Nickel-Catalyzed Formation of 1,3-Dienes via a ... - ACS Publications

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Cite This: J. Am. Chem. Soc. 2017, 139, 17795−17798

Nickel-Catalyzed Formation of 1,3-Dienes via a Highly Selective Cross-Tetramerization of Tetrafluoroethylene, Styrenes, Alkynes, and Ethylene Takuya Kawashima, Masato Ohashi,* and Sensuke Ogoshi* Department of Applied Chemistry, Faculty of Engineering, Osaka University, Suita, Osaka 565-0871, Japan S Supporting Information *

Scheme 1. Working Hypothesis

ABSTRACT: In the presence of a catalytic amount of Ni(cod)2 (cod = 1,5-cyclooctadiene) and PCy3 (Cy = cyclohexyl), the cross-tetramerization of tetrafluoroethylene (TFE), alkynes, and ethylene occurred in a highly selective manner to afford a variety of 1,3-dienes with a 3,3,4,4-tetrafluorobutyl chain. In addition, a Ni(0)catalyzed cross-tetramerization of TFE, alkynes, ethylene, and styrenes was developed. These catalytic reactions might proceed via partially fluorinated five- and sevenmembered nickelacycle key intermediates.

A

s organofluorine compounds are important components for a variety of commercial products, such as agrochemicals, drugs, and advanced materials,1 economical organofluorine feedstocks are needed in bulk as starting materials for their syntheses. In this context, we are interested in broadening the scope of tetrafluoroethylene (TFE) as a synthetic reagent, given that the conventional use of TFE has been limited mostly to the production of tetrafluoroethylene-based polymers and copolymers with other alkenes.2 Previously, we have reported the coupling of TFE with various organometallic reagents to yield (α,β,β-trifluoro)styrene derivatives.3 More recently, we became interested in the incorporation of TFE into organic frameworks as tetrafluoroethylene bridges (−CF2CF2−).4−6 During our studies, we rekindled our interest in oxidative cyclizations using Ni(0), as these may provide a straightforward and environmentally benign route to C−C bonds between a variety of unsaturated compounds.7−9 Thus, we discovered that a five-membered nickelacycle (A), generated from the oxidative cyclization of TFE and ethylene, is a key reaction intermediate in the Ni(0)-catalyzed cotrimerization of TFE and ethylene (Scheme 1, left).4 The key to the successful development of such chemo- and regioselective cotrimerizations is a sophisticated combination of TFE and ethylene; the oxidative cyclization, in general, between an electron-rich and -deficient substrate using Ni(0) is kinetically much more favorable than those occurring between other substrate combinations,10 thus leading to the selective formation of A. Consistent with this notion, we envisioned that the migratory insertion of an alkyne rather than ethylene into the Ni-CH2 bond in A, even in the presence of an excess amount of TFE and ethylene, should provide an unprecedented synthetic route to a cross-tetramer that consists of TFE, two molecules of ethylene, and an alkyne. This cross-tetramer should be formed due to the inability of the seven-membered nickelacycle (B) to undergo β-hydride © 2017 American Chemical Society

elimination (Scheme 1, right). Based on this hypothesis, we started investigating the feasibility of a highly selective crosstetramerization of TFE, ethylene, and 4-octyne (1a) in the presence of a Ni(0) catalyst. Based on the previously established optimum reaction conditions in the cotrimerization,4 the toluene solution of 1a at 40 °C was exposed for 24 h to a gas mixture containing TFE (partial pressure = 1.0 atm) and ethylene (partial pressure = 2.0 atm) in the presence of Ni(cod)2 and PCy3 (10 and 20 mol %, respectively). As a result, a desired cross-tetramer (2a), a 1,3diene derivative with a 3,3,4,4-tetrafluorobutyl chain, was formed in quantitative yield (Scheme 2). Encouraged by this result, we wanted to optimize the reaction conditions by varying the ligands. However, all our attempts confirmed that PCy3 is indeed the optimal ligand in this cross-tetramerization, similar to the cotrimerization.11 Subsequently, we examined the effect of the PCy3/Ni(0) ratio on the catalytic performance. The use of 4 equiv of PCy3 relative to Ni(cod)2 accelerated the catalytic reaction, while using 1 equiv of PCy3 led to notable retardations (Scheme 2). Thus, the optimal reaction conditions were determined as 10 mol % Ni(cod)2 and 40 mol % PCy3 in toluene at 40 °C.11 It should be emphasized that the potential side-reaction products, i.e., the cotrimer consists of TFE and two molecules of ethylene, the trimer of 1a, and 1,2-difluoro-3,4,5,6tetrapropylbenzene (vide inf ra) were not generated under the optimal reaction conditions. Although a few transition-metalReceived: November 13, 2017 Published: November 17, 2017 17795

