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Organometallics 2009, 28, 6142–6144 DOI: 10.1021/om900849m
Oxidatively Induced Carbon-Halogen Bond-Forming Reactions at Nickel Andrew T. Higgs, Paul J. Zinn, Sarah J. Simmons, and Melanie S. Sanford* Department of Chemistry, University of Michigan, 930 N. University Avenue, Ann Arbor, Michigan 48109 Received September 30, 2009 Summary: This communication describes the first reported example of carbon-halogen bond formation from an isolable nickel aryl halide precursor. In addition, oxidatively induced Ar-Br bond-forming reactions from the nickel(II) complex NiII(phpy)(Br)(pic) (phpy = 2-phenylpyridine; pic = 2-picoline) are demonstrated using CuBr2, Br2, ceric ammonium nitrate, and ferrocenium as oxidants. On the basis of several pieces of evidence, the intermediacy of Ni(III) species is proposed in these transformations. Carbon-halogen (C-X) bond-forming reactions serve as a key fundamental step in a variety of important metalcatalyzed processes, including the Monsanto acetic acid synthesis,1 the halogenation of alkanes and arenes,2 and the halo-functionalization of olefins.3 As a result, C-X bond-forming reductive elimination from many late-transition-metal centers (particularly Pd, Pt, and Rh) has been investigated extensively.4-6 In contrast, analogous carbon-halogen bond-forming reactions at Ni have received *To whom correspondence should be addressed. E-mail: mssanfor@ umich.edu. (1) Forster, D. Adv. Organomet. Chem. 1979, 17, 255. (2) For examples, see: (a) Fahey, D. R. J. Organomet. Chem. 1971, 27, 283. (b) Hull, K. L.; Anani, W. Q.; Sanford, M. S. J. Am. Chem. Soc. 2006, 128, 7134. (c) Wan, X.; Ma, Z.; Li, B.; Zhang, K.; Cao, S.; Zhang, S.; Shi, Z. J. Am. Chem. Soc. 2006, 128, 7416. (d) Kalyani, D.; Dick, A. R.; Anani, W. Q.; Sanford, M. S. Tetrahedron 2006, 62, 11483. (e) Mei, T.-S.; Giri, R.; Maugel, N.; Yu, J.-Q. Angew. Chem., Int. Ed. 2008, 47, 5215. (f) Wang, X.; Mei, T. S.; Yu, J. Q. J. Am. Chem. Soc. 2009, 131, 7520. (g) Kakiuchi, F.; Kochi, T.; Mutsutani, H.; Kobayashi, N.; Urano, S.; Sato, M.; Nishiyama, S.; Tanabe, T. J. Am. Chem. Soc. 2009, 131, 11310. (3) For examples, see: (a) Zhu, G.; Lu, X. J. Organomet. Chem. 1996, 508, 83. (b) El-Qisairi, A. K.; Qaseer, H. A.; Katsigras, G.; Lorenzi, P.; Trivedi, U.; Tracz, S.; Hartman, A.; Miller, J. A.; Henry, P. M. Org. Lett. 2003, 5, 439. (c) Lei, A.; Lu, X.; Liu, G. Tetrahedron Lett. 2004, 45, 1785. (d) Manzoni, M. R.; Zabawa, T. P.; Kasi, D.; Chemler, S. R. Organometallics 2004, 23, 5618. (e) Kalyani, D.; Sanford, M. S. J. Am. Chem. Soc. 2008, 130, 2150. (4) For a recent review, see: Vigalok, A. Chem. Eur. J. 2008, 14, 5102. (5) RhIII: (a) Frech, C. M.; Milstein, D. J. Am. Chem. Soc. 2006, 128, 12434. PtIV: (b) Goldberg, K. I.; Yan, J. Y.; Breitung, E. M. J. Am. Chem. Soc. 1995, 117, 6889. (c) Yahav-Levi, A.; Goldberg, I.; Vigalok, A.; Vedernikov, A. N. J. Am. Chem. Soc. 2008, 130, 724. (6) PdIV: (a) Whitfield, S. W.; Sanford, M. S. J. Am. Chem. Soc. 2007, 129, 15142. (b) Furuya, T.; Ritter, T. J. Am. Chem. Soc. 2008, 130, 10060. (c) Ball, N. D.; Sanford, M. S. J. Am. Chem. Soc. 2009, 131, 3796. (d) Arnold, P. L.; Sanford, M. S.; Pearson, S. M. J. Am. Chem. Soc. 2009, 131, 13912. PdIII: (e) Powers, D. C.; Ritter, T. Nat. Chem. 2009, 1, 302. PdII: (f) Roy, A. H.; Hartwig, J. F. J. Am. Chem. Soc. 2003, 125, 13944. (g) Roy, A. H.; Hartwig, J. F. Organometallics 2004, 23, 1533. (7) For examples of oxidatively induced carbon-heteroatom bondforming reactions from Ni, see: (a) Matsunaga, P. T.; Hillhouse, G. L.; Rheingold, A. L. J. Am. Chem. Soc. 1993, 115, 2075. (b) Koo, K.; Hillhouse, G. L.; Rheingold, A. L. Organometallics 1995, 14, 456. (c) Koo, K.; Hillhouse, G. L. Organometallics 1995, 14, 4421. (d) Lin, B. L.; Clough, C. R.; Hillhouse, G. L. J. Am. Chem. Soc. 2002, 124, 2890. (8) For a review on Ni-catalyzed Kharasch reactions, see: Gossage, R. A.; van de Kuil, L. A.; van Koten, G. Acc. Chem. Res. 1998, 31 423. pubs.acs.org/Organometallics
