Nickel(II) Bromide

NiBr2
(NiBr2)

[13462-88-9]  · Br2Ni  · Nickel(II) Bromide  · (MW 218.49) (NiBr2.2H2O)

[13596-19-5]  · Br2H4NiO2  · Nickel(II) Bromide  · (MW 254.53) (NiBr2.3H2O)

[7789-49-3]  · Br2H6NiO3  · Nickel(II) Bromide  · (MW 272.55) (NiBr2.6H2O)

[18721-96-5]  · Br2H12NiO6  · Nickel(II) Bromide  · (MW 326.61)

(mild Lewis acid for displacement;1-4 catalyst in cross-coupling reactions,5-9 and in combination with reducing agent for homocoupling reactions11-15)

Physical Data: mp 963 °C; d 5.098 g cm-3.

Solubility: sol water, alcohol, ether.

Form Supplied in: yellowish green for hydrate; golden yellow when anhydrous; widely available. Drying: anhydrous nickel bromide can be obtained by heating at 300 °C and storing in a desiccator.

Handling, Storage, and Precautions: nickel(II) is reputed to be toxic and a cancer suspect agent. Use in a fume hood.

General Considerations.

Most reactions promoted by Nickel(II) Chloride can also be mediated by nickel(II) bromide. This section covers certain specific applications using nickel bromide as a reagent.

Displacement Reactions.

Li2NiBr4 prepared from anhydrous Lithium Bromide and NiBr2 in THF serves as a source of soft nucleophilic bromide and reacts regioselectively with epoxides to give bromohydrins in high yield (eq 1).1

Like NiCl2, reduction of NiBr2 with a number of reducing agents generates useful catalytic species. To illustrate this, NiBr2-Zinc can catalyze the halogen exchange reaction of aryl bromides with Potassium Iodide under mild conditions.2 At elevated temperature, NiBr2-Tri-n-butylphosphine is also an effective catalyst for this transformation. With a catalytic amount of a Ni0 complex generated in situ from NiBr2, 1,1-Bis(diphenylphosphino)ferrocene, and zinc powder, aryl thiols react with an equimolar amount of aryl iodide at 25 °C or bromide at 60 °C to afford symmetric aryl sulfides in excellent yields (eq 2).3

The conversion of aryl and vinyl bromides into the corresponding iodides is also achieved using a low-valent nickel catalyst generated in situ.4 This reaction turns out to be useful to activate the carbon-chlorine bond in aryl chlorides in the Heck reaction (eq 3).4e

NiBr2-BuLi.

The addition of n-Butyllithium to a suspension of NiBr2 in THF at -78 °C forms material which catalyzes an efficient substitution reaction of lithium ester enolates with aryl or vinyl bromides or iodides (eqs 4 and 5).5 The reaction occurs with clean retention of stereochemistry at the halogen-bearing carbon. Addition of phosphine ligands gives totally inactive material.

Cross-Coupling Reactions.

Most nickel-promoted cross-coupling reactions use nickel halide phosphine complexes as the catalyst and are discussed under Nickel(II) Chloride. The addition of the phosphine ligand to a solution of nickel bromide also serves as a useful catalytic system for this purpose. For example, enol phosphates are converted into the corresponding allylsilanes when trimethylsilylalkyl Grignard reagents are employed (eq 6).6

Nickel bromide has been shown to convert aryl bromides into the corresponding aryl phosphine derivatives (eqs 7-9).7

NiBr2 catalyzes the reaction of aryl iodides with red phosphorus to give triphenylphosphine oxide in excellent yield after hydrolysis (eq 10). Under modified conditions, triphenylphosphine is obtained (eq 11).8

Five- and six-membered cyclic 3-iodo enones undergo spiroannulation with symmetric internal alkynes in the presence of NiBr2 and zinc powder to afford spiro[4.4]nonadienones and spiro[4.5]decadienones in good to excellent yields at temperatures of 60-100 °C (eq 12).9

Miscellaneous.