DOI: 10.1021/jacs.7b12007 J. Am. Chem. Soc. 2017, 139, 17795−17798

Communication

Journal of the American Chemical Society

was used as a catalyst precursor instead of Ni(cod)2/PCy3.6b As a result, 1g was transformed into 2g in 68% yield. Under these reaction conditions a variety of diarylacetylenes were able to participate in this cross-tetramerization, and the reaction using bis(tolyl), bis(p-anisyl), and bis(p-fluorophenyl)acetylene (1h− l) afforded the corresponding products (2h−l) in good yields. On the other hand, the use of bis(p-trifluoromethylphenyl)acetylene (1m) resulted in the formation of the desired crosstetramer (2m) in 27% yield together with the formation of a considerable amount of the undesired trimer of 1m in the crude reaction mixture. In addition, bis(p-boronatephenyl)acetylene (1n) was used to prepare the corresponding 1,3-diene (2n) in 62% yield, in which the boronate moiety was applied to a further cross-coupling reaction to synthesize highly functionalized products. However, the use of bis(2-thienyl)acetylene (1o) resulted in facile alkyne trimerization, and the yield of the product (2o) was diminished to 17%. The use of unsymmetrical alkynes (1p−r) gave the corresponding products (2p−r) with moderate regioselectivity. In the reactions with 1-aryl-1-hexynes (1r−t), an electron-withdrawing substituent on the aryl ring did not affect the selectivity in the alkyne insertion step, whereas an electron-donating substituent caused a substantial drop in the selectivity. On the other hand, when pent-4-en-1-yn-1ylbenzene (1u) was used, the corresponding product (2u) was obtained as a sole regioisomer in 13% yield. Moreover, the reaction with 1-methyl-2-(trimethylsilyl)acetylene (1v) and 1phenyl-2(trimethylsilyl)acetylene (1w) furnished the corresponding 1,3-diene derivatives (2v and 2w) in excellent yield.13 In the case of a terminal alkyne such as 1-octyne, a desired product was not obtained at all due to a rapid trimerization of the alkyne. Finally, when alkynes to give desired products in relatively low yield were used, major side reaction was trimerization of alkynes to result in the completely consumption of starting material alkynes. When we examined the scope and limitations with respect to the perfluoroalkene component, we noted that hexafluoropropylene (HFP) could participate in this cross-tetramerization by employing a Ni(cod)2/PPh3 catalyst to afford 4 in 58% yield (Scheme 4). In response to this finding, we re-examined the

Scheme 2. Ni(0)-Catalyzed Cross-Tetramerization of TFE, Ethylene, and 1aa,b

a General conditions: 1a (0.50 mmol), toluene (1.5 mL). The molar quantities of both gases were estimated based on the ideal gas equation, and were larger than that of 1a. bThe yield of 2a, based on 1a, was determined by 19F NMR analysis using α,α,α-trifluorotoluene as an internal standard.

catalyzed co- or cross-trimerizations have been reported,12 a cross-tetramerization with a such a high selectivity has not yet been reported. With the optimal reaction conditions in hand, we examined the scope and limitations of this Ni(0)/PCy3-catalyzed crosstetramerization with respect to various alkynes (Scheme 3). Scheme 3. Ni(0)-Catalyzed Cross-Tetramerization of TFE, Ethylene, and Alkynesa,b

a

Scheme 4. Ni(0)-Catalyzed Cross-Tetramerization of HFP, Ethylene, and 1a

Compound 2a could be successfully isolated in quantitative yield from the reaction of 1a with a gas mixture containing TFE and ethylene. The use of symmetrical aliphatic alkynes, such as 3-hexyne (1b), 5-decyne (1c), and 6-undecyne (1d), afforded the corresponding products (2b, 2c, and 2d) in good to excellent yields, whereas the unsymmetrical alkynes (1e and 1f) yielded a mixture of regioisomers (2e and 2f) in poor selectivity. When diphenylacetylene (1g) was used, the corresponding cross-tetramer (2g) was obtained in 9% yield (estimated by 19F NMR spectroscopy) due to the rapid trimerization of 1g prior to pressurization with TFE and ethylene. To inhibit this undesirable trimerization of 1g, (η2-CF2CF2)Ni(PCy3)2 (3)

