Macromolecules 1998, 31, 2779-2783
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Living Coordination Polymerization of Alkoxyallenes by π-Allylnickel Catalyst. 2.1 Effect of Anionic Ligands on Polymerization Behavior and Polymer Structure Koji Takagi,† Ikuyoshi Tomita,‡ Yoshiyuki Nakamura,† and Takeshi Endo*,† Research Laboratory of Resources Utilization, Tokyo Institute of Technology, Nagatsuta 4259, Midori-ku, Yokohama, 226-8503 Japan, and Department of Electronic Chemistry, Interdisciplinary Graduate School of Science and Engineering, Tokyo Institute of Technology, Nagatsuta 4259, Midori-ku, Yokohama, 226-8502 Japan Received November 28, 1997; Revised Manuscript Received March 4, 1998 ABSTRACT: The coordination polymerization of (n-octyloxy)allene (2) was carried out by π-allylnickel catalysts possessing various carboxylate ligands (1a-1c). The electronic character of the carboxylate ligand strongly influences the polymerization. Electron-withdrawing groups provide a living system that produces polymers with well-defined molecular weights and narrow molecular weight distributions in high yields. Without electron-withdrawing substituents, the reaction produces oligomeric byproducts. The ratio of 1,2- to 2,3-polymerization unit in the polymer increased with the electron-withdrawing character of carboxylate ligands. π-Allylnickel catalysts bearing halide ligands (1d, 1e, and 1f/Na2S2O3) also gave polymers from 2 in high yields, in which the polymerization rate, the microstructure, and the molecular weight distributions (Mw/Mn) of polymers were dependent upon the specific halide. The catalyst with chloride (1d) afforded a polymer with narrow Mw/Mn (1.03), possessing the ratio of 1,2- to 2,3-polymerization unit of 6:94, whereas with iodide (1f/Na2S2O3), the polymerization took place much faster to give a polymer (1,2-:2,3-polymerization unit ) 16:84) with a little broader Mw/Mn (1.10).
Introduction
Scheme 1
The living polymerization technique is a most promising route to obtain well-defined polymers with predictable molecular weights and narrow molecular weight distributions. Block copolymers, telechelic polymers, macromonomers, star-shaped polymers, etc. can be designed on the basis of living systems. Transition metal-catalyzed polymerizations of substituted acetylenes,2 cyclic olefins,3 R,ω-dienes,4 conjugated dienes,5 and heterocumulenes6 can be controlled by the structural modification of the initiating system. Polymerization rates and polymer microstructures can be systematically controlled by the catalyst structure (e.g., the valence state of the metallic center and the electronic and/or the steric feature of the ligated system). For instance, in the coordination polymerization of 1,3-butadiene by π-allylnickel carboxylates, electronwithdrawing carboxylate ligands have been reported to influence the polymerization rate of 1,3-butadiene.7 The addition of electron acceptors such as hexafluoroacetone to π-allylnickel trifluoroacetate also promotes the catalytic activity in the polymerization of isocyanides.8 Recently, we have reported the living coordination polymerization of alkoxyallenes by the [(π-allyl)NiOCOCF3]2/PPh3 system, where the polymerization proceeds under mild conditions to give polymers with narrow molecular weight distributions (Mw/Mn < 1.1) and controlled molecular weights9 (Scheme 1). The allylnickel catalyst, [(allyl)Ni(X)L], possesses both anionic (X) and neutral (L) ligands, which may influence the polymerization behavior of alkoxyallenes. Although the effect of the ligand character on the polymerization rate and the polymer structure has been discussed in the coordination polymerization of alkylallene by π-allylnickel halides, the polymerization does not proceed † ‡
Research Laboratory of Resources Utilization. Department of Electronic Chemistry.
