· (MW 538.27)
(source of nickel(0) useful for the formation of carbonates from epoxides2 and the coupling of alkenyl boranes with allylic epoxides3)
Physical Data: mp 155-157 °C dec. (N2).
Solubility: sol benzene, toluene, MeCN, THF.
Analysis of Reagent Purity: 1H NMR: (C6D6) d 7.67 (m), 7.13 (m); 31P NMR: (C6D6) d -22 ppm from (MeO)3PO.
Preparative Methods: by the Sodium Amalgam reduction of Dibromobis(triphenylphosphine)nickel(II).4 In the standard preparation, 22.3 g of Ni(PPh3)2Br2 were added to a mixture of sodium amalgam (1.73 g Na, 0.075 g-atom in 300 mL Hg) and 500 mL acetonitrile. After removal of Hg and solvent, the precipitate was dissolved in benzene to remove the insoluble Hg occluded NaBr. Concentration of the dark brown benzene solution in vacuo gave 13-15 g of red-brown Ni(PPh3)2 (74-84%) which could be used without further purification. Optional recrystallization from benzene (or toluene)/hexane is possible but significant loss of the product occurs due to high solubility. Sodium amalgam reductions of similar systems have been problematic and n-Butyllithium was found to be a superior reducing agent.5
Handling, Storage, and Precautions: highly oxygen sensitive. Special inert-atmosphere techniques must be used.6 Should be stored at 0 °C.
Reactions of Epoxides.
Bis(triphenylphosphine)nickel(0), Ni(PPh3)2, can react with epoxides by oxidative addition of Ni0 into the strained C-O bond. Insertion of CO2 into these organonickel complexes leads to alkenyl carbonates. Thus reaction of 1-chloro-2,3-epoxypropane (1) with Ni(PPh3)2 in the presence of CO2 catalytically produced chloromethylene carbonate (2) in good yield (eq 1).2
Alkenylboranes also react with these organonickel complexes to give alcohols in overall catalytic coupling reactions. When the hexenylborane (3) was reacted with 3,4-epoxy-1-butene (4) and the catalyst, a mixture of the two coupling products (5) and (6) was produced in 85% yield (eq 2).3 The regioselectivity of the reaction was found to depend upon the nature of the catalyst used. When metal complexes such as Bis(dibenzylideneacetone)palladium(0), Tetrakis(triphenylphosphine)palladium(0), or Ni(PPh3)
n were used the predominant product was (5), whereas when Palladium(II) Chloride or Nickel(II) Acetylacetonate were used the formation of (6) was favored. Overall, the palladium complexes proved to be superior catalysts for this transformation. The best yield (92%) was obtained using
Allene has been cyclooligomerized in the presence of a catalytic amount of Ni(PPh3)2 into a mixture of isomers with a cyclic pentamer being the major product.4 The linear dimerization of ethylene and propene also takes place when this nickel complex along with Diethylaluminum Chloride is used as the catalytic system.7
- 1. Jolly, P. W.; Wilke, G. The Organic Chemistry of Nickel; Academic: New York, 1974; Vols. I and II.
- 2. De Pasquale, R. J. JCS(C) 1973, 157.
- 3. Miyaura, N.; Tanabe, Y.; Suginome, H.; Suzuki, A. JOM 1982, 233, C13.
- 4. De Pasquale, R. J. JOM 1971, 32, 381.
- 5. Millard, A. A.; Rathke, M. W. JACS 1977, 99, 4833.
- 6. Shriver, D. F. The Manipulation of Air-Sensitive Compounds; McGraw-Hill: New York, 1969.
- 7. (a) Furman, D. B.; Kudryashev, A. V.; Ivanov, A. O.; Pogorelov, A. G.; Yanchevskaya, T. V.; Bragin, O. V. BAU 1990, 444. (b) Furman, D. B.; Ivanov, A. O.; Olenin, A. Y.; Vasil'kov, A. Y.; Munshieva, M. K.; Belyankin, A. Y.; Lisichkin, G. V.; Sergeev, V. A.; Bragin, O. V. BAU 1990, 448.
Paul A. Wender & Thomas E. Smith
Stanford University, CA, USA
Copyright © 1995-2000 by John Wiley & Sons, Ltd. All rights reserved.