Novel Group 6 Transition Metal Catalysts, MC12(Coh(Asph3)Z (M
Polymer Journal, Vol. 30, No. 7, pp 577-580 (1998)
Novel Group 6 Transition Metal Catalysts, MC1 2 (COh(AsPh3 )z (M= W, Mo), for the Metathesis Polymerization of Substituted Acetylenes
Hideo NAKAKO, Yoshihiko MISUMI, Toshio MASUDA,t Lajos BENCZE,* and Gabor SZALAI*
Department of Polymer Chemistry, Kyoto University, Kyoto 606-8501, Japan * Department of Organic Chemistry, University of Veszprem, P.O. Box 158, Veszprem H-820, Hungary
(Received December 4, 1997)
ABSTRACT: It was examined whether group 6 transition metal complexes, MClz(COh(AsPh3) 2 (M = W, Mo), work as catalysts in the polymerization of substituted acetylenes. WC1 2 (CO)3 (AsPh3)i polymerized phenylacetylene and its ring-substituted derivatives in good yields, while MoClz(COh(AsPh3)i polymerized l-chloro-1-octyne, tert-butylacetylene, and ortho-substituted phenylacetylenes in high yields. These complexes worked as catalysts alone and did not require either of
ultra violet (UV) irradiation and CC1 4 solvent unlike the M(CO)6--CClchv systems. Consequently, various solvents including toluene and cyclohexane were available. Addition of Lewis acids and organometallics did not enhance the catalytic activity of these complexes. The present catalysts are relatively stable to air and moisture, and hence convenient and versatile in the polymerization of various acetylenes. KEY WORDS Tungsten Carbonyl Complex / Molybdenum Carbonyl Complex / Transition Metal Catalyst / Metathesis Polymerization / Substituted Acetylene / Substituted Polyacetylene /
A variety of transition metal catalysts induce the lysts, and (ii) the influences of reaction conditions on the polymerization of substituted acetylenes. 1· 2 Among them polymerization. are group 6 transition metal (Mo, W) catalysts, which are roughly classified into metal chloride-based cata EXPERIMENTAL lysts, 3 metal hexacarbonyl-based catalysts, 4 •5 other metal carbonyl-based catalysts, 6· 7 Fischer-type metal carbene Materials catalysts, 8 •9 Schrock-type metal carbene catalysts, 10 - 12 MCli(COh(AsPh3)2 (M =Mo or W) complexes were etc. Metal chloride-based catalysts are usually employed prepared by chlorination of the corresponding M(CO)6 in conjunction with organometallic cocatalysts and complexes and the subsequent reaction of the resulting characterized by their high activity. The M(CO)6-CC14- MCli(CO)4 intermediates with AsPh3 in acetone, as hv systems, which are typical metal hexacarbonyl-based described in the literature. 15 Phenylacetylene (Aldrich), catalysts, generate active species when M(C0)6 is ultra 1-decyne (Aldrich), 1-ethynylcyclohexene (Aldrich), and violet (UV) irradiated in CC14 solution. Metal carbene l-phenyl-1-propyne (Aldrich) were distilled from calci catalysts have structures identical or close to those of the um hydride. p-Methylphenylacetylene, 16·17 m-trifluoro propagating species, and hence may work as living methylphenylacetylene, 16·17 o-trifluoromethylphenylace polymerization catalysts. In contrast, polymerizations by tylene, 16·17 o-trimethylsilylphenylacetylene, 18·19 tert-bu metal complexes having carbonyl and other ligands are tylacetylene, 20•21 and l-chloro-1-octyne22 were prepared rather rare, and their detailed behavior and mechanism according to literature method, and distilled from calcium remain unknown. hydride. Polymerization solvents were purified by the Beneze and coworkers have reported that group 6 standard methods. Lewis acids (SnC1 4 , AlBr 3, and ZrC1 4 ) transition metal complexes, MCli(COh(PPh3)i (M = W, and organometallic compounds (EtA1Cl2, n-Bu4 Sn, Mo), are effective in olefin metathesis and further that Et3Al, and Et2Zn) were commercially obtained and used MCli(COh(AsPh3)i (M=W, Mo) induce ring-opening