Scheme 2
sufficiently to give polymers in low yields.10 To clarify the effect of ligated systems on the polymerization behavior and to design the precise polymerization system for allene derivatives, we report the coordination polymerization of (n-octyloxy)allene (2) by π-allylnickel catalysts having various anionic ligands (1a-1e and 1f/ Na2S2O3) (Scheme 2). Results and Discussion Coordination Polymerization of (n-Octyloxy)allene (2) by π-Allylnickel Catalyst Bearing Carboxylate Ligands (1a-1c). Allylnickel carboxylates are accessible by the oxidative addition of Ni(0), from
S0024-9297(97)01740-3 CCC: $15.00 © 1998 American Chemical Society Published on Web 04/17/1998
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Macromolecules, Vol. 31, No. 9, 1998
Figure 1. GPC profiles of poly(2) produced by the polymerization of 50 equiv of 2 by 1 and those obtained by the further reaction of 50 equiv of 2, where two sets of the experiments were made by 1c (a) and 1a (b) as a catalyst, respectively. GPC profile of poly(2) obtained by 1c kept for 1 h under nitrogen at ambient temperature before the polymerization (c).
bis(1,5-cyclooctadiene)nickel (Ni(cod)2), with allyl carboxylates.11,12 On the basis of some of these complexes with different substituents on carboxylate moieties, PPh3 (2 equiv, relative to the nickel) was added, and the complexes thus obtained (1a-1c) were used as catalysts for the coordination polymerization. In our earlier work,9 the [(π-allyl)NiOCOCF3]2/PPh3 system was reported to give polymers which are soluble in organic solvents and consisting of both 1,2- and 2,3polymerization units in the ratio 23:77. On the other hand, by using the [(π-allyl)NiOCOCF3]2 system (without PPh3), polymers of methoxyallene and ethoxyallene were barely soluble, but those of allenyl ethers bearing longer aliphatic chains (e.g., n-butoxyallene and (noctyloxy)allene) were soluble in organic solvents and predominantly consist of 2,3-polymerization units. To avoid the formation of less soluble polymers in the systematic study of the catalyst system, a monomer bearing long aliphatic chains (e.g., n-octyloxyallene, 2) was used. When the polymerization of 2 (50 equiv) was carried out from 0 °C to ambient temperature in toluene, the reaction was complete within 12 h in a homogeneous solution, independent of the catalysts used. However, clear differences were observed in polymer yields and microstructures by varying the character of the carboxylate ligands. Although the catalyst bearing a CF3 group having the electron-withdrawing character on the carboxylate ligand (1a), which is known as a stable π-allylnickel complex, yielded a polymer (Mn ) 8710) quantitatively with a very narrow molecular weight distribution (Mw/Mn ) 1.03) (Table 1, run 1), those not possessing sufficient electron-withdrawing carboxylate ligands (1b and 1c) afforded products consisting of bimodal molecular weight distributions by GPC analyses (e.g., a polymer obtained by 1c was composed of a higher molecular weight fraction, Mn ) 8060, Mw/Mn ) 1.02 (61%), and a lower molecular weight fraction, Mn ) 2520, Mw/Mn ) 1.04 (38%)). The double bonds in polymers obtained by 1a-1c were detected quantitatively, as expected from 1,2- and 2,3-polymerization by 1H NMR spectra, in which the ratio of the 1,2- to 2,3polymerization unit increased with the electron-withdrawing character of carboxylate ligands. That is, the content of the 1,2-polymerization unit in poly(2) prepared by 1a was 22%, while that obtained by 1c decreased to 5%.
Table 1. Coordination Polymerization of 2 by π-Allylnickel Catalysts (1a-1c)a run
R
yield (%)b
Mnc
Mw/Mnc
unit ratio (%)d
1 2 3
CF3 (1a) CH2Cl (1b) CH3 (1c)
99 97e 99f
8710 6570 5380
1.03 1.12 1.30
22:78 8:92 5:95
a Conditions: [1] ) 2.0 × 10-2 mmol, [2] /[Ni] ) 50, at 0 °C f 0 room temperature, for 12 h, in toluene. b Isolated yield after precipitation into MeOH/H2O (v/v ) 1/1). c Estimated by GPC (THF, PSt standard). d Determined by 1H NMR spectra of the isolated polymers. e Products contained higher (Mn ) 8460, Mw/ Mn ) 1.03) and lower (Mn ) 2260, Mw/Mn ) 1.04) molecular weight fractions in 85% and 12% yields, respectively. f Products contained higher (Mn ) 8060, Mw/Mn ) 1.02) and lower (Mn ) 2520, Mw/Mn ) 1.04) molecular weight fractions in 61% and 38% yields, respectively.
