. 92 (1980) 138 and 19 (1980) 138; H. W.
Roesky, K. Keller, J. W. Bats, ibid. 95 (1983) 904 and 22 (1983) 881; Angew. Chem Suppl. 1983, 1323.
[Z] Houben- Weyl-Muller: Methoden der Organischen Chemie, Bd. VI1/4.
Threme, Stuttgart 1968, p. 264ff.
[3] A. H. Culbenk, US-Pat. 3471496 (1966), Dow Chemical Co.; Chem.
Abstr. 7/ (1969) P124489b.
[4] a) Y. C. Tong, J . Helerocycl. Chem. I2 (1975) 1127; b) Y. Yamashita, K.
Saito, T. Suzuki, C. Kabuto, T. Mukai, T. Miyashi, Angew. Chem 100
(1988) 428; Angew. Chem. Int. Ed. Engl. 27 (1988) 434.
[5] a) K. H. Biichel, H. Erdmann, Chem. Eer. I09 (1976) 1625; b) J. J. Baldwin, P. K. Lumma, F. C. Novello, G. S. Ponticello, J. M. Spragne, D. E.
Duggan, J . Med. Chem. 20 (1977) 1189; c ) A. W. Lutz, S. DeLorenzo, J .
Heterocycl. Chem. 4 (1967) 399.
Metal-free Carbanion Salts as Initiators for the
Anionic Polymerization of Acrylic and Methacrylic
Acid Esters**
By Manfred T. Reetz,* Thomas Knauf; Ulrich Minet, and
Carsten Bingel
The polymerization of alkyl acrylates at room temperature with quantitative formation of living potyacrylates
having a narrow molecular weight distribution has only recently been made possible.“’ Reaction of alkylthiosilanes
[*] Prof. Dr. M. T. Reetz, Dr. T. Knauf, DipLChem. U. Minet, C. Bingel
Fachbereich Chemie der Universitat
Hans-Meerwein-Strasse, D-3550 Marburg (FRG)
[**I This work was supported by the Fonds der Chemischen Industrie and
Bayer AG.
Angew. Chem In[. Ed. Engl. 27 (1988) No. 10
a. R = R‘ = C,H,
RC(CO,R‘)~
3
b, R
=
C2H5, R‘ = CH,
B”~N@
OHO
1
0
0
CH3C(CN),NBu4
5
No
I
CH3C(CN)2
6
B~,N@ OHQ
(CH3)2CHN02
7
8
I
Bu,N@CI@
(CH3),CN02
9
These carbanion salts are either colorless oils (2b) o r
white crystals (2a, 5 , 8) and have been characterized by
N M R and IR spectroscopy.[61They are storable for months
in a refrigerator, but can also be handled at room temperature without problems. When acrylic acid butyl ester 10 is
added dropwise to solutions of 2, 5 o r 8 in T H F o r toluene at room temperature, a spontaneous exothermic reaction takes place with formation of the polyacrylate 13
(> 95% conversion after acidic workup of 12).
Table 1 clearly demonstrates that the molecular weight
distribution is influenced by the solvent, the initiator, and
the monomer/initiator ratio (reflected in M , (calcd)). Low,
i.e. good M,.,/M, values (61.3) are achieved in particular
with the malonates 2 (e.g. Nos. 1, 3, 6, 8, lo), whereas the
nitromethanide 8 affords larger M,.,/M, values ( 02-3).
Significantly, a polymer with a molecular weight of ca.
20000 and relatively narrow molecular weight distribution
0 VCH Verlagsgesellschafi mbH, 0-6940 Weinheim, 1988
0570-0833/88/1010-1373 $ 02.50/0
1313
Table 1. Polymerization of butyl acrylate 10 with metal-free carbanions at
room temperature [a].
1
2
3
4
5
6
7
8
9
2a
2a
2a
2b
2b
2b
2b
2b
2b
2b
5
10
I1
12
13
14
15
16
THF
TH F
THF
THF
toluene
THF
toluene
toluene
TH F
toluene
THF
toluene
TH F
toluene
TH F
toluene
5
5
5
8
8
1.15
5.32
10.44
1.44
1.44
5.29
5.29
10.41
20.67
20.67
1.36
1.36
5.21
5.2 I
1.37
1.37
1.16
1.36
1.25
1.50
1.37
I .30
1.36
1.30
1.38
1.30
1.14
1.61
1.43
1.34
2.71
2.18
0.90
3.13
7.42
1.51
0.64
5.86
6.82
10.92
17.43
20.39
0.61
0.7 1
2.59
4.21
0.85
1.25
[a] The temperature rises 10-25°C during the polymerization. [b] Calculated
from the ratio [monomer]/[initiator]. [c] The breadth of a molecular weight
distribution can be characterized by MJM,. The M, values were determined
gel-chromatographically using a standard calibration. The calibration samples were supplied by Bayer AG.