Ni(0)-catalyzed cotrimerization of HFP with ethylene in the presence of Ni(0)/PPh3, because previous attempts of this cotrimerization under the optimal conditions using Ni(0)/PCy3 failed due to the occurrence of an undesired reaction between HFP and PCy3.4,14 However, the desired cotrimer was obtained when the Ni(0)/PPh3 catalyst systems was used.15 Moreover, this cotrimer was also not produced in the reaction mixture of the Ni(0)-catalyzed cross-tetramerization of HFP, ethylene, and 1a. On the other hand, the use of 1,1-difluoroethylene instead of HFP yielded no cross-tetramer. Recently, our group reported the oxidative cyclization of TFE and styrene (5a) with Ni(0), together with the reactivity of the generated five-membered nickelacycle.5c Based on this report, we employed 5a as a fourth component, which resulted in smooth progress of the catalytic reaction with TFE, 1a, and

General conditions: Ni(cod)2 (0.05 mmol), PCy3 (0.20 mmol), alkynes (1; 0.50 mmol), TFE (1.0 atm), ethylene (2.0 atm), and toluene (1.5 mL). bIsolated yield. The ratio of regioisomers is given in brackets. c10 mol % 3 was used instead of Ni(cod)2/PCy3. dIn THF, 20 mol % 3 was used instead of Ni(cod)2/PCy3. eIn THF, 20 mol % 3 was used instead of Ni(cod)2/PCy3, TFE (2.0 atm), ethylene (3.0 atm). f10 mol % 3 was used instead of Ni(cod)2/PCy3, TFE (2.0 atm), ethylene (3.0 atm). g20 mol % 3 was used instead of Ni(cod)2/PCy3. h 20 mol % Ni(cod)2 and 80 mol % PCy3 were used.

17796

DOI: 10.1021/jacs.7b12007 J. Am. Chem. Soc. 2017, 139, 17795−17798

Communication

Journal of the American Chemical Society ethylene, yielding 7,7,8,8-tetrafluoro-5-phenyl-3,4-dipropyl-1,3octadiene (6aa). An elaborate investigation into the reaction conditions concluded that, in the presence of Ni(cod)2/PCy3 catalyst (Ni:P ratio = 1:2), 6aa was obtained in 85% yield by using 5a (30 equiv) to accelerate the oxidative cyclization of TFE and 5a with Ni(0) rather than that of TFE and ethylene (Scheme 5).11 In this case, 2a (8%) was also observed as a minor

Scheme 6. Stoichiometric Reactions

Scheme 5. Ni(0)-Catalyzed Cross-Tetramerization of TFE, Styrenes, Alkynes, and Ethylenea,b

a

General conditions: Ni(cod)2 (0.05 mmol), PCy3 (0.10 mmol), vinylarenes (5; 15 mmol), alkynes (1; 0.50 mmol), TFE (1.0 atm), ethylene (1.0 atm), and toluene (0.75 mL). bIsolated yield. The ratio of regioisomers is given in brackets. The 19F NMR yield of the crosstetramers 2 is given in parentheses. c20 mol % 3 was used instead of Ni(cod)2/PCy3, TFE 2.0 atm. d20 mol % Ni(cod)2, 40 mol % PPh3.

product. This catalytic reaction was also applied to 1c, 1g, and 1r, which resulted in the formation of the corresponding crosstetramers (6ac, 6ag, and 6ar). When 4-tert-butylstyrene (5b) and 4-methoxystyrene (5c) were used instead of 5a, the formation of 6ba and 6ca was observed in moderate to high yield. In contrast, the use of 4-fluorostyrene (5d) retarded the reaction to give the desired product (6da) in 36% yield. Thus, using 5 with an electron-donating substituent on the phenyl ring, leads to higher yields of 6 than in the presence of electronwithdrawing group. Moreover, employing PPh3 as a ligand allowed the participation of HFP in this catalytic reaction, thus leading to the desired cross-tetramer (7aa) in 23% yield. To explore the reaction mechanism, we carried out a stoichiometric reaction between (CF2CF2CH2CH2)Ni(PPh3)2 (8)4 and 2 equiv of 1g in toluene at 40 °C for 5 h to furnish nickelacycle 9 in 74% isolated yield (Scheme 6a).16 The X-ray diffraction study of 9 clearly demonstrated that the phenyl ring in 9 coordinated to nickel to possess an η3-π-benzyl structure and that a cyclobutene ring should be formed via a [2+2] cycloaddition of 1g and a CC bond in a tentative sevenmembered nickelacycle (C), generated by an insertion of another molecule of 1g into a NiCH2 bond in 8 (Figure 1). When 9 in C6D6 was treated in the presence of an equimolar amount of PPh3 with ethylene (5.0 atm) at 40 °C for 24 h, crosstetramer 2g was obtained in quantitative yield. This result clearly indicates that an equilibrium between 9 and C exists, and that a gradual insertion of ethylene to C should occur to yield 2g. In other words, 9 would be located outside the catalytic cycle and exist as a resting state. In the 31P NMR spectrum of the crude reaction mixture, the concomitant formation of (η2-C2H4)Ni(PPh3)2 (10)17 was observed. In addition, successive treatment of (η1:η3-CF2CF2CH2CHPh)Ni(PCy3) (11)5c with 2 equiv of

