[26521-33-5]  · C19H37BrNiP2  · Bromo(o-tolyl)bis(triethylphosphine)nickel(II)  · (MW 466.06)

(Ullmann1 and cross-coupling2 reactions; halogen exchange of aryl and vinyl halides;1,3 oligomerization reactions4)

Physical Data: mp 102-103 °C.

Solubility: sol benzene, diethyl ether, THF, DMF, ethanol, DMSO, acetone, cyclohexane, cumene, nitromethane, dichloromethane.

Form Supplied in: brown, air stable, crystalline solid.

Preparative Method: prepared in 67% yield by treating a benzene solution of dibromobis(triethylphosphine)nickel(II) with an ethereal solution of o-tolylmagnesium bromide.2,5

Purification: recrystallization from ethanol.

Handling, Storage, and Precautions: although no special precautions are reported, this complex is likely to be toxic, as with many nickel reagents.6

Biaryl Syntheses and Cross-Coupling Reactions.

As part of a study examining the syntheses of biaryls under nickel catalysis,1 the title reagent (1) and other nickel(II) complexes were found to react with aryl halides to give biaryls via a radical chain process and were thus proposed as intermediates in nickel(0)-catalyzed Ullmann coupling reactions. The reactions of (1) are most efficiently conducted in a sealed, evacuated tube at 70 °C with a nonpolar organic solvent such as benzene or toluene. In a similar study (1) was found, upon treatment with Methyllithium and heating in hexanes, di-n-butyl ether, or 1,2-dimethoxyethane, to provide o-xylene, suggesting that nickel(II) species are intermediates in the cross coupling of Grignard reagents and aryl halides with nickel(0) reagents.2

Halogen Exchange with Aryl and Vinylic Halides.

A number of nickel complexes have been found to catalyze the substitution of aryl halides with nucleophiles such as amines, phosphines, and cyanide.7 Reagent (1) is well suited for the exchange of aryl and vinyl halides with more electronegative halides (eqs 1-4). These reactions are most frequently carried out in refluxing benzene or THF in the presence of an appropriate ammonium halide salt.1,3 In cases where cis- or trans-vinyl halides are used (eqs 3 and 4), no detectable isomerization is observed.

Oligomerization Reactions.

The cyclodimerization of butadiene to provide 2-methylenevinylcyclopentane (eq 5) is carried out quite efficiently with (1) and other nickel catalysts.4 This process is best carried out at an elevated temperature in benzene in the presence of (1) and methanol. The use of protic reagents other than methanol leads to a diminished yield of 2-methylenevinylcyclopentane and the formation of other cyclodimerized products.

1. Tsou, T. T.; Kochi, J. K. JACS 1979, 101, 7547.
2. Morrell, D. G.; Kochi, J. K. JACS 1975, 97, 7262 and references included therein.
3. Tsou, T. T.; Kochi, J. K. JOC 1980, 45, 1930.
4. Kiji, J.; Masui, K.; Furukawa, J. BCJ 1971, 44, 1956.
5. Parshall, G. W. JACS 1974, 96, 2360.
6. The Merck Index, 10th ed.; Windholtz, M., Ed.; Merck: Rahway, 1983; pp 932-933.
7. (a) Cramer, R.; Coulson, D. R. JOC 1975, 40, 2267. (b) Cassar, L.; Foà, M. JOM 1974, 74, 75. (c) Cassar, L. JOM 1973, 54, C57. (d) Cassar, L.; Ferrara, S.; Foa, M. Adv. Chem. Ser. 1974, 132, 252. (e) Favero, G.; Morvillo, A.; Turco, A. G 1979, 109, 27.

Edmund L. Ellsworth

Parke-Davis Pharmaceutical Research, Ann Arbor, MI, USA

Copyright 1995-2000 by John Wiley & Sons, Ltd. All rights reserved.