To clarify reasons for the bimodal molecular weight distribution in cases of 1b and 1c, additional experiments were carried out as follows: after the complete consumption of 2 (50 equiv) by 1c, the polymer solution was kept for 12 h at ambient temperature under nitrogen, to which 2 (50 equiv) was added again to carry out the further reaction for 12 h. Although the second fed monomer was consumed completely, GPC curves of the polymer indicated multimodal peaks, in which a shoulder peak was observed in the same molecular weight region as that of the main product at the first stage (Figure 1a). Accordingly, a part of the propagating end produced at the first stage was deactivated before the second monomer addition.13 In sharp contrast to this, when the same experiment was carried out by 1a, the molecular weight of the polymer obtained at the second stage (Mn ) 16000, Mw/Mn ) 1.04) shifted completely to the higher molecular weight region compared with that obtained at the first stage (Mn ) 8550, Mw/Mn ) 1.03), as reported previously using methoxyallene9 (Figure 1b). Likewise, the preparative condition of 1c was found to influence the polymerization behavior. When the catalyst (1c) was kept for 1 h at ambient temperature under nitrogen after the catalyst preparation and the polymerization was conducted, a polymer (Mn ) 10 000, Mw/Mn ) 1.07) was obtained in significantly lower yield (18%) (Figure 1c). According to the previous report, the complex (1c) decomposes into bis(π-allyl)nickel(II)14 and nickel(II) acetate by the disproportionation,15 which might be concerned with the oligomerization process.
Alkoxyallene Polymerization by π-Allylnickel 2781
Macromolecules, Vol. 31, No. 9, 1998 Scheme 3
Table 2. Coordination Polymerization of 2 by π-Allylnickel Catalysts (1d-1f)a run
X
yield (%)b
Mnc
Mw/Mnc
unit ratio (%)d
1 2 3e
Cl (1d) Br (1e) I (1f)
96 98 99
8730 8370 7450
1.03 1.05 1.10
6:94 14:86 16:84
4
I
97
6740
1.29
7:93
10-2
Conditions: [1] ) 2.0 × mmol, [2]0/[Ni] ) 50, at 0 °C f room temperature, for 12 h, in toluene. b Isolated yield of the polymer after precipitation into MeOH/H2O (v/v ) 1/1). c Estimated by GPC (THF, PSt standard). d Determined by 1H NMR spectra of the produced polymer. e Polymerization was carried out in the presence of sodium thiosulfate. a
Although no reaction took place when 2 and nickel(II) acetate tetrahydrate were exposed to the same conditions, the reaction of 2 with bis(π-allyl)nickel took place in the presence of PPh3 to afford oligomeric products (Mn ) 1780, Mw/Mn ) 1.44) in 90% yield. Accordingly, the disproportionation product of 1c (i.e., bis(π-allyl)nickel) most probably catalyzes the competitive oligomerization process. Polymerization rates were examined to estimate the influence of the ligand character on the polymerization rate by 1a-1c, although the concentration of objective propagating species in 1b and 1c may include some errors. From monomer conversion curves, observed kinetic coefficients (kobs in -d[2]/dt ) kobs[1][2]) for 1a, 1b, and 1c were evaluated to be 20.6, 5.08, and 4.27 L‚mol-1‚h-1, respectively. These results can be taken to mean that the polymerization is accelerated by the electron-withdrawing character of the carboxylate ligand, most probably due to the decrease of the electron density on the nickel atom. As reported previously, the polymerization of arylallenes16 was accelerated by increasing the electron density of the allene monomers, from which we proposed the electrophilic character of the propagating end. The results obtained in this study may support further this expression. The requirement of appropriate electron-withdrawing groups on the carboxylate ligand for the living polymerization may be proposed to be mainly because of the higher stability of the initiator and the propagating end. Coordination Polymerization of 2 by π-Allylnickel Catalyst Bearing Halide Ligands (1d-1f). The polymerization of methoxyallene and ethoxyallene with π-allylnickel halides has been reported by GhalamkarMoazzam et al., in which the polymerization behavior was not fully understood because of the barely soluble character of obtained polymers.17 In contrast, the coordination polymerization of 2 (50 equiv) by π-allylnickel halides bearing the PPh3 ligand (1d-1f)18 was complete within 12 h in homogeneous systems, giving soluble polymers in high yields (Table 2). From 1H NMR spectra, contents of the 1,2-polymerization unit in polymers were determined to be 6, 14, and 7% for 1d, 1e, and 1f, respectively (runs 1, 2, and 4). In cases of carboxylate ligands (1a-1c), the increase of the electron-withdrawing character of the anionic ligand tends to increase the content of the 1,2-polymerization unit. Since the electron-accepting ability of
Figure 2. 31P NMR spectra of [(π-allyl)NiX]2 (X ) Cl, Br, and I) with 0.8 equiv of PPh3 in toluene/benzene-d6 mixture (measured at 30 °C).