without purification. metathesis polymerization (ROMP) of norbornene.13 These complexes exhibit catalytic activity for themselves, Procedures i.e., in the absence of a chlorinated hydrocarbon and Polymerizations were carried out in a Schlenk tube without UV irradiation. Further, it has been revealed equipped with a three-way stopcock under dry nitrogen. that various MXi(CO)3L2 (M = W, Mo; X = Cl, Br, I; UV irradiation was carried out with a 200-W high L = PPh3, AsPh3, SbPh3) complexes effect ROMP. 14 pressure mercury lamp from a distance of 5 cm at 60°C These catalysts are expected to be applicable to meta for 1 h. The monomer conversions were determined by thesis polymerizations of substituted acetylenes, because gas chromatography using bromobenzene as internal the propagating species in the polymerization of sub standard. The resulting polymers were isolated by stituted acetylenes are also metal carbenes. precipitation in a large amount of methanol and dried In the present study, we investigated the polymeriza at reduced pressure. Number- and weight-average mo tion of substituted acetylenes by MCli(CO)iAsPh3)2 lecular weights (Mn and M w, respectively) of the polymers (M = W, Mo) to clarify (i) the effectiveness of MC12- were determined by gel permeation chromatography (COh(AsPh3)i (M = W, Mo) as polymerization cata- (eluent, chloroform; Shodex columns K804, K805 and K806; polystyrene calibration). t To whom correspondence should be addressed. 577 H. NAKAKO et al.
Table I. Polymerization of substituted acetylenes by employed for MoClz(COh(AsPh3)2 because phenylace MC!i(COh(AsPh3)z (M=W, Mo)• tylene hardly polymerized with this catalyst.
Monomer Effects of Halogen-Containing Solvents and UV Irradia Yield/% M. x 10- 3 Yield/% M. x 10- 3 tion Both a halogen-containing solvent and UV irradiation Hc=c-0 66 33.0 3 are necessary in the conventional metal hexacarbonyl based catalyst systems. Their effects were investigated in the present catalyst systems (Table II). Hc=c-OcH3 72 35.2 0 The polymerization of phenylacetylene by WClz (COh(AsPh3)i proceeded in toluene without UV HC"'C-{J> 45 27.4 0 irradiation to give a red polymer with Mn 33000 in a CF3 66% yield. Even though the catalyst solution was UV irradiated, the catalyst activity did not change. The HC"'CP 98 391 98 276 F3 catalyst exhibited in CCl4 an activity similar to that in toluene. The polymerization of l-chloro-1-octyne by HC"'C-0 100 440 100 439 MoClz(COh(AsPh3)z also proceeded in toluene to yield Me3Si' a white polymer with Mn 240000 in a 50% yield. Again, HCe:C-t-Bub 24 42.5 92 335 use of CC14 as solvent hardly affected the polymeriza
HCe:C-n-C8H17 13 0 tion. However, UV irradiation deactivated this catalyst, probably because of the decomposition of the Mo HC"'C-0 22 Insoluble 0 complex. These results show that the polymerization of substituted acetylenes by the present catalysts proceeds CH3C"'C-0 0 0 in toluene without UV irradiation as in the case of norbornene. This gives a contrast to the polymerization C!Ce:C-n-C6H, 3 0 50 226 by metal hexacarbonyl-based catalysts, which require • Polymerized in toluene at 60°C for 24 h; [MCl2 (COh(AsPh3 ) 2], both UV irradiation and CCl4 solvent to generate the 2.0 mM; [MJ0 , 0.50 M: the yield and M. are for the methanol-insoluble propagating species. product. b Polymerized at 40°C. Effects of Various Solvents RESULTS AND DISCUSSION Since CCl4 solvent proved to be unnecessary in the present polymerization, other solvents might be avail Polymerization of Various Substituted Acetylenes able. Thus, various solvents were examined as polym It was examined what substituted acetylenes can be erization solvents (Table Ill). polymerized by the present catalysts (Table I). The When aromatic solvents such as toluene, anisole, and WClz(COh(AsPh3)z