Copper(I) Bromide1


[7787-70-4]  · BrCu  · Copper(I) Bromide  · (MW 143.45) (CuBr.SMe2)

[54678-23-8]  · C2H6BrCuS  · Copper(I) Bromide-Dimethyl Sulfide  · (MW 205.59)

(precursor for organocopper(I) reagents and organocuprates;1a-f catalyst for diazo chemistry)

Alternate Name: cuprous bromide.

Physical Data: mp 504 °C; the complex with dimethyl sulfide (DMS) decomposes at ca. 130 °C; d 4.720 g cm-3.

Solubility: insol H2O and most organic solvents; partially sol dimethyl sulfide.

Form Supplied in: light green or blue-tinged white solid. 99.999% grade available. The DMS complex is a white solid.

Handling, Storage, and Precautions: maintenance of a dry N2 or Ar atmosphere is recommended. The DMS complex must be tightly sealed to prevent loss of DMS. Storage of this complex in a cold place is recommended.

Precursor for Organocopper(I) Reagents and Organocuprates.

Although Phenylcopper was prepared from Copper(I) Iodide by Reich in 19232 and Gilman in 1936,3 the material used for the modern characterization of this archetypal arylcopper(I) is prepared from CuBr,4 which continues to be a favored precursor for new organocopper(I) compounds.5-9 For example, Bertz discovered that halide-free organocopper compounds can be prepared from CuBr in Dimethyl Sulfide (DMS), owing to the precipitation of LiBr from this solvent.5 Thus it was possible to prepare and structurally characterize the first bona fide higher order cuprate.5a,6 Weiss recently reported the second example, a higher order alkynyl cuprate,9 prepared from CuBr.DMS. The chemistry of organocopper reagents in DMS has now become a flourishing subfield of organometallic chemistry.5-9

For the first decade of the modern era of organocopper reagents, CuI was used almost exclusively as the precursor to organocopper(I) and organocuprate reagents.1f In 1975, House introduced the DMS complex of CuBr, symbolized CuBr.SMe2 or CuBr.DMS, as a convenient precursor for the generation of lithium organocuprates.10 Unlike the commercial CuBr, which is invariably contaminated with traces of colored CuII impurities, CuBr.DMS is a microcrystalline white solid. This material should be stored under a dry, inert atmosphere in a refrigerator in order to minimize the loss of DMS, which is quite volatile (bp 38 °C). It is not surprising that Lipshutz found that low quality material gave poor results.11 This author has found that for ultraprecision work, where stoichiometry is of paramount importance, the ultrapure (99.999%) grade of CuBr is preferable.5

Nevertheless, in a side-by-side comparison of seven CuI salts (CuCN, CuI, CuBr, CuBr.DMS, CuCl, CuOTf, and CuSCN) as precursors of a typical alkyl and a typical aryl cuprate (Lithium Di-n-butylcuprate and Lithium Diphenylcuprate, respectively), CuBr.DMS and Copper(I) Cyanide were found to give the best results.12 The comparison between ultrapure CuBr and CuBr.DMS is especially interesting, as it demonstrates a dramatic effect for just 1 equiv of DMS in THF and especially in ether. Another example of a significant difference between CuBr and CuBr.DMS is provided by Davis's study of 1,6 vs. 1,4 and 1,2-addition (eq 1).13

Some of the most fundamental studies in organocopper chemistry have been carried out using CuBr or CuBr.DMS as starting materials. House showed that the chemoselectivity of Lithium Dimethylcuprate-Lithium Bromide could be completely controlled by the choice of solvent.14 Thus a molecule with remote bromoalkane and a-enone functional groups gave only conjugate addition in ether-DMS and only displacement of the Br when HMPA (Hexamethylphosphoric Triamide) was present (eq 2). In a recent 13C NMR study it was shown that phenylcuprates are dimeric in nonpolar solvents and monomeric in polar solvents.15 It was further conjectured that the dimer is responsible for the conjugate addition reaction, and the monomer is responsible for the (much slower) SN2-like displacement reaction.

The preparation of the first higher order cuprate, Ph5Cu2Li3 = [Ph3CuLi3][Ph2Cu] or Ph3CuLi2 + Ph2CuLi, from CuBr/DMS was mentioned above.5 House first proposed higher order Ph3CuLi2 in solutions prepared from 3 equiv of PhLi and CuBr in ether to account for the higher reactivity observed for this mixture in certain coupling reactions.16 However, 13C NMR and 6Li NMR studies did not detect any higher order phenylcuprate in ether or THF, only in DMS.5 While the presence of a small amount of higher order cuprate acting as a catalytic intermediate cannot be ruled out, a more plausible explanation involves the attack of PhLi on a cuprate-complexed intermediate.