halide ligands coordinated to the nickel(II) has been reported in the order Cl < Br < I,19 the content of the 1,2-polymerization unit might be expected to be in the order Cl < Br < I. Although we have done our best to purify allyl halides used for the catalyst preparation by distilling them just before use, in particular, the purity of allyl iodide might not be sufficient enough. By assuming the contamination of iodine through the decomposition of allyl iodide, other propagating species such as B might be taken into consideration, which might disturb the accurate observation of the 1,2polymerization content in the polymer obtained by the 1f system (Scheme 3). To exclude the possibility, the polymerization was carried out in the presence of a trace amount of sodium thiosulfate to produce a polymer (Mn ) 7450, Mw/Mn ) 1.10) in 99% yield. It is of notice that the polymer contained 16% of the 1,2-polymerization unit and the molecular weight distribution became much narrower (run 3).20 The electron density on the nickel atom of the initiating species was estimated by 31P NMR spectra of PPh coordinated to allylnickel 3 halides, where the peaks were observed at 21.0, 22.3, and 24.5 ppm for X ) Cl, Br, and I, respectively. Thus, it was confirmed that the nickel atom became more electron deficient in the order 1d < 1e < 1f, in accordance with the electron-accepting ability of the halide ligand (Figure 2), and that the content of the 1,2polymerization unit increased in this order.21 The good stability of the propagating end produced by catalyst systems 1d, 1e, and 1f/Na2S2O3 could be confirmed by the postpolymerization experiment, similar to the case of 1a. Polymerization rates of 2 by 1d, 1e, and 1f/Na2S2O3 were evaluated from monomer conversions followed by GC after designated reaction periods. In all cases, monomer conversions agreed with the first-order kinetic equation: -d[2]/dt ) kobs[1][2], from which observed kinetic coefficients (kobs) for 1d, 1e, and 1f/Na2S2O3 were estimated to be 21.6, 24.3, and 57.2 L‚mol-1‚h-1, respectively (Figure 3). Thus, the polymerization rate was found to increase in the order 1d < 1e < 1f/Na2S2O3 in accordance with the order of lowering of the electron density on the nickel atom.22,23 Conclusion The influence of anionic ligand on the polymerization behavior of alkoxyallene was examined by catalysts
2782 Takagi et al.
Macromolecules, Vol. 31, No. 9, 1998 Table 3. Microstructure of Polymers Obtained by 1a-1e and 1f/Na2S2O3 System peak intensities at δ (ppm)
catalyst
0.85
1.27
1.58
2.30 + 2.52 + 2.83
3.30
3.61
4.00
4.81 + 5.12
5.79 + 5.73
x:y (%)
1a 1b 1c 1d 1e 1f/Na2S2O3
3.00 3.00 3.00 3.00 3.00 3.00
10.0 10.0 10.0 10.0 10.0 10.0
4.00 4.00 4.00 4.00 4.00 4.00
1.56 1.84 1.90 1.88 1.72 1.68
0.44 0.16 0.10 0.12 0.26 0.32
1.56 1.84 1.90 1.88 1.72 1.68
0.22 0.08 0.05 0.06 0.14 0.16
0.44 0.16 0.10 0.12 0.28 0.32
0.78 0.92 0.95 0.94 0.86 0.84
22:78 8:92 5:95 6:94 14:86 16:84
Figure 3. Kinetic plots in the polymerization of 2 using 1 as an initiator ([2]0 ) 1.0 M, [1] ) 0.025 M).