(M,/M,= 1.3; No. 10) can be prepared; this is not possible with ammonium thiolates as initiators.'31
12
13
compounds generally lead to moderate yields and high
M J M , values, even at low temperatures?['] Perhaps this
has to d o with the fact that the typical side reactions and
chain-terminating reactions like the intramolecular Claisen
condensation require a metal ion for the activation of the
ester function and expulsion of the alkoxide, so that this
back-biting r e a ~ t i o n "cannot
~
compete in the same way in
the case of the metal-free system. Relevant is the observation that polymers with a wider molecular weight distribution ( M J M , > 3) are obtained in poor yields on using the
sodium or potassium salts instead of the ammonium salts
2, 5 and 8. In contrast to the group transfer polymerization, in which covalently bonded silyl groups migrate
along the growing
in the metal-free polymerization electrostatic forces between the anionic chain terminal
and the ammonium counterion are expected to play an important role. Mechanistic and theoretical investigations relating to this hypothesis are presently under way.'''
Received: May 16, 1988 [Z 2761 IE]
German version: Angew. Chem. 100 (1988) 1422
[I] M. T. Reetz, R. Ostarek, K.-E. Piejko, D. Arlt, 9. Bomer, Angew. Chem.
98 (1986) 1 1 16; Angew. Chem. Inr. Ed. Engl. 25 (1986) 1108.
[2] 0.W. Webster, W. R. Hertler, D. Y. Sogah, W. B. Farnham, T. V. RajanBabu, J. Am. Chem. SOC.105 (1983) 5706; W. R. Hertler, D. Y . Sogah, 0.
W. Webster, 9. M. Trost, Macromolecules 17 (1984) 1417.
[3] M. T. Reetz, R. Ostarek, J . Chem. SOC.Chem. Commun. 1988. 213.
[4] This is due to the fact that the thiolate ions are eliminated during the
chain growth and can then initiate a new chain.
IS] Carbanions with ammonium counterions are mentioned in the literature,
but have seldom been characterized. See, e.g.: W. Schlenk, J. Holtz,
Chem. Ber. 49 (1916) 603; G. Wittig, M. Heintzeller, M. W. Wetterling,
Justus Liebigs Ann. Chem. 557 (1947) 201: 1. N . Roshkov, I L Knunyants, Dnkl. Akad. Nauk S S S R 199 (1971) 614; A. Brandstrom, U.
Junggren, Acra Chem. Stand. 25 (1971) 1469.
[6] Spectroscopic data of the salt 2a: "C-NMR ([Da]THF): 6 = 14.2, 15.9,
17.2, 20.6, 24.9, 26.4, 56.5, 58.9, 75.8, 170.9; as expected, in the I R spectrum (THF) the carbonyl vibration is split (1740 and 1680 cm-').
[7] See, e.g.: W. K. Busfield, J. M. Methven, Po/>Jmer14 (1973) 137; Y . K.
Han, J. M. Park, S . K. Choi, J . Po/.vm. Sci. Potyrn. Chem. Ed. 20 (1982)
1549; W. Fowells, C. Schuerch, F. A. Bovey, F. P. Hood, J . Am. Chem.
Soc. 89 (1967) 1396.
[8] Preliminary investigations on the tacticity of poly(ethy1 acrylate) of molecular mass 4000 indicate a predominantly atactic product; solvent eflects have not yet been investigated.
Dianions of the type 14 also initiate the polymerization
2,2-Dirnethyl-3(2H)-thiophenone 1-Oxide
By Ronald Kowalewski and Paul Margaretha*
0
NBu4
3(2H)-Thiophenones 1 are cyclic enones. Upon excitation with light, l a forms tricyclic dimers"] and l b undergoes intramolecular [2 + 21 cycloaddition to give thiatricyclooctanones.Iz1 We now report that the sulfoxides 2,
which are readily accessible by oxidation of the cyclic yketovinyl sulfides l,l3]behave completely differently in
light-induced reactions.
10
_3
0
NBu,
CO,Et
14
15
Not only acrylic acid methyl and ethyl esters, but also
the less reactive methacrylic acid butyl ester can be polymerized in the same way. Surprisingly, the nitro-stabilized
carbanion 8 proved to be optimal in the polymerization
of methacrylates (e.g. M,(calcd) = 2090, M,(exp) = 2050;
M , / M , = 1.17; THF/room temperature).
Why can a-activated olefins such as acrylic acid alkyl
esters (and even the very reactive methyl ester) be
smoothly polymerized with 2, 5 and 8 at room temperature, while such classical initiators as bulky organolithium
1374
0 VCH Verlagsgesellschafr mbH. 0-6940 Weinheim, 1988
1
2
3
a: R1 = R2 = CH,
b: R' = COOCH3. R2 = CHzCH=CHz
['I
Prof. Dr. P. Margaretha, Dipl.-Chem. R. Kowalewski
lnstitut fur Organische Chemie der Universitat
Martin-Luther-King-Platz 6, D-2000 Hamburg 13 (FRG)
0570-0833/88/1010-1374 $ 02.50/0
Angew. Chem. I n t . Ed. Engl. 27 (1988) No. 10
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