complex polymerized phenylacety bromobenzene were used in the polymerization of lene and its p-Me, m-CF 3 , o-CF 3, and p-Me3Si derivatives phenylacetylene by WClz(COh(AsPh3)z, polymers with to give polymers in high yields. The phenylacetylenes Mn 10000-30000 were obtained in good yields (30- with bulky ortho-substituents provided very high mo 70%). Cyclohexane and CC14 were also useful as po lecular weight polymers (Mn= 380000-440000). Al lymerization solvents. On the other hand, n-hexane, though tert-butylacetylene, 1-decyne, and 1-ethynylcy which sparingly dissolves the catalyst and the polymer, clohexene were consumed, the polymer yields were rather polar CHCl3, and basic cyclic ethers were less favorable. low. Disubstituted acetylenes such as l-phenyl-1-propyne In the polymerization of l-chloro-1-octyne by MoClr and l-chloro-1-octyne did not polymerize with this (COh(AsPh3)z, the polymers were obtained in toluene, complex. When MoClz(COh(AsPh3)z was used as bromobenzene, and CC14, in good to moderate yields. catalyst, o-CF 3- and o-Me3Si-phenylacetylenes, l The polymers had high molecular weights of ca. chloro-1-octyne, and tert-butylacetylene polymerized in 14 x 104-23 x 104. Polymer was hardly or not at all high yields; the molecular weights of the polymers obtained in other solvents examined. reached 200000-300000. On the other hand, phenylace tylenes without bulky ortho-substituents hardly polym Effects of Additives erized. It is known that Lewis acids and organometallic The relationship between the catalysts and the mono compounds activate metal carbonyl-based catalysts23 mers is similar to those so far observed for other W and and metal chloride-based catalysts,24 respectively. Thus, Mo catalysts,4 and one can see that the central atom of the effects of Lewis acids and organometallic compounds the catalyst has a strong influence on the monomer on the present polymerizations were investigated (Table reactivity. The polydispersity ratios (Mw/Mn) of all the IV). The additives were used in an equivalent amount to formed polymers were 1.3-2.0. On the basis of the the catalysts. above-stated results, we further investigated the poly In the polymerizations of phenylacetylene by WClr merization of phenylacetylene by WClz(COh(AsPh3)z (COh(AsPh3h, the polymer yields were similar to or and that of 1-chloro-l-octyne by MoClz(COh(AsPh3)z lower than that by the catalyst alone (67-3%), when in detail. Phenylacetylene, commercially readily availa Lewis acids such as SnC14, A1Br 3 , ZrC14, and EtAIC12 ble monomer, was used in the WClz(COh(AsPh3)z were added. Organometallic compounds such as n• catalyzed polymerization, while l-chloro-1-octyne was Bu4Sn, Et3Al, and Et2Zn did not give positive effects, 578 Polym. J., Vol. 30, No. 7, 1998 Novel Catalysts for the Polymerization of Acetylenes
Table II. Effects of solvents and UV irradiation on the polymerization of substituted acetylenes by MC!i(COh(AsPh3) 2 (M = W, Mo)"
HC:eCPh/W CIC:eC-n-C6H 13/Mo Irradn Solvent time/h Monomer Monomer Yield/% M. X 10- 3 Yield/% M.x10- 3 convn/% convn/%
Toluene 0 85 66 33.0 52 50 226 Toluene I 84 65 34.0 37 32 204 CC1 4 0 98 82 12.0 25 23 209 CC1 4 1 99 72 14.0 9 7 132
"Polymerized at 60°C for 24h; [MC!i(COh(AsPh3) 2], 2.0mM; [MJ0 , 0.50M: the yield and M. are for the methanol-insoluble product.
Table III. Effect of various solvents on the polymerization (a) HC:CPh / WC!i{COh(AsPh3)z of substituted acetylenes by MCli(COh(AsPh3) 2 (M=W, Mo)" 100 60
HC:eCPh/W CIC= C-n-C6 H 13/Mo Solvent C: Yield/% M. X 10- 3 Yield/% M. X 10- 3 0 ·@ 40 > '"0 Toluene 66 33.0 50 226 "0 .- 0 50 Anisole 34 10.2 4 92.0 u
PhBr 35 10.0 18 140
"Polymerized at 60°C for 24h; [MCl2 (COh(AsPh3 )z], 2.0mM;
[M] 0 , 0.50 M: the yield and M. are for the methanol-insoluble product.