bearing carboxylate (1a-1c) and halide ligands (1d1f). The electron-withdrawing carboxylate ligand enhanced the stability of the initiator and the propagating end to provide a living system and increased the content of the 1,2-polymerization unit. π-Allylnickel catalysts having a halide ligand demonstrated the same trend; i.e., electron-withdrawing iodide increased the polymerization rate and the content of the 1,2-polymerization unit. The fact that the polymerization of alkoxyallene can be accelerated by using a stronger electronaccepting ligand may suggest that the present polymerization system proceeds via the electrophilic reaction of the propagating π-allylnickel species toward the allene monomer. Experimental Section Materials and Instruments. (n-Octyloxy)allene (2) was prepared as previously reported24 and was distilled under reduced pressure prior to use (37 °C/0.45-0.50 mmHg). Allyl trifluoroacetate, allyl chloroacetate, allyl acetate, allyl chloride, and allyl bromide were distilled under nitrogen. Allyl iodide was washed with sodium thiosulfate solution, distilled under nitrogen, and used instantly for the preparation of 1f. Bis(1,5-cyclooctadiene)nickel (Ni(cod)2) was purchased from Cica Chemical Co. Triphenylphosphine was recrystallized from dichloromethane/n-hexane. Toluene was dried over sodium and distilled under nitrogen. All polymerization reactions were carried out under nitrogen. 1H NMR and 13C NMR spectra were recorded in CDCl on 3 a JEOL EX-400 instrument (400 and 100 MHz, respectively, tetramethylsilane as an internal standard). 31P NMR spectra were recorded in a dried and degassed toluene/benzene-d6 mixed solvent under nitrogen on a JEOL FX-100 instrument (40.5 MHz, 80% aqueous phosphoric acid as an external standard). IR spectra were obtained on a JASCO FT/IR-5300 spectrometer. Gel permeation chromatographic analyses were carried out on an HLC-8020 (TSK gel G2500HXL + G3000HXL and G4000HXL + G5000HXL, THF as an eluent), calibrated against standard polystyrene samples. Purification by HPLC was made on a Japan Analytical Industry LC-908 (JAIGEL, THF as an eluent). Gas chromatographic (GC) analyses were performed on a Shimadzu GC-14B equipped with an FID detector using n-tetradecane as an internal standard (SE-30, 3 m, gradient temperature of 100-230 °C, 15 °C/min). Coordination Polymerization of 2 by 1a (Typical Procedure). π-Allylnickel complex 1a was prepared from Ni-
(cod)2 and an equimolar amount of allyl trifluoroacetate at ambient temperature under nitrogen11 followed by the addition of PPh3 (2 equiv, relative to the nickel) and used without purification. To a flask containing a magnetic stirrer bar and a toluene solution of 1a (2.0 × 10-2 mmol) was added 2 (0.168 g, 1.00 mmol, 50 equiv) at 0 °C, and the mixture was stirred for 12 h at ambient temperature. After the complete conversion of 2 was confirmed by GC, the solvent was removed under reduced pressure and the viscous product was dissolved in THF (2 mL) and then precipitated into MeOH/H2O (v/v ) 1/1) (100 mL) to give poly(2) in 99% yield (0.166 g, 0.993 mol): 1H NMR (CDCl3, δ, ppm) 0.85 (-CH3, 3H), 1.27 (-OCH2CH2(CH2)5-, 10H), 1.58 (-OCH2CH2(CH2)5-, 4H), 2.30, 2.52, 2.83 (dCsCH2sCd, 2H × 0.78), 3.30 (>CsOCH2-, 2H × 0.22), 3.61 (dCsOCH2-, 2H × 0.78), 4.00 (>CHsO-, 1H × 0.22), 4.81, 5.12 (dCH2, 2H × 0.22), 5.79, 5.93 (dCHsO-, br, 1H × 0.78); 13C NMR (CDCl3, δ, ppm) 14.1, 22.7, 25.8, 26.0, 26.4, 29.5, 30.0, 31.9, 32.8, 63.0, 71.8, 114.0, 142.4, 145.8; IR (neat, cm-1) 2928, 2859, 1664, 1466, 1433, 1377, 1265, 1128. The other polymerization systems obeyed this protocol, and polymers were isolated by HPLC separation after precipitating into MeOH/H2O (v/v ) 1/1) (Table 3). Estimation of the Kinetic Coefficients. The polymerization of 2 ([2]0/[1a] ) 40, [2]0 ) 1.0 M, [1a] ) 0.025 M) was likewise performed in toluene containing n-tetradecane (0.038 M) as an internal standard. After designated reaction periods at 0 °C, a trace reaction mixture was sampled by the syringe (ca. 10 µL), and the monomer conversion was estimated by GC analyses. Reaction of 2 with Bis(π-allyl)nickel. Bis(π-allyl)nickel was synthesized by the reaction of NiCl2 (4.37 g, 20 mmol) with allylmagnesium bromide (48 mmol) in 45% yield according to the previously reported procedure.25 To a flask containing a toluene solution of bis(π-allyl)nickel (0.05 mmol) and PPh3 (0.10 mmol) was added 2 (1.00 mmol) at 0 °C, and the reaction mixture was stirred for 12 h at ambient temperature. By precipitating into MeOH/H2O (v/v ) 1/1), the oligomeric products (Mn ) 1780, Mw/Mn ) 1.44) were obtained in 90% yield (1,2-:2,3-polymerization unit ) 30:70). Supporting Information Available: GPC profiles concerning the stability of the propagating end generated by π-allylnickel halides (1d, 1e, and 1f/Na2S2O3) (1 page). Ordering information is given on any current masthead page.
