Negishi couplings nickel complexes

The cross-coupling of organozinc compounds has been accomplished using a number of metal enolate complexes, namely Rh(acac)(H2C=CH2)2 (6) , Co(acac)3 (30) °, Ni(acac)2 (47) , Li(acac) (107) and Cr(acac)3 (108) . For instance, complex 47 proved to be an extremely effective catalyst system for the Negishi cross-coupling of arylzinc halides (109) with aryl (110), heteroaryl and alkenyl halides, triflates and nonaflates to give the corresponding biaryl compounds (111) (equation 30). The solvent played an important role in these reactions and optimal conditions were found with 8 1 mixtures of THF and A-ethylpyrrolidinone (nep). Only 0.05 mol% of the nickel complex... 

Negishi, E., Takahashi, T., Akiyoshi, K. Aspects of cross-coupling reactions catalyzed by palladium and nickel complexes. Chem. Ind. 1988, 33, 381-407. 

E. Negishi, T. Takahashi, and K. Akiyoshi, in Catalysis of Organic Reactions, P. N. Rylander, H. Greenfield, and R. L. Augustine, Eds., Mercel Dekker, New York, 1988, 381-407. Aspects of Cross-Coupling Reactions Catalyzed by Palladium and Nickel Complexes. 

Figure 13.20 NegIshI couplings using nIckel-NHC complexes.

Finally, the efficient Negishi coupling of unactivated aryl, heterocyclic, vinyl chlorides as well as aryl dichlorides catalyzed by binuclear and mononuclear NHC-Ni complexes was recently described by Chen and co-workers (Equation (10.18)). Elaborated heteroarene-functionalized NHC were found to be highly effective for the preparation biaryls and terphenyls in good to excellent yields under mild conditions. Notably, the binuclear nickel catalysts showed higher activities than mononuclear analogues, probably because of a bimetallic cooperative effect. 

To understand the effect of the concentrations, let us see an example in a Negishi cross-coupling, in this case with a nickel complex [48], based on an experimental work by Rovis fit /. [49] (Scheme 9.10). 

Unsymmetrical biaryh and diarylmethanes. Negishi et al have used a nickel-(0) complex or a palladium(0) complex as catalyst for the cross-coupling of aryl-or benzylzinc halides with aryl halides at room temperature to form biaryls or diarylmethanes. The zinc derivatives are prepared by reaction of aryl- or benzyl-lithium with zinc chloride or bromide. 

Alkenyl-alkenyl cross-coupling. Baba and Negishi have prepared a catalyst from this Pd(II) complex and 2 equiv. of diisobutylaluminum hydride that promotes this coupling reaction. Tetrakis(triphenylphosphine)palladium(0) is inactive, as is material prepared in situ from palladium chloride, triphenylphos-phine and HAKr-CtHg) . A nickel catalyst prepared from Ni(acac)2, PfCnHsja, and diisobutylaluminum hydride is somewhat less efficient. The coupling Involves (E)-alkenylalanes (4, 158, 159) and alkenyl halides. The products are (E,E)- and (E,Z)-dienes. 

E. Negishi, Acc. Chem. Res., 1982, 15, 340-348. Palladium- or Nickel-Catalyzed Cross-Coupling. A New Selective Method for Carbon-Carbon Bond Formation. T. Hayashi and M. Kumada, Acc. Chem. Res., 1982, 15, 395-401. Asymmetric Synthesis Catalyzed by Transition-Metal Complexes with Functionalized Chiral Ferro-cenylphosphine Ligands. 

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