Figure 1. ORTEP drawing of 9 with thermal ellipsoids at the 30% probability level. H atoms have been omitted for clarity.

1g, followed by ethylene, in C6D6 at 40 °C for 3 h resulted in the formation of 6ag in quantitative yield (Scheme 6b). The resulting Ni(0) was trapped by ethylene to afford (η2C2H4)2Ni(PCy3) (12).18 However, an attempt to isolate the seven-membered nickelacycle intermediate (D) failed.19 In addition, the oxidative cyclization of TFE and alkynes with Ni(0) should not occur in these cross-tetramerizations (Schemes 3 and 5), as evidenced by the following stoichiometric reactions of 3 with alkynes. Thus, treatment of 3 with 2 equiv of either 1a or 1g led to the isolation of 1,2-difluorobenzenes 14a or 14g in 49% or 48% yield, respectively,20 whereas 14 was not involved in the crude reaction mixture of the crosstetramerization reactions. Accordingly, the experimental results support our hypothesis (Scheme 1). In conclusion, we have demonstrated that the crosstetramerization of tetrafluoroethylene, ethylene, alkynes, and/ or styrenes affords a variety of 1,3-diene derivatives with a 3,3,4,4-tetrafluorobutyl chain. This is an unprecedented example of a highly selective transition-metal-catalyzed cross-tetramerization. This reaction allows the effective use of TFE as a starting material for the preparation of organofluorine compounds via the oxidative cyclization of TFE and unsaturated compounds with Ni(0). 17797

