Nitrate-Enhanced NHC-NiH Catalyzed Tail-to-Tail Vinyl Ether Dimerization

Abstract

The first tail-to-tail vinyl ether dimerization has been developed by using a newly identified synergistic effect between the NHC-NiH catalyst and organonitrate additive (PhNO₂ or t-BuNO₂). The additive enhanced the desired C–C bond-forming reactivity by a proposed competitive coordination with the alkoxyl group of the hydrometallated vinyl ether species to the Ni center. This combination addressed complications related to β-alkoxy (β-OR) elimination and polymerization, and gave unexpected dimerization regioselectivity.

Key words

N-heterocyclic carbenes - hydroalkenylation - nitrate additive - unsaturated ethers - nickel hydride

• References and Notes

• 1a Cowie JM. G. Polymers: chemistry and physics of modern materials . Blackie Academic; London: 1991. 2nd ed
• 1b Schröder G. Poly(Vinyl Ethers). In Ullmann’s Encyclopedia of Industrial Chemistry. Wiley-VCH; Weinheim: 2000
• 1c Odian G. Principles of polymerization . Wiley-Interscience; Weinheim: 2004. 4th ed

For reviews, see:
• 2a Goethals EJ, Du Prez F. Prog. Polym. Sci. 2007; 32: 220
• 2b Aoshima S, Kanaoka S. Chem. Rev. 2009; 109: 5245
• 3a Kojima K, Sawamoto M, Higashimura T. Macromolecules 1989; 22: 1552
• 3b Andersson H, Gedde UW, Hult A. Macromolecules 1996; 29: 1649
• 3c Lee J.-Y, Kim M.-J, Jin M.-K, Ahn M.-R. Bull. Korean Chem. Soc. 1999; 20: 1355
• 4a Goethals EJ, Reyntjens W, Zhang X, Verdonck B, Loontjens T. Macromol. Symp. 2000; 157: 93
• 4b Bernaerts KV, Du Prez FE. Polymer 2005; 46: 8469
• 4c Radchenko AV, Kostjuk SV, Ganachaud F. Polym. Chem. 2013; 4: 1883
• 5a Kim JJ, Alper H. Chem. Commun. 2005; 3059
• 5b Gopal D, Rajagopalan K. Tetrahedron Lett. 1987; 28: 5327
• 5c Wei X, Lorenz JC, Kapadia S, Saha A, Haddad N, Busacca CA, Senanayake CH. J. Org. Chem. 2007; 72: 4250
• 5d Shigemitsu Y, Katsuhara Y, Odaira Y. Tetrahedron Lett. 1971; 2887
• 5e Esquivias J, Gómez Arrayás R, Carretero JC. J. Am. Chem. Soc. 2007; 129: 1480
• 6a Terada Y, Arisawa M, Nishida A. Angew. Chem. Int. Ed. 2004; 43: 4063
• 6b Klet RC, Labinger JA, Bercaw JE. Organometallics 2012; 31: 6652
• 6c Liu S, Berry N, Thomson N, Pettman A, Hyder Z, Mo J, Xiao J. J. Org. Chem. 2006; 71: 7467
• 7a Aoyama H, Tokunaga M, Hiraiwa S, Shirogane Y, Obora Y, Tsuji Y. Org. Lett. 2004; 6: 509
• 7b Aoyama H, Tokunaga M, Kiyosu J, Iwasawa T, Obora Y, Tsuji Y. J. Am. Chem. Soc. 2005; 127: 10474
• 8a Reppe W. Justus Liebigs Ann. Chem. 1956; 601: 84
• 8b Kirk RE, Othmer DF. Encyclopedia of Chemical Technology . Vol. 1. John Wiley & Sons; New York: 1991: 4th ed
• 9a Watanabe WH, Conlon LE. J. Am. Chem. Soc. 1957; 79: 2828
• 9b McKeon JE, Fitton P, Griswold AA. Tetrahedron 1972; 28: 227
• 9c Handerson S, Schraf M. Org. Lett. 2002; 4: 407
• 9d Bosch M, Schraf M. J. Org. Chem. 2003; 68: 5225
• 9e Okimoto Y, Sakaguchi S, Ishii Y. J. Am. Chem. Soc. 2002; 124: 1590
• 9f Nakagawa H, Okimoto Y, Sakaguchi S, Ishii Y. Tetrahedron Lett. 2003; 44: 103
• 9g Nakamura A, Tokunaga M. Tetrahedron Lett. 2008; 49: 3729

For early-transition-metal-catalyzed dimerization reactions, see:
• 10a Christoffers J, Bergman RG. J. Am. Chem. Soc. 1996; 118: 4715
• 10b Janiak C. Coord. Chem. Rev. 2006; 250: 66

