Dibromobis(triphenylphosphine)nickel(II)1

NiBr2(PR3)2
(1; R = Ph)

[14126-37-5]  · C36H30Br2NiP2  · Dibromobis(triphenylphosphine)nickel(II)  · (MW 743.08) (2; R = Bu)

[15242-92-9]  · C24H54Br2NiP2  · Dibromobis(tributylphosphine)nickel(II)  · (MW 623.14) (3; R = Et)

[19224-77-2]  · C12H30Br2NiP2  · Dibromobis(triethylphosphine)nickel(II)  · (MW 454.81)

(catalysts for the cross-coupling reactions of various RX with Grignard reagents,1 C-X bond reduction,9,10 homocoupling of Csp2 halides,11 displacement of aryl halides,2 and oligomerization of dienes12,13)

Alternate Name: bis(triphenylphosphine)nickel(II) bromide.

Physical Data: (1) mp 222-225 °C; dark green. (2) mp 51-53 °C; red. (3) mp 106-107 °C; dark red.

Solubility: sol acetone, benzene, THF.

Form Supplied in: most nickel bromide phosphine complexes are commercially available.

Preparative Methods: conveniently synthesized by mixing a stoichiometric amount of Nickel(II) Bromide with the appropriate phosphine ligand.15

Handling, Storage, and Precautions: these complexes are somewhat air sensitive. Like other NiII compounds, they are cancer suspect agents and corrosive. These reagents should be handled in a fume hood.

General Considerations.

Most reactions promoted by Dichlorobis(triphenylphosphine)nickel(II) or related complexes can also be mediated by NiBr2(PPh3)2 or the like. This section covers certain specific applications using the nickel bromide reagents.

Displacement Reactions.

Aryl triflates readily participate in an in situ generated Ni0-catalyzed nucleophilic displacement with cyanide anion, thereby providing a convenient method for the preparation of aryl cyanides (eq 1).2

Reaction of allylic alcohols with morpholine in the presence of a catalytic amount of NiBr2(PPh3)2 and Potassium t-Butoxide gives the corresponding amines in good yields (eq 2).3

The regioselective rearrangement of propene oxide to propionaldehyde is reportedly promoted by NiBr2(PPh3)2.4 Surprisingly, the reaction of methylmagnesium iodide with t-BuO- in the presence of NiBr2(PPh3)2 yields isobutylene oxide (eq 3).5

Cross-Coupling Reactions.

Most of the cross-coupling reactions that use nickel halide phosphine complexes as the catalyst are discussed in the article on Dichlorobis(triphenylphosphine)nickel(II).1 The addition of the phosphine ligand to a solution of nickel bromide also serves as a useful catalytic system for this purpose.

In an electrochemical process, aryl halides react with a-haloacetic acid esters to give the corresponding arylacetic acid derivatives.6 The reaction of (E,E)-1,4-dilithio-1,4-diphenyl-1,3-butadiene at -78 °C with (Et3P)2NiBr2 produces the nickel complex of 1,2,5,6-tetraphenylcyclooctatetraene in good yield. The cot ligand can easily be liberated upon air oxidation.7

When chiral ligands are used, enantioselective cross-coupling reactions can be achieved. To illustrate, NiBr2[(S)-(R)-PPFOME] has been used for the synthesis of chiral ternaphthyl (eq 4).8

Reduction.

The carbon-sulfur bonds of thiols, thioethers, dithioacetals, and sulfoxides as well as sulfones are reduced upon treatment with NiBr2(PPh3)2 and Lithium Aluminum Hydride in moderate to good yields.1f,9 As sulfoxides and sulfones can readily be reduced to thioethers by low valent transition metal complexes or by complex hydrides,10 it has been suggested that nickel reagents first reduce sulfoxides or sulfones to the corresponding sulfides which are further reduced under the reaction conditions. Therefore an excess amount of the reducing agent is usually required to effectively reduce these substrates.