Published on Web 10/07/2009
little attention,7,8 despite the significant potential advantages of substituting expensive second- and third-row metals with Ni in catalytic processes. NiII(Ar)(X) complexes are typically generated by oxidative addition of Ar-X to a Ni0 precursor,9 and the microscopic reverse of this transformation, C-X bond-forming reductive elimination from NiII(Ar)(X), has not been demonstrated. Sporadic reports have suggested that higher oxidation state Ni complexes may participate in carbon-halogen bond-forming reactions.9d,10 For example, Muller has shown that the treatment of (PR3)2NiII(Ar)(Ar1) with Br2 affords aryl bromides in yields ranging from 5 to 93%.10 However, competing phosphine oxidation, electrophilic bromination of the products, and biaryl formation made this system unsuitable for detailed investigation. Seminal work by van Koten demonstrated that the NiII pincer complex 1 can be oxidized with CuBr2 to afford the stable NiIII bromide 2a (eq 1).11,12 However, surprisingly, the reactivity of 2a was not described. We disclose herein that this NiIII precursor reacts at elevated temperatures in pyridine to afford a C-Br coupled product. In addition, closely related NiIII intermediates are implicated in oxidatively induced C-Br coupling from NiII(phpy)(Br)(pic) (phpy=2-phenylpyridine, pic=2-picoline).
Our initial studies probed the reactivity of NiIII complex 2a11 toward C-Br bond-forming reactions. When 2a was heated to 150 °C for 12 h in toluene, dioxane, or DMSO, none of the aryl bromide 3 was observed.13 We hypothesized that this might be due to fast reinsertion of the NiI product (2b) into the Ar-Br bond of the coordinated ligand to regenerate 2a (eq 1). As such, this reaction was next exam(9) For examples, see: (a) Fahey, D. R.; Mahan, J. E. J. Am. Chem. Soc. 1977, 99, 2501. (b) Tsou, T. T.; Kochi, J. K. J. Am. Chem. Soc. 1979, 101, 6319. (c) Ceder, R. M.; Granell, J.; Muller, G.; Font-Bardía, M.; Solans, X. Organometallics 1995, 14, 5544. (d) Ceder, R. M.; Granell, J.; Muller, G.; Font-Bardía, M.; Solans, X. Organometallics 1996, 15, 4618. (10) Coronas, J. M.; Muller, G.; Rocamora, M. J. Organomet. Chem. 1986, 301, 227. (11) (a) Grove, D. M.; van Koten, G.; Zoet, R.; Murrall, N. W.; Welch, A. J. J. Am. Chem. Soc. 1983, 105, 1379. (b) Grove, D. M.; van Koten, G.; Mul, P.; Zoet, R.; van der Linden, J. G. M.; Legters, J.; Schmitz, J. E. J.; Murrall, N. W.; Welch, A. J. Inorg. Chem. 1988, 27, 2466. (12) Oguro, K.; Wada, M.; Sonoda, N. J. Organomet. Chem. 1979, 165, C10. (13) Heating was conducted in a sealed vessel that was >95% submerged in an oil bath. r 2009 American Chemical Society
Communication Scheme 1. Reaction of 4 with Brominating Reagents
ined in pyridine, which could potentially displace the pincer ligand from the NiI center. Gratifyingly, heating 2a at 150 °C for 8 h in pyridine13 resulted in the formation of 3 in 16% yield, as determined by gas chromatography (GC).14 The yield of 3 could be increased to 32% by heating the reaction in a sealed tube using microwave irradiation (500 min at 150 °C). To our knowledge, this is the first reported example of carbon-halogen bond formation from an isolable nickel aryl halide starting material. Despite the success of these initial experiments, the system has several limitations. Most significantly, the requirement for elevated temperature (150 °C) makes it difficult to definitively confirm the identity of the reactive Ni species. In addition, the yield of 3 remained