The first thermally stable phosphido- and amidocuprates were prepared from CuBr.SMe2.17 (It was also shown that LiBr has a beneficial effect on the reactions of organocuprates with typical substrates.17c) Chiral amidocuprates have been extensively studied because of their potential for asymmetric induction.18-20 The chiral auxiliary has also been put on the substrate, e.g. cuprates have been added to chiral unsaturated imides.21 A good recent review provides many more examples.1b

Whereas Grignard reagents and lithium reagents generally give thiophilic addition to dithioesters, the corresponding organocopper reagents give carbophilic addition.22 The best yields were obtained with CuBr.DMS and Copper(I) Trifluoromethanesulfonate; good results were also obtained with CuCN and CuI. This carbophilic addition has been applied to 1,3-thiazole-5(4H)-thiones.23 It is interesting to note that CuBr has also been used in the preparation of the dithioesters (eq 3).24

Nakamura and Kuwajima have reported the CuBr.DMS catalyzed acylation and conjugate addition reactions of the Zn homoenolate from 1-alkoxy-1-siloxycyclopropanes and Zinc Chloride.25a They have also reported the Chlorotrimethylsilane/HMPA accelerated conjugate addition of stoichiometric organocopper reagents prepared from CuBr.DMS,25b and of catalytic copper reagents,25c to a,b-unsaturated ketones and aldehydes. This procedure appears to be more general than that based on putative cuprates of intermediate stoichiometry (see Copper(I) Iodide). In a very significant observation, they report that reagents derived from cuprous iodide consistently gave lower yields.25b

Wipf has used CuBr.DMS to catalyze the addition of alkyl and alkenylzirconocenes to acid chlorides to yield ketones,26a and also the 1,4-addition of alkylzirconocenes to a-enones.26b The hydrozirconation of alkynes followed by transmetalation to CuI was devised by Schwartz et al.,27 who used CuI and Copper(I) Chloride. Transmetalation from Al, B, Pb, Mn, Hg, Sm, Sn, Te, Ti, Zn, and Zr to Cu has been reviewed recently.1h

Carbocupration of alkynes by organocopper reagents is a very important area, as judged by the number of citations.1a,i An interesting example involves the use of organocopper reagents bearing protected a-hydroxy or a-thio functions.28a The preparation of g-silylvinylcopper reagents via the addition of a-silylated organocopper reagents to alkynes has also been described.28b The carbocupration of alkynes is the key step in the synthesis of g,g-disubstituted allylboronates.29 The stannylalumination of 1-alkynes is catalyzed by CuI and involves stannylcupration by an intermediate stannylcopper(I) reagent.30

The use of Grignard reagents in conjunction with CuI salts has been thoroughly reviewed.1a,d A very edifying example of the difference between organocopper reagents prepared from lithium reagents vs. Grignard reagents has been provided by Curran (eq 4).31

In chemistry that is clearly related to that of organocopper reagents, aryl bromides and aryl iodides undergo a Gabriel reaction with potassium phthalimide in the presence of CuBr (or CuI).32 They also undergo coupling reactions with the sodium salts of active methylene compounds catalyzed by CuBr.33 Copper-assisted nucleophilic substitution of aryl halogen has been reviewed.1g In a potentially far-reaching development, thermally stable, yet reactive formulations of organocuprates suitable for commercialization have been patented.34

Catalysts for Diazo Chemistry.

CuBr has been used in other reactions besides those involving organocuprates. It is a popular catalyst for the activation of Diazomethane, e.g. tropylium perchlorate is isolated in 85% yield starting from benzene.35 CuBr has been used for the activation of diazoacetic esters,1j but not as often as CuCN, and especially CuCl. CuBr is the preferred catalyst for the Sandmeyer reaction of arenediazonium salts to afford bromoarenes,36 and for the Meerwein reaction, the arylation of alkenes by diazonium salts.37

Related Reagents.