Primary and secondary alcohols are oxidized to their respective carbonyl compounds in high yield by Dibenzoyl Peroxide through the action of NiBr2, which serves as an effective mediative catalyst and as an alcohol template in these transformations.10

The Ni0 species generated by electrochemical reduction of the NiBr2(bipy) complex exhibits catalytic activity for the dimerization of aryl, benzyl, alkyl, or vinyl halides in good yields.11 Zinc plays a similar role as reducing agent in the homocoupling reactions.12 Like the nickel chloride-mediated reactions, the presence of iodide ion and thiourea accelerates the reaction (eq 13).13 Aryl bromides can also be efficiently reduced with Sodium Hydride in the presence of NiBr2.14 In a manner similar to that observed with the NiCl2 catalyst, the reduction of NiBr2 by magnesium in a boiling THF solution of symmetrical alkynes quantitatively leads to cyclotrimerization products.15

The reaction of divinylphenylphosphine with 1-phenyl-3,4-dimethylphosphole in the presence of anhydrous NiBr2 leads to the formation of a single diastereomer of the product as the result of two sequential stereoselective intermolecular [4 + 2] Diels-Alder cycloadditions. This reaction provides a facile route to a new type of conformationally rigid tridentate phosphine (eq 14).16


1. Dawe, R. D.; Molinski, T. F.; Turner, J. V. TL 1984, 25, 2061. (b) Guo, Z. X.; Haines, A. H.; Taylor, R. J. K. SL 1993, 607.
2. Takagi, K.; Hayama, N.; Okamoto, T. CL 1978, 191.
3. Takagi, K. CL 1987, 2221.
4. (a) Takagi, K.; Hayama, N.; Inokawa, S. CL 1978, 1435. (b) Takagi, K.; Hayama, N.; Okamoto, T. CL 1978, 191. (c) Meyer, G.; Rollin, Y.; Perichon, J. TL 1986, 27, 3497. (d) Colon, I.; Kelsey, D. R. JOC 1986, 51, 2627. (e) Bozell, J. J.; Vogt, C. E. JACS 1988, 110, 2655.
5. (a) Millard, A. A.; Rathke, M. W. JACS 1977, 99, 4833. (b) Alcock, S. G.; Baldwin, J. E.; Bohlmann, R.; Harwood, L. M.; Seeman, J. I. JOC 1985, 50, 3526. (c) Wender, P. A.; Wolanin, D. J. JOC 1985, 50, 4418.
6. Hayashi, T.; Fujiwa, T.; Okamoto, Y.; Katsuro, Y.; Kumada, M. S 1981, 1001.
7. (a) Tavs, P. CB 1970, 103, 2428. (b) Cristau, H. J.; Chêne, A.; Christol, H. JOM 1980, 185, 283. (c) Horner, L.; Mummenthey, G.; Moser, H.; Beck, P. CB 1966, 99, 2782. (d) Hirusawa, V. Y.; Oku, M.; Yamamoto, K. BCJ 1957, 30, 667. (e) Horner, L.; Duda, U. M. TL 1970, 5177.
8. Cristau, H. J.; Pascal, J.; Plenat, F. TL 1990, 31, 5463.
9. Kong, K.-C.; Cheng, C.-H. OM 1992, 11, 1972.
10. (a) Doyle, M. P.; Patrie, W. J.; Williams, S. B. JOC 1979, 44, 2955. (b) Doyle, M. P.; Dow, R. L.; Bagheri, V.; Patrie, W. J. JOC 1983, 48, 476.
11. Rollin, Y.; Troupel, M.; Tuck, D. G.; Perichon, J. JOM 1986, 303, 131.
12. Takagi, K.; Hayama, N.; Inokawa, S. CL 1979, 917. (b) Takagi, K.; Hayama, N.; Inokawa, S. BCJ 1990, 60, 3691.
13. Takagi, K.; Mimura, H.; Inokawa, S. BCJ 1984, 57, 3517.
14. Brunet, J. J.; Vanderesse, R.; Caubere, P. JOM 1978, 157, 125.
15. (a) Mauret, P.; Alphonse, P. JOM 1984, 276, 249. (b) Alphonse, P.; Moyen, F.; Marzerolles, P. JOM 1988, 345, 209.
16. Solujic, L.; Milosavljevic, E. B.; Nelson, J. H.; Alcock, N. W.; Fischer, J. IC 1989, 28, 3453.

Tien-Yau Luh & Chi-Hong Kuo

National Taiwan University, Taipei, Taiwan



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