100 Table IV. Effect of various additives on the polymerization of substitute acetylenes by
MCl,(COh(AsPh3 )z (M = W, Mo)" C: ·§ <1) HC:eCPh/W CIC:eCn-C6 H 13/Mo > 0 0 Additive u 50 3 3 Yield/% M.xl0- Yield/% M.x 10- <1) 8 0 0 None 66 33.0 50 226 0 SnC1 4 60 21.0 17 165 :E A!Br 3 9 8.40 15 110 ZrC1 67 28.3 18 160 4 0 EtA1C1 3 30.0 29 196 2 (} 40 80 n-Bu4 Sn 65 40.0 38 224 Temperature, "C Et3 Al 32 26.0 42 292 Et2 Zn 31 38.5 11 69.0 Figure I. Effect of temperature on the polymerization of substituted
acetylenes by MCl,(COh(AsPh3)z (M = W, Mo) (in toluene, 24h; "Polymerized in toluene, at 60°C for 24h; [MCl,(COh(AsPh3 ) 2], [MCl,(COh(AsPh3 ) 2 ] = 2.0 mM; [M] 0 = 0.50 M). 2.0 mM; [Additive], 2.0 mM; [MJ 0 , 0.50 M: the yield and M. are for the methanol-insoluble product. vating temperature to 60 and 80°C, the monomer either; i.e., the polymer yields were 65-31 %, and were conversions increased up to 70--80%, and the Mn values not higher than that with the catalyst alone (66%). A reached 20000-30000. The polymerization of l-chloro- similar tendency was observed also in the polymeriza 1-octyne by MoClz(COh(AsPh3)z hardly proceeded at tions of l-chloro-1-octyne by MoC1 2(COh(AsPh3)z. 0 and 40°C. This polymerization gave the most favorable Hence it is assumed that the initiation reaction and/or result at 80°C, i.e., produced a polymer of Mn ca. 5 x 104 the properties of propagating species in the present virtually quantitatively. These results indicate that the polymerization differ from those for metal chloride- and activities of these catalysts are lower than that of the metal carbonyl-based catalyst systems. metal chloride-based catalysts and similar to those of the metal carbonyl-based catalysts. 1 •2 Temperature Dependence The effect of polymerization temperature was inves Effect of Monomer Concentration tigated (Figure 1). Polymerization of phenylacetylene by Figure 2 shows the effect of monomer concentration. WC1 2 (CO)iAsPh3)z hardly proceeded at low tempera In the polymerization of phenylacetylene by WClz(COh tures of 0-20°C, and the monomer conversions after (AsPh3)z, the monomer conversion slightly decreased 24h were no more than 10--20%. However, with ele- with increasing monomer concentration, whereas it Polym. J., Vol. 30, No. 7, 1998 579 H. NAKAKO et al.