For recent reviews on hydrovinylation by others and by us, see:
• 11a RajanBabu TV. Chem. Rev. 2003; 103: 1845
• 11b Hilt G, Weske DF. Chem. Soc. Rev. 2009; 38: 3082
• 11c RajanBabu TV. Synlett 2009; 853
• 11d Ho C.-Y, He L, Chan C.-W. Synlett 2011; 1649
• 11e Ceder RM, Grabulosa A, Muller G, Rocamora M. Catal. Sci. Technol. 2013; 3: 1446

We could not isolate the hydride catalyst generated in situ for characterization. Nevertheless, treatment of [(allyl)(IPr)NiCl] with AgOTf provided similar catalytic activity with the tentatively assigned hydride catalyst in the following publications:
• 12a Ho C.-Y, He L. Angew. Chem. Int. Ed. 2010; 49: 9182
• 12b Ho C.-Y, He L. Chem. Commun. 2012; 48: 1481
• 12c Ho C.-Y, He L. J. Org. Chem. 2014; DOI: 10.1021/jo5008477

For other recent representative examples, see:
• 13a Page JP, RajanBabu TV. J. Am. Chem. Soc. 2012; 134: 6556
• 13b Park J.-W, Park SJ, Jun C.-H. Org. Lett. 2012; 14: 1468
• 13c Kato T, Matsuoka S, Suzuki M. J. Org. Chem. 2014; 79: 4484

For Pd-catalyzed polymerization of vinyl ethers, see:
• 14a Luo S, Jordan RF. J. Am. Chem. Soc. 2006; 128: 12072
• 14b Chen C, Luo S, Jordan RF. J. Am. Chem. Soc. 2010; 132: 5273
• 14c Chen C, Luo S, Jordan RF. J. Am. Chem. Soc. 2008; 130: 12892
• 15 See ref. 11c; polymerization obtained with the use of [Ph₃P(allyl)Ni(OTf)].
• 16 For the dimerization of vinyl ethers to α,γ-unsaturated acetals, see: Chen C, Jordan RF. J. Am. Chem. Soc. 2010; 132: 10254
• 17 [NHC–NiH(OTf)] Catalyst Generation: In a glove box, Ni(cod)₂ (0.05 mmol) and IPr, SIPr, or IMes (0.05 mmol) were added to an oven-dried test tube equipped with a stir bar. After sealing with a septum, the tube was brought out of the glove box and connected to an N₂ line. The mixture was dissolved in dried degassed toluene (2 mL, or indicated amount) and stirred at r.t. for 1 h. 1-Octene (0.2 mmol), Et₃N (0.3 mmol), p-anisaldehyde (0.05 mmol), and TESOTf (0.1 mmol) were then added sequentially and the mixture was stirred at r.t. for 45 min. Catalytic Tail-to-Tail Vinyl Ether Dimerization by [IPr-NiH(OTf)] and PhNO₂; General Procedure: Catalyst (0.05 mmol) was generated according to the above general procedure except that only 0.5 mL toluene was used. PhNO₂ (1.5 mL) was then added to the above directly before adding vinyl ether (1.0 mmol for 5 mol% reactions or 2.0 mmol for 2.5 mol% reactions). After stirring at r.t. for 24 h, a spatula of Na₂CO₃ (s) was added and the mixture was diluted with hexane (4 mL), and stirred in open air for 30 min. The mixture was then filtered through a short plug of silica gel and rinsed with diethyl ether (75 mL). The solvent was removed under vacuum and the reside was purified by silica gel column chromatography (hexane–CH₂Cl₂ 5:1, 4:1, 3:1, 2:1, then 1:1, all with 1% Et₃N buffer) to give the dimers as colorless oils. When the vinyl ether dimers had boiling points similar to that of PhNO₂, the pure vinyl ether dimers for characterization were obtained by using t-BuNO₂ as additive.
• 18 The polymerization was also detected by ¹H NMR spectroscopic analysis and found to be comparable^1–4 with those previously reported.

According to Jones, the relative donor strength based on competitive displacement studies is: CH₃NO₂ < C₆H₅NO₂ < Et₂O < DMF, see:
• 19a Jones DE. H, Wood JL. J. Chem. Soc. A 1971; 3132
• 19b Jones DE. H, Wood JL. J. Chem. Soc. A 1971; 3135
• 20 For an example of using RNO₂ in polymerization, see: Huckfeldt JT. G, Risse W. Macromol. Chem. Phys. 1998; 199: 861
• 21 This might be due to catalyst deactivation or decomposition in the presence of those nitroalkanes. It was suggested by a control experiment: After adding 0.5 mL MeNO₂ to the cross-hydroalkenylation system reported in ref. 12a, no substrate conversion was observed.