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Kumada couplingA Kumada coupling or Kumada-Corriu coupling is a cross coupling reaction in organic chemistry between a alkyl or aryl Grignard reagent and an aryl or vinyl halocarbon catalysed by nickel or palladium. This reaction is relevant to organic synthesis because it gives access to styrene compounds. The reaction type was reported independently by two groups in 1972. Additional recommended knowledge
DevelopmentThis method builds on earlier work done by Tamura & Kochi in 1971 on couplings of Grignards with catalytical amounts of other metal halide catalysts than nickel for instance silver [1]. Stoichometric Grignard couplings and Grignard homo-couplings have been known well before that time.
In the 1972 Corriu report [3], beta-bromostyrene is reacted with phenylmagnesium bromide to trans-stilbene in diethylether also with nickel catalysts notably Nickel(II) acetylacetonate. Palladium was introduced to this chemistry in 1975 by Murahashi [4] when Tetrakis(triphenylphosphine)palladium(0) was found to catalyze the reaction of (Z)-bromostyrene with methylmagnesium iodide to (Z)-propenylbenzene. With the far more reactive methyl lithium, the palladium catalyst is not recycled fast enough and an elimination reaction to the alkyne predominates. Reaction mechanismThe Nickel reaction mechanism for Ni(II) catalysts is a sequence of several steps [5]:
The main steps in the mechanism for Ni(0) or Pd(0) catalysts are oxidative addition of the organohalide, transmetallation of the Grignard and reductive elimination.
ScopeRecently the scope of this reaction was extended to aryl-aryl couplings with improved functional group tolerance [6]: In this particular reaction the Grignard is prepared in situ by I/Mg exchange between an aryl iodide and isopropylmagnesium chloride / lithium chloride [7]. References
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This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Kumada_coupling". A list of authors is available in Wikipedia. |