References and Notes (1) For part 1, see ref 9a. (2) (a) Masuda, T.; Yoshimura, T.; Higashimura, T. Macromolecules 1989, 22, 3804. (b) Fujimori, J.; Masuda, T.; Higashimura, T. Polym. Bull. 1988, 20, 1. (c) Tabata, M.; Yang, Y.; Yokota, K. Polym. J. 1990, 22, 1105. (d) Wallace, K. C.; Liu, A. H.; Davis, W. M.; Schrock, R. R. Organometallics 1989, 8, 644. (3) (a) Gilliom, L. R.; Grubbs, R. H. J. Am. Chem. Soc. 1986, 108, 733. (b) Schrock, R. R.; Feldman, J.; Canizzo, L. F.; Grubbs, R. H. Macromolecules 1987, 20, 1172. (c) Wallace, K. C.; Liu, A. H.; Dewan, J. C.; Schrock, R. R. J. Am. Chem. Soc. 1988, 110, 4964. (d) Schrock, R. R.; Depue, R. T.; Feldman, J.; Schaverien, C. J.; Dewan, J. C.; Liu, A. H. J. Am. Chem. Soc. 1988, 110, 1423. (e) Basen, G.; Schrock, R. R.; Khosravi, E.; Feast, W. J.; Gibson, V. C. Polym. Commun. 1989, 30, 258. (4) (a) Wagener, K. B.; Patton, J. T. Macromolecules 1993, 26, 249. (b) Wagener, K. B.; Smith, D. W., Jr. Macromolecules
Macromolecules, Vol. 31, No. 9, 1998
(5) (6)
(7) (8) (9) (10)
(11) (12)
(13) (14) (15) (16) (17)
1993, 26, 1633. (c) Marmo, J. C.; Wagener, K. B. Macromolecules 1993, 26, 2137. (d) O’Gara, J. E.; Portmess, J. D.; Wagener, K. B. Macromolecules 1993, 26, 2837. (e) Cummings, S.; Smith, D.; Wagener, K. Macromol. Rapid. Commun. 1995, 16, 347. (a) Hadjiandreou, P.; Jule´mont, M.; Teyssie´, Ph. Macromolecules 1984, 17, 2455. (b) Fayt, R.; Hadjiandreou, P.; Teyssie´, Ph. J. Polym. Sci., Part A: Polym. Chem. 1985, 23, 337. (a) Patten, T. E.; Novak, B. M. Macromolecules 1993, 26, 436. (b) Patten, T. E.; Novak, B. M. J. Am. Chem. Soc. 1991, 113, 5065. (c) Hoff, S. M.; Novak, B. M. Macromolecules 1993, 26, 4067. (d) Deming, T. J.; Novak, B. M. Macromolecules 1991, 24, 326. (e) Shibayama, K.; Seidel, S. W.; Novak, B. M. Macromolecules 1997, 30, 3159. (f) Fukuwatari, N.; Sugimoto, H.; Inoue, S. Makromol. Chem., Rapid. Commun. 1996, 17, 1. Dawans, F.; Teyssie´, Ph. Polym. Lett. 1969, 7, 111. Deming, T. J.; Novak, B. M. Macromolecules 1993, 26, 7089. (a) Tomita, I.; Kondo, Y.; Takagi, K.; Endo, T. Macromolecules 1994, 27, 4413. (b) Idem. Acta Polym. 1995, 46, 432. (a) Otsuka, S.; Mori, K.; Suminoe, T.; Imaizumi, F. Eur. Polym. J. 1967, 3, 73. (b) Krentsel, B. A.; Mushina, E. A.; Khar′kova, E. M.; Shishkina, M. V. Eur. Polym. J. 1975, 11, 865. Dawans, F.; Marechal, J. C.; Teyssie´, Ph. J. Organomet. Chem. 1970, 21, 259. We have carried out the coordination polymerization of phenylallene by both the in situ and the isolated [(π-allyl)NiOCOCF3]2, which brought about the same results (see ref 16). The comparable results could be also obtained in the polymerization of alkoxyallenes. Accordingly, 1a was used without isolation in the present work. The other catalysts (1b and 1c) were also used without isolation because those could not be isolated successfully in the presence of PPh3, although the detailed discussion might include some errors. The decomposition of the π-allylnickel