Copper(I) Bromide-Lithium Trimethoxyaluminum Hydride; Copper(I) Bromide-Sodium Bis(2-methoxyethoxy)aluminum Hydride; Copper(I) Chloride; Copper(I) Chloride-Oxygen; copper(I) chloride-tetrabutylammonium chloride Copper(I) Chloride-Sulfur Dioxide; Copper(I) Cyanide; Copper(I) Iodide; Copper(I) Trifluoromethanesulfonate.

1. (a) Lipshutz, B. H.; Sengupta, S. OR 1992, 41, 135. (b) Rossiter, B. E.; Swingle, N. M. CRV 1992, 92, 771. (c) Chapdelaine, M. J.; Hulce, M. OR 1990, 38, 225. (d) Erdik, E. T 1984, 40, 641. (e) Posner, G. H. An Introduction to Synthesis Using Organocopper Reagents; Wiley: New York, 1980. (f) Posner, G. H. OR 1975, 22, 253; also see: Posner, G. H. OR 1972, 19, 1. (g) Lindley, J. T 1984, 40, 1433. (h) Wipf, P. S 1993, 537. (i) Normant, J. F.; Alexakis, A. S 1981, 841. (j) Dave, V.; Warnhoff, E. W. OR 1970, 18, 217.
2. Reich, M. R. CR(C) 1923, 177, 322.
3. Gilman, H.; Straley, J. M. RTC 1936, 55, 821.
4. Costa, G.; Camus, A.; Gatti, L.; Marsich, N. JOM 1966, 5, 568.
5. (a) Bertz, S. H.; Dabbagh, G. JACS 1988, 110, 3668. (b) Bertz, S. H.; Dabbagh, G. T 1989, 45, 425.
6. Olmstead, M. M.; Power, P. P. JACS 1990, 112, 8008.
7. Lenders, B.; Grove, D. M.; Smeets, W. J. J.; van der Sluis, P.; Spek, A. L.; van Koten, G. OM 1991, 10, 786.
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11. Lipshutz, B. H.; Whitney, S.; Kozlowski, J. A.; Breneman, C. M. TL 1986, 27, 4273.
12. Bertz, S. H.; Gibson, C. P.; Dabbagh, G. TL 1987, 28, 4251.
13. Davis, B. R.; Johnson, S. J. JCS(P1) 1979, 2840.
14. House, H. O.; Lee, T. V. JOC 1978, 43, 4369.
15. Bertz, S. H.; Dabbagh, G.; He, X.; Power, P. P. JACS 1993, 115, 11640.
16. House, H. O.; Koepsell, D. G.; Campbell, W. J. JOC 1972, 37, 1003.
17. (a) Bertz, S. H.; Dabbagh, G.; Villacorta, G. M. JACS 1982, 104, 5824. (b) Bertz, S. H.; Dabbagh, G. CC 1982, 1030. (c) Bertz, S. H.; Dabbagh, G. JOC 1984, 49, 1119.
18. Bertz, S. H.; Dabbagh, G.; Sundararajan, G. JOC 1986, 51, 4953.
19. Rossiter, B. E.; Eguchi, M.; Miao, G.; Swingle, N. M.; Hernández, A. E.; Vickers, D.; Fluckiger, E.; Patterson, R. G.; Reddy, K. V. T 1993, 49, 965.
20. Dieter, R. K.; Lagu, B.; Deo, N.; Dieter, J. W. TL 1990, 31, 4105.
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24. Westmijze, H.; Kleijn, H.; Meijer, J.; Vermeer, P. S 1979, 432.
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26. (a) Wipf, P.; Xu, W. SL 1992, 718. (b) Wipf, P.; Smitrovich, J. H. JOC 1991, 56, 6494.
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28. (a) Gardette, M.; Alexakis, A.; Normant, J. F. T 1985, 41, 5887. (b) Foulon, J. P.; Bourgain-Commerçon, M.; Normant, J. F. T 1986, 42, 1389.
29. Hoffmann, R. W.; Schlapbach, A. LA 1990, 1243.
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32. Bacon, R. G. R.; Karim, A. CC 1969, 578.
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34. Hatch, H. B.; Wedinger, R. S. WO Patent Appl. 91 11 494, 1991 (CA 1991, 115, 232 514s).
35. Müller, E.; Fricke, H. LA 1963, 661, 38.
36. Buck, J. S.; Ide, W. S. OSC 1943, 2, 130.
37. Cleland, G. H. JOC 1961, 26, 3362.

Steven H. Bertz & Edward H. Fairchild

LONZA, Annandale, NJ, USA

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