(a) HC:CPh / WCl2(CO)J(AsPh3)z (a) HC::CPh / WC12(COh(AsPh3)z
100 6 100 60
c:::· d' 0 -~ "§ ..,...... , 4 > 40 > ... i::: i::: 0 0 0 .... u u 50 .... 50 .... CL) CL) :::l s s 0 0 i::: i::: 2 0 20 0 ::E ::E
0'------'-----~-~o 0 '------'------'-----' 0 0 0.50 1.0 0 20 40 60 [M]o,M Time,h
100 8 100 300
d' c:::· 6 .!:I ·~ CL) CL) 200 > ~b > i::: i::: 0 .... 0 u 50 4 ...... u 50 sCL) :i sCL) 0 0 i::: i::: 100 0 2 0 ::E ::E
0 0 0 0.50 1.0 20 40 [M]o, M Time, h Figure 2. Effect of monomer concentration on the polymerization of Figure 3. Time profiles of the polymerization of substituted acety substituted acetylenes by MCl,(COh(AsPh3)z (M = W, Mo) (in lenes by MCl,(COh(AsPh3)z (M = W, Mo) (in toluene, 60°C; toluene, 60°C, 24 h; [MCl,(COh(AsPh3 ) 2] = 2.0 mM). [MCl2 (COh(AsPh3)z] = 2.0 mM; [M] 0 =0.50 M). increased to some extent in the polymerizations by 5. K. Tamura, Y. Misumi, and T. Masuda, Chem. Commun., 373 (I 996). MoClz(COh(AsPh3)z. However, the influence of mono mer concentration on conversion was rather small in 6. B.-Z. Tang and N. Kotera, Macromolecules, 22, 4388 (1989). 7. K. Tamura, T. Masuda, and T. Higashimura, Polym. Bull., 30, both cases. The molecular weight of polymer increased 537 (1993). with monomer concentration in both polymerizations; 8. T. J. Katz and S. J. Lee, J. Am. Chem. Soc., 102, 422 (1980). the molecular weights reached 53000 and 610000 in the 9. D.-1. Liaw and J.-S. Tsai, J. Polym. Sci., Part A: Polym. Chem., polymerizations of phenylacetylene and l-chloro-1- 35, 475 (1997). octyne, respectively. 10. H. H. Fox, M. 0. Wolf, R. O'Dell, B. L. Lin, R. R. Schrock, and M. S. Wrighton, J. Am. Chem. Soc., 116, 2827 (1994). I 1. M. Buchmeiser and R. R. Schrock, Macromolecules, 28, 6642 Time Profile (1995). Figure 3 shows time profiles of the polymerizations. 12. R. R. Schrock, S. Luo, J. C. Lee, Jr., N. C. Zanetti, and W. M. Both polymerizations proceeded without an induction Davis, J. Am. Chem. Soc., 118, 3883 (1996). 13. Beneze phase and leveled off at late stages. The molecular weight L. and A. Kraut-Vass, J. Mo/. Cata/., 28, 369 (1985). 14. L. Beneze, G. Szalai, J. G. Hamilton, and J. J. Rooney, J. Mo!. of polymer tended to increase with increasing monomer Cata/., 115, 193 (1997). conversion in both cases. 15. R. Colton and I. B. Tomkins, Aust. J. Chem., 21, 1143 (1966). 16. K. Sonogashira, Y. Tohda, and N. Hagihara, Tetrahedron Lett., Acknowledgments. L. Beneze thanks the Hungarian 50, 4467 (I 975). 17. A. Carpita, A. Lessi, Science Foundation (OTKA No T016326) for financial and R. Rossi, Synthesis, 571 (1984). 18. L. Brandsma, H. Hommes, H. D. Verkruijsse, and R. L. P. de support. Jong, Reel. Trav. Chim. Pays-Bas, 104, 226 (1985). 19. L. Brandsma, H. D. Verkruijsse, "Synthesis of Acetylenes, Allenes REFERENCES and Cumulenes," Elsevier, Amsterdam, 1981, p 85. 20. P. D. Bartlett and L. J. Rosen, J. Am. Chem. Soc., 64,543 (1942). 21. P. J. Kocienski, J. Org. Chem., 39, 3285 (1974). 1. T. Masuda, "Catalysis in Precision Polymerization," S. 22. H. C. Brown, "Organic Synthesis via Boranes," Wiley Kobayashi, Ed., Wiley, Chichester, 1997, Chapter 2.4. Interscience, New York, N. Y., 1975, p 184. 2. T. Masuda, "Polymeric Material Encyclopedia," Vol. I, J. C. 23. K. Tamura, T. Masuda, and T. Higashimura, Polym. Bull., 32, Salamone, Ed., CRC, New York, N.Y., 1996, pp 32-39. 289 (1994). 3. T. Masuda, K. Hasegawa, and T. Higashimura, Macromolecules, 24. T. Masuda, K.-Q. Thieu, N. Sasaki, and T. Higashimura, J. 7, 728 (1974). Polym. Sci., Polym. Chem. Ed., 9, 661 (1976). 4. T. Szymanska-Buzar, J. Mo/. Cata/., 48, 43 (1988).
580 Polym. J., Vol. 30, No. 7, 1998