complexes bearing acetate derivatives as the ligands has been also reported in the polymerization of 1,3-butadiene. See ref 6. Because bis(π-allyl)nickel(II) is thermally unstable, it should be converted to another form under the present polymerization conditions. Ishizu, J.; Yamamoto, T.; Yamamoto, A. Chem. Lett. 1976, 1091. Takagi, K.; Tomita, I.; Endo, T. Maclomolecules 1997, 30, 7386. Ghalamkar-Moazzam, M.; Jacobs, T. L. J. Polym. Sci., Part A: Polym. Chem. 1978, 16, 615.
Alkoxyallene Polymerization by π-Allylnickel 2783 (18) Allylic halides are known to react with Ni(cod)2 at or below 0 °C in nonpolar solvents to give dimeric π-allylnickel halides in almost quantitative yields. Cycloocta-1,5-diene dissociated from the nickel is reported to be inert toward the formed complexes. See: (a) Wilke, G. Angew. Chem., Int. Ed. Engl. 1966, 5, 151. (b) Billington, D. C. Chem. Soc. Rev. 1985, 14, 93. (19) (a) Scholten, J. P.; Play, H. J. Tetrahedron Lett. 1972, 17, 1865. (b) Gray, H. B.; Billig, E.; Wojcicki, A.; Farona, F. Can. J. Chem. 1963, 41, 1281. (20) In the cases of 1d and 1e, the addition of sodium thiosulfate gave no significant effect on the polymer structure, where contents of the 1,2-polymerization unit in polymers were determined to be 5% and 13% for 1d/Na2S2O3 and 1e/ Na2S2O3, respectively. The broader Mw/Mn and the smaller Mn of the polymer prepared in the absence of Na2S2O3 might be due to the chain transfer reaction. One possible explanation can be made by the fact that iodine is known to add to the double bond of allene moieties to yield allyl iodide derivatives, which may bring out the chain transfer reactions. In practice, the molecular weight of the polymer became much smaller (Mn ) 5820, Mw/Mn ) 1.30) by 1f in the presence of allyl iodide. See, for example: Friesen, R. W.; Bayly, C. I.; Fogg, J. A. J. Org. Chem. 1995, 60, 448. and references therein. (21) In ref 10a, the polymerization of 1,2-butadiene by [(π-allyl)NiX]2 (X ) Cl, Br, and I, without PPh3) were reported, where the ratio of the unsubstituted olefinic unit in the resulting polymer increased in the same order. (22) In ref 10a, the polymerization rate of 1,2-butadiene was also studied by [(π-allyl)NiX]2 (X ) Cl, Br, and I) in the absence of any ligands, where the rate is reported to increase in the order Cl < Br < I. (23) By comparing the kinetic coefficients of allylnickel carboxylates (1a-1c) with those of allylnickel halides (1d-1f), the higher polymerization activity of 1d-1f than 1a-1c can be observed, from which one might expect a higher content of 1,2-polymerization unit in the polymers by 1d-1f. However, 1d-1f provided polymers with lower 1,2-polymerization contents, which might be ascribed to the difference in the steric factor of the ligands. (24) Hoff, S.; Brandsma, R. S.; Arena, J. K. Trav. Chim. Pay-Bas. 1968, 87, 916. (25) Becconsall, J. K.; Job, B. E.; O’Brien, S. J. Chem. Soc., Part A 1967, 423.
MA9717404