The reaction of cumulenes with zero valent nickel catalyst generated in situ from NiBr2(PPh3)2, zinc, and Ph3P proceeds smoothly at rt to give the dimeric radialenes in moderate yield (eqs 5 and 6).11

1,1-Dibromo-2,2-diphenylethylene also dimerizes under similar conditions in benzene to give the butatriene (eq 7).11

Although low valent nickel complexes are very useful for the dimerization and oligomerization of alkenes or butadienes, the use of NiBr2(PPh3)2 or related complexes for this purpose is relatively rare (eq 8), because a number of isomeric products are occasionally obtained.12 Alternatively, NiBr2(PPh3)2-n-Butyllithium has been shown to catalyze the cyclodimerization of butadiene to give the five-membered ring product in excellent yield (eq 9).13

Allylic acetals react with allylzinc reagents in the presence of a catalytic amount of NiBr2(PPh3)2 followed by treatment with electrophiles, leading to double functionalization of a,b-unsaturated acetals (eq 10).14


1. (a) Kumada, M. PAC 1980, 52, 669. (b) Kalinin, V. N. S 1992, 413. (c) Naso, F. PAC 1988, 60, 79. (d) Fiandanese, V. PAC 1990, 62, 1987. (e) Felkin, H.; Swierczewski, G. T 1975, 31, 2735. (f) Luh, T.-Y.; Ni, Z.-J. S 1990, 89. (g) Luh, T.-Y. ACR 1991, 24, 257. (h) Klunder, J. M.; Posner, G. H. COS 1991, 3, 207. (i) Tamao, K. COS 1991, 3, 435. (j) Knight, D. W. COS 1991, 3, 481. (k) Jolly, P. W. In Comprehensive Organometallic Chemistry; Wilkinson, G., Ed.; Pergamon: Oxford, 1982, Vol. 8, p 713.
2. (a) Takagi, K.; Sakakibara, Y. CL 1989, 1957. (b) Sakakibara, Y.; Okuda, F.; Shimobayashi, A.; Kirino, K.; Sakai, M.; Uchino, N.; Takagi, K. BCJ 1988, 61, 1985.
3. Furukawa, J.; Kiji, J.; Yamamoto, K.; Tojo, T. T 1973, 29, 3149.
4. Miyashita, A.; Shimada, T.; Sugawara, A. CL 1986, 1323.
5. Miyashita, A.; Ishida, J.-y.; Nohira, H. TL 1986, 27, 2127.
6. Folest, J. C.; Périchon, J.; Fauvarque, J. F.; Jutand, A. JOM 1988, 342, 259.
7. Lawrie, C. J.; Gable, K. P.; Carpenter, B. K. OM 1989, 8, 2274.
8. Hayashi, T.; Hayashizaki, K.; Ito, Y. TL 1989, 30, 215.
9. Ho, K. M.; Lam, C. H.; Luh, T.-Y. JOC 1989, 54, 4474.
10. Madesclaire, M. T 1988, 44, 6537.
11. (a) Iyoda, M.; Tanaka, S.; Nose, M.; Oda, M. CC 1983, 1058. (b) Iyoda, M.; Tanaka, S.; Otani, H.; Nose, M.; Oda, M. JACS 1988, 110, 8494. (c) Iyoda, M.; Kuwatani, Y.; Oda, M. JACS 1989, 111, 3761. (d) Iyoda, M.; Sakaitani, M.; Miyazaki, T.; Oda, M. CL 1984, 2005.
12. Pittman, C. U., Jr.; Smith, L. R. JACS 1975, 97, 341.
13. Kiji, J.; Masui, K.; Furukawa, J. TL 1970, 2561.
14. Yanagisawa, A.; Habaue, S.; Yamamoto, H. JACS 1989, 111, 366.
15. Jensen, K. A.; Nielsen, P. H.; Pedersen, C. T. ACS 1963, 17, 1115.

Tien-Yau Luh & Chi-Hong Kuo

National Taiwan University, Taipei, Taiwan



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