DOI: 10.1021/jacs.7b12007 J. Am. Chem. Soc. 2017, 139, 17795−17798

Communication

Journal of the American Chemical Society

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(7) For reviews on nickel-catalyzed reactions via nickelacycle intermediates, see: (a) Ikeda, S.-I. Angew. Chem., Int. Ed. 2003, 42, 5120−5122. (b) Montgomery, J. Angew. Chem., Int. Ed. 2004, 43, 3890−3908. (c) Moslin, R. M.; Miller-Moslin, K.; Jamison, T. F. Chem. Commun. 2007, 4441−4449. (d) Ng, S.-S.; Ho, C.-Y.; Schleicher, K. D.; Jamison, T. F. Pure Appl. Chem. 2008, 80, 929−939. (e) Tanaka, K.; Tajima, Y. Eur. J. Org. Chem. 2012, 2012, 3715−3725. (f) Montgomery, J. Organonickel Chemistry. In Organometallics in Synthesis: Fourth Manual; Lipshutz, B. H., Ed.; Wiley: Hoboken, N.J., 2013; pp 319−428. (g) Tasker, S. Z.; Standley, E. A.; Jamison, T. F. Nature 2014, 509, 299−309. (8) For reviews on nickel-catalyzed reactions via nickelacycle intermediates by our group, see: (a) Ogoshi, S. Yuki Gosei Kagaku Kyokaishi 2013, 71, 14−28. (b) Hoshimoto, Y.; Ohashi, M.; Ogoshi, S. Acc. Chem. Res. 2015, 48, 1746−1755. (c) Ohashi, M.; Hoshimoto, Y.; Ogoshi, S. Dalton Trans 2015, 44, 12060−12073. (9) (a) Kaschube, W.; Schröder, W.; Pörschke, K. R.; Angermund, K.; Krüger, C. J. Organomet. Chem. 1990, 389, 399−408. (b) Schröder, W.; Bonrath, W.; Pörschke, K. R. J. Organomet. Chem. 1991, 408, C25− C29. (c) Bennett, M. A.; Hockless, D. C. R.; Wenger, E. Organometallics 1995, 14, 2091−2101. (d) Bennett, M. A.; Glewis, M.; Hockless, D. C. R.; Wenger, E. J. Chem. Soc., Dalton Trans. 1997, 3105−3114. (e) Baker, R. T.; Beatty, R. P.; Sievert, A. C.; Wallace, R. L., Jr. U.S. Patent 6,242,658, 2001. (f) Baker, R. T.; Beatty, R. P.; Farnham, W. B.; Wallace, R. L., Jr. U.S. Patent 5,670,679, 1997. (10) Hoshimoto, Y.; Ohashi, M.; Ogoshi, S. J. Am. Chem. Soc. 2011, 133, 4668−4671. (11) For further optimizations of the reaction conditions in the Ni(0)catalyzed cross-tetramerizations, see the Supporting Information. (12) For rare examples for transition-metal-catalyzed co- or crosstrimerizations, see: (a) Bowen, L. E.; Wass, D. F. Organometallics 2006, 25, 555−557. (b) Kaneda, K.; Terasawa, M.; Imanaka, T.; Teranishi, S. Tetrahedron Lett. 1977, 18, 2957−2958. (c) Ogoshi, S.; Nishimura, A.; Haba, T.; Ohashi, M. Chem. Lett. 2009, 38, 1166−1167. (d) Hoberg, H.; Hernandez, E. J. Chem. Soc., Chem. Commun. 1986, 544−545. (e) Kobayashi, M.; Tanaka, K. Chem. - Eur. J. 2012, 18, 9225−9229. (f) Horie, H.; Kurahashi, T.; Matsubara, S. Chem. Commun. 2010, 46, 7229−7231. (g) Sambaiah, T.; Li, L.-P.; Huang, D.-J.; Lin, C.-H.; Rayabarapu, D. K.; Cheng, C.-H. J. Org. Chem. 1999, 64, 3663−3670. (h) Ogoshi, S.; Nishimura, A.; Ohashi, M. Org. Lett. 2010, 12, 3450− 3452. (i) Nakao, Y.; Idei, H.; Kanyiva, K. S.; Hiyama, T. J. Am. Chem. Soc. 2009, 131, 15996−15997. (13) For the substrate scope with respect to other alkynes in the Ni(0)-catalyzed cross-tetramerization of TFE, ethylene, and 1, see the Supporting Information. (14) Burton, D. J.; Shinya, S.; Howells, R. D. J. Am. Chem. Soc. 1979, 101, 3689−3690. (15) For details on the Ni(0)-catalyzed cotrimerization of HFP with ethylene, see the Supporting Information. (16) When the reaction of 8 was conducted with an equimolar amount of 1g, 50% of 8 was converted into 9 while the rest remained unchanged. (17) Pörschke, K. R.; Tsay, Y. H.; Krüger, C. Angew. Chem. 1985, 97, 334−335. (18) (a) Jolly, P. W.; Tkatchenko, I.; Wilke, G. Angew. Chem., Int. Ed. Engl. 1971, 10, 328−329. (b) Krüger, C.; Tsay, Y.-H. J. Organomet. Chem. 1972, 34, 387−395. (19) Instead, we detected formation of a Ni(II) fluoride species (13g), of which structure was determined based on the comparison of its multinuclear NMR spectra with those of 4-octyne analogue (13a). These Ni(II) fluoride species 13 might be generated via α-fluorine elimination from the expected seven-membered nickelacycles. See ref 5c as well as the Supporting Information for the details. (20) Similar α-fluorine elimination would be involved in the formation of 14. See the Supporting Information for the details and the following literature: (a) Fujita, T.; Watabe, Y.; Ichitsuka, T.; Ichikawa, J. Chem. - Eur. J. 2015, 21, 13225−13228. (b) Ichitsuka, T.; Fujita, T.; Arita, T.; Ichikawa, J. Angew. Chem., Int. Ed. 2014, 53, 7564− 7568.

ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/jacs.7b12007. Detailed experimental procedures, analytical and spectral data for all new compounds (PDF) CIF data for 8 (CIF)

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AUTHOR INFORMATION

Corresponding Authors

*[email protected] *[email protected] ORCID

Sensuke Ogoshi: 0000-0003-4188-8555 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was partially supported by Grant-in-Aid for Scientific Research (A) (No. A16H02276) and (B) (Nos. 16KT0057 and 17H03057) from Japan Society for the Promotion of Science (JSPS).

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REFERENCES

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DOI: 10.1021/jacs.7b12007 J. Am. Chem. Soc. 2017, 139, 17795−17798