Kumada coupling

A 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, and was named after Makoto Kumada.

Development

This 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 [cite journal | title = Mechanism of the silver-catalyzed reaction of Grignard reagents with alkyl halides | author = Jay K. Kochi and Masuhiko Tamura | journal = J. Am. Chem. Soc. | year = 1971 | volume = 93 | issue = 6 | pages = 1483–1485 | doi = 10.1021/ja00735a028] . Stoichometric Grignard couplings and Grignard homo-couplings have been known well before that time.

The first report by the Kumada group [cite journal | title = Selective carbon-carbon bond formation by cross-coupling of Grignard reagents with organic halides. Catalysis by nickel-phosphine complexes | author = Kohei Tamao, Koji Sumitani, Makoto Kumada | journal = J. Am. Chem. Soc. | year = 1972 | volume = 94 | issue = 12 | pages = 4374–4376 | doi = 10.1021/ja00767a074] described the reaction of a Grigard reagent for instance phenylmagnesium bromide with an aryl or vinyl chloride such as vinyl chloride to the coupled product (styrene) catalyzed by a nickel chloride with two dppe ligands (NiCl₂dppe₂):

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In the 1972 Corriu report [cite journal | title = Activation of Grignard Reagents by Transition-metal Complexes. A Newand Simple Synthesis of trans-Stilbenes and Polyphenyls | author = Corriu, R. J. P.; Masse, J. P. | journal = J. Chem. Soc., Chem. Commun. | year = 1972 | pages = 144 | doi = 10.1039/c3972000144a] , "beta-bromostyrene" is reacted with phenylmagnesium bromide to trans-stilbene in diethylether also with nickel catalysts notably Nickel(II) acetylacetonate.

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Palladium was introduced to this chemistry in 1975 by Murahashi [cite journal | title = The reaction of σ-vinylpalladium complexes with alkyllithiums. Stereospecific syntheses of olefins from vinyl halides and alkyllithiums | journal = J. Organomet. Chem. | volume = 91 | issue = 2 | year = 1975 | pages = C39–C42 | author = Masaaki Yamamura, Ichiro Moritani and Shun-Ichi Murahashi | doi = 10.1016/S0022-328X(00)89636-9] 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 mechanism

The Nickel reaction mechanism for Ni(II) catalysts is a sequence of several steps ["Strategic Applications of Named Reactions in Organic Synthesis" Laszlo Kurti, Barbara Czako Academic Press (March 4, 2005) ISBN 0-12-429785-4 ] :
* Transmetallation: the dihalonickel catalyst reacts with the Grignard RMgX to a diorganonickel intermediate NiR₂L₂ and dihalonickel MgX₂
* Reductive elimination: reaction of NiR₂L₂ with the organohalide R'X forms the coupled product R-R together with the nickelorganohalide NiR'XL₂. In the overall reaction this step is negligible because the active nickel compound is formed in catalytical amounts
* Transmetallation: in the first step of the catalytic cycle nickelorganohalide NiR'XL₂ reacts with another equivalent of RMgX to mixed diorganonickel NiRR'L₂ compound and dihalomagnesium MgX₂
* trans-cis isomerization: with substrates trans-dichloroethylene and phenylmagnesium chloride, the resulting stilbene is enriched in the cis isomer.
* Coordination: a new equivalent of organohalide R'-X adds face-on to the mixed dihalonickel complex
* Oxidative addition: The cross-coupled product R-R' is released with regeneration of nickelorganohalide NiR'XL₂

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.

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Recently the scope of this reaction was extended to aryl-aryl couplings with improved functional group tolerance [cite journal | title = Pd-Catalyzed Kumada-Corriu Cross-Coupling Reactions at Low Temperatures Allow the Use of Knochel-type Grignard Reagents | author = Ruben Martin and Stephen L. Buchwald | journal = J. Am. Chem. Soc. | year = 2007 | volume = 129 | issue = 13 | pages = 3844–3845 | format = Communication | doi = 10.1021/ja070830d] :

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In this particular reaction the Grignard is prepared in situ by I/Mg exchange between an aryl iodide and isopropylmagnesium chloride / lithium chloride [cite journal | title = A LiCl-Mediated Br/Mg Exchange Reaction for the Preparation of Functionalized Aryl- and Heteroarylmagnesium Compounds from Organic Bromides | author = Arkady Krasovskiy, Paul Knochel | journal = Angewandte Chemie International Edition | volume = 43 | issue = 25 | pages = 3333–3336 | year = 2004 | doi = 10.1002/anie.200454084] .

References