Grignard reagents/nickel complexes

Alkyl- and aryl-pyridazines can be prepared by cross-coupling reactions between chloropyridazines and Grignard reagents in the presence of nickel-phosphine complexes as catalysts. Dichloro[l,2-bis(diphenylphosphino)propane]nickel is used for alkylation and dichloro[l,2-bis(diphenylphosphino)ethane]nickel for arylation (78CPB2550). 3-Alkynyl-pyridazines and their A-oxides are prepared from 3-chloropyridazines and their A-oxides and alkynes using a Pd(PPh3)Cl2-Cu complex and triethylamine (78H(9)1397). 

Grignard reagents in the presence of a nickel complex to give both normal products and the products of allylic rearrangement. 

A complex reaction takes place when dichlorobis(triphenylphosphine)-nickel (5) is treated with excess methylmagnesium bromide in ether. Detectable amounts of benzene, toluene, and biphenyl are formed, together with mixed phosphines. Nickel appears to be necessary for the substitution reaction since triphenylphosphine alone does not react with the Grignard reagent. 

In a Kumada-Corriu reaction, an aryl halide is oxidatively coupled with a homogeneous nickel(ll)-phosphine catalyst [2], This species reacts with a Grignard reagent to give biaryl or alkylaryl compounds. Later, palladium-phosphine complexes were also successfully applied. By this means, stereospecific transformations were achieved. 

Nickel(II) salts are able to catalyze the coupling of Grignard reagents with alkenyl and aryl halides. A soluble 6 -phosphine complex, Ni(dppe)2Cl2, is a particularly effective catalyst.266 The main distinction between this reaction and Pd-catalyzed cross... 

When secondary Grignard reagents are used, the coupling product sometimes is derived from the corresponding primary alkyl group.169 This transformation can occur by reversible formation of a nickel-alkene complex from the cr-bonded alkyl group. Reformation of the cr-bonded structure will be preferred at the less hindered primary position. 

Hayashi et al.74 described a process of kinetic resolution in the coupling of Grignard reagents R Mgx (having a chiral center at the point of attachment to the metal) with various alkenyl halides under the influence of chiral phosphine-nickel complexes. Chiral amino acid derivatives (35) were used as ligands. 

PHOSPHINE-NICKEL COMPLEX CATALYZED CROSSCOUPLING OF GRIGNARD REAGENTS WITH ARYL AND ALKENYL HALIDES 1,2-DIBUTYLBENZENE... 

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